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deno
05-30-2005, 11:59 AM
with no I/O's connected.· One is using a 14 volt supply, the other is using a 12.6 volt supply· and using a carrier board from Parallax, with a 9 volt battery, the 1121A5 chip runs up to 100 degrees F.

Is this normal operation?· How long can a $70 SX last with that kind of heat being dissapated? The spec sheet say the input voltage can range from 5 to 15 volts.

Deno

·

Chris Savage
05-30-2005, 12:14 PM
deno,

·· If you check out the link below you will see that while the BS2sx Module runs at the rated voltages, the optimal operating voltage for the BS2sx is around 7.5 volts.· It's a matter of the regulator being able to handle the full range, but the more you put into it, the more heat it has to dissapate in order to provide 5 volts.

http://www.parallax.com/html_pages/tech/faqs/fctl_info.asp#What_is_the_VIN_pin_used_for




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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Forrest
05-30-2005, 06:40 PM
If you're using wall warts to power your board - you might be surprised to find the wall wart is providing much higher voltage under no load or light loads. In my experience, your average 9V DC wall wart will be pumping out 14-16V DC - so you're already at the top end of the acceptable range.

Chris Savage
05-31-2005, 03:29 AM
Forrest,

·· Another good point...With no load unregulated supplies will be substantially higher than their rated voltage.



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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

deno
05-31-2005, 07:18 PM
Thanks for all the replys. With no loads (no I/O's connected), what is the difference in current draw between the BS2 and the BS2sx stamp? Is it that great as to cause the voltage regulator to have to work harder to produce 5 volts and make the BS2sx to run that hot? Is the heat output 2.5 times greater because the SX runs 2.5 times faster?

Has this 7.5 volt prameter been in existence since the SX was born by Parallax. As I don't remember seeing this operating condition being required when I bought my first SX several years ago and put it into operation.

Thank again to all who read....Deno

Jon Williams
05-31-2005, 07:31 PM
Speed = Current draw; so yes, the BS2sx will draw more current than the BS2.· The core micro is different too, accouting for some of the differences. Today's BS2 runs at about 3mA and the BS2sx runs at about 60mA.

In the end, it's best not to make the onboard regualtor work too hard -- it's very small and doesn't have the ability to disipate a lot of heat.· I learned the hard-way once: I actually witnessed the regulator unsolder itself and slide right off the module! (wiring error on my part).



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Jon Williams
Applications Engineer, Parallax

allanlane5
05-31-2005, 08:12 PM
Speed = Current draw, so the BS2sx draws 60 mA.

Heat == Power dissapated. Power = Current * Voltage.

So, if your voltage input is 7.5 volts, the regulator drops that to 5 volts, the voltage drop is 1.5 volts. The power is 1.5 * 60 mA == 0.09 watts. This is very low.

If your voltage input is 17 volts (a 14-volt wall-wart lightly loaded) then your voltage drop is 12 volts. The power is 12 * 60 mA == 0.72 watts. I believe the max heat dissappation of a TO220 package is 5 watts? The small regulator on the module can dissappate much less. Also, the more it is trying to dissappate, the hotter it gets.

The good news is, if you really over-heat the regulator, it will go into thermal shutdown to protect itself, so you're not doing any damage this way. 100 degrees F is not really that hot, actually.

Now, if you try to pull too much current out of a BS2sx PIN, then the BS2sx will get hot. This is really not a good thing. Again, 100 degrees F is not really that hot. 200 degrees F is probably too hot.

Chris Savage
05-31-2005, 11:07 PM
deno said...(Trimmed)
Has this 7.5 volt prameter been in existence since the SX was born by Parallax. As I don't remember seeing this operating condition being required when I bought my first SX several years ago and put it into operation.
deno,

·· It's not a requirement, it a recommended operating voltage for the reasons given above.


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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)