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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 '14 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 '14 at 19:57
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    \$\begingroup\$ Does it have a heat sink? (Is it a to-220 pack?) \$\endgroup\$ – George Herold Oct 27 '14 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 '14 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\$ – Bruce Abbott Oct 27 '14 at 22:37

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