Just built my first power supply around the LM7805. Wall Wart input was 9 volts volts but now it is around 12, output volts = 12.4. I have a 100 uf cap on the input side and 10 uf cap on the output side. The LM7805 gets warm to the touch. What's happenning! Thanks!
I don't think it's backwards, won't have a chance to check until later tonight. I'm going to take it out of the circuit and check it by itself. Thanks!
Without any load 7805 ic should be stone cold. If its get warm then there is a little problem which you have to fix, so do the following
1. remove the 10uf capacitor at the output and check it again
2. you can use a digital meter to check if your 7805 is ok, both input and ouput should read like a diode relative to the common, if it does otherwise then you have a defect on your 7805. so change it
when there is no current to load and 7805 is supplied with 12v, power dissipation according to your formular would be
(12-5)X 0 = 0
The point is that when power dissipation is 0 7805 should be stone cold. That was why i suggest the 10uf capacitor at the output be removed, it might just be defective and posing to be a load (or short circuit) at the output of 7805
good math. but i was telling about when there is a load current and was trying to relate the excess of heat because of the input vtg change from 9V to 12V.
Can u explain the thing with respect to the capacitor please.........