Hi,

Is feedback in this kind of SMPS only 0% and 100% ? because of optocoupler would be On or Off state !
If so, SMPS will work as a hammer current charge , not a smooth current suppler. please clear it for me guys.

 

This basic type of optocoupler is quite analogous.

And here the circuit can be perceived as completely analogous.

 

Yes it's a typical smps circuit using an Opto-coupler...Better regulation would be to use a TL431 zener for D6...

 

Feed back control is (roughly) proportional and so the output control is smooth.

 

Like a transistor, a transistor output optocoupler can be used as either an analog amplifier or a digital switch.
Here the optocoupler is used as an analog amplifier.

 

I am not asking about design quality, I ask about duty cycle in this kind of circuits.

Example:
TL431 or Zener is set to 12V
When output voltage rich to 12V PC817's Led will goes on, hence PC817's transistor will goes in bias and be conductive, KA2508b0 will understand that over-voltage is happens , I want to know what is the reaction of KA2508b0 with duty cycle.

 

When the opto switches on the transistor, the smps chip will alter the pwm timings to lower the output voltage, this will turn off the TL431 and the cycle repeats to maintain the voltage.

 

When the opto switches on the transistor, the smps chip will alter the pwm timings to lower the output voltage, this will turn off the TL431 and the cycle repeats to maintain the voltage.

No, that would produce large amounts of ripple on the output of the supply.
The TL431, transistor, and opto do not switch on and off. They settle at the correct steady level to maintain the desired output voltage due to the linear negative feedback similar to the way negative feedback around an opamp works.

 

No, that would produce large amounts of ripple on the output of the supply.
The TL431, transistor, and opto do not switch on and off. They settle at the correct steady level to maintain the desired output voltage due to the linear negative feedback similar to the way negative feedback around an opamp works.

No, the chip alters the output voltage by turning the mosfet off it does it so fast that you get the average voltage,,, otherwise if it did not the output would just keep rising to maximum...

 

No, the chip alters the output voltage by turning the mosfet off it does it so fast that you get the average voltage,,, otherwise if it did not the output would just keep rising to maximum...

True.
But AH was talking about the optocoupler, which operates in the linear mode, not the "chip" which performs an analog error signal, to PWM duty-cycle conversion.