可控硅（ thyristor）

“晶闸管”的各地常用别名中国大陆可控硅港台矽控整流器

 单向晶闸管SCR的电路符号

 一枚装载散热器上的SCR， 耐压1200V最大电流100A， 小接线是用来做闸极触发控制

晶体闸流管（英语：Thyristor），简称晶闸管，指的是具有四层交错P、N层的半导体装置。最早出现与主要的一种是硅控整流器（Silicon Controlled Rectifier，SCR），中国大陆通常简称可控硅，又称半导体控制整流器，是一种具有三个PN结的功率型半导体器件，为第一代半导体电力电子器件的代表。晶闸管的特点是具有可控的单向导电，即与一般的二极管相比，可以对导通电流进行控制。晶闸管具有以小电流（电压）控制大电流（电压）作用，并体积小、轻、功耗低、效率高、开关迅速等优点，广泛用于无触点开关、可控整流、逆变、调光、调压、调速等方面。

半导体的出现成为20世纪现代物理学其中一项最重大的突破，标志着电子技术的诞生。而由于不同领域的实际需要，促使半导体器件自此分别向两个分支快速发展，其中一个分支即是以集成电路为代表的微电子器件，特点为小功率、集成化，作为信息的检出、传送和处理的工具；而另一类就是电力电子器件，特点为大功率、快速化。1955年，美国通用电气公司发表了世界上第一个以硅单晶为半导体整流材料的硅整流器（SR），1957年又发表了全球首个用于功率转换和控制的可控硅整流器（SCR）。由于它们具有体积小、重量轻、效率高、寿命长的优势，尤其是SCR能以微小的电流控制较大的功率，令半导体电力电子器件成功从弱电控制领域进入了强电控制领域、大功率控制领域。在整流器的应用上，晶闸管迅速取代了水银整流器（引燃管），实现整流器的固体化、静止化和无触点化，并获得巨大的节能效果。从1960年代开始，由普通晶闸管相继衍生出了快速晶闸管、光控晶闸管、不对称晶闸管及双向晶闸管等各种特性的晶闸管，形成一个庞大的晶闸管家族。

但晶闸管本身存在两个制约其继续发展的重要因素。一是控制功能上的欠缺，普通的晶闸管属于半控型器件，通过门极（控制极）只能控制其开通而不能控制其关断，导通后控制极即不再起作用，要关断必须切断电源，即令流过晶闸管的正向电流小于维持电流。由于晶闸管的关断不可控的特性，必须另外配以由电感、电容及辅助开关器件等组成的强迫换流电路，从而使装置体积增大，成本增加，而且系统更为复杂、可靠性降低。二是因为此类器件立足于分立元件结构，开通损耗大，工作频率难以提高，限制了其应用范围。1970年代末，随着可关断晶闸管（GTO）日趋成熟，成功克服了普通晶闸管的缺陷，标志着电力电子器件已经从半控型器件发展到全控型器件。

晶闸管一词有时单指SCR；有时泛指具有四层或以上交错P、N层的半导体装置，如单向晶闸管（SCR）、双向晶闸管（TRIAC）、可关断晶闸管（GTO）、SIT、及其他种类等。

单向晶闸管是PNPN四层结构，形成三个PN结，可以等效为PNP、NPN两晶体管组成的复合管，具有三个外电极：阳极A（Anode），阴极K（Cathode）和控制极G（Gate）。在A、K之间加上正电压后，管子并不导通；当控制极G加上正电压（相对于阴极K而言）后才导通；此时再去掉控制极的电压，管子依然能够保持导通。

双向晶闸管可以等效为两个单向晶闸管反向并联。因双向晶闸管正负双向均可以控制导通，故控制极G外的另外两个电极不再称阴极阳极，而改称为主电极MT1、MT2或T1、T2。当G与MT1间给予适当的讯号时，MT2与MT1间即可导通。

“晶闸管”的各地常用别名中国大陆晶闸管、晶体闸流管港台闸流体、闸流器

A thyristor is a solid-state semiconductor device with four layers of alternating P- and N-type materials. It acts exclusively as a bistable switch, conducting when the gate receives a current trigger, and continuing to conduct until the voltage across the device is reversed biased, or until the voltage is removed (by some other means). A three-lead thyristor is designed to control the larger current of the Anode to Cathode path by controlling that current with the smaller current of its other lead, known as its Gate. In contrast, a two-lead thyristor is designed to switch on if the potential difference between its leads is sufficiently large (breakdown voltage).

Some sources define silicon-controlled rectifier (SCR) and thyristor as synonymous.[1] Other sources define thyristors as more ornately constructed devices that incorporate at least four layers of alternating N-type and P-type substrate.

The first thyristor devices were released commercially in 1956. Because thyristors can control a relatively large amount of power and voltage with a small device, they find wide application in control of electric power, ranging from light dimmers and electric motor speed control to high-voltage direct-current power transmission. Thyristors may be used in power-switching circuits, relay-replacement circuits, inverter circuits, oscillator circuits, level-detector circuits, chopper circuits, light-dimming circuits, low-cost timer circuits, logic circuits, speed-control circuits, phase-control circuits, etc. Originally, thyristors relied only on current reversal to turn them off, making them difficult to apply for direct current; newer device types can be turned on and off through the control gate signal. The latter is known as a gate turn-off thyristor, or GTO thyristor. A thyristor is not a proportional device like a transistor. In other words, a thyristor can only be fully on or off, while a transistor can lie in between on and off states. This makes a thyristor unsuitable as an analog amplifier, but useful as a switch.

晶闸管

晶闸管类型被动第一次生产1956年引脚配置阳极，栅极和阴极电子符号

甲晶闸管是一个固态 半导体器件具有交替的四层P-和N型材料。它专门用作双稳态开关，在栅极接收电流触发时导通，并继续导通，直到器件两端的电压反向偏置，或直到电压被移除（通过其他方式）。三引线晶闸管设计用于控制阳极到阴极路径的较大电流，方法是通过其另一个引线（称为栅极）的较小电流来控制该电流。相比之下，双引线晶闸管设计为在其引线之间的电位差足够大（击穿电压）时接通。

一些消息来源将可控硅整流器（SCR）和晶闸管定义为同义词。[1]其他来源将晶闸管定义为更加华丽的器件，其中包含至少四层交替的N型和P型衬底。

第一批晶闸管器件于1956年在商业上发布。由于晶闸管可以通过小型器件控制相对较大的功率和电压，因此它们在电力控制方面得到广泛应用，从调光器和电动机速度控制到高压直流电力传输。晶闸管可用于功率开关电路，继电器替换电路，逆变器电路，振荡器电路，电平检测器电路，斩波电路，调光电路，低成本定时器电路，逻辑电路，速度控制电路，相位 - 最初，晶闸管仅依靠电流反转将它们关闭，使得它们难以应用于直流电流; 可以通过控制门信号打开和关闭较新的设备类型。后者被称为门关断晶闸管或GTO晶闸管。晶闸管不是像晶体管那样的比例器件。换句话说，晶闸管只能完全接通或断开，而晶体管可处于接通和断开状态之间。这使得晶闸管不适合作为模拟放大器，但可用作开关。

1简介

1.1门终端的功能

1.2开关特性

2历史

2.1词源

3申请

3.1缓冲电路

3.2高压直流输电

4与其他设备的比较

5故障模式

6碳化硅晶闸管

7种类型

7.1反向导通晶闸管

7.2光电晶体管

8另见

9参考文献

10个来源

11外部链接

晶闸管是四层三端子半导体器件，每层由交替的N型或P型材料组成，例如PNPN。标记为阳极和阴极的主端子跨越所有四层。称为栅极的控制端子连接到阴极附近的p型材料。（称为SCS-硅控制开关的变体 - 将所有四层引出到端子。）晶闸管的操作可以通过一对紧密耦合的双极结晶体管来理解，其被布置成引起自锁闭动作：

物理和电子层面的结构，以及晶闸管符号。

晶闸管有三种状态：

反向阻断模式 - 电压施加在可被二极管阻挡的方向上

正向阻断模式 - 在导致二极管导通的方向上施加电压，但晶闸管未被触发导通

正向导通模式 - 晶闸管已触发导通并将保持导通，直到正向电流降至低于称为“保持电流”的阈值

晶闸管具有三个pn结（从阳极连续地命名为J 1，J 2，J 3）。

晶闸管的层图。

当阳极相对于阴极处于正电位V AK而栅极没有施加电压时，结J 1和J 3正向偏置，而结J 2反向偏置。当J 2反向偏置时，不发生传导（关闭状态）。现在，如果V AK增加到超过晶闸管的击穿电压V BO，则发生 J 2的雪崩击穿并且晶闸管开始导通（导通状态）。

如果在栅极端子处相对于阴极施加正电位V G，则结J 2的击穿发生在较低的V AK值处。通过选择适当的V G值，晶闸管可以快速切换到导通状态。

一旦发生雪崩击穿，晶闸管继续导通，无论栅极电压如何，直到：（a）电位V AK被移除或（b）通过器件的电流（阳极 - 阴极）变得小于指定的保持电流由制造商。因此，V G可以是电压脉冲，例如从UJT 张弛振荡器输出的电压。

栅极脉冲的特征在于栅极触发电压（V GT）和栅极触发电流（I GT）。栅极触发电流与栅极脉冲宽度成反比，这样很明显触发晶闸管所需的栅极电荷最小。

V - 我的特点。

在传统的晶闸管中，一旦通过栅极端子接通，器件保持锁定在导通状态（即，不需要连续供应栅极电流以保持导通状态），只要超过阳极电流锁存电流（I L）。只要阳极保持正偏压，就不能在阳极电流低于保持电流（I H）之前将其关闭。在正常工作状态下，锁存电流总是大于保持电流。在上图中我大号 具有落入上述我ħ由于在y轴我大号 > 我ħ。

如果外部电路导致阳极变为负偏压（称为自然或线路，换向的方法），则可以关闭晶闸管。在一些应用中，这通过切换第二晶闸管以将电容器放电到第一晶闸管的阴极来完成。此方法称为强制换向。

在晶闸管中的电流熄灭之后，必须经过有限的时间延迟才能使阳极再次正偏置并将晶闸管保持在断开状态。该最小延迟称为电路换向关断时间（t Q）。在此时间内试图使阳极正偏置导致晶闸管由尚未重新组合的剩余电荷载流子（空穴和电子）自触发。

对于频率高于国内交流电源（例如50 Hz或60 Hz）的应用，需要具有较低t Q值的晶闸管。这种快速晶闸管可以通过将作为电荷组合中心的重金属 离子（例如金或铂）扩散到硅中来制造。今天，快速晶闸管通常通过硅的电子或质子 辐射或通过离子注入制成。照射比重金属掺杂更通用，因为它允许以精细步骤调节剂量，即使在硅处理的相当晚的阶段也是如此。

1950年由William Shockley提出并由贝尔实验室的Moll和其他人提倡的可控硅整流器（SCR）或晶闸管由通用电气（GE）的电力工程师于1956年开发，由Gordon Hall领导并由GE的Frank W.商业化。比尔“Gutzwiller。

一组六个2000 A晶闸管（白色磁盘在顶部排成一排，可见边缘）

早期的一种称为闸流管的充气管装置提供了类似的电子开关能力，其中小的控制电压可以切换大电流。从“闸流管”和“ 晶体管 ” 的组合可以得出术语“晶闸管”。[2]

控制AC电流的晶闸管电路中的波形。红色迹线：负载（输出）电压蓝色迹线：触发电压。

晶闸管主要用于涉及高电流和高电压的地方，通常用于控制交流电流，其中电流极性的变化导致设备自动关闭，称为“过零 ”操作。该设备可以说是同步运行的; 因此，一旦器件被触发，它就与在其阴极上施加的电压同相地传导电流到阳极结，而不需要进一步的栅极调制，即器件完全偏置。这不应与不对称操作相混淆，因为输出是单向的，仅从阴极流向阳极，因此本质上是不对称的。

晶闸管可用作相角触发控制器的控制元件，也称为相位控制器。

它们也可以在数字电路的电源中找到，它们被用作一种“增强型断路器 ”，以防止电源故障损坏下游组件。晶闸管与连接到其栅极的齐纳二极管一起使用，如果电源的输出电压上升到齐纳电压以上，则晶闸管将导通并短路电源输出到地（通常还会使上游跳闸）断路器或保险丝）。这种保护电路称为撬棍并且具有优于标准断路器或保险丝的优点，因为它为损坏的供电电压创建了高导电通路，并且可能为被供电的系统中的存储能量创建。

晶闸管的第一次大规模应用，以及相关触发DIAC，在消费类产品与颜色相关的内部稳压电源电视台在70年代初期的接收器。[ 需要说明 ] 接收器的稳定高压直流电源是通过将晶闸管装置的开关点上下移动到交流电源输入正向上半部分的下降斜率来获得的（如果上升斜率用于输出电压）当器件被触发时，它总会上升到峰值输入电压，从而无法达到调节的目的。精确的开关点由直流输出电源的负载以及交流输入波动决定。

几十年来，晶闸管一直被用作电视，电影和影院中的调光器，它们取代了自耦变压器和变阻器等劣质技术。它们也被用于摄影作为闪光灯（闪光灯）的关键部分。

晶闸管可以通过高上升速率的断态电压触发。通过在阳极和阴极之间连接电阻 - 电容（RC）缓冲电路来限制dV / dt（即电压随时间变化的速率）可以防止这种情况。

阀厅含有晶闸管阀用于从电源的远距离传输栈马尼托巴水电水坝

由于现代晶闸管可以在兆瓦级别上切换功率，因此晶闸管阀已成为高压直流（HVDC）转换为交流电或来自交流电的核心。在这种和其他超高功率应用领域，电触发（ETT）和光触发（LTT）晶闸管[3] [4]仍然是主要选择。阀门布置成堆叠，通常悬挂在称为阀门大厅的传输建筑物的天花板上。晶闸管布置在二极管桥电路中并且减少谐波串联连接以形成12脉冲转换器。每个晶闸管用去离子水冷却并且整个装置成为多个相同模块中的一个，在称为四重阀的多层阀组中形成一层。三个这样的堆叠通常安装在地板上或悬挂在长距离传输设施的阀门厅的天花板上。[5] [6]

晶闸管的功能缺点是，像二极管一样，它只在一个方向上传导。一种类似的自锁式5层器件，称为TRIAC，能够在两个方向上工作。但是，这种增加的能力也可能成为不足之处。由于TRIAC可以在两个方向上传导，因此无功负载可能导致其在AC电源周期的零电压瞬间无法关闭。因此，使用具有（例如）重感应电动机负载的TRIAC 通常需要在TRIAC周围使用“ 缓冲 ”电路，以确保它在每半个主电源周期时关闭。反向平行SCR也可用于代替三端双向可控硅开关; 因为该对中的每个SCR都具有施加于其上的整个半周期的反极性，所以与TRIAC不同，SCR肯定会关闭。然而，为这种安排支付的“价格”是两个独立但基本相同的选通电路增加的复杂性。

虽然晶闸管大量用于交流到直流的兆瓦级整流，但在低功率和中功率（从几十瓦到几十千瓦）的应用中，它们几乎被其他具有卓越开关特性的器件所取代，如功率MOSFET或IGBT。与SCR相关的一个主要问题是它们不是完全可控的开关。该GTO晶闸管和IGCT是相关于解决这个问题晶闸管两个设备。在高频应用中，由于双极传导引起的开关时间较长，晶闸管是不良的候选者。另一方面，MOSFET具有更快的开关能力，因为它们具有单极导电性（仅限于此多数载波携带电流）。

