
User’s Manual G12702EJ8V0UM00
17
4.2 Application Circuit Set
This circuit set mainly is filled in for positive output voltage three-terminal regulators. However, the circuits also
can be applied to negative voltage three-terminal regulators by changing the polarity of parts employed.
1. High output current circuit
(without short circuit protection)
VIN
Q1
IOUT
IO V
OUT
6
R1
C1
0.1 F
IREG
C2
0.1 F
IN
OUT
GND
Drives the base of an external transistor using a three-
terminal regulator.
Here R1 is determined as follows.
In this circuit, the output current has an actual range
that is 5 to 6 times the three-terminal regulator rating.
2. High output current circuit
(with short circuit protection)
VIN
Q1
I1
IO V
OUT
R1
C1
0.1 F
IREG
C2
0.1 F
IN
OUT
GND
6
R1
R2
Q2
This is an expansion of circuit 1. Current detection is
performed using R2.
Therefore, since the current at Q1 is restricted by
I1(MAX.) =
the output current is as follows.
IO(MAX.) = I1(MAX.) + IREG(MAX.)
=
+ IREG(MAX.) …..………..……….….…. (4.3)
3. High output current circuit
(with short circuit protection)
VIN
Q1
I1
IO V
OUT
C1
0.1 F
IREG
C2
0.1 F
IN
OUT
GND
2
R2
R1
6
R3
0.4
D1
D1 cancels VBE at Q1.
Q1 and three-terminal current distribution is determined
by R1 and R2.
Caution
Absolutely do not connect output pins in parallel to increase the current capacity of a three-
terminal regulator. If the output voltage becomes unbalanced, certain ICs operate in a restricted
current vicinity and current hardly flows in certain ICs, and furthermore the current may flow in
reverse. Also refer to 15 Wired OR.
VBE1
R1 =
IOUT
…………………….…. (4.1)
IREG(MAX.)
hFEI(MIN.)
VBE1
IO =hFE1(MIN.)
IREG(MAX.)
R1
+ IREG(MAX.) … (4.2)
R2
I1
R1
=
IREG
……………………….…………….…… (4.4)
R1 + R2
IO(MAX.) =
R1
IREG(MAX.) …………………..….. (4.5)
VBE2
R2
VBE2
R2