Run a LM7805 off of a LM7812?

[c0nsumer]

In the MIDIbox SID implementation I'm working on, I'm using ~15VAC, rectifying it with four 1N4004 diodes, and feeding it to a LM7805 and LM7812. As you can imagine, the LM7805 gets quite hot while running. I've got heatsinks a heatsink on it, but this still doesn't seem ideal. As a solution, I was thinking of running the LM7805 off of the output of the LM7812.

Is there some reason I'm not yet understanding why this would be a bad idea? Or, is there a better way to provide both 12VDC and 5VDC off of a single supply?

Thanks!

-Steve

[TK.]

Hi Steve,

yes, this is a bad idea, because it will add some more digital noise to the 12V voltage domain. Therefore it's better to handle these two domains strictly seperated like you can see in the optimized PSU schematics (there are also some hints in the .pdfs which are worth to read).

However, so long no LCD backlight is connected, I guess that the 7805 won't get that hot

Best Regards, Thorsten.

[c0nsumer]

Ah, okay. Thanks. I am hoping to allow people to connect LCD displays to the board, but hopefully it won't be much of a problem.

Due to cost I'm trying to avoid the use of a switching power supply, nor do we have access to any C64 supplies. I'll just continue going down the path I've been with the separate regulators running off of whatever the DC input ends up being.

Thank you. :)

-Steve