Automatic light dimmer using SCR as switch control

[lizxay]

Hi guys, can u guys help me on this?? I want to design and construct an automatic light dimmer circuit that controls the energy delivered to a 12V or 24V DC light bulb corresponding to the ambient light intensity.
The control of energy will be established through switching action to improve efficiency and i will use SCR as means for switching.
I have no idea where should i start. any ideas guys? thank u very much and hope to hear from u guys soon =)

 

[MATLABdude]

Hi guys, can u guys help me on this?? I want to design and construct an automatic light dimmer circuit that controls the energy delivered to a 12V or 24V DC light bulb corresponding to the ambient light intensity.
The control of energy will be established through switching action to improve efficiency and i will use SCR as means for switching.
I have no idea where should i start. any ideas guys? thank u very much and hope to hear from u guys soon =)

I believe that SCRs (and the closely related triac) are usually used for AC power control, not DC. SCRs and triacs work by passing part of one AC cycle (or several cycles) in order to modulate power delivery; not by ballasting part of the voltage, or by chopping the DC, as you would need to do in order to modulate power delivery with DC.

I'm not sure if you can use Pulse Width Modulation with an incandescent (depending on the frequency you use, I'd think that it'd decrease the lifetime of the bulb), however you can do this with an LED (and that's how it's done all the time). You can probably begin here:
http://en.wikipedia.org/wiki/Pulse-width_modulation

 

[vk6kro]

Easy, but not with a SCR. These do not switch pure DC easily as they stay on once turned on until the power is removed. If you had pulsing DC you could probably do it like that. Very messy process though.

I would do it with a Picaxe IC detecting the ambient light level and delivering pulse width modulation to a switching transistor. The Picaxe 8M has 3 A to D converters, I think, and it can produce PWM from one of its outputs. So, it would be ideal.

If you are in the USA look up P.H.Anderson on Google.