Innovative technology: 360-degree LED filament bulb

Tungsten filament incandescent lamps are about to be eliminated. Many people are nostalgic for the incandescent lamps that have been used for more than 100 years. LED lighting will eventually replace tungsten filament incandescent lamps. This is an inevitable trend in the development of modern science and technology. Nowadays, the energy saving, power saving, pollution-free and high environmental protection of LED lighting are well known to passers-by. However, due to the high production cost of LED lighting, the current retail price of LED lighting is still difficult to make LED lighting fixtures enter thousands of households; at present, there is no perfect solution to the heat dissipation bottleneck of LED lighting fixtures that use low-voltage LED lamp beads as light sources. Only by relying on the systematic technological revolution and technological innovation of LED lighting fixtures can we make breakthroughs and create a new generation of more reasonable and cost-effective LED lighting fixtures for the enjoyment of ordinary people in the whole society.

Many people hope that LED lamps can be made as light as tungsten filament incandescent lamps and emit 360° light. This is difficult to achieve in the current LED lighting fixtures with low-voltage LED lamp beads as the light source. Reforming the shape of LED lamp beads and making innovative designs is the way to hope.

Figure 1 Heat dissipation of LED lamp bead board

LED light source packaging technology innovation

Innovative design of LED light source packaging technology is the key to the rebirth of LED lighting fixtures. Most of the current LED lamps use low-voltage LED lamp beads (LVLED) with low working voltage (VF=3.2V) and high current (IF=200-700mA). When LED lamp beads are working, only 30% of the electrical energy is converted into light energy, and 70% of the electrical energy is converted into heat energy. Therefore, if the heat dissipation of LED lamps is not done well, a large amount of heat will accumulate and the lamp cavity will always be in a high temperature environment. The electrolyte in the electrolytic capacitor of the switching constant current power supply will be exhausted due to the high temperature, resulting in failure; LED lamp beads will age prematurely due to being in a high temperature environment for a long time.

The birth of HVLED (high voltage LED) lamp bead technology has brought new vitality, new concepts, and new design ideas to indoor LED lighting fixtures. This will give birth to many new LED lighting products and new lamps with fantastic ideas. The biggest features of HVLED are high voltage (VF=50-280VDC) and low current (IF=20-60mA). Compared with LVLED lamp panels of the same power, its heat generation is much lower. HVLED is a module that connects N low-voltage LED tube cores in series to form a high-voltage module during packaging, and its application is also very convenient.

The packaging of LED tube cores has evolved from single-core packaging to N-core collective packaging, such as COB, COF, etc., and has also shifted from low-voltage LED modules with fewer strings and more parallels to HVLED modules with more strings and fewer parallels and multiple cores. The packaging technology of LED light sources is constantly innovating.

From the perspective of application technology, the central LED core of COB LED light source board still has the problem of difficult heat conduction and poor heat dissipation. The heat of LED will gather in the center of COB. Therefore, after long-term use of this kind of LED lamp, the central LED core will decay first. Multi-core packaged HVLED can use N-chip uniform distribution technology on the same power lamp board. The heat of each HVLED is quickly conducted and dissipated by the aluminum substrate. HVLED works under low current, and its own heat generation is much lower. The heat dissipation of these two LED lamp bead boards is described in Figure 1.

Figure 2 LED filament column of ELC die

Technologically innovative LED filament column packaging technology

The innovative LED filament column packaging technology is developed based on the concept of HVLED. N low-power LED tube cores are packaged in series on a glass substrate, which is a new package different from the past. Taiwan Jingyuan first proposed the new concept of LED filaments, encapsulating N ELC LED tube cores on a glass column substrate, connecting them in series with gold wire to form a high-voltage HVLED module, spacing them with reflectors, and coating them with yellow phosphor. Figure 2 shows the structure of the LED filament column with ELC tube cores.

