Multi-vibrator from 555 - Solutions - Huaqiang Electronic Network

Crystal oscillator

Quartz Oscillator 3225 20M OSC

Figure 2-66a is a multivibrator circuit consisting of 555 components, R1, R2 and C are external components. Its working principle is as follows:

After the power is turned on, VCC charges capacitor C via R1 R2. Since the voltage on the capacitor cannot be abrupt, when the power is turned on, Ï…C When Ï…C rises above Vcc/3, RD=1, SD=1, the basic RS flip-flop state is unchanged, that is, the output terminal Q is still high level, when VC rises to slightly more than 2VCC/3, Rn=0 , SD=1, the basic RS flip-flop is set to 0, and the output terminal Q is low. At this time, Q=1, the internal discharge tube is satisfactorily turned on. Thus, capacitor C is discharged through R2 and the internal discharge tube, and Ï…c is exponentially reduced.
When Ï…C falls slightly less than Vcc/3, the internal comparator A1 outputs a high level, A2 outputs a low level, and the basic RS flip-flop is set to 1 and outputs a high level. At this time, Q=0, the internal discharge tube is turned off. Then C ends the discharge and restarts charging. This cycle is not limited, the output will get a series of rectangular pulses, as shown in Figure 2-66b.