Is the LED light important for high PF or no flicker?

First, the origin of the problem

There are currently two types of light engines on the market, one is a high-PF but severely flashing electroless capacitive light engine, and the other is a flashless, low-PF electrolytic capacitor light engine. So which kind of light engine is better?

Second, the cause

ExClara, a company in Silicon Valley, invented an LED system. In order to improve the power factor PF, not only the electrolytic capacitor was removed, but also the LED string was divided into several groups and turned on in order to make the current waveform and the voltage waveform completely match. . The result of this must be that the LEDs are intermittently illuminated and produce severe flicker.

Third, the degree of flicker

LEDs originally need to have a certain starting voltage (2V or more) to turn on, and now it is necessary to wait until the input voltage rises to a certain height before turning on. This will inevitably make a big between the two half sine waves. The dark area (see the arrow area below) makes it more flickering than other fixtures (like incandescent, fluorescent).

Fourth, the consequences and problems caused by flicker

1. Impact on the human body:

· Will produce strain fatigue, blurred vision, and traditional headaches;

· can cause seizures in patients with photosensitive epilepsy;

· Increase repetitive behavior among children with autism.

2. Impact on production workers

· Workers who require vision and vision can cause a decline in performance;

• For workers who use or contact rotating machinery, the effect of slowing, stopping, or even reversing will occur, which will lead to work-related accidents.

3. Impact on athletes

For athletes who play at extremely high speeds such as table tennis badminton, there will be 2ms of darkness every 1/100th of a second. This kind of flashing of lights often causes problems such as misjudgment of the direction of the ball.

4. Influence on literary photography

· Leaves streaks on the photo;

· A long face will be generated when the lens is moved for a long time.

5. Impact on video, TV, and film production

The flashing of the lights has a bad influence on the production quality of the film and television dramas, and there are ghosting and interference streaks that cannot be played.

6. Impact on security and security systems

Because the camera's camera moment may be just when the light is dark, it is possible to take a black image at this time, that is, lose a complete frame. If this frame happens to be the moment of the mob, then it loses an important piece of evidence.

Five, how can we eliminate the flicker

The most thorough approach is to eliminate the source of this brightness flash. That is to use electrolytic capacitor filtering after rectification, thoroughly filter out this AC ripple.

After electrolytic capacitor filtering, the rectified sine wave is basically smoothed to a waveform close to DC, with only a small ripple, and the larger the capacity of the electrolytic capacitor, the smaller the ripple. In other words, the flicker is almost completely eliminated.

Sixth, the "disadvantages" of using electrolytic capacitors - low PF

Why is this "disadvantage" to be quoted? Because the test results are measured using the problematic power factor on the market! The test results of these power factor meters are very doubtful.

For example, we use the same 102W LED light engine system with electrolytic capacitors. The test results of different test instruments are as follows: The power factor of 0.6590 is measured by the digital power factor tester commonly used in the market.

However, if we use the Cosφ meter identified by the national CHNT to test the same system, we can get the result of PF=0.9. It can be seen that the test results of this digital power factor meter are very problematic.

So what is the power factor?

The power factor is originally cosφ in a linear AC electrical system, that is, the cosine of the angle between the voltage sine wave and the current sine wave, which represents the direction in which the current sine wave with a different phase of the voltage is projected into the voltage vector. Or it is the component value of the current vector that is in phase with the voltage vector. Multiplying this in-phase value by the voltage is the active power. Multiplication of two components by one component and voltage vector is reactive power. If cosφ=1, that is, PF=1, then there is no reactive power. In a linear AC system, a cosφ is defined as a power factor in order to be compensated by another device with the opposite phase angle, so that its reactive power is zero.

However, in a nonlinear system using a rectifier, the current wave is not a sine wave at all, so it is not known at all what its cosφ is equal to. That is, I don't know how PF should be defined. There are four different definitions that are said to be internationally known. But the strange thing is that there are now power factor meters available on the market that can measure nonlinear systems. Only all these digital power factor meters can't give the positive and negative power factor, because they all use the ratio of active power to reactive power as the power factor, the power is not negative, of course, the ratio of the two powers is not Positive and negative signs. This definition is clearly problematic, and the subject is now a master's thesis at a US university and a doctoral thesis at a Swedish university. This problem can be explained very simply: one of the most important characteristics of the power factor is that there are positive and negative signs. Because the power factor is divided into inductive load and capacitive load, the inductiveness is positive; the capacitiveness is negative, and the two can compensate each other. Usually household refrigerators, air conditioners, televisions, etc. are all inductive loads. Therefore, the electric power bureau often has to connect a large capacitor in the secondary of the transformer to compensate. The LED power supply and the electrolytic capacitor are obviously capacitive loads, so it should be beneficial to the compensation of the power factor of the home appliance! However, the digital power factor meter on the market does not give the sign!

As can be seen from the above description, this so-called "disadvantage" of low power factor for an electrolytic capacitor light engine is a problem that is not clear at all. If this problem is not ulterior motives, at least it is unnecessary. !

Seven, low-power LED lamps should not have power factor limitations at all

Originally, the country has very clear regulations on the power factor of small-power appliances, that is, low-power appliances below 75W have no power factor requirements and restrictions. For the lamps and lanterns, no power factor requirements have been proposed in the past. For example, most of the 36W fluorescent lamps commonly used in China use ballast inductors and starters, and its power factor is also very low, only about 0.51. The country has never said anything to it. Later high-power metal halide lamps, even with a power of up to 1000 watts, also used inductors as ballasts, with a power factor of only 0.51, and were also inductive loads, and no one has ever proposed a power factor. Later, it seems that there is no limit to 15W for energy-saving lamps (because almost all commonly used energy-saving lamps are less than 15W, so this requirement is meaningless!)

Just to the LED lights, but put forward very demanding requirements, power factor is not required below 5W. Everyone knows that the EU is usually the most demanding, and the EU proposes that only 25W or more requires power factor. Our country's requirements are actually five times higher than the EU! It seems to be intentionally difficult to make LED lamps.

Eight, the light engine without electrolytic capacitors is not just flashing, there are many more serious problems.

The biggest problem is that it uses a very inefficient linear power supply, which is only 85% efficient. 15% of the power has turned into heat. If this low efficiency linear power engines made of light onto the aluminum plate, it is necessary to heat to 15% above the LED. Take the light engine that should be 10W as an example. Remove the power consumption of 1.5W, only 8.5W supply LED, actually the LED's electro-optical efficiency is 40%, it is originally 8.5x0.6=5.1W heat, now it has increased 1.5W of heat, it is increased 1.5/5.1=0.3, which is equivalent to an increase of 30% of heat. That is, the junction temperature of the LED is increased by 30%. The heat sink designed under normal conditions should have a junction temperature of 85 degrees, and now it is increased to 110 degrees, which will reduce its thermal efficacy by 25% and life from 30,000 hours to 10,000 hours.

There is a linear constant current source with electrolytic capacitance up to 99%. With this constant current source, the light engine is not only flickering, but also does not add heat to the LED light source because it is highly efficient and hardly Power consumption, that is, no heat generation. Therefore, it will not reduce the thermal efficacy of the LED, nor shorten the life of the light engine! It can be said that only this highly efficient constant current source can be integrated into the aluminum substrate of the LED light source to become high-performance light. engine. All other so-called high PF AC light engines actually only reduce the thermal efficacy, shorten the life and flash the product.

IX. Conclusion

It should now be clear that the advantage of a flicker-free, high-performance light engine is that it is much higher than the so-called high-PF, severely flickering light engine!