# Is it possible to make an IGBT to work at duty cycles up to 100%?

#### yogece

##### Member level 3
I am designing an IGBT based chopper with single Low side switching IGBT (chosen low side switching because ease of driving the IGBT.)

There are plenty of resources available for SMPS (buck, boost, buck-boost,) PFC chopper, inverters, welding power sources, UPS and motor control applications. I presume all those applications work under duty cycles up to 50% and for motor applications it may go up to 95% (only during the peak of the SPWM signal) but none of the applications mentioned made it to work continuously in the duty cycle range of 90% or above.

I googled a lot and read the application notes, datasheets and reference designs of various IGBT/MOSFET manufacturers such as Infineon, ST, Semikron, Vishay, ROHM, Fuji, Mitubhishi, Hitachi, Toshiba, IXYS, ABB, Renesas, TI, NXP, Nexperia.

Some of the applications listed below which uses IGBT close to 100% duty cycle operation.

1. HVDC circuit breaker uses a hybrid approach. During operation the current will always flow through the bypass branch which has a mechanical circuit breaker and during the interruption of the current it will be allowed to pass through the IGBT, this application doesn’t help me to understand about the 100% operation of the IGBT.

2. Another application which uses the duty cycle up to 100% is separately excited DC motor which can use IGBT, but I couldn’t find any reference for the implementation using IGBT and there are plenty of resources available for thyristor based choppers and simulation of the same.

3. The DC electronic load which uses the MOSFET in DC operation and couldn’t find reference for high power electronics load using IGBT. Many of the manufacturers of IGBT mentioned not to operate the devices in the linear region.

I am designing an IGBT based chopper with single Low side switching IGBT (chosen low side switching because ease of driving the IGBT.)
There are plenty of resources available for SMPS (buck, boost, buck-boost,) PFC chopper, inverters, welding power sources, UPS and motor control applications. I presume all those applications work under duty cycles up to 50% and for motor applications it may go up to 95% (only during the peak of the SPWM signal) but none of the applications mentioned made it to work continuously in the duty cycle range of 90% or above.

I googled a lot and read the application notes, datasheets and reference designs of various IGBT/MOSFET manufacturers such as Infineon, ST, Semikron, Vishay, ROHM, Fuji, Mitubhishi, Hitachi, Toshiba, IXYS, ABB, Renesas, TI, NXP, Nexperia.

Some of the applications listed below which uses IGBT close to 100% duty cycle operation.

1. HVDC circuit breaker uses a hybrid approach. During operation the current will always flow through the bypass branch which has a mechanical circuit breaker and during the interruption of the current it will be allowed to pass through the IGBT, this application doesn’t help me to understand about the 100% operation of the IGBT.

2. Another application which uses the duty cycle up to 100% is separately excited DC motor which can use IGBT, but I couldn’t find any reference for the implementation using IGBT and there are plenty of resources available for thyristor based choppers and simulation of the same.

3. The DC electronic load which uses the MOSFET in DC operation and couldn’t find reference for high power electronics load using IGBT. Many of the manufacturers of IGBT mentioned not to operate the devices in the linear region.

I am intending to use IGBT modules of 1200V/400A (semikron SKM400GB125D half bridge module.) For the proof of concept I used discrete IGBT (IRFGP50B60PD) and drove it up to dutycycle of 50% @ 490Hz and it worked perfectly. The high power IGBT modules the manufacturer doesn’t provide FBSOA but they provide RBSOA and SCSOA details alone. For the short overload conditions recommend to refer the transient thermal impedance characteristics and for the steady state pulsing operations recommends to look at RthJ-C of IGBT & diode.

Many manufacturers have simulators which allows to simulate the electrical and thermal details of our circuit, but for which I couldn’t get some pointers regarding how far the simulation and bench test correlates (correlation of simulation Vs implementation) Semikron Semisel, Infineon (uses PLECS,) Fuji electric. By the simulator, we can estimate the losses of the switch (switching loss and conduction loss) and junction temperatures.

