The main challenges faced when designing LED lamps and replacing existing lighting solutions

This application note discusses the development trend of light emitting diodes (LEDs) in general lighting applications, compares the performance of LEDs with other lighting technologies, and analyzes the main challenges faced when designing LED lamps and replacing existing lighting solutions.

The development trend of LED lighting

Light-emitting diodes (LEDs) are a rapidly developing technology that is being widely used in many general lighting fields, commonly referred to as solid-state lighting. Typical applications of LED lighting are: indoor lighting (for commercial, industrial and residential environments), outdoor lighting (street lights, parking lot lighting), and architectural and decorative lighting. Initially, light-emitting diodes were used for decorative lighting because they can emit colors across the entire spectrum.

In some cases, LED has become an effective solution for architectural lighting. Compared with other lighting technologies, LED has better performance and has become the mainstream solution in the current general lighting market:

1. Compared with other lighting technologies, LEDs have a longer service life. LEDs have a working life of up to 50,000 hours, while incandescent lamps have a service life of only 1,000 to 2,000 hours and compact fluorescent lamps (CFLs) have a service life of approximately 5,000 to 10,000 hours. This significant advantage in service life makes LEDs very suitable for commercial and industrial applications that require a large investment in labor costs to replace lighting lamps.

2. Energy efficiency is better than incandescent and halogen lamps, and equivalent to fluorescent lamps. In addition, the efficiency of LEDs is also constantly improving; the efficiency of white light LEDs (WLEDs) is expected to increase by about 50% in the next 3 to 4 years.

3. Smaller form factor. The form factor of LED lamps is equivalent to MR16 and GU10, while CFL cannot meet such applications.

4. Appropriate drivers can be used to provide brightness adjustment. For applications that require brightness adjustment, fluorescent lamps have technical limitations. Although traditional LED designs have encountered similar problems, the innovative LED driver solutions provided by Maxim are compatible with thyristor dimming and trailing edge dimming designs.

5. It has strong directional light emission. Unlike other lighting technologies, LED is very suitable for applications that require directional lighting, such as small-angle reflector lamps.

6. Higher efficiency at lower temperatures. Fluorescent lamps have lower efficiency at low temperatures. In contrast, LEDs are very suitable for low-temperature working environments, such as refrigerator lights.

7. The color of light can be easily changed. This advantage makes RGB LED an ideal choice for architectural and scene lighting, which can change the color of light in real time according to specific requirements.

In summary, LEDs have many advantages over incandescent and fluorescent lamps. Based on these advantages, designers are constantly exploring more applications suitable for LED lighting, but due to limited space, we will not go into details here. This article will mainly discuss LED lighting replacement products, which are used to replace incandescent, halogen or fluorescent lamps of the same specifications. These LED lamps must be able to be installed within existing specifications and compatible with existing infrastructure.

LED replacement lamp

Many consider LED retrofit lamps to be the fastest growing market for LED lighting today. The reason for this rapid growth is simple: these lamps do not require an update to the electrical infrastructure (i.e. wiring, transformers, dimmers, and sockets), a significant advantage of LED technology.

For designers, there are two main challenges in installing LED lights into existing infrastructure:

1. Dimensions. The replacement lamp must be able to be installed in the frame of the previous lamp source.

2. Electrical compatibility. The replacement lamp must be able to work properly on the existing electrical architecture without light flickering.

Below, we discuss each challenge one by one.

Installing into existing frame

The existing framework imposes physical limitations (i.e. the driver board must be small enough) and thermal restrictions on the replacement lamps. These factors restrict designers to replace lighting solutions (such as PAR, R and A-type specifications), and the smaller the size, the greater the difficulty, such as MR16 and GU10.

Size is a key factor limiting the replacement plan, but thermal limitations are often more critical. LEDs only emit visible light, and unlike other technologies, they do not generate infrared wave radiant energy. Therefore, white light LEDs are more energy efficient than incandescent or halogen lamps, and most of the heat is dissipated through the conductors inside the lamp.

Heat dissipation is a key factor that limits the light intensity that a lamp can produce. The LED technology currently used in lighting upgrade products is difficult to achieve the brightness level that the mainstream market can accept. In order to break through the brightness limit, the heat dissipation problem needs to be solved, which is also an indispensable condition for the successful commercialization of the product.

Heat dissipation also has a direct impact on the life of the driver board. In order to emit higher light intensity, the lamp must operate at a relatively high temperature (+80°C to +100°C). At this temperature, the life of the driver board will limit the operation of the entire lamp, and electrolytic capacitors in particular become a difficult problem for the design. Because electrolytic capacitors will dry out quickly at high temperatures, under such conditions, the working life of such capacitors will not exceed thousands of hours, which also becomes a factor restricting the service life of the entire lamp. Longer operating life is a major selling point of LED lamps, and for designers, the relatively short life of electrolytic capacitors becomes a major barrier to design.

Maxim has introduced unique LED driver solutions for 120VAC/230VAC input and 12VAC input retrofit lamps. These LED driver solutions can eliminate electrolytic capacitors on the circuit board, extending the life of the LED lamp from the usual less than 10,000 hours to 90,000 hours. The elimination of electrolytic capacitors also helps to reduce the size of the solution, allowing the driver board to be installed in a small retrofit lamp frame.

Compatible with electrical infrastructure

LED retrofit lamps must work properly with existing infrastructure, including cut-angle (triac and post-delay) dimmers and electronic transformers.

When connected to a 120VAC/230VAC power supply, the lighting can first be adjusted through a triac dimmer. The triac dimmer is designed to work well with incandescent and halogen lamps, which are pure resistive loads. However, when using LED retrofit lamps, the LED driver is usually a non-linear, non-pure resistive load, and the input bridge rectifier usually absorbs large currents transiently when the AC input voltage is at the positive and negative peaks. The triac dimmer cannot guarantee this requirement of the LED because it can neither provide the required startup current nor the holding current. As a result, the dimmer cannot start normally or shut down normally during operation, and it will also cause LED flickering, which is also an unacceptable phenomenon for the system.

As a replacement product, its electrical architecture is more in line with the design of 12VAC input lighting, because the electronic transformer and trailing edge dimmer can be connected to the input of the lighting. However, the driver of the 12VAC input lighting adopts the traditional bridge rectifier and DC-DC converter topology, which will also produce flicker due to the incompatibility of the transformer and dimmer.

Maxim's solutions for 120VAC/230VAC and 12VAC input lamps use single-stage conversion. By shaping the input current, the lamps can be dimmed without flickering, and these solutions are compatible with triacs and trailing-edge dimmers and electronic transformer designs. Currently, no MR16 solution has this feature, and few PAR, R, and A type lamp solutions have this feature. In addition, our solutions have better than 0.9 power factor correction and require very few external components. No electrolytic capacitors are required, which can severely limit the operation of the driver circuit in high temperature environments. Both the 120VAC/230VAC and 12VAC solutions use the MAX16834 IC and are available for evaluation and mass production. These are Maxim's unique solutions, and Maxim is the only supplier that can provide this combination of advantages.

Block diagram of MR16 (above) and offline (below) lighting solutions