Abstract: With the electromagnetic compatibility standards GB 17743 and GB 17625 series of lighting appliances and the safety standard GB 19510 series of "light control devices" of electric light source accessories, the safety of lighting appliances has attracted great attention. .
The article analyzes the line principle and design of the electronic ballast, the most commonly used accessory for lamps, in combination with relevant standards, and proposes corresponding effective improvement measures.
Keywords: use safety U-OUT value correlation component high frequency capacitive leakage power factor positive harmonic interference conduction interference radiation interference insertion loss value
1 Introduction
At present, China has become the world's largest producer of lighting electrical products, maintaining a high-speed and stable growth every year. Because China has the advantages of wide population and abundant resources, the lighting electrical products produced are of high quality and low price, which can not only meet the needs of national economic construction and people's life, but also be exported to many overseas countries and regions, occupying a considerable position in the international market. Big share. With China's successful entry into the WTO, China's lighting electrical appliance manufacturers have ushered in greater development opportunities and gradually become the world's lighting industry research and development, manufacturing and processing centers.
Electronic ballasts have many advantages that traditional inductive ballasts can't match and are therefore favored by people. They have developed rapidly in recent years. Electronic ballasts for fluorescent lamps, featuring high power factor, light weight, no flicker, no noise, etc., can start fluorescent lamps with a lower power supply voltage, and can work normally in an environment with a wide range of input voltage fluctuations. And it is an electronic structure, easy to add other circuits, such as APFC (Active Power Factor Correction Circuit) technology to achieve energy saving and environmental protection by increasing power utilization, reducing harmonic content, avoiding damage to the public power grid, or increasing PWM ( Techniques such as pulse width modulation and FM (frequency modulation) dim the fluorescent lamps or increase abnormal protection circuits such as overvoltage, overcurrent, and overload to improve the safety of use.
However, due to factors such as technology and price, most electronic ballasts produced in China are products with low technical content and few additional functions. Therefore, in addition to price advantages in the international market, they lack innovation competitiveness. After joining the WTO, developed countries and regions such as Europe and the United States have set up market access barriers and technology bastions. In order to be in line with international trade, China's product standard setting is also moving closer to international standards. Therefore, the National Standardization Administration Committee of the General Administration of Quality Supervision, Inspection and Quarantine issued the series of safety standards for GB 19510 "Control Devices for Lamps" in 2004 and 2005. Equivalent to the IEC61347 series 2003 edition) and the corresponding performance standards, coupled with the electromagnetic compatibility standards promulgated in 2000 and 2003, make electronic ballast manufacturers face the difficulty of strengthening technological innovation, improving product quality and technical level. Severe test.
To this end, the author explains the reasons for the unqualified items in the daily inspection of electronic ballast products, and proposes corresponding rectification measures, hoping to provide reference for enterprises or related practitioners.
2 Safety and Electromagnetic Compatibility Standards for Electronic Ballast Products
In accordance with the principle of the "Uniform Certification Mark" of the World Trade Organization, and in order to facilitate the export of Chinese products and international certification, China has legally applied to more than 100 kinds of products (including electronic ballasts) after joining the WTO. Class products) implement a compulsory certification system, that is, China Compulsory Certification (CCC certification, also called 3C certification). Only products that pass the safety and electromagnetic compatibility test and are affixed with the 3C mark can be exported, shipped, and used in business services. . The mandatory certification standards for electronic ballast products in 3C include: GB 19510.4-2005 "Control devices for lamps - Part 4: Particular requirements for AC electronic ballasts for fluorescent lamps", GB 17743-1999 "Electrical lighting Limits and measurement methods for radio disturbance characteristics of similar devices and GB 17625.1-2003 "Electromagnetic compatibility limit harmonic current emission limits (device phase input current ≤ 16A)", these standards are basically the latest The series of standards and publications issued by the IEC (International Electrotechnical Commission) and CISPR (Special Committee on Radio Interference) are consistent.
3 GB 19510.4-2005 standard points and measures
As an electrical product, its safety requirements are the most important aspect recognized internationally. The electronic ballast is an important part of the luminaire. Its safety performance directly affects the luminous efficiency, luminescence stability, service life and safety of the whole luminaire. Among them, the safety of use is directly related to people's lives. Property security. Therefore, China's electronic ballast safety standard GB 19510.4-2005 (hereinafter referred to as the "new standard") has added a number of new content.
