Reference design reports for LinkSwitch-TN2 — 12 V / ~3 W (non-isolated)?
Posted by: rayan
on
Hi all,
I’m designing a ~3 W, 12 V non-isolated buck converter using the LinkSwitch-TN2 family (e.g. LNK3205). My input is universal AC (85–265 VAC).
I found the Power Integrations reference design RDR-721 (2.75 W, 5 V output) which covers 85–265 VAC and uses a LinkSwitch-TN2 device — screenshot attached. I also found RDR-912 which is for 12 V, 550 mA (~6.6 W).
My questions:
- Are there any Power Integrations RDRs (or similar reference designs) that specifically target ~3 W at 12 V (≈250–300 mA) using the LinkSwitch-TN2 family — with schematics, BOM, PCB layout, design notes, etc.?
- If no exact RDR exists, has anyone adapted the 5 V RDR (RDR-721) or another LinkSwitch-TN2 reference design to get a reliable 12 V / ~3 W non-isolated solution? Any tips on component selection / layout / thermal margins would be appreciated.
- Which LinkSwitch device would you recommend for a 12 V / 3 W target (LNK3205 vs LNK3207, etc.) assuming universal AC input and aiming for safe thermal margin?
Thanks — any document numbers, links, or practical anecdotes are extremely helpful.
Hi Rayan,
Good day and thank you for choosing Power Integrations.
To answer your questions:
1) Currently, we don't have an RDR that directly targets ~3 W at 12 V using the LinkSwitch‑TN2 family. However, as you noted, existing RDRs can be adapted to meet your target specifications.
2) While RDR‑721 (5 V) can be modified for a 12 V design, we recommend starting with RDR‑912 instead. This reference design already supports higher output current and similar output voltage, so adapting it to a lower‑current 12 V / 300 mA ~3 W solution requires minimal to no changes.
Here are some of the important things to check:
a) For the input capacitors, you may reduce the capacitance compared to what is used in the RDR. A minimum of 8 uF total capacitance can be use.
b) In terms of the input and output inductors (L1, L2), verify that their current ratings can handle the estimated RMS current from PI Xls.
c) Other components like feedback components (resistor, diode and capacitor), bypass resistors, freewheeling diode can be used as is.
d) Regarding the output capacitor, you may used the same component in RDR-912 if you are to proceed in using LNK3207 device. The ripple current at high frequency is sufficient to handle the estimated output ripple current specified in PI Xls.
(According to the design guide, "Capacitor values above 100 uF for LNK3202-6, 220 uF for LNK3207, and 330 uF for LNK3208/9 are not recommended as they can prevent the output voltage from reaching regulation during the 50 ms period prior to auto-restart. "
3) For a 12 V / 3 W design with universal AC input, LNK3206 can meet the requirements. However, if you want additional thermal margin and more robust operation, LNK3207 is the safer choice. Device selection within the LinkSwitch‑TN2 family is primarily based on output current capability, so choosing the next size up ensures better thermal headroom.
In summary, RDR-912 is suitable for your application without requiring modifications.
Please see attached PDF file containing the PI Xls I created for your desired specifications, you may also access it using the link below. I have set the total input capacitance used in RDR-912, but you may try to change it.
PI Xls: https://piexpertonline.power.com/fileManager/index?shared=9ada20678779113fb07140f3c67a90175d630016eeb3a5e60a92e35cbc874ab5
You may also refer to LinkSwitch-TN2 design guide.
Thank you and have a great day ahead!