![]() ![]() My simple circuit has not considered any of these issues, and it probably isn't too linear, but practically it appears to control brightness roughly in proportion to the angular twist of the potentiometer shaft. The AM modulation circuit, discussed, is trying to keep the light output at a certain colour temp, and is complex, compared to a simple resistor. The article goes on to discuss variation in colour, due to temp and current, but I doubt that that effect would be very worrying to us. I've attached a file on LED basics, wherein it states that LEDs brightness is proportional to its forward current, so by controlling the current thhe brightness is control, proportionally. Remember a square wave, by definition, is equal on and off times. You are partially right, however, that series resistor limits the current through the LED and, provided you don't exceed the rated operating voltage, you won't burn out the LED.Ī dimmer may at times give a square wave, but more usually it is a series of variable width pulses. The PWM frequency is high enough that our eyes can't perceive that the LED is actually flickering. if the LED is fully "on" 20% of the time it appears to be at 20% brightness). This makes it easy to control light output (e.g. off time during each cycle of the square wave. The PWM produces a fixed frequency square wave of a fixed voltage and varies the percentage of on vs. That is why a PWM circuit is used to drive the LEDs. Anyway, if the current goes too high the LED burns out. The problem with using a variable resistance dimmer in the circuit is that once the voltage across the diode drops below its forward bias voltage, the LED goes off and as the voltage across the diode increases past its bias voltage, the current increases rapidly (might be exponentially, but, I can't remember that level of detail from my electronics class 35 years ago). As I understand it different color LEDs have different forward bias voltages, so, the resistor value placed in series with the diode will be higher for diodes with less forward bias voltage and lower for ones with higher forward bias voltages. I believe that all LEDs sold to work in 12V systems have a built-in resistor in series with the light emitting diode to limit current. Sep 09 In Memoriam - For An MGB Fanatic.to replace the bypassed rheostat with an adapted, dash-mounted LED dimmer. Sep 10 All British Field Meet PIR Por. Its easy to make an LED dimmer if I want to dim those LED panel lights.Sep 14 Rear Brakes And How Not To Ins.Nov 18 FLBritish Invasion Car Show & F.Oct 22 ALSouth Alabama British Car Fes.Oct 02 CACentral Coast British Car Show.Oct 01 TXRed River European Car & Moto.Oct 01 VAShenandoah Valley British Car. ![]()
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