RN5RG

5

OPERATION

GND

GND

Vref

External PNP Transistor

EXT

OUT

IN

RA

RB

CE

+

–

2

4

3

Error

Amplifier

5

1

Feed-back Registers RA, RB, and the detected Output

Voltage is compared with a reference voltage by Error

Amplifier, so that the base current of External PNP

lated.

SELECTION GUIDE FOR EXTERNAL COMPONENTS

External PNP Transistor

EXT

OUT

R1

R2

3

4

Select External PNP Transistor from the view-

points of output current, input voltage and power dis-

sipation.

1.External PNP Transistor

EXT Pin of these ICs is protected by a current limit circuit from the destruction caused by excess current.

However, since this current limit circuit is provided for the purpose of protecting the IC, use a resistor R2 for the

protection of the External Transistor, although this IC can be operated without such a resistor. It is required that

the resistance of the Resistor R2 be determined with the input voltage, output voltage,output current, tempera-

mination, check the characteristics by calculating the respective values by using the following formula :

–

0.7(V)

>

R2

R1

2.Base Resistor R2

In these ICs, phase compensation is made for securing stable operation even when the load current is varied.

R1 with a resistance of about 10k

Ω between the base and the emitter.There may be the case the loop oscillation

quency characteristics.

3.Phase Compensation