My question is if I can connect 2 independent LM317 based 24 volt power supplys with one of the supply's plus and other's minus to get dual power supply config of -24v, 0v, +24v power supply.
I tried doing it and one of the regulator smoked. Logically it appeared to me that it should work. What am I doing wrong.
Is this the reason a LM337 exists?
Need some clarity.
Cheers
I tried doing it and one of the regulator smoked. Logically it appeared to me that it should work. What am I doing wrong.
Is this the reason a LM337 exists?
Need some clarity.
Cheers
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Yes, it should work.
Impossible to know why it did not work for you without details of what you did exactly. Schematic of what you built?
Impossible to know why it did not work for you without details of what you did exactly. Schematic of what you built?
You need to use transformers with separate 20- 22v, 0v , and 20-22, 0v
not a centre tap.
see carlosfm schematic and recommendations:
http://www.diyaudio.com/forums/chip-amps/56106-lm338-regulated-snubberized-psu-audio-amplifiers.html
Cheers / Chris
This is possible, if you have two isolated secondaries, instead of just one with a center tap.
If so, make two identical floating 24V regulator circuits, one on each secondary.
Then connect the +24V output of one to the common of the other.
This point is connected to the system ground. The remaining two output nodes will be at the
+/- 24V that you want. The LM337 can be used for the case of one winding with a center tap.
I'm having trouble understanding why a center-tap won't work, since the LM317 "floats" and I can't see the problem by looking at the schematic. What am I missing, please?
Without reading the schematic... Check the current loops, how much current is flowing from the V+ to 0V without any other path for it to go to V-
LM317 can source current but not sink it.
LM317 can source current but not sink it.
Did that.
The 24-0-24 outputs are equal to 48-24-0 (or 24-0 & 24-0) as far as the LM317s are concerned. Or so it seems. ???
Thanks. What I used is a fairly standard variable regulator using LM317 including diode protection for C1 and C2 in the generic schematic. The front for each regulator board is a onboard bridge rectifier.
Two of such boards are being fed by a single 24-0-24 centre tapped transformer. Each board is sharing one leg of the centre tap.
I will figure out a way to load the schematic.
Cheers.
Two of such boards are being fed by a single 24-0-24 centre tapped transformer. Each board is sharing one leg of the centre tap.
I will figure out a way to load the schematic.
Cheers.
Yes, anilva, we'd like to see your schematic.
My question involves only a single center-tapped transformer, single bridge rectifier, and cap filters. Followed by the regulators.
My question involves only a single center-tapped transformer, single bridge rectifier, and cap filters. Followed by the regulators.
That can't work. The "negative" regulator circuit is being shorted between its input hot and output hot terminals by the positive regulator circuit,
which has a direct connection between its input common and output common terminals.
Using two positive regulators for a bipolar supply requires two isolated secondaries. Then it's like connecting two batteries in series, no problem.
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It does sound like the OP's circuit could be just 2 paralleled supplies. So + of one to - of the other would surely smoke.
But my question still remains...
But my question still remains...
Can you show a schematic of what you are envisioning? It sounds to me like the same "+ to - and up in smoke" scenario.
Mike
A three terminal regulator (of either polarity) has a direct connection between the input common
and the output common. This means that connecting the two input commons of two regulators
together (as with a CT secondary winding) requires complementary regulators, because the
output commons must also be connected together to make a bipolar supply.
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Understood. I thought the bridge rectifier in front of each regulator board will isolate the centre tap from presenting as a short. Looks to me it should work with 2 different windings.
Thanks
With a bridge rectifier, both ends of the winding involved have to be free to flip around in polarity
for the rectifier to work right. Connecting one end of the winding somewhere constrains the circuit
too much, and the circuit then cannot function properly.
I can't upload my pic via my phone. (It was an ugly cut-n-paste job anyway).
I will try and provide value by keeping it less than 1k words.🙂
So we have a ct transformer, connected to a bridge rectifier. The center-tap is 0V gnd - that conductor extends to the output. And we have + and - coming out from the bridge. So that is 3 terminals for PSU output. Two filter caps across in the usual manner.
Now on the positive rail, just past its filter cap, insert LM317 and two set resistors.
Where the adj pin/resistor connects to the 0V line, move right and insert another LM317 and its set resistors. This one's adj pin/resistor connects to the - rail.
There you have it. Hope you can help. Sometimes these little mysteries can bug me.
I will try and provide value by keeping it less than 1k words.🙂
So we have a ct transformer, connected to a bridge rectifier. The center-tap is 0V gnd - that conductor extends to the output. And we have + and - coming out from the bridge. So that is 3 terminals for PSU output. Two filter caps across in the usual manner.
Now on the positive rail, just past its filter cap, insert LM317 and two set resistors.
Where the adj pin/resistor connects to the 0V line, move right and insert another LM317 and its set resistors. This one's adj pin/resistor connects to the - rail.
There you have it. Hope you can help. Sometimes these little mysteries can bug me.
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