Simple FET Driver...

[Rick C]

On Wednesday, December 2, 2020 at 10:56:22 PM UTC-5, Bill Sloman wrote:

On Thursday, December 3, 2020 at 2:39:20 PM UTC+11, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2357c8a-f038-477a...@googlegroups.com...
On Wednesday, December 2, 2020 at 9:32:45 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:f9beb047-d324-4bbf...@googlegroups.com...
On Wednesday, December 2, 2020 at 7:09:55 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:7d3d16b5-aaef-49f9...@googlegroups.com...
On Wednesday, December 2, 2020 at 5:46:57 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e4285dd9-ed97-4189...@googlegroups.com...
On Wednesday, December 2, 2020 at 3:26:58 PM UTC-5, Edward Rawde
wrote:
\"Edward Rawde\" <inv...@invalid.invalid> wrote in message
news:rq8q5r$l3r$1...@gioia.aioe.org...
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:6fce9360-b9e9-450f...@googlegroups.com...
On Wednesday, December 2, 2020 at 1:10:18 AM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:02352733-1a66-48f7...@googlegroups.com...
On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it
gets
some
shoot through during the switching.
[...]
Having the team distributed around the world isn\'t necessarily an issue
as
long as someone who knows what they\'re doing is in overall charge.
I don\'t think there is much else I can do for you.

Yes, I have that impression.
In that case I won\'t bother responding to your other points except to
point
out that your schematics show AO6407 FETs, the data sheet for which is
trivial to find.
Under Absolute Maximum Ratings Vgs is listed as +/- 8V Maximum.
If you want intermittent failures after production has started, just hit
it
with 12V.

Ok, my bad. I thought I had checked that but I got something wrong. The
parts on the board are something else, these were picked for the simulation
because they are in the LTspice library. I get tired of fighting the tool
to get third party models to work.
That\'s ok, I\'ve made worse design errors. I think resistors lower than 10K
and a circuit similar to the one on that web site will switch fast enough if
you pay attention to resistor power dissipation and Vgs max. R14 and R15 may
not be needed or can be a lot lower than 10K. Try a simulation with 4.7K and
100 ohms. You never did tell me what D3 is for. I haven\'t used 4000B logic
for um never mind how long. Is it still in production?
Element-14 in Australia (it used to be Farnell /Newark) has 306 different parts in stock that fit CD40**. Everything in the first sheet is labelled a \"best seller\", so it does seem to be still in production. Most if it will probably go into legacy products, but I certainly ran into design problems all though my career where logic that could run slowly from an up to 18V supply was just the solution I needed. Unlike the 555 which seems to persist because some designers are lazy and unimaginative, there weren\'t any better alternatives.

In this circuit the biggest problem I have is that some of the uses require the input to be higher than the supply which a FET can do well but a logic gate has issues with. Negative excursions are also a problem.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Bill Sloman]

On Thursday, December 3, 2020 at 3:07:33 PM UTC+11, Edward Rawde wrote:

\"Bill Sloman\" <bill....@ieee.org> wrote in message
news:b96cd3a0-1bbf-46bc...@googlegroups.com...
On Thursday, December 3, 2020 at 2:39:20 PM UTC+11, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2357c8a-f038-477a...@googlegroups.com...
On Wednesday, December 2, 2020 at 9:32:45 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:f9beb047-d324-4bbf...@googlegroups.com...
On Wednesday, December 2, 2020 at 7:09:55 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:7d3d16b5-aaef-49f9...@googlegroups.com...
On Wednesday, December 2, 2020 at 5:46:57 PM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e4285dd9-ed97-4189...@googlegroups.com...
On Wednesday, December 2, 2020 at 3:26:58 PM UTC-5, Edward Rawde
wrote:
\"Edward Rawde\" <inv...@invalid.invalid> wrote in message
news:rq8q5r$l3r$1...@gioia.aioe.org...
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:6fce9360-b9e9-450f...@googlegroups.com...
On Wednesday, December 2, 2020 at 1:10:18 AM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:02352733-1a66-48f7...@googlegroups.com...
On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...

<snip>

Yes I agree it\'s useful if you want a slow (by today\'s standards) system
working directly on 12V or more. I managed never to design a 555 into
anything.

Me either.

I\'ve seen some strange circuits using a 555 including SMPS PWM
controller.

If it\'s the only tool you\'ve ever bothered to master, you can do lots of different things with a 555. It\'s been about thirty years since this was a useful skill.

--
Bill Sloman, Sydney

 

[Edward Rawde]

\"Rick C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:5f1f4d13-a97e-45c6-a2bf-cc51dfa035c4n@googlegroups.com...
On Wednesday, December 2, 2020 at 10:48:03 PM UTC-5, Edward Rawde wrote:

jla...@highlandsniptechnology.com> wrote in message
news:u3ngsfhkn7u43qs1v...@4ax.com...
On Wed, 2 Dec 2020 17:12:04 -0500, \"Edward Rawde\"
inv...@invalid.invalid> wrote:

\"Edward Rawde\" <inv...@invalid.invalid> wrote in message
news:rq8q5r$l3r$1...@gioia.aioe.org...
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:6fce9360-b9e9-450f...@googlegroups.com...
On Wednesday, December 2, 2020 at 1:10:18 AM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:02352733-1a66-48f7...@googlegroups.com...
On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets
some
shoot through during the switching.

One further thought.
If the problem is what happens when both switches are on then control
them
independently and arrange for that not to be the case.
In other words you need a break before make switchover.
Hang sufficient capacitance on the rail to the motor control circuit so
it
doesn\'t see the join.


How about using two diodes? Too easy I guess.
Yes a couple of diodes producing Vmain would stop Vin and Vbatt ever
meeting
each other.
Yes, they will do that. But they won\'t allow the rest of the circuit to
work and the reason why has already been covered. It\'s also very obvious
if you look at what the circuit is doing.

In fact, the diodes are already there for the low current always on path.
They work like a champ!

Actually, the predecessor circuit to this one had a FET based diode pair to
combine the input and battery circuits. But that was with a higher voltage
input and now we are using a 12 volt input. Use diodes and the battery
will always be powering the circuit until it runs down.

I think some of us are having trouble fully understanding your system
topology. A block diagram may or may not help. In any case, why does it
matter if both switches are on for say 50uS, what is that going to hurt?
If it could possibly hurt anything at all then add a diode so it can\'t.

--

Rick C.

 

[Edward Rawde]

\"Rick C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:5f1f4d13-a97e-45c6-a2bf-cc51dfa035c4n@googlegroups.com...
On Wednesday, December 2, 2020 at 10:48:03 PM UTC-5, Edward Rawde wrote:

jla...@highlandsniptechnology.com> wrote in message
news:u3ngsfhkn7u43qs1v...@4ax.com...
On Wed, 2 Dec 2020 17:12:04 -0500, \"Edward Rawde\"
inv...@invalid.invalid> wrote:

\"Edward Rawde\" <inv...@invalid.invalid> wrote in message
news:rq8q5r$l3r$1...@gioia.aioe.org...
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:6fce9360-b9e9-450f...@googlegroups.com...
On Wednesday, December 2, 2020 at 1:10:18 AM UTC-5, Edward Rawde
wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:02352733-1a66-48f7...@googlegroups.com...
On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets
some
shoot through during the switching.

[...]

Also I don\'t see how any harm could come to the op amp working as a
comparator (some of them don\'t like that) if D3 is replaced by a short
circuit.
If D3 is really needed then MBRS140 seems overkill.

Your TLV333 will probably be fine as a comparator but in cases where it
isn\'t, the advice is clearly to use a comparator if you need a comparator:
https://e2e.ti.com/support/amplifiers/f/14/t/684067

--

Rick C.

 

[whit3rd]

On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

There is a reason why regular FET driver ICs can source and sink some
several amps.

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.

It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode if you go over 110 mA (or whatever the
package limit is nowadays). The power and ground wiring for a CMOS
logic chip aren\'t busbars....

 

[Rick C]

On Monday, December 7, 2020 at 1:29:49 PM UTC-5, whit3rd wrote:

On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

There is a reason why regular FET driver ICs can source and sink some
several amps.

