µA78Lxx

µA78Lxx

1N4001

or

Equivalent

µA78L15

0.1 µF

1N4001

0.1 µF

1N4001

0.33 µF

0.33 µF

1N4001

1N4001

20-V Input

-20-V Input

µA79L15

μA78L00

www.ti.com

SLVS010U – JANUARY 1976 – REVISED MAY 2011

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 (for example, operational amplifiers, level-shifting circuits, and so on). 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.

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.

Figure 7. Reverse-Bias-Protection Circuit

Copyright © 1976–2011, Texas Instruments Incorporated

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