Monostable Multivibrator Circuit Operation

A Monostable Multivibrator is an electrical circuit that can operate in both stable and astable modes as a two-stage amplifier. The output of the first stage of the multivibrator is sent to the second stage, which then feeds back to the first stage, causing the cutoff state to become saturate and the saturate state to become cutoff. The multivibrator can be utilised as oscillators, timers, and flip-flops due to the transfer of states.

Outline

• Types of Multivibrator:
• Monostable Multivibrator:
• Monostable Multivibrator Circuit Operation:
  • Circuit Diagram:
  • Circuit Operation:
  • Uses of Multivibrator:

Types of Multivibrator:

1. Astable Multivibrator: This multivibrator will not be stable in both states; it will switch from one to the other quickly. Oscillators are the most common application for this sort of multivibrator. There is no limit or duration for switching states in an astable multivibrator, also known as a free running multivibrator.
2. Multivibrator : One shot multivibrator is another name for monostable. There is one stable state and one astable state in a monostable multivibrator. To enter the astable state and return to the stable state after a length of time, this multivibrator requires a trigger (external signal). The user will pick the time period, and the monostable multivibrator will be primarily used as timer.
3. Bi-Stable Multivibrator: This circuit has both the stable states. Valid trigger will change state; it will be in that state only up to the next trigger. This circuit is mainly used as flip-flops.

Monostable Multivibrator:

One stable state and one semi stable state exist in a monostable multivibrator (astable state). The multivibrator will jump from stable to semi stable condition when an external trigger is applied to the circuit.

It will automatically return to the stable state once a length of time has passed; the multivibrator does not require an external trigger to return to the stable state. The time it takes for a circuit to recover to a stable condition is always determined by the circuit’s passive parts (resistor and capacitor values).

Monostable Multivibrator Circuit Operation:

Circuit Diagram:

Circuit Operation:

• When there is no external trigger to the circuit the one transistor will be in saturation state and other will be in cutoff state. Q1 is in cutoff mode and put at negative potential until the external trigger to operate, Q2 is in saturation mode.
• Once the external trigger is given to the input Q1 will get turn on and when the Q1 reaches the saturation the capacitor which is connected to the collector of Q1 and base of Q2 will make transistor Q2 to turn off. This is state of turn off Q2 transistor is called astable stable or quasi state.
• When capacitor charges to VCC the Q2 will turn on again and automatically Q1 is turn off. So the time period for charging of capacitor through the resistor is directly proportional to the quasi or astable state of multivibrator when a external trigger occurred (t=0.69RC).

Uses of Monostable Multivibrator:

The monostable multivibrators are used as timers, delay circuits, gated circuits etc.