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Basic Electronics » 9V transformer more like ~15V

October 31, 2011
by Gianni
Gianni's Avatar

I measure ~9V using my multimeter from a 9V battery, but 14.9V from the supposed 9V 300ma transformer that came with the LED kit. Why is it not 9V? I burned out a voltage regulator and had to replace it.

October 31, 2011
by hevans
(NerdKits Staff)

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Hi Gianni,

The wall warts we send with the LED Array Kit are unregulated power supplies. They are rated to deliver 9V at 300mA, but will be more when you meausre it unloaded (not drawing any current), and will actually drop below 9V if you draw more than 300mA. This is why run it through the 7805 to regulated down to 5 and get rid of this variability. This is perfectly normal operation and will not damaged the 7805. If your 7805 burned out there might be something else going in your circuit that is causing a large current draw.


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