Im trying to switch this common converter:http://www.ebay.com.au/itm/281807832840?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT 
With: https://www.fairchildsemi.com/datasheets/2N/2N7000.pdf
Connected direct to battery it works fine and does not pull a great deal of current.
But when switched with a mosfet, loads, such as an LED, cause the voltage coming out and into the converter to drop and the current consumed by the converter to increase to compensate. (I figure with these things the larger the voltage gap to get up to 5v the greater the current it pulls)
The reason I need to switch (eventually with a micro) is to get around its idle current because running off batteries.
Direct to batteries, measurement at Step-Up:
- No load: 3.7mA, inV: 2.48v outV: 4.98v
- With LED: 7.4mA, inV: 2.48v outV: 4.98v
Via Mosfet:
- No Load: inV: 24mA, inV: 0.38v outV: 4.34v
- With an LED: 24.4mA, inV: 0.36v outV: 3.44v
As far as i can tell this mosfet should be suitable for this sort of voltage and current range. But I am new to mosfet, so not sure how to work out what the problem is.
output voltage of mosfet at turn on
Eventually I want to drive a 5V sensor that pulls more current than an led ~ 10mA idle and a 3v3 voltage regulator that drives a rf module (~20mA). But the more load i add the worse this situation gets very quickly to the point that the step up is pulling like 80mA and only putting out about 3V.
simulate this circuit – Schematic created using CircuitLab
**Update" From the data sheet would this be the graph of interest to me, showing that with the voltage range i have i cant pull much current ?
Answer
There are two issues with your design. First and most important, replace that 100 Ohm resistor which is way too small with 10K. Second, the Vgs On of the mosfet could be bigger than the battery voltage. You may want to use another battery or another FET
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