LED bulb noise countermeasures: noise current has two modes

Japan's revised "electrical safety law" will be implemented from July 2012. After the revision, LED bulb has become the applicable object of the regulations. In particular, a number of restrictive criteria are of particular concern

On the limits of electromagnetic noise intensity. At present, the market appears with incandescent bulbs and bulb type fluorescent lamp compared to the electromagnetic noise of the larger LED lighting appliances, with the revised version of the "electrical safety law," the implementation of

Strict noise countermeasures. In this paper, according to the current situation of LED lighting, LED lighting noise types, evaluation methods and countermeasures are analyzed.

Due to the shortage of power supply in the East Japan earthquake, people's awareness of energy saving is rapidly rising, LED lighting appliances and LCD TV with LED backlight and other energy-saving products are gradually becoming the mainstream of the market. LED lighting appliances, light bulbs, fluorescent tubes, chandeliers and ceiling lamps have begun to enter the market.

One of the LED bulbs, not only well-known lighting manufacturers, new vendors involved in the product has begun to sell at home stores, LED bulbs Market is rapidly expanding.

At the same time, standardization and regulations, such as the introduction of the purpose is to achieve the popularity of LED bulb environment is being established. Previously, LED bulbs are not within the applicable object of the electrical appliances Safety act. Therefore, some of the electromagnetic noise of LED lighting products. As a result, if the light of the street lamp is replaced by a mercury lamp to a LED bulb, the reception barrier of the television and the radio can be caused.

An incandescent bulb is not power circuit internal resistive load, so there is no problem of this kind of electromagnetic noise. But when it comes to the LED bulb, the problem becomes apparent. If this way to promote the popularity of LED lighting, home will appear in a number of noise sources.

In overseas, LED lighting and general lighting appliances, must comply with the international standard CISPR15 ("electrical lighting and similar equipment Radio disturbance characteristics limits and methods of measurement"), countries have introduced restrictions based on the specified standard.

Japan will also begin to enable such restrictions. From the beginning of July 2012, LED bulb will become the "electrical appliance safety law" applicable object. It also includes the provisions on the intensity of noise (the noise of the terminal voltage of the band is 526.5kHz to 30MHz, the noise power of the band is 30MHz ~ 300MHz).

No matter whether the electrical appliance safety law is implemented, with the expansion of the LED lighting market, the problem of interference with other electronic products can not be avoided.

The electromagnetic noise source of LED bulb is its power supply circuit. Due to the limitation of the size of the power supply of the LED bulb, it is necessary to implement the electromagnetic noise with the least components. It is especially important for the noise countermeasure element

Selection of parts. Therefore, this paper will focus on the analysis of the types of electromagnetic noise and the measurement methods of the LED lighting power supply circuit, as well as the component selection method which can effectively suppress the electromagnetic noise.

There are two modes of noise current

In general, EMC (electromagnetic compatibility: electro-magnetic)

In the compatibility standard, two types of electromagnetic noise measurements are defined, namely, the radiation noise radiated into the air and the conduction noise (noise terminal voltage) flowing through the power line (Figure 1). Noise

The noise component of the two modes of "differential mode" and "common mode". Differential mode noise is the noise between the signal line and the ground wire. The common mode noise is the noise between the earth and the signal line and the earth and the earth

Noise, the signal line and the earth and the earth between the same type of noise, that is, with the same phase and the same amplitude.

Figure 1: examples of electromagnetic noise observed in a LED bulb

EMC defines the measurement of two kinds of electromagnetic noise, radiation noise and conduction noise, LED bulb is no exception. The noise of some LED bulb products exceeds the specified value of CISPR15 (quasi peak value: QP and mean value: AV).

The main component of radiated noise is the common mode noise (Figure 2 (a)). This is because the noise current loop area is much larger than the differential mode noise current loop area.

Figure 2: there are two modes of electromagnetic noise

There are two modes of differential mode and common mode. The common mode component (a) is radiated noise. In the conduction noise, the mixed mode of the difference mode and the common mode two (b)

In the conduction noise can be observed differential mode and common mode two components (Figure 2 (b)). If the conduction noise, the need to grasp the characteristics of the composition of the noise on the basis of its characteristics to take countermeasures. First of all, to introduce the way to suppress the conduction noise.

