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Jasen Betts
Guest
Tue Mar 16, 2010 8:36 am
On 2010-03-16, thermo102 <thermo102_at_comcast.net> wrote:
Quote:
Else you'll need to replace the DM7400N with someething stronger;
the DM7400N chip can only produce 0.4 ma so it's not going to work,
A SN74AHC00N chip can procude 8mA on the outputs which is probably
close enough to 20mA for it to work, replace the 1K resistors with
wire links.
Thanks for your help. My power transformer only had a rating of 1 Amp, so I
picked up another one today with a rating of 4 Amps. While at the
electronics store, I also picked up a couple of the SN74AHC00N chips you
mentioned. Is the logic the same as for the DM7400N?
As soon as I get the new transformer mounted and wired in, I'll remove the
1K resistors and replace with some of smaller value to see what happens.
The "74" series of logic chips have been reworked several times in
different variations of power ratings and speed, they all have the
same pinout for the same base part number. both those parts are
"7400" variants, I don't recall explicitly checking the pinpouts, but
I did compare the written descriptions and did glance at the pinout
diagram, but did not make a detailed comparison.
www.alldatasheet.com will find you the datasheets for both parts.
(or just google "SN74AHC00N datasheet")
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John Fields
Guest
Tue Mar 16, 2010 1:12 pm
On Mon, 15 Mar 2010 19:24:24 -0700, "thermo102" <thermo102_at_comcast.net>
wrote:
Quote:
Else you'll need to replace the DM7400N with someething stronger;
the DM7400N chip can only produce 0.4 ma so it's not going to work,
A SN74AHC00N chip can procude 8mA on the outputs which is probably
close enough to 20mA for it to work, replace the 1K resistors with
wire links.
Thanks for your help. My power transformer only had a rating of 1 Amp, so I
picked up another one today with a rating of 4 Amps. While at the
electronics store, I also picked up a couple of the SN74AHC00N chips you
mentioned. Is the logic the same as for the DM7400N?
---
Yes, and the pinouts are identical.
JF
thermo102
Guest
Fri Mar 19, 2010 2:27 am
Quote:
---
Yes, and the pinouts are identical.
JF
Thanks for the info! I think I fried tne DM7400N yesterday. At least I have
a replacement chip on hand.
I removed some heatsinks, etc so I could ID the unknown chip. It's a 7805 1
Amp positive voltage regulator with an output of 5 volts and max 1 Amp. The
input to this chip is approximately 32 VDC.
Am I correct in my thinking that I can replace the 7805 with a L78S05 2 Amp
positive voltage regulator to get approximately the 2 amps for my new motor.
I assume the other two motors would not be affected by this change as long
as the output voltage of the L78S05 is 5 volts???
The Darlington chips are configured as:
Emitter: Ground
Base: receives 5 volts from the 7805 (across a 1K ohm resistor)
This same 'feed' goes to the DM7400N
Collector: goes to a coil winding of a motor
Any suggestions on what I should do next?
Thermo
Jasen Betts
Guest
Fri Mar 19, 2010 10:19 am
On 2010-03-19, thermo102 <thermo102_at_comcast.net> wrote:
Quote:
---
Yes, and the pinouts are identical.
JF
Thanks for the info! I think I fried tne DM7400N yesterday. At least I have
a replacement chip on hand.
I removed some heatsinks, etc so I could ID the unknown chip. It's a 7805 1
Amp positive voltage regulator with an output of 5 volts and max 1 Amp. The
input to this chip is approximately 32 VDC.
Am I correct in my thinking that I can replace the 7805 with a L78S05 2 Amp
positive voltage regulator to get approximately the 2 amps for my new motor.
I assume the other two motors would not be affected by this change as long
as the output voltage of the L78S05 is 5 volts???
you're going to need a serious heatsink if you go that route.
you'll be burning 54 watts or energy up as heat in the regulator to supply
2A to the motor,
if you only need a few tens of milliamps to run the nand gate and the bases of
the darlintons then the 7805 was a good solution
the 78S05 from STmicro has a 3 degrees per watt thermal resistance
(TO220 case) so even if you weld it to a perfect heatsink in an
ice-water bath at 54W dissipation the junction would be at 3X54=162C
which is 12 degrees too high.
thses figures can be improved by putting a 50W 12 ohm resistor in
series with the input to the regulator, then mos of the heat will go
into the resistor and the regulator will only get about 8W of heat.
your first idea with the series resistors on the motor was better.
psaically P=VxA is your enemy when you want to run a low voltage
device from a higher voltage supply.
I'd consider a 2A 5V powersupply like this one:
http://jaycar.com/productView.asp?ID=MP3316
only get one with the right plug for the power outlets at your place,
although I guess you could use that one inside the machine and connect
it using insulated quick-connect terminals
Quote:
The Darlington chips are configured as:
Emitter: Ground
Base: receives 5 volts from the 7805 (across a 1K ohm resistor)
This same 'feed' goes to the DM7400N
Collector: goes to a coil winding of a motor
you can boost the current output of the 7400 by using NPN transistors (eg
PN2222) as emitter followers.
collector to 5V
base to the 7400 output
emitter to a 100 ohm 0.5W
resistor with the other end to the TIP120 base.
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thermo102
Guest
Sat Mar 20, 2010 1:58 am
Quote:
thses figures can be improved by putting a 50W 12 ohm resistor in
series with the input to the regulator, then mos of the heat will go
into the resistor and the regulator will only get about 8W of heat.
your first idea with the series resistors on the motor was better.
psaically P=VxA is your enemy when you want to run a low voltage
device from a higher voltage supply.
After reading your post, I studied the sketch I'm making up of my board
layout and it looked like I had a configuration similar. Then a google
search turned up the concept of a voltage divider circuit. Which I guess I
have.
Measuring the actual voltage at the input side of the 7805, I was surprised.
A really low value, somewhere around 2 volts, and the output was crazy. So
I started trial and error resistor values untill I had an actual 22 volt
input and a 5 volt output. (replaced a 500 ohm '2 watt' resistor with a 100
ohm '2 watt' )
Did not see any ill effects by operating 2 motors simultaneously for a short
period.
My 3rd motor still doesn't run, so I guess I blew the transistors also. Is
there a good way to check them with a multimeter without removing them from
the circuit?
Again, thanks for all your help,
Thermo
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