DC to DC boost circuit

[Jeff_sayz]

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 using only the power acquired from the source. *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 the 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.

 

[(*steve*)]

You need to get together with this guy.

Both of you have 5V with a series resistance of 120 ohms, and you want a DC to DC converter to get 5V at some higher current than the 120 ohm resistor limits your current to.

It just aint gonna work.

You need a higher voltage or a lower resistance. If the motor needs to run for only a short period of time I gave the other person a method using a capacitor.

What you're learning is that you can't get more power out than you put in.