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  • Article source - | Author - Administrator | Hits - | Published - 2013-09-26 09:20:43
  • WHPTC Resettable fuse for the electronic ballast circuit protection solutions

    一、Electronic ballast Industrial Status and development trends:

    1、Electronic ballasts advantages:

      Because gas discharge lamps (such as fluorescent lamps, neon, halogen, metal halide, etc.) is a negative resistive electric light, to make it normal and stable work, need to add a current limiting device. The current limiting device called a ballast. Currently gas discharge lamp ballasts used in two ways: (1) inductive ballast; (2) high-frequency electronic ballasts. Since inductive ballast operates at mains frequency, bulky, heavy, need to consume large amounts of copper and silicon steel and other metal materials, cooling difficulties, low efficiency, there are strobe. Using high-frequency electronic ballast circuit switching converter electronic ballast method, with no flicker, high efficiency, small size, light weight, adjustable light, do not use a lot of copper and silicon steel material characteristics, due to its small size high luminous efficiency, no stroboscopic effect, to adapt supply voltage range, saving 60% of a series of advantages, by the users. Gradually replace the inductive ballast has become an inevitable trend.

    2、Electronic ballasts trends:

      From the time of division, electronic ballasts mainly through the following stages: the first stage is the mid-1980s to the early 1990s . During this period , power electronics technology development from low to high frequency , APFC ( Active Power Factor Correction ) also started, advantages and disadvantages of electronic ballasts are beginning to appear . This stage electronic ballast main features are: ( 1 ) the ballast input uses uncontrolled rectifier and a large capacitor ( or without capacitor ) filter , the input current waveform serious distortion , when a lot of use , will cause neutral current increases, can cause severe damage or even cause a fire a lot of ballast . ( 2 ) the use of " per-flow " passive filtering techniques , making PF> 0.9, THD <30%. However, the crest factor of the harmonic 9 Cf ≈ 2, exceed the standard . Some people use this " KITE " passive filtering technique called second-generation electronic ballast electronic ballast . The second stage is the early 1990s to the mid-1990s. During this period , the APFC technology has matured, and introduced the related specific integrated chip. Electronic ballast circuit mainly uses two power conversion , the first stage uses APFC, the second stage uses power DC / AC inverter . People often will use this technology called third-generation electronic ballast electronic ballast , also suggested that the single-tube electronic ballast . Because it uses a PFC technology , so the PF of up to 0.99, THD and each harmonic index can meet the requirements. However, this high frequency electronic ballast taken two power conversion , the overall efficiency of 80% to 90%, or even lower, while the circuit is complicated and costly . In some places the big blind and manufacturers on energy-saving lamp project , because of its capital, technology, raw materials, and processes in the absence of full implementation of the case , rushed into making the product quality can not be guaranteed , the company's product quality uneven , malignant bidding confuse the market, do not follow the requirements of the production , assembly plant selection undesirable lamps and components patchwork composition, quality second lowest , seriously damaged the reputation of energy-saving lamps , light efficiency , low failure rate, life is short, poor consistency problems, resulting in the community have energy saving lamp to say money is not festival to promote energy-saving lamps is a big negative impact. It has been difficult to promote a wide range .

      Until 2006, gradually developed a passive filter pump technology electronic ballast circuit (Figure 1), high-frequency electronic ballast pump circuit (Figure 2), double pump electronic ballast circuit (Figure 3). By comparison APFC electronic ballasts using the best overall indicator, but it is relatively higher cost, the circuit is relatively complicated, and sometimes difficult to spread. Pump and two pumps the high frequency electronic ballast circuit is better overall index, the third harmonic content HD3: double pump 0.2 to 0.3, and the pump frequency is less than 0.1, the active filter type is less than 0.1. As a result of double-pump and high-frequency pump energy feedback circuit to add only a few passive components, low cost, have practical value, is the development direction of electronic ballasts.

