EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: RossK on January 15, 2013, 06:11:03 am
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I'm trying to setup a half H-Bridge drive for DC motors (10v-18v and 10A-50A), i'm expecting to drive them from a PWM signal in the 30-40kHz range (i'm open to being convinced otherwise, but i need to keep in the ultrasonic range 24kHz+).
I'm looking at this driver http://www.mouser.com/ds/2/405/slusaf9a-120356.pdf (http://www.mouser.com/ds/2/405/slusaf9a-120356.pdf)
and these N channel MOSFETs http://www.mouser.com/ds/2/302/PSMNR90-30BL-104176.pdf (http://www.mouser.com/ds/2/302/PSMNR90-30BL-104176.pdf)
This is my first project with MOSFETs and i'm feeling a little |O and a lot :-//
I believe I will need to include schottky diodes and a cap across the bridge to manage ripple - my questions are:
* Will this bridge drive these fets successfully?
* My attempt at mathing this out estimates that aprox 1.14A is needed to drive the fets at their rated turn-on time... will current limiting resistors be needed?
* What is the minimum and maximum duty cycle this bridge can be run at to keep the high-side driver operating? and how the heck did you answer this question?
Thanks a bunch!
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I'm trying to setup a half H-Bridge drive for DC motors (10v-18v and 10A-50A), i'm expecting to drive them from a PWM signal in the 30-40kHz range (i'm open to being convinced otherwise, but i need to keep in the ultrasonic range 24kHz+).
Not necessarily trying to convince you, but still. DC motors are usually driven at significantly lower frequencies, like 500 Hz or even below. If the motor absolutely needs to be silent then i guess you must drive it beyond the hearing range. That however will require more attention to the components and circuits used for driving
I'm looking at this driver http://www.mouser.com/ds/2/405/slusaf9a-120356.pdf (http://www.mouser.com/ds/2/405/slusaf9a-120356.pdf)
and these N channel MOSFETs http://www.mouser.com/ds/2/302/PSMNR90-30BL-104176.pdf (http://www.mouser.com/ds/2/302/PSMNR90-30BL-104176.pdf)
Those should work. The total gate charge of the FET is a bit on the high side at 243 nC, but at this low a switching frequency it won't really matter. A quick calculation makes the average gate current just 11 mA so no worries there.
This is my first project with MOSFETs and i'm feeling a little |O and a lot :-//
But if/when it works you'll feel %-B
I believe I will need to include schottky diodes and a cap across the bridge to manage ripple - my questions are:
* Will this bridge drive these fets successfully?
* My attempt at mathing this out estimates that aprox 1.14A is needed to drive the fets at their rated turn-on time... will current limiting resistors be needed?
* What is the minimum and maximum duty cycle this bridge can be run at to keep the high-side driver operating? and how the heck did you answer this question?
Thanks a bunch!
You already have substrate diodes across the bridge inside the FETs. The datasheet even give specs and the reverse recovery time is 67 ns and charge is 123 nC - that is a fast diode, i.e. no problem and you do not need anything else.
- Yes, it will drive the FETs
- Yes, do include gate resistors. Heavy overdriving causes ringing in the FET - you don't want that. Off the cuff 100 ohms and adjust as needed,
- the minimum and maximum duty cycles can be calculated from the steady state current drain of the gate circuit vs the capacitor available to supply the voltage. MAx duty is the time the cap is able to maintain Vg at saturation level and min duty is zero (unless i forget something that affects it).