Abstract: Provided is an improved electrofusion machine comprising: a power supply circuit having a triac configured to have a proper regulation for dropping a commercial voltage to a voltage adapted for a fitting; and a printer unit integrated with the electrofusion unit, for printing information regarding a work result of the fitting. According to the above construction, since the electrofusion machine does not use a transformer occupying 40% of a total weight of the machine, the mobility and portability are enhanced. Also, since the size of the machine is reduced, it is advantageous to deal with the machine on the spot.

Abstract: Provided is a constant voltage control apparatus capable of reducing feedback lines. In the constant voltage control apparatus, a first amplifier amplifies an output voltage applied to a pair of output terminals. A second amplifier amplifies a voltage drop between one of the output terminals and a load terminal connected thereto. A third amplifier amplifies output voltages from the first and second amplifiers, respectively. Comparing means receive an output voltage from the third amplifier and a reference voltage, and output an output voltage which makes a sum of the output voltage and the reference voltage of the third amplifier become zero. A triac drive unit amplifies the output voltage from the comparing means to control a triac installed on a power line that is connected with the first output terminal.