How does "LM317/ 337 Servo Rectified Filtered Power Supply" work?

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keilau

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keilau

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Joined 2013
I found this schematic from a PCB seller. It looks like the same circuit.
LM317-LM337_LF353ServoRectifier.jpg LM317-LM337_LF353ServoRectifier_picture.jpg
 
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chalky

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Joined 2003
Keilau, I think the purpose of the opamp in the schematic you show for "servo, rectifier, filter power supply board" is to take the ripple and noise from the output of the power supply, invert it, and feed it back into the lm317/337, thereby cancelling the ripple and noise on the output. Hence the "servo" in the title. I think the circuit was originally designed by a poster on this forum, maybe apex audio, but I'm not sure.
 
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keilau

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Joined 2013
chalky said:
Keilau, I think the purpose of the opamp in the schematic you show for "servo, rectifier, filter power supply board" is to take the ripple and noise from the output of the power supply, invert it, and feed it back into the lm317/337, thereby cancelling the ripple and noise on the output. Hence the "servo" in the title. I think the circuit was originally designed by a poster on this forum, maybe apex audio, but I'm not sure.
Click to expand...
chalky, I agree with you that the servo in the PCB seller posted circuit is likely for noise and ripple reduction. In this circuit, the servo takes the input from the same side of the output rail. I hope that some user may take some measurement of the LM317/337 pair with and without the servo to see how effective it is.

The servo can be used for output rail balance tracking as samsara suggested using his schematic. But it is a different topology. In the samsara schematic, there is only one trimmer on the positive side for output rail voltage adjustment.

When I tried to build a +/-15V PSU many years ago using the LM78xx/79xx pair, I could not get a close enough match of the output rails. I ended up using a very expensive tracking voltage regulator, Raytheon RC4195TK.
 
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FauxFrench

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Joined 2017
keilau said:
chalky, I agree with you that the servo in the PCB seller posted circuit is likely for noise and ripple reduction. In this circuit, the servo takes the input from the same side of the output rail. I hope that some user may take some measurement of the LM317/337 pair with and without the servo to see how effective it is.

The servo can be used for output rail balance tracking as samsara suggested using his schematic. But it is a different topology. In the samsara schematic, there is only one trimmer on the positive side for output rail voltage adjustment.

When I tried to build a +/-15V PSU many years ago using the LM78xx/79xx pair, I could not get a close enough match of the output rails. I ended up using a very expensive tracking voltage regulator, Raytheon RC4195TK.
Click to expand...

An interesting observation but is a UA741 fast enough for that?
 
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keilau

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Joined 2013
Samsara said:
You right, it's the right schematic, not mine.
Here it show complete PCB
LM317/LM337 DC Servo Adjustable Voltage Regulator Board, Positive and Negative Dual Band Rectification Filter-in Air Conditioner Parts from Home Appliances on Aliexpress.com | Alibaba Group
Click to expand...
Link to the English Alibaba website.
Aiyima LM317 / LM337 +/ 1.5V 37V Adjustable Dual Voltage Regulator Power Supply Module-in Voltage Regulators/Stabilizers from Home Improvement on Aliexpress.com | Alibaba Group
 
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