TNY286 or LNK626?

Posted by: LucasAndrews on 08/21/2014

I am using the PI provided tools and guides to determine which device to use and I am getting mixed and conflicting results.

Should I use TNY285, TNY286, or LNK626?

100-250VAC, 50Hz input; 4VDC, 0.5W output on PRIMARY side; 12VDC, 10W output on SECONDARY side

The power supply will be used to power an electrical energy meter and will always be on. There is no standby mode. Also, size and cost are more critical than efficiency.

The real decision is between Tiny or Link. What are the pros and cons?

Thanks,

Lucas Andrews

Comments

Do you need isolation between primary side and secondary side? I you need it, then you need to wind the transformer with the two outputs separated because isolation requirements. If you do not need, then you can stack the two outputs in a single winding.

For now I am assuming you need isolation.

LNK626 design will be trickier because you have two outputs isolated from each other. Your cross regulation will be loose. With tiny switch you can have a better cross regulation. But with tiny switch you need feedback like an opto-couples to sense your output voltage. So you need to find out what is better solution for you.

Design with LNK626 takes longer and more experience than with Tinyswitch because the way the feedback is implemented. Opto-coupler feedback is easier to achieve.

So I think I do not have a straight answer for you. Can you decide after you read my answer? If you still can not decide, then you can tell me more about your design and I may give you better suggestions

Thanks for the reply. I will move forward with the TNY286. Now for the transformer question. I do need 3,000V isolation for the 12V output. The 4V output needs to isolated from the 12V, but not from the primary circuit. The 4V will be used to power a meter IC which is connected off-line. I will use an LDO to go from 4VDC down to 3.3VDC, so poor regulation on this winding will be okay. I am only drawing 40mA from this bus, so the LDO will be small and low cost. I am thinking I can modify the transformer construction details to put the 4V winding right next to the primary winding and then isolate the 12V winding with tape and triple insulated wire.

Beyond this, I need to be able to power the unit with 120V single phase up to 480V three phase. I will use 6 diodes to create a full wave rectifier with Or'ing. This way if voltage is present between L1, L2, or N the unit will power. After the rectifier I am going to use a chopper circuit to keep the HVDC limited to 350VDC.

What do you think about this design method? I neglected to mention the chopper as the HVDC will be in the universal AC range.

I think you are approaching the design in the right way