N-Channel mosfet safe operating range help (brushless esc)  - Page 1
Forum section: electronics / general

author: bigjoncoop
author_rank: Regular Contributor
timestamp: June 09, 2022, 02:08:11 am
content: Hey,Hey guys I got a quick question about safe operating range of a particular and channel mosfet. Trying to purchase some brushless motor ESC (speed controllers) and there's not much info or reviews on them. They are rated to handle the voltage and amperage I will throw at them but just I want to make sure.There using QN3109 N-Channel mosfets which have:30volt - VDS (Drain-Source Voltage)and154amp - Is (Continuous Source Current)*(Complete Specs Below)All of our brushless motor ESC use 6 mosfets, 2 for each motor winding.In my particular situation each ESC will see:Between 25.2v(briefly) and 19v.&A maximum Current of MAYBE 35a - 40a for 1 or 2 seconds max.So I'm curious of your guys's thoughts on if these mosfets are capable of this...These particular brushless motor speed controllers are manufactured by a well-known brand. They are advertised to work I work with 6s batteries (25.2volts) and rated at 45amps.So they're advertised specs say they will work just fine, but in this situation I would rather make sure the mosfets are actually capable of the manufacturer's specs.Thank You for you help / advice!DATASHEET: (images below)https://drive.google.com/file/d/1B0YnRxAyfzqfwwsUTAo7Cm9ho7vRkPMH/view?usp=drivesdk

author: thm_w
author_rank: Super Contributor
timestamp: June 09, 2022, 09:35:20 pm
content: http://www.ubiq-semi.com/Quote from: bigjoncoop on June 09, 2022, 02:08:11 amWhat is the brand/model?I would trust the FETs I think its more a question of is the product properly designed and what continuous load it can take thermally.You could run it continuously and monitor the board temperature.

author: snarkysparky
author_rank: Frequent Contributor
timestamp: June 10, 2022, 05:31:20 pm
content: Most important is if the mosfet gate drive is going full on.Datasheet says 1.5 mohm if driven with 10VDissipation = .0015 * 40 * 40 = 2.4 WIf they are mounted properly and gate drive is sufficient then 40A is no problem

author: Benta
author_rank: Super Contributor
timestamp: June 10, 2022, 07:03:56 pm
content: That MOSFET is too small for your demands.Let's take maximum current first: the 154 A is at acasetemperature of 25 C. That's utopic. If you're in very controlled surroundings, anambienttemperature of 25 C can be possible. That drops max. current to 29 A. That would be an extremely marginal design,though.An ambient temperature of 70 C would be the prudent choice.Max. current has now dropped to 23 A, well outside of your specs. 1...2 seconds can be regarded as DC, not as pulsed.Alternately, you'll need to cool it properly. At a case temperature of below 100 C we're back in business. That will need quite a bit of PCB copper under it.The SOA calculation is more difficult. This depends a lot on your switching times. The toughest is mostly turn-off, where decreasing high current flow transverses increasing drain-source voltage. You'll probably need to do a SPICE simulation on that to see if you exceed the SOA.You do know that the QN3109 is obsolete?