Simple Diode Protection Circuits in Rectifiers ...

Simple Diode Protection Circuits in Rectifiers of Transformer Power Supply Sources As a rule build-up of filter capacitors are used in order to bring the voltage ripple level in transformer power supply units to as low as possible. This is not the most efficient method, as at the time of connection the uncharged filter capacitors as a whole act as the short circuit for the rectifier diodes and the secondary transformer winding. To limit the charge current of the filter capacitors, constructors often use current-limiting components that in the majority of cases get disconnected automatically. One of the examples here is the parallel rectifier diode protection circuit, where capacitance 1 is connected in series to the resettable fuse. The second option is the series diode protection circuit. In this case capacitors 1 and 2 are separated by the resettable fuse. As result of the current pulse, these protection fuses temporarily disconnect the entire capacitors circuit, and then connect again in a certain amount of time. The third circuit is diode protection at connection. Here a current-limiting resistor is added between the diodes and the filter capacitors. Mounted in parallel to the resistor is a resettable fuse that is designed for the maximum current flowing through the rectifier diodes. With a pulse of the charge current, the fuse resistance increases, and the capacitors get gradually charged through the current-limiting resistor. Later the resistance of the fuse decreases. At the same time, resetting fuses protect the rectifier elements from overcurrent and short circuits.