STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

S-8540/8541 Series

17

5. 2 Bipolar (PNP) transistor

Figure 12

shows a circuit diagram using Toshiba Corporation 2SA1213-Y for the bipolar transistor

(PNP). Using a bipolar transistor, the driving capacity for increasing the output current is determined

EXT

2SA1213-Y

VIN

Figure 12

EXTL

IN

I

0.4

I

0.7

V

R

b

b

−

−

=

efficiency. Determine the optimum value through experiment since the base current flows as pulses

and voltage drop may takes place due to the wiring resistance and so on.

the switching loss will be reduced, leading to a higher efficiency.

by using the following equation :

0.7

f

R

2

1

C

OSC

b

b

×

×

×

≤

π

upon the characteristics of the bipolar transistor.