Power supply units (PSUs) for AI servers and data centers keep climbing in power, and design teams are often asked "can this triple insulated wire (TIW) be used in an AI server?" That question has to be classified by stage before it can be answered. This article covers only the main power stage: the front-end PFC, the main LLC transformer, and the resonant and magnetizing inductors. The conclusion first: this stage is the territory of planar transformers (planar) and litz wire (litz); primary/secondary isolation is achieved by the insulation foil and spacing design of a multilayer PCB, and it is not the category of any single-strand triple insulated wire. The article gives power, magnetics, safety and procurement engineers an honest dividing line; for where TIW really lands inside the same PSU (auxiliary / standby / bias and gate drive), see Data-Center and AI-Server Power: Why the Main Power Stage Uses Planar and Litz. All DAH JIN product values are per the Approval Document.
Power supply units (PSUs) for AI servers and data centers keep climbing in power, and design teams are often asked "can this triple insulated wire (TIW) be used in an AI server?" That question has to be classified by stage before it can be answered. This article covers only the main power stage: the front-end PFC, the main LLC transformer, and the resonant and magnetizing inductors. The conclusion first: this stage is the territory of planar transformers (planar) and litz wire (litz); primary/secondary isolation is achieved by the insulation foil and spacing design of a multilayer PCB, and it is not the category of any single-strand triple insulated wire. The article gives power, magnetics, safety and procurement engineers an honest dividing line; for where TIW really lands inside the same PSU (auxiliary / standby / bias and gate drive), see Data-Center and AI-Server Power: Why the Main Power Stage Uses Planar and Litz. All DAH JIN product values are per the Approval Document.
1. First, isolate the "main power stage" on its own
A server PSU can be divided into a main power path and an auxiliary path, and the two have different magnetics requirements. The main power path is the trunk that rectifies the mains, performs power factor correction, and then delivers the energy to the output through an isolated DC-DC stage. Take, as an example, an Infineon 12 kW PSU reference design written for AI data centers and servers (application note AN133110): it is two-stage, with an interleaved three-level flying-capacitor totem-pole PFC at the front end (performing power factor correction and regulating the intermediate DC bus) and an isolated DC-DC LLC resonant converter at the back end (delivering a regulated output of about 50 VDC); the whole unit reaches a power density of 113 W/in³ and a peak efficiency of 97.8%. The magnetics on this trunk are what this article is about.
- PFC inductor / choke — What it does：Power factor correction; regulates the intermediate bus；How it is built：High-current wound magnetics (copper wire / litz wire)；Single-strand TIW category?：No
- Main LLC transformer — What it does：Primary/secondary isolation and regulation; delivers the main output；How it is built：Planar transformer (multilayer PCB windings)；Single-strand TIW category?：No (see §2)
- Magnetizing / resonant inductors (LLC resonant tank) — What it does：Form the LLC resonance; support ZVS soft switching；How it is built：Inductors wound with litz wire；Single-strand TIW category?：No (see §3)
The key point up front: the main power stage achieves isolation and windings through two methods, "planar plus litz", and nowhere does it rely on winding in a single-strand triple insulated wire. TIW does have a place in the PSU as a whole, but not at this stage (see §4).
2. The main LLC transformer: the territory of planar (multilayer PCB windings)
In that Infineon 12 kW design, the main LLC transformer uses a "hybrid planar" structure: two identical transformers with primaries in series and secondaries in parallel; each is built around a main planar-magnetics transformer, and its windings are not "a wire wound on", but etched copper layers of a multilayer PCB (the primary needs 9 turns, made up by connecting a four-turn and a five-turn 6-layer PCB in series, with several boards paralleled to reduce winding resistance and conduction loss).
The crux is where the isolation comes from. In that design, primary and secondary are separated by a 50 μm Kapton foil to raise the dielectric strength, and FR4 spacers widen the distance between primary and secondary windings to lower the interwinding capacitance. In other words, the reinforced isolation and withstand voltage at this stage are achieved jointly by the PCB interlayer insulation, the insulation foil and the creepage / clearance design, not by winding in a single-strand wire with a thick insulation.
Why does the main transformer go planar? The industry consensus on planar magnetics is: low profile, precisely settable and reproducible leakage inductance and parasitic capacitance, and better heat dissipation (large copper areas and core faces help spread heat), which makes them especially suited to high-frequency (often above 500 kHz), high-power-density power stages such as AI data centers and servers. The very fact that a planar transformer uses "a multilayer PCB as the winding" already rules "winding a single-strand wire" out of the main transformer.
3. Resonant and magnetizing inductors: the territory of litz wire (litz)
An LLC resonant tank needs a resonant inductor and a magnetizing inductor. At operating frequencies of several hundred kHz, the AC resistance of a winding rises far above its DC resistance because of the skin effect (current crowding ever more toward the outer surface of the conductor) and the proximity effect (adjacent conductors squeezing each other's current distribution). The industry's standard answer is litz wire (litz): dozens to hundreds of fine, mutually insulated strands twisted together to share the current evenly and suppress both of these high-frequency losses, typically used for magnetics from 10 kHz–5 MHz.