3.1 Requirements for mandatory signs
In addition to retaining the contents of the old standard, the new standard adds a U-OUT value (the maximum working voltage rms) as a mandatory content, which must be marked on the electronic ballast product. The U-OUT value is also the basis for judging whether the dielectric strength, creepage distance, clearance, and protective measures of the associated components meet the standard requirements. In the inspection work of such products, the author found that most of the products produced by the company did not indicate the U-OUT value or randomly marked. What's more, in order to be able to mark larger values ​​through the assessment of the protective measures of the associated components in the standard, the author found that the U-OUT value of individual products was 1.5kV. This phenomenon is due to the fact that the provisions of the provisions have not caused the attention of electronic ballast products manufacturers or related practitioners, or the understanding of standards is not thorough.
Due to the emergence of T4 and T5 thin-diameter lamps that are more energy efficient than T8 and T10 lamps, electronic ballasts must increase the starting voltage and operating voltage in order to match such lamps. As the starting voltage required by the fluorescent lamp increases, the high starting voltage of the electronic ballast output is applied to the lamp tube, and is also applied between the electrodes of different polarities of the lamp holder, the connector, and the like, and each An electrode is placed between the metal housing of the luminaire (grounded metal). In addition, the high voltage of this starting process also acts between the circuit inside the electronic ballast and the metal casing, and between the different polarity electrodes of the electronic ballast output circuit. Because the ballast is generally installed in the luminaire, in order to make the creepage distance and clearance between the lamp holder in the luminaire and the relevant device connector and the metal parts of the luminaire also meet the safety requirements for use, Therefore, the requirement of the U-OUT value is proposed.
The new standard states that the U-OUT value refers to the maximum operating voltage (effective value) between the "output terminals of the electronic ballast and between any applicable output and ground." When the working voltage is less than or equal to 500V, it should be marked with 10V as the first level; when the working voltage is greater than 500V, the mark should be made with 50V as the first level. The mark of the maximum working voltage should be given by the following two conditions, one is the maximum working voltage between the output terminals of the ballast; the other is the maximum working voltage between any output of the ballast and the ground. The U-OUT value is determined by the starting peak voltage value of the fluorescent lamp, and the peak value of the fluorescent lamp starting voltage is the design value of the open peak of the electronic ballast. By formula Up-p=fluorescent lamp minimum open circuit voltage RMS × ballast open circuit voltage peak ratio × insurance factor × 2 (fluorescent lamp minimum open circuit voltage RMS value can be found in standard IEC 60081 and IEC60901, ballast open circuit voltage peak ratio Generally take 1.7, the insurance factor is calculated as 1.5). After calculating the maximum peak value, refer to Table 1 of GB 19510.4-2005 to find the corresponding working voltage RMS value is the U-OUT value of the ballast. Just because the U-OUT value is determined in this way, the matching lamp type of the ballast should be clarified, which is also one of the contents of the standard for the evaluation of the marking clause. However, the author found in the inspection that most of the products did not mark this content, which is unfavorable for the enterprise. Because in the detection of such products, if the adaptation of the light source is not clearly stated, the general inspection agency will evaluate the most stringent conditions, that is, a variety of corresponding light sources may be used for testing.
3.2 Assessment of dielectric strength
The operating voltage of the electronic ballast specified in the IEC standard refers to the maximum steady-state effective voltage value generated between the terminals or the terminals to the ground during the operation of the ballast, including the normal state and the abnormal state. However, the voltage of the output terminals of more electronic ballasts under normal working conditions or abnormal operating conditions is generally higher than the power supply voltage, so the test voltage for the dielectric strength assessment of the ballast should be 2U+1000V. The U value should be the maximum operating voltage of the ballast, that is, the U-OUT value, not the power supply voltage value, which is different from the dielectric strength test of ordinary lamps. The reason for this project failure is usually that the leakage current across the ground capacitance (Y capacitor) is too large. The safety capacitor with high heat resistance, high withstand voltage and small leakage current should be selected as the cross-ground capacitance to ensure the passing of the clause.
3.3 Moisture and insulation requirements
In terms of moisture and insulation, the new standard adds high-frequency capacitive leakage current requirements based on the original provisions of the old standard. The purpose of establishing this clause is to prevent the high-frequency current generated by the electronic ballast when the lamp is replaced at high altitude. This current will cause the person to numb and instinctively dodge, causing high-altitude falls. accident. For high frequency capacitive leakage current measurements, the ballast must have an abnormal protection function. Because when the lamp is replaced, it is generally installed first and then the other end, so that the ballast is in an abnormal working state, this clause is to simulate such a situation to measure. For series resonant preheating electronic ballasts, this is a more rigorous test, and if no corresponding measures are taken, the ballast will generally be damaged within one minute.
