Analysis of LED de-energization

Among them, the basic functions of the power supply include: voltage transformation, rectification and providing constant current. The high voltage chip can be used to remove the transformer part of the power supply. The AC low voltage chip connected in the forward and reverse parallel can remove the rectification part in the power supply. The AC high voltage chip and the bridge AC high voltage chip connected in the forward and reverse parallel can remove the rectification in the power supply. Part and transformer part.

However, one of the inadequacies of the AC LED chip and the AC direct drive LED lamp using the DC LED chip is: stroboscopic.

Therefore, it is necessary to reduce the strobe to an acceptable level.

What level of strobe is acceptable? Let's take a look at the strobe of other luminaires and "DC" LED luminaires with low-cost power supplies.

In fact, AC-driven lamps (including: LED lamps, OLED lamps, induction lamps, energy-saving lamps, halogen lamps, incandescent lamps, fluorescent lamps, etc.), regardless of whether there is a power supply, have different degrees of stroboscopic. The following shows some strobe lamps and measurement results.

1.1. "DC" LED lamps

Figures 1 and 2 show the strobe of a power-emitting LED luminaire (photo taken at Guangzhou Guangya Exhibition 2013).

Figures 3 and 4 show not only the strobe of LED luminaires, but more importantly, the power supply.

The instability of performance, that is, in the same company's products, some of the lamps do not strobe, and some lamps have different degrees of strobe. The six LED luminaires in Figure 4 are a company's product. The four LED luminaires in Figure 3 are products of another company. The upper two panels of Figure 3 show the vases illuminated with LED luminaires. The two figures below are LED luminaires.

The strobes of the "DC" LED luminaires shown in Figures 1 through 4 are consistent with the US Department of Energy's National Laboratory's stroboscopic test results for certain powered "DC" LED luminaires: Figure 5a shows "DC" The test results of the LED luminaire show that the percentage strobe reaches 54% (Fig. 5b).

The stroboscopic test results for the "DC" LED luminaire shown in Figure 6a are better than the luminaire of Figure 5a with a percentage strobe of 22% (Figure 6b).

1.2.ACLED lamps

The stroboscopic test results of the ACLED luminaire of Figure 7a show that the percentage strobe reaches 98.7% (Fig. 7b).

ACLED lamps with stroboscopic elimination (Figures 8 and 9, taken at Guangzhou Guangya Exhibition 2013) still have different levels of stroboscopic light. At present, the US Department of Energy has not seen the test results of the percentage strobe of such ACLED lamps.

1.3. OLED lamps, induction lamps, energy-saving lamps, fluorescent lamps, halogen lamps, incandescent lamps

DC-driven OLED lamps (Fig. 10), induction lamps, energy-saving lamps (Fig. 11), halogen lamps (Fig. 12), etc. (photographed at Guangzhou Guangya Exhibition) with power supply have different levels of stroboscopic light.

The US Department of Energy's National Laboratory measures strobes for certain luminaires, including:

(1) The percentage stroboscopic test result of the fluorescent lamp (Fig. 13a) using the magnetic ballast is 28% (Fig. 13b);

(2) The percentage stroboscopic test result of the incandescent lamp (Fig. 14a) is: 8.4% (Fig. 14b).

(3) The percentage strobe of the energy-saving lamp (Fig. 15a) using the electronic ballast is 5% (Fig. 15b).

in conclusion:

Comparing the strobe of ACLED luminaires with strobe-removing technology with the strobe of "DC" LED luminaires and the strobes of other luminaires, it can be seen that the difference is not significant. Therefore, from the point of view of stroboscopic requirements, de-energization is feasible, and there are many different technical routes.

The industry is currently discussing "de-energization", which includes some functional modules that do not use power or remove power. De-energization can also be performed at different levels, including at the chip level, at the electronic component level, at the luminaire level.

The current situation: de-energization at different levels, using a variety of patented technology routes with completely different principles.

Question: Is there a general-purpose stroboscopic reduction principle and a patented technology route based on this principle that can be applied to all levels, without the need to develop different technical approaches using different principles for different levels?

This paper introduces a general principle of reducing strobe and a technical route based on this principle.

The technical route is characterized by the principle that it can be applied to both chip level, electronic component level, and lamp/circuit level.

The following is a brief introduction to the general principle of reducing strobe.

To simplify drawing and analysis, assume:

(1) The waveform of the alternating current after phase shifting remains unchanged, and is still a sine wave. Although the waveform changes after phase shifting, it does not affect the general principle of reducing stroboscopic. It only needs to adjust the phase difference between different input AC currents in order to achieve the desired result;

(2) In the operating current range, the luminance of the light is substantially proportional to the current (Lumileds). Therefore, although only the current is analyzed below, the conclusion applies to the luminance of the light.

It is well known that the effect of stroboscopic light on the human eye depends mainly on the difference between the maximum and minimum brightness (percent stroboscopic) and the oscillation frequency of the maximum.

The basic principle of general use is: input AC currents of different phases, respectively rectify and superimpose to form a total current, and drive the LED lamps with the total current. The result is:

(1) the oscillation frequency of the maximum value of the total current increases, and therefore, the oscillation frequency of the maximum value of the lightness increases;

(2) the difference between the maximum value and the minimum value of the total current is reduced, and therefore, the percentage stroboscopic of the brightness is reduced;

(3) The total voltage after superposition is not equal to 0 (or less than 2.8 volts). Therefore, the lamp has no moment of non-lighting.

Therefore, the strobe of the brightness of the total current driven LED luminaire is reduced to the same or even better level as other luminaires, ie, this principle can achieve the stroboscopic requirements for the luminaire.

Here are a few examples to illustrate how the general principle of reducing strobe reduces strobe.

An input sinusoidal AC current: The normalized waveform after rectification is as follows (Figure 16):

For two input sinusoidal alternating currents with a phase difference of 90°: rectified separately, but not superimposed on each other, the normalized pattern of two pulsating DC currents is shown in Figure 17:

The pulsating DC currents obtained by rectifying the input sinusoidal alternating currents of two input phases with a phase difference of 90° shown in FIG. 17 are superimposed to obtain a total current. The normalized total current waveform is as shown in Fig. 18 (the maximum value of the total current after rectification by the sinusoidal alternating current of two input without phase difference is 1).

In order to demonstrate the general function of reducing the principle of stroboscopic, compare: In Figure 18, the diamond ( ) indicates the normalized total current of the sinusoidal alternating currents of the two inputs without phase difference, respectively, square ( ) Indicates the normalized total current after rectification and superimposition of two input sinusoidal alternating currents with phase difference of 90° (the sinusoidal alternating current with two inputs without phase difference is rectified, and the maximum value of the superimposed total current is 1).

For three input sinusoidal alternating currents with phase 0°, 60°, and 120° respectively: the normalized total current waveform after rectification and superimposition is shown in Figure 19 (sinusoidal alternating with three inputs without phase difference) The maximum current of the current after rectification and superposition is 1):

In order to demonstrate the general function of reducing the principle of stroboscopic, a comparison is made: in Fig. 19, the diamond represents the normalized total current of the sinusoidal alternating currents of the three input without phase difference, and the superposition, and the square represents three phases. The normalized total current is superimposed after the input sinusoidal alternating current of 60° is rectified separately.

Figure 18 and Figure 19 show very clearly:

(1) The difference between the maximum value and the minimum value of the total current superimposed after rectification of the alternating currents of different phases is reduced, and therefore, the percentage strobe of the brightness of the total current is reduced;

(2) an increase in the oscillation frequency of the total current and the maximum value of the generated light luminance;

(3) The total current and the brightness of the generated light are not zero.

Therefore, the effect of using a general stroboscopic light on the human eye is reduced.

If you continue to increase the number of input AC currents, for example, input 4 phases are: 0°, 45°, 90°, 135° AC current, even input 8 phases are: 0°, 22.5°, 45° , 67.5°, 90°, 112.5°, 135°, 157.5° alternating current, respectively superimposed and rectified, the difference between the maximum and minimum values ​​of the total current is further reduced, and therefore, the percentage of the generated light is strobed Further reduction; the total current and the oscillation frequency of the maximum value of the generated light luminance are further increased.

In Fig. 18 and Fig. 19, four alternating currents having a phase difference of 45° and eight alternating currents having a phase difference of 22.5° were analyzed, and the results shown in Fig. 20 were obtained.

In Fig. 20, the diamond indicates the percentage of the minimum value and the maximum value of the total current superimposed after rectification (right ordinate), and the square indicates the oscillation frequency (left ordinate) of the maximum value of the total current superimposed after rectification.

Taking 50 Hz AC as an example, after rectification, the oscillating frequency of the maximum pulsating current is 100 Hz.

Figure 20 shows:

1) For two input AC currents with a phase difference of 90°, the minimum value of the total current superposed after rectification is 70% of the maximum value, and the oscillation frequency of the maximum value is greater than 200 Hz. Therefore, the percentage of light intensity produced by the total current strobes = 18%. The percentage of fluorescent lamps that use magnetic ballasts is strobed by 28% (Fig. 13b).

2) For three input AC currents whose phase angles are 0°, 60°, and 120°, respectively, the minimum value of the total current superposed after rectification is 85% or more of the maximum value, and the oscillation frequency of the maximum value is close to 400 Hz. Therefore, the percentage of light intensity produced by the total current strobes = 8%. The percentage of incandescent lamps reached a level of 8% (Fig. 14b).

3) For the input AC currents with phase angles of 0°, 45°, 90°, and 135°, the minimum value of the total current superposed after rectification is more than 90% of the maximum value, and the oscillation frequency of the maximum value is close to 500Hz. Therefore, the percentage of light intensity produced by the total current strobes = 5%. The percentage of energy-saving lamps that use electronic ballasts is 5% strobed (Figure 15b).

4) The more the number of input AC currents is, the smaller the angle of the corresponding phase difference is. The closer the ratio of the minimum value to the maximum value of the total current superposed after rectification is closer to 1, the larger the oscillation frequency of the maximum value. Therefore, the smaller the stroboscopic percentage of the luminance produced by the total current, the larger the oscillation frequency of the maximum luminance, and the smaller the effect of the stroboscopic effect on the human eye.

Among them, the percentage strobe is calculated according to the formula of Energy Star (Figure 21).

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