Hello,
I used the LM5160 to get 2 isolated voltages. As I need a reinforced isolation we use 2 Transformers in parallel, which works perfekt. The input voltage is 24V and I got 5V(unisolated) and 2x 12V isolated. The function is perfect.
But I get a lot of EMC Problems radiated emissions.
I think the layout is OK. For testing i cut the 2. transformer (blue line), so that the switched node is only a very small area - but this changed nearly nothing. We disconnected the complete secondary part of the transformer and used only a diode, cap and a 2k resistor at the secondary side, but this changed nothing. When we connect the primary GND and sec. GND the result is more or less the same. So for me the problem comes not from the sec. side, or the leakage capacity of the transformer.
When we replace the transformer by a simple inductor - the EMC problem is OK, but we do not have a strong load on the prim. 5V.
It would be great, if you have any idea what we can do now. We tried a lot (more capacities on prim/sec, different switching frequ, etc.), but nothing would really improve the problem.
Many thanks
Juergen