The reason for the failure of this project is due to the large preheating current of the ballast to the lamp and the long duration. Because the high frequency capacitive leakage current when the ballast is started is related to the preheating current of the fluorescent tube. Therefore, when designing the ballast, the ballast should be made to generate a large preheating current at the moment of energization, and with sufficient warm-up time to make the filament of the lamp reach the temperature required to emit electrons, before the electron emission state is reached in the filament. A sufficient electron cloud is formed around it, and the voltage applied to both ends of the lamp tube is quickly lowered to a safe level to avoid gleaming discharge damage to the filament. If the preheating temperature of the filament is too low, the electron emission will be insufficient. If the temperature is too high, the preheating time is too long, which will inevitably cause the high frequency capacitive leakage current to increase, making the ballast unable to pass the assessment of this clause.
At present, the relatively popular filament preheating circuit uses the characteristic that the thermistor has a switching function to preheat the filament. The preheating time is generally between 0.4 and 2 s. The larger the thermistor diameter, the longer the warm-up time and vice versa. This preheating circuit can generally meet the requirements of the standard as long as the thermistor is properly selected. However, the use of the thermistor has the disadvantage of increasing the power consumption, and the thermistor PTC can be connected in series with a trigger diode or a bidirectional Zener diode to form a powerless preheating circuit.
3.4 Fault status, abnormal status and assessment of related components
Internationally, the life expectancy of ballasts is very high, usually reaching more than 40,000 hours. Therefore, ballasts that are replaceable and replaceable as lamps must have an abnormal protection function. When the ballast fails or is in abnormal working condition, it should not be damaged. Once the abnormal state is eliminated, it should continue to work normally. The old version of the IEC standard has long introduced the "abnormal state" clause, mainly to simulate the abnormality of the fluorescent lamp as the ballast load from the lamp holder, the lamp leakage, the filament fuse or the cathode deactivation (rectification effect). In case of conditions, the ballast can avoid being damaged.
The terms of protection for associated components have been added to the new standard. The clause mainly evaluates the ballast connected to the analog resistor (resistance R=11.0/(2.1×In), where In is the nominal operating current of the lamp), after the 0.9~1.1Un supply voltage is at Under normal working conditions or abnormal working conditions, the voltage of the output terminal to ground should not be greater than the maximum peak voltage corresponding to the standard; when the power is turned on or started for 5s, any output of the output terminal to the ground or the output terminal The voltage (effective value) should not exceed the U-OUT value of the ballast; when the ballast is in an abnormal state under the rectification effect, any output terminal is grounded after the power is turned on or started for 30s. Or the voltage (effective value) between the outputs should not exceed the U-OUT value of the ballast.
Whether the ballast can pass the above two provisions, the key is whether the ballast is designed with a protection circuit, and whether the time adjustment of the protection circuit is suitable. The protection circuit operates too early, which may cause the fluorescent lamp to not light up or accelerate the aging of the lamp filament to shorten the life; if the time is too long, the ballast may pass the assessment of the protective measures of the associated components.
The protection circuit of the electronic ballast generally includes an overcurrent protection circuit, an overvoltage protection circuit, and an abnormal state protection circuit. After the ballast is connected to the power supply voltage, the rectifier diode starts to charge the electrolytic capacitor, which generates a surge current much larger than the normal operating current in a short time. If no measures are taken, the ballast may be damaged at the moment of power-on. . A current limiting resistor or a negative temperature coefficient resistor NTC can be connected in series with the input circuit to reduce the inrush current. In addition, when the grid voltage is excessively fluctuating or lightning is disturbed, the ballast is also damaged by overvoltage. To solve this problem, a varistor Z1 is connected in parallel with the ballast input circuit to eliminate the sharp pulses generated. In order to prevent the rectifier circuit from being broken or short-circuited due to damage of the rectifier diode and electrolytic capacitor, a fuse or fuse F1 should be added to the power input stage to enhance the safety of the ballast.
