IGBTs for switch which must break mains short circuit current.

[cupoftea]

Hi,
We are adjusting power in lots of paralleled resistive heaters on the 240VAC mains by trailing edge "phase cutting".
Total power when on full power is some 3kW.
Would you agree, we really must use back-to-back IGBTs rather than FETs as the phase cutting switch,
since FETs would not be able to switch off when a short circuit occurs (eg a heater goes short circuit).
A FET would die, an IGBT would not.
Better would be a GTO Thyristor, but they have more loss than IGBT.

We do plan to have a short circuit detector, which triggers a comparator and turns off the IGBTs when short circuit occurs...unfortunately the short cct current will rise very quickly and so the IGBTs will have to break a very high current.

MOSFET datasheets do not even have a "maximum breaking current" rating, whereas IGBT datasheets do.....some people mistake the "pulsed current rating" of a MOSFET as the allowable breaking current....but if the MOSFET tried to break such a current, it would explode due to the switching loss.

Eg this SIHG70N60 FET has a "pulsed current " rating of 170 Amps, but it would die if it tried to break that current (switch it off)

https://www.vishay.com/docs/91997/sihg70n60aef.pdf

 

[D.A.(Tony)Stewart]

It must be still running and far ahead of us since they did these tests with their infinite heatsink.

I suppose with pulse transformers and the additional diode loss on the heatsink to protect from reverse voltage it's ok

But I might consider SiC devices.

"The best way to use the SiC MOSFET is to fully
understand the device characteristics. The different
characteristics of SiC MOSFET and Si IGBT have an
impact on their short circuit protection schemes"

REF: https://www.ti.com/lit/ab/slua863c/slua863c.pdf

1 vote for SiC IGBT for OCP.

With the ROHM RGS series of IGBTs, a minimum short circuit withstand time of 8 µs is guaranteed with 5 us of margin depending on heatsink.

Short Circuit Withstand Time (SCWT) of IGBTs | About IGBTs | TechWeb

Short Circuit Withstand Time (SCWT) of IGBTs IGBTs and other power devices

techweb.rohm.com

--- Updated Jan 12, 2024 ---

FWIW What's All this Stuff about Punch-thru IGBT's

IGBTs can be classified into the following

• PT (Punch Through) – Punch-through IGBTs are those that have an n+ buffer layer. These IGBTs are used in inverter and chopper circuits and have symmetrical voltage blocking capabilities.
• NPT (Non-Punch Through) – Non-punch through IGBTs are those that don’t have an n+ buffer layer. They are used in rectifier applications and have symmetric voltage blocking capabilities.
• Symmetrical IGBTs - These IGBTs have equal forward and reverse breakdown voltage and are mostly used in AC circuits.
• Asymmetrical IGBTs – These IGBTs have a reverse breakdown voltage less than the forward breakdown voltage. They are commonly used in DC circuits.

Key Specifications of IGBT

• Collector-Emitter Voltage: It represents the voltage drop that occurs between the collector and the emitter terminals and is expressed in volts (V).
• Saturated Collector-Emitter Voltage: It represents the maximum voltage drop that occurs between the collector and emitter terminals and is expressed in volts (V).
• Gate Emitter Voltage: It represents the voltage drop that occurs between the gate and emitter terminals and is expressed in volts (V).
• DC collector Current: It represents the amplified output current that flows through the collector terminal of an IGBT and is expressed in Ampere (A).
• Peak Collector Current: It represents the maximum collector current that can be handled by the IGBT and is expressed in Ampere (A).
• DC Forward Current: It represents the current that the diode part inside an IGBT requires to conduct at room temperature conditions. It is expressed in Ampere (A).
• Peak Forward Current: It represents the maximum peak current that the diode inside an IGBT requires to conduct. It is expressed in Ampere (A).
• Gate Emitter Leakage Current: It refers to the leakage current that occurs due to the voltage drop between the gate and emitter terminals.
• Power dissipation (W): It represents power dissipated by the IGBT. It is equivalent to the product of collector current and collector-emitter voltage and is measured in Watts (W).

PT-IGBT	NPT-IGBT
Has asymmetrical configuration	Has symmetrical configuration
Has low conduction loss which increases with temperature	Has higher conduction loss which is independent of temperature
Not preferred for parallel configuration application circuits	Better parallel operation due to better temperature coefficient and shared heating dissipation
Offers less thermal stability	More Thermal stability
Low switching losses	Higher switching losses
Less rugged in short circuit failure mode	More rugged in short circuit failure mode
Lower lifetime	Relatively higher lifetime
Mostly used in DC circuits	Mostly used in AC circuits REFs https://www.everythingpe.com/community/what-are-the-different-types-of-igbt IGBTs - everything PE www.everythingpe.com

 

[cupoftea]

Thanks for the info on IGBTs, much appreciated.
Ayk, in the electric drive industry, its well known that IGBTs must be used in inverters,
simply because NFETs cant break the short circuit currents that can often occur in electric drives, due to the
motor coils becoming short circuit.

 

[Easy peasy]

We have a product called an electronic fuse - used by quite a few companies in the power electronics field - it can handle AC and DC up to your typical mains rating, 30A peak and 600V pk
the user can set a knob to determine the trip current - and save your psu under test if it goes west ( quite often the booster section )

We use SiC 1200V 60A mosfets in inverse series with suitable protection - and they work a treat - they open in under a uS from pk curr detect

2 x 9V batteries to hold them ON under normal conditions

We have had quite the number of emails from people who have bought these and said how much hair it has saved after using it on their run up benches !

Not to mention blown up pcb's, semis and gate drive / control ....

 

[cupoftea]

Thanks very much , just went to your products page but didnt see it there. Any word on price and size?

 

[Easy peasy]

They are about 150 x 110 x 60 high ( sometimes bigger due to case availability, plastic case ) 3 wire mains cable in and out - 2 x 9V batts needed internally for operation.

Fixed current trip ( 20, or 25, or 30A pk ) with PB for reset = USD $ 680.00 + shipping

Unit with pot for setting trip = USD $ 780.00 + shipping

Made and tested by our technicians prior to shipping