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Current Sourced from Voltage Regulator Circuit — Parallax Forums

Current Sourced from Voltage Regulator Circuit

mstarrs1mstarrs1 Posts: 1
edited 2005-10-10 14:14 in BASIC Stamp
Be gentle I'm new to stamp programming!!

I'm currently using a BASIC Stamp 2 module and I am wondering what the normal currents sourced from the voltage regulator circuit are. I'm sure someone out there will have info.
Curiosity will get the better of me and I'll end up attacking my module with a soldering Iron!

Thanks.

Mark

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-10 14:14
    Mark,

    ·· The on-board regulator on the BASIC Stamp 2 Module supplies ~50mA, not counting anything connected to the I/O pins.· The BASIC Stamp uses a few mA leaving you ~45mA at the Vdd pin and to power external devices.· Be careful when powering anything off this regulator so you don't burn the on-board regulator.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-10-10 14:14
    I believe the BS2 normally uses around 5 mA when processing, much less when 'Paused'.

    A TO220 package voltage regulator (the tab with three leads) usually can dissapate 1 to 1.5 Amps -- though it does get warm doing that. The voltage regulator on the BS2 itself (fed by Vin, output on Vdd) is probably limited to around 50 mA. Each LED you have lit usually uses around 15 to 20 mA (depends on the LED, and the current limiting resistor you use)

    Note one key factor with a linear voltage regulator is the amount of power it has to disappate. A linear regulator basically acts like a very fast variable resistor. It's resistance changes as needed to make sure the output stays at 5 volts, no matter what the current draw is on the output 'load'.

    So, if you are using a 12 volt input, the regulator has to drop (12 - 5 == 7) 7 volts. Now, Power = Current * Voltage. So, 5 mA * 7 volts is 0.035 watts. That's really low. At 1 amp, (1 * 7 == 7) it's 7 watts. Now 7 watts is a lot for a little device like that, but can be done with a good heat-sink, heat-sink grease, and maybe a fan.

    If you double the voltage to 24 volts, at 1 amp it has to drop 24 watts. That's too much heat, and the regulator will go into thermal shutdown.

    Smaller devices have less area to dissapate heat from -- which is why the little regulator on the BS2 itself is limited to 50 mA. Really good for 9-volt battery useage, or for 4 AA cells for longer life.
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