# How to Choose Best 650 V , 60A GaN Transistors for Switching Losses ?

#### Ali Z

Joined Mar 22, 2022
23
Hi ,
I will calculate GaN transistors switching losses in Dc DC converter Systems.
The formula is , Psw= Vds*Id*fsw*((Ton+Toff)/2) .
Vds and Id are drain-source voltage and drain current of the device at OFF and ON intervals respectively.
fsw switching frequency and Ton is switching time during ON transition, and Toff is switching time during OFF transition.
Ton and Toff times important , how much lower its best to get less switching loss. So how can I undertand from datasheet which GaN transistor or Fet or mosfet is best for this ?

#### ronsimpson

Joined Oct 7, 2019
2,878
Formula = Id at Ton is the same as Id at Toff. This is probably not true.
Formula has no DC losses.
A MOSFET with low Rds-on will have low DC losses but probably high AC losses.
I use a spread sheet like Excel. Make a column for each device. List data from data sheet. Some GaN devices do not have good data for AC losses. They are new and have not been tested well.
In the case of GaN you can switch at 10x faster.
Make a place for data for each device.
Make a place for data for your power supply. 450V. turn on current=15A Turn off current=20A. Frequency=500khz
Make a place for formulas. DC losses, AC losses, Gate Drive Loss, total loss,
 company GaNPower Transphorm Nexperia GaNPower Vds 650 Ids 15 Rds on 0.085 Qg nC 3.9 Ton nS 4.9 DC losses =formula for DC losses =formula for DC losses =formula for DC losses =formula for DC losses

When you are done, please post your work. We also want to know.

#### MrSalts

Joined Apr 2, 2020
2,767
First, there are only a handful of GaNFET devices that can handle that voltage/current. Second, actual switching power dissipation is much more complicated than your simplified formula. The time to charge the Gate is critical and depends on your drive circuit. If you assume some high / fast switching current drive with little or no resistance, you can start with your formula.
you can also discard the devices with the highest input gate charge.
you'll have a tough time beating this device but, it really depends on your board layout and space.
https://www.digikey.com/en/products...SBAAYRJgvmx8ABMPL18AoNDwhSUQZn0AcUxpdHwhbgUgA

#### Ali Z

Joined Mar 22, 2022
23
Formula = Id at Ton is the same as Id at Toff. This is probably not true.
Formula has no DC losses.
A MOSFET with low Rds-on will have low DC losses but probably high AC losses.
I use a spread sheet like Excel. Make a column for each device. List data from data sheet. Some GaN devices do not have good data for AC losses. They are new and have not been tested well.
In the case of GaN you can switch at 10x faster.
Make a place for data for each device.
Make a place for data for your power supply. 450V. turn on current=15A Turn off current=20A. Frequency=500khz
Make a place for formulas. DC losses, AC losses, Gate Drive Loss, total loss,
 company GaNPower Transphorm Nexperia GaNPower Vds 650 Ids 15 Rds on 0.085 Qg nC 3.9 Ton nS 4.9 DC losses =formula for DC losses =formula for DC losses =formula for DC losses =formula for DC losses

When you are done, please post your work. We also want to know.
I am using DC DC converter ( Multi device interleaved boost converter) . it will boost 27kW battery which is 201.6 volt Dc input voltage to the 650 V dc . So the switching process will be with GaN transistors . so I have to wrk 60A Gan transistors with 650 V.
Actually Ton and Toff switching time is getting after simulation. But How can I understand from datasheet Ton and Toff will be short time ? So How i will choose best GaN for this process.

#### MrSalts

Joined Apr 2, 2020
2,767
Here is another good one

https://www.digikey.com/en/products/filter/transistors-fets-mosfets-single/278

You'll have to look at the datasheets to get the fall time and rise time. These values are more important than the turn off delay or turn on delay. The fall time is the time when switching power will be seen.

Use a parametric search tool on an electronics distributor's website to look at important parameters across many devices.
here is the link to many Mosfets/GANFets on digikey.com
https://www.digikey.com/en/products/filter/transistors-fets-mosfets-single/278

You can select GanFET as type of device and select your voltage and current. Then look at datasheets for details on the few devices left out of the thousands in that category.

