A PWM circuit does not need a triangle-wave that goes from 0V to the supply voltage. I
View attachment 81267 ts voltage swing from an ordinary opamp just needs to have enough amplitude to switch the switching transistor or Mosfet on and off.
I used the standard one opamp as a positive feedback square-wave oscillator that feeds a second opamp as an integrator.
My PWM frequency was about 3kHz which is very audible, it could have been ultrasonic.
I used this circuit to drive a 4A motor on an electric model airplane: