Dc to Dc voltage booster

Discussion in 'The Projects Forum' started by Ascendant, Mar 28, 2011.

  1. Ascendant

    Thread Starter New Member

    Mar 27, 2010
    I have project Ive been working on for a while now, the basic objective of the circuit is to take a DC voltage and boost it to 5v DC to run a small motor at the output. The source voltage is 5v DC but it has a series resistance of 120 ohms which drops enough voltage to leave me with as low as 2 volts (depending on the thevinin resistance of the boosting circuit that's used.) The small DC motor needs about 40 mA to start the motor and about 20 mA to run. I've tried using a MAX756 IC, which would only get the output voltage up to 4v using a 240 ohm resistor as the load, but when I switch out the load resistor with the motor the voltage drops into the .5mV - 1V range.

    So in other words I need to take source voltage and boost it up to 5 volts using ONLY the power from that source, and I CANNOT bypass the resistor at the source.

    Any help is greatly appreciated. I will try and post some pictures of the MAX756 circuit I'm working on as soon as possible.
  2. SgtWookie


    Jul 17, 2007
    20mA @ 5v to keep it running? Not going to happen.

    If it will run with ~20mA @ ~2.5v, that can happen.

    Why don't you just start by placing a large capacitor on the output of the source and 120 Ohm resistor, let it charge up to 4v or so, and then you'll have the starting current and run current available?

    Otherwise, you're not going to have enough power output from the source to run it.
    Last edited: Mar 28, 2011