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More  Driver Circuits    LEDs    White LEDs

Ramping LED Driver  


The circuit below was designed to drive a LED with an intensity ramping mode.  Two 555 timers generate two different triangle waveforms.  The upper device generates a 10KHz signal while the lower unit produces a 1Hz signal.  The two signals are fed to a voltage comparator.  The result is a pulse width modulation (PWM) signal, which with the aid of the FET, drives the LED in such a way that its average light output slowly ramps from about zero light to maximum and then slowly dims back down.  The circuit should operate over a supply voltage ranging from 3v to 12v. You can easily vary the ramping time by changing the value of the 1M resistor.  For an interesting effect, you can place a 1N4148 diode in parallel with the 1M resistor, with the cathode (banded end) side connected to pin 3. 

Click on Drawing Below to view PDF version of Schematic

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