AN78Lxx/AN78LxxM Series
I Basic Regulator Circuit
Input
Output
1
2
AN78Lxx
CO
CI
3
CI is necessary when the input line is long.
CO improves the transient response.
I Usage Notes
1. Cautions for a basic circuit
CI: When a wiring from a smoothing circuit to a three-pin regulator
Di
is long, it is likely to oscillate at output. A capacitor of 0.1µF to
0.47µF should be connected near an input pin.
CO: When any sudden change of load current is likely to occur,
connect an electrolytic capacitor of 10µF to 100µF to improve a
transitional response of output voltage.
Di: Normally unnecessary. But add it in the case that there is a
residual voltage at the output capacitor Co even after switching
off the supply power because a current is likely to flow into an
output pin of the IC and damage the IC.
VI
VO
1
3
CO
2
CI
Figure 1
2. Other caution items
1) Short-circuit between the input pin and GND pin
If the input pin is short-circuitted to GND or is cut
off when a large capacitance capacitor has been con-
nected to the IC's load, a voltage of a capacitor con-
nected to an output pin is applied between input/out-
put of the IC and this likely results in damage of the
IC. It is necessary, therefore, to connect a diode, as
shown in figure 2, to counter the reverse bias between
input/output pins.
出力�
1
3
In
Out
+
−
CO
2
GND
Figure 2
2) Floating of GND pin
If a GND pin is made floating in an operating mode, an unstabilized input voltage is outputted. In this case, a
thermal protection circuit inside the IC does not normally operate. In this state, if the load is short-circuited or
overloaded, it is likely to damage the IC.
I Application Circuit Examples
VI
Q1
VO
VI
1
2
20Ω
IO
AN78Lxx
VO'
R2
R1
3
1
VO
2
AN78Lxx
0.1µF
0.33µF
IBias
3
VO'
VO = VO' + IBias + ꢀ R1
R2
Note) VO varies due to sample to sample variation of IBias
.
�
Never fail to adjust individually with R1 .
SFF00005CEB
10
PANASONIC [ PANASONIC ]
