I am building a LED driver for 90V, 0.5A based on TI's chip TPS92310 for 230Vac input line.
The schematic used is basically the one found in the data sheet. The transformer is built on ferrite core E25 with air gap 0.5mm and turns ratio Np/Ns=47/36.
I have to use a primary shunt resistor of 0.33 Ohms to adjust the output power to the required level. For this resistor the peak primary switch current is VISNS-OCP/0.33=3.4V / 0.33 Ohm = 10 A. The calculated saturation current for the transformer is about 2.5A.
Primary current in steady state is under the calculated saturation limit. Even if during a transient the primary current jumps over 2.5 A, the transformer will go to saturation and the fast current peak appearing can distroy the switching transistor. How can I change the design to reduce the peak current limit and avoid this problem?