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Tim Wescott
Guest
Guest
Wed Jan 25, 2012 6:44 pm
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
John Larkin
Guest
Guest
Wed Jan 25, 2012 8:27 pm
On Wed, 25 Jan 2012 11:44:25 -0600, Tim Wescott <tim_at_seemywebsite.com>
wrote:
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
You can charge pump off the switcher node of one of the positive
switchers to get negative volts, essentially a classic "voltage
doubler" capacitor-diode thing. It will make roughly -24, which is a
lot to regulate to -5. A small series resistor is a good idea... some
switchers don't like this being done to them.
But if it's low current, you may as well buy a standard charge-pump
voltage inverter chip and run that off +5.
The LTC "LTM" module series can be used to make -5 from +24. Not real
cheap, but easy. Or build a Cuk switcher.
Another possibility: buy one of those cheap SIP dc/dc converters, $4
roughly.
John
Joerg
Guest
Guest
Wed Jan 25, 2012 8:53 pm
Tim Wescott wrote:
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If you run a buck to make +5V you can use a dual inductor instead of a
single, plus another diode -> There's your -5V. Dual inductors have
become cheap catalog items these days.
As for the model, the LTSpice group on Yahoo has some. I think the best
one was from Helmut.
--
Regards, Joerg
http://www.analogconsultants.com/
Spehro Pefhany
Guest
Guest
Wed Jan 25, 2012 9:17 pm
On Wed, 25 Jan 2012 11:44:25 -0600, Tim Wescott <tim_at_seemywebsite.com>
wrote:
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
I've used another winding on the inductor, but it worries me a bit.
Jim Thompson
Guest
Guest
Wed Jan 25, 2012 9:20 pm
On Wed, 25 Jan 2012 11:44:25 -0600, Tim Wescott <tim_at_seemywebsite.com>
wrote:
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
Here's how I did a +5V/-12V switcher at GenRad ~1980...
http://www.analog-innovations.com/SED/OldStyleBuckSwitcherWithAddedNegativeOutput.pdf
I don't know if modern switcher chips will allow for such shenanigans
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Joerg
Guest
Guest
Wed Jan 25, 2012 9:48 pm
Spehro Pefhany wrote:
Quote:
On Wed, 25 Jan 2012 11:44:25 -0600, Tim Wescott <tim_at_seemywebsite.com
wrote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
I've used another winding on the inductor, but it worries me a bit.
wrote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
I've used another winding on the inductor, but it worries me a bit.
Why? Me no worry :-)
It does require the converter to keep running though. If the positive
supply is not loaded much the negative can drop off. But with analog
stuff that usually isn't a concern. On sync bucks one can force many
chips to remain in sync-mode even under light loads and not let them go
into burst mode.
--
Regards, Joerg
http://www.analogconsultants.com/
Fred Bartoli
Guest
Guest
Wed Jan 25, 2012 9:51 pm
Tim Wescott a écrit :
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
I guess the +12V switcher is a buck.
Just use a double winding coil in lieu of a simple inductor, and use the
secondary so that it copies the buck output voltage at your negative
output (energy taken back from the buck output bypass cap).
If your main buck is *not* a synchronous rectification one, then you
even have the buck free wheeling diode drop making for your negative
branch diode drop.
--
Thanks,
Fred.
John Devereux
Guest
Guest
Wed Jan 25, 2012 9:52 pm
Joerg <invalid_at_invalid.invalid> writes:
Quote:
Tim Wescott wrote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If you run a buck to make +5V you can use a dual inductor instead of a
single, plus another diode -> There's your -5V. Dual inductors have
become cheap catalog items these days.
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If you run a buck to make +5V you can use a dual inductor instead of a
single, plus another diode -> There's your -5V. Dual inductors have
become cheap catalog items these days.
NICE that seems a general and very useful technique.
I have used those dual inductors for flyback but never thought of them
used like that.
[...]
--
John Devereux
Joerg
Guest
Guest
Wed Jan 25, 2012 9:59 pm
John Devereux wrote:
Quote:
Joerg <invalid_at_invalid.invalid> writes:
Tim Wescott wrote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If you run a buck to make +5V you can use a dual inductor instead of a
single, plus another diode -> There's your -5V. Dual inductors have
become cheap catalog items these days.
NICE that seems a general and very useful technique.
I have used those dual inductors for flyback but never thought of them
used like that.
Tim Wescott wrote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If you run a buck to make +5V you can use a dual inductor instead of a
single, plus another diode -> There's your -5V. Dual inductors have
become cheap catalog items these days.
NICE that seems a general and very useful technique.
I have used those dual inductors for flyback but never thought of them
used like that.
Shhht! If was meant to be a secret. Oh wait ...
If you want it to be extra cool, there's lots of amps flowing or it has
to be tracking more precisely in voltage then you can use a FET instead
of the diode and control that from your sync buck chip. This cuts out
the diode losses.
--
Regards, Joerg
http://www.analogconsultants.com/
Joerg
Guest
Guest
Wed Jan 25, 2012 11:08 pm
HardySpicer wrote:
Quote:
On Jan 26, 6:44 am, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
Unless you are looking for really low ripple then buck/boost is the
modern way to go for everything. Far more efficient - up in the 95%
odd.
