[PIC] PIC16F73 Buck converter design problem

[anand78pankaj]

Dear all, I am facing problem in designing buck converter. I have successfully tested my code written in assem. language in logic analyzer. The PWM Freq. is 100 Khz.

The problem is i am not getting reduced voltage as per duty cycle at the output. Please suggest.

 

[FvM]

Show your circuit.

Do you know that the output voltage will be proportional to duty cycle only in continuous conduction mode (CCM) of the buck converter, in other words with sufficient load current?

 

[anand78pankaj]

I have attached the circuit for your kind perusal. What I have noticed is, when I give only high or low command to Pin RC2 one by one, the Power MOSFET works well and load cuts off. But, when i give PWM than Power Mosfet remains always On.
The Voltage at the Gate of M2 remains at 3.36 Volt approx.

https://obrazki.elektroda.pl/5898832800_1439388664.jpg

 

[Najmul_I]

you should reduce the Gate-Source resistance(100k) of M2. Because the gate-source capacitor need to be discharge. you could use 100 ohm.

 

[HULK28]

Hello,

have you some references for M1 and M2? It's easier for validate your application
Be careful, you must also protect gate-source of M1 (VGS(max) is generally 20V for absolute maximum rating) with a zener (15V) and a 220 resistor in M2 drain, because your solar panel, i suppose a 12V model with OCV at 22V, can reach over this 20V rating and transistor will break down...
Here an exemple for your need with some add features for high speed.
Regards.
JY