tinyswitch_pk feedback design problem
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dear pi engineer, please see the attached picture. and its from the seminar about the tinyswitch_pk series products.
and my problem is how to design the resistor of the feedback which arethe resistors RA and RB, their resistance and the power level? thanks in advance.
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ok, assume the output is +5v. and the test current of the 4.3v zener is about 1ma, so the corespond resistance rb equals to: rb= (5-4.3)v/1ma=700ohm, am i right?
that should work
RA is not that critical -- value should be about 100 ohms for 5v output and perhaps 300 if regulating +12V. Rb sets this bias current for zener so it is operating at it's vendor specified current (typically 1mA). the relation is simple -- example for 1mA specified zener --- 1V/1mA = Rb where 1V is the forward drop of opto LED.