Need a mosfet...What the heck is a Mosfet?

[Rothman]

I built an 3.7v 18650 mod a while back. It is not much bigger than the battery itself and I don't have much room to work with. I can only fit the super small tactile switches in it.

Problem is, I have burned out 4 of them (2 different kinds). Some other folks have suggested using a mosfet. I have googled them and read all about them on wiki. It all reads like hyroglyphs to me.

I know I want one that has a gate that opens fully at low volts and that it basically acts like a switch when it recieves current. That's about as far as my understanding goes.

How does this stop my itty bitty switches from dying? How the heck do you wire it?

madvapes has a 5v 1.5 amp regulator that is small enough to fit in my unit. Will that work? Is that a mosfet? Sorry, I would post a link but I can't. (darned low post count!!)

Before you guys hit me with some serious knowledge, just know that I am slightly mentally deficient when it come to electronics. Metaphores are good...

Thanks in advance!

 

[instamix]

The 5V regulator wont do any thing for you unless your above 5V...

as far as the mosfet I never use them so I'll leave that for someone who does to answer.

Maybe someone can point you to a better switch(would seem the better option)

 

[Sci]

Rothman, take a look here. It doesn't explain what a Mosfet is, but shows you how to wire one in a mod.
Take a look at the rest of the pics, it's a great tutorial on how to build a mod. It's a juice box, but it has the same wiring that you need.

This one explains what a Mosfet is.

 

[Bahnzo]

Rothman, take a look here. It doesn't explain what a Mosfet is, but shows you how to wire one in a mod.
Take a look at the rest of the pics, it's a great tutorial on how to build a mod. It's a juice box, but it has the same wiring that you need.

This one explains what a Mosfet is.

Thanks, I've been looking for something similar. One thing tho, the MOSFET listed there wouldn't work for a 3.7v, right? It's a 4.5v gate threshold. http://parts.digikey.com/1/parts/1540678-mosfet-n-ch-40v-42a-i-pak-irlu3114zpbf.html <---here's that MOSFET. Which one shows the gate threshold?

Would the one Radio Shack sells work?

 

[Scubabatdan]

Thanks, I've been looking for something similar. One thing tho, the MOSFET listed there wouldn't work for a 3.7v, right? It's a 4.5v gate threshold. MOSFET N-CH 40V 42A I-PAK - IRLU3114ZPBF <---here's that MOSFET. Which one shows the gate threshold?

Would the one Radio Shack sells work?

This is the one I use for a touch switc, it can also be used for a simple .5ma mechanical switch.
Digi-Key - IRF8736TRPBFCT-ND (Manufacturer - IRF8736TRPBF)
This bugger is small! I also use SMD resistors and CAPs with this. Tis allows for a VERY small package for smaller mods that a small tactile switch is prefered in.

Here is a post I made on a home made PCB:
http://www.e-cigarette-forum.com/forum/modders-forum/110368-cast-resin-juicer-7.html#post1694577

Schematics for use:

Note the touch switch can actually be replaced with a tactile switch, and in this schematic IF you are going to make a touch switch then you would want to replace the 4.7M resistor with a 100M resistor.

Home made PCB:


Hope this helps ya...

Dan

 

[Bahnzo]

The one problem I have with digikey....it seems like I need to buy like $5 in parts and it's $9 to ship them. Kinda ridiculous that.

 

[Whistle_Pig]

The one problem I have with digikey....it seems like I need to buy like $5 in parts and it's $9 to ship them. Kinda ridiculous that.

Yeah, I see that as a bit of an issue. Once I've figured out what I want to build, I've thought about seeing who's interested in a group buy. That's actually one of the motivators behind setting up a state social group. Hmm. I wonder whether there's an EE in our bunch.

 

[Bahnzo]

Yeah, I see that as a bit of an issue. Once I've figured out what I want to build, I've thought about seeing who's interested in a group buy. That's actually one of the motivators behind setting up a state social group. Hmm. I wonder whether there's an EE in our bunch.

Not only that, but there's got to be places to buy stuff either in Denver or along the Front Range somewhere. Denver's large enough to have just about anything. Hell, I rebuilt some pinball machines a few years ago...there's a place for that in Denver.

 

[j21blackjack]

The one problem I have with digikey....it seems like I need to buy like $5 in parts and it's $9 to ship them. Kinda ridiculous that.

