Diode Applications 1 The HalfWave Rectifier This diode

Diode Applications

1 - The Half-Wave Rectifier • This diode application changes ac into dc. • The voltage is most often a sinusoidal and diode is ideal.

During Positive half-cycle • Diode conduct (“ON”) • VD=0 • Vo=VS During Negative half-cycle • Diode conduct (“OFF”) • VD=VS • Vo=0, i. D=0

2 - A Typical Battery Charging Circuit In the Figure • VBATTRY represents the battery to be charged

• Rtotal includes all resistance (wiring, diode, battery) reflected to the transformer secondary winding. • Charging current flows only when Vm sin ωt >VBATTRY. • Inertia of meter movement allows indication of average current

3 - The Filtered Half-Wave Rectifier • Also called a peak rectifier, a half-wave rectifier with smoothing capacitor, or a halfwave rectifier with a capacitor-input filter. In this figure

In this figure • When Vs> VL, the diode is on, and the voltage source charges the capacitor. • When Vs< VL, the diode is off, and C discharge exponentially through RL. • We define peak to peak ripple voltage Vr, as the total change in VL over one cycle.

Relating Capacitance to Ripple Voltage • Because the diode is off for nearly the entire period, T, the capacitor must supply the “dc” load current during this interval. • The charge taken from the capacitor in this interval is: • The capacitor voltage decreases by Vr in this interval, which requires a decrease in the charge stored in the capacitor

• Equating these equations and solving for C gives us a design equation that valid only for small Vr:

4 - The Filtered Half-Wave Rectifier • During Positive half-cycle Diode 1 is ON and diode 2 is OFF • During Negative half-cycle • Diode 1 is OFF and Diode 2 is ON

• The load voltage in this case is represented as: Full wave rectifier