A mains-powered smart LED bulb has two electrical jobs that should not be collapsed into one. Its LED array needs controlled current at a voltage determined by the LED string, while its Wi-Fi or Bluetooth controller needs a stable low-voltage supply.

A simplified architecture is:

220-240 V AC
     |
input protection and rectification
     |
     +--> LED power stage --> R / G / B / WW / CW channels
     |
     +--> low-voltage supply --> MCU + Wi-Fi/Bluetooth + control logic

The exact topology varies between products. The important boundary is the separation between LED power and logic power.

The LED path regulates current

LED brightness is closely related to forward current. Forward voltage changes with LED type, temperature, manufacturing variation, and the number of junctions connected in series.

For an idealized string:

Vstring ≈ Vf1 + Vf2 + ... + Vfn
PLED = Vstring × ILED

A driver regulates current through the string while allowing its output voltage to settle within the required operating range. A 5 V constant-voltage supply solves a different problem: it attempts to hold its output near 5 V while the connected circuit determines current.

That makes a 5 V supply suitable for electronics designed around a 5 V rail, but not automatically suitable for a bare high-power LED array.

The wireless controller needs a low-voltage rail

A smart bulb also contains a microcontroller or wireless SoC and supporting control circuitry. These parts operate at much lower voltages than many series LED strings.

The logic rail can come from a dedicated AC-DC stage, an auxiliary supply associated with the LED converter, or another regulator connected to an internal DC bus. The implementation differs, but its function remains distinct:

LED path    -> controlled LED current
logic path  -> regulated low-voltage supply

An ESP32 development board that accepts 5 V normally regulates that input further for its 3.3 V logic. A bare module must be powered according to its own specification; the input rating of a development board cannot simply be copied to the module.

RGBWW adds five controllable channels

An RGBWW lamp typically has red, green, blue, warm-white, and cool-white channels. Requested color and brightness are produced by controlling the contribution of those channels rather than varying one global supply voltage.

wireless command
      |
 MCU / wireless SoC
      |
      +--> red
      +--> green
      +--> blue
      +--> warm white
      +--> cool white

PWM is a common control technique, but the power stage must still respect the current limit of each LED channel. Warm-white and cool-white channels provide the normal white-light path and allow the lamp to vary its correlated color temperature.

COB describes packaging, not supply voltage

COB means Chip on Board. Multiple LED dies are mounted closely on a common substrate and presented as one light-emitting module.

COB does not imply 5 V, 12 V, or mains voltage. Different modules contain different series-parallel arrangements, so their required current and forward-voltage range must come from their specifications.

Two COB modules with similar dimensions can therefore have different electrical operating points. Mechanical fit is not evidence of electrical compatibility.

Thermal design also remains necessary. A compact high-power COB concentrates heat into a small area, making the substrate, thermal interface, and heat sink part of the reliability design.

A 5 V LED simplifies the low-voltage prototype

LED products designed for 5 V DC do exist. USB lamps, small LED boards, and addressable LEDs are common examples. They can simplify a prototype because the controller and lighting circuit may share a 5 V source.

A low-voltage smart-light prototype can use:

certified isolated 5 V adapter
       |
       +--> controller
       |
       +--> compatible 5 V LED stage

This does not turn an integrated mains bulb into a 5 V appliance. A product connected directly to 220-240 V AC still needs a mains-rated conversion stage before its low-voltage circuitry.

AC-DC and DC buck converters are different stages

The term step-down is often applied to both, but their input domains are different.

A DC buck converter converts a higher DC voltage to a lower DC voltage. It must not be connected directly to 220-240 V AC unless its specification explicitly supports that mains input.

A mains AC-DC supply instead performs:

220-240 V AC -> regulated low-voltage DC

A smart bulb may contain several conversion stages. Identifying the voltage and function at each node is more precise than calling every converter a step-down module.

A low voltage label does not guarantee touch safety

Smart bulbs can use isolated or non-isolated power architectures. In a non-isolated design, a rail that measures only a few volts between its own conductors can still sit at a hazardous potential relative to earth.

A node labeled 5 V is therefore not automatically safe to touch. Galvanic isolation from mains, enclosure construction, insulation, and accessibility determine the safety boundary.

This is particularly important on a bench. Connecting a USB programmer, oscilloscope, or grounded computer to an unknown non-isolated bulb circuit can create a hazardous current path. For firmware development, a properly isolated external adapter keeps mains away from the controller and debugging equipment.

Power and heat constrain a compact bulb

A nominal 12 W smart bulb cannot allocate all input power to its LEDs. The LED driver, low-voltage regulator, wireless controller, and switching devices all consume or dissipate power.

A simplified balance is:

Pin = PLED + Pcontrol + Ploss

The enclosure also limits heat removal. Increasing LED current can increase light output while also raising junction temperature and driver stress. Copying only the wattage printed on a commercial bulb is therefore insufficient. LED current, string voltage, conversion efficiency, thermal resistance, enclosure temperature, and component ratings must work together.

Keep mains outside early prototypes

For smart-light firmware experiments, an isolated 5 V adapter, an ESP32-class development board, and a compatible low-voltage RGB or RGBWW stage preserve the important control behavior without exposing a mains power stage on the workbench.

Moving that prototype into a 220-240 V bulb is a separate power-electronics and product-safety task. The integrated design must account for mains input protection, insulation or isolation strategy, PCB clearances, thermal behavior, fault conditions, enclosure construction, and applicable safety requirements.

The useful architectural boundary is not simply 220 V versus 5 V. It is the separation between mains conversion, the constant-current LED path, and the regulated logic rail. Keeping those functions distinct makes a Wi-Fi RGBWW bulb easier to design, diagnose, and modify safely.

Smart Bulb LED Driver Power Supply Wi-Fi