Hi – I recently built a simple voltage regulator circuit using LM350, straight off the datasheet. (I’m looking to power a piece of equipment requiring 12.6V at 2.6 Amps.) I first tested it with about a 1 Amp load and everything was fine. I then hooked it to an automotive bulb (printed rating 27W). It stayed lit for a few seconds and then the chip’s thermal and/or current protection kicked in. I had the 350 on what I thought was a reasonable heatsink for the job, but to make sure I replaced it with a large 3”x4” heatsink and added a fan too. The bulb stayed on a few more seconds until it dimmed out. The big heatsink wasn’t that hot.
The LM350 says it’s “guaranteed” to put out 3 Amps. What am I doing wrong?
- In a perfect world, 27W / 12.6V would be 2.1A. I understand that AC Watts are derated based on efficiency, but I thought DC Watts equaled V x A? My ammeter shows just over 2 Amps while the bulb is lit.
- Do you think I might just have a bad LM350, or that there is some reason why it’s acting like a regular 1.5A LM317? Or do I really need gi-mongous cooling for such a seemingly modest circuit?
- Sure, I could redo the circuit with a pass transistor to share the load, but there would seem no reason to – the 350 says it can handle the Amps.
I would appreciate any ideas you might have. Thanks!
- Steve