unipolar spwm question. - how to generate it?

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unipolar spwm question.

There are sine wave input and triangular input.the sine wave input 2V and -2V that input to the comparator LM111.

i want to generate the unipolar spwm that apply to n-channel MOSFET in my h-bridge circuit.

the problem is how to make the inverted sine waveform that apply to the comparator,u7

by inserting the inverting amplifier at the pin 2 of comparator,U7?
 

unipolar spwm question.

I don't understand the problem. Doesn't your circuit give you all the signals you need for driving the H-bridge? Also, you don't need two sine generators - just use V3 for U7 but swap pins 2 & 3. Maybe you should show the the waveforms you want. Also, I assume V1 has the same peak-peak amplitude as the sine waves?

Keith.
 

Re: unipolar spwm question.

i mean in practical how to generate the invert sine wave?
 

Re: unipolar spwm question.

Also, you don't need two sine generators
Click to expand...
Unipolar PWM generation needs either an inverted triangular or sine waveform, because two edges are generated.
by inserting the inverting amplifier at the pin 2 of comparator,U7
Click to expand...
Yes, obviously an inverting amplifier (G=-1) will do, what you want.
I assume V1 has the same peak-peak amplitude as the sine waves?
Click to expand...
Yes, if maximum output voltage is intended.
 

Re: unipolar spwm question.

kspalla said:
can u tell us about triangular signal?
can u share the complete pict as bottom of pic got cut.
Click to expand...

the triangular signal is generated by the function generation,the value is 2.5V peak.
i have no problem in getting this triangular signal.

the problem is sine signal with 180 degree in phase.anyone know how to invert the sine wave?

Added after 4 minutes:


i already try to put the inverting amplifier,u741 op-amp with the resistor input,20kOhm and feedback 20kOhm,but some how the sine wave cannot be invert.
 

Re: unipolar spwm question.

but some how the sine wave cannot be invert.
Click to expand...
It surely works with a correct circuit, e.g. good old 741, unless the signal frequency isn't too high. I assume it's 50 or 60 Hz.

But your MOSFET driver circuit is completely wrong. You're missing a suitable high-side driver, e.g. a level-shifting bootstrap
driver IC as IR2110. As shown, the high side FET could be immediately destroyed by a -400V gate voltage. Or it's simply
not turned on.Also driving the gate voltage leading edge with a 1K pull-up resistor results in a poor switching performance.
 

Re: unipolar spwm question.


yes.signal frequency is 50Hz..
i had change the DC supply to 5V and replace MOSFET with IRF540.
ok,i will try the op-amp 741 method.
 

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