Hello,
I'm working on a project where I use a pair of LM2940s in cascade to get a 12V and 5V. Here is what I do for the power supply:
What I am powering up is:
a) a pair of 7-segment LEDs - only one digit is on at any time, i.e. 7- LEDs maximum are on; b) a 12V / 0.18A fan (powered directly from the output of the 12V LM2940); c) a PIC16F690 microcontroller, working on 3.58MHz.
The LMs get pretty hot when all this junk is running. When I stop the fan, the LMs are just warm (just a note here - the fan's purpose is _not_ to cool down the LMs - it is running in a separate compartment).
I put a heatsink and they don't get really hot anymore, but this worries me. Is it normal for LM2940s to get hot? I've been working with 7805s, and in my experience those do not get hot that easy - but on the other hand, I haven't used the 7805s to power up much more than a microcontroller and a couple of LEDs.
I checked the LM2940 specs (here it is:
Regards,
- Alex