Back to that Infineon design: its magnetizing inductor is wound with litz wire (placed on top of the planar transformer structure and connected in parallel with the primary to obtain the magnetizing inductance needed for ZVS), and the resonant inductor is built as a separate magnetic, likewise wound with litz wire (about 1.65 μH, split into two cavities so the fluxes cancel and core loss is reduced). In other words, the two inductors in the main power stage that "need winding" use multi-strand litz wire, not a single-strand wire, because what has to be solved here is high-frequency copper loss, not creepage-free safety isolation.
4. Why this stage is not the category of single-strand triple insulated wire
Putting the two previous sections together, the division of labour in the main power stage is clear: the main transformer, for isolation and regulation, goes planar (multilayer PCB + insulation foil + spacing), and the inductors of the resonant tank go litz (many twisted strands to keep AC resistance down). The design positioning of triple insulated wire (TIW) is exactly something else: it is a single-strand (or few-strand twisted) enamelled wire with a thick three-layer insulation, whose value is "reinforced (Reinforced) isolation with a single wire, dispensing with creepage distance and insulating tape", letting small isolation transformers of low to medium power be made smaller. That strength matches the small isolation transformers of the auxiliary / standby / bias and gate-drive stages, not the isolation and windings of the main power stage.
A common misconception needs clearing up here: although TLW-B7S among DAH JIN's four types is a stranded wire (seven strands, 0.10–0.30 mm per strand, per the Approval Document), its stranding exists to achieve reinforced insulation and flexibility on small isolation transformers; the litz wire that main-power inductors use to keep AC resistance down is a fine twisted bundle of dozens to hundreds of even finer strands (in the design above, 300 strands for the magnetizing inductor and 512 strands for the resonant inductor, each strand 50 μm). The two differ in strand count, strand diameter and purpose, and are different engineering objects; equating them because both are "stranded" would mistake a TIW meant for safety isolation for a litz meant for main-power loss management.
So, to the question "should the main power supply of an AI server use triple insulated wire", the honest answer is: the main power stage does not, and should not be thought of in terms of single-strand TIW; that is the territory of planar and litz. DAH JIN is the manufacturer (own factory in Guiren, Tainan, Taiwan; the manufacturing site stated in the UL file is this plant), its four triple insulated wire types (TLW-B / TLW-BB / TLW-B7S / TLW-F) belong on small isolation transformers, and all conditions are per the Approval Document; this article does not claim that DAH JIN products have been designed into any specific AI server or data center, nor does it take any value from the third-party design above as a DAH JIN condition. For the auxiliary power stage where TIW can genuinely come into play in the same PSU, see Data-Center and AI-Server Power: Why the Main Power Stage Uses Planar and Litz; for the first branch of type and thermal class, see the Triple Insulated Wire Selection Guide and Wire Thermal Class vs. Insulation System Thermal Class.
Frequently Asked Questions
Why doesn't the main LLC transformer of an AI server use triple insulated wire?
The main LLC transformer mostly uses a planar structure, with windings implemented as etched copper layers of a multilayer PCB, and primary/secondary isolation achieved by the PCB interlayer insulation, an insulation foil (such as 50 μm Kapton) and creepage / clearance (as in Infineon's 12 kW AI data-center PSU). Isolation and windings at this stage do not pass through a single-strand winding wire, so it is not the category of single-strand triple insulated wire.
What wire do the resonant and magnetizing inductors use, and why not TIW?
Litz wire (litz). At several hundred kHz, the skin and proximity effects send AC resistance soaring, and the standard answer is to spread the current over dozens to hundreds of fine twisted strands (in the Infineon design above, 300 strands for the magnetizing inductor and 512 strands for the resonant inductor, each 50 μm). This is to keep high-frequency copper loss down, not to provide creepage-free safety isolation, so it uses multi-strand litz wire rather than single-strand TIW.
DAH JIN's TLW-B7S is also stranded; can it serve as the litz wire of a main-power inductor?
The two should not be confused. TLW-B7S has seven strands of 0.10–0.30 mm each (per the Approval Document) with a three-layer insulation on the outside, to achieve reinforced insulation on small isolation transformers; the litz wire of a main-power inductor has dozens to hundreds of finer strands, to keep AC resistance down. Strand count, strand diameter and purpose all differ. To evaluate your design, please contact our sales team to define the scope per the Approval Document.
Then where is DAH JIN triple insulated wire used in an AI server?
Not in the main power. Main power is the territory of planar transformers and litz wire. DAH JIN's four triple insulated wire types belong on the small isolation transformers of the auxiliary / standby / bias and gate-drive stages, with conditions per the Approval Document, and registration of an insulation system additionally requires an Authorization Letter. See Data-Center and AI-Server Power: Why the Main Power Stage Uses Planar and Litz.