Reliable and Flexible Switching System

[EMJunkie]

Chris there are a couple of things that you should look at in your circuit.

1. Critical:  The MOSFET avalanche protection is limited to the snubber network.  With a big inductive load that will either end up dissipating a lot of power or you will blow the MOSFET.  The flyback diode anode should be on the MOSFET drain, and the cathode on +DC where it is decoupled through a long inductance back to the MOSFET source.  The size of the decoupling capacitor depends on how much inductance there is back to the +DC supply.   This is particularly true given that you have a 1 Ohm gate turn-off resistor.

2. Design Improvement:  One section of the MCP1403 should be more than adequate for each MOSFET.  If you are going to drive more than 4.5A of gate current, you will have more issues with layout than driver strength.  The only reason that I would allocate by halves of that driver to one MOSFET would be if that made a big difference in the parasitic inductance in the layout.

3. Design Improvement:  You should place a 200uF capacitor in series with a 0.5 Ohm resistor across C4.  This will keep the filter L1/C4 from resonating uncontrollably when the MOSFETs are driven near 3kHz.

4. Design Improvement:  C5 should have a 47 Ohm or so resistor in series so as to limit the peak current load on the ATMEGA.  Otherwise you can kill the output pin from electromigration.

5. Design Consideration:  Z1 will only be effective if it has a very low inductance between the MOSFET gate and source.  Also, a typical zener will not act quickly enough to protect the MOSFET gate.  A TVS device rated at 16V that will trip by 20V would be a better choice.

5. Documentation Error:  The notes say D2 is for asymmetric gate drive.  It should say D3 and R4.

Hey MarkE,

Excellent! Thank you! We are a step ahead! Anyone an Eagle expert? Anyone like to put these changes MarkE has suggested/proposed into an updated schematic?

Thanks MarkE! Excellent Post!

All the Best

  Chris

[MarkE]

Hey MarkE,

Excellent! Thank you! We are a step ahead! Anyone an Eagle expert? Anyone like to put these changes MarkE has suggested/proposed into an updated schematic?

Thanks MarkE! Excellent Post!

All the Best

  Chris

Chris, you are welcome.  One thing that may be as important as the design itself is what tools you decide to use to express it in.  The last time I looked you could use Eagle for free if the design is only one page.  You might want to conduct another survey to see what tools people use.

[MarkE]

Gunther has put a lot of effort into this design:
http://www.source-for-innovations.com/switch.htm

I have used the circuitry myself and it works quite well.


@MarkE

Jump in here Mark, make improvements and post some EAGLE files we can use to build breakout boards.  As sharp as you are in this area it shouldn't take you more than an hour or two to get us all setup.

Doug, I use OrCAD.  Is Eagle the choice around here for low cost?

[EMJunkie]

Gunther has put a lot of effort into this design:
http://www.source-for-innovations.com/switch.htm

I have used the circuitry myself and it works quite well.


@MarkE

Jump in here Mark, make improvements and post some EAGLE files we can use to build breakout boards.  As sharp as you are in this area it shouldn't take you more than an hour or two to get us all setup.

Hey Dog-One,

Yes its a very swish unit! Very professional looking! Thanks for posting!

@All

Have seen the FEZ Hydra Board has had a price drop. This board is open source also. See: -->FEZ Hydra - Open Source Board<-- This is a 240Mhz ARM9 Processor (running at 200Mhz). Its .NET Gadgeteer compatible. Its got loads of extra cool features.

It does have only 4 PWM Pins. This can only allow for dual H-Bridge Mode, and single switching mode.

Ideally it would be nice to have a board with all the Microcontroller built in, but it may not be practical and may push the cost up dramatically.

Any thoughts on this?

All the Best

  Chris

[Dog-One]

Doug, I use OrCAD.  Is Eagle the choice around here for low cost?

I use DipTrace, but have had to learn EAGLE as it appears to be more compatible in the community.  Concepts are the same and there are a lot of tutorials out there to get up to speed quickly.