Logic-Level Signals Dim -48V L
logic-level signals dim -48v led driver
abstract:a 65v hysteretically controlled led driver (max16822a) has its ground pin connected to -48v and its power input connected to the system ground. for dimming, the circuit's logic-level control signal (control) is level-shifted down to -48v and applied to the dim input, using an 80v/500ma high-voltage pnp transistor (cmpt5551).
this design idea appeared in the june 23, 2009 issue of ed magazine.
the main source of power in a telecommunication system is -48v. not only the negative polarity of this source, but also its large magnitude with respect to ground pose a challenge when including low-power ics in the application circuits of a telecom system. the emergence of high-voltage ics with operating voltages of 75v and higher, however, has enabled the use of simple biasing techniques in designing circuits for -48v systems.
in figure 1, a 65v hysteretically controlled led driver (max16822a) has its ground pin connected to -48v and its power input connected to the system ground. for proper dimming, therefore, the circuit's logic-level control signal (at control) must be level-shifted down to -48v and applied to the dim input. the high-voltage pnp transistor cmpt5551 (80v/500ma) enables a simple solution to that problem.
figure 1. this led driver applies -48v to the leds, but accepts a 0-to-5v dimming signal.
the transistor circuit is made to operate at approximate unity gain by setting r1 equal to r2. with the control input at 0v the transistor is biased at cut-off, pulling the collector (connected to dim) down to -48v. with the control input at 5v, the collector pulls up to -43v. thus, the ground-referenced 0-to-5v dimming signal at the control input is replicated at dim, but referenced to the -48v rail. average led current vs. pwm duty cycle is shown in figure 2. a data sheet and other information on the max16822 is available at www.maxim-ic.com.
figure 2. in figure 1, the led current vs. the duty cycle at dim is quite linear.
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abstract:a 65v hysteretically controlled led driver (max16822a) has its ground pin connected to -48v and its power input connected to the system ground. for dimming, the circuit's logic-level control signal (control) is level-shifted down to -48v and applied to the dim input, using an 80v/500ma high-voltage pnp transistor (cmpt5551).
this design idea appeared in the june 23, 2009 issue of ed magazine.
the main source of power in a telecommunication system is -48v. not only the negative polarity of this source, but also its large magnitude with respect to ground pose a challenge when including low-power ics in the application circuits of a telecom system. the emergence of high-voltage ics with operating voltages of 75v and higher, however, has enabled the use of simple biasing techniques in designing circuits for -48v systems.
in figure 1, a 65v hysteretically controlled led driver (max16822a) has its ground pin connected to -48v and its power input connected to the system ground. for proper dimming, therefore, the circuit's logic-level control signal (at control) must be level-shifted down to -48v and applied to the dim input. the high-voltage pnp transistor cmpt5551 (80v/500ma) enables a simple solution to that problem.
figure 1. this led driver applies -48v to the leds, but accepts a 0-to-5v dimming signal.
the transistor circuit is made to operate at approximate unity gain by setting r1 equal to r2. with the control input at 0v the transistor is biased at cut-off, pulling the collector (connected to dim) down to -48v. with the control input at 5v, the collector pulls up to -43v. thus, the ground-referenced 0-to-5v dimming signal at the control input is replicated at dim, but referenced to the -48v rail. average led current vs. pwm duty cycle is shown in figure 2. a data sheet and other information on the max16822 is available at www.maxim-ic.com.
figure 2. in figure 1, the led current vs. the duty cycle at dim is quite linear.
关于配酸装置操作的详细说明
能够取代用于尖端活检技术手术刀的激光技术
PLC信号出错一般是什么导致的？
变频负载分类以及变频选型原则
组装电脑的主板上那些插槽接口都是什么
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防爆监测系统的介绍，它的功能特点有哪些
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卡片相机
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号称重化工业初具规模的印度 为何连氧气都无法足额供给？
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有哪些常用方法可以保护设备免遭ESD的毒手
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