Fiddy wrote:Still incorrect, data sheet says typical 35ns MAX 50ns, the max for the FGA60N65SMD is a whopping 212ns at 175degC.
the MUR1560 can handle up top 150A <10us; rep. rating, much higher than the 30A. then there's the whole power dissipation factor where its not being dissipated inside the TO-247 package with the IGBT.
Im leaving them in there either way.
My last comments for this topic and as a caution to everyone else reading - As I said and from my experience in power engineering, the t_rr is only given at for I_F = 1A, di/dt = 50A/us and T_j = 25C. This changes significantly with temperature and di/dt and so on, usually getting significantly longer. There are varying datasheets on the MUR1560 (see attached below). The FGA's diode is characterized at 200A/us and I_F = 30A. Typical t_rr for the MUR160 at 28A 200A/us (100C) then becomes 140ns. The FGA's trr would then be somewhere between 47(25C) and 212ns(175C) typical, looking closer to less than 140ns if you really want to compare t_rr.
The same idea goes for the recovery charge. So my point is, the comparison is not straightforward as comparing numbers, and you will also be more interested in the t_a and t_b or diode reverse recovery periods, which are not in the FGA datasheet and will affect power dissipation and recovery characteristics.
Will adding the diode be harmful to your circuit? It depends on when the IGBTs do the switching among others, but a really quick calculation shows the lead inductance (vs on-die) of the off-board diode is about an order of magnitude greater (though still small), so more of the current is going to flow through the co-pack diode at the high frequencies during switching anyway. Then depending on how much current is flowing through the outside diode during switching, the added inductance can only increase the voltage spikes! - making your overall fix less robust than if you had left out external diodes in the first place. This is a big enough problem for careful inductance management to be a big part of industrial design, as well as highlighted in many application notes where even the leads of TO247 packages cause a big enough inductance in high current switching leading to significantly higher voltage spikes as well as switching losses.
You can do the same exercise with power dissipation w.r.t conduction losses (about the same V_F at same I_F) as well as switching losses due to reverse conduction and reverse charge. The thermal resistance of your TO220 to air will also be about an order of magnitude more than the co-pack's diode thermal resistance to the heatsink. I will refrain from going through more specifics but the internet has lots of good reverse recovery diode application and technical notes.
I know you have good intentions to make the coil more robust, but I didn't want to encourage everyone else to add their own unnecessary reverse diodes, or do something else which might inadvertently make the coil less robust. You'd be better off buying a better IGBT instead.
Diode:
http://www.micropik.com/PDF/mur1560.pdfIGBT:
https://www.fairchildsemi.com/datasheet ... N65SMD.pdf