FIGURE 1(a) shows a power supply using a full-wave bridge rectifier circuit. The main supply is stepped down by the transformer T1 and the secondary voltage Vs rectified by the four diodes D1 -D4; diodes D1 and D3 conduct on one half cycle and D2 and D4 on the other. The diodes are provided in a single 4-pin bridge-rectifier package which can be mounted directly onto a printed circuit board. The transformer has a turns ratio 10:1 and the average load resistance is 30. The output of the power supply is protected by a 3 A fuse which is designed to 'blow' within 5 ms if the current is in excess of ten times the rated value.
FIGURE 1(b) shows the voltage waveforms at various points in the circuit. Of interest here is the effect of switching on and off the mains supply; this has the effect of producing large transient voltages across the diodes.
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Solution: We first consider the worst-case peak voltage of the secondary when the switch is closed at primary peak:
Then we consider the worst-case peak voltage of the secondary when the switch is open at ...
The expert examines proper bridge rectifier for PSU.