Hot sx key

SamTheMan

My SX Key makes the 7805 regulator very very hot!
the thing is it never burnt my 7805 or the the SX_key went bad!
I checked the voltage and it is 5V
I changed the 7805 but the same !
I checked the to see the current and it was something very small like 50mA

Why··does it get HOT???


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PJAllen

What's the input to the 7805?·

If it's 12V, then, rule-of-thumb, you have 7V·"across" the regulator and at 50mA you're close to 1/2W dissipation (7V X 50mA = 350mW) and that can be pretty hot when it's concentrated so.

SamTheMan

I'm using 7v source

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PJAllen

Using output capacitors?

I don't get this part --

Sam the Man said...
the thing is it never burnt my 7805 or the the SX_key went bad!

pwillard

I guess it hasn't failed... yet. 1) add some heat dissipation to you 7805... a heatsink is always a good idea. 2) how stable is that 7V?

SamTheMan

I have Cap(s) 10uf, .01uf, 100uf at the input and output

7v is very stable.

Just can anyone tell me if his/her 7805 gets HOT (not warm)

I just need to know if this is normal or my Key is not functional right.

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PJAllen

Up till now in my SX experiments I've always used a bench supply.· For the project I'm working on, I used a 7805 for the SX, and a 7809 for the other stuff, both running from the same appx 15V.· The 7805 (running only the SX) gets hotter than I can comfortably keep hold of.· I put a typical heatsink to it with a chunk of aluminum on the other side of that and there's no more "heat issue" so far as I can tell.