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    Figure 1 uses an electronic ballast circuit passive filter

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    Figure 2 High-frequency electronic ballast circuit pump

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    Figure 3 double pump electronic ballast circuit

    3、Electronic ballast industry status:

      Also known as energy-saving compact fluorescent lamps (CFL lamps referred abroad) in 1978 it was first invented by the foreign manufacturers, we are talking about energy-saving products are mainly for incandescent speaking. Ordinary incandescent light efficiency of about 10 lumens per watt or so, life is about 1000 hours, it works: When the lamp access circuit, current flows through the filament, heating effect of current, the incandescent lamp emits a continuous visible and infrared, this phenomenon is the filament temperature is raised to 700K can be perceived, as a result of the filament temperature is high, most of the energy is wasted in the form of infrared radiation, because the filament temperature is high, evaporates quickly, so life expectancy significantly shortened, about 1000 hours.

      CFL works mainly through the ballast to the lamp filament heating temperature of about 1160K, the filament began to emit electrons (because the filament coated with a number of electronic powder), electron impact inelastic collisions produce argon atoms, argon atomic energy after the collision and impact of mercury atoms and mercury atoms absorb the energy generated after the transition ionization, emit 253.7nm ultraviolet light, ultraviolet excited light-emitting phosphors, fluorescent work Because the filament temperature of about 1160K, working temperature than incandescent 2200K-2700K much lower, so that its life is greatly improve, reaching more than 5000 hours, Because it does not exist as current incandescent heat effect, the energy conversion efficiency of the phosphor is also very high, more than 60 lumens per watt. An energy-saving 80% energy than incandescent lamps, the average life expectancy eight times, only 20% of the thermal radiation. Under non-stringent conditions, a 5-watt light energy may be considered according to the incandescent lamp is 25 watts, 7 watts of energy approximately equal to 40 watt light shines incandescent, 9 watt incandescent lamp is approximately equal to 60 watts achieve a green light.

      October 1, 1997, China's "Green Lighting Project" was officially launched, the standard has been formally introduced, but there is still very much on the market of energy-saving lamps manufacturers, disregard for national laws, regulations, regardless of the interests of consumers, mass production is still not called energy saving lamp energy saving lamps, due to its mass times the lowest bidder, the limited recognition of consumer products in rural areas and most of the city, as well as a large part of the market, Because the market accounted for most of the market dominated by the low-end products, making good energy-saving lighting products more difficult to enter the market, which gives the green light to promote to bring a certain degree of difficulty, but with consumer awareness and understanding of energy-saving lighting products, good quality energy saving light products in the market in an expanding day by day, poor quality energy-saving lamp market shrinking day by day, it also gave us hope and opportunity.

      According to statistics, the world's electricity for lighting accounts for the world's total electricity generated 1/4, as only the active 20 billion light bulbs in 5 billion into energy-saving electronic ballast bulb, can save 200GW of energy, and thus reduce the construction of dozens of power plants. Because high-frequency electronic ballasts for energy and huge market potential, into the 1990s, the various gas discharge lamps are widely used high-frequency electronic ballast to form a "green light" for new industries. United States, Britain, France, Japan and other major developed countries and some developing countries has developed a "green light" program, and has achieved remarkable results.

      At present, China has become the largest producer of lighting fixtures, the existing more than 4,500 lighting manufacturers, electric light source products are more than 60 categories over 3500 varieties and specifications, lighting products more than 30 categories of more than 500 varieties and specifications. China's lighting energy saving potential to be tapped. Currently, fluorescent, compact fluorescent rare earth tricolor has produced a variety of products for home use. Such lamps and fluorescent illumination compared to the same tube about saving 27% compared with incandescent lamps, saving 70%. Only one energy-saving lamps per household basis, the country 400 million energy-saving lamps could be saving 20 million kilowatts electricity, so in our energy-saving lighting is a very important issue.

      And now, due to price effects, and there is no universal electronic ballast fluorescent lamp used, this is the status quo of China. But with lower costs, lower market prices, quality improvement, and 30% of national subsidy policy support will be vigorously promoted.

