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.

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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.

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