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I have a Cree LuxDrive LED powered by a 3.7V 750mAh LiPo Battery hooked up in a circuit with a latching switch.

For some reason every time I turned it on, the driver gets really hot and almost starts to melt so I have to immediately shut it off.

The light works but can’t use it if the driver keeps getting so hot. I’ve tried replacing the switch with the new one and still the problem persists. I have to use the type of switch currently pictured because it’s for a very small application. Maybe I’m using the wrong type of switch? It’s a double pole double throw but I’m only using 2 of the 3 pins on each side of the switch.

enter image description here

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  • \$\begingroup\$ "I have to use the type of switch currently pictured" There is no picture of a switch in your question. Judging by the answers, the omission of that picture might not be required for an answer. Nevertheless, it is confusing for the question to refer to a picture which doesn't exist! \$\endgroup\$ – SamGibson Feb 17 '18 at 23:29
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    \$\begingroup\$ Hi Sam, Yes, I realized I forgot to add the picture! Here it is attached to the post. \$\endgroup\$ – Vbs Feb 18 '18 at 3:01
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If you want to keep using the same Li-Po battery, put 2 1N5408 diodes in series with the battery output (+), but tiny and cheap 1N4007 types will work. This will drop the voltage by 1.2 volts to 1.5 volts, depending on the load. These diodes are rated for 3 amps at 1 kV. The 1N4007 is rated for 1 amp at 1 kV.

Now your regulator will only get 2.25 to 2.5 volts, well within its safety margin. Diodes are not resistors, so little energy is wasted as heat (1.2 watts if a 1 amp load).

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Ok I could try that. If you could recommend anything smaller that could still do the job, I’m open to suggestions. Smaller is better as I’m doing a very tiny project, thanks! \$\endgroup\$ – Vbs Feb 17 '18 at 21:06
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    \$\begingroup\$ "diodes are not resistors, so no energy is wasted as heat" ... citation needed \$\endgroup\$ – Brian Drummond Feb 17 '18 at 23:09
  • \$\begingroup\$ @BrianDrummond. If you want the fine details, a .7 volt drop * current consumed is wasted heat, but is much less wasteful than resistors, which have a variable voltage drop. So yes, if the circuit consumes 1 A of current, then the diodes waste 1.2 to 1.5 watts as heat total. Still a simple and tiny solution. Battery will not last as long with a 1.2 volt drop, but the alternative was an active SMPS pre-regulator. \$\endgroup\$ – Sparky256 Feb 17 '18 at 23:19
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    \$\begingroup\$ I would say the alternative would be to use a proper driver for the application... this one is boost only so its application would be driving a white LED from 1-2 AA batteries, not one LiIon cell. \$\endgroup\$ – peufeu Feb 18 '18 at 0:02
  • \$\begingroup\$ @peufeu, it’s a LiPo 3.7V 750maH Battery not LiIon cell..not sure if this changes the answer but just wanted to clarify. The driver came with the LED already wired up as a “kit”. I guess what I’m trying to say is if there is an alternative power source to the Lipo battery that’s very small (like the size of AAA or smaller/coin cell) and wouldnt overheat the driver that would be great. \$\endgroup\$ – Vbs Feb 18 '18 at 3:05
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Micropuck LED driver gets really hot
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3.7V 750mAh LiPo Battery

  • As others have said, 3.7V exceeds the allowed input voltage for the MicroPuck LED driver in the typical "boost" configuration.

    Worse than that, according to the MicroPuck documentation / datasheet, the Absolute Maximum Rating for input voltage in that configuration is 3V. Using the usual interpretation for "Absolute Maximum Rating", that means that by connecting more than 3V (e.g. perhaps 3.7V or more, depending on the state-of-charge of the battery) you might have permanently damaged that MicroPuck, even if you now try to use it in a valid configuration. :-(

  • However, the good news is that the LEDdynamics, Inc. 2009 Micro Puck Application Note COM-DRV-2009-APP "Additional Applications of the 2009" shows an alternative "buck/boost" configuration where the document explains:

    This topology boasts an extremely wide input voltage range that will continue to supply effective power as batteries become exhausted, but is 15% less efficient than boost.

    Here is the original diagram from page 4 - see the document for more information.


MicroPuck 2009 as buck/boost driver


(Original source document)

As you can see, the allowed input voltage range for that MicroPuck buck/boost configuration is 1V to 7V, which includes the voltage range (e.g. 3V to 4.2V) for a single Li-Po battery which you mentioned (although with a reduced efficiency compared to the boost configuration). However, as I explained above, that original MicroPuck might already be damaged, due to the input over-voltage in the "boost" configuration.

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  • \$\begingroup\$ Yes, correct I think the original micropuck is fried. Thanks for including this documentation! And do you suggest a better power source? Would prefer to use something smaller and also less dangerous than a LiPo battery....Been looking at some of the batteries, commonly sold at grocery stores. There are coin cell batteries that are 3 V but I don’t think they will last that long powering this LED. Anything along those lines that you could suggest that would last longer? \$\endgroup\$ – Vbs Feb 18 '18 at 16:32
  • \$\begingroup\$ Maybe two tiny AAA batteries in a battery holder? They are usually 1.5 V each, correct? \$\endgroup\$ – Vbs Feb 18 '18 at 16:33
  • \$\begingroup\$ @Vbs - Engineering is about compromise :-) You need a list of what you require from your power source & another list of what you want (but can compromise). AAA alkaline batteries might suit you, but are non-rechargeable. Is that important to you? I also suspect that 2 x AAA batteries in a holder, will be larger than a 750mAh Li-Po battery. You wouldn't need recharging components, but must pay for replacement batteries. Again, only you know the importance of different factors in your project. Google AAA battery datasheet for electrical info e.g. data.energizer.com/pdfs/e92.pdf \$\endgroup\$ – SamGibson Feb 18 '18 at 17:16
  • \$\begingroup\$ The most important element of concern is size. I want the power source to be as small as possible, but powerful enough to light up the LED...The ability to recharge would be great, however if there is something out there that is smaller that I would need to replace every once in a while I wouldn’t mind. \$\endgroup\$ – Vbs Feb 18 '18 at 17:41
  • \$\begingroup\$ I only have a circular diameter of 1.75 in and 0.5in depth to work in so very tight space if this helps \$\endgroup\$ – Vbs Feb 18 '18 at 17:44
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https://www.ledsupply.com/led-drivers/micropuck-boost-dc-led-driver - "Input Voltage Range: 0.8VDC to 3VDC." You need to step down your battery voltage.

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  • \$\begingroup\$ Ah good catch! Are there any other batteries that I could use instead that would be smaller in size? It’s needed for a very tight space to be wired into. Basically I have a diameter of 1.75 in Circle that everything including the battery has to fit into. I’ve seen a wide variety of small coin cell batteries at the grocery store along with even smaller but powerful batteries for hearing aids. The smaller the better. Any suggestions along these lines would be great! \$\endgroup\$ – Vbs Feb 17 '18 at 20:59

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