Problems With Rectifier Circuits

Ripple

• When an AC voltage is sent through a filter, such as a rectifier circuit, the output voltage is converted to what resembles a DC voltage. Because rectifier circuits are not perfect, a small AC voltage will remain after the conversion process. This small AC voltage rides on top of the DC voltage. This is called ripple. An example of this would be a 12-volt output voltage, which continuously fluctuates between 12.1-volts and 11.9-volts. The 0.2-volt difference is considered the AC voltage riding on the average 12-volts of DC voltage. As the amount of ripple decreases, the cost of the rectifier increases.

Size and Power Dissipation

• As the magnitude of the AC voltage increases, the rectifier circuit has to be able to handle the additional power. If the circuit is not sized properly, the rectifier will overheat and self destruct. This can be a very costly item to replace.

Diode Failure

• Because it takes four diodes to properly rectify an AC voltage, it is important that each diode operates properly and that these diodes be evenly matched in characteristics. If one diode fails in a 120-volt AC rectifier, the resulting output voltage can damage the equipment to which the rectifier is connected. Some rectifiers have emergency shut off switches and circuits, which monitor the circuit for normal operation.

Diodes Are not Perfect

• Diodes, like other electronic components, are not perfect. There are time delays in these components between different stages of operation. For example: when the positive side of an AC voltage begins to switch over to the negative side, there is a time delay between the resulting DC voltage outputs. This is due to one pair of diodes switching off and the next pair switching on.