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Thanks for the schematic, charged! I'll order up the FETs when I get home tonight and hopefully those and the rest of the parts I ordered will be in by the end of the week.
I appreciate everybody's help with this. This will be (I think) a pretty unique build. I'll take pics along the way and post the results when I'm done.
I appreciate everybody's help with this. This will be (I think) a pretty unique build. I'll take pics along the way and post the results when I'm done.
Quick question.
If you use the 3.7v side too long and then use the 5v side later won't you have an unbalanced battery situation for possible failure of the batteries due to their power and maybe go kaboom?
I ask this as I designed and built a box mod capable of dual operation at 3.7v and 5v. Both worked as designed but then I thought about the potential unbalanced batteries and stopped using the 3.7v side just to be on the safe side.
If you use the 3.7v side too long and then use the 5v side later won't you have an unbalanced battery situation for possible failure of the batteries due to their power and maybe go kaboom?
I ask this as I designed and built a box mod capable of dual operation at 3.7v and 5v. Both worked as designed but then I thought about the potential unbalanced batteries and stopped using the 3.7v side just to be on the safe side.
There is only one battery. The jumpstart circuitry bumps it up to 5v. One button will pull 3.7v directly (bypassing the circuitry), the other will pull 5v from the USB connector.
1/4W should be plenty for those 100k resistors, right?Here you are.
According to Scottbee, diodes aren't necessary as the FETs will not allow backfeed.
Yes... source to your battery or USB voltage, drain to the atty.
You don't need to use the battery. Putting the switches in the correct places in a resistor network on the gate will allow you to control the gate current, and therefore the drain current. Limiting the current across the atomizer controls the voltage drop. I do this on my pass through, but I use a 100ohm pot and a few 2n4403's as a current sink instead of the FETs, which are too fragile IMO.
Woah.... not with the FETs that he is using. There is no way that I would try to operate those FETs in the linear range at all (they're not really designed for that). You try to dissipate anything more than a watt or so across them, and they'll smoke. They're just too small without enough surface area to dissipate the heat. Use them as "switches" with just their small parasitic internal effective resistance and you'll be fine.
If you want to generate multiple voltage outputs from a single source.. there are better ways.
You could sink the excess current elsewhere, but yes, device selection is important. That is why I like the 2n4403 for my switches, I can drive a few of them in parallel and get 2v ~ 4.2v across the atomizer from the USB. Just sayin that it could be done without the battery if desired.
I absolutely agree. But... if he wants to get the full 5V output (or close to it), he'll need to select a transistor that has good linear performance and a very low parasitic voltage drop as well. Right?
Your USB port would need to be able to push almost 2A to get a full 5v across the atty. Most USB ports can't do that anyway, but some can. Whatever the P type analogue of the IRF150 is would probably work, it has a saturation resistance of ~0.5ohms or thereabouts, so you could get about 4.7v across the atty.
No.. your terminology is correct. Atty = atomizer.
And for the sake of this conversation... a 2.7Ω cartomizer is close enough to most of the atomizers that we are running.
Carry on!
(P.S. But a transistor with an RDSon of .5Ω is going to have way too high of a V-drop for our use. At 2A you'd be dropping a full volt at the transistor.)
Try this out guys !! VERY COOL
Design Resources | National Semiconductor ? Online Design Tools, App Notes, Eval Boards, Models & Software
Design Resources | National Semiconductor ? Online Design Tools, App Notes, Eval Boards, Models & Software
The FETs and resistors from digikey have arrived, but the battery connector from madvapes has not. In any case, most of my tools are in storage at my mother's house and I won't have a chance to retrieve them until the weekend. Hopefully I can get this all made up and working by monday. Should be interesting. 
The FETs and resistors from digikey have arrived, but the battery connector from madvapes has not. In any case, most of my tools are in storage at my mother's house and I won't have a chance to retrieve them until the weekend. Hopefully I can get this all made up and working by monday. Should be interesting.
Just remember: most electronic devices run on "smoke". And if you let the smoke out, they will quit working.
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