裕兴新概念英语第二册
An overview of the thyristor
enabled是什么意思
一、 the introduction of the thyristor
Crystal thyratron referred to as thyristors, also known as silicon controlled rectifier elements (SCR) by the three PN structure into a high-power miconductor devices. In performance, the thyristor is not only with unidirectional conductivity, but also more valuable than the silicon rectifier elements controllability, it only turns on and off two states.Thyristor has many advantages, such as: low-power control of high-power, power magnification of up to dozens of times; fast respon, opening within microconds, the shutdown; non-contact operation, no spark, no noi; high efficiency and low cost. Therefore, especially in high-power UPS system, the thyristor circuit of the rectifier circuit, the static bypass switch, contact output switches, etc. has been widely ud.The thyristor weakness: static and dynamic overload less susceptible to interference and misleading pass.Thyristor from the shape classification are: bolt-shaped, tablet-shaped-shaped end of the peace.
二、The structure and working principle of the ordinary thyristor
Thyristors PNPN four-story three-terminal devices, there are three PN junction. Analysis theory, can it be en as compod by a PNP and NPN transistors, the equivalent diagram in Figure 1 (a) as shown in Figure 1 (b) thyristor circuit symbols.
Figure 1 thyristor equivalent diagram in Figure
1. The work process of the thyristor
The thyristor is a four-story three-terminal devices, J1, J2, J3 three PN junction, it can be the middle of the NP is divided into two parts, constitute a PNP-type transistor and an NPN type transistor composite pipe.
When the thyristor to withstand a positive anode voltage, the thyristor must be made to withstand the rever voltage of PN junction J2 loss of blocking. The collector current of each transistor is another transistor ba current. Thus, two composite transistor circuit, when sufficient gate current Ig flows will form a strong positive feedback, resulting in saturation of the two transistor conduction.
homework什么意思Set the PNP and the NPN collector current IC1 and IC2, the emitter current of the corresponding Ia and Ik, the current amplification factor corresponding α1 = IC1/Ia α2 = IC2/Ik, to t flow through the J2 junction of invertingthe leakage current of the ICO, the thyristor anode current equal to the sum of the two collector current and the leakage current:
Ia=IC1+IC2+ICO
=α1Ia+α2Ik+ICO (1)
If the gate current Ig, the thyristor cathode current: Ik=Ia+Ig。
Therefore, the thyristor anode current can be drawn as follows:lastminute
(2)
Silicon PNP transistor and silicon NPN emitter current changes in the corresponding current amplification factor α1 and α2 with its rather dramatic changes. When the thyristor to withstand a positive anode voltage, the gate did not receive the voltage ca, equation (1) of Ig = 0, (α1 + α2) is very small, so the thyristor anode current Ia ≈ the ICO, the thyristor tube in the forward blocking state; when the positive gate voltage from the thyristor gate G flowing into the current of Ig large enough Ig flows through the NPN emitter junction, thereby increasing the amplification factor of α2, resulting in a large enough collector current IC2 flowing through the emitter-ba junction of PNP and the PNP transistor current amplification factor α1, resulting in a larger collector current IC1 through the NPN emitter junction, so that the strong positive feedback process is quick. Α1 and α2 with the emitter current increa makes the (α1 + α2) ≈ 1, equation (1) in the denominator of 1 - (α1 + α2) ≈ 0, thus increasing the thyristor anode current Ia. At this time, the current flowing through the thyristor is completely decided by the main circuit vol
南京新东方少儿英语tage and loop resistance, the thyristor in the forward pass state. Thyristor, (1), 1 - (α1 + α2) ≈ 0, the gate current Ig = 0, thyristor can still maintain the anode current Ia conduction, the gate has been lost. Thyristor constantly reduce the supply voltage or increasing the loop resistance, so that the anode current Ia is reduced to maintain current IH below, due to the rapid decline of α1 and α2, the thyristor recovery to the blocking state.
2. Working conditions of the thyristor
Thyristor only turn on and off the two working conditions, it has the switching characteristics of this feature requires certain conditions to conversion, (1) thyristor withstand rever anode voltage, regardless of the gate under whatvoltage thyristors are in off state. (2) thyristor to withstand a positive anode voltage, the only gate under forward voltage conditions thyristor only conduction. (3) of the transistor in the ca of conduction, as long as the positive anode voltage, regardless of the gate voltage is how thyristors remain conduction, the thyristor gate lost (4) crystal thyristor conduction ca, when the main circuit voltage (or current) is reduced to clo to zero, the thyristor turn-off.英语在线翻译
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三、Volt-ampere characteristics and main parameters of the thyristor
1. Volt-ampere characteristic of the thyristor
mentally
Called thyristor volt-ampere characteristic relationship between the voltage and the thyristor anode current in the thyristor anode A and cathode K, as shown in Figure 2 as shown. Positive features in the first quadrant, the rever features in the third quadrant.
兴奋用英语怎么说Figure 2 thyristor volt-ampere characteristic parameters schematic
（1） Rever characteristics
Gate G open anode coupled with a rever voltage (e Figure 3), the J2 junction is b
iad, but the J1, J2 junction rever biad. Can only flow through a small rever saturation current when the voltage was further incread to the J1 junction avalanche breakdown voltage, the J3 junction breakdown, the current rapid increa, as shown in Figure 2, curve OR gment began to bend, bend the voltage the URO called "rever breakover voltage. Since then, the thyristor will be the permanent rever breakdown.
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