A PWM circuit with a NE555 is already presented in the constructor datasheet as 555 in monostable configuration with a clock input on the trigger pin and a modulator signal in the control pin.
Here, i used a 555 as clock that generate a pulse wave. Also, i wanted to use constant current sources made of matched transistors to charge the capacitors instead of resistors, providing a better sawtooth slope between the capacitors terminals.
