Rev.1.0
Application
Circuits
HIGH OPERATING VOLTAGE CMOS VOLTAGE REGULATOR
S-812C Series
1. Output Current Boost Circuit
As shown in Figure 11, the output current
can be boosted by externally attaching a
PNP transistor.
The S-812C controls the
base current of the PNP transistor so that the
output voltage V
OUT
becomes the voltage
specified in the S-812C if the sufficient base-
emitter voltage V
BE
to turn on the PNP
transistor is obtained between input voltage
V
IN
and S-812C power source pin VIN.
Tr1
VOUT
V
OUT
V
IN
C
IN
GND
S-812C
Series
R1
ON/OFF
VSS
VIN
C
L
•
As the transient response characteristics
of the circuit shown in figure 11 is not enough in some applications, evaluation for output variation due to
power-on, power line variation and load variation in actual condition is needed before massproduction.
•
Note that the short-circuit protection incorporated in the S-812C series does not work as a short-circuit
protection for the boost circuit.
2. Constant Current Circuit
The S-812C series can be served in a
constant current circuit as shown in the
figure 12. Constant current I
O
is calculated
from the following equation:
I
O
= (V
OUT
(E)
÷
RL) +I
SS,
where V
OUT
(E) is
the effective output voltage.
Please note that in case of the circuit
shown in the figure 12 (1) the magnitude of
the constant current I
O
is limited by the
driving ability of the S-812C.
The circuit shown in the figure 12 (2) can,
however, provide the current beyond the
driving ability of the S-812C by combining a
constant current circuit with a current boost
circuit. The maximum input voltage for the
constant current circuit is the sum of the
voltage V
O
of the device and 16 V. It is not
recommended to attach a capacitor
between the S-812C power source VIN
and VSS pins or between output VOUT
and VSS pins because rush current flows
at power-on.
Figure 11 Output Current Boost Circuit
(1) Constant Current Circuit
V
IN
VIN
S-812C
Series
VSS
C
IN
GND
ON/OFF
VOUT
RL
V0
I
O
V
O
Device
(2) Constant Current Boost Circuit
Tr1
V
IN
R1
VIN
S-812C
Series
VSS
C
IN
GND
ON/OFF
VOUT
RL
Io
V0
Device
V
O
Figure 12 Constant Current Circuits
3. Output Voltage Adjustment Circuit
The output voltage can be increased using the configuration shown in the figure 13. The output Voltage V
OUT
1
can be calculated using the following equation;
V
OUT
1 = V
OUT
(E) x (R1 + R2)
÷
R1 + R2 x I
SS
,
where V
OUT
(E) is the effective output voltage
.
Value of R1 and R2 should be determined so as not to be affected by the current consumption I
SS
.
Seiko Instruments Inc.
9
SII [ SEIKO INSTRUMENTS INC ]