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.
It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode if you go over 110 mA (or whatever the
package limit is nowadays). The power and ground wiring for a CMOS
logic chip aren\'t busbars....

Are you suggesting there would be a current significantly higher than V/R? With a 400 ohm output resistance I would expect that to be sufficient to prevent an explosion. Let\'s see, 12V/400 = 30 mA.

Am I missing the point of your post?

This is not a switching power supply. These events will happen with an expected frequency of 1 microhertz or so.

--

Rick C.

++- Get 1,000 miles of free Supercharging
++- Tesla referral code - https://ts.la/richard11209

 

[whit3rd]

On Monday, December 7, 2020 at 12:00:26 PM UTC-8, gnuarm.del...@gmail.com wrote:

On Monday, December 7, 2020 at 1:29:49 PM UTC-5, whit3rd wrote:
On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.
It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode if you go over 110 mA (or whatever the
package limit is nowadays). The power and ground wiring for a CMOS
logic chip aren\'t busbars....

Are you suggesting there would be a current significantly higher than V/R? With a 400 ohm output resistance I would expect that to be sufficient to prevent an explosion. Let\'s see, 12V/400 = 30 mA.

Well, yes. CMOS, in particular, can go to 18V, and at low temperature, R isn\'t 400 ohms
either. I\'ve blown up wires with 4000 series CMOS, in a liquid-nitrogen level monitor,
because... it did get cold, and a 2n2222 only has emitter wire for 500 mA ( it was
the level-shifter that applied 12V power). Opened the (dead transistor) can, and
the wire was completely gone/evaporated. The cold plastic-package chip survived, though.

> This is not a switching power supply. These events will happen with an expected frequency of 1 microhertz or so.

It\'s not necessarily heat that does it in, but shock; dI/dt, not I^2.

 

[Rick C]

On Monday, December 7, 2020 at 10:34:04 PM UTC-5, whit3rd wrote:

On Monday, December 7, 2020 at 12:00:26 PM UTC-8, gnuarm.del...@gmail.com wrote:
On Monday, December 7, 2020 at 1:29:49 PM UTC-5, whit3rd wrote:
On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.
It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode if you go over 110 mA (or whatever the
package limit is nowadays). The power and ground wiring for a CMOS
logic chip aren\'t busbars....

Are you suggesting there would be a current significantly higher than V/R? With a 400 ohm output resistance I would expect that to be sufficient to prevent an explosion. Let\'s see, 12V/400 = 30 mA.
Well, yes. CMOS, in particular, can go to 18V, and at low temperature, R isn\'t 400 ohms
either. I\'ve blown up wires with 4000 series CMOS, in a liquid-nitrogen level monitor,
because... it did get cold, and a 2n2222 only has emitter wire for 500 mA ( it was
the level-shifter that applied 12V power). Opened the (dead transistor) can, and
the wire was completely gone/evaporated. The cold plastic-package chip survived, though.
This is not a switching power supply. These events will happen with an expected frequency of 1 microhertz or so.
It\'s not necessarily heat that does it in, but shock; dI/dt, not I^2.

Ok, we will put in the spec that this ventilator should not be used in liquid nitrogen.

I\'m sorry, I have no freaking idea what you are talking about. Why are you talking about liquid nitrogen temperatures? This device may be used at 20°C, who knows, maybe 15°C. But not even at 0°C much less -200°C.

So what exactly is your concern?

--

Rick C.

+++ Get 1,000 miles of free Supercharging
+++ Tesla referral code - https://ts.la/richard11209

 

[whit3rd]

On Monday, December 7, 2020 at 7:59:45 PM UTC-8, gnuarm.del...@gmail.com wrote:

On Monday, December 7, 2020 at 10:34:04 PM UTC-5, whit3rd wrote:
On Monday, December 7, 2020 at 12:00:26 PM UTC-8, gnuarm.del...@gmail.com wrote:
On Monday, December 7, 2020 at 1:29:49 PM UTC-5, whit3rd wrote:
On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.
It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode...

Well, yes. CMOS, in particular, can go to 18V, and at low temperature, R isn\'t 400 ohms
either. I\'ve blown up wires with 4000 series CMOS, in a liquid-nitrogen level monitor,
because... it did get cold, and a 2n2222 only has emitter wire for 500 mA ( it was
the level-shifter that applied 12V power). Opened the (dead transistor) can, and
the wire was completely gone/evaporated. The cold plastic-package chip survived, though.

I\'m sorry, I have no freaking idea what you are talking about. Why are you talking about liquid nitrogen temperatures? This device may be used at 20°C, who knows, maybe 15°C. But not even at 0°C much less -200°C.

So what exactly is your concern?

If one parallels six inverter outputs to do a drive, the power pins on the IC see a high
transient current that (with all six outputs driving a near-short) can create mechanical
stress that damages the wire. The old ULN2003 is infamous for having a package
limit that means you can\'t use the full drive of all the outputs at once.

 

[Rick C]

On Tuesday, December 8, 2020 at 7:24:37 PM UTC-5, whit3rd wrote:

On Monday, December 7, 2020 at 7:59:45 PM UTC-8, gnuarm.del...@gmail.com wrote:
On Monday, December 7, 2020 at 10:34:04 PM UTC-5, whit3rd wrote:
On Monday, December 7, 2020 at 12:00:26 PM UTC-8, gnuarm.del...@gmail..com wrote:
On Monday, December 7, 2020 at 1:29:49 PM UTC-5, whit3rd wrote:
On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.
It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode...
Well, yes. CMOS, in particular, can go to 18V, and at low temperature, R isn\'t 400 ohms
either. I\'ve blown up wires with 4000 series CMOS, in a liquid-nitrogen level monitor,
because... it did get cold, and a 2n2222 only has emitter wire for 500 mA ( it was
the level-shifter that applied 12V power). Opened the (dead transistor) can, and
the wire was completely gone/evaporated. The cold plastic-package chip survived, though.
I\'m sorry, I have no freaking idea what you are talking about. Why are you talking about liquid nitrogen temperatures? This device may be used at 20°C, who knows, maybe 15°C. But not even at 0°C much less -200°C.

So what exactly is your concern?
If one parallels six inverter outputs to do a drive, the power pins on the IC see a high
transient current that (with all six outputs driving a near-short) can create mechanical
stress that damages the wire. The old ULN2003 is infamous for having a package
limit that means you can\'t use the full drive of all the outputs at once.

I was not planning to parallel all six inverters. I was planning to use one to invert the signal while the other two are drivers from the original signal and the inverted signal. So one driving up and one driving down.

I\'m not trying to drive anything fast at all. In fact, I want to have a controlled transition so there are not large surges through the power FETs. That\'s the reason for using drivers that are relatively even handed with the pullup and pulldown. 400 ohms is great being a good value to limit the current. Gives the circuit some time to turn off and on.

I don\'t think this circuit is going to be used though. The guy doing the board is in love with Linear Technology and uses their parts for everything. A 50 cent buck switcher is being done with a $2 LT switcher. He has a $3-$4 power path control chip in the circuit. The total battery drain when off is not as low as it should be, but I don\'t think he\'s going to get rid of it because of that. His approach doesn\'t turn off all power to the board because I think the chip can\'t do that. I also don\'t see anything in the data sheet that indicates the design will prevent shoot through when switching.

Hmmm.... I just thought of a simplification to the circuit. A Schotky diode of sufficient capacity would handle the line input side even if it does drop a bit more voltage than the FETs will. It won\'t allow shoot through at all in that direction. There is still the issue of the capacitor surge however, but only when the battery voltage is lower than the line minus the diode drop.

--

Rick C.

