Suggestion needed, low Rds MOSFET for 3v operation ?.

Buzby

Buzby

Senior Member
I'm modifying a child's lamp to make battery life more respectable.

The circuit is simple, two AAA batteries, a switch, and a white multi-LED display panel.
This display draws a whacking 150mA !.
If the switch is left on the batteries get flattened in a few hours.

My solution is to limit 'on' time to about an hour. Programming an 08M2 to do the switching is easy, but I'm struggling to find the right MOSFET.
It needs a really low Rds to switch the LEDs, but all the ones I've looked at only start switching when the gate is about 2.4v, and are not fully switched until about 4.5v.

Can anyone suggest a suitable FET that can do the job, or maybe even a single-chip device that does what I need ?

Cheers,

Buzby
 
Have a look at the Vishay Si2301DS data sheet. It's one that I have in my "library" of data sheets. It is a SOT23 package, P-channel MOSFET but may give you a lead into other, more suitable devices if you're looking for an N-channel.
 
Thanks !

The Si2302DS is the N-channel version, Rds is about 0.1 ohm at 2.5v gate, I'll order some now.

Cheers,

Buzby
 
Hi Buzby, you could try a voltage doubler if you have space for a couple of small diodes and caps. My idea would be to feed PWM to the doubler and then the gate. There's always old school BJT too if you can manage a little Vce.
 
I can't find a "proper" supplier (Farnell, RS, CPC, Mouser etc) of Si2303DS, but they seem to be available on eBay, Amazon etc.

I use the following, with +V supplied from a 3.3v LDO regulator (MCP1700-3302E/TO) powered by 3x AA batteries (over 1000 units built, no issues)

LED load, connected to "MOSFET" is 200mA

1775474745320.png
 
Too bad I didn't see this earlier, but I too would have recommended the AO3400A. Vgs ~ 1V, Id ~ 5A. I buy them in lots of 10 (about $0.47 ea) and use them for nearly everything except where I need much more power. I always have these and good old 2N7000s on hand. Surely $5 is not out of your reach to do this project a bit better? You can always find a use for them.
 
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