I am studying and studying a circuit. I want to know how the oscillation frequency is controlled, the function of the PNP transistor and the function of the diode D1. I hope I can enlighten you.
Lindy ポストする October 29, 2020
What circuit to study
Do you use multium simulation?
What control is given?
The C pole of Q4 is not connected,
The oscilloscope has output from port B
Juno ポストする October 29, 2020
This is a simulation diagram. The simulation results may not be very accurate.
It is possible for this circuit to oscillate, but according to the component values in the figure, it is possible to not oscillate.
This circuit is a relaxation oscillator, not a sinusoidal oscillator.
If oscillation occurs, it may be that after C3 is charged to a certain voltage, the U1A input is high and the U1A output is low. U1A pulls down the voltage across C3 through the Q4 emitter junction (used as a diode), and the output of U1A becomes high again.
Berkeley ポストする October 29, 2020
I think this diode D2 is not useful for oscillation.
D2 is in the reverse state, which is roughly equivalent to a capacitor, in parallel with capacitor C3 (the diode junction capacitance is generally greater than 1pF), only to increase the capacitance of capacitor C3.
