简单的电路断开负载-Simple Circuit Disco
placing a load-disconnect circuit on the output of a bootstrapped step-up regulator allows the regulator to start with load currents much higher than would otherwise be possible (figure 1). during shutdown, the disconnect completely isolates the battery from the load. the circuit boosts a single nimh-cell output to 3.3v and delivers output currents to 600ma. step-up regulators are excellent for portable applications because they exhibit high efficiency, low supply current (120µa operating, 20µa in shutdown), and ample current once started.many, however, cannot start withmaximum load from low supply voltages, such as those from single-cell batteries. this problem arises because most low-voltage cmos boost regulators derive power from their own outputs, which equal vin minus a diode drop at start-up. low values of input voltage don't allow the switching transistor to become fully enhanced at start-up, so the transistor presents a high impedance that limits the peak inductor current. as a result, the circuit cannot produce enough current to simultaneously supply the load and charge the output capacitor.
figure 1. the addition of a couple of transistors enables a switching regulator to start with full load and low input voltages.
to get around this problem and ensure reliable start-ups, most regulator ics incorporate an undervoltage lockout (uvlo). ic1 , for example, is a synchronous boost converter whose bootstrapped operation cannot start until its output voltage exceeds the internal uvlo threshold of 2.3v. you can overcome this start-up limitation with an external power mosfet, q1 , operating as a load-disconnect switch, and by using the power-ok (pok) comparator built intomany low-voltage switching regulators. r3 and r4 set the pok threshold at 2.5v, allowing vin to rise above the uvlo threshold. q2 inverts the pok output before driving q1. q1 disconnects the load, allowing vout to rise to a level (above uvlo) that ensures full enhancement of q1 when it turns on. as a result, the circuit can start under full load with input voltages as low as 0.8v (figure 2a). because the circuit takes the regulator feedback before this switch, the mosfet you choose for a given application depends on the load current and minimum acceptable level of load regulation. the mosfet shown is a low-threshold device. connecting the fb terminal (pin 2) to ground and removing r1 and r2 produces a 5v regulated output, whose performance is similar to that of the 3.3v version (figure 2b). (di #2487)
figure 2. the load-disconnect switch in figure 1 allows the regulator to start up with heavy loads and low input voltages (a). a slight modification of the circuit in figure 1 provides 5v-output operation (b).
reprinted from ednmagazine february 17, 2000
copyright cahners business information 2000
a division of reed elsevier inc.
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figure 1. the addition of a couple of transistors enables a switching regulator to start with full load and low input voltages.
to get around this problem and ensure reliable start-ups, most regulator ics incorporate an undervoltage lockout (uvlo). ic1 , for example, is a synchronous boost converter whose bootstrapped operation cannot start until its output voltage exceeds the internal uvlo threshold of 2.3v. you can overcome this start-up limitation with an external power mosfet, q1 , operating as a load-disconnect switch, and by using the power-ok (pok) comparator built intomany low-voltage switching regulators. r3 and r4 set the pok threshold at 2.5v, allowing vin to rise above the uvlo threshold. q2 inverts the pok output before driving q1. q1 disconnects the load, allowing vout to rise to a level (above uvlo) that ensures full enhancement of q1 when it turns on. as a result, the circuit can start under full load with input voltages as low as 0.8v (figure 2a). because the circuit takes the regulator feedback before this switch, the mosfet you choose for a given application depends on the load current and minimum acceptable level of load regulation. the mosfet shown is a low-threshold device. connecting the fb terminal (pin 2) to ground and removing r1 and r2 produces a 5v regulated output, whose performance is similar to that of the 3.3v version (figure 2b). (di #2487)
figure 2. the load-disconnect switch in figure 1 allows the regulator to start up with heavy loads and low input voltages (a). a slight modification of the circuit in figure 1 provides 5v-output operation (b).
reprinted from ednmagazine february 17, 2000
copyright cahners business information 2000
a division of reed elsevier inc.
我国完成首个采用相控阵卫星天线的基站回传试验
2022中国（深圳）集成电路峰会延期至10月举办
JBL的Quantum One提供了一种类似vr的音频体验
色选机远程监控运维系统解决方案
两部委建立统计指标监测预警新兴产业产能过剩
简单的电路断开负载-Simple Circuit Disco
韩国政府计划明年投入约合人民币276亿元推动部分产业实现创新发展
30多家PCB企业的产品类型及应用领域
德国反垄断批准博世、英飞凌和恩智浦入股台积电
共享单车摩拜E轮融资后获6亿，风投的疯狂
干货分享：你想知道的二极管特性都在这儿
ZS2934SL-24W电源适配器方案
福昕鲲鹏出席大连信创技术赋能军工行业数字化转型专题研讨活动
小派电视智能音响评测 1599元的视听神器
网络远程一卡通系统设计原理及解决方案
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Reno2于9月10日发布！对于游戏党来讲无疑是十分友好的
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