Diode Applications in Electronic Circuits

Diode Application: Rectifier

• A rectifier is a circuit that converts AC voltage to DC voltage, and it's found in all power supplies.
• The rectifier uses the diode's ability to conduct current in one direction and block current in the other direction.
• A simple rectifier circuit consists of a diode (D) and a resistor (R) connected in series.

Half-Wave Rectifier

• During the positive half-cycles of the input sinusoid, the diode is forward-biased and conducts current, producing an output voltage across the load resistor.
• During the negative half-cycles of the input sinusoid, the diode does not conduct, and the output voltage is zero.
• The output voltage waveform has the same shape as the positive half-cycle of the input voltage.
• The circuit is called a half-wave rectifier because it only rectifies the positive half-cycles of the input voltage.

Effect of Barrier Potential on Half-Wave Rectifier Output

• When the practical diode model is used, the barrier potential of 0.7 V must be overcome before the diode becomes forward-biased.
• This results in a half-wave output with a peak value that is 0.7 V less than the peak value of the input voltage.
• The expression for the peak output voltage is Vp - 0.7 V.

Average Value of the Half-Wave Output Voltage

• The average value of the half-wave rectified output voltage is the value measured on a DC voltmeter.
• It is determined by finding the area under the curve over a full cycle and then dividing by pi.
• The result is expressed in the equation VAVG = Vp / π.

Half-Wave Rectifier with Transformer Coupling

• The transformer is used to couple the AC input voltage from the source to the rectifier.
• The transformer allows the source voltage to be stepped down as needed.
• The amount of voltage stepping down is determined by the turns ratio of the transformer, n = Nsec / Npri.
• A transformer with a turns ratio less than 1 is a step-down type, and one with a turns ratio greater than 1 is a step-up type.
• The secondary voltage of a transformer equals the turns ratio, n, times the primary voltage.