Single phase uncontrolled full bridge rectifier supplying R-L-E Load - circuit diagram &Waveforms
Single phase uncontrolled full bridge rectifier supplying R-L-E Load:
Even though split supply full wave single phase rectifiers have better performances than their half wave counterparts in terms of output voltage form factor and ripple factor, it possesses certain disadvantages too
- They require a split power supply which is not always available.
- Each half of the split power supply carries current for only one half cycle. Hence they are underutilized.
- The ratio of the required diode PIV to the average output voltage is rather high.
These problems can be diverted by using a single phase full bridge rectifier.
- This is one of the most popular rectifier configuration and are used widely for applications requiring dc. Power output from a few hundred watts to several kilo watts. The rectifier supplying an R-L-E type load which may represent a dc. motor or a storage battery. These rectifiers are also very widely used with capacitive loads particularly as the front end of a variable frequency voltage source inverter.
When the switch S is turned on at the positive going zero crossing of vi no current flows in the circuit till vi crosses E at point A. Beyond this point, D1 & D2 are forward biased by vi and current starts increasing through them till the point B. After point B, vi falls below E and io starts decreasing. Now depending on the values of R, L & E one of the following situations may arise.
- io may become zero before the negative going zero crossing of vi at point C.
- io may continue to flow beyond C and become zero before the point D.
- io may still be non-zero at point D.
- It should be noted that if io >0 either D1D2 or D3D4 must conduct.
- If io >0 at point C the negative going input voltage reverse biases D1 & D2. Current io commutates to D3 and D4 as shown in the associated “conduction Diagram.
- It shows pictorially the conduction interval of different devices. The current io continues to decrease up to the point D beyond which it again increases. It should be noted that in this mode of conduction io always remain greater than zero. Consequently, this is called the continuous conduction mode of operation of the rectifier. In the other two situations the mode of operation will be discontinuous.