There are many types of devices available for the respective applications of transistors and thyristors: Transistors are essentially double diodes, which are used for controlling electric voltages and currents, mostly at low values. Thyristors on the other hand can be thought of as voltage gates. The gate is a control electrode, which switches the thyristor. In the default condition, the current is blocked in both directions. A thyristor becomes conductive only when an electrical impulse is initiated by the control electrode. For small and medium power applications they control the speed of electric motors, for instance in vacuum cleaners, mixers or power drills.