Sawtooth generating circuit composed of 555

Crystal oscillator

Quartz Oscillator 3225 20M OSC

As shown in the figure, a sawtooth wave generating circuit composed of 555 is shown. The circuit is a temperature-independent audio sawtooth generator with a linearity of less than 1%. It is connected to an astable multivibrator using the timer NE555.

Capacitor C1 is charged by the power supply (5V) through resistors R1, R2, and R3, while the discharge passes through the transistor channels inside R3 and NE555, thus forming a sawtooth wave at pin 7 of the NE555. The sawtooth wave is output through a Darlington emitter emitter output Q1 (MPS-AB). Because the output of Q1 is positively fed back to the upper end of R2 through C2, the voltage drop across R2 during C1 is a constant during charging, so the output is a linear ramp. With this method of increasing linearity, the temperature stability of the circuit can be significantly improved.

The oscillation frequency of this circuit is calculated as follows:

Frequency corresponding to different component values: