第2个回答 2009-06-14
Two-way design and application of silicon-controlled analytical studies
Abstract: Analysis of a two-way thyristor design and parameters selection methods and at the same time introduced the method of bi-directional SCR installation.
Keywords: SCR; current rate of increase; thermal Silicone Grease
Introduction
In 1958, the General Electric Company from the United States successfully developed the first industrial SCR beginning of the transformation and control of electrical energy from the rotating unit converter, static converter ions into the semiconductor devices in power converter composed of the times. SCR sub-one-way and two-way thyristor SCR. SCR is generally used one-way flow of color, over-voltage protection circuit. TRIAC circuit generally used for the exchange regulator, such as lamp dimmers and automatic washing machines control the AC power.
Two-way thyristor SCR is based on the general evolved, it can replace not only two anti-parallel thyristor polarity, but only as a trigger circuit, is the exchange of more satisfactory switching devices, has been for the home appliance industry, the main power control device. In recent years, with the development of semiconductor technology, high-power bi-directional SCR emerging and widely used in the converter, frequency area, SCR technology has become more sophisticated applications. This article focused on the widely used two-way household electrical appliance industry, the design and application of SCR.
TRIAC characteristics
Bi-directional SCR can be regarded as a general anti-parallel connected SCR's integration with the general principle of the same one-way thyristor. Figure 1 The basic structure of a two-way thyristor and its equivalent circuit, it has two main electrodes T1 and T2, a gate G, the device gate electrode in the main direction can trigger both positive and negative conduction, Therefore, two-way thyristor in the first quadrant 1 and 3 have symmetrical volt-ampere characteristics. TRIAC gate plus positive and negative trigger pulse can trigger the conduction tube so that, it means there are four types of trigger.
Figure 1 a two-way thyristor structure and equivalent circuit
Application of bi-directional Thyristor
TRIAC for normal use, the need to master the main quantitative parameters of a two-way selection of SCR and to take appropriate measures in order to achieve the requirements of each parameter.
Voltage level of choice: usually VDRM (repeat peak off-state voltage) and VRRM (repetition peak reverse voltage) the smaller the value of S for the rated voltage of the device. Selected, the rated voltage should be the peak for the normal working voltage of 2 to 3 times, as to allow the operation of over-voltage margin.
Determination of current: As the bi-directional SCR circuit is usually used in the exchange, so no need to use the RMS to the average that it's rated current value. SCR过载能力as a result of the electromagnetic devices than the average small household electrical appliances in general and therefore choose the current value of thyristor current actual value of 2 ~ 3 times. At the same time, under SCR repeat peak off-state voltage VDRM and peak reverse voltage VRRM repeat of the peak current when the device should be less than the provisions of IDRM and IRRM.
State (peak) voltage VTM option: it is to provide a multiple pass thyristor rated current at the time of the peak transient voltage drop. SCR to reduce heat loss, as far as possible to choose smaller SCR VTM.
To maintain the current: IH is to maintain the SCR necessary to maintain the state of the minimum principal current, it is related to junction temperature, the higher the junction temperature, the smaller the IH.
The rate of increase in resistance to voltage: dv / dt refers to the state in the turn-off voltage rise slope, which is triggered to prevent the misuse of a key parameter. Exceeded this value may lead to misleading SCR's phenomenon appeared. SCR of the manufacturing process as a result of the decision of the A2 and G exists between the parasitic capacitance, as shown in Figure 2. We know that dv / dt of the change in capacitance will be equivalent at both ends of the current, this current will become Ig, that is, a trigger current, leading to false trigger.
Figure 2 Schematic diagram of two-way thyristor equivalent
The rate of increase in switching voltage dVCOM / dt. Drive high electrical resistance of the load, the load voltage and current waveform usually occurs between the substantive phase shift. When the load current zero-off switch TRIAC occurred, as the phase voltage is not zero. TRIAC when the voltage to be blocked immediately. Resulting increase in the rate of switching voltage (dVCOM / dt) in excess of allowable value will be forced to return two-way thyristor conduction, because carriers did not have sufficient time to withdraw from the end, as shown in Figure 3.
