Describe the operation of an astable multivibrator using transistors.
1 Answer
An astable multivibrator is a type of oscillator circuit that generates a continuous square wave output without requiring an external triggering signal. It's also known as a free-running multivibrator. The astable multivibrator circuit using transistors typically consists of two transistors and a few passive components, such as resistors and capacitors.
Here's a basic description of how an astable multivibrator using transistors operates:
Transistor Setup: The circuit usually employs two transistors, often of the NPN type. Let's call them Q1 and Q2.
Initial State: Assume Q1 is initially in an active state (saturated) and Q2 is in an off state (cut-off). This means that the collector of Q1 is connected to the positive supply voltage (Vcc) and the emitter is grounded. The collector of Q2 is also connected to the positive supply voltage (Vcc), but the emitter is disconnected from the ground.
Charging of Capacitor C1: The collector of Q1 is connected to the base of Q2 through a resistor R1 and a capacitor C1 in series. Since Q1 is saturated, its collector voltage is near Vcc, and capacitor C1 begins to charge through R1. This causes a voltage drop across R1 and gradually raises the base voltage of Q2.
Turning on Q2: As the voltage across the base of Q2 rises, it eventually reaches the threshold voltage required to turn on Q2. Once Q2 turns on, its collector voltage drops, and capacitor C1 begins to discharge through Q2's collector-emitter junction and resistor R1.
Discharging of Capacitor C1: As capacitor C1 discharges, the voltage at the base of Q2 decreases. This eventually causes Q2 to enter the cut-off state, turning it off.
Feedback and Cycle Reversal: The collector of Q2 is connected to the base of Q1 through a resistor R2 and a capacitor C2 in series. When Q2 turns off, the voltage at its collector rises sharply. This increased voltage is coupled through C2 to the base of Q1, turning it off as well.
Cycle Repeats: With both Q1 and Q2 turned off, capacitor C2 begins to charge through resistor R2. This process is similar to step 3, but now for the opposite side of the circuit. As the voltage across the base of Q1 increases, it eventually turns Q1 on, and the cycle repeats.
The process outlined above continues to oscillate, with Q1 and Q2 alternating between active and inactive states. This generates a continuous square wave output at the collectors of the transistors. The frequency of the square wave is determined by the values of the resistors R1, R2, and the capacitors C1, C2, along with the transistor characteristics.
Overall, the astable multivibrator using transistors provides a simple and self-triggering method to generate square wave signals for various applications like clock generators, tone generators, and pulse generators.
Here's a basic description of how an astable multivibrator using transistors operates:
Transistor Setup: The circuit usually employs two transistors, often of the NPN type. Let's call them Q1 and Q2.
Initial State: Assume Q1 is initially in an active state (saturated) and Q2 is in an off state (cut-off). This means that the collector of Q1 is connected to the positive supply voltage (Vcc) and the emitter is grounded. The collector of Q2 is also connected to the positive supply voltage (Vcc), but the emitter is disconnected from the ground.
Charging of Capacitor C1: The collector of Q1 is connected to the base of Q2 through a resistor R1 and a capacitor C1 in series. Since Q1 is saturated, its collector voltage is near Vcc, and capacitor C1 begins to charge through R1. This causes a voltage drop across R1 and gradually raises the base voltage of Q2.
Turning on Q2: As the voltage across the base of Q2 rises, it eventually reaches the threshold voltage required to turn on Q2. Once Q2 turns on, its collector voltage drops, and capacitor C1 begins to discharge through Q2's collector-emitter junction and resistor R1.
Discharging of Capacitor C1: As capacitor C1 discharges, the voltage at the base of Q2 decreases. This eventually causes Q2 to enter the cut-off state, turning it off.
Feedback and Cycle Reversal: The collector of Q2 is connected to the base of Q1 through a resistor R2 and a capacitor C2 in series. When Q2 turns off, the voltage at its collector rises sharply. This increased voltage is coupled through C2 to the base of Q1, turning it off as well.
Cycle Repeats: With both Q1 and Q2 turned off, capacitor C2 begins to charge through resistor R2. This process is similar to step 3, but now for the opposite side of the circuit. As the voltage across the base of Q1 increases, it eventually turns Q1 on, and the cycle repeats.
The process outlined above continues to oscillate, with Q1 and Q2 alternating between active and inactive states. This generates a continuous square wave output at the collectors of the transistors. The frequency of the square wave is determined by the values of the resistors R1, R2, and the capacitors C1, C2, along with the transistor characteristics.
Overall, the astable multivibrator using transistors provides a simple and self-triggering method to generate square wave signals for various applications like clock generators, tone generators, and pulse generators.