motor driver (without pre-driver ICs)-possible? - Page 1
Forum section: electronics / beginners

author: sjd.aliyan
author_rank: Contributor
timestamp: May 09, 2016, 08:51:55 am
content: I want to use this driver for both servos and steppers.i think a processor like STM32F3xx or STM32F4xx and couple of logic level mosfets could do this job.is it possible or i forgot something?

author: danadak
author_rank: Super Contributor
timestamp: May 09, 2016, 09:34:37 am
content: Its a problem because the UP outputs cannot get the charge out of themotor driver fets fast enough. The result is driver fets spending too muchtime in linear region, overheating. Possibly not even getting fets intosaturation. This is all dependent on PWM frequency, thermals, etc..A good motor driver H bridge has thermal management, gate chargemanagement, current limiting...Wise to use one.Infineon, On Semi, TI, ST......Regards, Dana.

author: sjd.aliyan
author_rank: Contributor
timestamp: May 09, 2016, 11:16:45 am
content: Almost all cortex series(A-M) theoretically have up to 24 mhz IO pins.and new mosfets can be driven at high frequencies.so i don't see a problem about speedI agree logic level mosfet have less diversity than normal mosfet so gate driver is necessary .current limit needs a DAC and a Op-AMPPre designed ICs are limitation and they're designed for a specific rules and applications.I prefer to design from scratch.anyone can help?

author: langwadt
author_rank: Super Contributor
timestamp: May 09, 2016, 11:43:20 am
content: Quote from: sjd.aliyan on May 09, 2016, 11:16:45 amthe 24MHz are at no load, there is a reason for the gate drivers that can deliver several amps of current. The gate of a mosfet is basically a big capacitor it takes a lot of current to switch it fast

author: danadak
author_rank: Super Contributor
timestamp: May 09, 2016, 11:44:42 am
content: "Almost all cortex series(A-M) theoretically have up to 24 mhz IO pins.and new mosfets can be driven at high frequencies."Yes, at 20 pF Cload, but looking into gate of low Rdson power mosfetanswer is a problem of large gate charge that has to be removed/addedto effect switching, to avoid spending much time in the linear region, themiller region. Typical gate drivers handle amperes of current when drivinggates, clearly not ARM I/O pin capable.http://www.infineon.com/dgdl/mosfet.pdf?fileId=5546d462533600a4015357444e913f4fhttps://www.fairchildsemi.com/application-notes/AN/AN-558.pdfhttp://www.microsemi.com/document-portal/doc_view/14692-mosfet-tutorialRegards, Dana.

author: sjd.aliyan
author_rank: Contributor
timestamp: May 09, 2016, 12:16:16 pm
content: OK,i accept your reasons on gate driver i would use a lm5109,it think it would be good enough it supports current up to 1 amp.what mosfet do you suggest for 10 amp brushless motors?witch one of mosfet or power transistor is suitable for this application?

author: danadak
author_rank: Super Contributor
timestamp: May 09, 2016, 12:55:23 pm
content: If you contact sales rep/fae at vendor of choice they can guideyou based on your requirements. Plus they will have market knowledge."For example we MAKE 25,000,000 of these a year, they are a highrunner, and costs are reflected by that whereas your other choicedoes not get much volume (read won't be around much longer)"................If you go to vendor site they have tools that filter out for the package,current, V you want to make life easy.Regards, Dana.