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I connected around 10m of christmas light LEDs to a 5V voltage regulator (lm7805). It gets quite hot, put I can still touch it without burning my finger. So in is within its temperature range (120 C max). It's a self regulating voltage regulator so I am not affraid of it burning itself.

But to ensure that my christmas tree wont burn, can I put 2 regulators in parallel to dissipate the heat better?

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    \$\begingroup\$ basically, no, not really. There are many problems associated with paralleling voltage regulators. \$\endgroup\$
    – KyranF
    Oct 27, 2014 at 19:55
  • \$\begingroup\$ Please see the question and answers (there are many, all are good to read) here: electronics.stackexchange.com/questions/32690/… \$\endgroup\$
    – KyranF
    Oct 27, 2014 at 19:57
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    \$\begingroup\$ Does it have a heat sink? (Is it a to-220 pack?) \$\endgroup\$ Oct 27, 2014 at 20:05

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No, but depending on what your power source is you may be able to do 2-stage regulation to spread the heat - for instance, if your source is 12V then lower it to say 9V first with a 7809 then drop it from 9V to 5V with the 7805. If you're even higher than that, then you could use a 7812 first to drop to 12, then the 9V, then the 5V.

Either that or just use a switching regulator, such as a UBEC used by RC vehicle enthusiasts (available for a couple of $ from eBay or most RC model shops).

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Hot but touchable is entirely within the normal operating conditions of an 7805.

If you are concerned about the effect on your Christmas tree simply add a heat sink (which can be as simple as a 10 x 10 cm metal plate) to spread the heat over a larger area and thus reduce the temperature. (This assumes you are using a TO220 version. If you are using a TO92, swap it for a TO220.)

You could also spread the heat by dissipating part of the heat in a pre-regulator, series resistor, or extra power transistor, but that makes little sense in this case as it creates two hot-spots instead of one, which is a little bit better but not as good as a heat sink.

Another option is to use a switching regulator, which will dissipate much less heat for the same current.

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Yes, you can. However if both regulators are not putting out identical voltages then one will draw more current and get hotter than the other. The traditional way to fix this is to add a small resistor (eg. 0.1Ω) in series with each output.

If you can touch the regulator without it burning you then it's probably not getting too hot. If your Christmas tree is really sensitive to heat then you could put a heat sink on the regulator to reduce its surface temperature.

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    \$\begingroup\$ Paralleling linear regulators is not a good idea. They both want to regulate the voltage, but not necessarily to the same precise value. Which one wins? Which one melts down? You can do it with adjustables like the LM317, where you have control over the output voltage, but it's still not recommended. The proper way of increasing the current handling of a linear regulator is with a bypass transistor. \$\endgroup\$
    – Majenko
    Oct 27, 2014 at 20:15
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    \$\begingroup\$ ...and another myth is perpetuated :(. Paralleling regulators is a widely used technique for increasing current handling (I own several commercial products which use 2, 3 or even four fixed linear regulators in parallel to get higher current). A heat sink is more commonly used when one regulator can deliver the current, but would otherwise get too hot. \$\endgroup\$ Oct 27, 2014 at 22:37
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I have successfully done it but I had a batch of 5v regulators and tested each one to 1/100th of the same voltage output before parallelizing them to ensure pretty even distribution. I needed to do this with heat sinks too and it works well but the trick was perfectly matching the regulators. My requirements were super small space and just heat dissipation, not a current increase.

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    \$\begingroup\$ Could you add more details as to what IC you used and maybe include a schematic? How did you match the regukators? \$\endgroup\$ Apr 5, 2021 at 22:05
  • \$\begingroup\$ Input gnd output from looking at the front of your standard 5 volt 1.5 amp regulators. The constant voltage input was 7,4 volts,. I hooked up the voltage meter which showed 1/100th of the voltage output. I found about 3 out of 7 which exactly match 5 volt output and used those with heat sinks. My load was between 200ma to 1 amp well within tolerance. I could touch them without getter burned finger tips. As the load goes up they even out further. I had a light load so accuracy was more important. \$\endgroup\$
    – Hack
    Apr 12, 2021 at 5:48
  • \$\begingroup\$ You should edit: electronics.stackexchange.com/posts/558380/edit your answer, not add more details as comments. Edit your answer to include this comment and maybe add a schematic so others can understand your answer better. :) \$\endgroup\$ Apr 12, 2021 at 15:29

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