designing switch mode power supply

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You have to provide more details, do you want to make a mains power supply or a switching circuit to output 5v for example from 12v input,
or maybe you want to step up a voltage.
I have only done a current regulator once for power led, AVR driving a mosfet with PWM and measuring the output current
with the ADC and reducing or increasing the duty cycle according to that measurement, but my source was 12v.

Alex
 

Well, you may want to use transformer traditional rectifier or power semiconductor switches such as MOSFT/IGBT. And then produce PWM swithing signals with MCU by giving feedback.
 

To Mithun_K_Das,

You need a flyback controller IC. You can search on Fairchild or PI website.
 

ya. I want to control the circuit with uC( atmega8 ). I tried based on some PC power supply circuit but unfortunately I found nothing without damaging my uC. I used capacitor voltage divider biasing (220µF/400V*2) then connected with another series capacitor(1µF/630V) with pc smps transformer. MOSFET used>>IRF740 and 55KHz(26%duty cycle) pulse used to drive the MOSFET. finally I lost uC & MOSFET too.

I know the basic principle but why it is not working with such principle while driving with uC?



have you any link? or diagram to understand the whole thing?
 
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Your circuit is open-loop control? It is not easy to design a simple AC/DC with uC. AC/DC needs accurate analog feedback control and many protection circuit. Soft start control is needed too. Otherwise, it will have big overshoot that is enough to damage the circuit. MOS driving slew rate need good controlling too.
 
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