JPS6419967A - Switching control type power device - Google Patents

Abstract

PURPOSE:To adjust a load-current set value finely and accurately by varying the magnitude of load currents under the state of constant-current operation by a control signal transmitted from the outside. CONSTITUTION:A switching control type power device is composed of a blocking oscillation section 1, an output extracting section 2, a constant voltage control section 3, a constant current control section 4 and a chopper section 5 for preparing negative voltage. The constant current control section 4 has a first circuit section 4a converting a load-current value setting signal transmitted over a terminal T3 into negative control voltage, a second circuit section 4b comparing the control voltage with the detecting output voltage of load currents, and a second control transistor Q3 controlling the quantity of shunt of the positive feedback currents of a switching transistor Q1 by a comparison output from the second circuit section 4b. A primary side transistor Q1 for a converter transformer CT is controlled and load currents are turned into constant currents, and the constant currents are regulated in response to the load-curent value setting signal.