    二、Electronic ballast circuit protection current problems:

    1、Electronic ballast works Description:

      Circuit shown in Figure 4: The circuit is present, most manufacturers use of electronic ballast typical circuit configuration, R1, C1, D4, R4 starting circuit components; Q1, Q2, T1, Lp, EL, Cp, EL common oscillating half-bridge circuit composed of high-frequency inverter. After power is turned on, the circuit will soon start generating high-frequency oscillations, so that the voltage across C2 gradually increases until the lamp ignition voltage, the lamp starts lighting. Lamp is lit, the entire circuit has been in a steady operating state.

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    Figure 4, the electronic ballast operating principle

    2、Electronic ballast circuit problems:

      The electronic ballast with small size, light weight, simple circuit, less original, high conversion efficiency and low cost characteristics, therefore, the electronic ballast in the traditional lighting such as shopping malls partial lighting, home decoration lighting is widely used. However, because the circuit is imperfect, there will be security in the use of many problems, but also the reason many manufacturers are eliminated. Specific issues are summarized below:

    (1)No filament preheat function, turn on the power indicator will illuminate and easy to produce filament electrode sputtering effect, which will reduce the life of the filament, use over time could easily lead to the lamp end blackening phenomenon;

    (2)Because the circuit is not set protection circuit, so once the mains power supply failure (such as grid voltage rises too much), not only will cause circuit damage, serious fire accidents will happen;

    (3)When a lamp rupture, lamp black end, such as aging or end of life failure, the inverter output current is increasing, and usually this current will rise to more than five times the nominal current. If you then do not take effective protection measures, will cause great harm. First, excessive current will cause the inverter transistor as a switch or a FET and other peripheral components due to overload and burned, and even cause smoke, explosion and other accidents. Meanwhile, light foot on the ground or neutral will form a long high voltage, for 20W, 36W, 40W, and most of the other GB / non-standard lamps, electronic ballasts, this voltage tends to reach a kilovolt or more high, not only for the national standard GB15143 are strictly prohibited, but also endanger the personal and property safety. GB15143-94 "11.14" and GB15144-94 "5.13" section of the electronic rectifier abnormal state tests include: open lamp cathode damage, deactivation, rectifier effect, etc., also provides electronic ballasts After the above tests shall take place safety failures and be able to work properly.

    (4)Driven to do the use of IC, IC internal protection functions to complete the sampling points set at three times the current position, when the current time is in between 2-3 times, IC not only not protected, and will produce high damage to the IC and the switch.

    三、PPTC in the electronic ballast circuits and methods to resolve the issue:

      Abnormal state for the protection of electronic ballasts, often using the following four measures, and the application of the electronic ballast Polymer PTC protection program is the best and most sensible choice, specifically as follows:

    1、In series with the AC input circuit Fuse. Series fuse in this position will make some people mistakenly believe that will play the role of an overcurrent or overload; And in fact, such protection is generally not in the filament activation provides protection under overload conditions, it is often the switching device fuse until after the breakdown, you can not play a real sense of the abnormal state protection.

    2、In the rectified output loop to adopt SCR, bipolar transistor or FET as the core of the protection circuit. This electronic circuit protection to protect the biggest advantage is that time is short, but there are some of the following disadvantages:

    ①Prone to error protection: If for some reason, the SCR trigger end formation sharp even very short pulses can cause the inverter is stopped, resulting in light goes out.

    ②Design and commissioning work more cumbersome: Under normal circumstances, this protection circuit will include resistors, capacitors, pulse transformer secondary winding at least six, including electronic components, while using so many elements combined with silicon and other active devices discrete and drift problems will increase the difficulty of debugging, and thus the impact on production efficiency.

    ③This type of protection is also present high cost, PCB space occupied by the larger shortcomings, this is a substantial number of electronic ballast manufacturers headaches.

    ④SCR electronic circuit protection mode, when dual / multi-lamp in a lamp to activate, it will cause the entire ballast to stop working, so that even if the normal fluorescent lamps extinguished simultaneously, which is often disturbing.

