Thyristors are solid state switches that are normally open (high impedance) circuits, capable of withstanding a rated blocking voltage until triggered to an on state. Once triggered, thyristors become a low impedance current path until the main current either stops or drops below a minimum holding current. Thyristors are normally two or three terminal devices for either uni-directional or bi-directional circuit configurations. An SCR is a uni-directional device. A Triac is a bi-directional device. Thyristors are offered in a variety of surface mount and thru-hole packages. Thyristors are used to control the flow of electrical current in an application. They are typically used in home appliances such as lighting (dimmer switch), heating and temperature control, alarm activation and fan speed control. They are also used in power tools for controlled actions such as motor speed, a stapling event or battery charging. Outdoor equipment including water sprinklers, gas engine ignition, electronic displays, area lighting and sports equipment also use thyristors.