When the electronic ballast is in an abnormal state, the protection circuit is complicated. In order to save costs, some companies only have a recoverable overcurrent protection component (polymer switch) in the ballast output circuit. This kind of component is composed of specially treated polymer resin and conductor. Under normal conditions, its resistance is very low, which can be regarded as short-circuit conduction. When the current flowing through the polymer resin becomes large in a short time, a large amount of heat is generated to cause the temperature to rise rapidly in a short time, so that the impedance is rapidly increased, thereby limiting the magnitude of the abnormal current, thereby achieving the protection town. The purpose of the flow device. However, this method will keep the ballast in a vicious circle of protection, triggering and protection, so that the ballast protected by this method can work for more than one hour under abnormal conditions (standard requirements for ballasts need to be Working in an abnormal state for 1 hour), but can not pass the assessment of the protective measures of the associated components. I often encounter this situation in the test. Some ballast products have a very high U-OUT value (500V). In fact, the maximum working voltage of the ballast is not so large. In the first test, the voltage measured after 5 seconds of abnormal state operation and 30s after rectification effect operation exceeds 400V (effective value), but exceeds 500V voltage (effective value) when repeating the second test, the first time occurs. The test passed and the second test failed but failed.
In fact, the best protection measure is that when the ballast is in an abnormal state, its voltage or current will fluctuate greatly in a short time. Just take this abnormal voltage or current and use it to try to make the ballast. The half-bridge inverter circuit of the device stops working, and the starting circuit is no longer triggered. There are two kinds of sampling methods for this protection circuit. One is to add a set of secondary windings in the output inductor, and integrate and rectify to obtain a voltage to drive the thyristor, so that the base and ground of the switching transistor of the half-bridge inverter circuit Short-circuit and stop working; Second, it is directly drawn at the output inductor, and then the voltage obtained by integration and rectification directly drives the thyristor, so that the half-bridge inverter circuit stops working (see Figure 2, the first sampling method in the wave coil) The dotted line is the second sampling method). The working mode is as follows: a voltage is obtained in the sampling circuit to turn on VD2, and this voltage drives Q4 through R7, so that the collector and the emitter are turned to ground, so that the switching transistor Q2 stops working; this voltage is also passed through R8. Driving the thyristor Q5 action causes the current shunted by R3 to be directly connected to the ground, so that the integration circuit can no longer charge C8, so that VD1 cannot obtain sufficient voltage to turn on, and the ballast will not start working again. Protective effects.
3.5 Heat and fire resistance requirements for insulating parts
Regarding the requirements of insulating parts, the new standard is the same as the old standard, and the insulating parts of the plastic materials used for the ballast should be sufficiently heat-resistant, and can withstand the "needle flame test" specified in GB/T 9169.5. As long as it is a heat-resistant (above 150 ° C), flame-retardant material, plastic materials can basically pass the test of heat and fire resistance in the standard.
4 Electromagnetic compatibility requirements for electronic ballast products
4.1 The basic concept of electromagnetic compatibility and the electromagnetic compatibility problem of the product
In China's 3C certification system, electronic ballast products include electromagnetic compatibility (EMC) certification in addition to safety certification. Electromagnetic compatibility is the study of a variety of electrical equipment that can coexist without causing degradation in a limited space, time and spectrum. It contains two aspects: on the one hand, it is required to prevent or reduce electromagnetic interference, so as to avoid the performance degradation or damage of other electrical equipment; the second is to require the product to have certain resistance to electromagnetic interference generated by external electrical equipment, so as to avoid Degraded or damaged performance. The above requirements indicate that in designing the product, in addition to meeting the expected functions and performance, it must also be considered that the product should be able to “peacefully coexist†with other electrical equipment in a complex electromagnetic environment, without interfering with other equipment. It will not be interfered by other equipment, which is the electromagnetic compatibility of the product.
Electromagnetic compatibility consists of two parts: electromagnetic interference (EMI) and electromagnetic sensitivity (EMS). Products produced or sold in China are currently only mandatory to meet electromagnetic interference indicators. For electronic ballast products, as long as they can pass the GB 17743-1999 standard and GB 17625.1-2003 standard terms, Obtained China's 3C electromagnetic compatibility certification. Although China issued the standard to enforce the electromagnetic compatibility standards for lighting products as early as 2000, most of the electronic ballast products produced in China failed to meet this requirement. This is also the author’s failure in the inspection of such products. The most qualified item.
