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參數(shù)資料
| 型號(hào)： | S-8520 |
| 廠商： | Seiko Instruments Inc. |
| 英文描述： | PWM Control Step-Down Switching Regulator-Controller(PWM 控制，步降開關(guān)穩(wěn)壓器-控制器) |
| 中文描述： | PWM控制降壓型開關(guān)穩(wěn)壓控制器（脈寬調(diào)制控制，步降開關(guān)穩(wěn)壓器-控制器） |
| 文件頁數(shù)： | 12/30頁 |
| 文件大小： | 650K |
| 代理商： | S-8520 |
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PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
Rev.6.1
S-8520/8521 Series
Seiko Instruments Inc.
11
Immediately after the power is turned on, or when the power is turned off (that is, when the step-down operation is terminated), the
input voltage will be imposed across the drain and the source of the MOS FET. Therefore, the transistor needs to have a drain-
source breakdown voltage that is also several volts higher than the input voltage.
The total gate capacity and the on-resistance affect the efficiency.
The power loss for charging and discharging the gate capacity by switching operation will increase, when the total gate capacity
becomes larger and the input voltage rises higher. Therefore the gate capacity affects the efficiency of power in a low load current
region. If the efficiency under light loads is a matter of particular concern, select a MOS FET with a small total gate capacity.
In regions where the load current is high, the efficiency is affected by power losses caused due to the on-resistance of the MOS FET.
Therefore, if the efficiency under heavy loads is particularly important for your application, choose a MOS FET with as low an on-
resistance as possible.
As for the current rating, select a MOS FET whose maximum continuous drain current rating is higher than the peak current Ipk.
For reference purpose, some efficiency data has been included in this document. For applications with an input voltage range of 10V
or less, data was obtained by using TM6201 of Toyoda Automatic Loom Works, Ltd. IRF7606, a standard of International Rectifier,
was used for applications with an input voltage range over 10V. Refer to "Reference Data."
5.2 Bipolar PNP type
Figure 7 shows a sample circuit diagram using Toshiba 2SA1213-Y for the bipolar transistor (PNP). The driving capacity for
increasing the output current by means of a bipolar transistor is determined by the hFE-value and the Rb-value of that bipolar
transistor.
VIN
EXT
2SA1213-Y
VIN
Rb
Cb
Figure 7
The Rb-value is given by the following equation:
Rb=
-
Find the necessary base current Ib using the hFE - value of bipolar transistor by the equation, Ib = Ipk/hFE, and select a smaller
RB-value.
A small Rb-value will certainly contribute to increasing the output current, but it will also adversely affect the efficiency. Moreover, in
practice, a current may flow as the pulses or a voltage drop may take place due to the wiring resistance or some other reason.
Determine an optimum value through experimentation.
In addition, if speed-up capacitor Cb is inserted in parallel with resistance Rb, as shown in Figure 7, the switching loss will be reduced,
leading to a higher efficiency.
Select a Cb-value by using the following equation as a guide:
Cb
￡
Ib
|IEXTL|
2
p
xRb x f
OSC
x 0.7
0.4
1
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| S-8520A20MC-AVFT2G | 功能描述:DC/DC 開關(guān)控制器 Step Down SWR PWM 180kHz 60uA Iq RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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