Can an LM337 "sort of" work?

neutron7 · 02:20 AM

I have built a simple LM317 / LM337 bipolar power supply (from a half wave doubler) the transformer had a spare 8v tap and i needed a bipolar adjustable supply to power a roland GK guitar pickup preamp

The circuit is basically the datasheet not unlike, well exactly the same actually, as after the resistors and coils on the twisted pear lcbps_schematicversion but with wave rectification (2 diodes give +- 10.6 volts from 8VAC input)

it is adjusted with 5k 21 turn trimmers, the same ones in fact.

anyways the positive side is perfect, the meter does not budge from where i adjust it to and i cant see any AC on the scope even at the most sensitive scale.

on the negative side there is a ripple that looks just like the input except the DC level is varied by the trimmer. the 337 does not get hot or anything, and there is high (megohm range, but not as high as the 317) reistance between the pins. (oh and with a very small cap on the output the bottom each cycle of the ripple is accompanied by a nice high frequecy oscillation)

is it just a dead regulator? im a bit annoyed because it was my last one

MJL21193 · 12th December 2009, 03:02 AM

Hi,
How much voltage are you looking for after the regulators? You may not be allowing for the regulators dropout voltage (I can't seen to find it for the LM337 but would be around 2V?). The reg might be fine, just not getting enough voltage.

neutron7 · 12th December 2009, 05:23 AM

the voltage is - 10.6v and the voltage i am trying to get is in the range of -5 to -8 v, even when i adjust the trimmer so it is only putting out 4v or so it still has the ripple. the positive side works perfectly

Enzo · 12th December 2009, 05:26 AM

ANy chance you overlooked the different pinouts between 317 and 337?

The tabs are active, any chance either tab is connecting to someplace it ought not?

neutron7 · 06:00 AM

no not at all, i have not put a heatsink on them yet, it is only supposed to power 3 dual opamps. the circit has been checked and checked again, right now it is just powering LED (which is on the board to show its working) the in outs are carefully set up, i spent ages on the board and it is right.

reason everything is so fat is because its only a 1/2 oz board, used pulsar toner transfer

woody · 12th December 2009, 06:43 AM

Are you doing the measurements with a load? Rember if these regulators arn't
supplying some minimum load and I think it's about 5ma they will nor work right.
A 1k resistor across the output would be enough of a load to check if this is the problem.

neutron7 · 12th December 2009, 04:20 PM

Yes they have a small load, a resistor and indicator LED on the board, 750 ohms.

pjp · 05:00 PM

That is a very unusual looking board! What did you use to draft it ?

woody · 12th December 2009, 05:29 PM

I just looked at the data sheet on the lm337. In your case it may need
a full 6ma of load current. I don't think the led and 750ohm will pull that much.
You might try just shorting the led out and try that.

neutron7 · 12th December 2009, 05:59 PM

Ok i just replaced it, after going out in the freezing cold to get some more, which i didnt want to do

and everything is fine now.
Thanks for the suggestions.

12th December 2009, 02:09 AM	#1
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	Can an LM337 "sort of" work? I have built a simple LM317 / LM337 bipolar power supply (from a half wave doubler) the transformer had a spare 8v tap and i needed a bipolar adjustable supply to power a roland GK guitar pickup preamp The circuit is basically the datasheet not unlike, well exactly the same actually, as after the resistors and coils on the twisted pear lcbps_schematicversion but with wave rectification (2 diodes give +- 10.6 volts from 8VAC input) it is adjusted with 5k 21 turn trimmers, the same ones in fact. anyways the positive side is perfect, the meter does not budge from where i adjust it to and i cant see any AC on the scope even at the most sensitive scale. on the negative side there is a ripple that looks just like the input except the DC level is varied by the trimmer. the 337 does not get hot or anything, and there is high (megohm range, but not as high as the 317) reistance between the pins. (oh and with a very small cap on the output the bottom each cycle of the ripple is accompanied by a nice high frequecy oscillation) is it just a dead regulator? im a bit annoyed because it was my last one Last edited by neutron7; 12th December 2009 at 02:20 AM.

12th December 2009, 05:53 AM	#5
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	no not at all, i have not put a heatsink on them yet, it is only supposed to power 3 dual opamps. the circit has been checked and checked again, right now it is just powering LED (which is on the board to show its working) the in outs are carefully set up, i spent ages on the board and it is right. reason everything is so fat is because its only a 1/2 oz board, used pulsar toner transfer Last edited by neutron7; 12th December 2009 at 06:00 AM.

12th December 2009, 05:00 PM	#8
pjp diyAudio Member Join Date: Nov 2006 Location: under the rainclouds	That is a very unusual looking board! What did you use to draft it ? Last edited by pjp; 12th December 2009 at 05:00 PM. Reason: removed unnecessary image link

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12th December 2009, 03:02 AM	#2
MJL21193 Account disabled at member's request Join Date: Mar 2007	Hi, How much voltage are you looking for after the regulators? You may not be allowing for the regulators dropout voltage (I can't seen to find it for the LM337 but would be around 2V?). The reg might be fine, just not getting enough voltage.

12th December 2009, 05:23 AM	#3
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	the voltage is - 10.6v and the voltage i am trying to get is in the range of -5 to -8 v, even when i adjust the trimmer so it is only putting out 4v or so it still has the ripple. the positive side works perfectly

12th December 2009, 05:26 AM	#4
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	ANy chance you overlooked the different pinouts between 317 and 337? The tabs are active, any chance either tab is connecting to someplace it ought not?

12th December 2009, 06:43 AM	#6
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	Are you doing the measurements with a load? Rember if these regulators arn't supplying some minimum load and I think it's about 5ma they will nor work right. A 1k resistor across the output would be enough of a load to check if this is the problem.

12th December 2009, 04:20 PM	#7
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	Yes they have a small load, a resistor and indicator LED on the board, 750 ohms.

12th December 2009, 05:29 PM	#9
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	I just looked at the data sheet on the lm337. In your case it may need a full 6ma of load current. I don't think the led and 750ohm will pull that much. You might try just shorting the led out and try that.

12th December 2009, 05:59 PM	#10
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	Ok i just replaced it, after going out in the freezing cold to get some more, which i didnt want to do and everything is fine now. Thanks for the suggestions.

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