#### Ali Z

Joined Mar 22, 2022
23
Rise time and fall time is lower for GS-065-060-5-B-A than GS66516T.
Should we check Switching energy during turn on and turn off ?
I mean how much is lower , switching power loss lower ?

#### ronsimpson

Joined Oct 7, 2019
2,878
Are you going to put 650V on a 650V part?

#### Ali Z

Joined Mar 22, 2022
23
Are you going to put 650V on a 650V part?
I know it should be more , but I wanted to see in simulation firstly. I will not design it in real life.

#### ronsimpson

Joined Oct 7, 2019
2,878
I think the two parts you are looking at are the same part. One is automotive grade!
They have the same foot print! so you can try the two parts.
The energy loss for both parts was done at 20A so the compare is simple.
The switching speed is done at 20A and 16A so there will be a speed difference.
I am using a older part with only one Gate which makes the layout harder. The two gate connections is better for the PCB.
If your layout is not perfect there will be ring on the gate. I found the part likes a little negative turn off voltage. That helps with AC losses.

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#### ronsimpson

Joined Oct 7, 2019
2,878
it will boost 27kW battery which is 201.6 volt Dc input voltage to the 650 V dc
I see "boost 100 or 200V to 450" is common.
There are many ways to boost. It is possible to boost to 650 using low voltage transistors. For many years I make 30000V supply using 1000V transistors.
I am thinking of having 450V on the transistors with 650 as a output.

#### Ali Z

Joined Mar 22, 2022
23
I am not so professional even I can say beginner level .
So I need 650 V Dc out. So I should choose a GaN transistor more than 650 V but I need 60A Id too.
Should I choose this GaN transistor for real life design ?
I need something Id=60A and more than 650 Vds

#### Ali Z

Joined Mar 22, 2022
23
I see "boost 100 or 200V to 450" is common.
There are many ways to boost. It is possible to boost to 650 using low voltage transistors. For many years I make 30000V supply using 1000V transistors.
I am thinking of having 450V on the transistors with 650 as a output.
Ah I didn't know about it. So I can use 650 V GaN transistors or even lower like your said 450 v in real life design ?

#### BobTPH

Joined Jun 5, 2013
8,653
Do you have a circuit in mind or are you choosing parts without knowing the requirements?

Bob

#### Ali Z

Joined Mar 22, 2022
23
Do you have a circuit in mind or are you choosing parts without knowing the requirements?

Bob
You can check mdibc circuit topology.

#### BobTPH

Joined Jun 5, 2013
8,653
Thanks. I see that it is multiple boost converters paralleled but operating in different phases to make the output smoother with the same capacitance.

It looks to me like the switch element needs to withstand the entire output voltage.

Bob

#### Ali Z

Joined Mar 22, 2022
23
Thanks. I see that it is multiple boost converters paralleled but operating in different phases to make the output smoother with the same capacitance.

It looks to me like the switch element needs to withstand the entire output voltage.

Bob
For my circuit design in mdibc topology from 200 volt to 650 volt circuit , in real life design Can I use 650V

• TDG650E601TSP Space GaN E-mode Transistor with 900 V transient drain-to-source maximum voltage
?

#### BobTPH

Joined Jun 5, 2013
8,653
You need a margin, never operate a component at its max voltage.

Bob

#### ronsimpson

Joined Oct 7, 2019
2,878
Does the output need to be isolated?

Many boost PWM designs the input voltage runs to the output without control. Like this one. This is a simple 3V to12V but here you can see the 3V will drive the output if Q1 is never turned on. This is the simplest circuit. Q1 voltage will be 13V.

Here the inductor is "center tapped", or you can call it a transformer. The FET voltage is under 8V. Output is 12.
I could have made the tap at any point in the inductor. I could have 8V or 10V or 11V or 6V on the MOSFET. That is set by the ratio of the tap.

I know this is a low V, low I example that is very simple.
I could have shown a multi-phase, isolated PWM but it would have taken many pages to explain.
I did not show GaN because that is also complicated.

Do you have LT SPICE?