    3、PTC ceramic resonant circuit being connected in parallel to the resonant capacitor, which is the earlier methods used to achieve the purpose of the soft-start, promote extended lamp life. However, the actual reach conservation purposes, there are still many problems (Figure 5,6) as follows:

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    Figure 5 PTCR "Ceramic PTC" temperature resistance curve

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    Figure 6 CPTC "Ceramic PTC" warm start circuit diagram

      In order to solve the problem preheated cathode fluorescent lamp, the use of the positive temperature coefficient thermistor (hereinafter referred to as CPTC "Ceramic PTC"). The temperature-resistance characteristic curve shown in Figure 5. TB of the curve points are CPTC "ceramic PTC" switching temperature (resistance value increases to the minimum temperature twice). CPTC "Ceramic PTC" TB point above body temperature, as the temperature rises, CPTC "ceramic PTC" will be sudden change to a high resistance value, using the CPTC "Ceramic PTC" The characteristics of the design of the pre-hot start circuit shown in Figure 7.\

    Figure 7 using the CPTC "Ceramic PTC" warm start circuit diagram

      The moment when the circuit is switched on, high-frequency power supply output voltage V0 applied to the tube ends, because the thermistor CPTC "Ceramic PTC" right shunt resonant circuit configuration, the Q value of the circuit is low, the lamp can not be formed at both ends high pressure, it can not light the lamp. Meanwhile, the high-frequency current through the inductor Lp, filament, thermistors PTCR "ceramic PTC", of the cathode preheating time after 0.4 second (GB required than 0.4 seconds), CPTC "ceramic PTC" because by the current, the temperature increases, the resistance value increases rapidly, weakened to the resonant circuit shunt. When the resistance increases to a certain value, the resonant circuit start-up, the resonant voltage amplitude V2 increases to the lamp lit. Lamp is lit, the lamp negative resistance characteristics, namely the lamp current increases, the voltage across the lamp down to the rated working voltage V3 value, preheat the boot process completes, the lamp into work.

     The problem is that the lamp is working properly, the thermal resistance CPTC "Ceramic PTC" always in a state of thermodynamic equilibrium, because the thermistor can not completely block the lamp cathode shunt thermistor temperature affect the level of current through the size. Through the current size and affects the thermistor temperature changes. Specifically, when the CPTC "ceramic PTC" presents a high impedance state, the current decreases, CPTC "ceramic PTC" temperature decreases, the resistance will decrease, and causes the flow through CPTC "Ceramic PTC" current increases, so the cycle thermistor protection and not always in a state of protection changes.

    This state has the following hazards:

    ① CPTC "Ceramic PTC" in warm-start circuit there is always power, typically 4% of the total power. The electronic ballast or electronic energy saving lamps lumen factor decreases. After testing, 40W Electronic Ballast CPTC "ceramic PTC" power greater than 1.6W, 18W energy saving lamp CPTC "ceramic PTC" power at 0.8W or so. Emit luminous flux per watt 50 lumens meter, 40W and 18W electronic ballast thus lost 70 and 40 lumens respectively.

    ②CPTC "Ceramic PTC" heat generated by the power consumption of compact fluorescent lamps and electronic ballasts shell temperature increase will cause other electronic components especially transistors and electrolytic capacitors damaged, so the failure rate rises.

    ③Fluorescent light, the filament circuit because CPTC "Ceramic PTC" the existence of a current always flows through the filament, thereby forming the emission current, reducing the life of the cathode.

    ④ Preheating circuit CPTC "ceramic PTC" after the lamp is lit, still above 80 ℃ high temperature environment, could easily lead to CPTC "Ceramic PTC" grain boundary resistance properties of degenerate, so that changes in temperature resistance coefficient, preheating time longer. Degenerate severe impact of current at the moment of starting the power tube will burn. If the cathode preheat start a long time in the state, will ultimately damage the lamps and electronic ballasts.

    ⑤CPTC "Ceramic PTC" hardest to meet the high pressure of this indicator. Figure 7, when the CPTC "ceramic PTC" in parallel with the tube ends, to withstand higher open circuit voltage Vtrig (typically 1000V or so), then CPTC "ceramic PTC" temperature curve above the switching temperature resistance after , rising slowly. Long-term work in the pressure to protect the state, its life expectancy is shorter than the life of fluorescent lamps, fluorescent lamps not broken before the ceramic PTC on early broken.

    ⑥ CPTC "Ceramic PTC" across the resonant capacitor is connected in parallel, the normal work in a high impedance state (protected), if the circuit overcurrent fault overcurrent function can not be completed.

    ⑦ When the high-frequency current through the CPTC "Ceramic PTC", it will also make it higher temperature resistance characteristic curve increased after switching temperature TB slow. These will make the CPTC "ceramic PTC" the filament preheating performance deteriorated.

    ⑧ Tested to CPTC "Ceramic PTC" presents a considerable capacity. In the circuit of high frequency, using the CPTC "ceramic PTC" in parallel with the start capacitor C, will cause direct damage of the output characteristics of the ballast. Especially T5 fluorescent lamps, electronic ballasts generally require operating frequency above 50kHz, output characteristics of its more serious.

      Despite the use of CPTC "ceramic PTC" the way of the cathode preheating above disadvantages exist, but the current production of electronic ballasts for the lighting industry, who have the preheating function of electronic ballasts, compact electronic energy saving lamps, there are still many manufacturer also uses CPTC "ceramic PTC" preheating.

    The main reason for these problems is generated in the electronic ballast PTC application errors:Some electronic ballast design engineers who know PTC is the positive temperature coefficient thermistor, but do not know "Polymer thermistor-PPTC", and "ceramic thermistor-CPTC", as well as its electrical properties and applications difference, because ceramic PTC first used in electronic ballast, and there is a problem, but the resulting increase in cost and the sales blocked, has been difficult and the process is a pair of good contradiction.

    4、Using Polymer PTC overload protection for electronic ballast:

      Using Polymer PTC overload protection for electronic ballasts, Polymer PTC aka PPTC, referred to as the "PTC" or "WHPTC", "WHPTC" I was the Secretary of the "Wan and" brand "PTC". Polymer PTC not only overcome the ceramic PTC (CPTC) shortcomings, but also to achieve a good start soft start, overcurrent protection, overtemperature protection purposes. Discussed in detail below:

      Using Polymer PTC overload protection for electronic ballast method, in which the resonant capacitor resonant circuit next series WHPTC thermistor. Shown in Figure 8.

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    Figure 8 Polymer PTC characteristics and application of electronic ballast block diagram abnormal protection

     When the lamp is normal, after power electronic ballasts, inductors, capacitors, and PTC thermistor resonant circuit consisting of the fluorescent lamp start working. If the lamp filament aging or due to other reasons leak away when activated, PTC thermistors in action within a few seconds, forcing the LC series resonant circuit to stop vibration, thereby cutting pressure, while protecting the inverter switching devices. Shown in Figure 9.

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    Figure 9 Polymer PTC abnormal protection for electronic ballast application schematic

    The protection of the advantages and achieve the purpose of:

    ①Seen from Figure 6: In normal operation, due to the resistance WHPTC small (WH130-300 is 1.3-2.6. Ohms) partial pressure is low, the voltage of the main capacitor capacitance Cp (708.567 ohms) minutes to go, so pressure on PTC's requirements are not high. The WHPTC 130V voltage is sufficient. (Xcp = 1/2πf c = 1/2 × 3.14 × 35 × 103 × 6.8 × 10-9 = 708.567 ohms, Cp = 6n8; f = 35KHz).

    ② Due to the resistance WHPTC small insertion loss when working very small (can be neglected), there is no loss for lamp lumen, does not affect the fluorescent brightness.

    ③ Although WHPTC resistance is small, but the resistance of the filament is only about 10 ohms, which is equal in this circuit by adding a quarter of the DC resistance of the tube during start-limiting effect, can greatly reduce the filament electrode sputtering effect, thus truly protect the filament, greatly extending the life of the lamp.

