Power Supply Circuits

A power supply circuit provides the steady voltage and current that electronic equipment needs to operate. Most equipment requires direct current at a well-controlled voltage, but the mains supply is alternating current at a much higher voltage. A conventional linear power supply converts one into the other in four stages: a transformer changes the mains voltage to a lower value, a rectifier converts the alternating current to pulsating direct current, a filter capacitor smooths those pulses, and a regulator holds the output steady despite changes in load and input.

The rectifier is built from diodes; a full-wave or bridge rectifier uses the whole of each cycle and is more efficient than a half-wave design. After smoothing, some ripple remains, which the voltage regulator removes by maintaining a fixed output. A voltage multiplier is a related circuit that uses diodes and capacitors to produce a direct voltage several times higher than the peak input, useful where a high voltage at low current is needed.

Battery-related circuits form another large group. Battery chargers control the current delivered to a cell so that it is replenished without being overcharged; lead-acid and nickel-cadmium cells each need their own charging regime, and a constant-current charger holds the charging current steady throughout. Monitoring circuits warn when a battery’s voltage falls too low, protecting both the battery and the equipment it powers.

Frequently asked questions

What are the main stages of a linear power supply?

A transformer lowers the mains voltage, a rectifier converts it to direct current, a filter capacitor smooths the result, and a regulator holds the output voltage steady.

What does a voltage multiplier do?

It uses a ladder of diodes and capacitors to produce a direct voltage several times higher than the peak input, suited to applications needing high voltage at low current.

Why is a constant-current charger used for batteries?

Holding the charging current steady gives a controlled, predictable charge that suits cells such as nickel-cadmium, helping to avoid overcharging and extend battery life.