可以耗尽电池全部能量的LED手电筒电路


这个驱动电路使用4节1.5v的干电池组成的6V电池组作为电源，产生类似PWM的占空比可调的脉冲信号，脉冲可以高达26V，驱动7个串联高亮LED发光。这个驱动信号即使在电源下降50%达到3V时，仍然能够继续产生和工作，只是占空比更小而已。

工作原理：

The circuit is best described in two parts: one, the boost circuit function of
Q1 and Q2, and two, the control circuit of Q3 and JFET1. Assume Q1 is off. With
the battery voltage slightly above Q2''''s VVB, a positive Q2 base
current [iB = (battery voltage VBE)/RJET1]
would flow. Q2 turns on, which switches inductor L1 to ground.

Energy stored within L1''''s magnetic field builds as L1''''s current rises with a
positive di/dt. As this current rises, it also flows through Q2''''s RSAT.
(SD1 and the LED string are off.) Q2''''s collector voltage becomes sufficiently
large to turn on Q1. Q1''''s base voltage is connected to Q2''''s collector by the
feed-forward network of R1 and C1. R1 also serves as Q1''''s base current limit.

With Q1 turning on, the previous base drive to Q2 is now shunted to ground, and
Q2 turns off. The switching off of Q2 enables L1''''s energy to be discharged into
the LED string as the magnetic field collapses.

This flyback action of L1 forward-biases the LEDs at greater than 26 V, which
emits photon illumination in the form of white light. The human eye integrates
the LED''''s flashing frequency into a constant illumination. With L1 discharged,
Q1 turns back off.

The self-oscillating action repeats under normal operation unless the battery
voltage falls below Q2''''s VBE plus the IR drop of JFET1 (about 1 V).
Then, Q2 no longer turns on. L1, Q2''''s RSAT, and the switching
characteristics of Q1 and Q2 also contribute to the period and duty cycle of
oscillation.

Battery Stack Drives Seven White LEDs

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posted on 2008-05-08 20:52  xlander  阅读(302)  评论(0)    收藏  举报

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