Reliable and Flexible Switching System

[MarkE]

Hello MarkE

Well then I believe we have to agree on the task......
How LOW of a voltage and how HIGH of a current?

How much current *should* an O.U. device have to switch?

Usually when dealing with D.S. or S.M. devices, my biggest problem has been to switch *High* voltage , not current.

ie: EMF generated from inductor switching can give very *high* voltage spikes.......

These SiC can be paralleled very easily for higher current if need be, and have *almost*  unmatched switching speeds and one of the fastest body diodes available.... and better thermal characteristics then most lower voltage mosfets and Avalanche rated.

....they cost more and driver design is more involved than required for the garden variety MOSFET .

Maybe designing different *Driver Modules* that can be interchanged easily would be the solution.  I for one would want to continue using my SiC MOSFETs!

take care, peace
lost_bro

I like SiC MOSFETs, they are killer for DC-AC inverter, and vector controlled motor drive designs.  But they are not what I would use for a 100V design.  You should never have to deal with spikes more than 4X Vcc.  I see a lot of people designing stuff where they put a diode around the MOSFET.  That doesn't protect the MOSFET.  When the MOSFET turns off, an inductive load will flyback, always increasing the drain to source voltage.  A properly designed clamp redirects the current typically limiting the voltage to no more than Vcc*2, but in some cases such as in some resonant designs:  4X Vcc.  A lot of the "magic" is in understanding how to do the circuit board layout to minimize stray inductance in the switching loop.

The amount of gate charge that is required depends on the die size and number of devices.  If we just parallel parts then we throw more and more power away at getting the devices to switch.  All high efficiency power converters I am familiar with carefully choose the power switching and energy storage components according to the intended load.  The switch voltage and current rating should be reasonable for the task.  What might be helpful is to come up with as simple and  low cost a board as possible that just has the driver, the switch and any monitoring circuits without the isolation components.  That would plug into a board that has the isolation components.  Then you could have several different incarnations of that simple board using components that are well matched to a reasonably narrow range of specifications.  The trick is to do that in a way that people can work with these things and still keep the inductance down.

[EMJunkie]

Maybe designing different *Driver Modules* that can be interchanged easily would be the solution.  I for one would want to continue using my SiC MOSFETs!

Hey Lost_Bro,

Agree Fully! Make it as flexible as possible! Imagine the idea, Plug N' Play FET Slot for easy swap outs of FET's! I think the TO247 Package for the best range of High Speed FET's. We could use a 3 Pin Terminal Block if we had to!

@Dog-One,

I agree. Terminals for easy connection of Scope Probes for Oscilloscope and Spectrum Analyser is really important too!

@MarkE

What might be helpful is to come up with as simple and  low cost a board as possible that just has the driver, the switch and any monitoring circuits without the isolation components.  That would plug into a board that has the isolation components.

For sure this is a good idea! Even a board that has all the driver Circuits up to the isolation barrier! Then we could have a Plugin board for the switching and we could have as many as one needs of these with different FET's for different Jobs and vice versa for the Driver Circuits!

Problem is this would start getting more expensive the more boards that would need to be used. Most people are doing it tough on the money front and if this is to be a success, we need to do the best we can to keep the cost down!

All the Best

  Chris

P.S: If we have 100 people all join this movement and want a board it will make this much cheaper than 5 or 6. Common Lurkers, Join the party!

[lost_bro]

  A lot of the "magic" is in understanding how to do the circuit board layout to minimize stray inductance in the switching loop.

..... carefully choose the power switching and energy storage components according to the intended load.  The switch voltage and current rating should be reasonable for the task.  What might be helpful is to come up with as simple and  low cost a board as possible that just has the driver, the switch and any monitoring circuits without the isolation components.  That would plug into a board that has the isolation components.  Then you could have several different incarnations of that simple board using components that are well matched to a reasonably narrow range of specifications.  The trick is to do that in a way that people can work with these things and still keep the inductance down.

Well I agree, in as much as everyone will have a *different* end use for the device, we must work out a *buildable modular* type system that will accommodate a range of different MOSFETs while keeping an integrated Low stray inductance design of the *switching loop*.

What type of isolation components do you recommend?  Are we talking optos or emulators?

Do we use an integrated mosfet driver with active miller clamping?   What about a driver with integrated schmidt trigger waveform shaping?  pro, cons anyone?

What's the max. frequency we are shooting for?

I think a design for a double ended GDT driver would make a great modular board option.

take care, peace
lost_bro

[EMJunkie]

Hi All,

I am going to share a Circuit that Is NOT mine Its the next step to the Circuit I posted in the first post.

Its from a friend of mine. I can not guarantee this is complete and or working.

However, this is what My Unit is based on in my original post. Its works very well, in fact I have not had a single issue with it!

Its an independently Driven H-Bridge, meaning each FET is switched individually from the Micro Controller.

All the Best

  Chris

[avalon]

Hi MarkE,

I agree! Choosing the best components for the job is essential!

I have used: 5N3003
Turn-On Delay Time: 60ns
Turn-Off Delay Time: 220ns

So far this is one of my favourite N Channel MOSFET's!

All the Best

  Chris

Have a look at this...


~A