For the following questions I am expecting some inputs from the community:
1. Is it possible to operate IGBT up to 100% duty cycle? I couldn’t find many application references for IGBTs, which works in the duty cycle close to 100%. The question is similar to https://www.researchgate.net/post/Can_the_IGBT_MOSFET_turn_on_all_time_long_just_as_a_diode

2. Need some information regarding how far the simulation and bench test correlates (correlation of simulation Vs implementation.)

3. Reference designs or some resources for DC chopper using IGBT/MOSFET.

4. Suggest me some technical forum and resources dedicated to power electronics.

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#### Easy peasy

short answer = yes, as long as the load can handle the current, and the IGBT, and the source ...

#### yogece

##### Member level 3
short answer = yes, as long as the load can handle the current, and the IGBT, and the source ...

Here the source and load is okay. But selection of IGBT for close to 100% duty cycle operation seems not possible.
Can you point me some resources?

#### iop95

##### Full Member level 3
100% duty cycle mean IGBT is turned on for long time... can't speak about a switching converter anymore.
Many application limit duty cycle to 95-96% because need some time for turn-off... so can't go above this limit, but can have "100%", aka IGBT turn-on for long time.

#### yogece

##### Member level 3
100% duty cycle mean IGBT is turned on for long time... can't speak about a switching converter anymore.
Many application limit duty cycle to 95-96% because need some time for turn-off... so can't go above this limit, but can have "100%", aka IGBT turn-on for long time.

If possible can you provide the link for the applications which mentions about the continuous operation in the duty cycle of 95% or above

#### iop95

##### Full Member level 3
Sorry, but may add more details at your question? What you looking for in fact / what is main concern?
In any switching converter there are a minimum turn-on and turn-off time... can't have 0.0000001% or 99.9999999% duty cycle because IGBT/MOSFET need some time to turn-on or off in a safety mode that can't lead to a catastrophic failure.
As frequency increase, duty cycle must be more apart from 0%, respectively 100%.
As you mention, there are not applications that go above 95-96% because switching times limitation.
So, depending of application, can go with duty cycle up to 95-96% and if want to reduce switching loses, keep turned on IGBT/MOS after this. Keeping it turn-on mean 100% duty cycle... no switchings anymore, so no switching loses. But range between 95-96% and 100% can't be used, as well as 0% to 4-5%.

yogece

### yogece

points: 2

#### KlausST

##### Super Moderator
Staff member
Hi,

Every IGBT can work with 100% duty cycle.
It's not a problem of the IGBT, it's a problem of the gate driver circuit.
And only high side and only if a bootstrap supply circuit i)s used.

As long as you connect the proper drive voltage to gate-emitter the IGBT will be ON.

Klaus

yogece

### yogece

points: 2

#### yogece

##### Member level 3
Hi,

Every IGBT can work with 100% duty cycle.
It's not a problem of the IGBT, it's a problem of the gate driver circuit.
And only high side and only if a bootstrap supply circuit us used.

As long as you connect the proper drive voltage to gate-emitter the IGBT will be ON.

Klaus
I don't have problem with the gate driver i have Semikron SKYPER 32R

#### KlausST

##### Super Moderator
Staff member
Hi,

I wonder why you use that expensive driver circuit.
It is designed for
* high side switching
* high speed switching
* power supply
* and a lot of other features that you don't need (at least according the informations you gave until now)

