# Another 7805 Question

I am sorry to ask this because there are so many of these topics on the board but I can not seem to find a solution. I am fairly new to electronics in this regard, but in school Lab we were hooking up a 9v power supply to the MC7805CT to output 5v for a hex inverter. It was working then but when I came home I bought a 9v regulated power supply with 300mA and it would only output 1v and get pretty hot while doing it. I am not completely sure what the one we were using in Lab was beyond it was 9v as well. In lab the source was outputting around 9v, however mine is more like 10v. Any help would be greatly appreciated.

• Assuming the power supply is the one getting hot and outputting 1V, sounds like you're drawing too much current on your 9V power supply. How much current are you drawing on the 5V (i.e. if there is only the hex inverter, what's it drawing)? That's effectively how much you are drawing on the 9V. More than 300mA just for a hex inverter is rather odd though. Sep 7, 2015 at 18:40
• Are you sure it's a regulated power supply? it might not be. Sep 7, 2015 at 19:15
• You could use this as an educational opportunity. Draw out the circuit on paper. Measure all the voltages and put them on your diagram. See what conclusions you can reach about where the current is going. Remember that the current flowing into a connection equals the current flowing out because electrons can't collect in one place. Notice which things are hot, and remember that power (heat) equals voltage (across) times current (through). If your meter measures current, great, but be careful (read electronics.stackexchange.com/questions/86401 first). Sep 7, 2015 at 19:26
• Right now I am just trying to get 5v from the voltage regulator so that I can power the the hex inverter. I have the left pin going to the 9v power supply (that is acutally +10v), middle pin going to ground, and the right pin going out so it can be measured.
– enki
Sep 7, 2015 at 20:28