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Diode Applications

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”) V D =0 V o =V S During Negative half-cycle Diode conduct (“OFF”) V D =V S

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Diode Applications

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  1. Diode Applications

  2. 1- The Half-Wave Rectifier • This diode application changes ac into dc. • The voltage is most often a sinusoidal and diode is ideal.

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

  4. 2- A Typical Battery Charging Circuit In the Figure • VBATTRY represents the battery to be charged

  5. 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

  6. 3- The Filtered Half-Wave Rectifier • Also called a peak rectifier, a half-wave rectifier with smoothing capacitor, or a half-wave rectifier with a capacitor-input filter. In this figure

  7. 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.

  8. 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

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

  10. 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

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

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