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Can LNK3696 be used for a wide range input isolated flyback?

Posted by: jane_y on 10/04/2022

Hi

I saw that the LinkSwitch LNK3696 embedded a 900V MOSFET. I'm looking for an alternative SMPS with 100V-480VAC +/-10% input and one 12VDC/0.6A output for industrial use. Can the LNK3696 be used? The circuit needs to be isolated by using an auxiliary winding in the primary side of the transformer not by opto-coupler. 

Thanks

Comments

Submitted by PI-Wrench on 10/05/2022

I have used a circuit like the one shown in the attached file to make a small flyback bias supply using the Link-TN. If the output side of the supply needs to be isolated from the primary side, cross-regulation between the secondary output and the primary bias may be an issue. I suspect some sort of preloading may be necessary to keep the isolated output in regulation at light/no load conditions. Sandwiching the isolated secondary between two halves of a split bias winding (using multiple strands on the bias  winding to increase coverage) may help improve cross regulation. Using an active preload may be another option to improve regulation without the added burden of a fixed preload resistor.

Attachment Size
LNK_BIAS.png 28.15 KB
Submitted by PI-Wrench on 10/06/2022

You might also try looking at the LinkSwitch-XT2, which may have a simpler implementation for bias feedback.

Submitted by jane_y on 10/06/2022

Hi

Thank you for replying me! Sorry I was actually asking about LinkSwitch LNK3696 which belongs to LinkSwitch-XT2 family (just corrected the post). The reference design I saw online are either non-isolated or isolated by opto-coupler feedback. I wonder if it can be used in an isolated SMPS circuit without the opto-coupler.

Thanks

Submitted by PI-Wrench on 10/06/2022

Here is a PIXLS spreadsheet for a Link-XT2 supply utilizing bias winding feedback, There is a warning for peak drain voltage, but if you use a 130V TVS to clamp the drain voltage (maybe with an R and C across it), drain voltage should be OK.

Attachment Size
LinkSwitch-XT2900V Flyback Design2.pdf 532.54 KB
Submitted by jane_y on 10/06/2022

For the design above, could you provide a sample circuit schematic?

Thanks

Submitted by PI-Wrench on 10/06/2022

Working on schematic - will be off tomorrow,  but I should have something by Monday.

Submitted by PI-Wrench on 10/10/2022

Attached are two schematics using different methods for EMI filtering. The spark gaps shown in the schematic using  a common mode  choke are pointed spark gaps generated during layout, and are part of the printed circuit board, rather than being separate components. 

I have also attached  a suggested transformer winding stackup that sandwiches the bias winding in between two halves of the secondary for better coupling, and hopefully, better output regulation. The secondary and bias winding are sandwiched between two primary winding halves to reduce leakage inductance. You may need to use an EEL16 core instead of a standard EE16 in order to fit the windings.

I have included a picture of three bobbins that have extended creepage that might be useful  for the transformer design. One is an EEL16 vertical bobbin with extended creepage, the second is a vertical EE19 bobbin with extended  creepage (similar bobbins are available for EE16 cores) . The third bobbin is a horizontal EE16 bobbin with an extended "back porch" for improved creepage. 

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12V_IND_SUPPLY_SCH1.png 32.81 KB
12V_IND_SUPPLY_SCH2.png 36.21 KB
Img_0239.jpg 114.14 KB
XFMR_WDG_DATA.png 498.48 KB
Submitted by jane_y on 10/11/2022

Hi 

Thank you very much for providing me the reference design schematics and transformer suggestions, they are pretty useful for me!

I plan to buy a few samples and try to play with some prototype boards and see how it works.

Thanks