Chose mosfet tranzistor in smps

[vvlladdd]

Hey, i want to make an smps booster with uc3843. what are the criteria for choosing a good mosfet for high eficiency and low drops in smps?

Can you tell me if this schematic is good?

 

[gigabyte091]

You should look for MOSFET with low on resistance, the lower, the better. And should be able to withstand at least 60V. Also I would have change R7 from 15k to 6.8k to increase switching frequency to about 100 kHz. Also i think there's no need for pulldown resistor. C6 should be about 1-10 nF, ceramic, and instead of R2, put ceramic capacitor, 100-680 pF. Shunt resistor in series with MOSFET source and ground, and smal RC filter to filter out switching spikes. 1k and about 1nF should be enough. Slope compensation if duty cycle exceed 50%

 

[vvlladdd]

Thanks, how can I make a limitation of maximum output current? same kind of short circuit protection

 

[Tahmid]

By monitoring current across a shunt in between MOSFET source and ground, you can protect for over-current and short-circuit when MOSFET is on, but not when the MOSFET is off. You could add another sense resistor in the path between the load ground and circuit/power ground and monitor the voltage across this, thus monitoring current through this for output short-circuit/overload protection.