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
Unless you are looking for really low ripple then buck/boost is the
modern way to go for everything. Far more efficient - up in the 95%
odd.
WRT ripple the MC34063 is absolutely horrid because of its regulating
method. But sometimes it's good enough. I wouldn't use it in sensitive
anlog apps.
--
Regards, Joerg
http://www.analogconsultants.com/
HardySpicer
Guest
Guest
Thu Jan 26, 2012 12:01 am
On Jan 26, 6:44 am, Tim Wescott <t...@seemywebsite.com> wrote:
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
Unless you are looking for really low ripple then buck/boost is the
modern way to go for everything. Far more efficient - up in the 95%
odd.
Hardy
Martin Riddle
Guest
Guest
Thu Jan 26, 2012 12:38 am
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in
message news:4fl0i7psgj6um168fi77ri84vo42ucsjdq_at_4ax.com...
Quote:
On Wed, 25 Jan 2012 11:44:25 -0600, Tim Wescott <tim_at_seemywebsite.com
wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V
and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one
of the positive supplies? I'm thinking that if I can get some
negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
You can charge pump off the switcher node of one of the positive
switchers to get negative volts, essentially a classic "voltage
doubler" capacitor-diode thing. It will make roughly -24, which is a
lot to regulate to -5. A small series resistor is a good idea... some
switchers don't like this being done to them.
But if it's low current, you may as well buy a standard charge-pump
voltage inverter chip and run that off +5.
The LTC "LTM" module series can be used to make -5 from +24. Not real
cheap, but easy. Or build a Cuk switcher.
Another possibility: buy one of those cheap SIP dc/dc converters, $4
roughly.
John
wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V
and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one
of the positive supplies? I'm thinking that if I can get some
negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
You can charge pump off the switcher node of one of the positive
switchers to get negative volts, essentially a classic "voltage
doubler" capacitor-diode thing. It will make roughly -24, which is a
lot to regulate to -5. A small series resistor is a good idea... some
switchers don't like this being done to them.
But if it's low current, you may as well buy a standard charge-pump
voltage inverter chip and run that off +5.
The LTC "LTM" module series can be used to make -5 from +24. Not real
cheap, but easy. Or build a Cuk switcher.
Another possibility: buy one of those cheap SIP dc/dc converters, $4
roughly.
John
If there is board space a MAX232 can be used for it's +/- 10 v charge
pump.
Cheers
MarkK
Guest
Guest
Thu Jan 26, 2012 3:13 am
"Joerg" <invalid_at_invalid.invalid> wrote in message
news:9obcq6Fh32U1_at_mid.individual.net...
Quote:
HardySpicer wrote:
On Jan 26, 6:44 am, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V
and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
On Jan 26, 6:44 am, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V
and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If the - (something) is low current and you are going to post regulate it,
and you have a switcher already operating, you can pretty simply AC couple
the switching off of the switcher and use 2 diodes to rectify it to a
negative voltage = to the P-P of the switching waveform (less the diode
drops). Its basically a charge pump put you already have the waveform.
Check the full range of loads and line though.
Mark
Joerg
Guest
Guest
Thu Jan 26, 2012 10:12 pm
MarkK wrote:
Quote:
"Joerg" <invalid_at_invalid.invalid> wrote in message
news:9obcq6Fh32U1_at_mid.individual.net...
HardySpicer wrote:
On Jan 26, 6:44 am, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V
and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If the - (something) is low current and you are going to post regulate it,
and you have a switcher already operating, you can pretty simply AC couple
the switching off of the switcher and use 2 diodes to rectify it to a
negative voltage = to the P-P of the switching waveform (less the diode
drops). Its basically a charge pump put you already have the waveform.
Check the full range of loads and line though.
news:9obcq6Fh32U1_at_mid.individual.net...
HardySpicer wrote:
On Jan 26, 6:44 am, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V
and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
If the - (something) is low current and you are going to post regulate it,
and you have a switcher already operating, you can pretty simply AC couple
the switching off of the switcher and use 2 diodes to rectify it to a
negative voltage = to the P-P of the switching waveform (less the diode
drops). Its basically a charge pump put you already have the waveform.
Check the full range of loads and line though.
I've done that when I needed a voltage above the input voltage. The idea
was implemented but was met with disgust, grunting and scoffing at the
design review :-)
--
Regards, Joerg
http://www.analogconsultants.com/
Fred Bloggs
Guest
Guest
Thu Jan 26, 2012 10:42 pm
On Jan 25, 12:44 pm, Tim Wescott <t...@seemywebsite.com> wrote:
Quote:
I've got a 24V incoming supply, and a need for a number of supplies (+12,
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
+5, -5, and +3.3). The +/- 5V supplies are for a bit of analog circuitry
on a largely digital board, so they have low current requirements. My
plan for the +5V supply is to just hang a 78xx05 off the +12V. +12V and
+3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from one
of the positive supplies? I'm thinking that if I can get some negative
voltage for cheap from one of the existing switchers that I can then
regulate it to -5V with a 79xx05. I expect I'll end up using a charge
pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
The 34063 is false economy with its low frequency operation, internal
heat dissipation, and primitive PWM architecture.
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