Background: I have a handheld Wonderswan with an IPS display and flash cart. These mods mean that it uses more power than the original. The handheld uses a 1.5v AA battery, so I've been working on an extra mod that allows a 3.7v lithium battery with an LDO (to drop to 1.5v) to give it a longer life. This part works. I'm also a beginner with electronics design.

The part that I'm trying to solve is that the LDO has a max draw of around 700mAh and when the handheld boots with a flash cart, the display can't get the amps it needs to turn on. Additional note is that there's a soft power button (ie. there's no physically connecting switch).

Here's where I'm getting stuck.

I've added a MOSFET (IRLML2502PBF) connected as such:

• Source connected to 3.7v battery
• Gate connected to 1.5v rail that is only powered when the handheld is turned on (otherwise it's 0v, not ground)
• Drain connected to IPS display

This is the schematic (where EN is the 1.5v rail):

This design ends up with the MOSFET never putting any positive (or useful) voltage out on the drain (so the display remains off).

I'm sure it's my lack of knowledge that's got this wrong. Can anyone advise (gently!) how to fix this?

A side note: I originally designed this with a 2N2222 transistor, and it did (mostly) work, but I found that sometimes the display wouldn't come on, and my guess was that either the transistor wasn't switching fast enough, or it was limiting the voltage (whereas this MOSFET, I thought wasn't supposed to have much/if any voltage drop).