A thyristor is a switchable power electronic semiconductor component. Connected as a rectifier, it does not change the voltage level, but converts alternating current into direct current. Connected as an inverter, it converts direct current into alternating current, whereby the frequency and phase of the alternating current can be precisely controlled by clocking the thyristors. Modern thyristors are made of semiconductor material. The mode of operation corresponds to that of a classic diode: current is only ever passed in one specific direction. With thyristors, however, the timing and duration of the conduction can be controlled extremely precisely.