Pulse generating circuit multivibrator

Infineon / Mitsubishi / Fuji / Semikron / Eupec / IXYS

Pulse generating circuit multivibrator

Posted Date: 2024-02-12

Pulse generating circuit

The principle of the pulse generation circuit is to utilize the positive feedback effect between the input terminal and the output terminal of the flip-flop. When the input pulse occurs, the state of the flip-flop will change, thereby generating an output pulse of limited width. Common monostable triggers include 555 timers and flip-flops. The working principle is that when the input pulse occurs, the 555 timer will charge the capacitor and store energy. When the capacitor reaches the preset threshold, the output will send out a pulse signal of limited width.


A multivibrator is a self-excited oscillator that can generate rectangular waves, also called a rectangular wave generator. It uses deep positive feedback to alternately turn on and off two electronic devices through resistance-capacitance coupling, thereby self-exciting to generate a square wave output. The multivibrator can automatically generate rectangular pulses without external pulses and is widely used in the generation and shaping of pulse signals.

In various applications of digital technology, pulse waveforms such as rectangular waves, square waves, and sawtooth waves are often used, among which rectangular waves and square waves are the more important waveforms. Multivibrators are widely used in fields such as power electronics and Internet of Things technology. It has the ability to generate rectangular waves, square waves, sawtooth waves and other waveforms, and has good frequency stability and waveform quality.

Advantages of multivibrators include:

The output waveform is stable and reliable, and the output frequency can be adjusted within a wide frequency range.
The circuit is simple, low cost and easy to implement.
The output waveform is easy to control and adjust, enabling precise timing and synchronization.

Disadvantages of multivibrators include:

The generated rectangular wave contains rich harmonic components, which may cause interference to other circuits.
It requires a certain amount of stabilization time and is not suitable for occasions requiring quick response.
It is highly sensitive to component parameters, and improper parameter selection will affect the quality and stability of the output waveform.
Multivibrators are basic pulse generating circuits.

The pulse generating part shown in Figure 1 is a multivibrator. Figure 2(a) shows its circuit structure, and Figure 2(b) shows its output pulse.

LED (Light Emitting Diode) flashing circuit

pulse generating circuit

In this circuit, its basic structure is a CR-coupled 2-stage amplification circuit using 2 transistors. The output of Tr2 is 100% forward feedback (the polarity of the output is consistent with the input and all is returned to the input terminal) to Tr1. oscillator circuit.

Simply put, it uses the charging and discharging functions of C1, R1 and C2, R2 to change the input voltage of the base of the other party's transistor, so that the transistor acts as a switch.

For example, when Tr1 is ON, the collector voltage is almost close to 0. Since C1 applies a negative voltage to the base of Tr2, it turns OFF.

With Tr1 and Tr2 as the center, the circuit is symmetrical, so the action is exactly the opposite. When Tr1 is ON, Tr2 is OFF; when Tr2 is ON, Tr1 is OFF. In this way, the output Vc1 and Vc2 are shown in Figure 2(b).

Therefore, the light-emitting diodes in Figure 1 can be made to flash alternately.

#Pulse #generating #circuit #multivibrator