Diodes are commonly used in voltage-clipping circuits to limit or "clip" the output voltage of a signal to a certain level. These circuits are useful for protecting sensitive electronic components from voltage spikes or for shaping the waveform of a signal. There are two types of voltage-clipping circuits: positive voltage-clipping and negative voltage-clipping.
Positive Voltage-Clipping Circuit:
In a positive voltage-clipping circuit, the positive part of the input signal is clipped or limited to a certain voltage level, while the negative part of the signal remains unaffected. This is achieved by connecting a diode in series with a load (resistor) across the output.
Here's a basic schematic of a positive voltage-clipping circuit:
Vin -----|>|---- Output
When the input voltage (Vin) is positive and greater than the forward voltage drop of the diode (usually around 0.6 to 0.7 volts for silicon diodes), the diode becomes forward-biased and acts like a closed switch. The current flows through the diode and the resistor, generating an output voltage across the resistor. However, when the input voltage goes negative (below the forward voltage drop), the diode becomes reverse-biased and acts like an open switch. As a result, no current flows through the resistor, and the output voltage remains at the diode's forward voltage drop, effectively clipping the positive part of the signal.
Negative Voltage-Clipping Circuit:
In a negative voltage-clipping circuit, the negative part of the input signal is clipped, while the positive part remains unaffected. This is achieved by connecting a diode in the opposite direction compared to the positive voltage-clipping circuit.
Here's a basic schematic of a negative voltage-clipping circuit:
Vin -----|<|---- Output
When the input voltage (Vin) goes negative and exceeds the reverse voltage of the diode (maximum allowable reverse voltage), the diode becomes reverse-biased and acts like an open switch. In this case, no current flows through the resistor, and the output voltage across the resistor remains at zero volts. However, when the input voltage becomes positive (above the reverse voltage of the diode), the diode becomes forward-biased, and the circuit behaves like a normal forward-biased diode, allowing the positive part of the signal to pass through unaffected.
It's important to choose appropriate diodes for voltage-clipping circuits to ensure that they can handle the current and voltage levels of the input signal. Additionally, the resistor's value can be adjusted to set the desired clipping level. Voltage-clipping circuits are commonly used in audio applications to limit the amplitude of audio signals, preventing distortion and protecting speakers and amplifiers from excessive voltage levels.