TL780 SERIES

POSITIVE-VOLTAGE REGULATORS

SLVS055F – APRIL 1981 – REVISED DECEMBER 1999

7

POST OFFICE BOX 655303

APPLICATION INFORMATION

Figure 2. Positive Regulator in Negative

–VO

GND

VI

–

+

COMMON

In

Out

TL780-xx

IL

Figure 3. Current Regulator

IO

OUTPUT

R1

0.33

µF

C1

INPUT

TL780-xx

VO(Reg)

IO = (VO/R1) + IO Bias Current

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 4. This protects the regulator from output

polarity reversals during startup and short-circuit operation.

VI

Equivalent

or

1N4001

–VO

VO

TL780-xx

Figure 4. Output Polarity-Reversal-Protection Circuit

reverse-bias protection

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.

VO

VI

TL780-xx

Figure 5. Reverse-Bias-Protection Circuit