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| 型号： | S-8338ACAA-T8T1 |
| 元件分类： | 稳压器 |
| 英文描述： | 0.16 A SWITCHING CONTROLLER, 1133 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | TSSOP-8 |
| 文件页数： | 9/49页 |
| 文件大小： | 554K |
| 代理商： | S-8338ACAA-T8T1 |
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STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLERS
Rev.2.1_01
S-8337/8338 Series
Seiko Instruments Inc.
17
4. External transistor
A bipolar (NPN) or enhancement (N-channel) MOS FET transistor can be used as the external
capacitor.
4-1. Bipolar (NPN) type
The driving capability when the output current is increased by using a bipolar transistor is
determined by hFE and Rb of the bipolar transistor. Figure 10 shows a peripheral circuit.
Nch
Pch
Rb
VIN
IPK
EXT
Cb
2200 pF
1 k
Figure 10 External Transistor Periphery
1 k
is recommended for Rb. Actually, calculate the necessary base current (Ib) from hFE of the
bipolar transistor as follows and select an Rb value lower than this.
Ib =
hFE
IPK
Rb =
Ib
VIN – 0.7
–
IEXTH
0.4
A small Rb increases the output current, but the efficiency decreases. Actually, a pulsating
current flows and a voltage drop occurs due to the wiring capacitance. Determine the optimum
value by experiment.
A speed-up capacitor (Cb) connected in parallel with Rb resistance as shown in Figure 10
decreases the switching loss and improves the efficiency.
Select Cb by observing the following equation.
Cb
≤
2
π Rb fOSC 0.7
1
However, in practice, the optimum Cb value also varies depending on the characteristics of the
bipolar transistor employed. Therefore, determine the optimum value of Cb by experiment.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| S-8338ACAC-P8T1G | 制造商:Seiko Instruments Inc (SII) 功能描述:STEPUP1.2MHZ PWM SWR |
| S-8338ACBB-P8T1G | 制造商:Seiko Instruments Inc (SII) 功能描述:STEPUP1.2MHZ PWM SWR |
| S-8338ACBC-P8T1G | 制造商:Seiko Instruments Inc (SII) 功能描述:STEPUP1.2MHZ PWM SWR |
| S-8338ACBC-T8T1G | 制造商:Seiko Instruments Inc (SII) 功能描述:STEPUP1.2MHZ PWM SWR |
| S-8338ACCA-P8T1G | 制造商:Seiko Instruments Inc (SII) 功能描述:STEPUP1.2MHZ PWM SWR |
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