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Overcurrent Monitor Operates up to 26V

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描述

Widespread use of the Universal Serial Bus (USB) has led to a selection of overcurrent-protection circuits for supply rails in the +2.7V to +5.5V range, but few products are available for voltages above that range. The circuit breaker in Figure 1 operates on supply voltages to +26V and trips at a programmed current threshold.

Figure 1. This circuit provides overcurrent protection for supply-rail voltages to +26V.

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设计,建造,测试

图中的电路板已完全组装并经过测试。

 

细节部分

细节部分

Widespread use of the Universal Serial Bus (USB) has led to a selection of overcurrent-protection circuits for supply rails in the +2.7V to +5.5V range, but few products are available for voltages above that range. The circuit breaker in Figure 1 operates on supply voltages to +26V and trips at a programmed current threshold.

Figure 1. This circuit provides overcurrent protection for supply-rail voltages to +26V.

IC1 is a high-side current-sense amplifier that monitors supply current via the voltage across R2 and generates a proportional but smaller current at the OUT terminal:

IOUT = (R2 ITRIP)/100.

R1 and R2 determine the trip current:

R1 = 120/(R2 ? ITRIP).

R1 in the figure was chosen for a trip current of 1A, but values to 10A are acceptable. Supply current at the trip level produces a voltage across R1 that triggers the "low-battery" comparator in IC2 (a high-side, N-channel MOSFET driver). The comparator output (LBO) turns on Q2 to saturation, causing the latched output of IC3 (a micropower voltage monitor) to go low. Applied to IC2's pin 2, this signal disconnects the power by turning off Q1.

Power remains off until IC3 is unlatched (by depressing the reset button). (You may also need to push the button following initial power-up, to ensure the correct circuit state at that time.) Choose R6 according to Table 1 (in Figure 1) for supply voltages of +12V and above. For supply voltages below +12V, D1 and R6 are not required. The signal delay from IC3 to the load (via IC2 and Q1) is as follows: turn-off time is about 5µs (Figure 2a), and turn-on time is about 400µs (Figure 2b).

Figure 2. With Figure 1's load-current trip threshold set at 1A, the load voltage (middle waveform) turns off (a) and on (b), as shown. (VOFF is the signal at IC2, pin 2.)

Figure 2. With Figure 1's load-current trip threshold set at 1A, the load voltage (middle waveform) turns off (a) and on (b), as shown. (VOFF is the signal at IC2, pin 2.)

A similar idea appeared in the 9/11/98 issue of EDN.

Maxim设备 (3)

器件号 名称 产品线 购买 设计套件和评估模块
MAX4172 低成本、高精度、高边电流检测放大器 放大器 立即购买 Not Available
MAX835 微功耗、具有锁存功能的电压监测器,SOT23-5封装 电路监控、电压监测器及排序器 立即购买 Not Available
MAX1614 高边、N通道MOSFET开关驱动器 MOSFET驱动器和控制器 立即购买 Not Available

Maxim设备 (3)

器件号 产品线
放大器
低成本、高精度、高边电流检测放大器
Not Available
电路监控、电压监测器及排序器
微功耗、具有锁存功能的电压监测器,SOT23-5封装
Not Available
MOSFET驱动器和控制器
高边、N通道MOSFET开关驱动器
Not Available

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