Figure 3 when the switch current and voltage changes
High dVCOM / dt by the bearing capacity of two conditions:
dICOM/dt- switching load current rate of decline. dICOM / dt high dVCOM / dt drop in affordability.
The higher surface temperature Tj node, dVCOM / dt decreased ability to bear. If the two-way thyristor dVCOM / dt of the allowable value may be over, so as to avoid false triggering, T1 and T2 in the RC snubber circuit between the device in order to limit the voltage rise rate. 47 ~ 100Ω usually selected can withstand the surge current of the carbon film resistors, 0.01μF ~ 0.47μF capacitor, the process of turn-off thyristor main current zero reverse rapidly after the restoration of the reverse peak to zero current, this process can be generated at both ends of the components of the normal work of 5-6 times the peak voltage of the peak voltage. General recommendations as close as possible components in their own local loop access to the RC absorption.
Disconnect voltage rate of change of state dvD / dt. If two-way cut-off thyristor (or gate thyratron sensitive) the role of a very high rate of voltage change, in spite of not more than VDRM, internal capacitive current can produce a sufficiently large gate current, and trigger on-pieces. Gate with temperature and increased sensitivity. If this problem occurs, T1 and T2 (or between the anode and cathode) should be added to the RC snubber circuit to limit the dvD / dt.
Increase in the rate of current inhibition: the impact of current rate of increase reflected primarily in the following two aspects:
① dIT / dt (at the time of turn-on current rate of increase) - When the bi-directional SCR or thyratron trigger the next gate conduction current, gate turn-on near the Department immediately, and then the rapid expansion of the effective area to the whole. This late time after there is a limit, that is, the rate of increase in load current value of the license. High dIT / dt may lead to partial burning, and short T1-T2. If the restrictions on the process of dIT / dt to a lower value, may be able to survive a two-way thyristor. Thus, if two-way thyristor VDRM in the serious, abnormal course of the instantaneous power may be in excess of or at the time of conduction dIT / dt may be exceeded, the load on the series in a few unsaturated μH (hollow) inductance.
② dICOM / dt (the rate of change of switching current) - lead to high dICOM / dt values are: high-load current, high frequency power system (assuming the current sine wave) or non-sinusoidal load current, which caused the rate of change of switching current in excess of the largest allowable values, so that even can not support two-way thyristor 50Hz waveform to rise from zero small dV / dt, by adding a few mH inductor and load in series, can restrict dICOM / dt.
To address the high dv / dt and di / dt caused by the problem, you can also use two-way Hi-Com triac, it and the traditional two-way thyristor differentiated internal structure. One difference between the two internal "thyratron" better separated, reducing the impact of each other. This brings the following benefits:
① high dVCOM / dt. Electrical resistance of the load can be controlled, in many occasions do not need a buffer circuit to ensure trouble-free switch. This reduces the component count, size and cost backplanes, but also eliminates the power dissipation of snubber circuit.
② high dICOM / dt. Switching high-frequency current or non-sinusoidal current performance has been greatly improved, without the need for the series inductance in the load to limit the dICOM / dt.
③ high dvD / dt (off state voltage change rate). TRIAC is more sensitive at high temperatures. High temperature, in a closed state, it is easy because of high dV / dt of the turn-on trigger false. Two-way Hi-Com triac to reduce this trend. Which can be used in high-temperature electrical appliances, control resistive loads, such as the kitchen and heating appliances, the traditional bi-directional SCR can not be used.
The choice of gate parameters:
Gate Trigger Current - In order to make reliable SCR trigger, trigger current Igt choose max value of 25 degrees at times of the α, α for the gate trigger current - characteristics of junction temperature coefficient, manual inspection of data available, from the lowest curve of work temperature coefficient. If the ambient temperature of the device without special needs, usually 1.5 times greater than α can take.
Drop gate - can choose Vgt 25 degrees of β times the max value. β for the gate trigger voltage - characteristics of junction temperature coefficient, manual inspection of data available, from the lowest curve of the temperature coefficient of work. If the ambient temperature of the device without special needs, usually β-fold from 1.2 to 1.
Trigger resistance-Rg = (Vcc-Vgt) / Igt
Trigger pulse width - for the sake of thyratron conduction (or bi-directional SCR), in addition to gate current ≥ IGT, also to make the load current to achieve ≥ IL (live current engine), and may have to consider the minimum temperature. Therefore, it is desirable to under 25 degrees and reliable SCR trigger pulse width of 2 times higher than Tgw.
Full of electronic noise in the environment, if the interference voltage exceeds the trigger voltage VGT, and have sufficient gate current, false triggering can occur, resulting in a two-way thyristor switch. The first line of defense is to reduce the clutter near space. Gate wiring as short as possible and to ensure that the gate drive circuit to return to the common line to connect directly to TI-pin (on the cathode thyratron). If the gate is hard-wired connection, to be used in two-spiral, or simply to use shielded wire, these measures are necessary in order to reduce the absorption of clutter. To increase the resistance of electronic noise can be between gate and T1 string into 1kΩ or less resistance, thereby reducing the sensitivity of gate. If high-frequency bypass capacitor has been adopted, it is proposed that the inter-gate capacitance and join the resistance, in order to reduce the gate capacitance through the peak current to reduce the two-way thyristor gate region may be destroyed over-current.
Tj Junction Temperature control: In order to long-term reliability should be sufficient to ensure low Rth ja maintain Tj does not exceed 80% Tjmax, the value corresponding to the highest possible ambient temperature.
The installation of bi-directional Thyristor
Small load, or current short duration (less than 1 second) bi-directional SCR can work in free space. However, the majority of cases, the need to install in the radiator or cooling of the stent, in order to reduce the thermal resistance between the thyristor and heat sink thermal conductivity to be coated with Silicone Grease.
TRIAC radiator fixed to the main three ways, namely by compression clamp, bolt and rivet fixed. Method before the installation of two kinds of tools are readily available. On many occasions, the rivet is not a recommended method, not introduced in this article.
Press-fit clip
This is the recommended method, the smallest thermal resistance. The plastic clip on the device to exert pressure. The same applies for non-insulation packages (SOT82 and SOT78) and insulation package (SOT186 F-pack and updated SOT186A X-pack). Note, SOT78 is TO220AB.
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双向可控硅的设计及应用分析研究
摘要：分析了双向可控硅的设计及参数选取方法，同时介绍了双向可控硅的安装方法。
关键词：可控硅；电流上升率；导热硅脂
引言
1958年，从美国通用电气公司研制成功第一个工业用可控硅开始，电能的变换和控制从旋转的变流机组、静止的离子变流器进入以电力半导体器件组成的变流器时代。可控硅分单向可控硅与双向可控硅。单向可控硅一般用于彩电的过流、过压保护电路。双向可控硅一般用于交流调节电路，如调光台灯及全自动洗衣机中的交流电源控制。
双向可控硅是在普通可控硅的基础上发展而成的，它不仅能代替两只反极性并联的可控硅，而且仅需一个触发电路，是目前比较理想的交流开关器件，一直为家电行业中主要的功率控制器件。近几年，随着半导体技术的发展，大功率双向可控硅不断涌现，并广泛应用在变流、变频领域，可控硅应用技术日益成熟。本文主要探讨广泛应用于家电行业的双向可控硅的设计及应用。
双向可控硅特点
双向可控硅可被认为是一对反并联连接的普通可控硅的集成，工作原理与普通单向可控硅相同。图1为双向可控硅的基本结构及其等效电路，它有两个主电极T1和T2，一个门极G，门极使器件在主电极的正反两个方向均可触发导通，所以双向可控硅在第1和第3象限有对称的伏安特性。双向可控硅门极加正、负触发脉冲都能使管子触发导通，因此有四种触发方式。
图1 双向可控硅结构及等效电路
双向可控硅应用
为正常使用双向可控硅，需定量掌握其主要参数，对双向可控硅进行适当选用并采取相应措施以达到各参数的要求。
·耐压级别的选择：通常把VDRM（断态重复峰值电压）和VRRM（反向重复峰值电压）中较小的值标作该器件的额定电压。选用时，额定电压应为正常工作峰值电压的2~3倍，作为允许的操作过电压裕量。
·电流的确定：由于双向可控硅通常用在交流电路中，因此不用平均值而用有效值来表示它的额定电流值。由于可控硅的过载能力比一般电磁器件小，因而一般家电中选用可控硅的电流值为实际工作电流值的2~3倍。同时，可控硅承受断态重复峰值电压VDRM和反向重复峰值电压VRRM时的峰值电流应小于器件规定的IDRM和IRRM。
·通态（峰值）电压VTM的选择：它是可控硅通以规定倍数额定电流时的瞬态峰值压降。为减少可控硅的热损耗，应尽可能选择VTM小的可控硅。
·维持电流：IH是维持可控硅维持通态所必需的最小主电流，它与结温有关，结温越高，则IH越小。
·电压上升率的抵制：dv/dt指的是在关断状态下电压的上升斜率，这是防止误触发的一个关键参数。此值超限将可能导致可控硅出现误导通的现象。由于可控硅的制造工艺决定了A2与G之间会存在寄生电容，如图2所示。我们知道dv/dt的变化在电容的两端会出现等效电流，这个电流就会成为Ig，也就是出现了触发电流，导致误触发。
图2 双向可控硅等效示意图
切换电压上升率dVCOM/dt。驱动高电抗性的负载时，负载电压和电流的波形间通常发生实质性的相位移动。当负载电流过零时双向可控硅发生切换，由于相位差电压并不为零。这时双向可控硅须立即阻断该电压。产生的切换电压上升率（dVCOM/dt）若超过允许值，会迫使双向可控硅回复导通状态，因为载流子没有充分的时间自结上撤出，如图3所示。
图3 切换时的电流及电压变化
高dVCOM/dt承受能力受二个条件影响：
