INN3676C vs LNK364 vs LNK562 — Which Power Integrations Flyback Switcher Do You Actually Need?

What Are the Key Differences Between INN3676C, LNK364, and LNK562?

Read the table as three decisions, not twelve rows. The power column settles 80% of designs. The feedback column settles most of the rest — tight regulation and multi-output cross-regulation push you to a secondary-side loop, and only the INN3676C gets you there without an optocoupler.

The power ladder, 85–265VAC: the INN3676C out-rates the LNK364 by 6× and the LNK562 by nearly 19×. The gaps are the family boundaries — parts between 6W and 20W live in other PI families (TinySwitch, TopSwitch).

How Do the Three Feedback Architectures Compare?

Three ways to cross the isolation barrier. The opto sends a signal across with an LED and a transistor — proven, but the LED's light output degrades over life and the CTR drifts. The bias winding senses without any wire — cheapest, but it watches a proxy, not the output.

FluxLink is the third way: a magnetic link molded into the IC package itself. The secondary die senses the real output and the primary die receives the signal — bidirectional, no CTR drift, no light degradation. It's secondary-side regulation with a primary-side BOM.

Which Part for Which Application?

One question settles most designs. Output power in — part out. The 2W and 6W boundaries are real datasheet lines, not marketing: the LNK562 is 1.9W flat across its table, and the LNK364 holds about 6W universal input.

✅ Choose LNK562DN for sub-2W isolated rails. Standby supplies, trickle chargers, linear-transformer replacements — the CV/CC characteristic comes free and the BOM is about 14 parts. Accept the looser load regulation.

✅ Choose LNK364DN for 2–6W with a real regulation spec. Appliance control rails, metering, smart-home pods. The opto loop senses the actual output, and the self-powered design skips the bias winding.

✅ Choose INN3676C for 20–40W adapters and open-frame supplies. The 36W open-frame rating, 94% efficiency, integrated SR, and <30mW standby make it the low-BOM choice for USB-PD class adapters and industrial supplies. No heatsink below 40W in most open-frame builds.

What about the 6–20W gap? These three parts don't cover it. TinySwitch and TopSwitch families live there — the LNK364 tops out around 9W at 230VAC, and the INN3676C starts at 20W. If you're at 12W, neither of these is the right part.

The efficiency story. The INN3676C's 94% comes from synchronous rectification plus quasi-resonant switching — at 36W that's 2W+ of loss avoided versus a diode-rectified design. The LNK562's ~70% is the price of the 14-part BOM; at 1.9W nobody notices.

Frequently Asked Questions About INN3676C vs LNK364 vs LNK562

Q1: What's the actual difference between LinkSwitch and InnoSwitch?

A: Feedback architecture — primary-side regulation versus FluxLink. LinkSwitch families regulate without a secondary-side signal (or with an opto in the XT's case); InnoSwitch uses FluxLink, a magnetic link in the package, to bring secondary-side regulation to a no-opto design — tighter regulation and better transient response.

Q2: Why not use an InnoSwitch3 for a 3W supply?

A: The smallest InnoSwitch3-EP parts start around 10W. At 3W you'd pay for a package, a secondary-side controller, and an SR driver you don't need. The LNK562's 14-component BOM wins at that power — cost and board area.

Q3: Is the optocoupler actually a problem?

A: It's the weak point of an otherwise solid loop. The LED's light output degrades with age and current, CTR drifts, and the one-way path can't send secondary status back. For most products it's fine — for 10-year industrial life or tight transient specs, FluxLink removes the failure mode entirely.

Q4: Does the INN3676C need a heatsink?

A: Not for most open-frame builds. The heatsink is the source tab on the package, connected to primary ground copper. An EEVblog user running a 15W InnoSwitch3 build measured about 50°C on the chip — cooler than the transformer and rectifiers.

Q5: How does primary-side regulation behave with two outputs?

A: Cross-regulation suffers when one output loads and the other doesn't. A PI forum design thread on a dual-output flyback warned that PSR watches the winding, not each rail — a heavily loaded output can pull the lightly loaded one off-spec. Secondary-side regulation (opto or FluxLink) controls cross-regulation properly.

Q6: Which one has the lowest standby power?

A: The INN3676C at under 30mW; the LNK562 is also under 30mW. The LNK364's EcoSmart design keeps no-load low too, but the InnoSwitch3's integrated secondary controller wins the standby race at meaningful power levels — it's the one built for adapter standby specs.

Q7: Can I move a design between these parts?

A: Only within the SO-8C family. The LNK562 and LNK364 share the SO-8C footprint but not the feedback wiring — a PSR-to-opto move is a schematic change, not a swap. The INN3676C's InSOP-24D is a different footprint entirely.

Q8: What is FluxLink's isolation rating?

A: 4000VAC reinforced isolation, production-tested to 6kV DC. The magnetic link sits inside the package across a solid insulation layer — no air gap to fill, no creepage path to design, no external components at the barrier.

Q9: Which is cheaper to assemble?

A: The LNK562DN — roughly 14 total components and no secondary side at all. The LNK364 adds an opto, a TL431, and their resistors. The INN3676C adds an SR MOSFET but deletes the opto's circuitry — and at 36W, the efficiency saves enough that the part pays for itself.

Q10: How do I choose if I need CV/CC charging behavior?

A: The LNK562 and INN3676C both give CV/CC; the LNK364 regulates voltage only. For battery charging at sub-2W the LNK562 is the whole charger. For USB-PD class charging the INN3676C's CV/CC engine is the point of the part.