Is FET operating within SOA?....Pulsed linear regulator

[Flyback]

Hello,

We have the following waveform in the STD1NK80Z FET (DPAK). It recurs every 10ms as shown.
We need to know if this violates the SOA.
To me, these pulses equate to repetitive pulses of [45V and 430mA and 650us long].
How from the datasheet can we tell that this is acceptable?
The SOA graph on page 4 shows what’s acceptable for a “single pulse”……..but how are we supposed to know what’s ok for our pulse train?
Also, the SOA graph on page 4 says “Tj=150degC and Tc = 25degC”..
What does this mean?......surely it’s the junction temperature, Tj, that is the significant parameter, so why do they bother to specify that the case temperature, Tc, is at 25degc?

STD1NK80Z datasheet:

https://www.st.com/resource/en/datasheet/CD00058073.pdf

 

[crutschow]

To me, these pulses equate to repetitive pulses of [45V and 430mA and 650us long].

I can't see the current scale in your plot, so can't comment further on that.

The SOA graph on page 4 shows what’s acceptable for a “single pulse”……..but how are we supposed to know what’s ok for our pulse train?

Difficult to know for sure.
But for that low a pulse duty-cycle there's probably sufficient time for temperature to equalize in the transistor chip between pulses, so it can be considered a single pulse for SOA purposes.

Also, the SOA graph on page 4 says “Tj=150degC and Tc = 25degC”..
What does this mean?......surely it’s the junction temperature, Tj, that is the significant parameter, so why do they bother to specify that the case temperature, Tc, is at 25degc?

Likely to show that the device is operating at it's maximum (worst-case) power dissipation.
At a lower power dissipation, the SOA rating would be higher since the SOA rating is limited by local heating on the chip.

 

[Flyback]

Thanks sorry please find the full waveform attached

Likely to show that the device is operating at it's maximum (worst-case) power dissipation.

Thanks, do you know why the SOA for the SPD03N60C3 FET only specifies that "Tc"=25degc?

SPD03N60C3 (SOA on page 5)

https://www.infineon.com/dgdl/SPD03N60C3_rev+2+6.pdf?fileId=db3a3043191a246301192907f3b27f4b

 

[shortbus=]

Ta vs TC vs Tj Ratings

Many of our semiconductor products have ratings that are dependent on temperature. you many see something like Current-Continuous Drain (Id) @25°C and it shows a rating of 30mA(Tc) or 30mA(Tj) or 30mA(Ta). Often time customer does not understand what these ratings mean. It gets even more...

forum.digikey.com

https://en-support.renesas.com/knowledgeBase/16981030