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Parts Express Linear LM317/337 Bipolar Power Supply Board

Posted: Sun Jun 24, 2018 6:01 pm
by mediatechnology
Adjustable Voltage Regulator Power Supply Board +/- 1.25V to 37V DC Output LM317/LM337 Design.
Looks to be a useful conventional LM317/LM337 design for a great price of $11 US. Parts Express Part # 320-616.

Product Page: https://www.parts-express.com/adjustabl ... g--320-616
Specs and schematic: https://www.parts-express.com/pedocs/sp ... ations.pdf

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Re: Parts Express Linear LM317/337 Bipolar Power Supply Board

Posted: Mon Jun 25, 2018 11:19 am
by JR.
I like the 1000uF across the outputs.

I discovered decades ago with 7800/7900 series three terminal regulators that the falling impedance with frequency of large electrolytic capacitor could nicely compliment the rising output impedance of those active 3 terminal regulators. I suspect the more modern 317/337 series have better output impedance than old 78/79 that were based on 741 era gain bandwidth internals.

FWIW I used 2200uF across the 78/79 regulators. I can't find an output impedance plot for 317/337 but suspect the break starts at higher frequency, so smaller cap (1000 uF) probably makes better match.

Of course since those days the regulators have improved and so have the capacitors, so YMMV.

JR

Re: Parts Express Linear LM317/337 Bipolar Power Supply Board

Posted: Mon Jun 25, 2018 1:07 pm
by mediatechnology
This TNT Audio link has a nice analysis of LM317/337 output impedance and noise: http://www.tnt-audio.com/clinica/regula ... se1_e.html

Re: Parts Express Linear LM317/337 Bipolar Power Supply Board

Posted: Mon Jun 25, 2018 1:33 pm
by JR.
I'm shocked, bypassing the adj terminal reduces noise. :o


Didn't really address output impedance other than observing some interactions with load capacitance. In fact modern low esr capacitors could be ever worse, or not for that... Hard to say without investing some bench time. I injected an AC current via a cap coupled series resistance from a signal generator so I could impute impedance vs frequency by looking at the rail with a scope.

It is worth observing that circuits with poor PSRR are the obvious weak link to address but some topologies are too attractive to ignore. IIRC one of Brad's (RIP) last head amp topologies had a PSRR sensitivity. I went overboard with the vreg in my p100 but everything about that design was overkill.

JR

Re: Parts Express Linear LM317/337 Bipolar Power Supply Board

Posted: Mon Jun 25, 2018 2:20 pm
by mediatechnology
Yeah that wasn't the exact source I was looking at WRT output impedance. There's another one I need to find that directly compares LM3X7 regulators to the TL431.

I owe Brad big-time for his last heads-up regarding the ZTX851.

Re: Parts Express Linear LM317/337 Bipolar Power Supply Board

Posted: Mon Jun 25, 2018 3:46 pm
by JR.
mediatechnology wrote:
Mon Jun 25, 2018 2:20 pm
Yeah that wasn't the exact source I was looking at WRT output impedance. There's another one I need to find that directly compares LM3X7 regulators to the TL431.

I owe Brad big-time for his last heads-up regarding the ZTX851.
Yes, Brad is missed. He was one of a small handful of engineers unwilling to leave good enough alone, and capable to do something about it. :lol:

JR