A monostable multivibrator, commonly referred to as a "one-shot" circuit, is an electronic circuit that produces a single output pulse in response to an input trigger or pulse. This type of circuit is widely used in various applications, including timing, signal conditioning, and pulse generation.
The primary component in a monostable multivibrator is typically a combination of resistors, capacitors, and one or more transistors or operational amplifiers. The circuit's operation can be broken down into several key steps:
Stable State (Quiescent State): In the stable state, the circuit's output is in a defined state, which is typically one of the logic levels (high or low). For the purpose of explanation, let's assume the output is initially in a low state (logic 0).
Trigger Input (Initiation): When a trigger pulse is applied to the circuit's trigger input, it briefly disturbs the stable state. This trigger pulse can come from an external source, such as a sensor, switch, or another circuit. The trigger pulse transitions the circuit from its stable state to an unstable state.
Unstable State (Transition): Upon receiving the trigger pulse, the circuit's output switches to a high state (logic 1). This transition initiates a process where the circuit is temporarily unstable and starts to recover back to its stable state.
Timing Components and Recovery: The timing components (resistor and capacitor) in the circuit determine how long the circuit remains in the unstable state before it recovers back to the stable state. During this time, the capacitor charges through the resistor. The time it takes for the capacitor to charge to a certain threshold voltage level is known as the "pulse width" or "time delay" of the one-shot circuit. This time delay can be calculated using the RC time constant formula: Time Delay (t) = R * C.
Return to Stable State: Once the capacitor charges to the threshold voltage, the circuit begins to return to its stable state. The output transitions back to its low state (logic 0), and the circuit is ready to receive another trigger pulse.
It's important to note that the monostable multivibrator generates only a single output pulse in response to each trigger pulse, regardless of the pulse width or duration of the trigger. Subsequent trigger pulses received during the recovery phase will not produce additional output pulses until the circuit has fully returned to its stable state.
In summary, a monostable multivibrator (one-shot) circuit is a timing circuit that generates a single output pulse of a specified duration in response to an input trigger pulse. It is commonly used in applications where precise timing and pulse generation are required.