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Starter Kit with 3 amp power? — Parallax Forums

Starter Kit with 3 amp power?

brianandrusbrianandrus Posts: 5
edited 2012-10-04 10:31 in Propeller 1
Ok, I just bought my first propeller in the form of the starter kit, so yes, I am a bit of a newbie here.
I have a 5.5v 3amp power supply that I want to use with it (it is the power supply to the device I want to use the propeller to control).

The specs for the demo board say:
Power requirements: 6-9 VDC, 2A regulator on board

How might I make it ok to use the power supply I have?

Thanks in advance,

Brian

Comments

  • LeonLeon Posts: 7,620
    edited 2012-10-03 07:13
    You need 6-9 V DC, as specified.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2012-10-03 07:19
    Leon wrote: »
    You need 6-9 V DC, as specified.
    You are so helpful Leon, bless you :)

    Welcome to the Prop forum Brian!
    Of course the board is regulating down to 3.3V and possibly 5V but you may be able to connect the 5V from your power supply directly to the 6V input as most board have low dropout regulators. I don't know which board you are using though and the 5V that is regulated on the board will be a little bit less than 5V if that doesn't worry you although the 3.3V will be fine.
  • dnalordnalor Posts: 222
    edited 2012-10-03 07:46
    Datasheet of the LM2937IMP(used in demoboard) says:
    typical dropout voltage at the max. I of 500 mA is 500 mV (but can be until 1V). At a I of 50mA the dropout voltage is only 110 mV (until 250 mV).
    So your 5.5 Volt will be enough if you draw not too much current.
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2012-10-03 07:57
    if its not enough power just use a 9 volt battery for the time being.

    i would defintaley suggest going to wal mart and getting an adjustable wal wart the come in so handy its rediculous. there are two at my local wal mart they both have a buch of interchangable tips (easy to make your own adapter for also) but the 15 dollar one is what you want. it is a 1300mA 1.3amp supply with voltages from 4.5 to 12 and a usb charger...
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-10-03 08:08
    dnalor wrote: »
    Datasheet of the LM2937IMP(used in demoboard) says:
    typical dropout voltage at the max. I of 500 mA is 500 mV (but can be until 1V). At a I of 50mA the dropout voltage is only 110 mV (until 250 mV).
    So your 5.5 Volt will be enough if you draw not too much current.

    When you get into the Low-Dropout region of regulation, there is a big jump in current demand. Look again at the curves for Quiescent Current on the PDF. There is nothing wrong with using that region, but it will run hotter.

    NOTE- The curve charts in a PDF are more detailed than the text and tables.

    The 3 amps rating of the wall wart just means you have 1 amp unusable capacity. If the regulator can only deliver 2 amps, it likely has a thermal shut down for demands in excess of that rating.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2012-10-03 08:17
    Loopy Byteloose wrote: »
    When you get into the Low-Dropout region of regulation, there is a big jump in current demand. Look again at the curves for Quiescent Current on the PDF. There is nothing wrong with using that region, but it will run hotter.

    NOTE- The curve charts in a PDF are more detailed than the text and tables.
    Higher quiescent current is not a problem and that won't make it get hot either. In fact the regulator only has to worry about it's minimum voltage drop at 5V in so it probably won't even get warm.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-10-03 08:32
    The LM2937IMP is a 500ma regulator. Need the exact regulator to know what is really going on and if it will get a bit hotter. But admittedly it would not be much. Face it, it quiescent current jumps from less that 20ma to near 60ma at 5v output from near 5v input, there is an increase in heat. Of course .04 x 5 is only 0.2 watts, but it is heat.

    Id there is a 2amp load instead of a 50ma load, the quiescent current goes up as well.

    It does look like there is a typo at the Propeller Demo Board page and that 2 amps should read 1/2 amp regulator 6-9 volt.
  • brianandrusbrianandrus Posts: 5
    edited 2012-10-03 13:40
    Loopy Byteloose wrote: »
    It does look like there is a typo at the Propeller Demo Board page and that 2 amps should read 1/2 amp regulator 6-9 volt.

    Hmm. I am using the Demo Board and was looking at the 2amp capability of the regulator. If that is a typo (which it seems to be) I probably shouldn't use the 3amp power supply.
    It does look like some folks have successfully driven the lights with 3.3 volts, so I may be ok with trying that out.

    Thanks for the responses everyone!
    Let's see what I can do to start running some programmable lights for Halloween (and Christmas)!

    Brian
  • mindrobotsmindrobots Posts: 6,506
    edited 2012-10-03 15:36
    Welcome, Brian!

    The 3 amp rating on the power supply is how much you CAN draw from it not how much it forces into anything connected to it. If you had a 500 ma power supply and a device that required 1 amp, there would be a problem.
  • kwinnkwinn Posts: 8,697
    edited 2012-10-04 10:31
    If you wanted to use the external 5V supply you could always bypass the on board regulator by soldering a jumper between the input and output.
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