---- Get 1,000 miles of free Supercharging
---- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Tuesday, December 8, 2020 at 7:24:37 PM UTC-5, whit3rd wrote:

On Monday, December 7, 2020 at 7:59:45 PM UTC-8, gnuarm.del...@gmail.com wrote:
On Monday, December 7, 2020 at 10:34:04 PM UTC-5, whit3rd wrote:
On Monday, December 7, 2020 at 12:00:26 PM UTC-8, gnuarm.del...@gmail..com wrote:
On Monday, December 7, 2020 at 1:29:49 PM UTC-5, whit3rd wrote:
On Sunday, December 6, 2020 at 10:16:19 PM UTC-8, boB wrote:

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.
It\'s perilous, though, to feed a capacitive load that way; the bond wires
on CMOS logic might explode...
Well, yes. CMOS, in particular, can go to 18V, and at low temperature, R isn\'t 400 ohms
either. I\'ve blown up wires with 4000 series CMOS, in a liquid-nitrogen level monitor,
because... it did get cold, and a 2n2222 only has emitter wire for 500 mA ( it was
the level-shifter that applied 12V power). Opened the (dead transistor) can, and
the wire was completely gone/evaporated. The cold plastic-package chip survived, though.
I\'m sorry, I have no freaking idea what you are talking about. Why are you talking about liquid nitrogen temperatures? This device may be used at 20°C, who knows, maybe 15°C. But not even at 0°C much less -200°C.

So what exactly is your concern?
If one parallels six inverter outputs to do a drive, the power pins on the IC see a high
transient current that (with all six outputs driving a near-short) can create mechanical
stress that damages the wire. The old ULN2003 is infamous for having a package
limit that means you can\'t use the full drive of all the outputs at once.

I was not planning to parallel all six inverters. I was planning to use one to invert the signal while the other two are drivers from the original signal and the inverted signal. So one driving up and one driving down.

I\'m not trying to drive anything fast at all. In fact, I want to have a controlled transition so there are not large surges through the power FETs. That\'s the reason for using drivers that are relatively even handed with the pullup and pulldown. 400 ohms is great being a good value to limit the current. Gives the circuit some time to turn off and on.

I don\'t think this circuit is going to be used though. The guy doing the board is in love with Linear Technology and uses their parts for everything. A 50 cent buck switcher is being done with a $2 LT switcher. He has a $3-$4 power path control chip in the circuit. The total battery drain when off is not as low as it should be, but I don\'t think he\'s going to get rid of it because of that. His approach doesn\'t turn off all power to the board because I think the chip can\'t do that. I also don\'t see anything in the data sheet that indicates the design will prevent shoot through when switching.

Hmmm.... I just thought of a simplification to the circuit. A Schotky diode of sufficient capacity would handle the line input side even if it does drop a bit more voltage than the FETs will. It won\'t allow shoot through at all in that direction. There is still the issue of the capacitor surge however, but only when the battery voltage is lower than the line minus the diode drop.

--

Rick C.

---- Get 1,000 miles of free Supercharging
---- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

I\'ve worked on this further. It occurred to me to set up the driver circuit a bit differently. Rather than drive the two sets of pass transistors from inverted signals, I thought it might work better to use a differential pair so that as one turns on the other turns off. I managed to get that to work pretty well on the transition when external power comes up, but not as well when power fails. I also realized I was leaving out an important component, the rather large caps on the motor circuit, 2000 uF. That greatly changes the picture with the shoot through but adds another dimension, the surge current in the caps.

So with this simulation the input power up is handled very well with the capacitor surge current less than an amp each (two capacitors, so 2 amps total). But on removal of input power is not so smooth with up to 3 amps each on the caps and shoot through of 8 amps into the line and 14 amps from the battery. Those may be tolerable numbers given the short duration of 1.5 ms or so.

There is also the power up and down of the unit. My simulation has the full motor current on during these times, which is not realistic. Turn on is the worst with 10 amps into the caps (5 each) and the same amount from the line of course. My sim doesn\'t test this on battery, but I expect the same since it\'s pretty much the same circuit. Turn off shows 4.5 amps out of the caps, but that\'s the motor current which would normally be off when the machine is turned off, so no problem.

Here is the latest version.

