Circuit design on LT3001

Hello, dear colleagues!

To clarify: my customer wants to design isolated power supply on flyback converter LT3001 (electrical principal scheme in attachment, transformer is 744889020330 by Wurth Elektronik), he made a board according to this scheme. He tries to start the board, but this power supply begins the work only without load (even with disconnected LDO). If the load turn on after steady mode has been settled, then circuit works well.

When the circuit turn on at connected load (even low load current), output voltage is not corresponding to that set the resistor R3. In some times the circuit does not start.

 

When my customer use controller LT8303 in the same scheme, the circuit works the same manner. By way of experiment my customer try to limit the charging current of the output capacitors (in case that big current turn on internal fault protection function). According to the customer – “the feeling is that the circuit goes in to working mode (stabilization) at several determined output voltage values, but we couldn’t find clear pattern (between R3 value and output voltage).

 

 

Could you clear, what we are doing wrong? It seems that the transformer is chosen correctly (according the datasheet). What the difference between LT3001 and LT8303 (it isn’t clear, for the LT3001 there is not RC circuit design method in the datasheet)? Perhaps there is more complete method for circuits design on these ICs?

Thanks a lot!

Sincerely,

Kirill