Datasheet

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APPLICATION INFORMATION
V
O
GND
V
I

+
COMMON
INPUT
OUTPUT
TL780-xx
I
L
I
O
OUTPUT
R1
0.33 Fµ
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 2. Positive Regulator in Negative Configuration (V
I
Must Float)
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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