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Here's half your problem: http://2.bp.blogspot.com/_Jt8jI5P6sEU/SZsk-yXxSII/AAAAAAAAC6c/pUxEMVTd8hU/s400/Half-wave+Rectifier.JPG A quick google search and you'll find the other half, no pun intended! ;-)
PRELIMINARIES: A Practical diode dropes some voltage across it for activation. 0.7V for Silicon(Si) and 0.3V for Germenium(Ge). A diode is activated in forward bias, know as activation mode. A diode is not activated in reversed bias, known as diode is in cut off mode. HALF WAVE RECTIFIER:(Assuming Ideal diode for simplicity i.e. it will activate instatnly and doesn't drop 0.7V across it) See figure; A diode is connected to an ac source and to a load resistor. RL forming a half-wave rectifier. 1)Positive half wave rectifier: When +ve cycle of input comes then diode becomes forward bias(acts as a wire) and all voltage drops across resistor. Hence we will get output wave form. When -ve cycle of input comes then diode becomes reversed bias(acts as a high resistance) and all voltage drops across diode. Hence we will not get output wave form i.e. a straight line. Two types of Half wave rectifiers. 2)Negative half wave rectifier: Just reverse the diode position and all working same as above described.
PRELIMINARIES: It is a full wave rectifier using Center-tapped Transformer. Another full wave rectifier is also used, in which 4 diodes are connected as a bridge. A center-tapped transformer is center-tapped(its center is grounded or earthed) and it opposites the polarity of coming cycle. For example, a positive cycle comes, center-tapped transformer sent +ve cycle in upper portion and then opposite polarity cycle(negative) in its lower portion. See figure#A FULL WAVE RECTIFIER:(Assuming Ideal diode for simplicity i.e. it will activate instantly and doesn't drop 0.7V across it) See figure#A; Two diodes are connected to an AC source and to a load resistor RL forming a full-wave rectifier. 1)Positive half wave rectifier:(See figure#1 and figure#2) When +ve cycle comes then D1 is forward bias and D2 is reversed bias. Hence just D1 is activated and we will get +ve half wave output. When -ve cycle comes then D1 is reversed bias and D2 is forward bias. Hence just D2 is activated and we will get another +ve half wave output. 2)Negative half wave rectifier: Just reverse the positions of both diodes and examine. Same working as described above. Note: Remember the working of Center-tapped Transformer. Regards, Electronics Engineer
If you have any problem then you can without hasitation asked it 1000 thousand times, I will be happy to help you out. Although its my facourite subject. :) If you want to know full wave rectifier using diode bridge then I will also post them.