Sx tech voltage regulator heat

duffling

I am using a Sx tech board and have a Comtech serial LCD with backlight connected in the normal way to VSS VDD and serial to Pin on the sx board.

when im testing the display it works fine .. but the heatsink on the tech board gets quite warm even HOT to the touch, is this normal . .or am i drawing too much current for my power supply ?
i have other LED and such connected to it .. but my project is not using them while im testing the LCD
what am i doing wrong in this case

thanks again.
·

Chris Savage

duffling,

·· How hot is the heatsink.· Can you hold your finger on it?· Do you know how much current the LCD draws with the backlight enabled?· Also, how much voltage is going into the Vin?



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Chris Savage
Parallax Tech Support
csavage@parallax.com

duffling

Yes you can hold your finger on it but i havent run it for longer than 10mins just to be sure ,
·and the same project running on my BS2sx with same LCD same power supply, the heatsink doesnt get anywhere near this warm using the BOE

by the way i have the SXkey plugged in .. ,

the LCD specs i cant seem to find on the makers web site but ill keep looking

The power supply is a 300 ma 9v wall adaptor ..

Post Edited (duffling) : 4/12/2005 5:56:28 AM GMT

Jonb

I dont know if you should compare the SX to the BS2sx. It is however normal for the heatskink to get hot so dont worry too much about that if you are within spec for the component. If you find the heatsink warming up too much, you can purchase a micro fan and mount it atop the IC, or simply a small fan blowing across it. Airflow makes a huge difference and could give you peace of mind at the expense of power usage. Try running the SX at slower speeds or dropping your input voltage.

The LM2940CT(http://www.national.com/ds/LM/LM2940.pdf) has protection for thermal overload among other things.

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Rsadeika

I would say that it is your power adapter. When I first got my SX Tech kit I was using the BS2 power adapter. It runs the tech board, but it does tend to get a little warm, and starts to get a little hot after awhile. You will also find out that if you remove the SX Key and run it as a stand alone, it will not run, I believe the docs say you need at least 600 ma. I switched to an adjustable power adapter, and set it for the recomended specs,·no problems.

Chris Savage

·· Okay, yes, with the SX Key plugged in it will definately get hot.· The SX Key draws some power, and that is normal.· Even 10 mins, the fact that you can hold your finger on it means it's probably with tolerable parameters.· usually if it overheats or is in overcurrent the regulator will be shut down.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

duffling

ok thanks for the help everyone..

pjv

Hi All;

A useful simple little fact about sensing temperatures, is that your finger can *JUST* continuously hold on to 120F (about 50C); any higher, even a couple of degrees F, and you must let go after 5 to 10 seconds.

Cheers,

Peter (pjv)