Help designing Buck Converter in PSpice

[jurassicbond]

I'm trying to design a buck converter in PSpice for class and I followed the design found here on page 3.
https://www.scribd.com/doc/6834949/dc-to-dc-converters-using-ORCAD-spice

My circuit is here:


and the plot of the capacitor voltage is here:



The capacitor voltage is around 1.2 volts when it should be around 10 Volts. For some reason, the Capacitor voltage only changes if I change the parameters of the control voltage, but if I change the input voltage nothing changes. I can't figure out what I'm doing wrong. I'm pretty sure that I followed the book correctly and my design is right, but I'm probably doing something wrong in PSpice since it's been a long time since I last used it.

 

[atripathi]

You need to connect negative pin of V2 source to MOSFET source pin instead of GND.
Hope this helps.

 

[wowo1215]

Yes,just do as atripathi told you!

 

[FvM]

or increase the magnitude of V2 to 15V

This doesn't result in correct switching operation. V2 has to be at least 5 to 10 V above input voltage V1, which would exceed FET maximum Vgs ratings (although the simulation models possibly ignores the dangerous operation condition).

As a general question, do you intend to simulate a real-world buck converter or a simplified functional model? For the real converter, a feasible gate drive method should be included with the simulation, because the actual gate voltage waveform affects the buck converter's efficiency and switching behaviour considerably.

 

[wowo1215]

And u must also pay more attention to the working mode of MOSFET,what we want is switch, not a resistor,right?

 

[hock]

pspice is not a good choice for simulating a switching circuit.
it will take too long a time for simulation.
hock

 

[chucksd]

You need to study how to turn on P-mos to the N-mos. The left of the inductor, L1, is 20V when the switch is supposedly first turned on. For N-mos, the gate voltage needs to be higher than source voltage.

In this case, the gate voltage turns on the N-mos, but as soon as N-mos conducts, it is quickly turned off. After you study the N-mos to P-mos or how to bias them, you can go to Maxim website. There is a pretty good tutorial.

 

[arunprakash]

u done one mistake tat is connecting the negative end of gate pulse to ground. u have to connect Vgs instead of gnd . connect -ve of gate pulse to mosfet tat connecting to diode