Protoboard current: 35ma!?
rokicki
Posts: 1,000
I'm observing something odd on my protoboard. When completely idle, running no code
(just a repeat waitcnt(0)) using the RC clock and nothing attached, it consumes 34.5ma.
This is true for all the protoboards I've tested.
The LED (which doesn't seem to be on the protoboard schematic, by the way) accounts
for 12.2ma by my calculations (I observed 2.93V across the "241" marked resistor which I
believe means it's a 240 ohm resistor).
By comparison, my demo board running the exact same trivial program consumes only
9.4ma (but my demo board doesn't have a power LED somehow).
Is this expected? Are the regulators consuming that much current idle? Or is there
something else that I'm missing?
This may have some implications for powering the protoboards off 9V batteries.
(just a repeat waitcnt(0)) using the RC clock and nothing attached, it consumes 34.5ma.
This is true for all the protoboards I've tested.
The LED (which doesn't seem to be on the protoboard schematic, by the way) accounts
for 12.2ma by my calculations (I observed 2.93V across the "241" marked resistor which I
believe means it's a 240 ohm resistor).
By comparison, my demo board running the exact same trivial program consumes only
9.4ma (but my demo board doesn't have a power LED somehow).
Is this expected? Are the regulators consuming that much current idle? Or is there
something else that I'm missing?
This may have some implications for powering the protoboards off 9V batteries.
Comments
Did you account for the low drop regulator? The LM1086 also uses a few mA in "quescient" mode, and there are two of them in series!
Maybe its also the pullup resistors of the I2C EEPROM interface, perhaps you need to set the I/O ports high, and to inputs after booting.
Mahjongg
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Who says you have to have knowledge to use it?
I've killed a fly with my bare mind.
Linear Circuits offers free SwithcerCad with plenty of example diagrams and simulations, link at their front page http://www.linear.com/index.jsp
This one looks good.. High efficiency (well over 90%), small, couple USD and little extra components needed for 5V or 3.3V output. LTC1877 - High Efficiency Monolithic Synchronous Step-Down Regulator http://www.linear.com/pc/productDetail.do?navId=P1881
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
Post Edited (Paul Baker (Parallax)) : 2/20/2007 9:37:01 PM GMT
I've built two for a project I'm currently doing. While it is designed to run on a 48vdc power supply, for testing I have been using a 12vdc power supply. Makes no difference to the output voltage. It would probably run on anything as low as 6 volts, though I haven't tested this. Anyway, heres a pic of my circuit boards : i157.photobucket.com/albums/t41/gyro_gearloose/Circuits.jpg
Starting from the left we have both power supplies, then the Propellor board in the middle, and finally a dual stepper motor driver board. Of the two power supplies, the one at the top is a 5.1 volt supply for the motors, and the other is the 5.1/3.3 volt supply for the logic circuits (I need a 5 volt logic suppply as that is what the motor driver chips need)
If anyones interested, I can post the stripboard diagram I came up with (you can just see it in the background of the photo above). I used standard stripboard as I've never seen the point of adding the extra hassle of etching my own PCBs.
Post Edited (big_mark) : 2/21/2007 1:36:48 PM GMT
Stripboard is OK as long as it works, but I'd recommended cheap (1side) etch board for making more than one...
- better for high currents, less losses
- causes less RF interference (normally not problem on Hobbyboards).
Mahjongg