One-Chip Regulators

Many, if not most, small power supplies today are built with the aid of a family of one-chip regulators which use zener diodes and several transistors to regulate the output of a rectifier. These remarkable devices provide stable, ripple-free output DC voltages under a wide range of operating conditions.

An example is Fairchild's mA7800 series of 3-terminal positive voltage regulators. In a single monolithic package they incorporate two zener diodes, 17 transistors, 21 resistors and a capacitor according to the manufacturer's equivalent circuit. They incorporate internal current limiting and thermal shutdown features and can produce on the order of an ampere of output current.

Zener Role in Power Supplies

The zener diode is widely used as a voltage regulator because of its capacity to maintain a constant voltage over a sizeable range of currents. It can be used as a single component across the output of a rectifier or incorporated into one of the variety of one-chip regulators.