^Bridge rectifier

It uses four diodes is shown in figure.

For positive half of input cycle diodes D₁ and D₂ are forward biased and D₃ and D₄ are reverse biased. So D₁ and D₂ conduct but D₃ and D₄ don’t. Current through R_L flows from X to Y.

For negative half of input cycle D₃ and D₄ are forward biased and D₁ & D₂ are reverse biased. So in this half cycle D₃ and D₄ conduct but D₁ and D₂ do not. Current again flows from X to Y through R_L.

Thus, we see that current through R_L always flows in one direction from X to Y.

^Parallel capacitor filter 

The resistance offered by a capacitor is it offers high resistance to low frequency currents (i.e. dc) or it blocks low frequency currents through it. As a result these low frequency currents can pass through R_L only.

 

^Full wave rectifier

If during the positive half cycle of the input the end A becomes positive and the end B becomes negative with respect to the center tap C then diode D₁ gets towards biased and conducts current D₂ is reverse biased and does not conduct. During the negative half cycle the diode D₁ gets reverse biased and does not conduct & D₂ conducts current. As during both half cycles of input ac the current through load R_L flows in the same direction F to C.

^Principle

A diode so offers very low resistance in forward biasing & very high resistance during the reverse biasing. For an ideal diode we assume it offers zero resistance in forward biasing & infinite resistance during the reverse biasing & thus will conduct for only during those cycles in which it is forward biased & doesn’t conduct when reverse biased.

^Uses of diode

A diode can be used as

• rectifiers (to convert dc to ac),
• LED (produce light on forward biasing a diode)
• solar cells (using solar energy to produce emf)
• photodiodes (to produce reverse current which can be controlled with intensity of light)
• Zener diodes (to converting fluctuating dc to constant dc)
• fast switching OR – gate & AND – gate