Version 4
SHEET 1 1752 916
WIRE 288 -608 272 -608
WIRE -608 -576 -672 -576
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WIRE -32 -176 -80 -176
WIRE 224 -176 192 -176
WIRE 368 -176 224 -176
WIRE 608 -176 608 -192
WIRE -432 -144 -464 -144
WIRE -352 -144 -352 -160
WIRE -80 -144 -80 -176
WIRE -432 -128 -432 -144
WIRE -464 -112 -464 -144
WIRE 224 -112 224 -176
WIRE 256 -112 224 -112
WIRE 368 -112 336 -112
WIRE -608 -96 -608 -272
WIRE -560 -96 -608 -96
WIRE -496 -96 -560 -96
WIRE 368 -96 368 -112
WIRE 496 -96 480 -96
WIRE 560 -96 496 -96
WIRE -384 -80 -432 -80
WIRE -256 -80 -256 -160
WIRE -256 -80 -384 -80
WIRE -608 -64 -608 -96
WIRE -496 -64 -544 -64
WIRE -80 -64 -80 -80
WIRE 608 -64 608 -80
WIRE 16 -48 16 -160
WIRE 112 -48 16 -48
WIRE 368 -48 112 -48
WIRE 416 -48 416 -160
WIRE 416 -48 368 -48
WIRE -464 0 -464 -48
WIRE -400 0 -464 0
WIRE -352 0 -400 0
WIRE -240 0 -288 0
WIRE -224 0 -240 0
WIRE 368 0 368 -48
WIRE 688 16 656 16
WIRE 848 16 768 16
WIRE -608 32 -608 16
WIRE 848 32 848 16
WIRE 48 48 32 48
WIRE 32 64 32 48
WIRE 480 80 416 80
WIRE 544 80 480 80
WIRE 560 80 544 80
WIRE -544 96 -544 -64
WIRE -512 96 -544 96
WIRE -400 96 -432 96
WIRE 848 128 848 112
WIRE 224 144 208 144
WIRE 336 144 304 144
WIRE 368 144 368 96
WIRE 368 144 336 144
WIRE 432 144 416 144
WIRE 544 144 544 80
WIRE 544 144 496 144
WIRE 32 160 32 144
WIRE 208 160 208 144
WIRE 416 160 416 144
FLAG -432 -128 0
FLAG -608 32 0
FLAG -672 -576 Vin
IOPIN -672 -576 In
FLAG -560 -96 Vth
FLAG 432 -432 VbatOn_n
FLAG -80 -432 VinOn_n
FLAG 288 -608 V_main
IOPIN 288 -608 Out
FLAG 64 -576 VinSS
FLAG 576 -576 VbatSS
FLAG 816 -576 Vbatt
IOPIN 816 -576 In
FLAG -704 -368 0
FLAG -688 -496 Vin
IOPIN -688 -496 In
FLAG 800 -384 0
FLAG 816 -512 Vbatt
IOPIN 816 -512 Out
FLAG -400 96 Vref
IOPIN -400 96 In
FLAG -240 0 Vin
FLAG 32 160 0
FLAG 48 48 V_main
IOPIN 48 48 In
FLAG -304 -272 VinOn
FLAG 656 -192 PwrFail_n
IOPIN 656 -192 Out
FLAG 464 -288 Vbatdrv
FLAG 64 -272 Vindrv
FLAG 208 160 0
FLAG 480 80 PwrOn_g
FLAG 112 -48 SoftStart
FLAG 704 -384 Vbatt
IOPIN 704 -384 In
FLAG 576 -384 Vin
IOPIN 576 -384 In
FLAG 736 -256 V12_always
IOPIN 736 -256 Out
FLAG 560 80 PwrOn
IOPIN 560 80 In
FLAG 240 -464 0
FLAG 336 -464 0
FLAG 656 16 PwrOn
IOPIN 656 16 Out
FLAG 848 128 0
FLAG 416 160 0
FLAG 192 -176 Vref
IOPIN 192 -176 Out
FLAG 336 144 Vreg
FLAG 608 -64 0
FLAG -80 -64 0
FLAG 368 -96 0
FLAG -384 -80 Vcmp
FLAG -400 0 U1pwr
FLAG -544 -64 V4Ref
FLAG 496 -96 Vcmp
FLAG 848 16 PwrOnDrv
FLAG -352 -144 0
FLAG -80 -272 Vinon_g
SYMBOL nmos 368 -256 R0
SYMATTR InstName M7
SYMATTR Value 2N7002
SYMBOL res -624 -80 R0
WINDOW 0 -11 40 Right 2
WINDOW 3 -11 65 Right 2
SYMATTR InstName R7
SYMATTR Value 27K
SYMBOL res -624 -448 R0
SYMATTR InstName R8
SYMATTR Value 47K
SYMBOL res -368 -448 R0
SYMATTR InstName R10
SYMATTR Value 10K
SYMBOL res 16 -560 R0
SYMATTR InstName R11
SYMATTR Value 2K
SYMBOL res -416 -288 R90
WINDOW 0 2 93 VBottom 2
WINDOW 3 1 29 VBottom 2
SYMATTR InstName R12
SYMATTR Value 330K
SYMBOL voltage 800 -496 R0
WINDOW 123 0 0 Left 0
WINDOW 39 10 98 Left 2
WINDOW 3 -324 -53 Invisible 2
SYMATTR SpiceLine Rser=0.1
SYMATTR Value PULSE(10 13 0.1s 0.1s 0.3s 0.45s)
SYMATTR InstName Batt
SYMBOL voltage -704 -480 R0
WINDOW 123 0 0 Left 0
WINDOW 39 -20 -49 Left 2
WINDOW 3 -8 153 Invisible 2
SYMATTR SpiceLine Rser=0.05
SYMATTR Value PULSE(0 12.5 0.2s 0.1s 0.1s 0.3s)
SYMATTR InstName In
SYMBOL res 16 48 R0
SYMATTR InstName LOAD
SYMATTR Value 2
SYMBOL res 400 -416 R0
SYMATTR InstName R14
SYMATTR Value 47
SYMBOL res 528 -560 R0
SYMATTR InstName R16
SYMATTR Value 2K
SYMBOL res 0 -384 R0
WINDOW 3 35 66 Left 2
SYMATTR InstName R15
SYMATTR Value 47
SYMBOL schottky 704 -352 R0
SYMATTR InstName D1
SYMATTR Value MBRS140
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 576 -352 R0
SYMATTR InstName D2
SYMATTR Value MBRS140
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky -288 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D3
SYMATTR Value MBRS140
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res -416 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1Meg
SYMBOL res 784 0 R90
WINDOW 0 -12 72 VRight 2
WINDOW 3 -12 57 VLeft 2
SYMATTR InstName R2
SYMATTR Value 1Meg
SYMBOL pmos -96 -528 R270
WINDOW 0 88 16 VRight 2
WINDOW 3 65 -18 VRight 2
SYMATTR InstName M1
SYMATTR Value AOD4185
SYMBOL pmos 192 -528 M270
WINDOW 0 87 62 VLeft 2
WINDOW 3 66 75 VLeft 2
SYMATTR InstName M2
SYMATTR Value AOD4185
SYMBOL pmos 416 -528 R270
WINDOW 0 88 38 VRight 2
WINDOW 3 65 -21 VRight 2
SYMATTR InstName M3
SYMATTR Value AOD4185
SYMBOL pmos 704 -528 M270
WINDOW 0 83 66 VLeft 2
WINDOW 3 63 74 VLeft 2
SYMATTR InstName M4
SYMATTR Value AOD4185
SYMBOL nmos -32 -256 R0
SYMATTR InstName M5
SYMATTR Value 2N7002
SYMBOL nmos 416 0 M0
WINDOW 0 62 34 Left 2
WINDOW 3 61 8 Left 2
SYMATTR InstName M8
SYMATTR Value 2N7002
SYMBOL Comparators\\\\LTC1841 -464 -80 M180
WINDOW 0 28 -18 Left 2
WINDOW 3 44 82 Right 2
SYMATTR InstName U1
SYMBOL polcap 224 -544 R0
WINDOW 3 24 56 Left 2
SYMATTR Value 1000µ
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=35 Irms=1.95 Rser=0.03 Lser=0 mfg=\"Panasonic\" pn=\"ECA1VFQ102L\" type=\"Al electrolytic\"
SYMBOL polcap 320 -544 R0
WINDOW 3 24 56 Left 2
SYMATTR Value 1000µ
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=35 Irms=1.95 Rser=0.03 Lser=0 mfg=\"Panasonic\" pn=\"ECA1VFQ102L\" type=\"Al electrolytic\"
SYMBOL voltage 848 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 3 -16 101 Invisible 2
WINDOW 0 -25 84 Right 2
SYMATTR Value PULSE(3.3V 0V 0.4S 1us 1us 99.998ms 0.5s)
SYMATTR InstName PwrOn
SYMBOL cap 496 128 R90
WINDOW 0 -11 41 VRight 2
WINDOW 3 -12 29 VLeft 2
SYMATTR InstName C3
SYMATTR Value 22nF
SYMBOL res 320 128 R90
WINDOW 0 -13 75 VRight 2
WINDOW 3 -13 56 VLeft 2
SYMATTR InstName R3
SYMATTR Value 330
SYMBOL nmos 560 -176 R0
SYMATTR InstName M9
SYMATTR Value 2N7002
SYMBOL res -272 -256 R0
SYMATTR InstName R4
SYMATTR Value 3.6K
SYMBOL cap -96 -144 R0
SYMATTR InstName C5
SYMATTR Value 150nF
SYMBOL voltage 240 -112 R270
WINDOW 123 0 0 Left 0
WINDOW 39 -20 -49 Left 2
WINDOW 3 37 76 VRight 2
WINDOW 0 37 38 VLeft 2
SYMATTR Value 4V
SYMATTR InstName Vref
SYMBOL res -368 -256 R0
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -128 -288 R90
WINDOW 0 -12 72 VRight 2
WINDOW 3 -12 57 VLeft 2
SYMATTR InstName R6
SYMATTR Value 100K
TEXT 160 -384 Left 3 !.tran 1sec
TEXT -552 -544 Left 2 ;Nominal range\\n11.4 < Vin < 12.6
TEXT -416 -64 Left 2 ;11.2V rising, 10.6V falling
TEXT 656 -160 Left 3 ;To Control Board
TEXT 560 160 Left 3 ;From Control Board

 

[Rick C]

I\'ve worked on this further. It occurred to me to set up the driver circuit a bit differently. Rather than drive the two sets of pass transistors from inverted signals, I thought it might work better to use a differential pair so that as one turns on the other turns off. I managed to get that to work pretty well on the transition when external power comes up, but not as well when power fails. I also realized I was leaving out an important component, the rather large caps on the motor circuit, 2000 uF. That greatly changes the picture with the shoot through but adds another dimension, the surge current in the caps.

So with this simulation the input power up is handled very well with the capacitor surge current less than an amp each (two capacitors, so 2 amps total). But on removal of input power is not so smooth with up to 3 amps each on the caps and shoot through of 8 amps into the line and 14 amps from the battery. Those may be tolerable numbers given the short duration of 1.5 ms or so.

There is also the power up and down of the unit. My simulation has the full motor current on during these times, which is not realistic. Turn on is the worst with 10 amps into the caps (5 each) and the same amount from the line of course. My sim doesn\'t test this on battery, but I expect the same since it\'s pretty much the same circuit. Turn off shows 4.5 amps out of the caps, but that\'s the motor current which would normally be off when the machine is turned off, so no problem.

Here is the latest version.

