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How does this feedback network work?

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Red_Micro:
Hello,

In the circuit below, what's the function of D18 and C37 at the junction of R24 and R27? Do R24 and R27 look like they are in series with R26?

T3sl4co1l:
VFB is the AUX winding, and I guess U1 is a quasi-resonant or BCM controller?  Guessing they wanted to adjust the rising and falling timings slightly.  Or maybe D18-R24-C37 serves as a snubber for D28 and the winding, and they're just taking feedback from there for whatever reason.

Tim

Wimberleytech:
I don't get it.  R24 appears to be a 205 ohm 1% resistor.   :-//

bson:
R24 and C37 will make the driver briefly overshoot during start and acceleration.

D18 allows fast discharge of C37 when VFB drops, so it doesn't undershoot when slowing.  Well, maybe a little due to the diode Vf.

Wimberleytech:

--- Quote from: bson on February 28, 2020, 05:51:20 pm ---R24 and C37 will make the driver briefly overshoot during start and acceleration.

D18 allows fast discharge of C37 when VFB drops, so it doesn't undershoot when slowing.  Well, maybe a little due to the diode Vf.

--- End quote ---

Is there a reason for the 1% value for R24?

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