2019-09-07 2 LED Lights On One Supply

I got some 10W warm white LEDs, and I have some cool white LED strips and they’re both running in parallel off the same 12V supply. But they’re not the same voltage so I had to do some experimenting.

The 10W LED is actually a group of 3 by 3 in series – parallel on one slug. It requires about 10.5 volts to draw 1/2 amp. That’s only 5 watts but I have it mounted on a heatsink that gets quite warm so I’m not going to run it full power.

The LED strip has four cool white LEDs in series mounted on a 15 inch strip of PC board that acts as a heatsink. The current is 1/4 amp at 12VDC and it seems to be okay, that’s about 1 watt per LED.

I connected them in parallel and of course the warm white LED took almost all the current when the voltage was at 10.5V, and the strip barely lit. I dug a 1N5402 3 amp diode out of the cannibalized parts box and connected it in series with just the warm white LED and turned up the voltage past 11 volts, and now the strip is much brighter, but not full brightness. I went and dug out another 3 amp diode like the 1N5402 and added it in series with the original diode. I turned up the voltage to 12VDC and both the warm white and the strip are full brightness, and the total current is about 3/4 amp. The 2 diodes get slightly warm to the touch, no problem. I thought about using 1A diodes, but they drop more voltage, so less voltage would be across the warm white LED and less current would flow through it. It might be possible to use four 1A diodes, in series-parallel to get lower voltage drop. But the two 3 amp diodes work well, they drop just about the right amount of voltage.

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