Version 4
SHEET 1 1752 916
WIRE 288 -608 272 -608
WIRE -608 -576 -672 -576
WIRE -352 -576 -608 -576
WIRE -96 -576 -352 -576
WIRE 32 -576 0 -576
WIRE 64 -576 32 -576
WIRE 96 -576 64 -576
WIRE 240 -576 192 -576
WIRE 272 -576 272 -608
WIRE 272 -576 240 -576
WIRE 336 -576 272 -576
WIRE 416 -576 336 -576
WIRE 544 -576 512 -576
WIRE 576 -576 544 -576
WIRE 608 -576 576 -576
WIRE 816 -576 704 -576
WIRE 32 -544 32 -576
WIRE 240 -544 240 -576
WIRE 336 -544 336 -576
WIRE 544 -544 544 -576
WIRE 816 -512 800 -512
WIRE -688 -496 -704 -496
WIRE 800 -480 800 -512
WIRE -704 -464 -704 -496
WIRE 240 -464 240 -480
WIRE 336 -464 336 -480
WIRE -608 -432 -608 -576
WIRE -352 -432 -352 -576
WIRE -80 -432 -96 -432
WIRE -16 -432 -16 -528
WIRE -16 -432 -80 -432
WIRE 16 -432 -16 -432
WIRE 32 -432 32 -464
WIRE 32 -432 16 -432
WIRE 112 -432 112 -528
WIRE 112 -432 32 -432
WIRE 432 -432 416 -432
WIRE 496 -432 496 -528
WIRE 496 -432 432 -432
WIRE 544 -432 544 -464
WIRE 544 -432 496 -432
WIRE 624 -432 624 -528
WIRE 624 -432 544 -432
WIRE 416 -400 416 -432
WIRE 592 -384 576 -384
WIRE 720 -384 704 -384
WIRE 800 -384 800 -400
WIRE -704 -368 -704 -384
WIRE 16 -368 16 -432
WIRE 592 -352 592 -384
WIRE 720 -352 720 -384
WIRE 416 -288 416 -320
WIRE 464 -288 416 -288
WIRE 480 -288 464 -288
WIRE -608 -272 -608 -352
WIRE -512 -272 -608 -272
WIRE -352 -272 -352 -352
WIRE -352 -272 -432 -272
WIRE -304 -272 -352 -272
WIRE -256 -272 -304 -272
WIRE -224 -272 -256 -272
WIRE -80 -272 -144 -272
WIRE 16 -272 16 -288
WIRE 64 -272 16 -272
WIRE 80 -272 64 -272
WIRE 16 -256 16 -272
WIRE 416 -256 416 -288
WIRE 592 -256 592 -288
WIRE 720 -256 720 -288
WIRE 720 -256 592 -256
WIRE 736 -256 720 -256
WIRE -352 -240 -352 -272
WIRE -256 -240 -256 -272
WIRE 656 -192 608 -192
WIRE -80 -176 -80 -272
WIRE -32 -176 -80 -176
WIRE 224 -176 192 -176
WIRE 368 -176 224 -176
WIRE 608 -176 608 -192
WIRE -432 -144 -464 -144
WIRE -352 -144 -352 -160
WIRE -80 -144 -80 -176
WIRE -432 -128 -432 -144
WIRE -464 -112 -464 -144
WIRE 224 -112 224 -176
WIRE 256 -112 224 -112
WIRE 368 -112 336 -112
WIRE -608 -96 -608 -272
WIRE -560 -96 -608 -96
WIRE -496 -96 -560 -96
WIRE 368 -96 368 -112
WIRE 496 -96 480 -96
WIRE 560 -96 496 -96
WIRE -384 -80 -432 -80
WIRE -256 -80 -256 -160
WIRE -256 -80 -384 -80
WIRE -608 -64 -608 -96
WIRE -496 -64 -544 -64
WIRE -80 -64 -80 -80
WIRE 608 -64 608 -80
WIRE 16 -48 16 -160
WIRE 112 -48 16 -48
WIRE 368 -48 112 -48
WIRE 416 -48 416 -160
WIRE 416 -48 368 -48
WIRE -464 0 -464 -48
WIRE -400 0 -464 0
WIRE -352 0 -400 0
WIRE -240 0 -288 0
WIRE -224 0 -240 0
WIRE 368 0 368 -48
WIRE 688 16 656 16
WIRE 848 16 768 16
WIRE -608 32 -608 16
WIRE 848 32 848 16
WIRE 48 48 32 48
WIRE 32 64 32 48
WIRE 480 80 416 80
WIRE 544 80 480 80
WIRE 560 80 544 80
WIRE -544 96 -544 -64
WIRE -512 96 -544 96
WIRE -400 96 -432 96
WIRE 848 128 848 112
WIRE 224 144 208 144
WIRE 336 144 304 144
WIRE 368 144 368 96
WIRE 368 144 336 144
WIRE 432 144 416 144
WIRE 544 144 544 80
WIRE 544 144 496 144
WIRE 32 160 32 144
WIRE 208 160 208 144
WIRE 416 160 416 144
FLAG -432 -128 0
FLAG -608 32 0
FLAG -672 -576 Vin
IOPIN -672 -576 In
FLAG -560 -96 Vth
FLAG 432 -432 VbatOn_n
FLAG -80 -432 VinOn_n
FLAG 288 -608 V_main
IOPIN 288 -608 Out
FLAG 64 -576 VinSS
FLAG 576 -576 VbatSS
FLAG 816 -576 Vbatt
IOPIN 816 -576 In
FLAG -704 -368 0
FLAG -688 -496 Vin
IOPIN -688 -496 In
FLAG 800 -384 0
FLAG 816 -512 Vbatt
IOPIN 816 -512 Out
FLAG -400 96 Vref
IOPIN -400 96 In
FLAG -240 0 Vin
FLAG 32 160 0
FLAG 48 48 V_main
IOPIN 48 48 In
FLAG -304 -272 VinOn
FLAG 656 -192 PwrFail_n
IOPIN 656 -192 Out
FLAG 464 -288 Vbatdrv
FLAG 64 -272 Vindrv
FLAG 208 160 0
FLAG 480 80 PwrOn_g
FLAG 112 -48 SoftStart
FLAG 704 -384 Vbatt
IOPIN 704 -384 In
FLAG 576 -384 Vin
IOPIN 576 -384 In
FLAG 736 -256 V12_always
IOPIN 736 -256 Out
FLAG 560 80 PwrOn
IOPIN 560 80 In
FLAG 240 -464 0
FLAG 336 -464 0
FLAG 656 16 PwrOn
IOPIN 656 16 Out
FLAG 848 128 0
FLAG 416 160 0
FLAG 192 -176 Vref
IOPIN 192 -176 Out
FLAG 336 144 Vreg
FLAG 608 -64 0
FLAG -80 -64 0
FLAG 368 -96 0
FLAG -384 -80 Vcmp
FLAG -400 0 U1pwr
FLAG -544 -64 V4Ref
FLAG 496 -96 Vcmp
FLAG 848 16 PwrOnDrv
FLAG -352 -144 0
FLAG -80 -272 Vinon_g
SYMBOL nmos 368 -256 R0
SYMATTR InstName M7
SYMATTR Value 2N7002
SYMBOL res -624 -80 R0
WINDOW 0 -11 40 Right 2
WINDOW 3 -11 65 Right 2
SYMATTR InstName R7
SYMATTR Value 27K
SYMBOL res -624 -448 R0
SYMATTR InstName R8
SYMATTR Value 47K
SYMBOL res -368 -448 R0
SYMATTR InstName R10
SYMATTR Value 10K
SYMBOL res 16 -560 R0
SYMATTR InstName R11
SYMATTR Value 2K
SYMBOL res -416 -288 R90
WINDOW 0 2 93 VBottom 2
WINDOW 3 1 29 VBottom 2
SYMATTR InstName R12
SYMATTR Value 330K
SYMBOL voltage 800 -496 R0
WINDOW 123 0 0 Left 0
WINDOW 39 10 98 Left 2
WINDOW 3 -324 -53 Invisible 2
SYMATTR SpiceLine Rser=0.1
SYMATTR Value PULSE(10 13 0.1s 0.1s 0.3s 0.45s)
SYMATTR InstName Batt
SYMBOL voltage -704 -480 R0
WINDOW 123 0 0 Left 0
WINDOW 39 -20 -49 Left 2
WINDOW 3 -8 153 Invisible 2
SYMATTR SpiceLine Rser=0.05
SYMATTR Value PULSE(0 12.5 0.2s 0.1s 0.1s 0.3s)
SYMATTR InstName In
SYMBOL res 16 48 R0
SYMATTR InstName LOAD
SYMATTR Value 2
SYMBOL res 400 -416 R0
SYMATTR InstName R14
SYMATTR Value 47
SYMBOL res 528 -560 R0
SYMATTR InstName R16
SYMATTR Value 2K
SYMBOL res 0 -384 R0
WINDOW 3 35 66 Left 2
SYMATTR InstName R15
SYMATTR Value 47
SYMBOL schottky 704 -352 R0
SYMATTR InstName D1
SYMATTR Value MBRS140
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 576 -352 R0
SYMATTR InstName D2
SYMATTR Value MBRS140
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky -288 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D3
SYMATTR Value MBRS140
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res -416 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1Meg
SYMBOL res 784 0 R90
WINDOW 0 -12 72 VRight 2
WINDOW 3 -12 57 VLeft 2
SYMATTR InstName R2
SYMATTR Value 1Meg
SYMBOL pmos -96 -528 R270
WINDOW 0 88 16 VRight 2
WINDOW 3 65 -18 VRight 2
SYMATTR InstName M1
SYMATTR Value AOD4185
SYMBOL pmos 192 -528 M270
WINDOW 0 87 62 VLeft 2
WINDOW 3 66 75 VLeft 2
SYMATTR InstName M2
SYMATTR Value AOD4185
SYMBOL pmos 416 -528 R270
WINDOW 0 88 38 VRight 2
WINDOW 3 65 -21 VRight 2
SYMATTR InstName M3
SYMATTR Value AOD4185
SYMBOL pmos 704 -528 M270
WINDOW 0 83 66 VLeft 2
WINDOW 3 63 74 VLeft 2
SYMATTR InstName M4
SYMATTR Value AOD4185
SYMBOL nmos -32 -256 R0
SYMATTR InstName M5
SYMATTR Value 2N7002
SYMBOL nmos 416 0 M0
WINDOW 0 62 34 Left 2
WINDOW 3 61 8 Left 2
SYMATTR InstName M8
SYMATTR Value 2N7002
SYMBOL Comparators\\\\LTC1841 -464 -80 M180
WINDOW 0 28 -18 Left 2
WINDOW 3 44 82 Right 2
SYMATTR InstName U1
SYMBOL polcap 224 -544 R0
WINDOW 3 24 56 Left 2
SYMATTR Value 1000µ
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=35 Irms=1.95 Rser=0.03 Lser=0 mfg=\"Panasonic\" pn=\"ECA1VFQ102L\" type=\"Al electrolytic\"
SYMBOL polcap 320 -544 R0
WINDOW 3 24 56 Left 2
SYMATTR Value 1000µ
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=35 Irms=1.95 Rser=0.03 Lser=0 mfg=\"Panasonic\" pn=\"ECA1VFQ102L\" type=\"Al electrolytic\"
SYMBOL voltage 848 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 3 -16 101 Invisible 2
WINDOW 0 -25 84 Right 2
SYMATTR Value PULSE(3.3V 0V 0.4S 1us 1us 99.998ms 0.5s)
SYMATTR InstName PwrOn
SYMBOL cap 496 128 R90
WINDOW 0 -11 41 VRight 2
WINDOW 3 -12 29 VLeft 2
SYMATTR InstName C3
SYMATTR Value 22nF
SYMBOL res 320 128 R90
WINDOW 0 -13 75 VRight 2
WINDOW 3 -13 56 VLeft 2
SYMATTR InstName R3
SYMATTR Value 330
SYMBOL nmos 560 -176 R0
SYMATTR InstName M9
SYMATTR Value 2N7002
SYMBOL res -272 -256 R0
SYMATTR InstName R4
SYMATTR Value 3.6K
SYMBOL cap -96 -144 R0
SYMATTR InstName C5
SYMATTR Value 150nF
SYMBOL voltage 240 -112 R270
WINDOW 123 0 0 Left 0
WINDOW 39 -20 -49 Left 2
WINDOW 3 37 76 VRight 2
WINDOW 0 37 38 VLeft 2
SYMATTR Value 4V
SYMATTR InstName Vref
SYMBOL res -368 -256 R0
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -128 -288 R90
WINDOW 0 -12 72 VRight 2
WINDOW 3 -12 57 VLeft 2
SYMATTR InstName R6
SYMATTR Value 100K
TEXT 160 -384 Left 3 !.tran 1sec
TEXT -552 -544 Left 2 ;Nominal range\\n11.4 < Vin < 12.6
TEXT -416 -64 Left 2 ;11.2V rising, 10.6V falling
TEXT 656 -160 Left 3 ;To Control Board
TEXT 560 160 Left 3 ;From Control Board

