LED light shrinks size, cost with non-isolated driver

March 11, 2013 // By Margery Conner

LED bulb prices are dropping. A year ago you could expect to pay $50 for a Philips dimmable 60W-replacement LED bulb, while today you can go to Best Buy and purchase its house brand 8W, 800 lumens Insignia 60W-replacement bulb for just $17. What has changed in LED bulb design to allow this price drop? Tearing apart the bulb gives us a look into some design trends in LED lighting, such as how the LEDs are placed within the bulb and what driver architecture is used.

The Insignia bulb has a shape similar to the familiar incandescent light, with the addition of three metal heat sink fins, and a plastic bulb instead of glass ( Figure 1 ).

                                        Figure 1

Dimming is an important bulb characteristic for the US market. I used a Lutron Maestro dimming switch, with a programmable dimming control, and did a side-by-side comparison with an incandescent bulb. The Insignia dimmed consistently and smoothly, with a dimming profile similar to the incandescent bulb. You can watch a video of the dimming test here .

The next step was to look inside the bulb and see how the LEDs are mounted. Figure 2 shows the plastic bulb cover removed with a Dremmel tool, exposing the six Cree white LEDs that illuminate the bulb's light mixing chamber that allow an even glow with no pixelation. The metal fins that the LEDs are mounted on serve to both elevate the LEDs and serve as heat sinks.

                                        Figure 2

At the bottom of the mixing chamber is a paper-thin aluminum reflector that helps reflect the light up and out of the bulb.

All of the electronics for this bulb lie beneath the mirror in the base of the bulb, in a separate and encapsulated compartment ( More detailed photos are here ).

Removing the rubbery potting compound shows that the electronics are mounted on two separate pc boards that