[SOLVED] MOSFET control problem

[dxtr]

Hey everybody
i wanna simulate a chopper using mosfet but i can't get it to work.

i used NE555 to generate pwm signal
here is the result

**broken link removed**


why i don't get a a chopped signal between 0 and 100v

 

[BradtheRad]

The scope trace alternates between 96.7 and 100.2 V. I believe you expected it to alternate between 0V and 100V.

I think it will resemble that if you were to add a load, with the other end connected to zero ground.

Since a voltage will appear across it, this may change the gate-to-source differential...
which may change the internal resistance of the mosfet...
which may change the voltage on the load, etc.

 

[rohitkhanna]

Try connecting the Source pin of MOSFET to gnd. Right now i can't figure where it's going. Whats the <arrow> and '+' symbol mean ??
And a Voltmeter is certainly not gnd.

And of course some sort of load R on the drain going to the supply positive.

 

[dxtr]

And a Voltmeter is certainly not gnd.

And of course some sort of load R on the drain going to the supply positive.

Thank you , it works now
another question , is there any circuit to trace the average of the chopped signal ?

 

[rohitkhanna]

..is there any circuit to trace the average of the chopped signal ?

you can try your voltmeter (an actual physical one.. not a simulated one) between Drain and Gnd. Set it to read DC volts. This will give you an approximate idea of the average voltage.

 

[dxtr]

you can try your voltmeter (an actual physical one.. not a simulated one) between Drain and Gnd. Set it to read DC volts. This will give you an approximate idea of the average voltage.

thats good , but i want the average value , i want a physical circuit if possible !

 

[BradtheRad]

thats good , but i want the average value , i want a physical circuit if possible !

If you mean a simulated physical circuit...
:^)

Add a high ohm resistor and a low value capacitor, to get an averaged reading.

Screenshot:



The 10V pulses come at 70% duty cycle. The average is 7V.

 

[dxtr]

If you mean a simulated physical circuit...
:^)

Add a high ohm resistor and a low value capacitor, to get an averaged reading.

Screenshot:



The 10V pulses come at 70% duty cycle. The average is 7V.

Thank you so much