PS linear regulator issues

[Jon Slaughter]

A PS I build a while back was screwed up yesterday when I was messing
around. Its a variable split PS using 317's with, I think, about +-35V that
it handles(20 somethign for the regulators).

I'm not exactly sure what happened(well, I think I know) but in any case
what happened after was that the voltage would read either about 2 voltage
when the turned down or around 25+ volts when up.

I think I fixed it as I replaced one of the protection diodes(the one from
that goes from output to input). (I figured it was the diode since thats
what there for). In any case it seems to be working but I'm not sure if any
other damage happened.

When I built the circuit I didn't design it to be able to remove components
easily(didn't have the room in the box). I thought that the protection
diodes were there to protect the 317(even though it has its own protection)
but I didn't know it would destroy the diodes in the process. Is this
normal? (if it did I would have made it easier to replace them).

Also, in the case that the protection diodes do go does that completely
eliminate(99%) any other things in the regulator circuit from being ruined.
It wouldn't be fun to check the other protection diode I have or the 317.
(since I probably would have to take them out of circuit to be completely
sure).

I'm worried about the other diode but really don't want to try and take it
out to check it and since the PS looks like its working.

(BTW, I think I essentially shorted the negative supply to ground and that
is what caused it... but on the positive side ;/)

What do you guys think I should do?

Thanks,
Jon

 

[Chris]

A PS I build a while back was screwed up yesterday when I was messing
around. Its a variable split PS using 317's with, I think, about +-35V that
it handles(20 somethign for the regulators).

I'm not exactly sure what happened(well, I think I know) but in any case
what happened after was that the voltage would read either about 2 voltage
when the turned down or around 25+ volts when up.

I think I fixed it as I replaced one of the protection diodes(the one from
that goes from output to input). (I figured it was the diode since thats
what there for). In any case it seems to be working but I'm not sure if any
other damage happened.

When I built the circuit I didn't design it to be able to remove components
easily(didn't have the room in the box). I thought that the protection
diodes were there to protect the 317(even though it has its own protection)
but I didn't know it would destroy the diodes in the process. Is this
normal? (if it did I would have made it easier to replace them).

Also, in the case that the protection diodes do go does that completely
eliminate(99%) any other things in the regulator circuit from being ruined.
It wouldn't be fun to check the other protection diode I have or the 317.
(since I probably would have to take them out of circuit to be completely
sure).

I'm worried about the other diode but really don't want to try and take it
out to check it and since the PS looks like its working.

(BTW, I think I essentially shorted the negative supply to ground and that
is what caused it... but on the positive side ;/)

What do you guys think I should do?

Thanks,
Jon

Hi, Jon. From what you're saying, I'll bet you've got the D1s but not
the D2s shown in the ASCII diagram below (view in fixed font or M$
Notepad):

|
| .---------|<-----------------.
| | D1 |
| | .-------------. |
| | | | |
| V+o----o---o o-----o----o
| | | + Regulator | | |
| + | | | + | |
| C --- | | C --- D2-
| --- | | --- ^
| | '------o------' | |
| | | | |
| GNDo----o----------o------------o----o
| | | | |
| + | .------o------. + | |
| C --- | | C --- D2-
| --- | | --- ^
| | | | | |
| | | - Regulator | |
| V-o----o---o o-----o----o
| | | | |
| | '-------------' |
| | D1 |
| '--------->|-----------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

A lot of funny things can happen with dual supplies on turn-on and
short circuit conditions. Many of these have to do with wiring
inductance causing unexpected things to happen, some with the
transformer at the input.

Just put a couple of 1N5402 6 amp barrel diodes across the outputs of
your power supply (put 'em right at the banana jacks, inside the box),
and this should keep your problem from recurring. If your D1s are
1N400X, you could also upgrade those to 1N540X, also. Just clip the
plastic body of the diode, and solder the heavier 1N5402 diode lead to
what remains of the 1N400X lead on the circuit board. Be sure to use
a clip on the smaller lead to prevent the solder under the circuit
board from melting and spoiling your quick fix. Remember, your output
caps aren't current limited to 1.5A like the ICs. Your power supply
will be a lot more loyal if it knows you've spared no expense to
protect it from itself.

Cheers
Chris

 

[Jon Slaughter]

Hi, Jon. From what you're saying, I'll bet you've got the D1s but not
the D2s shown in the ASCII diagram below (view in fixed font or M$
Notepad):

|
| .---------|<-----------------.
| | D1 |
| | .-------------. |
| | | | |
| V+o----o---o o-----o----o
| | | + Regulator | | |
| + | | | + | |
| C --- | | C --- D2-
| --- | | --- ^
| | '------o------' | |
| | | | |
| GNDo----o----------o------------o----o
| | | | |
| + | .------o------. + | |
| C --- | | C --- D2-
| --- | | --- ^
| | | | | |
| | | - Regulator | |
| V-o----o---o o-----o----o
| | | | |
| | '-------------' |
| | D1 |
| '--------->|-----------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

No, I have both(which I mentioned but maybe wasn't clear). I haven't
checked them both though. There are a total of 4 diodes but I was just
refering to one side of the supply since the other seemed to work fine.

A lot of funny things can happen with dual supplies on turn-on and
short circuit conditions. Many of these have to do with wiring
inductance causing unexpected things to happen, some with the
transformer at the input.

Just put a couple of 1N5402 6 amp barrel diodes across the outputs of
your power supply (put 'em right at the banana jacks, inside the box),
and this should keep your problem from recurring. If your D1s are
1N400X, you could also upgrade those to 1N540X, also. Just clip the
plastic body of the diode, and solder the heavier 1N5402 diode lead to
what remains of the 1N400X lead on the circuit board. Be sure to use
a clip on the smaller lead to prevent the solder under the circuit
board from melting and spoiling your quick fix. Remember, your output
caps aren't current limited to 1.5A like the ICs. Your power supply
will be a lot more loyal if it knows you've spared no expense to
protect it from itself.

Thanks, I'm designing another power supply that has a bit more current to it
and I'll try to keep this stuff in mind next time I do it.

Jon