 

[Joe Gwinn]

On Tue, 1 Dec 2020 20:55:13 -0800 (PST), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets some
shoot through during the switching. Mostly it\'s a concern because of the
slow turn off using a resistive pullup. Then there\'s the issue of the two
power supplies being somewhat different voltages. The high drive has to
turn off the FETs completely. The modes are for one or the other to be on
or for both to be off.

I\'m wondering if a digital logic device can be used to drive this circuit.
4000 series CMOS can handle the 15V max levels but I don\'t know if it is
capable of adequate drive to switch a 10 amp FET. I guess it can\'t be much
worse than the 10k ohm pull up I\'m using now.

Not sure how to power this. Could use diodes to route power to the CMOS
device. I\'d still be concerned about the inputs though. A low input
voltage could provide too little drive for the CMOS input. So everything
would have to be referenced to the diode routed power which might draw too
much current from the battery when it\'s all off.
After reading that I am unable to get a clear picture of what you\'re trying
to do. I would have posted a reference to a scan of the intended circuit,
complete with labels showing what power is coming from where and going where
and when and why.
Any suggestions on a driver that isn\'t high quiescent drain? Most of what
I find are bipolar. It should be very cheap too.
I don\'t see anything wrong with using slow switching FETs to switch power
rails, provided it\'s not so slow that the FET heats up too much.
Maybe you need a transistor or two to get the FET gate drive right but hard
to tell without a schematic.

It\'s not switching in the sense of motor control or a DC converter. It is a switch over from line to battery when input power fails. Each switch is two pFETs to prevent back feed of current. The battery is 12V nominal SLA and the input is a 12V DC for running a motor with 10 amp peaks and 4 amp nominal. I use a comparator on the input DC to detect when it is absent which switches between the two power sources. Using transistors with pull ups means the pull up is slow and there are some 50 us where current passes through both switches between the two power sources. Maybe this isn\'t much of a real problem, but 15 or more amps seems like something to minimize the time duration of if the current itself can\'t be minimized.

If logic gates are used instead of the transistors with pullups the transition time will be much shorter and the issue of shoot through current will be less significant. But I\'m probably showing my ignorance of what is needed for this circuit to work well. One guy on the team has picked a LT part at $4 to control the pFETs. It\'s a nice part, but when was an LT part ever cheap? It just doesn\'t seem like a hard circuit for an experienced power designer to pull off.

The outputs of 4000B series CMOS logic hates have an impedance of
about 400 ohms, and can source a milliamp. To control 10 amps, the
beta would need to be 10,000. A darlington pair maybe, but a driver
stage seems simpler and more robust.

Joe Gwinn

 

[Rick C]

On Sunday, December 6, 2020 at 5:59:17 PM UTC-5, Joe Gwinn wrote:

On Tue, 1 Dec 2020 20:55:13 -0800 (PST), Rick C
gnuarm.del...@gmail.com> wrote:

On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets some
shoot through during the switching. Mostly it\'s a concern because of the
slow turn off using a resistive pullup. Then there\'s the issue of the two
power supplies being somewhat different voltages. The high drive has to
turn off the FETs completely. The modes are for one or the other to be on
or for both to be off.

I\'m wondering if a digital logic device can be used to drive this circuit.
4000 series CMOS can handle the 15V max levels but I don\'t know if it is
capable of adequate drive to switch a 10 amp FET. I guess it can\'t be much
worse than the 10k ohm pull up I\'m using now.

Not sure how to power this. Could use diodes to route power to the CMOS
device. I\'d still be concerned about the inputs though. A low input
voltage could provide too little drive for the CMOS input. So everything
would have to be referenced to the diode routed power which might draw too
much current from the battery when it\'s all off.
After reading that I am unable to get a clear picture of what you\'re trying
to do. I would have posted a reference to a scan of the intended circuit,
complete with labels showing what power is coming from where and going where
and when and why.
Any suggestions on a driver that isn\'t high quiescent drain? Most of what
I find are bipolar. It should be very cheap too.
I don\'t see anything wrong with using slow switching FETs to switch power
rails, provided it\'s not so slow that the FET heats up too much.
Maybe you need a transistor or two to get the FET gate drive right but hard
to tell without a schematic.

