Help! I’m clueless and need an fet to control ~300 mA from a single Li-ion. Any good choices in a smallish package? Trying to build a touch switch. Thanks.
2N7002
Some are listed at 300mA max some at 115 mA max. How do I tell them apart and will 300 mA stress the chip?
This is one of my favorite small N-Channel MOSFETs
http://www.rohm.com/web/global/products/-/product/RJK005N03FRA
Compared to a 2N7002, it has a very low RDSon - meaning that it will generate less heat at the same current flow. It's rated for 500mA.
I know mouser stocks them, and I'm sure many other places do as well.
PPtk
I’ve used some Fairchild Semi fets for high side switching like the FDN3XX. Here is a catalog of small package, logic level, fets (look for N ch and low Rds-on at 2.5V): fairchild mobile solutions guide
Thank you all for the response.
Would it work with this?
is that from ecf, and is that an atty connector? lol. swear ive seen that before
You should use your middle finger… J)
I’ll be damned if I can tell what the heck that does.
Finger touches both black squares and light comes on (supposedly).
i think the finger is supposed to touch the brass atty connector and switch activates. the atty connector has an outer ring and a center pin isolated from the outer ring.
The “led” will be a laser(3V,200-250mA) that I would like on only when contacts are being touched rather than touch on-touch off.
oh, is that gold colored item a diode?
search ECF for a touch switch. lots of info on different types over there. all of them will be momentary, as you dont want a latching switch on an ecig
Ah, ok, now I get it.
Short answer: Yes, it will 'work'.
Long answer: An LED/Laser Diode is not an atty. It doesn't have an internal resistance, per se. It's a diode, and as such, it will not do anything to limit it's own current. When you touch the on switch, the battery will push as hard as it can and you'll be direct drive - Depending on the Vf of the LED and the load voltage of the battery, you'll blow up the LED or the FET or both.
Toss a current limit resistor or an AMC7135 style regulator in the circuit, and then you've got something.
PPtk
It is probably switching power to a laser module with a driver in it…
Exactamundo Texas, what I don’t know (among many other things) is since its spec’d at 3V do I need to add a dropping diode or resistor since I’m using 4.2V max?Or as Pilot says, add in a 7135 instead. It’s the green Fastech laser sku 1057303 but not much other info as usual.
It has a current regulator built in, but no telling how large of a voltage it can handle. That big power resistor does not look encouraging. Maybe run it off a CR123 primary cell?
That would definitely complicate matters. I’ll ask if anyone else has one and how they power it. If you haven’t already guessed, this is for the MTM raygun that has 3x 18650’s. I’d like to activate the laser by moving my thumb onto the contacts located at the top of the handle where there’s just space left for the wiring and maybe an fet. No problem fitting a 7135 in there either if that would do the trick.