LNK604DG-TL — LinkSwitch-II LED Driver IC, Primary-Side CC/CV (SO-8C)

What Are the Technical Specifications of LNK604DG-TL?

Key numbers that matter. The 700V MOSFET rating isn't just headroom — it's what lets this chip connect directly to rectified 230V AC (325V DC bus) with margin for leakage spikes. The 4.1W rating is open-frame; in an enclosed GU10 bulb with poor airflow, derate to ~3W.

The FB pin does double duty. In CV mode (FB = 1.88V), the resistor ratio sets output voltage. In CC mode (FB drops below 1.88V), the absolute resistor value sets output current.

Same two resistors control both modes. Smart design with a catch: changing output current means recalculating both values — keep the ratio, adjust the absolutes. Use the PIXLS spreadsheet; don't calculate by hand.

When Should You Use (and NOT Use) the LNK604?

✅ Use LNK604 when:

• You need an isolated LED driver under 4W. GU10 bulbs, small downlights, indicator/signage lighting. The internal 700V MOSFET and primary-side control make this a 17-component solution — including the transformer.
• Safety isolation is mandatory. If the LED heatsink is user-accessible, you need isolation between mains and the LED. The LNK604's flyback topology with an isolated transformer gives you that. Non-isolated bucks (LinkSwitch-TN) don't.
• You want to eliminate the optocoupler. Traditional isolated flybacks need an optocoupler + TL431 on the secondary side for feedback. The LNK604 senses output conditions from the primary side through the FB pin. Fewer parts, smaller board, no optocoupler aging drift.
• BOM count and board space are tight. With integrated 700V MOSFET, integrated controller, and primary-side feedback, you're looking at roughly half the component count of a discrete flyback LED driver at the same power level.
• EMI compliance matters. The frequency jittering spreads EMI across a band instead of concentrating it at a single frequency. This can save you a filter stage — meaningful in a GU10 bulb where there's no room for a bulky common-mode choke.

❌ Don't use LNK604 when:

• You need dimming. The LNK604 has no dimming input. No TRIAC dimming, no PWM dimming, no 0-10V. If the LED needs to dim, step up to a LYTSwitch family part or add a secondary-side PWM dimmer.
• Power exceeds 4W. At 5W and above, the LNK604 runs out of thermal margin, especially in enclosed fixtures. Use LNK605 (5.5W) or LNK606 (6.5W) from the same family.
• You don't need isolation. For non-isolated LED drivers (where the LED assembly is double-insulated and inaccessible), LinkSwitch-TN with buck topology is cheaper and simpler. Same company, different family, significantly lower BOM cost.
• Output voltage needs to be adjustable in the field. The LNK604's CC/CV transition point is set by fixed resistors. There's no trim pin. Changing output current means swapping resistors — fine for production, useless for field adjustment.

What Are the Alternatives to LNK604?

LNK604 vs LNK306 — isolated or not? This decision drives your entire design. The LNK604 gives isolation through a flyback transformer — essential when the LED heatsink can be touched. The LNK306 uses a non-isolated buck, cheaper and simpler, but the LED board sits at mains potential.

If the fixture keeps the user away from anything conductive, LNK306 saves money. If a safety standard says "isolate," LNK604 is the answer.

LNK604 vs TNY280 — LED driver or general-purpose? The TNY280 is a more powerful switcher, but it's a blank canvas. No built-in CC mode, no primary-side CV/CC transition — you build your own feedback loop.

For LED driving, the LNK604's built-in CC regulation and auto-restart fault protection save at least 5 components. Use TNY280 when you need the extra watts and are willing to design the CC loop yourself.

What Are the Typical Applications of LNK604?

GU10 LED Bulb (3W, 9V/330mA). The reference design is DER-351 — Power Integrations wrote the datasheet around this application. Universal 90–265VAC input, isolated flyback, 17 components total. Efficiency ≥75%.

Meets EN55015 Class B EMI without an external filter stage. If you're building a GU10 bulb, start with DER-351 and adjust the transformer for your LED voltage.

Small LED Downlight (3–4W). Recessed ceiling fixtures where the driver sits in a tight enclosure behind the LED. The LNK604's 150°C junction rating and auto-restart thermal shutdown let it run in hot, poorly ventilated cavities without dying on the first summer day.

LED Signage / Channel Letter Driver. Powers LED strings at constant current for illuminated signs. Primary-side regulation keeps high-voltage traces on the AC side of the PCB. Only the transformer secondary winding goes to the LED string.

Appliance Indicator Lighting. Washing machines, refrigerators, ovens — the LED that tells you the machine is on needs a driver that survives 10 years of heat, vibration, and power cycles. The LNK604's auto-restart protection means it recovers from a momentary line dropout without latching off.