    ④ When a lamp rupture, lamp black, such as failure at one end, the resonant capacitor voltage will rise causes the current increases rapidly, and the breakdown of the switching transistor will burn resonant capacitor, the use of WHPTC, will rise in the current high in the process in a timely manner to protect, protect the oscillation circuit stops oscillating or weaken, limiting the voltage increases, so there is no pressure damage PTC and resonant capacitor.

    ⑤ When electronic ballasts inside when the temperature exceeds a predetermined temperature, PTC will promptly protected against loss.

    ⑥ Driven to do the use of IC, IC internal protection functions to complete the sampling points set at three times the current position, when the current time is in between 2-3 times, IC not only not protected, and will produce high damage to the IC and the switch, however, when using WHPTC, can over-current exceeding the operating current 1.7 to 2 times, the time protection, which can compensate for the lack of protection IC brought.

    ⑦ Once the mains power supply failure (such as grid voltage rises too much), the electronic ballast internal current is too high, PTC will promptly protect the entire circuit, the circuit will not cause damage, but will not fire accident.

    ⑧ Fluorescent lamp is a negative resistance device (negative temperature coefficient of the element), use a positive temperature coefficient WHPTC series in its back on the road, not only over-temperature, over-current protection, but also within a certain range to play the role of temperature compensation.

    ⑨ WHPTC only can be used in series with the resonant capacitor, but also for the power input and the rectifier filter circuit between the high-frequency inverter circuit (Figure 10), flexible and simple.

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    Figure 10 WHPTC can be installed using the location

    ⑩For a multiple fluorescent lamps with electronic ballasts, when one lamp is damaged, due to the protective effect WHPTC enable other fluorescent continue normal use without the damaging impact of fluorescent light. Figure 11: three fluorescent lamps if one or two fluorescent lamp circuit is damaged, the other lamp will work fine.

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    Figure 11 a fluorescent electronic ballast block diagram with three

      Because of Polymer PTC exception for electronic ballast circuit protection of these advantages, so gradually recognized by many manufacturers, gradually applied.

      Many electronic ballast has now been recognized by the manufacturer, our company has developed WH130-XXX or WH250-XXX series electronic ballasts PTC thermistor even at 70 ℃ high temperature environment can still maintain fluorescent work, while at room temperature under conditions to ensure good protection characteristics; hand, even after repeated or prolonged protection after, PTC can still maintain performance is very stable.

    5、WHPTC electronic ballast circuit fault protection for application methods:

    ①WHPTC the installation location can be used and Figure 11, Figure 12, which is used in series for applications at higher Cp.

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    Figure 12 WHPTC can be installed using the location

      WHPTC instead of glass in the AC input fuse applications are also common, because WHPTC protection movement speed is much faster than the glass tube fuse, its speed is relatively protected following graph:\

    ②WHPTC in single lamp electronic ballast application shown in Figure 13:

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    Figure 13 WHPTC in single lamp electronic ballast Applications

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    Figure 14 WHPTC in single lamp electronic ballast Applications

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    Figure 15 WHPTC the IC driven single lamp electronic ballast Applications

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    Figure 16 WHPTC the IC driven single lamp electronic ballast Applications

    \Figure 17 WHPTC in single lamp electronic ballast Applications

    ③ WHPTC dual lamp electronic ballast in the application shown in Figure 18-19: Assuming a fluorescent lamp which deactivate the corresponding action WHPTC corresponding filament current is close to 0; but other fluorescent job will not be affected. Thus, the user will not have to in the end is the end of which only the lamp life or damage to the ballast troubled by such problems.

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    Figure 18 WHPTC in dual-lamp electronic ballast Applications

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    Figure 19 WHPTC in dual-lamp electronic ballast Applications

    ④WHPTC in dual-lamp electronic ballast application shown in Figure 20:

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    Figure 20 WHPTC in dual-lamp electronic ballast Applications

    ⑤ WHPTC in a single U-shaped, double U-saving lamp electronic ballast application shown in Figure 21:

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    Figure 21 WHPTC in a single U-shaped, double U-saving lamp electronic ballast Applications

    四、WHPTC in the electronic ballast circuit protection features and advantages:

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