super carrier board and the lm2940 voltage reg

roverx

Hello all!

I have a super carrier board with a bs2px .. with the following attached/configured - all working-transmitting etc

-all pins 220 ohm protected
- pins 9 - 15 accessible for relay use on the other side of a uln2003 ( v++ wil be 12-15 volts, 12.5 average)
- I2C RTC from gravitech .. based on DS1340-33 IC.
- ADC 0831 after 150K/51K divider - (20 volt upper range)· - used to monitor raw voltage 12-17V range grom solar/wind
-912 Mhz transmitter/receiver - parallax
Other
- No relays at this point, but figure 12v 30-50 mA each x 4
- 4x20 LCD serial LCD on order (20-90mA)

Question, After doing a lot of forum searching after being concerned about current draw through the lm2940 5.0, I decide to feel the heat sink, and damn if it wasn't hot ... at 12.1 V+. I really don't want to unsolder it (but will if needed), my expected V+ range is 11 to 15 volt, mean at 12.5 (wind/solar powered and monitoring use) . Actuall current draw ·is ~ .1 A at 12V

should I regulate upstream with a LM7806 ? or just replace the reg? If I run upstream with another reg , any isues with my ADC? and its ground points?

FYI ... product descriptoin for super carrier is "On-board voltage regulator accepts 6-30 VDC, from wall-pack or battery "

add. note --- this is all hard wired at this point... [noparse]:)[/noparse]

Mike Green

It would make sense to replace the regulator with one of those switching regulators that's a "drop-in" replacement for an LM78xx or equivalent. The existing regulator is indeed rated for inputs from 6 to 30V, but everything above 5V will have to be dissipated as heat and that depends on the current drawn. 12-5V x 0.1A = about 3/4W which is not a lot of power, but will heat up the regulator.

You could also add an "upstream" regulator, maybe an LM7808 which would produce 8V input for the super carrier board and reduct the "headroom" there to only 3V.

The ground points are all going to be in common. You'll want to be careful about where you tie in the ADC's analog ground (to avoid ground loops).

roverx

Thanks Mike, I think I'll go for the replacement as my current draw could go as high as 300 mA

most likely the DE=SW050

http://www.dimensionengineering.com/datasheets/DE-SW0XX.pdf

roverx

To close this out...the DE-SW050 works perfectly on the board. Temperature is almost ambient and current draw fell as well.

I just clipped the pins on the original lm2940,·soldered wires to the remaining posts comming off the board which then went to the new reg

pins match 1:1