How to Achieve Power factor in TOP267EG SMPS

Hi amolgupta,

Thank you for using PI product on your design. The switch valley-fill single stage PFC technique can be best use with an ON-OFF controller (i.e LYTSwitch-6) and will be hard to implement for PWM controller (i.e TopSwitch). Your requirement is 0.9 which is diffiecult to achieve. You may refer to the below link for some possible solution to increase your PF.

https://ac-dc.power.com/sites/default/files/product-docs/an53.pdf

If cost is not a concern, you can try to add another stage (PFC circuit) before your flyback design. Thank you.

Best Regards,
PI-SevenofNine

Hi SevenofNine.. I am glad to inform that i have achieved 0.92 PF by designing passive filter. Now the next issue i am facing is that i have placed 4 Mohm resistor at VOLTAGE MONITOR(V) pin as suggested. But it is getting in shutdown retry mode even at 211 Vdc(150 Vrms). I would be thankful if you can share the resistor configuration for cut-off at 85-305 Vrms.

Hi amolgupta2001,

Nice to hear from you that you achieved 0.92 PF with just a passive solution. And with regards to the 4M resistor, the value was correct. Did you try to short the VPIN to SOURCE pin and the auto-retry disappears? Can you provide us the schematic circuit of your design to check if you have other components connected to the VPIN. Thank you.

Best Regards,
PI-SevenofNine

Hi SevenofNine, thanks for the appreciation. I have attached the schematic of my design. I have not tried shorting VPIN to SOURCE as it will disable the function of the pin and i need precise cut- off on line UV/OV. As i am newbie to PI, i would request you to kindly guide me on below topics if possible -
1. How to Calculate the current limit resistor as I am not able to find the value for 1.5A limit from the graph in the datasheet.
2. How to calculate R13(Rd - DC gain resistor).

Hi Amolgupta,

The reason why I ask to short the VPIN to SOURCE, is just to verify that the auto-restart was caused by the VPIN. If you short the 2 pins and still going into auto-restart then it is not from the VPIN, some other fault is triggering the auto restart. For number 2 questions, you are referring to the upper resistor of the feedback? Am I right? Thank you.

Best Regards,
PI-SevenofNine

Hi SevenofNine, I have connected VPIN to source, but still it is getting in to auto restart mode at 85Vac. Can you suggest me what points i have to consider for correction. I would also correct myself as referring to my schematic attached above, i was asking calculation for R10(21Kohm) instead of R13.

Hi SevenofNine, I think the issue was related to thermal shutdown. I have changed the heatsink and now it is not shutting down at 85 but at 60 Vac which is also a concern. Also need help regarding R10.

Hi Amolgupta,

You may refer to page 15 or slide 85 of this document for biasing the optocoupler. In this case, the recommended value for 5V output is 100ohms and 470ohms for a 12V output. And since your output is 32V you can use around 1k to 1.5k. Thank you.

https://www.power.com/sites/default/files/PDFFiles/seminars/highpwr_flyback.pdf

Best Regards,
PI-SevenofNine

hi SevenofNine, hope you are doing well. I completed my design and testing. The problem i am facing right now is of efficiency. I am able to achieve maximum of 53% efficiency at 230 Vac. Can you suggest what all things need to be considered and how to make system efficient. thanks

Hi amolgupta,

Nice hearing that you already completed your design. As for the efficiency improvement, you may try to do the following:

1. You may try to use a schottky diode on D3, but higher voltage rating schottky is hard to find. Maybe you can try 150V, schottky if the voltage stress is still within the maximum rating of the device. Shottky diode have lower Vf, so its power dissipation is lower.

2. You can try to retune the snubber circuit. You can lower the value of C3 to lets say 1.5nF and increase the resistor value of R1 to more than 100K. But always check if the stress on the MOSFET is within the maximum rating of the device. Check also the EMI.

3. You can try to reduce the leakage inductance of your transformer. You can sandwich secondary turns (output side) on a split primary.

4. Is output ripple a requirement? If not, you can omit L2.

Best Regards,
PI-SevenofNine

Hi SevenofNine,

Did all the changes you shared except modifying the transformer. But i regret that no change has been detected in efficiency. Also, current harmonics(Ithd) are above 100. Kindly suggest the modification that i can do for the improvement of the same.

Hi amolgupta,

Quite surprising that it didn't improve by retuning the RCD snubber and changing to Schotkky diode. Please try the lower leakage inductance if it can help increase the efficiency. As for the THD, what is the total input capacitors? You may try to reduce this value to improve THD as long as you can still deliver the full power to the output. Thanks.

Best Regards,
PI-SevenofNine

Hi SevenofNine,
W.R.T schematic, c1 and c2 are bulk capacitors with 56uF and 68uF value respectively.

Hi amolgupta,

It seems that the capacitors were already designed for 48W output wide range application, but you may try to 56uF/56uF combination or 56uF/47uF combination. Did you already try to modify your EMI filter and check THD?

Thanks,
PI-SevenofNine