Driving an IGBT in 100% is fairly simple. It just needs a short pulse of some current to switch the IGBT ON, then about no current is needed for the rest of the time. No isolated supply, no precise voltage, no high current, nothing special.
Any BJT or dedicated low side gate driver FAN3100 (below 1 $at Farnell) should do. But we don't have detailed informations about your requirements... You surely know that 100% duty cycle means "DC operation condition", no frequency, no switching. But you have chosen an IGBT that is meant for high speed switching applications, so don't be surprised when the datasheet focusses on this. It's a bit like this: You want to use a plow, you know it needs a high power engine to operate it. Now you see that a Ferrari has a lot of power. But the Ferrari's operating manual does not mention about a plow. I'm not sure whether the IGBT or the driving circuit is suitable for your application. But if you don't want switching, just ignore all the "switching" specifications in the datasheet Btw: If a device (not important whether it is an IGBT, BJT, MOSFET or any other device) is not able to operate at 100% duty cycle, then this needs to be mentioned in it's datasheet. I can't remember ever have seen an IGBT specification that says that it is not able to be operated at 100% duty cycle. Klaus #### yogece ##### Member level 3 Hi, I wonder why you use that expensive driver circuit. It is designed for * high side switching * high speed switching * power supply * and a lot of other features that you don't need (at least according the informations you gave until now) Driving an IGBT in 100% is fairly simple. It just needs a short pulse of some current to switch the IGBT ON, then about no current is needed for the rest of the time. No isolated supply, no precise voltage, no high current, nothing special. Any BJT or dedicated low side gate driver FAN3100 (below 1$ at Farnell) should do.

You surely know that 100% duty cycle means "DC operation condition", no frequency, no switching.
But you have chosen an IGBT that is meant for high speed switching applications, so don't be surprised when the datasheet focusses on this.

It's a bit like this:
You want to use a plow, you know it needs a high power engine to operate it. Now you see that a Ferrari has a lot of power.
But the Ferrari's operating manual does not mention about a plow.

I'm not sure whether the IGBT or the driving circuit is suitable for your application. But if you don't want switching, just ignore all the "switching" specifications in the datasheet
Btw: If a device (not important whether it is an IGBT, BJT, MOSFET or any other device) is not able to operate at 100% duty cycle, then this needs to be mentioned in it's datasheet. I can't remember ever have seen an IGBT specification that says that it is not able to be operated at 100% duty cycle.

Klaus
The issue is not about the gate driver.Anyway i accept your suggestions.
Regarding the 100% duty cycle operation of IGBT i have asked the manufacturer for some application note/guide lines for using an IGBT module duty cycle above 95% but they don't have any reference for these kind of applications.

#### c_mitra

You surely know that 100% duty cycle means "DC operation condition", no frequency, no switching.
Right.

If you want a 100% duty cycle, why do you need a switch at all? It is not going to be turned off, right?

But how a chopper is going to work with a 100% duty cycle? MY knowledge is rusted, but I think choppers would love to live with 50% duty cycle.

Duty cycle is defined for a pulse train for which ton and toff can be variable. But if either ton OR toff is zero, the pulse train ceases to be a pulse train.

My understanding is that the duty cycle cannot be 0% or 100% - because in these two extreme cases the pulse train ceases to be a pulse train.

On the other hand, IGBT is essentially being used as a switch and duty cycle is not a meaningful specification for a switch.

Or am I missing something?

#### iop95

##### Full Member level 3
Right.

If you want a 100% duty cycle, why do you need a switch at all? It is not going to be turned off, right?

But how a chopper is going to work with a 100% duty cycle? MY knowledge is rusted, but I think choppers would love to live with 50% duty cycle.

Duty cycle is defined for a pulse train for which ton and toff can be variable. But if either ton OR toff is zero, the pulse train ceases to be a pulse train.

My understanding is that the duty cycle cannot be 0% or 100% - because in these two extreme cases the pulse train ceases to be a pulse train.

On the other hand, IGBT is essentially being used as a switch and duty cycle is not a meaningful specification for a switch.

Or am I missing something?
I agree regardind 0% and 100% values for a "switching" converter... these values are extreme cases for turn-off and turn-on for long time.

Regarding chopper duty cycle, that is in fact a buck converter, with range between DCmin to DC max, that can be 4-5% to 95-96%, which mean translated in voltage 4-5% of Vin to 95-96% of Vin.
In traction system or similar application, after acceleration from near zero voltage to maximum posible with chooper, to eliminate switching losses may go to turn-on for long time (equivalent to 100% DC) of IGBT/MOS, to have Vout = Vin.

