mosfet configuration doubt to control voltage

[renga92]

I am planning to control input voltage using micro controller. I was planning to use MOSFET and apply the control signal from micro controller to the gate, input voltage at the drain and output at the source. Please help to tell if design concept ll work out.

One more doubt is that for the above configuration should the gate voltage be higher than the source voltage.

 

[barry]

Could you give us a schematic? With voltages? This is a little vague

 

[renga92]

I have attached the circuit and the simulated output...I figured my question out....I made terrible mistake in the understanding of the MOSFET working...
I have few doubt about this circuit output...
I am planning to control the voltage using PWM from the micro controller and I have given 50% duty cycle for this output....
I want to know if this output after becoming DC ll be half the value of the voltage at the drain that is around 27v according to the math across drain and source...

thanks in advance...

 

[barry]

When you say "becoming DC" what do you mean? Do you mean after filtering? The short answer is: yes, if you've got a 50% duty cycle, the average(i.e., filterered) voltage will be half the peak value.

 

[renga92]

Yes I was asking about the filtered output...
I am now working on designing a filter for this circuit...
Can I output low frequency(50hz) to the MOSFET gate and control them or is it beneficial to use high frequency to drive the gate of the MOSFET...
I thought using low frequency I can rectify it using bridge rectifier itself....
For high frequency I need to use the filter using LC components....
thanks in advance....

 

[barry]

Why do you want to use 50 Hz? Not sure what you are driving, but at low frequency you may get mechanical issues-resonances and so forth if you're driving a motor. What is your load?

 

[renga92]

I am basically planning to make a bench top power supply with output 0-55vdc. So I made got an smps with constant output of 55vdc and I was planning to use MOSFET and micro controller to control the output voltage using PWM. Now I am able to drive the MOSFET gate with an PWM. I am still thinking on what frequency I need to drive the gate of the MOSFET. After I was planning to filter the output and make pure dc output which will be available at the user end.

thanks in advance

 

[barry]

Using a higher switching frequency will make the design of your output filter easier (unless you like huge capacitors or ripple)