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High voltage buck converter
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ocset:
your spec is ok for buck...you need slope compensdation if current mode and D>50%...or else you can just use constant off time and then you dont need slope compensation.
Ptzf:
Right!

I now have this buck converter operating at 325 Vin, 500 kHz and 300 W, 80% and over duty cycle. I have a 600+ uH inductor at the output. I chose to go with a asynchronous design, as it dissolves any problems with shoot trough. They flyback diode is based on SiC technology and seems to be very low loss and bulletproof all in all (I've killed the HS mosfet and the driving circuitry several times now, but the diode does not want to die).

However I'm having trouble with blowing up my HS driver. Most likely due to a too large negative transient on Vs pin (Vb-Vs surpasses the allowed limit of 25V). The HS driver is FAN73711. Here is a microscope shot of the "uncapped" IC:

In the upper left quadrant of the uncapped chip is a deep hole that runs from the die to the pin - and it is on pin 6, which is the Vs pin (pin 5 on the very tippy-top in the left upper quadrant is NC).

The load of the converter is very inductive and a fast di/dt will definitely induce negative transients on Vs.

ON-Semiconductor AN-6076 describes methods for relieving negative voltages on Vs pin in bootstrapped drivers, most notably relocating the HS mosfet gate resistor to the Vs output-input pin. Doing this, however, starts to have pretty drastic effects on the switching waveform on the switch gate. Compensation drives up the component count and, well, development and testing time.

My question: are there high voltage HS drivers out there that mitigate Vs transients to begin with, non-bootstrap? I mean, some other technology, like isolated drives etc. I'm thinking that Infineon EiceDRIVER family (1EDCxxI12MH) might do the trick?
I need this converter to be very robust.

Thank you for the help!
ocset:
You can have a high side isolated supply and just  use say a digital isloator to drive a hi side gate driver.
But what is you input capacitor size?
I am sure you are aware that at 300W, you really need a boost pfc stage up front.
If its just for hacking about with, then yes, use a isolated module to give you a "ground" at the source of the hi side fet...then you can just drive it freely with an isolated drive signal.
Or you could use a gate drive transformer and pnp turn off circuit.

one of these is good to give you an isolated hi side supply....it doesnt have much pri-sec capacitance which is good.
https://power.murata.com/data/power/ncl/kdc_nxj1.pdf
double check the isolation voltage is ok for you.
Wolfram:

--- Quote from: Ptzf on October 28, 2018, 11:03:44 am ---
My question: are there high voltage HS drivers out there that mitigate Vs transients to begin with, non-bootstrap? I mean, some other technology, like isolated drives etc. I'm thinking that Infineon EiceDRIVER family (1EDCxxI12MH) might do the trick?
I need this converter to be very robust.

Thank you for the help!

--- End quote ---

Yes, fully isolated drivers will solve the problem of switching node undershoot killing the driver. There are plenty of devices available, including the Infineon drivers you've mentioned, the TI ISO5xxx series and UCC53* series, Silabs have a bunch of nice parts and Analog Devices also make some good devices. The only thing to watch out for is the common mode transient imunity of these drivers (this also applies for the non-isolated bootstrap drivers). With your MOSFETs and bus voltage, I would expect somewhere around 20 kV/µs, which should be well within the ratings of many (but not all!) of the available devices.

I've used the TI UCC53* series and the Silabs SI8271 in a 30 kW buck converter (750 V input, 400 V output), and the only problems I've experienced was caused by us exceeded the CMTI rating on an older generation of Silabs drivers.
T3sl4co1l:
If you somehow can't fix the inductance problem in layout, yes, you need a fully isolated system.

This should only be necessary in higher power industrial systems, where you won't mind the added cost anyway.

Tim
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