So of course I am always setting my goals high and this is no exception. I am looking to put together a 12v 300-350 amp pwm motor control. I am planning on using a pic for the operator interactions, (pwm parameters, 8-seg displays, start/stop, backup relay disconnect) which i have under control. My problems begin with the pwm driving circuit and paralleling the mosfets to reach these power levels. The drive only needs to be unidirectional with a duty cycle around probabaly 1-3 min on 30+ min off. I have seen multiple designs use dedicated Mosfet Driver ICs but I wasn't sure if this was the way to go. What is the benifit of using a driver chip over over driving a transistor from the the 12v rail and the mosfet gates. Any suggestions or input is welcome,

 

A driver IC will simplify your drive electronics, and enable you to use N-ch power MOSFETS for both the high and low side. It would be very difficult for you to improve on the price/performance/simplicity by using discrete components.

As far as the power MOSFETs, take a look at ST Microelectronics' STV300NH02L - an N-ch Power STRIPFET (Vdss=24,Rds(on)=0.8m,Ids=280A). Id (pulsed) can be up to 1120A. However, you'd probably want to use two of them in parallel for each leg of your H-bridge, giving about 160A-170A per MOSFET.

 

You can also use

IRF1324S-7PPBF
24V 429A D2PAK-7
1mOhm RDSon

Will dissipate about 184W though! Which I would think to be impossible for the D2PAK. Try IXYS, they make some really heavy-duty stuff that can be cooled.

Good luck! You may need to match some MOSFETs/Drivers in order to parallel many.

Steve

 

I think you need only one transistor or set of transistors and not a whole H-bridge, is that right?

 

I think you need only one transistor or set of transistors and not a whole H-bridge, is that right?

Yes, he DID say that. That simplifies the problem considerably. I'd just use a couple of high-amp MOSFETs to switch the ground side of the motor. He's going to need one heck of a flywheel diode across the motor.

 

As for the flywheel diodes, i've seen a lot of diodes with the surge rating around 6x the continuous surge rating which i understand why but given the low duty cycle can i get away under rating the continuous current. I"m having a hard time finding any diodes for reasonable prices that are 80Amps + to parallel. I"m not to keen on trying to parallel more than 4 of these things and trying to keep this controller size down including heatsinks.

As for component selections up to this point
Mosfets - 511-STB230NH03L TO-247 package Rdon 3.6 mOhm
*this choice was mainly due to the package to make it easier to mount to heatsinks
I wasn't sure the best way to manage mounting with the smaller options that
Were recomended above.

Mosfet Driver - MAX4420EPA+
Flywheel Diodes - ?
Controller - PIC (not sure which yet dependent on features i want to add)

 

Yes, he DID say that. That simplifies the problem considerably. I'd just use a couple of high-amp MOSFETs to switch the ground side of the motor. He's going to need one heck of a flywheel diode across the motor.

" Afast-recovery diode with a voltage and current rating at least equal to that of the [ Darlington ] transistor should be used _ordinary rectifier diodes are not suitable." At present gold -doped diffused-junction diodes or Schottky diodes are quite suitable. -- From " POWER CONTROL WITH SOLID STATE DEVICES BY IRVING M GOTTLIEB "
Just a thought--how about a combination of Schottky , rectifier diodes, high V FETs & trapisoidal gate pulses && slower repitition rate.

 

So i'm looking to use 747-IXTH240N055T and in looking at the datasheet and it is a 240 amp max Id but reading more it looks like in the t220 package its limited to around 75 amps. Is this accurate or am I misinterpreting something. It doesn't make sense to me for a manufacturer to have the higher rating of 240 amps only to stick it into a limited package.

 

Take a look at "Fig. 6" in the datasheet. The 120 Amp rating applies only to a TO263 case.

 

Where are you using this ?

I'm guessing an industrial complex because you sure aren't getting that output from a residential feed.

 

Thingmaker3 : ya its 120 amps with the to263 its 75 with the to220 but the mosfet is rated for 240 as seen at the top but i can't find any other packages that can support this.

AchMED: If you look above this is only a 12v system which there are quite a few ways to get that current residential or not.

 

Where are you using this ?

I'm guessing an industrial complex because you sure aren't getting that output from a residential feed.

Residential feeds are ten or twenty times the voltage specified, with only a tenth or twentieth of the specified current. If the needed transformer is not available, some car batteries in parallel will easily source the needed current for a brief experiment.

 

Thingmaker3 : ya its 120 amps with the to263 its 75 with the to220 but the mosfet is rated for 240 as seen at the top but i can't find any other packages that can support this.

The 240 amp rating is for short pulses with the die no hotter than 25 C. It the datasheet had a "safe operating area" chart, this would be evident. I am quite suspect of any MOSFET datasheet lacking said chart.

What kind of heat sink are you using? And are you prepared to run MOSFETs in parallel?

 

Yes planning on running several in parallel, the heatsink is one of my concerns. I was first looking into using

511-STV300NH02L but its a powerso-10 package that i'm concerned about mounting to a heatsink. I haven't worked with that package before and even running several in parallel gets my mind going of how to securely mount them. Thats why i turned to the to220 package or something smiliar just to make the mounting easier which i'm starting to think could just cause more issues.
The powerso chip is better suited but what is the best method of dealing with mounting them? The through pcb hole or the solder vias to a heat sink on the backside just don't seem like they would be enough.
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