#### KlausST

##### Super Moderator
Staff member
Hi,

i have asked the manufacturer for some application note/guide lines for using an IGBT module duty cycle above 95% but they don't have any reference for these kind of applications.
I'm not surprised.
100% duty cycle is nothing special, no stressing situation.
It's rather the most "non stressing" situation for an IGBT....except "continously OFF".

For this situation I see no need for an application note.

Klaus

#### yogece

##### Member level 3
1.I couldn’t find many application references for IGBTs but many resources are available for MOSFETs DC and linear Mode operation , which works in the duty cycle close to 100%.

2. Need some information regarding how far the simulation and bench test correlates (correlation of simulation Vs implementation.)

3. Reference designs or some resources for DC chopper using IGBT/MOSFET.

4. Suggest me some technical forum and resources dedicated to power electronics.

#### Easy peasy

That gate driver: the Semikron SKYPER 32R can be run at 100% on time for the upper IGBT, we have made many hysteretic controllers for 50kVA power stages where the upper devices ( and lower and middle devices ) are on for several mS to get a certain current slew (e.g. -100A to + 100A ) on 3 phase mains - so take many of the above comments with a grain of salt ( i.e. just ignore them ).

Our controllers have an average sw freq of 15kHz, but range from effectively DC ( 100% on ) to 30kHz max

If your control design requires long ON times the Semikron SKYPER 32R will be able to do it ...

yogece

### yogece

points: 2

#### yogece

##### Member level 3
That gate driver: the Semikron SKYPER 32R can be run at 100% on time for the upper IGBT, we have made many hysteretic controllers for 50kVA power stages where the upper devices ( and lower and middle devices ) are on for several mS to get a certain current slew (e.g. -100A to + 100A ) on 3 phase mains - so take many of the above comments with a grain of salt ( i.e. just ignore them ).

Our controllers have an average sw freq of 15kHz, but range from effectively DC ( 100% on ) to 30kHz max

If your control design requires long ON times the Semikron SKYPER 32R will be able to do it ...
Thank you so much Indeed for sharing your experience with Semikron SKYPER 32R.This gives confidence about the capability of the gate driver.

This is what i expect from the community; some one might have worked with DC choppers,DC SSR,DC circuit breaker,DC load Switch it would be helpful if they could shed some knowledge about the DC operation of IGBT and its thermal details.

#### KlausST

##### Super Moderator
Staff member
Hi,

I wonder why you still ask the same vague question.
It is already answered that there is no problem in continously operating an IGBT. There is nothing special to take care of.
All information for this situation is given in the datasheet. (And already written in the link of your post#1l

For any electronic device (IGBT, BJT, MOSFET, diode, resistor, LED...) the critical situations are:
* overvoltage
* overcurrent
* temporary too high power dissipation
* overheating

Thus I recommend to ask a detailed question.
Like diagrams about the expected voltage and current waveform with timing information. And other detailed iformations about what is your concern.

Klaus

#### c_mitra

This is what i expect from the community; some one might have worked with DC choppers,DC SSR,DC circuit breaker,DC load Switch it would be helpful if they could shed some knowledge about the DC operation of IGBT and its thermal details
I presume you got the idea by now.

If you see the waveforms in the typical datasheets, they do not appear square, they are trapezoidal. And there is a reason for that.

You cannot go from 0v to 10v in zero time. And the reverse is also correct. Hence total period is equal to the turn on time + turn off time + off-to-on time + on-to-off time.

As a conservative user, I suggest you should keep some margins. Use the max specified values for the above (transition times).

Because of other reasons, you need to also include some dead time in the above calculations. Hence the total period will be equal to turn-on time + turn off time + dead time + off-to-on time + dead time +on-to-off time.

How much dead time you will use depends on you and your circuit (very fast transitions can have other problems). So the final answer is simple.

You can have 100% duty cycle without any problem but very close to 100% duty cycle (say 99.99%; just an example) at reasonably high frequency IS a serious problem.