晶闸管制造商通常指定安全点火区域，其限定给定操作温度的可接受水平的电压和电流。该区域的边界部分地由不超过给定触发脉冲持续时间规定的最大允许栅极功率（P G）的要求确定。[7]

除了由于超过电压，电流或额定功率而导致的常见故障模式外，晶闸管还有其特定的故障模式，包括：

打开di / dt - 其中触发后导通电流的上升速率高于有源导通区域（SCR和三端双向可控硅）的扩展速度所支持的速率。

强制换向 - 其中瞬态峰值反向恢复电流在子阴极区域中引起如此高的电压降，使其超过栅极阴极二极管结的反向击穿电压（仅SCR）。

接通dv / dt - 如果阳极 - 阴极电压上升速率太大，晶闸管可以在没有触发器的情况下进行虚假发射。

近年来，一些制造商[8]开发了使用碳化硅（SiC）作为半导体材料的晶闸管。它们适用于高温环境，能够在高达350°C的温度下运行。

ACS

急性重症胆管炎

AGT - 阳极栅极晶闸管 - 在阳极附近的n型层上具有栅极的晶闸管

ASCR - 非对称SCR

BCT - 双向控制晶闸管 - 双向开关器件，包含两个带有独立栅极触点的晶闸管结构

BOD - 转换二极管 - 由雪崩电流触发的无门晶闸管

DIAC - 双向触发设备

Dynistor - 单向开关设备

Shockley二极管 - 单向触发和开关装置

SIDAC - 双向开关设备

Trisil，SIDACtor - 双向保护设备

BRT - 基极电阻控制晶闸管

ETO - 发射极关断晶闸管[9]

GTO - 栅极关断晶闸管

DB-GTO - 分布式缓冲栅极关断晶闸管

MA-GTO - 改进的阳极栅极关断晶闸管

IGCT - 集成门极换向晶闸管

点火器 - 用于点火器的火花发生器

LASCR - 光激活SCR，或LTT - 光触发晶闸管

LASS - 光激活半导体开关

MCT - MOSFET控制晶闸管 - 它包含两个额外的FET结构，用于开/关控制。

CSMT或MCS - MOS复合静电感应晶闸管

与栅型的n型层上邻近甲晶闸管用作功能替换为阳极- PUT或PUJT -可编程单结晶体管单结晶体管

RCT - 反向导通晶闸管

SCS - 可控硅开关或晶闸管四极管 - 具有阴极和阳极栅极的晶闸管

SCR - 可控硅整流器

SITh - 静电感应晶闸管，或FCTh - 场控晶闸管 - 包含可关闭阳极电流的栅极结构。

TRIAC - 交流电三极管 - 双向开关器件，包含两个具有共栅极接触的晶闸管结构

Quadrac - 特殊类型的晶闸管，将DIAC和TRIAC组合到一个封装中。

反向导通晶闸管（RCT）具有集成的反向二极管，因此不能反向阻断。在必须使用反向或续流二极管的情况下，这些装置是有利的。由于SCR和二极管不会同时导通，因此它们不会同时产生热量，并且可以很容易地集成和冷却在一起。反向导通晶闸管通常用于变频器和逆变器。

光激活SCR（LASCR）的电子符号

光电晶体管由光激活。光电晶体管的优点是它们对电信号不敏感，这可能导致电噪声环境中的错误操作。光触发晶闸管（LTT）在其栅极中具有光敏区域，电磁辐射（通常是红外线）通过光纤耦合到该光敏区域中。由于不需要在晶闸管的电位上提供电子板以触发它，因此光触发晶闸管在HVDC等高压应用中具有优势。。光触发晶闸管具有内置过压（VBO）保护功能，当晶闸管上的正向电压变得过高时触发晶闸管; 它们也采用内置的前向恢复保护，但不是商业化的。尽管它们可以为HVDC阀门的电子设备带来简化，但光触发晶闸管可能仍然需要一些简单的监控电子设备，并且只能从少数制造商处获得。