In view of the fact that the price of setting up an electromagnetic compatibility test system is unbearable for small and medium-sized enterprises, general lighting design engineers suffer from lack of knowledge about electromagnetic compatibility, and do not know how to design to meet both performance requirements and relevant electromagnetic compatibility standards. Electronic ballast products required. Therefore, the author analyzes the working principle of the electronic ballast and the causes of electromagnetic interference and proposes corresponding corrective measures.
First, simply understand the issue of electromagnetic compatibility, or electromagnetic interference. The electromagnetic compatibility problem must have three conditions: one is the interference source (the circuit or device that generates the interference); the other is the sensitive source (the circuit or device affected by the interference); the third is the coupling channel (the interference source can be used) The resulting interference energy is transmitted to the sensitive source).
This is the three elements of electromagnetic compatibility. As long as one of these three elements is eliminated or measures are taken to suppress it, electromagnetic interference will disappear or decrease. Therefore, electromagnetic compatibility technology is researched around these three elements.
4.2 Working principle of electronic ballast
For an electronic ballast, it consists of a rectifier circuit, a half-bridge inverter circuit, and an LC resonant circuit (see Figure 2). The working principle is: the rectifier circuit (diodes D1 ~ D4 constitute bridge rectifier) ​​first converts the power frequency alternating current (220V) into direct current, and the electrolytic capacitor (C7) filters to obtain a stable DC voltage (about 300V or more) output, and then The high-frequency transformers (N1, N2, and N3) drive the switching transistors (Q1 and Q2) to turn them on, producing a controlled high-frequency voltage, which is then illuminated by the output inductor (L2) and continues to illuminate.
4.3 Harmonic generation and improvement measures
Due to the unidirectional conductivity of the rectifier diode and the energy storage of the electrolytic capacitor, only when the input voltage exceeds the voltage across C7, D1 to D4 will be forward biased and turned on. In addition to supplying the half-bridge inverter circuit, the rectifier circuit current also charges the C7. However, when the instantaneous value of the input voltage is lower than the voltage at the C7 terminal, the rectifier will be turned off by conduction and stop charging C7, and C7 supplies current to the half-bridge inverter circuit to maintain its operation. The C7 capacity is generally larger (generally 15-22μF). When the load current is small, the charging time of C7 is short and the discharge time is too long. The conduction time of the rectifier is shortened, so that the input voltage is only at the peak of the sine wave. The current is charged to C7 for a short period of time. This current is a very narrow but high peak periodic spike current. In addition to the fundamental wave, this distorted input current also contains a wealth of higher harmonic components, which can have a severe impact on the public power grid, resulting in harmonic interference.
Some people think that it is completely possible to use a small-capacity electrolytic capacitor instead of C7, which can reduce the harmonic content and reduce the cost (many engineers and technicians who contacted me have adopted this method in the harmonic project rectification). In fact, this method is not advisable. If the value of C7 is too low, the filtering effect will be poor. Because the discharge time of C7 is greatly shortened, the cycle of charge and discharge gap is shorter, and the periodic pulse current flowing into C7 is narrower, which will make the DC ripple voltage fluctuate and increase the peak coefficient of the lamp current, which is extremely large for the lamp. unfavorable. Similarly, the luminous flux of the lamp is also increased, which causes great damage to human vision. If the DC ripple voltage fluctuates and becomes large, Q1 and Q2 will not be in the best working condition, and it will be easy to generate heat and cause damage. The service life of the ballast will be greatly shortened and it will not be worth the loss.
In summary, the improvement measure for suppressing harmonics is to increase the power factor as much as possible and reduce the harmonic distortion of the input current. To achieve this goal, it is necessary to increase the conduction rate of the rectifier (ie, extend the conduction time of the input current), so that the waveform of the power supply current is close to the sine wave of the voltage, reducing the waveform distortion of the current; at the same time, ensuring the power supply filter capacitor It can smoothly supply power continuously to the load (ie, reduce the phase difference between the input current and the input voltage). This is what we usually call the power factor correction circuit. The power correction circuit is divided into passive correction (PPFC) and active correction (APFC). At present, the electronic ballast products produced in China are limited to cost and price factors, and most of them use passive harmonic suppression circuits composed of improved flow-by-flow circuits. This technology has developed relatively maturely, and the harmonic content of the ballast can be effectively suppressed as long as it is properly debugged. However, such a circuit has difficulty in debugging, and it is difficult to control the quality of the product in mass production, and basically cannot meet the requirements of electromagnetic compatibility standards and performance standards at the same time, and is only used in some low-power ballasts or energy-saving lamps. The active correction is a harmonic suppression circuit composed of discrete active devices such as a triode or a harmonic suppression circuit using an ASIC. The latter is simpler to debug than the former, and has higher reliability, but the cost is also higher. Figure 2 shows an active power correction circuit composed of a typical discrete active device. The circuit characteristic is that Q3 is responsible for controlling the charging and discharging of C7. Power factor correction ASICs (APFC controllers) are mostly developed using this principle.
