I'm in the process of developing a 3-phase inverter and I'm designing a flyback DC/DC for the gate drivers. I feel this is a common use case so I expected I'd find more flyback transformers with a single primary, an aux and 4 secondary windings (one for each phase high-side switches and one for the low-side switches). So far I've been able to find only TDK VGT series, but I'm not happy with the turn ratios and inductances.
https://product.tdk.com/system/file...ate-drive/catalog/trans_gate-drive_vgt_en.pdf

Am I wrong in assuming this would be a common use case and I'd expect to find more transformers, or am I just not searching for the right thing?

This will not go into production, I'm just looking to make a few prototypes so I'm looking to avoid designing my own custom transformer.

 

There are DC/DC converters for isolated gate driver application but it's one converter for each switch, not common converter for all three phases. There is high du/dt involved and converter isolation capacitance should be lower than in less demanding application. Here are examples that I found

IGBT DC/DC converter driver RECOM

Mornsun power module for IGBT driver

 

I feel this is a common use case

Not so common that I have ever heard of it. Typically, gate driver ICs use a flying capacitor to produce the high gate voltage.

 

There are DC/DC converters for isolated gate driver application but it's one converter for each switch, not common converter for all three phases. There is high du/dt involved and converter isolation capacitance should be lower than in less demanding application. Here are examples that I found

IGBT DC/DC converter driver RECOM

Mornsun power module for IGBT driver

The drive circuit I'm designing will need 18V at 6A, is that really something these IC's can take? Their maximum current ratings are in mA, I feel these would be used for lower switching speed applications.

 

The drive circuit I'm designing will need 18V at 6A

Is the gate driver power 108 watts? 18V x 6A continuous. The DC/DC converter supplies average power to the gate driver and the gate driver supplies actual turn on and turn off pulses. Average power is then much less than peak power.
If average power requirement is 108w, it's likely that you have to design your own gate driver supply.

 

Try coilcraft.com. I have used their gate drivers for 40 years. Back to when we were driving the Base of transistors. lol
coilcraft gate drivers

 

I’ve seen the technique in application notes as an alternative to the usual charge pump, the advantage being that it can give 100% duty cycle.
However, anyone making a 3-please inverter is probably going to need a lot of custom magnetics, so one more little transformer is neither here not there.

 

What duty cycle range do you need. Transformers do not do well at near zero and near 100%. I have made them go 0 to 100% but it is not easy. Ask questions if you want.
Many of the isolated gate driver ICs will not do over 90%.

 

What duty cycle range do you need. Transformers do not do well at near zero and near 100%. I have made them go 0 to 100% but it is not easy. Ask questions if you want.
Many of the isolated gate driver ICs will not do over 90%.

If he's thinking of a flyback transformer with four outputs then the idea is to produce a floating DC supply for each transistor, not to drive the gate with a transformer.

 

I expected I'd find more flyback transformers with a single primary, an aux and 4 secondary windings (one for each phase high-side switches and one for the low-side switches) .......... but I'm not happy with the turn ratios and inductances.

I post #1 you are talking about a transformer.
With out a schematic I can't help much. The words are confusing. Some of us think you are looking for an isolated DC to DC supply like in post #2.

The drive circuit I'm designing will need 18V at 6A, is that really something these IC's can take?

The Gate can take 6A but that is for a very short time. (Duty cycle is very low) The average current is very low.

I expected I'd find more flyback transformers with a single primary, an aux and 4 secondary windings (one for each phase high-side switches and one for the low-side switches) .......... but I'm not happy with the turn ratios and inductances.

flyback transformer?
It sounds like you want to drive 4 IGBTs with the same signal. I don't understand.

Lets start over. What are you making? Are you pushing power into the power line in 3 phases? 120V or 230V ac 60/50hz?

 

Like this:
Though it only really needs three outputs, as the negatives forboth lower transistors are common. (Drive signals and gate resistors not shown)

 

Would this work for you?

 

Though it only really needs three outputs, as the negatives forboth lower transistors are common.

Just to make sure we are on the same page. You are making the power supply for the Gate Driver IC? You are not sending signals through the transformer.
I know if three winding high isolation transformers but not 4 or 5.
You can combine the bottom two supplies. Not the top two.

 

Just to make sure we are on the same page. You are making the power supply for the Gate Driver IC? You are not sending signals through the transformer.
I know if three winding high isolation transformers but not 4 or 5.
You can combine the bottom two supplies. Not the top two.

It's a bit of a detective story to work out what the TS wants to do, but the only explanation that makes sense is that he is making a power supply for the gate drivers, to use instead of the usual charge pump.

 

What about the isolated drivers on a chip I linked? Are they not a decent solution? They provide up to 10A gate drive of up to 10000pF.

 

What about the isolated drivers on a chip I linked? Are they not a decent solution? They provide up to 10A gate drive of up to 10000pF.

Yes, they'd go beautifully with the flyback supplies.
With the flyback supplies, you can have the low side drivers isolated from the control circuitry, and you'd need an isolated driver for that.

 

Apologies everyone, got caught up with life and forgot about this post

The DC/DC converter supplies average power to the gate driver and the gate driver supplies actual turn on and turn off pulses.

I've realized this in the meantime, the peak power is provided by the decoupling capacitors and the lower power DC/DC charges them in the downtime. This makes perfect sense for my use case so it's probably the solution I'll go with.

If he's thinking of a flyback transformer with four outputs then the idea is to produce a floating DC supply for each transistor, not to drive the gate with a transformer.

This is entirely correct, my original idea was to use a flyback supply to create 4 floating voltages to power the gate drivers. Not quite like the schematic you posted, I'm designing a 3 phase inverter and I was looking for, as the original post states, 4 secondary windings (one for each phase high-side switches and one for the low-side switches).

Would this work for you?

As for the driver, it would probably work, but this post isn't about the driver, it's about finding a way to supply 4 of those drivers with floating supplies.