Design of electronic neon transformer
Abstract: The design method of electronic neon transformer is discussed from the perspective of low cost and high performance.
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Keywords: electronic neon transformer design inverter
1 Introduction
With the development of the socialist market economy, along with the needs of spiritual and material civilization construction, the requirements for the bright and beautiful city are getting higher and higher. As a traditional means of commodity promotion, neon has become one of the main landscapes of urban and rural lighting projects, and its quantity and quality requirements have also increased accordingly. The transformers for neon lights will also become indispensable for urban lighting projects and commodity promotion. Components.
The world's first commercial neon appeared in 1910, and the first neon made in China was in 1927. Inductive neon transformers for neon lights, their production technology is still in use today. It has problems such as large power consumption (power factor of 0.5 to 0.6), heavy weight (8 to 1 kg), large volume, and short life (because the temperature rises). In particular, the problem of large power consumption is particularly serious. It is understood that the annual demand for inductive neon transformers in Beijing is 1 million units. Assuming that each transformer uses an average of 4 hours per day, the annual electricity consumption is 1.9 million kWh (kWh). Compared with an electronic neon transformer with a power factor of 0.9, the power equivalent to a medium-sized power station is wasted. Nationally, wasted electricity is more serious.
From the perspective of energy saving, the upgrading of neon transformers has become an urgent problem to be solved. The electronic neon transformer is an ideal product for upgrading. Compared with the inductive product, it has energy saving (power factor is 0.9 to close to 1), weight is about 4 times lighter, volume is reduced by 1/3, and life is long. The fully automatic protection function and brightness of the open and short circuit of the lamp do not change with the change of the input mains voltage.
However, many of the electronic neon transformers currently on the market are not ideal. For example, it can only be used indoors (because it is an open structure), the brightness is not high enough, the reliability of the automatic protection system is poor, and the cost is high. The technical economy has become one of the main obstacles to promote and apply it.
Due to the lack of publicly published technical monographs, Comrade Cai Zuquan’s book "Neon Principles and Manufacturing Techniques" is the first comprehensive technical work on the principles and manufacturing of neon lights and its transformers. It is to improve the technical level of China's neon industry. Played a big role. However, there are few discussions on how to design an electronic neon transformer. Papers and special issues published in other newspapers have only specific circuits and do not address the issue of how to design. This article discusses some of the issues of how to design.
2 electronic neon transformer load characteristics
The cold cathode neon lamp emits a glow discharge after the low-pressure inert gas in the lamp tube is broken down by high voltage. When the neon enters the normal glow discharge state, the lamp drop that maintains a constant discharge current is not very high, usually a constant value. A 10 m long neon lamp generally has a starting voltage of about 15 kV, a lamp operating voltage of about 8 to 10 kV, and an operating current of about 20 to 60 mA. A power source that adapts to the working characteristics of neon lights is an inductive neon transformer commonly known as a leakage transformer. It is essentially a high leakage transformer, and its volt-ampere characteristics are shown in Figure 1.
The curve a in the figure is the load characteristic curve of the transformer, and the intersection of the curve and the horizontal axis is the short-circuit current of the transformer, which is larger than the operating current of the lamp. The intersection of the curve and the longitudinal axis is the no-load voltage at the output of the transformer, which is higher than the starting voltage of the lamp. Curve b is the volt-ampere characteristic curve of a cold cathode glow discharge neon lamp. The intersection point p of the curves a, b is the stable working point of the neon.
figure 1
Like the inductive products, the electronic neon transformer is also a high leakage transformer, and its load characteristics are also non-linear. However, its ignition voltage, operating voltage and operating current are lower than inductive, which is determined by its high operating frequency.
3 electronic neon transformer design
The electronic neon transformer is essentially a switching power supply, that is, the 220V mains is converted into a high frequency voltage higher than 20 kHz by AC/DC/AC/, and is input to a high frequency step-up transformer to start the neon lamp. If the economical efficiency of the product is not considered, the comparison is made. Easy to design, performance can also be done very well. However, the products designed in this way will have a high cost and cannot enter the market. This is also the root cause of the slower technical advancement of electronic neon lights. Therefore, it is necessary to carry out the design under the condition that the cost is low and the performance is good, and the difficulty is great.
3.1 Designed with a transformer as the center
When designing a switching power supply, it is generally designed with a circuit as the center, and then the switching transformer is required to satisfy the performance of the circuit. If this design method is adopted, it is difficult to meet the requirements of an electronic neon transformer. For this reason, it is necessary to design the transformer as the center, because only the transformer with high leakage resistance can satisfy the working characteristics of the neon lamp, and the circuit is in an auxiliary position to meet the leakage reactance requirement of the transformer.
3.2 Best leakage design
When designing the switching power supply, it is desirable that the leakage inductance of the switching transformer is not too large, so as to prevent the switching voltage from being damaged by the spike voltage generated by the leakage inductance. However, from the load characteristics of the electronic neon transformer, it is known that an optimum leakage inductance is required at the optimum lamp operating current. This leakage inductance is much larger than the leakage inductance of a general switching power supply transformer because its number of turns is thousands of turns, and the leakage inductance is proportional to the square of the number of turns.
When designing an electronic neon transformer, first determine the magnetic flux leakage structure of the winding, and then select the appropriate core according to the power, but should be appropriately increased (the calculation method is the same as the switching transformer). Then, according to the output voltage of the transformer and the working voltage of the lamp and the switching frequency, the leakage reactance is determined, and finally the leakage inductance is calculated (the calculated leakage inductance value is inaccurate and needs to be corrected by experiment). At the same time, the circuit is determined as needed.
3.3 circuit selection principle
Various single-ended and double-ended switching power supply types without power frequency transformers can be used as switching power supplies for electronic neon transformers. However, it must meet the requirements of low cost and good performance. Therefore, under the premise of meeting the performance requirements, the circuit must be simple and the components must be small.
From the perspective of the working characteristics of electronic neon transformers (such as high peak voltage), it is generally appropriate to use a half bridge type.
3.4 Insulation of the safe working area of ​​the switch tube and the high voltage winding of the transformer
Because the electronic neon transformer has a large leakage inductance and its peak voltage is >1000V, it is necessary to consider the selection of the switching tube blocking voltage and the calculation of the snubber circuit to make the switching tube work in the safe area.
The no-load voltage at the output of the electronic neon transformer is as high as ten kV. Therefore, it is necessary to pay attention to the insulation design between the high and low voltage windings and the ground. The ideal insulation structure is made of epoxy resin filled winding, and the thickness of the filling should not be less than 3mm.
The above two design links are the guarantee for improving product reliability and the key point in the product quality assurance system.
3.5 Ways to improve brightness
Low brightness is a problem in most electronic neon transformers and one of the obstacles to promotion. Consider starting with two aspects of design.
(1) Increase the output power. The output power of the inductive neon transformer is about 250W. Due to the high frequency, the electronic neon transformer can be considered to increase to 130-180W (the lower frequency power can be larger, the higher frequency can be smaller).
(2) Increase the switching frequency. The switching frequency can be designed to be 20 to 80 kHz.
After improving from the above two aspects, it is estimated that the brightness can be increased from 800 to 1100 lumens to 1500 lumens or even higher.
4 Conclusion
This paper proposes the design of electronic neon transformers from five aspects. There are experiences and lessons, as well as design strategies, which are not necessarily correct. Please criticize and correct. There are still many in-depth research work in the future, such as: increasing the frequency can improve the principle of brightness, using computer simulation to theoretically improve the design level, how to increase the length of the electronic neon transformer lighting tube (currently domestic 12m), How to further promote the use of etc.
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