I don't know where you got that shipping price, but here is the shipping prices for digikey. I just ordered $25 worth of stuff from them, and only paid $5.15 for priority shipping. First class mail is $2, that's as cheap as it gets.

 

[st0nedpenguin]

I'm sure I read somewhere that the 5v regulators from Madvapes will act as a mosfet when using the control pin at 3.7v.

 

[Bahnzo]

I don't know where you got that shipping price, but here is the shipping prices for digikey. I just ordered $25 worth of stuff from them, and only paid $5.15 for priority shipping. First class mail is $2, that's as cheap as it gets.

Might've been somewhere else then. One place I was looking at mosfets wanted to charge me $9 shipping for $5 worth of chips.

I'm sure I read somewhere that the 5v regulators from Madvapes will act as a mosfet when using the control pin at 3.7v.

I'd like to know if that's true, would solve a lot of problems since I need to order from them soon anyways.

 

[Whistle_Pig]

When you're looking at voltage regulators, you'll see 'em with 3 and 4 pins. The ones with 4 pins, one is a control pin. It's like an on/off switch. At least, that's my understanding.

 

[Scubabatdan]

When you're looking at voltage regulators, you'll see 'em with 3 and 4 pins. The ones with 4 pins, one is a control pin. It's like an on/off switch. At least, that's my understanding.

Yes but the OP said he was space restricted, that why I suggested the mosfet chip I did, the thing is tiny, and if you use SMD resistors and CAPs it is very thin.
Dan

 

[5cardstud]

Bahnzo, you might want to check this thread, your answer may be there.
http://www.e-cigarette-forum.com/forum/madvapes/64214-mosfet-3-7-volt.html

 

[Bahnzo]

Bahnzo, you might want to check this thread, your answer may be there.
http://www.e-cigarette-forum.com/forum/madvapes/64214-mosfet-3-7-volt.html

Thanks, I'll have a gander.

 

[Bahnzo]

When you're looking at voltage regulators, you'll see 'em with 3 and 4 pins. The ones with 4 pins, one is a control pin. It's like an on/off switch. At least, that's my understanding.

Alright......I looked at madvapes, and the description for their LDO 5v says it can be used as a mosfet at 3.7v. So there I go. Also, just for fun I ordered a bunch of free ones from ti.com. They look small, but they are free so can't break something that's free, right?

 

[Rothman]

Thanks for all the input guys. My head is still kinda spinning on the subject though. So, I do need to wire in resistors as well if I plan to use a mosfet? I definitely don't have room to run any kind of circuit board. The on from TI seems like it would be good but The whole inline resistor still tows me off.

I'm sorry to be a pain but, I really don't know anything about electrical circuitry. The post with the pic of the TI mosfet, he says there is a resistor....I can't see it. That is about the size I need though and with it being free and all, I supose I'll go that route.

Scubabatdan, would I just use the 100m resistor with the TI mosfet as well?

 

[Bubo]

Rothman - I'm with you on not knowing anything about all of this stuff - but somehow I have managed to make it work (Listen to Scubabatdan!)

In this thread/post I have a picture of what I made up last week -- it should give you a starting point.. Not knowing how small a space or what you are working with it's a bit tough to be more helpful..

 

[Scubabatdan]

For smallest size, I would go with the TI chip:
Power MOSFET - Power MOSFET Transistor - CSD16325Q5C - TI.com

The resistor would go here on the TI chip:

So the only wires you have left to run would be pos to the atty and pos to the switch directly from the battery.

Yes you can use the 100M, but I would use it only if I was running a touch switch, otherwise I would use the 4.7M. Remember if you run a touch switch you still need the 47k resistor between the G terminal and the touch point.

I would really recommend using SMD resistors as you can solder them directly to the TI chip and your foot print would be very samll ulike the through hole resistors.

Rothman - I'm with you on not knowing anything about all of this stuff - but somehow I have managed to make it work (Listen to Scubabatdan!)

Thanks for the vote of confidence Bubo

Hope this helps
Dan

 

[Rothman]

Rock on Scubbatdan! That last post makes perfect sense to me. Heck, I even understand the diagram (guess that's not much too most but, it makes me feel better). Thanks a ton for your help. I'll post pics when I'm able.