3.2 D’Arsonval Meter Movement with half-wave rectifier

3.2 D’Arsonval Meter Movement with Half-Wave Rectifier :

A half wave rectifier is defined as a type of rectifier that only allows one half-cycle of an AC voltage waveform to pass, blocking the other half-cycle. Half-wave rectifiers are used to convert AC voltage to DC voltage, and only require a single diode to construct.
A half wave rectifier is the simplest form of rectifier available
A half wave rectifier circuit diagram looks like this:

First, a high AC voltage is applied to the to the primary side of the step-down transformer and we will get a low voltage at the secondary winding which will be applied to the diode.
During the positive half cycle of the AC voltage, the diode will be forward biased and the current flows through the diode. During the negative half cycle of the AC voltage, the diode will be reverse biased and the flow of current will be blocked. The final output voltage waveform on the secondary side (DC) is shown above.

Rectifier efficiency (η) is the ratio between the output DC power and the input AC power. The formula for the efficiency is equal to: η =P_dc/P_ac
The efficiency of a half wave rectifier is equal to 40.6% (i.e. ηmax = 40.6%)
For a half-wave rectifier, the RMS load current (I_rms) is equal to the average current (I_DC) multiple by π/2. Hence the RMS value of the load current (I_rms) for a half wave rectifier is: I_{rms =}I_m/2
The ripple factor of half wave rectifier is equal to 1.21 (i.e. γ = 1.21).
Peak Inverse Voltage (PIV) is the maximum voltage that the diode can withstand during reverse bias condition. If a voltage is applied more than the PIV, the diode will be destroyed.

DC Voltmeter is modified to measure AC voltage by adding a diode into the circuit.
The meter known as D’Arsonval Meter Movement with Halfwave Rectifier.
Types of diodes that can be used such as copper oxide , vacuum diode, semiconductor or crystal diode and etc.
It produces an approximate half sine wave across the load resistor.
The average value of this circuit is referred to as the dc voltage.
Assume that a multiplier of ten times of this value means a 10Vdc input will cause exactly full-scale deflection of d’A.
Replace 10Vdc with 10Vrms, the voltage across the meter movement is just the positive half cycle of the sine wave.

The D’arsonval instrument will respond to the average (DC) value of the ac sine wave

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