Single phase fully controlled converters are obtained by replacing the diodes of an uncontrolled converter with thyristors. It is one of the most popular converter circuits and is widely used in the speed control of separately excited dc machines. In a fully controlled converter the output voltage can be controlled by controlling the firing delay angle (α) of the thyristors. Thyristors T1 and T2 are fired together while T3 and T4 are fired 180º after T1 and T2. Depending on the load condition and the firing angle a fully controlled bridge converter can operate either in the continuous conduction mode or in the discontinuous conduction mode. In the continuous conduction mode, the load voltage depends only on the firing angle and not on load parameters. In the discontinuous conduction mode, the output voltage decreases with increasing load current. However, the output voltage is always greater than that in the continuous conduction mode for the same firing angle.