Design and Testing of a Simplified AC-AC-DC Power Supply Having Adjustable Output Voltage

Variable DC power supply units are widely used in the university laboratories to demonstrate different experiments to the engineering students. Mostly such power supply units are imported one, thereby expensive and cannot be repaired if gets out of order due to unavailability of spare parts and adequate servicing facilities. In this paper an indigenously developed DC power supply unit is presented. In this unit a TRIAC based ac voltage controller is used which provides the adjustable ac power at the input of a conventional bridge rectifier which converts the ac power to DC output. The novelty is that here a RC based modified triggering circuit is used to control the TRIAC. Thus variation of the output voltage over a wide range (0-300V) is possible. The design is such that the triggering circuit is very simple, uses a smaller number of components and it can be fabricated collecting all the parts from the local market. A prototype is made and tested in the laboratory using R, RL and motor load. The results are very satisfactory in accordance with the theoretical expectation.