µA78L00 SERIES
POSITIVE-VOLTAGE REGULATORS
SLVS010I – JANUARY 1976 – REVISED JULY 1999
APPLICATION INFORMATION
1N4001
20-V Input
µA78L15
V
O
= 15 V
1N4001
0.33 µF
0.1 µF
0.1 µF
0.33 µF
1N4001
–20-V Input
µA79L15
V
O
= –15 V
1N4001
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
V
I
V
O
1N4001
or
Equivalent
– V
O
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.
V
I
V
O
µA78Lxx
Figure 7. Reverse-Bias-Protection Circuit
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