Hi There,
I have somewhat a bit of a challenge. For equipment, I need to control more than 100, 24V halogen lamps simultaneously. They are on for only a few 3-4 seconds at a time, every 15s.
Each lamp is controlled through optical feedback with a photodiode.
The thing is, I want precise control while keeping it as cheap as possible.
The current implementation is a large AC/DC power supply bringing down the voltage to 25V, then each lamp has its own buck converter controlled by a micro that takes the photodiode as feedback and adjusts the PWM signal.
Another implementation would be to bypass the power supply, just have rectifier/cap and directly feeds 300VDC to a buck converter, but this would require either very large coil or high frequency.
For the high frequency, the problem arises that the duty cycle would only be around 8% for maximum power. On the controller, it then becomes difficult to control the lamp as the definition of the PWM signal is too large.
One idea was to chop the PWM signal with another, fixed and higher frequency signal through an AND gate to generate a composite hashed PWM, but I'm not sure if that would be a good solution and if then the switching losses would be acceptable.
Another concept is to chop the main AC with a triac before to drop the voltage, rectify it and feed it to the buck, but in that situation, I'm not sure what it would be to draw 10kW of power on the main being chop only at specific point on the sine.
Any other ideas or pointer would be very welcome as I'm kind of stuck so far, the 24V supply so far is the only viable choice I see.