kratosrazor
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The diode must be 400V rated in the first place.I doubt that an 1N4148 is suitable to charge a 47uF capacitor in very short time. Expect high current peaks... while you want low voltage drop.
--> I recommend a 1A schottky diode.
Hi,
I assume the high value R22, R24, R25, R26 cause problems. Especially the slow switch OFF, while the high side has fast switch ON.
Don´t you have a scope?
Or an simulation software?
Klaus
Added:
the driver schematic is really hard to read. Please follow these rules:
* signal flow: from left to right
* positive supply on top
* negative supply (GND) on bottom of the page
* use GND symbols.
* avoid 45° in schematic
* avoid unnecessary bends
C10 is the VCC reservoir capacitor. It should keep VCC stable.
Now with every falling edge C9 is charged. but C9 is 4700 times bigger than the reservior... makes no sense to me...
--> I recommend: C10 should be bigger than C9. Both should be fast and LOW ESR. Maybe ceramics ones.
I doubt that an 1N4148 is suitable to charge a 47uF capacitor in very short time. Expect high current peaks... while you want low voltage drop.
--> I recommend a 1A schottky diode.
***
Your GND plane (red layer) is good. But you use that big isolation that many important GND connections are made with the blue layer. This causes unnecessary high line impedance. Don´t do this, especially not with switching power applications.
if you are using 4148's as bootstrap - at some point above 75V they will go bang ... you need 10E turn off res and 1k turn on to provide extra dead time
above about 200V you will start to make RFI which can affect every thing ...
There's a number of dubious circuit details, e.g. using low voltage 1N4148 as bootstrap diode, 1k gate resistors. Can we trust the schematic? Also the swhat's the switching pattern? Do you provide sufficient dead time to avoid shoot through?
The closed loop problem observation also suggests a possibility of output overcurrent, e.g. inductor saturation.
Switching of the other bridge branch?Where are those > 100V narrow spikes coming from?
I have used 7n40 MOSFET transistor instead of Fg25n120 IGBT transistor and the output was just fine.
DC link voltage was 200*sqrt(2), the maximum VDS was 350V and output was 170 V RMS. But when I use Fg25n120 again, IGBTs got short circuit in one leg.
So does my IGBT has a problem? under what condition a 1200 V 50 A IGBT get short?!
thank you for helping.
I have asked the same question, I'm using STGW25H120F2 and are experiencing problems too, my working theory is that somehow collector and emitter gets "shorted" when it's off. I was about to prepare a current measurement of Ic but now you gave me a good idea to try with a MOSFET to confirm my suspicion. But under which conditions an IGBT will do that? Nobody really knows yet.
I have used IR2111 as gate driver and it gives 650ns deadtime. isn't that enough?Easy peasy said:the total turn off time for the IGBT can be as high as 354nS ( see data sheet ) so it it likely that minor shoot thru is killing them, try 500nS dead time for the IGBT ...
Easy peasy said:please specify exactly which mosfet you used?
Easy peasy said:IGBT's can turn on very fast ( < 20nS ) I see you have no turn on gate resistors - this likely means that when a top device turns on, for example, the dv/dt across the lower device is so high the capacitive coupling to the lower gate is pulling the gate up and then you have both devices on briefly - with enough peak current to kill them after a short time - this is common for power electronics engineers with little experience of driving IGBT's ...
Good idea. I will check that and post soon.Easy peasy said:easy to check with a high speed scope ( 200MHz ) across the lower gate ...
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