Dimmable LEDs?

[Chasman]

I know that it isn't possible to dim LEDs because below a certain voltage they just go out... however, I'm guessing that by pulsing the power to the LED you can give the appearance of dimming. You can see where I'm going with this... dashboard lights with 100,000 hours of life...

[curlyks2]

I know that it isn't possible to dim LEDs because below a certain voltage they just go out... however, I'm guessing that by pulsing the power to the LED you can give the appearance of dimming. You can see where I'm going with this... dashboard lights with 100,000 hours of life...

Yes this is definitely possible - it's known as Pulse Width Modulation (PWM) whereby some form of clock circuit generates a constant frequency of pulse, and some other bits and pieces control the width of the pulse (known as duty cycle), e.g.

Clock Pulse: ____|____|____|____|____|____
1 / 4 Width: ____|~___|~___|~___|~___|____
1 / 2 Width: ____|~~__|~~__|~~__|~~__|____
3 / 4 Width: ____|~~~_|~~~_|~~~_|~~~_|____
Fulll Width: ____|~~~~|~~~~|~~~~|~~~~|____

Where _ is off, ~ is on, and | is the clock pulse. (That looks so much better when it's not done using ASCII characters!)

This principle is used in various applications - "classics" being in speed control of models - model trains, some speed controllers in radio control kit, dimming circuits, etc.

It is also now seeing increasing use with LEDs in profesional lighting and other places, like this, which maybe uses chips like this, and home applications can be built like circuits listed here, which includes a (simple) LED dimmer circuit.

Cheers,

Ck.

[Chasman]

Cool, thanks for the info...

I found a really good source for LEDs, including 12v ones, here
UltraLEDs. I bought an LED upgrade for my AA Maglite from here - man what a difference, far brighter and whiter, you get longer battery life and none of that fading to a useless orange glow (though on the downside you get less warning the batteries are knackered)...

I need to take my dash apart to replace the condenser for the aircon so I thought I'd replace all the bulbs with LEDs at the same time. How much will a circuit like this cost to build and how does it interface to the exisitng dimmer?

Yes this is definitely possible - it's known as Pulse Width Modulation (PWM) whereby some form of clock circuit generates a constant frequency of pulse, and some other bits and pieces control the width of the pulse (known as duty cycle), e.g.

Clock Pulse: ____|____|____|____|____|____
1 / 4 Width: ____|~___|~___|~___|~___|____
1 / 2 Width: ____|~~__|~~__|~~__|~~__|____
3 / 4 Width: ____|~~~_|~~~_|~~~_|~~~_|____
Fulll Width: ____|~~~~|~~~~|~~~~|~~~~|____

Where _ is off, ~ is on, and | is the clock pulse. (That looks so much better when it's not done using ASCII characters!)

This principle is used in various applications - "classics" being in speed control of models - model trains, some speed controllers in radio control kit, dimming circuits, etc.

It is also now seeing increasing use with LEDs in profesional lighting and other places, like this, which maybe uses chips like this, and home applications can be built like circuits listed here, which includes a (simple) LED dimmer circuit.

Cheers,

Ck.

[curlyks2]

I need to take my dash apart to replace the condenser for the aircon so I thought I'd replace all the bulbs with LEDs at the same time. How much will a circuit like this cost to build and how does it interface to the exisitng dimmer?

Best of luck with the dismantle. I've not had to get behind there (yet), so don't know how it would interface. You can get prices for most of the parts that I imagine you'd need at somewhere like Maplin
Ck.