JPS55123713A - Constant-current power unit - Google Patents

Abstract

PURPOSE: To obtain a superior constant-current characteristic and prevent a high voltage from being generated at an anomaly time, by controlling the conduction angle of a phase control circuit according to a load current.

CONSTITUTION: Phase control circuit 11 is inserted between output ends of resonance circuit 3, and this circuit 11 is so constituted that this circuit 11 may be controlled by feedback circuit 12. Here, though circuit 12 is operated according to the load current, circuit 12 controls the conduction angle of circuit 11 in the relation opposite to increment and reduction of the load current. In this constitution, when the load current becomes small, circuit 12 is operated according to the load current to make the conduction angle of circuit 11 smaller than that for normalcy. As a result, the output voltage becomes large, and the load current becomes larger proportionally, and the load current is held at a fixed value before change. Otherwise, when the load current becomes large, the load current is made small reversely by phase control, and the load current is held at a fixed value before change. Though the output voltage is changed according to increment and reduction of the load, namely, lamp 10, circuit 11 is not affected by increment and reduction of lamp 10 because the load current is fixed.

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