I'm building a solar powered light. The idea of this light is that its output is proportional to the brightness of the sun. At night, no light. During daylight, full light. So it's basically as simple as attaching my 12v 0.5A LED setup to a 12v 6w solar panel.
But not so fast. The 12V 6w panel won't produce enough voltage at lower sunlight levels – I want the LEDs to be brighter in the AM than a 6w panel will drive them. So I want to use a 12V 10W panel. In full sunlight, however, I fear it'll overdrive the LEDs. So I need to cap the output at 12V 0.5A. Below that, the output should just follow the output of the panel.
I assume I'll need a zener diode circuit, but am not sure how to make the circuit. Please help me design one with the correct values for my system.
EDIT: I'm hacking an existing LED strip that runs off of a 12V .5A wall wart to operate from a hobbyist-type panel. This isn't a pre-existing system.
EDIT: like this http://www.amazon.com/Solaro-Energy-SD1000-Daylight-Simulator/dp/B0053AL5LA only not $600
EDIT: so-called "12V" panels are actually >12V because the typical use is to charge a 12V battery. Both models available (the 5W and 10W) actually have nominal voltage of ~18V in full sun and OCV of ~21V in full sun. I can limit the amount of sun to prevent the voltage from peaking so high, but that kinda defeats the purpose of having an efficient system that will drive the LEDs fairly brightly at lower sunlight levels.
Best Answer
A Zener would work in this situation, where the maximum excess power supplied by the panel isn't very high. 1N5349BG (12V, 5W) seems suitable. You should make sure it has adequate heatsinking; perhaps firmly screwing the ground lead to metal casework would be sufficient.