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参数资料
| 型号： | MAX638 |
| 元件分类： | DC/DC变换器 |
| 英文描述： | 48V-to-5V DC-DC Converter Using MAX638 Switching Step-Down Regulator Borrows Power from Phone Lines |
| 中文描述： | 5V/可调、CMOS、降压型、开关稳压器 |
| 文件页数： | 3/4页 |
| 文件大小： | 36K |
| 代理商： | MAX638 |
For systems operating on 250mW or less, the circuit eliminates need for battery packs or ac
adapters by drawing power from ordinary phone jacks. Built into peripheral equipment such
as PCMCIA modem cards, the circuit can spare the main battery in a portable computer.
The current available from subscriber lines in the on-hook state is virtually zero. In the off-
hook state, however, current is limited only by the sum of impedances in the central-office
battery and the intervening telephone wires. Regulations such as Part 68 of the FCC rules do
not restrict the current a subscriber can draw; you can even short out the line (which is what
the hold button does). There is one condition: the off-hook current must exceed 20mA to
ensure activation of a network-access relay in the central office.
For maximum power transfer, your impedance should match that of the line, but line
impedance varies greatly, according to distance from the central office. Impedance matching
is also in conflict with the need to draw at least 20mA. The 12V zener clamp, however,
provides a termination that works well for line impedances up to 1700
. This line impedance
sharply restricts the power available to you
(Figure 2)
.
Figure 2.
Available power from the Figure 1 circuit declines steeply with line impedance.
Because the circuit allows normal telephone communications while drawing power, it must
block the switching noise (generated by IC1) from entering the hybrid transformer (not
shown). Q1 and C1 perform this function by simulating an inductor that chokes off the noise
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相关代理商/技术参数 |
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| MAX6380UR33 | 制造商:Maxim Integrated Products 功能描述:3-PIN ULTRA-LOW-POWER SC70 VOLTAG - Cut Tape Product |
| MAX6380UR33+ | 制造商:Maxim Integrated Products 功能描述:VOLT SUPERVISOR DETECT 3.3V 3PIN SOT-23 - Cut Tape Product |
| MAX6380UR33+T | 功能描述:电压监测器/监控器 3-Pin ULow-Power Voltage Detector RoHS:否 制造商:Texas Instruments 监测电压数:2 监测电压:Adjustable 输出类型:Open Drain 欠电压阈值: 过电压阈值: 准确性:1 % 工作电源电压:1.5 V to 6.5 V 工作电源电流:1.8 uA 最大工作温度:+ 125 C 封装 / 箱体:SON-6 安装风格:SMD/SMT |
| MAX6380UR33-T | 功能描述:电压监测器/监控器 RoHS:否 制造商:Texas Instruments 监测电压数:2 监测电压:Adjustable 输出类型:Open Drain 欠电压阈值: 过电压阈值: 准确性:1 % 工作电源电压:1.5 V to 6.5 V 工作电源电流:1.8 uA 最大工作温度:+ 125 C 封装 / 箱体:SON-6 安装风格:SMD/SMT |
| MAX6380UR34 | 制造商:Maxim Integrated Products 功能描述:3-PIN ULTRA-LOW-POWER SC70 VOLTAG - Cut Tape Product |
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