The simplest of all rectifier category is diodes rectifier. In the simplest type of diode rectifier does not provide any means of controlling output current and voltage values. In order to apply to industrial processes, and output value must be within a certain range can be controlled. By applying mechanical so-called on-load tap changer can complete this control. As a typical situation of on load tap changer in transformer primary side control input AC voltage, so it can control output DC values within a certain range. Usually on-load tap changer and series in the rectifier output saturable reactor used in the circuit. By introduction of DC current in the reactor, produces a variable makes the line impedance. Therefore, by controlling the reactor both ends of voltage drop, output can be controlled in a relatively narrow range.