两种常见的光电晶体管包括光激活SCR（LASCR）和光激活TRIAC。LASCR充当开关，当暴露在光线下时会打开。在曝光后，当不存在光时，如果没有移除电源并且阴极和阳极的极性尚未反转，则LASCR仍处于“接通”状态。光激活的TRIAC类似于LASCR，除了它是为交流电设计的。

电子门户网站

闭锁

Quadrac

晶闸管驱动

阀门大厅

晶闸管

跳起来^ Christiansen，唐纳德; Alexander，Charles K.（2005）; 标准电气工程手册（第5版）。McGraw-Hill，ISBN 0-07-138421-9

跳过^ [1] 2012年9月5日归档，在Wayback Machine。

跳起来^ “第5.1章”。高压直流输电 - 经验证的电力交换技术 （PDF）。西门子。检索2013-08-04。

跳过^ “ETT与高压直流输电的LTT” （PDF）。ABB Asea Brown Boveri 。检索到2014-01-24。

跳起^ “HVDC晶闸管阀门”。ABB Asea Brown Boveri。于2009年1月22日原版存档。检索2008-12-20。

跳起来^ “高功率”。IET。于2009年9月10日原版存档。检索到2009-07-12。

跳起来^ “晶闸管的安全燃烧”上powerguru.org

跳起来^ 示例：碳化硅逆变器在电力电子技术中表现出更高的功率输出（2006-02-01）

跳起来^ 拉希德，穆罕默德H.（2011）; 电力电子（第3版）。Pearson，ISBN 978-81-317-0246-8

Wintrich，Arendt; 尼古拉，乌尔里希; 图尔斯基，沃纳; Reimann，Tobias（2011年）。2011年功率半导体应用手册 （PDF）（第2版）。纽伦堡：赛米隆。ISBN  978-3-938843-66-6。源自2013-09-16 的原始版 （PDF）。

晶闸管理论与设计考虑 ; 安森美半导体 240页; 2006; HBD855 / d。（免费PDF下载）

Ulrich Nicolai，Tobias Reimann，JürgenPetzoldt，Josef Lutz：应用手册IGBT和MOSFET功率模块，1。版，ISLE Verlag，1998，ISBN  3-932633-24-5。（免费PDF下载）

SCR手册 ; 第6版; 通用电气公司; 普伦蒂斯霍尔; 1979年。

The thyristor is a four-layered, three-terminal semiconductor device, with each layer consisting of alternately N-type or P-type material, for example P-N-P-N. The main terminals, labelled anode and cathode, are across all four layers. The control terminal, called the gate, is attached to p-type material near the cathode. (A variant called an SCS—silicon controlled switch—brings all four layers out to terminals.) The operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction transistors, arranged to cause a self-latching action:

Structure on the physical and electronic level, and the thyristor symbol.

Thyristors have three states:

Reverse blocking mode – Voltage is applied in the direction that would be blocked by a diode

Forward blocking mode – Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not been triggered into conduction

Forward conducting mode – The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current"

The thyristor has three p-n junctions (serially named J1, J2, J3 from the anode).

Layer diagram of thyristor.

When the anode is at a positive potential VAK with respect to the cathode with no voltage applied at the gate, junctions J1 and J3 are forward biased, while junction J2 is reverse biased. As J2 is reverse biased, no conduction takes place (Off state). Now if VAK is increased beyond the breakdown voltage VBO of the thyristor, avalanche breakdown of J2 takes place and the thyristor starts conducting (On state).

If a positive potential VG is applied at the gate terminal with respect to the cathode, the breakdown of the junction J2 occurs at a lower value of VAK. By selecting an appropriate value of VG, the thyristor can be switched into the on state quickly.

