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DC motor Controller

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EDY19

Mon Apr 03 2006, 11:29PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
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Posts: 408

Im building a motor controller for a school funded project, and I need to make 3 H-bridges. I have the mosfets (IRFZ20) which are rated for 40W maximum dissipation. In my application, 2 h bridges will be operating with each mosfet dissipating 1.6W, and the other mosfets will be dissipating 6.4W each. Do the 1.6 watters need heatsinking? If so, Im guessing mounting them all on one small insulated heatsink would be fine? Also, does anyone have suggestions on a PCB for the TO220 devices to get them all in a straight line for easier mounting to the heatsink? I'll try to work something out on ExpressPCB as well. Thanks!

Part Scavenger

Tue Apr 04 2006, 02:59PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

I think there was something in the "H bridge design pictures" on the old fourm that had this design.

Reaching and blackplasma I believe had designs to this effect?

ragnar

Wed Apr 05 2006, 09:00AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

I've drawn a demo of my track layout here for you:

If you're driving with a four-secondary gate-driver transformer, reverse the phase of the inner two.

The red/green crosses denote the connections to the gate-driver transformer.

The two red lines are e.g. 10-ohm gate resistors, the two green lines are the gate resistors of the inverted-drive FETs. The BLUE line is a single link on the board.

Top-left is DC positive input, bottom-right is DC negative input. Bottom-left and top-right are the switched output.

Note the "G..D..S..." - Gate-Drain-Source of MOSFETs, with the hot (heatsunk) side facing the top of the image. Same with the diodes, "K..A.." with the hot (heatsunk) side facing the top of the image.

You can bolt all devices (FETs and diodes in TO-247/TO-220) along a straight heatsink.

Of course, you'll need to make the traces much thicker, but this is the layout I've been working with.

If necessary, you can put zener clamps between gate-source connections where the GDT windings attach to the board - make the pads larger so you can fit the gate resistor, zener, AND transformer winding onto them.

Good luck =)

[Edit: Go here

to learn how to post pictures.]

Steve Conner

Wed Apr 05 2006, 10:22AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Gate drive transformers are no good for motor controllers because the gate drive signal needs to have a DC component. Nevertheless most of the things BP said still apply.

Steve Ward

Thu Apr 06 2006, 10:21PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I joined a robot team here at school and the day before the competition i found one of the motor controllers the team had from last year was all goofed up, so i built a new PWM full-bridge driver. I basically copied Conners brick gate driver/ flyback driver. Since our on-board computer was doing all the PWM and direction signals, all i needed was 2 gate drivers, 4 fets and 2 diodes. It worked exactly as planned

. Anyway, the boot-strapped driver seems pretty ideal for motor drivers. You just have to be sure you turn the lower fet on at least once (so that you charge up the cap that supplies gate drive for the upper fet).

EDY19

Thu Apr 06 2006, 11:14PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

There is actually no GDT like other people said, and I got some TC4427 dual 1.5A mosfet drivers so there will be just three driver chips and 12 mosfets (3 seperate H bridges for left and right motors, and the up and down motors (its an underwater robot). I think I have a design too that should work well for each H bridge.
Edit- got the PCB drawn up including the drivers and a regulator for the drivers. Just wondering how thick of traces should I use for 4 amp motors with a PCB with 1 ounce copper deposition? I can put a layer of solder over them too in order to add some current carrying capability.

ragnar

Fri Apr 07 2006, 07:07AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Go as wide as you can... 10mm + tinning wouldn't be unreasonable. Would you agree, Dr Conner?

EDY19

Fri Apr 14 2006, 06:45PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I found a better way, and it wasn't complicated and it didn't get too messy, either. The thick Red and Black leads are the power for the 4 bridges, and the skinny wires are the wires that go to the gates- 2 for each bridge for forward and backward. The Thick red and black wires on the Bridges with the middle stripped off go to each motor. I still have to make the driver circuit for the gates, using TC4427As, dual 1.5A gate drivers. I know its overkill for only turning on and off the mosfets less than 1 time every 3 seconds or so, but thats my SSTC bug getting into other things i do

. Also, The mosfets shouldn't need heatsinking because each one is only passing about 4 amps, and the on resistance of the mosfets is .1 ohms, so I^2*R losses are only 1.6W each.

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