Does anyone have a schematic/ experience on isolated secondary feedback on the SG3525, I only need 5% regulation. lots of people mention using an opto, but I have never used this on 3525, only non isolated feedback, and I cannot fing an apps note on the subject. regards & TIA Anthony
isolated feedback for SG3525
Jun 12, 2006
2 Replies
go look at some TI appnotes, they have one in particular about how to isolate the feedback network.
for 5% regulation you could get away with a zener + opto. Zener in series with opto led in series with resistor, across output.
opto transistor pulls up (or down) on 3525 error amp, such that output too high turns on opto transistor which reduces duty cycle.
pick Vz = Vout_desired - Vopto_led - Iopto_led*R
after picking Iopto_led (say 5-10mA).
Cheers Terry
The opto collector goes to the 3525 supply, emitter goes to pin 1.
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