hi ,

Im plannig to build a DC-DC buck converter ( 12-6)V and I have calculated each components on my circuit and when i try to run it oi PSPICE Capture CIS program or Multisim program i get around 12 v at output.

my output current should be about 0.5A and Fsw = 10KHz. I have use N-MOSFT ( IRF520) im my circuit. You can see my circuit diagram below. I couldnt figure out where is the problem. The pic below is from Multisim program. I use a VPULSE source instead of the PWM circuit for now which it should give me 10Khz.

So can any when help to find the problem and sorry for my poor english.

 

The circuit you have posted is not visible. Can you check again to make sure you have uploaded it?

 

I'll give posting the pic a shot:

 

The circuit u send seems ok

using 50% duty cycle you can do that

if you still find issue check ur N-MOSFET ..... other component looks ok.....

 

That's not true, ashish.

The basic problem is that there is no feedback from the output (voltage across the load) back to control the PWM percentage.

The inductor is very large, so response time will be rather poor. There will be a considerable amount of overshoot of the target voltage. The 100k Ohm load resistor is a very high value; if the output is at 6v, only 60uA current will be required to maintain it.

 

To repeat what Sgt has commented, use a 12Ω resistor for load instead of 100K at the output and you will get a more realistic output voltage.

 

Thanks for fast replys.
It finally work with 5.6V. I spend the last month trying to find where is the problem. But I get 27A at the output, it should be abound 0.5.

About the PWM, Dose any one advise me a good PWM circuit which provid me a frequency of 10KHz.


and thanks again for evrey one helped me