EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR

S-816 Series

Seiko Instruments Inc.

13



Application Circuits

1. Overcurrent Protection Circuit

Figure 11 shows a sample of overcurrent protection implemented with an external circuit connected.

The internal overcurrent protection function of the S-816 Series is designed to detect the sink current

(base current of the PNP transistor) at the EXT pin, therefore it may not be able to protect the external

PNP transistor from collector overcurrents caused by an EXT-GND short-circuiting or other phenomenon

occurring outside the IC.

This sample circuit activates the regulator intermittently against collector overcurrents, thereby

suppressing the heat generation of the external PNP transistor.

The duty of the on-time and off-time of the intermittent operation can be regulated through an external

component.

10

μF

+

−

2 k

Ω

100 k

Ω

0.5

Ω

2 k

Ω

Tr1

2 k

Ω

0.22

μF

Tr2

0.22

μF

10

μF

+

−

VIN

EXT

VOUT

S-816 Series

VSS

OUT

2SA1213Y

ON/OFF

Figure 11

Caution The above connection diagram and constant will not guarantee successful operation.

Perform through evaluation using the actual application to set the constant.

=4 V)

1 A

Load Current

(0.5 A/div)

0 A

2 V

(1 V/div)

0 V

t (2 ms/div)

=4 V)

1 A

Load Current

(0.5 A/div)

0 A

2 V

(1 V/div)

0 V

t (100

μs/div)

Figure 12 Output Current Waveforms during Intermittent Operation Prompted by Load Short-Circuiting