This application note explores the trends in light-emitting diodes (LEDs) in general-purpose lighting applications, compares the performance of LEDs with other lighting technologies, and analyzes the design of LED lights and the main challenges in replacing existing lighting solutions.
LED lighting trends
Light-emitting diodes (LEDs) are a rapidly evolving technology that is being widely used in many general-purpose lighting applications, often referred to as solid-state lighting. Typical applications for LED lighting are: indoor lighting (for commercial, industrial and residential environments), outdoor lighting (street lights, parking lot lighting), and architectural, decorative lighting, etc. Initially, LEDs were used because they were capable of emitting color throughout the spectrum. For decorative lighting.
In some cases, LEDs have become an effective solution for architectural lighting. Compared with other lighting technologies, LEDs have superior performance and thus become the mainstream solution for the current general lighting market:
1. LEDs have a longer life than other lighting technologies. LEDs have a working life of up to 50,000 hours, while incandescent lamps have a lifespan of only 1,000 to 2,000 hours, and compact fluorescent lamps (CFLs) have a lifetime of about 5,000 to 10,000 hours. The significant advantages in service life make LEDs ideal for commercial and industrial applications that require significant labor costs to replace lighting.
2. Energy efficiency is better than incandescent and halogen lamps, equivalent to fluorescent lamps. In addition, the efficiency of LEDs is also increasing; the efficiency of white LEDs (WLEDs) is expected to increase by about 50% in the next three to four years.
3. Smaller form factor. LEDs are the same size as MR16 and GU10, and CFLs are not suitable for this type of application.
4. Brightness adjustment can be provided with a suitable driver. Fluorescent lamps are technically limited for applications that require brightness adjustment. Despite the similar problems with traditional LED designs, Maxim's innovative LED driver solutions are compatible with TRIAC dimming and trailing edge dimming.
5. Has a strong directionality of illumination. Unlike other lighting technologies, LEDs are ideal for applications that require directional lighting, such as small angle reflectors.
6. Higher efficiency at lower temperatures. The operating efficiency of fluorescent lamps decreases at low temperatures. In contrast, LEDs are ideal for low temperature work environments such as refrigerator lights.
7. Easily change the color of the glow. This advantage makes RGB LEDs ideal for architectural and scene lighting, allowing you to change the color of the lights in real time, depending on your requirements.
In short, LEDs have many advantages not found in incandescent and fluorescent lamps. Based on these advantages, designers are constantly exploring more applications for LED lighting, but due to limited space, we will not repeat them here. This article will focus on LED lighting replacement products to replace incandescent, halogen or fluorescent lamps of the same specification. These LED lights must be able to fit into existing sizes and be compatible with existing infrastructure.
LED replacement lamp
Many people think that LED replacement lamps are the fastest growing market for LED lighting. The reason for the rapid growth is simple: these lights do not need to update the electrical infrastructure (ie wiring, transformers, dimmers and sockets), which is a significant advantage of LED technology.
For designers, there are two main challenges to installing LED lights onto existing infrastructure:
1. Dimensions. The replacement lamp must be able to be installed in the frame of the previous lamp source.
2. Electrically compatible. The replacement lamp must be able to work properly on the existing electrical architecture without flashing lights.
Below, we will discuss each challenge one by one.
Install to an existing framework
The existing frame imposes physical limitations on the replacement lamp (ie, the drive board must be small enough) and thermal limit requirements. These factors constrain the designer's ability to change lighting schemes (such as PAR, R, and A specifications), and the smaller the size, the greater the difficulty faced by applications such as MR16 and GU10.
Size is a key factor in the replacement scheme, and thermal constraints are often more critical. LEDs emit only visible light. Unlike other technologies, they do not generate infrared radiation energy. Therefore, white LEDs are more energy efficient than incandescent or halogen lamps, and most of the heat is dissipated through the inner conductor of the lamp.
Heat dissipation is a key factor that limits the light intensity that can be produced by a lamp. At present, the LED technology used in lighting replacement products is difficult to reach the brightness level acceptable to the mainstream market. In order to break through the brightness limit, it is necessary to solve the heat dissipation problem, which is also an indispensable condition for the product to successfully commercialize.
The heat dissipation problem also directly affects the service life of the drive board. In order to emit higher light intensity, the illuminator must be operated at a relatively high temperature (+80 ° C to +100 ° C). At this temperature, the life of the drive board limits the operation of the entire light, especially electrolytic capacitors become a thorny issue in design. Because electrolytic capacitors dry quickly at high temperatures, the operating life of such capacitors does not exceed thousands of hours under such conditions, which is a factor that limits the life of the entire lamp. A longer working life is a major selling point for LED lamps. For designers, electrolytic capacitors with relatively short life have become the main barriers to design.
Maxim has introduced a unique LED driver solution for 120VAC/230VAC input and 12VAC input replacement lamps. These LED driver solutions eliminate the need for electrolytic capacitors on the board, extending the life of LED lamps from typically less than 10,000 hours to 90,000 hours. Since the electrolytic capacitor is omitted, it also helps to reduce the size of the solution, so that the driver board can be installed into the frame of the small size replacement lamp.
Compatible with electrical infrastructure
LED replacement lamps must operate under existing infrastructure, including chamfering (triacs and post-delay) dimmers and electronic transformers.
When connected to a 120VAC/230VAC power supply, the illuminator can be first adjusted by a triac dimmer. The triac dimmer is designed to work well with incandescent and halogen lamps, all of which are purely resistive. However, when using LED retrofit lamps, LED drivers are typically non-linear, non-pure resistive loads, and input bridge rectifiers typically absorb large currents transiently when the AC input voltage is at positive and negative peaks. Triacs do not guarantee this requirement for LEDs because they do not provide the required startup current or provide hold current. As a result, the dimmer does not start properly or shuts down normally during operation, and it also causes the LED to flicker, which is also unacceptable to the system.
As a replacement, its electrical architecture is more in line with the design of 12VAC input illuminators, as electronic transformers and trailing edge dimmers can be connected to the input of the illuminator. However, the driver for the 12VAC input illuminator uses a traditional bridge rectifier and DC-DC converter topology, which also produces flicker due to incompatibility between the transformer and the dimmer.
Maxim's 120VAC/230VAC and 12VAC input illuminator solutions use a single stage of conversion. By shaping the input current, the illuminator does not flicker in the dimmed state. These solutions are compatible with bidirectional triacs and trailing edge dimmers and electronic transformer designs. At present, there is no MR16 solution with this feature, and few PAR, R and A lamp solutions have this feature. In addition, our solution has a power factor correction better than 0.9, requiring very few external components. Without electrolytic capacitors, these capacitors can severely restrict the operation of the driver circuit in high temperature environments. Both the 120VAC/230VAC and 12VAC solutions use the MAX16834 IC, which can be evaluated and put into mass production. These are Maxim's unique solutions, and Maxim is the only supplier that can offer this combination of advantages.
Block diagram of MR16 (top) and offline (bottom) lighting
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