Once avalanche breakdown has occurred, the thyristor continues to conduct, irrespective of the gate voltage, until: (a) the potential VAK is removed or (b) the current through the device (anode−cathode) becomes less than the holding current specified by the manufacturer. Hence VGcan be a voltage pulse, such as the voltage output from a UJT relaxation oscillator.

The gate pulses are characterized in terms of gate trigger voltage (VGT) and gate trigger current (IGT). Gate trigger current varies inversely with gate pulse width in such a way that it is evident that there is a minimum gate charge required to trigger the thyristor.

V – I characteristics.

In a conventional thyristor, once it has been switched on by the gate terminal, the device remains latched in the on-state (i.e. does not need a continuous supply of gate current to remain in the on state), providing the anode current has exceeded the latching current (IL). As long as the anode remains positively biased, it cannot be switched off until the anode current falls below the holding current (IH). In normal working condition the latching current is always greater than holding current. In the above figure ILhas to come above the IH on y-axis since IL>IH.

A thyristor can be switched off if the external circuit causes the anode to become negatively biased (a method known as natural, or line, commutation). In some applications this is done by switching a second thyristor to discharge a capacitor into the cathode of the first thyristor. This method is called forced commutation.

After the current in a thyristor has extinguished, a finite time delay must elapse before the anode can again be positively biased and retain the thyristor in the off-state. This minimum delay is called the circuit commutated turn off time (tQ). Attempting to positively bias the anode within this time causes the thyristor to be self-triggered by the remaining charge carriers (holes and electrons) that have not yet recombined.

For applications with frequencies higher than the domestic AC mains supply (e.g. 50 Hz or 60 Hz), thyristors with lower values of tQ are required. Such fast thyristors can be made by diffusing heavy metal ions such as gold or platinum which act as charge combination centers into the silicon. Today, fast thyristors are more usually made by electron or proton irradiation of the silicon, or by ion implantation. Irradiation is more versatile than heavy metal doping because it permits the dosage to be adjusted in fine steps, even at quite a late stage in the processing of the silicon.

The silicon controlled rectifier (SCR) or thyristor proposed by William Shockley in 1950 and championed by Moll and others at Bell Labs was developed in 1956 by power engineers at General Electric (G.E.), led by Gordon Hall and commercialized by G.E.'s Frank W. "Bill" Gutzwiller.

A bank of six 2000 A thyristors (white disks arranged in a row at top, and seen edge-on)

An earlier gas-filled tube device called a thyratron provided a similar electronic switching capability, where a small control voltage could switch a large current. It is from a combination of "thyratron" and "transistor" that the term "thyristor" is derived.[2]

Waveforms in a thyristor circuit controlling an AC current.Red trace: load (output) voltageBlue trace: trigger voltage.

Thyristors are mainly used where high currents and voltages are involved, and are often used to control alternating currents, where the change of polarity of the current causes the device to switch off automatically, referred to as "zero cross" operation. The device can be said to operate synchronously; being that, once the device is triggered, it conducts current in phase with the voltage applied over its cathode to anode junction with no further gate modulation being required, i.e., the device is biased fully on. This is not to be confused with asymmetrical operation, as the output is unidirectional, flowing only from cathode to anode, and so is asymmetrical in nature.

Thyristors can be used as the control elements for phase angle triggered controllers, also known as phase fired controllers.

They can also be found in power supplies for digital circuits, where they are used as a sort of "enhanced circuit breaker" to prevent a failure in the power supply from damaging downstream components. A thyristor is used in conjunction with a Zener diode attached to its gate, and if the output voltage of the supply rises above the Zener voltage, the thyristor will conduct and short-circuit the power supply output to ground (in general also tripping an upstream breaker or fuse). This kind of protection circuit is known as a crowbar, and has the advantage over a standard circuit breaker or fuse in that it creates a high-conductance path to ground for the damaging supply voltage and potentially for stored energy in the system being powered.

