Once again, we have another "trickier" rectifier. As you see, the bridge rectifier has 4 diodes. A transformer is optional. Now, what's the purpose? Well, once again efficiency! IF you recall the full-wave, the transformer was centre-tapped, so the pulsating DC output is only half the voltage from the transformer. (I.E.- Vin=12.6Vrms, Vout=6.3Vrms) In the bridge rectifier, you only lose 1.4V across the two forward biased diodes at a time.  As you can see, the output waveform looks just like the full-wave. Well, the bridge rectifier is a full-wave rectifier....... with a slight difference. See, when the Voltage source is on the positive alternation, two diodes are being forward biased. Looking at the schematic on top of the page, we'll say that the upper left diode is D1, the upper right is D2, the lower right is D3, and the lower left is D4.  I would have labeled them, but the program I have would not let me label the individual diodes on the bridge. Anyway........... During the positive alternation, D2's anode is more positive than its cathode causing it to be forward biased. At the same time, D4's anode is more positive than its cathode, causing it to be forward biased!  This is the first alternation you see on the waveform. Now during the negative alternation, D1 and D3's anodes are more positive than their cathodes, causing them to be forward biased. Therefore causing the second positive output alternation. This concludes our lesson on rectifier's. Main Menu