Low-Power Battery Charger (CV mode). The LNK604's CV/CC characteristic works for small battery chargers, not just LEDs. CC phase charges at constant current, CV phase holds float voltage.

At 4.1W, it suits single-cell Li-Ion or 2–3 cell NiMH packs where a dedicated charger IC is overkill.

Why Buy LNK604DG-TL from ICMASS?

Factory-authorized supply, not broker stock. The LNK604 is a niche part — low volume compared to general-purpose switchers, which makes it a target for counterfeiters who re-mark cheaper ICs. We source direct from Power Integrations authorized distribution with lot traceability back to the fab.

We stock the full LinkSwitch-II lineup. Need the 5.5W LNK605 for your next spin? The 6.5W LNK606? We carry the whole family. Same SO-8C footprint, same reference design, just adjust the transformer and resistors for the higher power level.

Know your application, get the right variant. The "DG" in LNK604DG means SO-8C package. The "-TL" suffix means tape and reel (2,500 units/reel). We also stock tube packaging for prototyping. Tell us whether you're building 100 or 100,000 and we'll quote the right packaging.

Shenzhen warehouse, global DHL/FedEx. Same-day shipping for orders before 15:00 CST. International delivery in 5–10 days. Contact us for current pricing on your quantity.

Frequently Asked Questions About LNK604

Q1: Why is my LNK604 output current lower than expected?

A: Transformer design is the #1 culprit. The LNK604's CC setpoint depends on both the FB resistor values and the transformer turns ratio. If you substituted a different transformer core or changed the winding structure from the reference design, your actual output current will deviate. Second suspect: FB resistor tolerance. Use 1% resistors on the FB divider.

Q2: My LNK604 output shoots up to 35V with no load. Is this normal?

A: Yes — the LNK604 regulates current, not voltage, at light load. With no LED connected, the flyback has nowhere to dump energy except the output capacitor. Voltage rises until the over-voltage protection kicks in or the cap rating is exceeded. Always test with a load connected, or add a zener clamp across the output.

Q3: How do I set output current vs output voltage on the FB pin?

A: The FB pin resistors control both, but differently. CV mode (FB = 1.88V): the ratio of the upper to lower resistor sets V_out. CC mode (FB < 1.88V): the absolute value of the lower resistor sets I_out. To change current while keeping voltage the same: change both resistors proportionally (keep the ratio, adjust the values). Use the PIXLS spreadsheet — don't calculate by hand.

Q4: Does LNK604 need an optocoupler?

A: No. That's the whole point of the LinkSwitch-II family. Primary-side control senses the output condition through the transformer's reflected voltage on the FB pin. It eliminates the optocoupler, TL431 reference, and secondary-side compensation network that a traditional isolated flyback needs.

Q5: Can I dim LEDs with the LNK604?

A: No. The LNK604 has no dimming input of any kind. No TRIAC dimming, no PWM pin, no analog dimming input. It's a fixed-output CC/CV controller. For dimmable LED drivers, look at Power Integrations' LYTSwitch family or add a secondary-side PWM dimmer after the output.

Q6: What's the difference between LNK604, LNK605, and LNK606?

A: Only the power rating. Same pinout, same package, same control scheme. LNK604 = 4.1W, LNK605 = 5.5W, LNK606 = 6.5W (all open frame). The higher-power parts have a larger internal MOSFET die. You can drop an LNK605 or LNK606 into an LNK604 footprint if you need more headroom — just verify the transformer can handle the higher peak current.

Q7: Do I need a bias winding on the transformer?

A: Not for most LNK604 designs. The IC can self-power from the drain pin through an internal regulator. A bias winding improves efficiency by ~2–3% and reduces no-load consumption below 30mW, but it's optional. The reference design DER-351 doesn't use one.

Q8: Why does my LNK604 design fail EMI testing?

A: The frequency jittering helps, but it doesn't replace good layout. Keep the input filter loop (bulk cap → transformer primary → drain pin → source pin → sense resistor → bulk cap return) as short as possible. Add a snubber across the primary winding. If you're still failing, add a small common-mode choke before the bridge rectifier.

Q9: Can LNK604 run from a DC input instead of AC?

A: Yes, but the minimum DC voltage matters. The IC needs the drain voltage to exceed the UVLO threshold (~50V DC) to start switching. Below that, it won't turn on. For 12V or 24V DC input, you need a boost-front-end before the LNK604, or use a different IC designed for low-voltage DC input.

Q10: LNK604 vs LNK306 — which one for my LED bulb?

A: Depends on isolation requirements. If the bulb's LED board is enclosed in an insulated housing that can't be touched, the LNK306's non-isolated buck is cheaper and simpler. If the housing is metal or the LED heatsink is exposed, you need the LNK604's isolated flyback. Safety certification will tell you which one — don't guess.