100ish amps mosfet pwm circuit - Page 1
Forum section: electronics / projects

author: Boschi
author_rank: Regular Contributor
timestamp: May 11, 2017, 08:27:29 pm
content: so... somehow someone asked me if i could design him a 100 amps vape circuit, and well.. thats it.the circuit is powered by a 2S2P pack, composed of four IMR26650. At the output is able to give me 100 Amps at 7,4Volts (i contacted the battery producer, as soon as they give me the datasheet ill post it).i want to use an ATmega328 to do over discharge protection, thermal protection and things like that.a very important feature is the PWM. as im too lazy to reinvent the wheel, i want to use the arduino IDE, and as i dont want to mess with the registers, the switching frequency will be 500 or 1000Hzfor now i just selected the mosfet, wich is the AUIRFS 9409-7P (datasheet).i have done a bit of homework and just to be on the safe side i want to parallel more of them (2 or 3), in order to decrease the Rds and dissipate about 5 or less watts.my main concern is the switching power disspation.please help me out here, my math is still not this developed ( im just 18). tomorrow ill study something, i just need an AN or something like that.another thing that im not able to find is how to dimensionate cable for pulsed current. the battery impose me to use a 50% (or less) duty cycle at 0.1Hz @100A (at least, on a generic datasheet it was measured like this), but on the internet i didnt found anything about.im still a young player, if you see something that im missing please tell me! thanks.

author: Leon23
author_rank: Contributor
timestamp: May 11, 2017, 08:56:37 pm
content: Hey BoschiWelcome to the forum.Could you provide a schematic of your suggested solution? What is a vape Circuit?

author: firehopper
author_rank: Frequent Contributor
timestamp: May 11, 2017, 10:27:21 pm
content: vape circut probably means he wants to make a ecigarette aka vape device.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 12, 2017, 02:03:41 am
content: well 740W infront of the face of a 18yrs old noobs, thats something. a wire jumper diy fuse in a DMM is a lot safer than that... my advice, try to make smaller toy before moving to a big thing.

author: BravoV
author_rank: Super Contributor
timestamp: May 12, 2017, 06:39:27 am
content: Just take a wild guess what kind of current these people used in their vape ...https://youtu.be/Svyv8jgwq0Y

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2017, 05:51:20 pm
content: A simple gate drive method that works reasonably well is to just use a totem pole follower with an NPN and PNP transistor, similar to the output stage of an audio amplifier. There are some examples here:http://uzzors2k.4hv.org/index.php?page=flybacktransformerdrivers

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2017, 07:25:37 pm
content: True, but it's easy enough to add level shifting. One more transistor and a resistor will get you there. Of course there are also dedicated gate drive ICs.

author: Boschi
author_rank: Regular Contributor
timestamp: May 12, 2017, 09:52:34 pm
content: Quote from: Leon23 on May 11, 2017, 08:56:37 pmthanksQuote from: firehopper on May 11, 2017, 10:27:21 pmwoops, i thought it was its proper english name!Quote from: blueskull on May 11, 2017, 10:46:25 pmuhm.. before responding i should probably read deeplythis. as now im just trying to understand the source of that 42nF, and miller effect is not helpingQuote from: blueskull on May 11, 2017, 10:46:25 pmyep, you are right, 5v are barely enough to turn the mosfet on.nice thing theUCC27524, its 3.3v logic compatible and even available through RS!@james_s: its not a bad idea, but probably ill just stick with a mosfet driver. the totem pole (aka push-pull?) it takes up too much room if done with discrete components, and i want to use less space possible, after all, is still an handheld device!Quote from: BravoV on May 12, 2017, 06:39:27 amQuote from: Mechatrommer on May 12, 2017, 02:03:41 amyou are both right, this is not a toy, and im not treating it like a toy.even if im a 18yrs old noob this doesnt mean safety is not crucial for me, way before ill turn the schematic in someting that you could put near your face i want to stress it over its normal point of work for a while.also, i have already created a "little" box to play with. its my little 70A 250W beast.well, not mine really, im not a vaper. it worked flawlessly for few months before going in to the junkbox, but it was just a bare mosfet with a switch and few resistor, this would be something way better.thanks for the replies

author: Boschi
author_rank: Regular Contributor
timestamp: May 16, 2017, 07:38:58 pm
content: i was trying to ran the mat, but i have dubts about the meaning of Vds,off(page 4, the lower right corner), what actually mean?EDITWhy i cant see any mention of inductance in the FET datasheet? Am i missing something or is the D²Pak inductance free?

author: mariush
author_rank: Super Contributor
timestamp: May 16, 2017, 08:16:13 pm
content: Your battery may be able to give you 7.4v at 100A but what's the output voltage of your circuit? Surely you're not going to need 700 watts of output power...

author: Boschi
author_rank: Regular Contributor
timestamp: May 16, 2017, 09:00:43 pm
content: Well, actually yes.Not continuosly, 5sec on every 10, but i get wat you mean, i also hope the user will lower the power, otherwise the vapor will start exit out of his earsInviato dal mio A0001 utilizzando Tapatalk

author: Boschi
author_rank: Regular Contributor
timestamp: May 19, 2017, 04:21:04 pm
content: after digging a bit into the web i found my answers, and i ran the math.the circuit should work ok, the switching power disspiation should be in the mW range,but the D2pak has 7nH of inductance in the source and by paralleling 3 FET and the two driver the optimal Rgate should be about -2.6 Ohms, so... if i dont put any gate resistor the gate mesh resistance and the driver one should damp any ringing more than adeguately, at the cost of a slower rising/falling time, right?also, the calculated switching period (t2 and t3 Fig 4, page 6 of SLUP169) are respectively 7 and 34 nS, are them in the ballpark?

author: JPortici
author_rank: Super Contributor
timestamp: May 19, 2017, 06:27:09 pm
content: Quote from: Boschi on May 11, 2017, 08:27:29 pmOT: I saw this question posted various times in the last months in the various italian electronics facebook groups... are you the same guy who went on asking? (just curious)

author: Boschi
author_rank: Regular Contributor
timestamp: May 19, 2017, 07:01:50 pm
content: Hi, nice to see another italiananyway no, actually i didnt even know about the existence of facebook electronic groups, im active just here and on the italian Arduino forum.

author: Boschi
author_rank: Regular Contributor
timestamp: August 24, 2017, 10:19:46 am
content: im back!i designed the PCB of the power board and i already sended it to the fab (i whish i posted it before sending it in, i have already spotted some error in the layout). ill discuss it better once i assembly it.now im in the process of routing the logic board. ill post some screen of the circuit once i get home.incredibly i fitted almost everything on the board, and i still have 1/3 of the board free.i just realized that the logic board would be very close (~1cm) to the power board, and thanks to the high current flowing around i should probably lay out a bit better the crystal part. its a ground plane under the crystal enough or i have to do something even to the trace that get connected to the uC? they are pretty short (3cm i think)Regards