Typical Applications - Epson Power Supply IC S1F70000 Technical Manual

S1F79100Y Series
Differential amplifier
The built-in differential amplifier generates a potential
at point X that adjusts the gate bias of the output transis-
tor if there is any difference betweeen V
V
SS
V
P1
REF
X
N1

TYPICAL APPLICATIONS

Current Booster
At the cost of a small increase in current consumption,
the voltage is regulated while maintaining high current
output.
V
SS
V
V
I
External Voltage Converter
The following circuit raises the output voltage of a
S1F79100Y series IC.
V
SS
GND
V
I S1F79100Y
V
I
3–36
and V
REF
V
P2
REG
To output
transistor
N2
V
I
GND
V
I
O
S1F79100Y
R
1
I
OPR
I
B
R
V 2
r
V
O
V
O
Output transistor
The output side of the p-channel MOS transistors in the
output transistor circuit is connected to the voltage di-
. vider resistors in the feedback loop.
REG
V
SS
V
The following equation shows the relationship between
the old and new voltages.
R + R
1 2
V = — — — — — V
O
R
2
Note that the application must supply a bias current, I
high enough to offset the increase in voltage across R
due to I .
OPR
An alternative circuit for raising the output voltage is
shown in the following figure.
V
SS
V
O
C
I
V
I
This configuration, however, introduces two design
problems.
1. It reduces the output voltage by V
age drop across the diode.
2. It is sensitive to fluctuations in V
in diodes, operating temperatures and I
EPSON
REF
+
–
R
I
SS
GND
V V
I O
S1F79100Y
, the forward volt-
F
due to differences
F
R
1
V
REG
R
2
V
O
V
1
,
B
1
C R1
O
V
O
.
SS
S1F70000 Series
Technical Manual