A smoothed full-wave consists of four diodes in a circuit as in the bridge rectifier but also includes a capacitor, as shown in Fig. 33.26. This results in the capacitor charging up as voltage goes one way and discharging as it reverses. This causes a lag in voltage output and smoothens out the pulsing waveform to closer represent a steady d.c. waveform. As seen in Fig. 33.27, this improved waveform has a smoother output than the other two rectifiers.
a.c. input + V
0 V – V
Rectifier output
voltage source
a.c.
D4 D2
D1 D3 C load
FIG. 33.26 A smoothed full-wave rectifier circuit
0 V – V
charges C discharges C waveform Time
with capacitor ripple
waveform without capacitor
Time Resultant output waveform
FIG. 33.27 A smoothed full-wave rectifier voltage output
Light-emitting diode (LED) An LED is a semiconductor capable of emitting light as current flows through it.
Generally made from semiconductors of gallium arsenide or gallium phosphide, LEDs are diodes which when forward biased undergo ‘electroluminescence’, as electrical energy excites electrons and they emit light. The type of material and transparent casing around LEDs determine the colour of light given off. LEDs are used in many appliances, such as torches, digital watches, displays on billboards and signs, remote controls, calculators and recently in optical decorations.
