TL780 Datasheet, PDF (7/8 Pages) Texas Instruments – POSITIVE-VOLTAGE REGULATORS

TL780 SERIES
POSITIVE-VOLTAGE REGULATORS
SLVS055F – APRIL 1981 – REVISED DECEMBER 1999
APPLICATION INFORMATION
+
In _TL780-xx
Out
VI _COMMON
–
GND
IL
–VO
Figure 2. Positive Regulator in Negative
Configuration (V_I Must Float)
INPUT
TL780-xx
C1
0.33 µF
VO(Reg)
R1
OUTPUT
IO
IO = (VO/R1) + IO 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.
VI
TL780-xx
VO
1N4001
or
Equivalent
–VO
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.
VI
TL780-xx
VO
Figure 5. Reverse-Bias-Protection Circuit
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