µA78L00 SERIES

POSITIVE-VOLTAGE REGULATORS

SLVS010S − JANUARY 1976 − REVISED FEBRUARY 2004

10

POST OFFICE BOX 655303

APPLICATION INFORMATION

µA78L15

0.1

µF

1N4001

0.1

µF

1N4001

0.33

µF

0.33

µF

1N4001

1N4001

20-V Input

−20-V Input

µA79L15

Figure 5. Regulated Dual Supply

operation with a load common to a voltage of opposite polarity

In many cases, a regulator powers a load that is not connected to ground, but instead, is connected to a voltage

source of opposite polarity (e.g., operational amplifiers, level-shifting circuits, etc.). In these cases, a clamp

diode should be connected to the regulator output as shown in Figure 6. This protects the regulator from output

polarity reversals during startup and short-circuit operation.

µA78Lxx

1N4001

or

Equivalent

Figure 6. Output Polarity-Reversal-Protection Circuit

reverse-bias protection

Occasionally, the input voltage to the regulator can collapse faster than the output voltage. This can occur, for

example, when the input supply is crowbarred during an output overvoltage condition. If the output voltage is

greater than approximately 7 V, the emitter-base junction of the series-pass element (internal or external) could

break down and be damaged. To prevent this, a diode shunt can be employed as shown in Figure 7.

µA78Lxx

Figure 7. Reverse-Bias-Protection Circuit