A comparison is made with the reference and the output of the opamp will feed the opto directly. I think this feedback is not good because with this feedback the transformer produces a noisy sound like tik-tik-tikabout twice every second and the voltage. You can insert a voltage divider network with the output feeding an opamp input, the TL431 will be used as a reference for the opamp other input. ( Download PDF file ) Backward DC-AC schematic, using conventional circuit too, there is nothing new places, the unique is the additional high. The circuit is conventional SG3525 + LM393. One other thing that I noticed was when giving the smps an continuous load at full power the output inductor started heating a bit and as the core changes the value due to heat the output voltage did drift a little. SMPS circuit SG3525 and IR2110 integrated on the board in the primer drive MOSFETs IRPF450 transformer, the ETD44 feedback 4N33 opto-Kubla with the provided. One other thing that I added was a 200nF cap across the zener and it helped a lot with a stable regulation. I suggest you insert a preset at first until you get the right resistor value than you can put a fixed one when the value is known. In your case I guess you have to go somewhat lower with the resistor. and feeding the reference, The circuit values shown are for 50v I needed 60v the resistor on the circuit shows a 33K resistor in my case I ended up using a 47K instead and got a 60v output. What I found out was that the resistor before the zener has to be tailored in such a way to the point where the zener starts to conduct when it hits the target voltage. Well when I first tried this feedback circuit I asked myself the same question.
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