I bought 2 trusted brand LED drivers. They are LPC-20-700. Spec says it's constant current 700mA, but I blew my whole project. After (yes, I know) that I tested the driver and while it gives me the correct voltage 30V, the current is 1.1A, which is 400mA more.

I have a hard time believing the drivers are bad, because I've read that this is a safe brand. I bought good ones to avoid house fires and such.

Is there any possibility that I'm doing something wrong? It seems very simple but the results are wrong.

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    \$\begingroup\$ How did you perform the testing? \$\endgroup\$ – Ignacio Vazquez-Abrams Nov 17 '17 at 18:59
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    \$\begingroup\$ A non-blurry photo of the device label might tell us something. \$\endgroup\$ – pjc50 Nov 17 '17 at 19:01
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    \$\begingroup\$ I'd be plugging that red probe into the 10A socket \$\endgroup\$ – Trevor_G Nov 17 '17 at 19:01
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    \$\begingroup\$ YOur meter, plug the red cable into the 10 socket \$\endgroup\$ – Trevor_G Nov 17 '17 at 19:05
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    \$\begingroup\$ What is the load anyway... ? \$\endgroup\$ – Trevor_G Nov 17 '17 at 19:05

Answer: test configuration error

Specs: Output 0.7A at 9-30Vdc

Putting a current meter across the output is a short circuit with very little voltage drop. (Note fuse limit on DMM on + terminal )

You must have LEDs in series with meter such that LED voltage is between 9-30Vdc and the LEDs are thermally protected with adequate heatsinks.

The Req linear load would be 9V/0.7 to 30V/0.2 or 12.8 to 30.8 Ω. You might try a Halogen lamp for a test load but R cold is 10% of Rated R when hot. V^2/W


Beware that ESD can easily be hundreds of voltages even though we think of kV when we say ESD. Yet LED's are only rated for -5V and -30Vdc or even a cable with sufficient capacitance and voltage can discharge to kill or wound them them.

I suspect you connected them backwards.

  • \$\begingroup\$ I don't understand half of your answer, but you are correct. Embarrassing mistake. I'm still learning. Why my leds blew up is another question. If I touched the led(s) with wires, they blew up. If I soldered them beforehand, they worked. I'm not sure why did that happen. \$\endgroup\$ – Badr Hari Nov 17 '17 at 19:25
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    \$\begingroup\$ @BadrHari what are you trying to do. You never did explain that. YOu did not try any hook them up singly to that supply did you? ANd what are the LEDs? \$\endgroup\$ – Trevor_G Nov 17 '17 at 19:28
  • \$\begingroup\$ @Trevor I had series of leds that are rated to take up to 700ma. I connected led driver to AC and connected by hand negative and positive wire. They blew up! Then I had nother series but I soldered it, not just touch. They worked and didn't blew up. I don't understand why I can't just things by making contact with wires by hand. \$\endgroup\$ – Badr Hari Nov 17 '17 at 19:29
  • \$\begingroup\$ @BadrHari Static perhaps, or you did not have enough in series. \$\endgroup\$ – Trevor_G Nov 17 '17 at 19:40
  • \$\begingroup\$ @Trevor I had 10 in series, I guess it was static then. My hands are also shaking while doing it. \$\endgroup\$ – Badr Hari Nov 17 '17 at 19:42

With no load...

  1. Measuring the voltage, the regulator will put out it's max volts, which is why you read 30V.

  2. Measuring the short circuit current with the meter will prevent the regulator from reaching the 9V out it needs to begin regulation. As such it looks like it has an additional current limit of 1.1A. That may be by design, or it may just be working as hard as it can, either way I would not leave the meter on there long lest you fry the driver.

You need a test load. A 15R 10W resistor should put the voltage out to 10.5V.

  • \$\begingroup\$ Thank you for the tips, now I'm investigating how to use resistors as test load. I'm always confused about measuring load/amps because you need a load. \$\endgroup\$ – Badr Hari Nov 17 '17 at 19:28

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