TL780_15 Datasheet, PDF (6/17 Pages) Texas Instruments – POSITIVE-VOLTAGE REGULATORS

TL780 SERIES
POSITIVE-VOLTAGE REGULATORS
SLVS055M – APRIL 1981 – REVISED OCTOBER 2006
APPLICATION INFORMATION
INPUT
OUTPUT
+
TL780-xx
V
I
COMMON
GND
I
L
V
O
Figure 2. Positive Regulator in Negative Configuration (V_I Must Float)
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INPUT
TL780-xx
C1
0.33 µF
V_O(Reg)
R1
OUTPUT
I_O
I_O = (V_O/R1) + I_O Bias Current
Figure 3. Current Regulator
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.
V_I
TL780-xx
V_O
1N4001
or
Equivalent
–V_O
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.
V_I
TL780-xx
V_O
Figure 5. Reverse-Bias-Protection Circuit
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