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Why is my power supply over-herating? Answered

I have a very simple power supply build to power effect pedals 

220VAC --> regular 12vDC wall wart rated at 1A --> 9vDC (7809) regulator with 220uF on the in and 1uF on the out -->1  load rated at 250 mA 

It's perfect except one thing... it over heats quickly, which will eventually lead to damage in a way or another. 


Please advise 
Thanks 

Discussions

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Yonatan24

3 years ago

What heats up: The power supply, Or the 7809 V-regulator?

7805 heats up: Enhance the size of the heat-sink

Power Supply Heats Up: Try this, Or use a power supply that is able to deliver more current/amps

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mhanna3Yonatan24

Answer 3 years ago

the wall wart adapter board is heating up. It delivers 1A and only a regulator connected to it. Im confused why its heating up.

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-max-mhanna3

Answer 3 years ago

Do a easy calculation, see what voltage is going into the regulator, subtract 9V, then multiply that difference to the current you are pulling from it when it is working. That will tell you how much power is being dissipated in the regulator.

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-max--max-

Answer 3 years ago

I calculate it is about 2W, Not much heat at all. There could be a short circuit present somewhere, or faulty wiring. It could be that one of the diodes for the full wave bridge rectifier has failed and is overheating.

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rickharris

3 years ago

1. Because you are drawing more current than the regulator can provide.

2. Heatsink as below or higher rated regulator.

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mhanna3rickharris

Answer 3 years ago

I just did some tests, the regulators dont heat up.. Only the wallwart board does.

Can the regulator be sucking current from the wallwart adapter ? Does that make sense ?

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steveastrouk

3 years ago

What sort of heatsink have you got on the 7809, which is dissipating nearly a watt ????

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icengsteveastrouk

Answer 3 years ago

+750mw

A wall wart rated 12v at 1A may be delivering 15Volts at 3/4amp

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mi5aiceng

Answer 3 years ago

the wall wart i'm using outputs 12.5 VDC with no load connected and rates at 1A

it is then connected to a 7809 circuit with a 250mA load 3V drop ... so power is 0.250*3= 0,75W thats around 49degC rise based on the datasheet

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icengmi5a

Answer 3 years ago

Probably a good switcher wall wart.

We can just touch a 50degC plate but adding ambient makes the.

Only you can best decide how to cool your supply.

May be you could hack the wall wart to be a 9v output.

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mi5aiceng

Answer 3 years ago

Thats actually an idea worth tackling !
ill give it a though
Thank you iceng

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mi5asteveastrouk

Answer 3 years ago

i have no heatsinks on there !
I'm currently testing and reporting to see which component (7809 or wallwart) is dissipating the heat.

Will report back