The innovative design of LED engineers in mainland China is to directly package N low-power LED tube cores on the glass column substrate. For example, 28 1016 LED tube cores with a power of 0.02W each are packaged on a glass column substrate with a length of 38mm and a diameter of 1.5-1.6mm, and connected in series with gold wire. The VF of this LED filament column is 3.2X28=89.6V, IF=10mA. The biggest feature of the LED filament column is that it emits light at all angles at 360 degrees, and uses high voltage (75-90VDC) and low current (10-15mA) to drive the working state; using high-quality LED tube cores, it can produce high-brightness (75-95lm), high-light efficiency (120-130lm/W), high-color rendering index (90-95Ra), and high-reliability LED filament columns; mixing blue and red LED tube cores in different proportions can produce LED filament columns with different color temperatures (2870-6020K). The structure of the high-voltage LED filament column is shown in Figure 3. The blue and red LED cores are encapsulated on the glass column substrate and arranged according to a pre-set rule. Lead electrodes are set at both ends. After the gold wires are connected in series, yellow or yellow-green phosphor is sprayed and the whole is wrapped. Pay attention to high voltage protection during the power-on test. This type of LED filament column works in a low current and low power state of 10-15mA. The entire LED filament column is suspended in full contact with the air, with smooth heat dissipation and low heat generation, and is basically not hot.

Figure 3 Structure of high-voltage LED filament column LED filament bulb

It is very easy to design various small and medium power LED bulbs using LED filament columns. Taking candle lamps as an example, two LED filament columns connected in series can be designed into a 1.8W candle lamp with 360° light emission, and the light emission brightness can be equivalent to that of an 8-10W incandescent lamp (Figure 4). Two series and two parallel LED filament columns can be designed into a 360° light emission 3.6W bulb, and the light emission brightness is equivalent to that of a 22W incandescent lamp (Figure 5).

Figure 4 LED filament column and candle lamp

Figure 5 3.6W bulb with 360° light emission

Any incandescent lamp factory can use existing technology and assembly lines to produce LED filament bulbs, and use the original glass bracket of incandescent lamps to design the connection of LED filament columns (Figure 4); use the special glass with high light transmittance of incandescent lamps and automatic glass blowing bulb production technology to design and produce bulb covers that are similar to incandescent lamps, thereby producing cost-effective LED filament bulbs and a new generation of glass decorative lamps that are popular in the European and American markets and have good profits.

Design technology of LED filament bulb

The design technology of LED filament bulbs includes the design of LED filament column, the design of driving power supply, and the shape design of glass bulb. LED filament column is professionally designed and produced by LED packaging factory. Traditional incandescent lamp factory is not suitable to invest in LED packaging. If there are electronic engineers in incandescent lamp factory, they can design and produce driving power supply by themselves. Driving power chip companies generally provide a variety of power supply solutions that are applicable and can be used for production. In the early stage, ready-made driving power supply can be purchased to reduce the risk of initial production.

The system structure of LED filament bulb is shown in Figure 6, which consists of LED filament column, driving power supply, glass lamp column bracket, glass bulb, and standard lamp holder hardware. All of them are low-cost devices, which can produce affordable LED lighting fixtures for mass lighting needs. For example, the BOM cost of 1.8W LED filament candle lamp is less than RMB10; the BOM cost of 3.6W LED filament bulb is less than RMB15.

Figure 6 System structure of LED filament bulb

Selection of driving power supply

LED light sources must be driven by constant DC current to emit light stably without flickering. For the selection of driving power supply, it is recommended to use a non-isolated switch constant current source, which has the advantages of high efficiency, good PF, high chip integration, and simple application circuit. For example, BP2831/2832 has high functional integration, built-in MOSFET, high PF value, very simple application circuit, only 14 peripheral original components, high reliability, excellent linear regulation rate, load regulation rate, can be achieved through conduction and radiation, the area of ​​PCB board is Φ25mm, and the cost of the entire power supply is less than RMB2.50 (Figure 7).

Figure 7 BP2831 non-isolated driver power supply

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