Technical troubleshooting and solutions for LED lighting and solar charging

As an environmentally friendly and energy-efficient solution, LED lighting has found its place in a wide range of applications, including automobiles, homes, office buildings, hotels, airports and street lamps. However, in addition to overcoming cost barriers, its large-scale commercialization needs to solve technical problems such as dimming, heat dissipation, and color uniformity. In addition, concerns about clean energy and the decline in solar panel costs have also driven the current solar industry boom in the industry. In order to help readers grasp this business opportunity faster and better, this magazine specially invited Linear power expert Tony Armstrong to share his unique insights.

Q: How to eliminate the LED flicker when using PWM or analog dimming?

A: In the face of increasing penetration of high-power, high-brightness LEDs, electronic lighting designers must provide efficient, accurate and simple LED driver solutions. This task is made more difficult by the interchangeability of high-power lighting, such as automotive headlamps or large LCD display backlights, with commercial tandem LED arrays.

Traditionally, the use of accurate currents to drive high-power LED strings is incompatible with simplicity and high efficiency, often requiring some inefficient linear regulator scheme or more sophisticated multi-IC Switching regulator configuration. In addition, ensuring that each LED has uniform brightness without producing any flicker has also become a major design challenge.

There are two popular LED brightness control methods, analog dimming and PWM digital dimming. When analog dimming is used, the LED current can be adjusted from a certain maximum to about 10% of the maximum (10:1 dimming range). Since the chromatogram of an LED is related to current, this method is not suitable for some applications. However, PWM digital dimming switches between zero current and maximum LED current at a rate that is fast enough to mask visual flicker (typically above 100 kHz). This duty cycle changes the effective average current, resulting in a dimming range of up to 3000:1 (limited only to the minimum duty cycle). Since the LED current is either at its maximum or turned off, the method also has the advantage of avoiding LED color shift, which is common in analog dimming.

Q: How should the heat dissipation problem of high-power LED lighting be solved?

A: The two most expensive and highest power LED lighting applications are the back lighting and headlights of large LCD TV displays. Take a look at the standard LED car headlights used by Lexus, Audi, and even GM's Cadillac Escalade. The overall lighting structure of all these cars is very similar. Each automotive headlamp includes five LED-powered beams optimized for a variety of lighting requirements, including: low beam, high beam, turn assist lights, daytime running lights, and turn signal indicators.

Standard LED illumination beams typically will require 35W to 50W of power. This may not seem like a lot of power; however, LEDs provide 10 times the brightness of HID halogen lamps, so the LED's light output is equivalent to a 500W halogen lamp. The power required for a high beam is generally the same or slightly higher than a standard illumination beam, while the power required for a turn assist light, a daytime running light, and a turn signal indicator is lower. However, the overall automotive headlamps consume more than 200W of electrical energy, which may cause significant thermal power dissipation problems. This is really not a good thing, because as the operating temperature increases, the light output and working life of the LED will decrease rapidly.