It\'s not switching in the sense of motor control or a DC converter. It is a switch over from line to battery when input power fails. Each switch is two pFETs to prevent back feed of current. The battery is 12V nominal SLA and the input is a 12V DC for running a motor with 10 amp peaks and 4 amp nominal. I use a comparator on the input DC to detect when it is absent which switches between the two power sources. Using transistors with pull ups means the pull up is slow and there are some 50 us where current passes through both switches between the two power sources. Maybe this isn\'t much of a real problem, but 15 or more amps seems like something to minimize the time duration of if the current itself can\'t be minimized.

If logic gates are used instead of the transistors with pullups the transition time will be much shorter and the issue of shoot through current will be less significant. But I\'m probably showing my ignorance of what is needed for this circuit to work well. One guy on the team has picked a LT part at $4 to control the pFETs. It\'s a nice part, but when was an LT part ever cheap? It just doesn\'t seem like a hard circuit for an experienced power designer to pull off.

The outputs of 4000B series CMOS logic hates have an impedance of
about 400 ohms, and can source a milliamp. To control 10 amps, the
beta would need to be 10,000. A darlington pair maybe, but a driver
stage seems simpler and more robust.

Joe Gwinn

Beta applies to a junction transistor. I\'m using FETs which are typically characterized by transconductance. Since the CMOS device can provide the full voltage swing there should be no problem controlling the maximum current the FET can handle. The current can be an issue with switching speed charging the gates of the pass FETs, but the present design is using a 5 mA current limiter using a reference voltage on the gate of a FET and a source leg resistor of 330 ohm. Then there is a 47 ohm series resistor after the controlling FETs, so nearly 400 ohms.

If the circuit could be timed appropriately, a 400 ohm driving resistance would be very useful. The problem I\'m seeing is from the difficulty of controlling the switching on vs. off of the two paths. Enable one too early and there is shoot through, enable too late and there is a gap during which the voltage droops. Add in large capacitors on the load and too fast of a switching time and the capacitor sees large surge currents from the different voltages, especially when being turned on.

I\'m wondering if any of this is avoided by using the \"magic\" power path controller from LT. I bet it has the same problems.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Sunday, December 6, 2020 at 5:59:17 PM UTC-5, Joe Gwinn wrote:

On Tue, 1 Dec 2020 20:55:13 -0800 (PST), Rick C
gnuarm.del...@gmail.com> wrote:

On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets some
shoot through during the switching. Mostly it\'s a concern because of the
slow turn off using a resistive pullup. Then there\'s the issue of the two
power supplies being somewhat different voltages. The high drive has to
turn off the FETs completely. The modes are for one or the other to be on
or for both to be off.

I\'m wondering if a digital logic device can be used to drive this circuit.
4000 series CMOS can handle the 15V max levels but I don\'t know if it is
capable of adequate drive to switch a 10 amp FET. I guess it can\'t be much
worse than the 10k ohm pull up I\'m using now.

Not sure how to power this. Could use diodes to route power to the CMOS
device. I\'d still be concerned about the inputs though. A low input
voltage could provide too little drive for the CMOS input. So everything
would have to be referenced to the diode routed power which might draw too
much current from the battery when it\'s all off.
After reading that I am unable to get a clear picture of what you\'re trying
to do. I would have posted a reference to a scan of the intended circuit,
complete with labels showing what power is coming from where and going where
and when and why.
Any suggestions on a driver that isn\'t high quiescent drain? Most of what
I find are bipolar. It should be very cheap too.
I don\'t see anything wrong with using slow switching FETs to switch power
rails, provided it\'s not so slow that the FET heats up too much.
Maybe you need a transistor or two to get the FET gate drive right but hard
to tell without a schematic.

It\'s not switching in the sense of motor control or a DC converter. It is a switch over from line to battery when input power fails. Each switch is two pFETs to prevent back feed of current. The battery is 12V nominal SLA and the input is a 12V DC for running a motor with 10 amp peaks and 4 amp nominal. I use a comparator on the input DC to detect when it is absent which switches between the two power sources. Using transistors with pull ups means the pull up is slow and there are some 50 us where current passes through both switches between the two power sources. Maybe this isn\'t much of a real problem, but 15 or more amps seems like something to minimize the time duration of if the current itself can\'t be minimized.

If logic gates are used instead of the transistors with pullups the transition time will be much shorter and the issue of shoot through current will be less significant. But I\'m probably showing my ignorance of what is needed for this circuit to work well. One guy on the team has picked a LT part at $4 to control the pFETs. It\'s a nice part, but when was an LT part ever cheap? It just doesn\'t seem like a hard circuit for an experienced power designer to pull off.

The outputs of 4000B series CMOS logic hates have an impedance of
about 400 ohms, and can source a milliamp. To control 10 amps, the
beta would need to be 10,000. A darlington pair maybe, but a driver
stage seems simpler and more robust.

Joe Gwinn

Beta applies to a junction transistor. I\'m using FETs which are typically characterized by transconductance. Since the CMOS device can provide the full voltage swing there should be no problem controlling the maximum current the FET can handle. The current can be an issue with switching speed charging the gates of the pass FETs, but the present design is using a 5 mA current limiter using a reference voltage on the gate of a FET and a source leg resistor of 330 ohm. Then there is a 47 ohm series resistor after the controlling FETs, so nearly 400 ohms.

If the circuit could be timed appropriately, a 400 ohm driving resistance would be very useful. The problem I\'m seeing is from the difficulty of controlling the switching on vs. off of the two paths. Enable one too early and there is shoot through, enable too late and there is a gap during which the voltage droops. Add in large capacitors on the load and too fast of a switching time and the capacitor sees large surge currents from the different voltages, especially when being turned on.

I\'m wondering if any of this is avoided by using the \"magic\" power path controller from LT. I bet it has the same problems.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[boB]

On Sun, 6 Dec 2020 16:56:27 -0800 (PST), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, December 6, 2020 at 5:59:17 PM UTC-5, Joe Gwinn wrote:
On Tue, 1 Dec 2020 20:55:13 -0800 (PST), Rick C
gnuarm.del...@gmail.com> wrote:

On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets some
shoot through during the switching. Mostly it\'s a concern because of the
slow turn off using a resistive pullup. Then there\'s the issue of the two
power supplies being somewhat different voltages. The high drive has to
turn off the FETs completely. The modes are for one or the other to be on
or for both to be off.

I\'m wondering if a digital logic device can be used to drive this circuit.
4000 series CMOS can handle the 15V max levels but I don\'t know if it is
capable of adequate drive to switch a 10 amp FET. I guess it can\'t be much
worse than the 10k ohm pull up I\'m using now.

Not sure how to power this. Could use diodes to route power to the CMOS
device. I\'d still be concerned about the inputs though. A low input
voltage could provide too little drive for the CMOS input. So everything
would have to be referenced to the diode routed power which might draw too
much current from the battery when it\'s all off.
After reading that I am unable to get a clear picture of what you\'re trying
to do. I would have posted a reference to a scan of the intended circuit,
complete with labels showing what power is coming from where and going where
and when and why.
Any suggestions on a driver that isn\'t high quiescent drain? Most of what
I find are bipolar. It should be very cheap too.
I don\'t see anything wrong with using slow switching FETs to switch power
rails, provided it\'s not so slow that the FET heats up too much.
Maybe you need a transistor or two to get the FET gate drive right but hard
to tell without a schematic.

It\'s not switching in the sense of motor control or a DC converter. It is a switch over from line to battery when input power fails. Each switch is two pFETs to prevent back feed of current. The battery is 12V nominal SLA and the input is a 12V DC for running a motor with 10 amp peaks and 4 amp nominal. I use a comparator on the input DC to detect when it is absent which switches between the two power sources. Using transistors with pull ups means the pull up is slow and there are some 50 us where current passes through both switches between the two power sources. Maybe this isn\'t much of a real problem, but 15 or more amps seems like something to minimize the time duration of if the current itself can\'t be minimized.