The first large-scale application of thyristors, with associated triggering diac, in consumer products related to stabilized power supplies within color television receivers in the early 1970s.[clarification needed] The stabilized high voltage DC supply for the receiver was obtained by moving the switching point of the thyristor device up and down the falling slope of the positive going half of the AC supply input (if the rising slope was used the output voltage would always rise towards the peak input voltage when the device was triggered and thus defeat the aim of regulation). The precise switching point was determined by the load on the DC output supply, as well as AC input fluctuations.

Thyristors have been used for decades as light dimmers in television, motion pictures, and theater, where they replaced inferior technologies such as autotransformers and rheostats. They have also been used in photography as a critical part of flashes (strobes).

Thyristors can be triggered by a high rise-rate of off-state voltage. This is prevented by connecting a resistor-capacitor (RC) snubber circuit between the anode and cathode in order to limit the dV/dt (i.e., rate of voltage change over time).

Valve hall containing thyristor valve stacks used for long-distance transmission of power from Manitoba Hydro dams

Since modern thyristors can switch power on the scale of megawatts, thyristor valves have become the heart of high-voltage direct current (HVDC) conversion either to or from alternating current. In the realm of this and other very high-power applications, both electrically triggered (ETT) and light-triggered (LTT) thyristors[3][4] are still the primary choice. The valves are arranged in stacks usually suspended from the ceiling of a transmission building called a valve hall. Thyristors are arranged into a diode bridge circuit and to reduce harmonics are connected in series to form a 12-pulse converter. Each thyristor is cooled with deionized water, and the entire arrangement becomes one of multiple identical modules forming a layer in a multilayer valve stack called a quadruple valve. Three such stacks are typically mounted on the floor or hung from the ceiling of the valve hall of a long-distance transmission facility.[5][6]

The functional drawback of a thyristor is that, like a diode, it only conducts in one direction. A similar self-latching 5-layer device, called a TRIAC, is able to work in both directions. This added capability, though, also can become a shortfall. Because the TRIAC can conduct in both directions, reactive loads can cause it to fail to turn off during the zero-voltage instants of the AC power cycle. Because of this, use of TRIACs with (for example) heavily inductive motor loads usually requires the use of a "snubber" circuit around the TRIAC to assure that it will turn off with each half-cycle of mains power. Inverse parallel SCRs can also be used in place of the triac; because each SCR in the pair has an entire half-cycle of reverse polarity applied to it, the SCRs, unlike TRIACs, are sure to turn off. The "price" to be paid for this arrangement, however, is the added complexity of two separate, but essentially identical gating circuits.

Although thyristors are heavily used in megawatt-scale rectification of AC to DC, in low- and medium-power (from few tens of watts to few tens of kilowatts) applications they have virtually been replaced by other devices with superior switching characteristics like Power MOSFETs or IGBTs. One major problem associated with SCRs is that they are not fully controllable switches. The GTO thyristor and IGCT are two devices related to the thyristor that address this problem. In high-frequency applications, thyristors are poor candidates due to long switching times arising from bipolar conduction. MOSFETs, on the other hand, have much faster switching capability because of their unipolar conduction (only majority carriers carry the current).

Thyristor manufacturers generally specify a region of safe firing defining acceptable levels of voltage and current for a given operating temperature. The boundary of this region is partly determined by the requirement that the maximum permissible gate power (PG), specified for a given trigger pulse duration, is not exceeded.[7]

As well as the usual failure modes due to exceeding voltage, current or power ratings, thyristors have their own particular modes of failure, including:

Turn on di/dt – in which the rate of rise of on-state current after triggering is higher than can be supported by the spreading speed of the active conduction area (SCRs & triacs).

Forced commutation – in which the transient peak reverse recovery current causes such a high voltage drop in the sub-cathode region that it exceeds the reverse breakdown voltage of the gate cathode diode junction (SCRs only).

Switch on dv/dt – the thyristor can be spuriously fired without trigger from the gate if the anode-to-cathode voltage rise-rate is too great.