Noise pattern of power supply

Conduction noise measurement, the general use of V type artificial power network, for the power line 1 (L1) and power line 2 (L2) of their respective electromagnetic noise, the measurement of quasi peak * (QP) and the average (AV)

3 (a). Although the V type artificial power supply network can measure the noise voltage between the power line and the earth, but the difference between the two modes of noise and common mode noise is not clear.

Figure 3: the use of V and delta artificial power network measurement

In the measurement of conducted noise, the electromagnetic noise of power line 1 (L1) and power line (L2) is generally used to measure the peak value and the average value (a) of the V artificial power network. In this measurement, differential mode noise

Noise and common mode noise together, it is difficult to distinguish which noise mode is the main body. And if the use of artificial neural network, easy to distinguish the type of noise patterns (B). The power network can be based on the noise mode (Sym: difference)

Mode, ASym: common mode to measure its frequency characteristics.

Quasi peak value: the value measured by the method of enlarging the detector time constant for the detection of electromagnetic noise. Is the value between the maximum and the average. When the quasi peak value of electromagnetic noise is large, it is easy to cause the radio reception barrier. The correlation with the same sensitivity is stronger than the peak value.

However, if the use of "delta artificial power network" can determine the type of noise patterns (Figure 3 (b)). The circuit can measure the frequency characteristics of the noise modes in the conducted noise.

The frequency characteristics vary by product type. For example, there is a difference in the frequency of electromagnetic noise between the LED bulb, the chandelier, and the large size LCD TV (Figure 4). The LED lamp is the main body of the differential mode noise, while the LED chandelier is a mixture of differential mode noise and common mode noise. Large size LCD TV with common mode noise as the main body.

Figure 4: noise components vary by product

The types of electronic products have changed, and the composition of noise components will change. For example, the LED lamp is mainly a differential mode noise, LED chandelier in the differential mode noise and common mode noise mixed together (a, B). The large size LCD TV is the common mode noise (C).

Why, then, is there a specific tendency for the transmission noise and noise components of different products? By analyzing this tendency by electromagnetic field simulation, we know why.

Noise mode depends on size

Measurement of conducted noise in shielded room. The measurement conditions are defined as "CISPR16-2" or "ANSI63-4". The provisions of the two standards, the datum of shielding chamber and the measured object distance should be maintained at 0.4m, the length of the wire connecting the artificial power supply network and the measured object is 0.8m, the measured object is arranged in the high 0.8m table (Figure 5).

Figure 5: measurement of conducted noise in a shielded room

This is the measurement of conducted noise. The measurement of the shielding room. Specific measurement conditions by "CISPR16-2" or "ANSI63-4" specification.

At this point, the common mode noise will be screened through the distribution of the indoor wall (metal) and the distribution of the object between the capacitance. We model this situation, and then use the electromagnetic field simulation to analyze the relationship between the size of the measured object and the common mode noise.

We through the electromagnetic simulation analysis of 4 kinds of sizes (5 x 5 x 5cm3, 10 x 10 x 10cm3, 20 x 20 x 20cm3100 x 80 x 20cm3) object, were calculated by artificial network observation of the object to be measured when the impedance (Figure 6).

Figure 6: noise mode depends on the size of the product

4 kinds of objects with different sizes are used to simulate the electromagnetic field, and the common mode impedance (a) of the observed object is calculated. Based on the results, it is found that the larger the shape is, the larger the distribution capacitance of the reference plane and the measured object is, the lower the impedance of the common mode path (B). In addition, the higher the frequency, the lower the common mode impedance (C).

Figure 6 shows the common mode impedance of the 1MHz and the conversion of the impedance to the distributed capacitance.

Based on the analysis of 4 kinds of objects by electromagnetic field simulation, it can be seen that the larger the shape, the larger the distributed capacitance between the shield and the measured object. In other words, the larger the size of the product, the lower the impedance of the common mode path, the easier the current of the common mode noise, the greater the noise component.