S-8540 SII [Seiko Instruments Inc], S-8540 Datasheet - Page 17

• Manufacturer Part Number: S-8540
• Description: STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
• Manufacturer: SII [Seiko Instruments Inc]

Rev.3.2
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
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
by the h
The R
Calculate the necessary base current Ib using the h
I
A small R
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.
In addition, if speed-up capacitor C
the switching loss will be reduced, leading to a higher efficiency.
by using the following equation :
Select a C
upon the characteristics of the bipolar transistor.
b
_00
= I
PK
b
/h
value is given by the following equation:
FE
FE
R
C
b
, and select a smaller value for R
value and the R
b
b
b
value will certainly contribute to increase the output current, but it will also decrease the
value after performing sufficient evaluation since the optimum C
≤
=
2
V
π
IN
×
−
I
R
b
0.7
b
×
1
f
OSC
−
I
0.4
b
EXTL
×
value.
0.7
V
2SA1213-Y
R
IN
b
b
Seiko Instruments Inc.
is inserted in parallel with resistance R
C
EXT
VIN
b
b
which is calculated from the above equation.
Figure 12
FE
value of the bipolar transistor from the relation,
b
S-8540/8541 Series
b
, as shown in Figure 12 ,
value differs depending
17