As a result, the primary main winding inductance Lpcan be defined and calculated as:
(3)
Based on core cross-sectional area, Ae= 120.1 mm2and saturation flux density at 100°C, Bsat(T=100°C) = 0.41 Tesla
for TDG PQ26/20 core with TPW33 material, the transformer primary main winding turns Npcan be defined as:
(4)
Where Df,Bsat is the derating factor to ensure the designed transformer maximum flux density Bmax is below
Bsat(T=100°C) by a margin of (100 percent - Df,Bsat) from saturation, and itis typical to set Df,Bsat in the range of 85
percent to 95 percent for a margin of 5 percent to 15 percent from transformer core saturation.
Taking Df,Bsat = 90 percent, Npcan then be calculated as:
Based on the above, Np= 32 is selected.
The transformer secondary main winding turns Nscan then be calculated as:
To ensure fast VCC supply takeover from the primary auxiliary winding for avoiding IC reset during start-up, and
also to be able to deliver peak gate-drive voltage VGD,peak of 12 V with high enough primary auxiliary winding VCC
supply during steady-state, the minimum primary auxiliary winding demagnetization voltageVa,min is therefore
defined as 14 V. As a result, the recommended minimum primary auxiliary winding turns Na,min can be defined
and calculated as:
(5)
To ensure proper HV pin line synchronization, VCC voltage should be lower than 19 V, the maximum auxiliary
winding demagnetization voltageVa,max is therefore defined as 19 V. As a result, the recommended maximum
primary auxiliary winding turns Na,max can be defined and calculated as:
(6)
Based on the calculation results of equations (5) and (6), primary auxiliary winding turns Na= 3 is selected.
A secondary auxiliary winding is added to supply the operating voltage of the Secondary Side Regulation (SSR)
FB circuit, since its op-amp or shunt regulator’s maximum operating voltage is less than Vout,setpoint of 54 V. The
recommended minimum secondary auxiliary winding turns Na,sec,min and recommended maximum secondary
auxiliary winding turns Na,sec,max can be defined respectively as per Na,min and Na,max, as shown below:
(7)
(8)
Based on the calculation results of equations (7) and (8), secondary auxiliary winding turns Na,sec = 3 is selected.
