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APPLICATION INFORMATION

V

O

GND

V

I

+

COMMON

INPUT

OUTPUT

TL780-xx

I

L

I

O

OUTPUT

R1

0.33 F

µ

C1

INPUT

TL780-xx

V (Reg)

O

I = (V /R1) + I Bias Current

O

O

O

Operation With a Load Common to a Voltage of Opposite Polarity

V

I

Equivalent

or

1N4001

–V

O

V

O

TL780-xx

Reverse-Bias Protection

V

O

V

I

TL780-xx

TL780 SERIES

POSITIVE-VOLTAGE REGULATORS

SLVS055M – APRIL 1981 – REVISED OCTOBER 2006

Figure 3. Current Regulator

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 4. This protects the regulator from output

polarity reversals during startup and short-circuit operation.

Figure 4. Output Polarity-Reversal-Protection Circuit

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

could occur 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 5.

Figure 5. Reverse-Bias-Protection Circuit

6

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