4.4 Conducted interference, radiated interference and corresponding measures
In Figure 2, Q1 and Q2 generate a large surge current in the coil of the high-frequency transformer at the moment of conduction, thus forming a high surge peak voltage; at the moment when Q1 and Q2 are disconnected, due to the high-frequency transformer In the magnetic core, under the action of the pulse current, the magnetic flux changes to form part of the accumulated energy. This part of the energy is not transmitted in time, and the high-level transient voltage or current is formed with the interelectrode capacitance and resistance of Q1 and Q2. Parasitic oscillations will occur. When the repetition frequency of Q1 and Q2 is higher and the switching speed is faster, the interference pulse voltage is larger. This voltage is superimposed on the voltage generated by Q1 and Q2 at the turn-on and turn-off instants to form a higher pulse voltage. And then feedback to the input loop to form conducted interference (electromagnetic interference). The high-frequency transformer and the high-frequency switching current loop formed by Q1, Q2 and C7 may also generate large space radiation, and the glow discharge and arc discharge of the fluorescent tube may also cause electromagnetic interference, and these interferences form radiation interference. Therefore, the high-frequency transformer and the switching transistor are both the core components of the electronic ballast and the main component (interference source) that generates electromagnetic interference, which is the main cause of the direct failure of the electronic ballast to pass the EMI assessment. The high-frequency pulse voltage interference generated by the high-frequency transformer and the switching transistor has both common mode interference (additional interference with the same potential of the signal itself and the same direction), and differential mode interference (interference with the same signal amplitude and opposite phase).
After a large amount of data analysis of the conduction test of the electronic ballast, we know that the electromagnetic interference generated by the electronic ballast products is mainly dominated by differential mode interference in the frequency range of 9 to 150 kHz; the frequency range of 150 kHz to 30 MHz is mainly It is based on common mode interference. Finding the source of the interference and knowing the cause of the interference, only need to take corresponding measures to suppress the interference, so that it is not difficult to pass the assessment of the clause.
To suppress conducted interference, the PCB layout is generally as short as possible, and the power line (ie, the input) should be away from the conductor with high-frequency current (ie, the output). Since the electronic ballast itself does not have many components, the wiring is not difficult. The product is shielded from the outside world to weaken the interference caused by external noise. The reasonable grounding method not only ensures the safety of the ballast, but also prevents the user from being exposed to electricity due to leakage of the ballast, and can also reduce the conducted interference noise of the ballast.
In order for electronic ballast products to pass the EMI clause, the focus should be on the filter. According to the type of interference source, it is only necessary to install an EMI filter circuit at the input end of the power supply and the rectifier circuit, which can basically be evaluated by this clause. The EMI filter circuit is mainly a low-pass filter composed of a series inductor and a parallel capacitor to form a bidirectional network. The impedance mismatch principle is used to suppress the pulse interference generated by the circuit, and the filtering range is usually between 9 kHz and 30 MHz. We know from the filter frequency characteristic curve that one of its characteristics, that is, the technical index, is the insertion loss value. In order for the filter to have the best attenuation performance for the interference signal, the filter impedance should be mismatched with the power supply impedance, the more the mismatch is, the better the attenuation achieved, and the greater the insertion loss; the larger the insertion loss, the filtering The better the effect, the greater the inhibition of conducted interference.
The insertion loss of an EMI filter is mainly determined by the quality of the copper wire, the winding method, and the quality of the core used. The magnetic core is made of a magnetic material, so the magnetic material is an indispensable component of the filter. There are many kinds of magnetic materials, and different magnetic materials have different electrical characteristics, resistivity, bandwidth, impedance, etc., and the suppression effect on conducted interference is also different. To suppress interference in different frequency segments, it is necessary to select a magnetic material suitable for the frequency segment, because from the material point of view, the role of the filter is to block unwanted signals and to consume harmful interference signals in the form of heat, so that useful The signal passes without attenuation or with almost no attenuation. In the actual rectification work, the author found that even if the filter uses the same copper wire and the same winding method, the number of turns is the same. The difference between using different cores to suppress the conducted interference signal is great, especially the high frequency. transformer. The use of metallic magnetic materials is much better than the use of ferrite magnetic materials when suppressing low frequency interference signals.