dICOM/dt—切换时负载电流下降率。dICOM/dt高，则dVCOM/dt承受能力下降。
结面温度Tj越高，dVCOM/dt承受能力越下降。假如双向可控硅的 dVCOM/dt的允许值有可能被超过，为避免发生假触发，可在T1 和T2 间装置RC缓冲电路，以此限制电压上升率。通常选用47~100Ω的能承受浪涌电流的碳膜电阻，0.01μF~0.47μF的电容，晶闸管关断过程中主电 流过零反向后迅速由反向峰值恢复至零电流，此过程可在元件两端产生达正常工作峰值电压5-6倍的尖峰电压。一般建议在尽可能靠近元件本身的地方接上阻容吸 收回路。
断开状态下电压变化率dvD/dt。若截止的双向可控硅上（或门极灵敏的闸流管）作用很高的电压变化率，尽管不超过VDRM，电容性内部电流能产生足够大的门极电流，并触发器件导通。门极灵敏度随温度而升高。假如发生这样的问题，T1 和T2 间（或阳极和阴极间）应该加上RC 缓冲电路，以限制dvD/dt。
·电流上升率的抑制：电流上升率的影响主要表现在以下两个方面：
①dIT/dt（导通时的电流上升率）—当双向可控硅或闸流管在门极电流触发下导通，门极临近处立即导通，然后迅速扩展至整个有效面积。这迟后的时间有一个极限，即负载电流上升率的许可值。过高的dIT/dt可能导致局部烧毁，并使T1-T2 短路。假如过程中限制dIT/dt到一较低的值，双向可控硅可能可以幸存。因此，假如双向可控硅的VDRM在严重的、异常的电源瞬间过程中有可能被超出或导通时的dIT/dt有可能被超出，可在负载上串联一个几μH的不饱和（空心）电感。
②dICOM/dt (切换电流变化率) —导致高dICOM/dt值的因素是:高负载电流、高电网频率（假设正弦波电流）或者非正弦波负载电流,它们引起的切换电流变化率超出最大的允许值，使双向可控硅甚至不能支持50Hz 波形由零上升时不大的dV/dt，加入一几mH的电感和负载串联，可以限制dICOM/dt。
·为了解决高dv/dt及di/dt引起的问题，还可以使用Hi-Com 双向可控硅，它和传统的双向可控硅的内部结构有差别。差别之一是内部的二个“闸流管”分隔得更好，减少了互相的影响。这带来下列好处：
①高dVCOM/dt。能控制电抗性负载，在很多场合下不需要缓冲电路，保证无故障切换。这降低了元器件数量、底板尺寸和成本，还免去了缓冲电路的功率耗散。
②高dICOM/dt。切换高频电流或非正弦波电流的性能大为改善，而不需要在负载上串联电感，以限制dICOM/dt。
③高dvD/dt（断开状态下电压变化率）。双向可控硅在高温下更为灵敏。高温下，处于截止状态时，容易因高dV/dt下的假触发而导通。Hi-Com双向可控硅减少了这种倾向。从而可以用在高温电器，控制电阻性负载，例如厨房和取暖电器，而传统的双向可控硅则不能用。
·门极参数的选用：
门极触发电流—为了使可控硅可靠触发，触发电流Igt选择25度时max值的α倍，α为门极触发电流—结温特性系数，查数据手册可得，取特性曲线中最低工作温度时的系数。若对器件工作环境温度无特殊需要，通常α取大于1.5倍即可。
门极压降—可以选择Vgt 25度时max值的β倍。β为门极触发电压—结温特性系数，查数据手册可得，取特性曲线中最低工作温度时的系数。若对器件工作环境温度无特殊需要，通常β取1~1.2倍即可。
触发电阻—Rg=（Vcc-Vgt）/Igt
触发脉冲宽度—为了导通闸流管（或双向可控硅），除了要门极电流≥IGT ，还要使负载电流达到≥IL（擎住电流），并按可能遇到的最低温度考虑。因此，可取25度下可靠触发可控硅的脉冲宽度Tgw的2倍以上。
在电子噪声充斥的环境中，若干扰电压超过触发电压VGT，并有足够的门极电流，就会发生假触发，导致双向可控硅切 换。第一条防线是降低临近空间的杂波。门极接线越短越好，并确保门极驱动电路的共用返回线直接连接到TI 管脚（对闸流管是阴极）。若门极接线是硬线，可采用螺旋双线，或干脆用屏蔽线，这些必要的措施都是为了降低杂波的吸收。为增加对电子噪声的抵抗力，可在门 极和T1 之间串入1kΩ或更小的电阻，以此降低门极的灵敏度。假如已采用高频旁路电容，建议在该电容和门极间加入电阻，以降低通过门极的电容电流的峰值，减少双向可控硅门极区域为过电流烧毁的可能。
·结温Tj的控制：为了长期可靠工作，应保证Rth j-a 足够低，维持Tj不高于80%Tjmax ,其值相应于可能的最高环境温度。
双向可控硅的安装
对负载小，或电流持续时间短（小于1 秒钟）的双向可控硅，可在自由空间工作。但大部分情况下，需要安装在散热器或散热的支架上，为了减小热阻，可控硅与散热器间要涂上导热硅脂。
双向可控硅固定到散热器的主要方法有三种，夹子压接、螺栓固定和铆接。前二种方法的安装工具很容易取得。很多场合下，铆接不是一种推荐的方法，本文不做介绍。
夹子压接
这是推荐的方法，热阻最小。夹子对器件的塑封施加压力。这同样适用于非绝缘封装（SOT82 和SOT78 ） 和绝缘封装（ SOT186 F-pack 和更新的SOT186A X-pack）。注意，SOT78 就是TO220AB。本回答被提问者采纳