If logic gates are used instead of the transistors with pullups the transition time will be much shorter and the issue of shoot through current will be less significant. But I\'m probably showing my ignorance of what is needed for this circuit to work well. One guy on the team has picked a LT part at $4 to control the pFETs. It\'s a nice part, but when was an LT part ever cheap? It just doesn\'t seem like a hard circuit for an experienced power designer to pull off.

The outputs of 4000B series CMOS logic hates have an impedance of
about 400 ohms, and can source a milliamp. To control 10 amps, the
beta would need to be 10,000. A darlington pair maybe, but a driver
stage seems simpler and more robust.

Joe Gwinn

Beta applies to a junction transistor. I\'m using FETs which are typically characterized by transconductance. Since the CMOS device can provide the full voltage swing there should be no problem controlling the maximum current the FET can handle. The current can be an issue with switching speed charging the gates of the pass FETs, but the present design is using a 5 mA current limiter using a reference voltage on the gate of a FET and a source leg resistor of 330 ohm. Then there is a 47 ohm series resistor after the controlling FETs, so nearly 400 ohms.

If the circuit could be timed appropriately, a 400 ohm driving resistance would be very useful. The problem I\'m seeing is from the difficulty of controlling the switching on vs. off of the two paths. Enable one too early and there is shoot through, enable too late and there is a gap during which the voltage droops. Add in large capacitors on the load and too fast of a switching time and the capacitor sees large surge currents from the different voltages, especially when being turned on.

I\'m wondering if any of this is avoided by using the \"magic\" power path controller from LT. I bet it has the same problems.

There is a reason why regular FET driver ICs can source and sink some
several amps.

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.

If your FET is small though and especially if you aren\'t going to
switch it fast, then 1 mA might be plenty. Maybe.

 

[boB]

On Sun, 6 Dec 2020 16:56:27 -0800 (PST), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, December 6, 2020 at 5:59:17 PM UTC-5, Joe Gwinn wrote:
On Tue, 1 Dec 2020 20:55:13 -0800 (PST), Rick C
gnuarm.del...@gmail.com> wrote:

On Tuesday, December 1, 2020 at 9:56:01 PM UTC-5, Edward Rawde wrote:
\"Rick C\" <gnuarm.del...@gmail.com> wrote in message
news:e2a6129f-a999-4b9d...@googlegroups.com...
I have a circuit with a pair of pFETs to switch power and it gets some
shoot through during the switching. Mostly it\'s a concern because of the
slow turn off using a resistive pullup. Then there\'s the issue of the two
power supplies being somewhat different voltages. The high drive has to
turn off the FETs completely. The modes are for one or the other to be on
or for both to be off.

I\'m wondering if a digital logic device can be used to drive this circuit.
4000 series CMOS can handle the 15V max levels but I don\'t know if it is
capable of adequate drive to switch a 10 amp FET. I guess it can\'t be much
worse than the 10k ohm pull up I\'m using now.

Not sure how to power this. Could use diodes to route power to the CMOS
device. I\'d still be concerned about the inputs though. A low input
voltage could provide too little drive for the CMOS input. So everything
would have to be referenced to the diode routed power which might draw too
much current from the battery when it\'s all off.
After reading that I am unable to get a clear picture of what you\'re trying
to do. I would have posted a reference to a scan of the intended circuit,
complete with labels showing what power is coming from where and going where
and when and why.
Any suggestions on a driver that isn\'t high quiescent drain? Most of what
I find are bipolar. It should be very cheap too.
I don\'t see anything wrong with using slow switching FETs to switch power
rails, provided it\'s not so slow that the FET heats up too much.
Maybe you need a transistor or two to get the FET gate drive right but hard
to tell without a schematic.

It\'s not switching in the sense of motor control or a DC converter. It is a switch over from line to battery when input power fails. Each switch is two pFETs to prevent back feed of current. The battery is 12V nominal SLA and the input is a 12V DC for running a motor with 10 amp peaks and 4 amp nominal. I use a comparator on the input DC to detect when it is absent which switches between the two power sources. Using transistors with pull ups means the pull up is slow and there are some 50 us where current passes through both switches between the two power sources. Maybe this isn\'t much of a real problem, but 15 or more amps seems like something to minimize the time duration of if the current itself can\'t be minimized.

If logic gates are used instead of the transistors with pullups the transition time will be much shorter and the issue of shoot through current will be less significant. But I\'m probably showing my ignorance of what is needed for this circuit to work well. One guy on the team has picked a LT part at $4 to control the pFETs. It\'s a nice part, but when was an LT part ever cheap? It just doesn\'t seem like a hard circuit for an experienced power designer to pull off.

The outputs of 4000B series CMOS logic hates have an impedance of
about 400 ohms, and can source a milliamp. To control 10 amps, the
beta would need to be 10,000. A darlington pair maybe, but a driver
stage seems simpler and more robust.

Joe Gwinn

Beta applies to a junction transistor. I\'m using FETs which are typically characterized by transconductance. Since the CMOS device can provide the full voltage swing there should be no problem controlling the maximum current the FET can handle. The current can be an issue with switching speed charging the gates of the pass FETs, but the present design is using a 5 mA current limiter using a reference voltage on the gate of a FET and a source leg resistor of 330 ohm. Then there is a 47 ohm series resistor after the controlling FETs, so nearly 400 ohms.

If the circuit could be timed appropriately, a 400 ohm driving resistance would be very useful. The problem I\'m seeing is from the difficulty of controlling the switching on vs. off of the two paths. Enable one too early and there is shoot through, enable too late and there is a gap during which the voltage droops. Add in large capacitors on the load and too fast of a switching time and the capacitor sees large surge currents from the different voltages, especially when being turned on.

I\'m wondering if any of this is avoided by using the \"magic\" power path controller from LT. I bet it has the same problems.

There is a reason why regular FET driver ICs can source and sink some
several amps.

I have seen CD4000 hex drivers or hex inverters used for FET drive
with ALL sections paralleled. That can also help speed up that gate
drive.

If your FET is small though and especially if you aren\'t going to
switch it fast, then 1 mA might be plenty. Maybe.

 

[Piotr Wyderski]

Rick C wrote:

> His approach to the switching circuit is to use the LTC4416 which is a $4 part. It\'s also not at all clear to me that it won\'t have the same shoot through current issue.

But how do you know if it is an issue at all? How many amps are you
switching?

There is another LT power prioritiser that modulates V_gate in order to
keep the switching currents sane, forgot the number, 14-something.

Best regards, Piotr

 

[Rick C]

On Wednesday, December 9, 2020 at 2:50:47 AM UTC-5, Piotr Wyderski wrote:

Rick C wrote:

His approach to the switching circuit is to use the LTC4416 which is a $4 part. It\'s also not at all clear to me that it won\'t have the same shoot through current issue.
But how do you know if it is an issue at all? How many amps are you
switching?

There is another LT power prioritiser that modulates V_gate in order to
keep the switching currents sane, forgot the number, 14-something.

The currents depend heavily on the details of the circuit in a way that I don\'t trust the simulation to be accurate.

The currents tend to be from the battery into the external 12V PSU or from the caps to the PSU or from the battery. I\'m willing to bet the guy designing the circuit has not looked at these currents at all. I don\'t see an LTspice model for the 4416 or I would run the simulation myself. Shoot! I just looked harder and rather than power they have it under \"SpecialFunctions\". So I\'ll give this circuit a test run and see what it does.

So how would they measure the currents? I guess the voltages across the FETs? The internal workings of the chip are a bit complex.

So I ran the simulation with the LTC4416 and the huge capacitor charging current is still there. So much for the purported soft start. 16 amps into the cap when the input power drops and the battery is fully charged at 13 V.. So the battery is the irresistible force and the capacitor is the immovable object?

--

Rick C.

---+ Get 1,000 miles of free Supercharging
---+ Tesla referral code - https://ts.la/richard11209