Buck Converter with PİC16F877A

[(*steve*)]

i have another circuit, why this signals like that ,is it about duty values?

There's some superfluous stuff there (D1, C1), but what would be the effect of changing Q1 for a P channel mosfet? Would it address one of Harald's criticisms? What is the minimum voltage between drain and source in this circuit vs. one with a P channel mosfet? Is this important?

Also, what is the Vgs(max) for Q1? is that a consideration in this circuit?

 

[Harald Kapp]

why this signals like that

The signals are perfect for the circuit you simulate. Duty cycle is of no concern here.
A high voltage at the output of the PIC drives Q1 into the on state. What does this to the gate-source voltage of Q2?

My impression is that you haven't understood how a MOSFET is controlled. I cannot explain your ignoring my instructions in post #17. Maybe you understand this explanation better?

 

[emrebay]

There's some superfluous stuff there (D1, C1), but what would be the effect of changing Q1 for a P channel mosfet? Would it address one of Harald's criticisms? What is the minimum voltage between drain and source in this circuit vs. one with a P channel mosfet? Is this important?

Also, what is the Vgs(max) for Q1? is that a consideration in this circuit?

should i use P canal mosfet?

 

[emrebay]

The signals are perfect for the circuit you simulate. Duty cycle is of no concern here.
A high voltage at the output of the PIC drives Q1 into the on state. What does this to the gate-source voltage of Q2?

My impression is that you haven't understood how a MOSFET is controlled. I cannot explain your ignoring my instructions in post #17. Maybe you understand this explanation better?

this is last version of my circuit what do you think Mr.Kapp and Mr.Steve, does it work?

 

[emrebay]

There's some superfluous stuff there (D1, C1),

ii created my circuit according to this circuits
https://www.re-innovation.co.uk/uploads/solarregulator_Bootstrapped Mosfet (1)-640x315.png
https://www.re-innovation.co.uk/uploads/solarregulator_Bootstrapped Mosfet (1)-640x315.png

 

[Harald Kapp]

This should work, but it is not inherently safe: if the PIC is off, the MOSFET will be on, thus powering the load.
If you use the bipolar transistor to turn the gate voltage on (instead of off, as your circuit does), then the MOSFET will be off when no drive is present. This is a safe state.

 

[WHONOES]

At the risk of attracting ire from the other contributors, may I suggest that you.
1) Replace Q1 with an IRF9540 which is a P channel device.
2) Connect the source of Q1 to +24V and the Drain to the top of R3.
3) Delete D2 and C4.
4) Connect the top of R2 to +24V.
5) Insert a 1K resistor in the collector of Q2 so that it connects to the junction of R2 and the gate of Q1.
6) Connect your virtual scope across R3 and see what happens.

You may or may not need to invert the sense of the output pin of the PIC.