Another buck converter design

[ybreethi]

i am in hardware design of buck converter with MOSFET as switch...i have designed L and C values...i use R load....
input voltage=24v
output voltage=18v
L=1mH
C=100uF
R=100 ohm
switching frequency=48.828KHz
i use microcontroller program to drive pulse for MOSFET.....but it is very difficult for me to capture pulses and the output is very low....
can u just plz explain me what i have made mistake in my design?

 

[ybreethi]

@ sanmoy:
am not using PWM directly..am using microcontroller chip along with driver IC to obtain gate pulse.....

 

[ybreethi]

@MrAl
i dunno how to attach my simulink model...bcoz it displays thee file has incorrect extension....

 

[ybreethi]

this is my simulink model:

 

[Ian Rogers]

Ybreethi!!! Ihave moved this to another thread.... It's bad practice to hijack other peoples threads.... Hopefully you'll get more help now...

 

[simonbramble]

Are you using an N channel FET? If so, you need to take the gate higher than the source to turn it on (and keep it on). I would use a P channel MOSFET. What is the input to the LC filter looking like?Can you see a square wave there? It should have a duty cycle equal to the input voltage/output voltage.

See my tutorials if you want to design one properly - link below... Hope these help

 

[ronv]

What is the minimum and maximum current?

 

[ybreethi]

@simonbarble
i am using irf640. am getting voltage pulse after LC filter..not a square wave..

 

[ybreethi]

@ronv

in simulation am getting max current 0.21A

 

[Mr RB]

...
i am using irf640. am getting voltage pulse after LC filter..not a square wave..

You need to use a PFET (as Simonbramble said) and ALSO you need to swap the Drain and Source pins on your FET, so the gate voltage is now referenced to V+ and not to the unstable voltage on the inductor!

 

[ybreethi]

can anyone tell me what kind of load i can use instead of resistance(other then LED bulb)????

 

[ybreethi]

how to reduce mosfet loss??