In Fig. 2, an EMI filter circuit composed of a common mode filter (T1) and a differential mode filter (T2/T3) and capacitors (C1 to C4), and C5 is a capacitance across the ground. As long as the components with the appropriate parameters and the appropriate magnetic materials are selected, the requirements of the EMI clauses in the standard can generally be assessed.
In addition to the string EMI filter at the input (power supply) of the ballast, it is also possible to work on the components that cause interference in the ballast. From the previous analysis, it is known that the switching transistors Q1 and Q2 generate a higher amplitude pulse voltage or current at the moment of their turn-on and turn-off, and the interference voltage of the ballast can be reduced by eliminating or weakening the pulse voltage or current. The deep saturation of the transistor can be reduced between the base and emitter of Q1 and Q2 and a ceramic capacitor C15/C16 (0.01μF), which helps to reduce the amplitude of the pulse voltage and also prevents the total of Q1 and Q2. The state is turned on so as not to damage the switch tube; or a damping network (composed of D14, R18, C20 and D15, R19, C21) is added between the collector and emitter of Q1 and Q2 to absorb the surge generated between the switch. The current protects the switch tube and effectively reduces the interference intensity (see Figure 2). However, in this circuit, C20 and C21 should not be too large, otherwise the power consumption of the ballast will increase.
The effect of these measures on suppressing common mode interference is quite obvious. Especially for those compact electronic energy-saving brackets, it is a good choice because the space is limited and the filter with large inductance cannot be used. Figure 3 and Figure 4 are the test curves of the author before and after the rectification of the bracket, and the EMI filter is the same.
Since GB 17743-1999 stipulates that the test frequency range of lighting electrical products is within 9 kHz to 30 MHz, and the frequency range in which antenna effect is generally easy to occur is above 30 MHz, as long as the conduction interference amplitude of electronic ballast products does not exceed the standard Limit requirements, usually also meet the requirements of the standard for radiated electromagnetic interference limits.
5 Conclusion
Today, with the rapid development of science and technology, new light sources are constantly being introduced, such as LED lighting, fiber optic lighting, etc., users have more room to choose lighting appliances. However, the light source such as LED or fiber is limited to the current technology and production technology level, and its price is high, and the power and luminous flux are far from meeting the needs of people. At this stage, incandescent lamps, fluorescent lamps and discharge lamps are also the main lighting fixtures. Especially in the vast rural areas of China, incandescent lamps are mostly used as illumination sources, while incandescent lamps consume less electricity and have low luminous flux. A large number of incandescent lamps can cause a great waste of electrical energy. Fluorescent lamps are currently the ideal lighting source to replace incandescent lamps. If a large number of fluorescent lamps are used instead of incandescent lamps as illumination sources, the energy saved is considerable, which is of great benefit to protecting China's natural environment and enhancing China's sustainable development. Electronic ballasts with fluorescent lamps have a large market, and it is the unshirkable responsibility of researchers to develop new, efficient and reliable electronic ballast products.
references:
1 "Control devices for lamps - Part 4: Particular requirements for AC electronic ballasts for fluorescent lamps" GB 19510.4-2005
2 Limits and methods of measurement of radio disturbance characteristics of electric lighting and similar equipment GB 17743-1999
3 General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China. Issued by China National Standardization Administration Committee. "Electromagnetic Compatibility Limits Harmonic Current Emission Limits (Device Input Current per Phase ≤ 16A)" GB 17625.1-2003
4 National Lighting Appliance Standardization Technical Committee. China Green Lighting Project Office, edited by China National Institute of Standardization. National Standard for Lamp Control Devices and National Standards for Metal Halide Lamps
5 Mao Guangwu. I wish David to edit. "The Principle and Manufacturing of Electronic Ballasts"
6 Yu Anqi, “The Points to Be Concerned in the Design of Electronic Ballastsâ€
Pluggable Terminal Block,Terminal Block,Screw Terminal Block
Wire Harness,Automotive Cnnectors Co., Ltd. , http://www.nswireharness.com