Power adapter arc characteristics

　　This article will discuss the arc characteristics in the gas of the power adapter in a further step. Although this is not necessarily necessary, it is of great reference value for certain decisions made by an engineer designing Korean power adapter ballasts at certain times. The intensive research on the electrical conductivity of gases began in the 19th century. This has also led to people's in-depth understanding of the properties and essence of electrons, as well as a preliminary understanding of the atomic structure and the use of X-rays in medical diagnosis.

　　Paschen studied the relationship between the DC breakdown voltage and the gas pressure between a pair of electrodes in the air in 1889. The diameter of the spherical electrode he used is much larger than the distance between the two electrodes, which avoids the generation of high voltage gradients near the tip or edge. His conclusion, the famous Paschen curve, is shown in Figure 16.6. When the two electrodes are separated by 0.3~0.5cm, the breakdown voltage is close to 1000V under one atmosphere. As the air pressure drops, the breakdown voltage will continue to drop to the lowest point around 300V, and then rise rapidly. Other gases also exhibit the same characteristics, except that the critical pressure at the lowest breakdown voltage point is different.

　　Paschen's law provides an experimental explanation for the phenomenon mentioned above, namely impact ionization. At high pressures, the average distance between atoms (ie, the mean free path) is very small. In this way, when an electron or positive ion is accelerated by the electric field to a speed large enough to ionize a neutral atom, it will collide with other atoms. As the gas pressure drops, the mean free path will increase, and electrons or positive ions will accelerate through a longer distance before colliding, thereby accumulating sufficient speed. In the final collision, they have enough energy to ionize the atoms, which creates an avalanche effect of carriers, which triggers an electric arc.

　　Arc characteristics of 12V charger under DC voltage

　　As early as the end of the 19th century, physicists studied the visible light characteristics of electrode arc discharge under DC voltage. In their early experiments, cold-emitting solid electrodes were placed on both ends of a glass tube, and then a high voltage of several hundred volts was applied to both ends of the electrodes through a current-limiting resistor.

　　When the air pressure inside the tube dropped to a low enough level, they observed the bright and dark areas extending from the cathode to the anode, as shown in the picture. Starting near the cathode, you can first see a small light-emitting area CG, followed by a long dark isolation area CDS, then a longer light-emitting area NG, and then a dark area FDS of equal length. After that, near the anode is a light strip PC of alternating light and dark. These areas are named in order the cathode light area (CG), Crookes dark area (CDS), negative light area (NG), Faraday dark area (FDS), and positive arc column area (PC).

　　The above phenomenon can be explained as follows.

　　As the pressure drops to near the lowest point on the Paschen curve, stray free electrons (they are generated by the cosmic rays or the high voltage gradient of the cathode) are accelerated to gain enough energy to ionize the neutral gas atoms . The positive ions thus ionized, due to their large mass, do not move very quickly and will not move away from the cathode. Therefore, a positive charge area is established here and a high voltage gradient is formed near the cathode. This voltage gradient, now called the cathode voltage drop, will accelerate the positive ions to hit the cathode, causing the cathode to emit some electrons.

　　When the neutral or ionized mercury atoms near the cathode are bombarded by electrons with sufficient energy, some of the electrons in their atoms will absorb the energy and jump to higher energy orbitals. When these electrons transition back to their original orbits again, they will emit visible light in the CG region.

　　At the outer edge of the CG zone, all the power adapter electrons exhaust their energy on the way to the anode, so that the speed drops, so they do not have enough energy to excite the neutral atoms to a higher energy state. After passing through the CDs zone, these electrons are accelerated again. At the edge of the NG zone, they regain the energy that can excite the neutral atoms to a higher energy state. When passing through the NG zone, the electrons in the excited neutral atoms It returns to the original orbit again, and it emits visible light in the NG area. When the free electrons pass through the FDS zone, they can no longer excite the neutral atoms to a higher energy state because they have exhausted their energy, thus forming a dark zone.

　　At the beginning of the PC area, there is another bright area. Then in the entire P area, dark and light alternately appear. The dark area is the electron acceleration segment, and the light area is the area where electrons have enough energy to excite atoms to emit visible light. Most of the voltage applied to the electrode mainly falls on this section, whose length accounts for 80% to 90% of the total length of the lamp.

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