Toshiba and Sharp's new LED bulb internal structure secret

Lighting fixtures using light-emitting diodes (LEDs) as a light source have gradually entered the market due to their low power consumption and long life. Among them, bulb-type LED lighting (hereinafter, referred to as LED bulbs) intended to replace conventional bulbs such as incandescent bulbs and bulb-type fluorescent lamps has recently attracted much attention. Since the unit time price of a bulb calculated according to the life of the LED has been comparable to that of a conventional bulb, it is expected to be popularized in an ordinary household.

The first to introduce low-cost LED bulbs is Sharp. Sharp announced on June 11, 2009 that the company will enter the LED bulb market at a low price of less than 4,000 yen at the actual price. This price setting is very impactful, and the LED bulb is commercially available at that time. Half the price. Toshiba Lighting, which began selling LED bulbs in March 2009, responded quickly. After 11 days of Sharp's product release, on June 22nd, a new low-cost LED that was launched on July 15 with Sharp was released. Light bulb products *1, *2.

New LED bulb

The lower half of the bulb is a heat sink

Low price does not mean that LED bulbs can abandon the unique advantages of low power consumption and long life. Moreover, if the product is to be based on the market, it needs to have a higher heat dissipation capability.

The light emitted by the LED bulb has less infrared components. Therefore, compared with the incandescent bulb and the bulb type fluorescent lamp, the light irradiation portion is heated slowly by *3. However, the LED itself will generate heat, so the heat dissipation countermeasure is indispensable. Once the allowable temperature of the LED chip is exceeded, the luminous efficiency of the LED will decrease, which will adversely affect the life of the bulb.

From the outside, the characteristics of the LED bulb can be said to be the result of improved heat dissipation. Looking at the LED bulb from the side, more than half of the overall lower side is the heat sink (Figure 1). Toshiba Lighting and Sharp have used radiators made of aluminum alloy castings.

Comparing the heat sinks of the two, in addition to the color, the shape difference is also very obvious. Although the Sharp product is slightly more in terms of height, the channel area of ​​the radiator is larger than that of Toshiba. The channel depth of Toshiba's lighting products gradually increases from bottom to top, while Sharp's is basically the same height.

The larger the surface area of ​​the heat sink, the higher the heat dissipation performance. In the case of a limited external dimension, increasing the channel depth is one of the methods of increasing the surface area, but as the channel depth increases, the internal mounting space of the power circuit board, the resin case, and the like is reduced by *4.

The internal space of the Toshiba lighting radiator is cylindrical, and the Sharp product is a conical shape close to the shape (Fig. 2). The resin case is mounted on the bulb housing while maintaining insulation.

Figure 2: The main structure of the LED bulb The Toshiba Illumination LED bulb radiator (housing) has 16 right-angled triangular channels on the side of the cylinder, which are covered with a circular plate. The LED substrate is directly fixed on the top. The power circuit bottom plate is fixed in the cup-shaped resin case and inserted from below the heat sink. On the other hand, the Sharp LED bulb has a tapered cylindrical shape with 60 blades with a height of less than a few mm. The LED substrate is fixed to a circular plate-shaped metal plate covered above the heat sink. The base plate of the power supply circuit is fixed in a conical (but mostly hollowed out) resin case A inserted above the heat sink.


The LED chip is the largest heat source for the LED bulb. In the bulb, a plurality of LED chips are packaged together and then mounted on a substrate made of an aluminum alloy. This aluminum alloy LED substrate is fixed to the upper portion of the heat sink. In Sharp's products, there is a metal plate between the LED substrate and the heat sink.

This article will combine the Toshiba lighting products and Sharp's LED bulb disassembly diagram to detail its internal structure.

*1: Sharp's initial scheduled time to market is July 15, 2009. However, on July 9, the company issued a decision to postpone the listing due to “scheduled over expectations”. LED bulbs that support dimmers and dimming/toning functions will be available on September 1 of the same year. Other LED bulbs will be available on August 1 of the same year.

*2: Bulb giant Panasonic has exhibited a bulb-type LED at the "LightingFair2009" exhibition held in March 2009, but as of early August 2009, the company "has not yet put into production a specific plan."

*3: The LED bulb has a small amount of ultraviolet light, so it has the advantage of not attracting UV-sensitive insects.

*4: Increasing the surface area requires increasing the blade height or reducing the blade spacing (increasing the number of sheets). Toshiba Lighting refers to the air flow (convection) around the radiator when determining the spacing and height of the blades.

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