High-brightness LEDs improve home energy efficiency

High-power LEDs require high drive currents of 350 to 1000 mA. Using the latest technology, each LED can produce 40 to 80 lumens of light, and the power is generally 1 to 3W. According to the information on the website of the U.S. Department of Energy, the main LED manufacturers are Cree, Philips, and Osram. The following will compare HBLEDs with widely used white paper lamps and fluorescent lamps, and give a circuit example for home applications.

Comparison of light sources

Consumers who are well aware of the benefits of HBLED (high brightness LED) will try to use HBLED as much as possible. By comparing the data in Table 1, it can be found that HBLED is obviously the lighting solution with the highest brightness.

Let's take a closer look at Table 1. The energy efficiency of a light source is similar to its efficiency. How much of the energy put into the bulb turns into light, compared to the heat it generates? Users want this number to be higher, and HBLEDs clearly provide this. The color hue of an incandescent lamp is most likely to change if the drive current fluctuates.

Compared with incandescent lamps, the main advantage of fluorescent lamps and HBLEDs is lifespan, so incandescent bulbs are being phased out in many countries. In the future, HBLEDs may surpass fluorescent lamps in popularity because HBLEDs are solid-state (made of silicon material, not fragile), very small in size, and do not contain harmful chemicals (no special environmental treatment is required).

Design goals of HBLED lighting

To get consumers to switch to HBLEDs, HBLEDs must be high quality. Consumers require a power factor of at least 90% and an efficiency of 80% or more. In DC applications, the maximum input voltage cannot exceed 40V. In AC applications, an input voltage of 120V or 240V (maximum 270V) may be used. HBLEDs must be driven with a pulse width modulator operating at a frequency exceeding 120Hz to reduce annoying visible light flicker. Sometimes, this frequency also needs to be variable. In addition to these design constraints, it is up to the engineer and the application to decide whether to use an isolated or non-isolated design. If necessary, complex dimming circuits may also be considered in the end.

As you can see, there is no one-size-fits-all solution. There are many design considerations that go hand in hand. Each solution requires a specific design based on the number of LEDs and the current flowing through them. Designers also need to make adjustments based on the different electromagnetic components, as well as the power devices and output capacitors selected. Application Circuit

The price of HBLED is about 1~2 USD. Since HBLEDs are used in strings in each design, the cost constraint of the converter does not need to be considered during the design.

The first controller introduced is the ISL6721. The ISL6721 is a single-ended pulse width modulation current mode controller. Its peak current mode control can effectively solve the instantaneous power problem and provide built-in overcurrent protection. A large contract manufacturer has adopted the ISL6721 to produce a product that can replace the currently used T8 circuit (replacing the traditional ballast circuit in the fluorescent lamp starter). The ISL6721 can also be set up as an incandescent lamp replacement solution. The non-solid-state flyback solution is currently in use in a shopping mall in Asia. The solution uses 10 HBLEDs and outputs 10W with an efficiency of 82%.

To be truly competitive in the home market, HBLED lighting solutions must also provide dimming capabilities. Smart circuits can do this. Remember, the LED is driven by a pulse width modulation controller. That is, the LED is not always in the "on" state. The number of pulses that power the LED is controlled by the controller and is variable. As it happens, this job is also done by the "controller".

Figure 1 shows a complete schematic of a spotlight solution consisting of a 6-LED adapter and dimming circuit. The heart of the design (minus the HBLEDs, of course) is the ISL6745A controller. The devices in the upper right corner form a SEPIC controller that drives the 6 HBLEDs in series. The surrounding amplifiers perform current regulation, short-circuit protection, and overvoltage protection. In the lower left corner, you can find the AC dimming circuit. The amplifier output of the dimmer is filtered and then used as a reference point for the current regulator, which is fed back into the control loop.

The ISL6745A has a bias voltage VDD range of 6.5 to 20V, and a low-side FET driver output of 12V, 1A, which can drive a low-side FET (such as Q1 in this design), the gate of a high-voltage driver IC, or a gate drive transformer.

Among Intersil's products, the ISL6745A is the most popular HBLED driver. In addition to the usage shown in Figure 1, the switching frequency, soft start, and over-temperature protection of the ISL6745A can also be adjusted, and the "dead time" can also be precisely adjusted. The ISL6745A uses a space-saving MSOP-10 package. The flexibility of the ISL6745A is also a major feature. It can work in both isolated and non-isolated modes, and the dimming function is also optional.

in conclusion

HBLED is the greenest alternative for consumer lighting, and technology has advanced enough to make it a viable solution. Alternatives to incandescent and fluorescent lamps are already on the market. Save energy, extend life, improve safety and increase reliability, use HBLED.