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Engineering
Electrical Engineering
Understanding operation of specific SMPS example (is it a flyback?)
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[QUOTE="Jony130, post: 5482174, member: 381547"] It will depend on the past. If the circuit was just turn-on or we have a "short" on the output. In general case IC will increase the duty cycle to bring Vo to the "set" value. Set by R204; R205 IC201 is not a "zener diode". KA431 is much more then a ordinary Zener diode. It more like a op-amp with built-in reference voltage and output stage is open collector type, so it only can sink current. [URL]http://www.righto.com/2014/05/reverse-engineering-tl431-most-common.html[/URL] In this circuit IC201 work as a error amplifier and this is why Vo = 1 + R204/R205 * Vref = 1 + 4k/4k * 2.5V = 2*2.5V = 5V. When the output voltage Vo increases (load current decreasing), the sampling voltage obtained after the voltage division (R204,R205) is compared with the 2.5V reference voltage in IC201. And if this voltage is larger then 2.5V the IC201 it will start to conduct more (large current in sink by IC201). This will increase optocoupler LED and optotransistor current so the feedback pin voltage is pull down. And this will reduce the duty-cycle and Vo is bring back to its set value. C205 and R203 are loop compensation network together with C105 and internal resistor. No, C102 and LF101 are the part of EMI input filter. [URL]https://www.fairchildsemi.com/application-notes/AN/AN-4150.pdf[/URL] (page 2) Or this [MEDIA=youtube]OKAVhEBNeZw[/MEDIA] [SIZE=6][B] [/B][/SIZE] [/QUOTE]
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Understanding operation of specific SMPS example (is it a flyback?)
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