Hobbies And Interests
Diode Clampers
The voltage of an alternating current signal oscillates between a negative and a positive voltage, with zero volts as the average. A diode only conducts in one direction, and therefore only conducts during half of the AC cycle.
In a diode clamper circuit, the capacitor charges during the first half of the AC cycle when the diode is conducting and the voltage rises to that of the input voltage and adds to it. During the second half of the cycle, the voltage across the capacitor opposes the input voltage as the capacitor discharges. This prevents the voltage from falling or rising -- depending on the orientation of the diode and capacitor -- above or below zero volts.
Diode clamper circuits are an integral part of the circuitry on analog television broadcasting and receiving equipment.
Biased Clamper Circuits
The introduction of a DC voltage, or bias, into a diode clamper circuit further shifts, or biases, the AC signal. For example, a 2.5 volt biased clamper shifts a 5 volt AC signal to 2.5 volts above or below zero volts. The 5 volt AC signal now oscillates between 2.5 volts and 12.5 volts.
A DC bias voltage may also shift the AC signal in the opposite direction. In our example, if the DC bias is reversed, the output AC signal is from -2.5 volts to +7.5 volts.
Use a biased clamper circuit to shift a voltage to a specific level other than zero volts.
Power Supplies
DC power supplies use diode rectifier circuits to convert AC current into a pulsing DC current. After filtering, the output is smoothed to a nearly pure DC form that does not pulse. If the rectifier input current is 10 volts AC, the maximum output of a rectifier is 10 volts DC, under ideal conditions.
A diode clamper circuit sets the incoming AC voltage at a specific level, often biased above or below zero volts on the power supply.
Voltage Multipliers
High-voltage camera flashes and similar circuits utilize diode clampers to raise voltages to high levels. The output of a clamper circuit supplies the input of a second clamper circuit. Each successive clamper circuit feeds another and raises the voltage.
An ideal circuit has no losses, but each diode uses 0.7 volts of electricity to function, so each diode causes a loss of 0.7 volts. This makes it impractical to raise a voltage to an infinite level using diode clamper circuits.
Data Communications
Early communication between earth-based stations and experimental rockets used various types of pulse modulation to carry data. One form of telemetry was pulse width modulation. As a simplistic example, a pulse that lasted 1/10th of a second might equal a zero, while a pulse that lasted 2/10th of a second might equal a two.
Diode clamping circuits were an integral part of pulse modulation systems and clamped the incoming signal above zero volts. The DC component of the signal was removed with a filter -- and the pulses analyzed for the data they carried.