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Old 12-23-16, 03:55 PM   #3
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I just got some more driver boards for these high-power LED stars to play with:
New 10W Constant Current LED Light Chip Efficient Driver Fit Supply DC9-24V

Under $1 each with free shipping. In case the fleabay listing goes away, here is another on alibaba:

These little gems are pretty tinkerable, despite the low price tag. There are a lot of flavors of these little postage stamps for whatever power source you need to connect. I was planning on using the thing on a 10W chip LED in a car, so I got a 12VDC compatible board.

This family of driver boards is based on the PT4115, a single-ended primary-inductor (SEPIC) converter. The chip is good for lots of other things besides lighting LED's, but I don't care about that. What I do care about is that these little buggers are good for up to 30 Watts (max at about 1 Watt per input volt) of power source, are dimmable, and can easily be warped to work off of AC or DC with very little trouble. Plus they are teeny tiny and don't generate heat doing the job.

Here's what another of these boards looks like:

Here's the circuit schematic for these buggers:

Depending on how the maker stuffs the board, individual component values may vary. Also, the chip is available in 6 or 8 pin packages. The datasheet tells all about what components do what and how to change values to suit specific needs. They are commonly available in 1W, 3W and 10W max output power to suit those sizes of LED chips.

As they ship, these boards are not rigged as dimmable. This functionality is easily tapped into by tacking a jumper wire to the DIM pin. This pin has a 200k pullup resistance tied to a 5VDC reference inside the chip. For analog control, the pin is pulled below 2.5 VDC to dim the output. The output power is linear, with zero output below 0.5VDC and max output at or above 2.5VDC. For digital control, the DIM pin is fed a pwm signal that pulls the pin low to dim the output. The chip can take 3.3V or 5V logic signals, and is linear with respect to duty cycle.

In the past, I have used these PWM boards with these high-power LED chips with great success. For testing, a 10K NTC thermistor can be attached to the LED chip (and its heatsink) to limit the max temperature. I tied the thermistor between the DIM pin and ground, and a 27k resistor between the DIM pin and the + pin of the big capacitor. As the LED heats up, it dims, both saving the LED chip and giving a visual indication of heat soak vs intensity. I found that the NTC balances out about right at the point where the heatsink is almost too hot to hold onto, but not quite. For the daring, a smaller resistor value will make the thermistor balance out hotter.
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Last edited by jeff5may; 01-08-21 at 12:39 AM.. Reason: Update links
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