AN78Lxx/AN78LxxM Series
I
Basic Regulator Circuit
Input
1
2
Output
AN78Lxx
C
I
3
C
O
C
I
is necessary when the input line is long.
C
O
improves the transient response.
I
Usage Notes
1. Cautions for a basic circuit
D
i
V
I
1
2
3
V
O
C
I
C
O
Figure 1
C
I
: When a wiring from a smoothing circuit to a three-pin regulator
is long, it is likely to oscillate at output. A capacitor of 0.1µF to
0.47µF should be connected near an input pin.
C
O
: 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.
D
i
: 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.
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.
In
1
2
GND
3
Out
出力
+
−
C
O
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
V
I
Q
1
V
I
20Ω
1
0.33µF
2
0.1µF
I
O
V
O
1
3
2
V
O
'
R
2
V
O
AN78Lxx
AN78Lxx
3
I
Bias
R
1
V '
V
O
=
V
O
'
+
I
Bias
+
O
R
1
R
2
Note) V
O
varies due to sample to sample variation of I
Bias
.
Never fail to adjust individually with R
1
.
10
SFF00005CEB
PANASONIC [ PANASONIC SEMICONDUCTOR ]
