I want to design a phase shifted full bridge with IGBTS and therefore I cannot use the formulas given for calculating the MOSFET losses in UCC28950 excel file. I looked at https://www.ti.com/seclit/ug/slyu036/slyu036.pdf but the value given for t1 does not seem right. Should not t1 be the interval shown below:
Hello,
The excel design for the UCC28950 was developed on the equations in the application note SLUA560 which you can find in the following link.
https://www.ti.com/lit/pdf/slua560
This excel tool uses the transformer transformer RMS current to estimate the H Bridge FET losses (QA..QD). This transformer RMS current was
based on the following equations that can be found in some power supply design text books.
After reviewing this the transformer RMS current is actually 2X the individual H Bridge FET RMS current. This is because the H Bridge FETs are only on every other primary switching cycle. So the RMS current losses in the FET are half of what the tool calculates.
I reviewed the H Bridge FET loss calculation and there is a 2X factor in front of QAg which is also and over estimate. So the calculation for the H Bridge FETs will actaully over estimate by a factor 2.
I will let the application team know that the H Bridge FET losses are over estimated. If you use the excel design tool please note that a better estimate of FET losses will be half of what the excel tool calculates.
Regards,
Hello,
For a phase shifted full bridge average the average H Bridge FET current (Iavg) is:
Iavg = ((Imax+Imin)*D/2 + (Imax+Imin)*((1-D)/2))*(1/2)
Regards,
