| 摘要 |
PURPOSE:To prevent freezing of pump, by switching/regulating the width of a waveform a phase control signal for limiting the conduction angle of an A.C. current limiting element and suppressing the temperature maintaining current for a pump motor into rippling wave corresponding to the pump displacement by means of a changeover switch. CONSTITUTION:If the temperature detected through a temperature sensor 41 is lower than about 2 deg.C, a microcomputor 11 carries out full-wave rectification of the voltage of a commercial power source through a full-wave rectifier circuit 26 and limits the conduction angle of a triac 17 which serves as an A.C. current limiting element based on a phase signal synchronized with said full-wave rectified signal so as to suppress the temperature maintaining current for a pump motor 2 into ripping wave for every half period of the commercial power source. Furthermore, the width of waveform of a phase control signal is switched/regulated corresponding to the pump displacement by means of changeover switches 47, 48. Since the conduction angle of the driving current of the pump motor 2 is controlled under temperature maintaining operation so as to suppress the driving current into ripping wave, noise of the pump motor and a noise caused by surge current are suppressed thereby psufficient quantity of heat for preventing freezing of pump can be maintained.
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