Proteus Buck converter simulation problem

[nohutpilav]

Hello friends. Let me summarize quickly. I am designing a buck converter. However, I have a problem. The Vo=Vi*D formula does not work in this circuit. My input voltage is fixed at 12V. My frequency is 50kHz. My pulse width is 25%. My trigger voltage is 15V. But my output is 7.5V.

Even if I change my pulse width, I cannot get a reasonable output. Please help

 

[24vtingle]

Are you in Continuous mode? Thats where Vout = DVin works.

 

[nohutpilav]

Are you in Continuous mode? Thats where Vout = DVin works.

My inductance value is greater than the critical inductance value. Isn't that enough?

 

[KlausST]

Hi,

good old V_gs problem .. many times discussed here .. and even more in the internet.

Klaus

 

[nohutpilav]

Could you please explain briefly?

Hi,

good old V_gs problem .. many times discussed here .. and even more in the internet.

Klaus

 

[24vtingle]

well spotted Klaus...yes, you turn your FET on with 15V...then vd = vs...and vs = vin = 12V...and so you only have 3v between gate and source..probably not enough to keep the fet on.

 

[nohutpilav]

well spotted Klaus...yes, you turn your FET on with 15V...then vd = vs...and vs = vin = 12V...and so you only have 3v between gate and source..probably not enough to keep the fet on.

Do I need to increase the gate voltage?

 

[24vtingle]

Drive the FET with a voltage from Gate to source. Find the NFETs datasheet to see how to drive it.
If its a general FET try 10V drive for ON and 0V for off.

 

[KlausST]

Do I need to increase the gate voltage?

Hi,

I recommend to learn MOSFET basics.
And you are free to search the froum for "MOSFET problems".
Or do searches for "high side mosfet", or - what you ureally want to design "BUCK converter circuits".
Just use the internet.

In short:
MOSFETs are controlled by V_GS = the voltage between Gate and Source.
But your control voltage is referenced to GND instead of Source.

Klaus