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Old 13th July 2003, 02:32 PM   #1
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Join Date: Nov 2002
Location: London
Default Wallplug Issue


I have a wallplug rated at 15V/750mA which I'm using to power a synth I'm building that calls for 13-15V 600mA. The prob is the wallplug measures 22.05V not 15V as stated. This is turn is causing the voltage regulators (7808 and 7805) to get very hot! Then after about 5mins of operation, the power just seems to drift away ...

How can i better control this wallplug to get the power to more suitable levels b4 goin into the regulators and on to the synth pcb...? Is it just a case of bigger heatsinks? Or should I add a 7812 before the 7808 too?

Any pointers appreciated...


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Old 13th July 2003, 02:41 PM   #2
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JOE DIRT®'s Avatar
Join Date: Apr 2003
Location: Brantford, ON
I would use a larger heatsink and a current limiting resistor before each regulator as then they will share the load.
wall transformers are unregulated sources so they are always higher than stated they will drop to the right voltage under a load
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Old 13th July 2003, 03:18 PM   #3
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Location: London
Hey Joe...

Okay, would 2x 7W 15R resistors placed in series before the input to the 7808 be okay d'ya rek?


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