Stamp Homework Board Rev. B Voltage Regulator
Ross
Posts: 15
Anyone know what type of voltage regulator was used on the Rev. B version of the BASIC Stamp·Homework Board?· Specifically, I'd like to know what's the acceptable voltage range for Vin.
Thanks,
Ross
Thanks,
Ross
Comments
Try this!
Rev B Note
The BASIC Stamp HomeWork Board Rev B’s voltage regulator supplies current to the embedded BASIC
Stamp, certain circuits built on the breadboard and connected to I/O pins, and any devices drawing
current from the Vdd sockets. The current budget for the HomeWork Board Rev B’s voltage regulator is
50 mA. Most devices featured in Stamps in Class texts only draw a few extra milliamps of current and will
work fine when powered by HomeWork Board Rev B’s Vdd Pins. However, there are a few exceptions,
including servos, pumps, and heating elements. These devices should not be connected to Vdd, or it
could damage the board’s voltage regulator. Instead, these higher current devices should be connected
to Vin. The voltage supplied to Vin should in turn be limited to a level that is compatible with the device
(servo, pump, heating element).
Heres the link http://www.parallax.com/Portals/0/Downloads/docs/prod/boards/28158-HWB-10pack-v2.0.pdf
schematic link http://www.parallax.com/dl/docs/prod/boards/HomeWorkBoard-v1.3.pdf·
Page 4 shows REV A&B also C&D Voltage Regs used.
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Post Edited ($WMc%) : 8/5/2010 2:39:53 AM GMT
There's two limiting factors here. The first is if you go over 50 mA, the regulator will detect "over-current" and shut-down (non-destructively) until the load is removed.
The other is heat. If you're dropping 4 volts (9-5==4) across the regulator, then the power dissapated as heat is (P=IV, 50 mA * 4 volts == 0.2 watts) 0.2 watts. The heat dissapation for the TO-223 surface mount package maxes out at 0.5 watts at 80 degrees F. So 0.2 watts is okay.
But, if you put say 20 volts across it, that's 15 volts * 50 mA == 0.75 watts. That's too much, it's going to get very hot, and several things can happen. The chip can go into thermal shutdown until it cools. Or (and I've heard of this happening) the chip can soften its solder and slide off its pad.
Let's see, 12 volts -- 12 - 5 == 7, 7 * 50 mA == 0.35 watts. That should be okay. Note also a "12-volt un-regulated wall-wart" probably puts out 14 volts at low-loads. 9 * 50 mA == 0.45 watts. That's awfully close, it's going to run very warm, make sure you check with a voltmeter what the actual voltage your regulator is seeing on 'Vin'.
Bottom line -- 6 to 12 volts all should work, much above that probably won't.
Regards,
Ross