LM5022 - Wide Input - Transformer design verification

The procedure is correct.  Ipk calculation is wrong.  Ipk = Isec_pk / turns_ratio.  Correct this and I believe you can select a small core.

Thanks,

Youhao Xi, System/Applications Engineering, Texas Instruments SVA-PPD 

Hi, Thanks for your suggestion. But, with a turns ratio of 12 and the peak secondary current being 4.8 AMps, the peak primary current will be 4.8 / 12 = 0.4 Amps , which is TOO................... LESS.

I have assembled the board with the transformer as per my calculations. The power supply is starting up at 35V ac or 45VDC, but not at the designed 17VDC. What could be the issue ? KIndky advise

Regards  Atul Bhakay

Hi, 

The power supply is ‘starting’ at 35VAC or 45VDC but not at the designed 17VDC. (this start up is on no-load)

Subsequently, the PSU operates up to the high line i.e. 265VAC

With ref to the schematic (attached herewith) do the R2, R7 , R39 resistors need to be altered ? Or does the transformer need to be changed ?

2364.PSU BOARD V3 0 SCH (3).pdf

Regards   Atul Bhakay

The resistors in the voltage divider are too big in value, and Q8 does not have enough base current...   Delete Q8 and R42, tie the UVLO pin directly to the 5.6 Zener,  and change R39 to 12.4k, and reduce R2 and R7 by 10x.  Do not forget to use higher power rating resistors for R2 and R7. 

Thanks,

Youhao Xi, System and Applications Engineering, TI SVA-PPD

Hi, Thanks for the detailed suggestions. Will rivert back to you once these suggestions are implemented and have been tested.

BTW, can you provide the transformer details of PMP7760 ?

Regards

Atul Bhakay 

Hi, there is no improvement in the start up of the power supply even after incorporating the suggestions. I have now modified the primary inductance from 283uH to 160uH. I am still awaiting the transformer details of PMP7760

Regards

Atul bhakay

For LM5022 to start, you must have the VIN voltage at least at 6V.  D6's leakage current may cause too much voltage drop across R3 and R8, and D6 and Q7 cannot not produce 6V for VIN when the input is at 12V input.   Please check VIN pin voltage.

Thanks,

Youhao Xi, System and Applications Engineering, TI SVA-PPD

Hi There;

I am looking to use the Isolated LM5022 device to be used an Wide Band Input up to 800V - the same as the PMP7763 which is on the TI website.

The only difference I am looking to implement is the Output Voltage - Rather than having 24V 250mA - I am looking possibly of steping down further to 5V@ 200mA

Can this be done??

Paul.