| 摘要 |
PURPOSE: To obtain a power device, which stably conducts oscillation and cost of which is reduced, by turning a transistor on when a current flowing through a switching element reaches a specified level and holding the bias voltage of a bias-voltage generating circuit at stable voltage. CONSTITUTION: A resistor R8 for start and a capacitor C2 for generating bias voltage are connected in series between power terminals A and B, and a node is connected to the gate of an FET 1 through a feedback winding L3. In a transistor Q1, a base is connected to the node of resistors R3, R4, an emitter to the power terminal B, a collector to the cathode of a diode D4, and an anode to the gate of the FET 1. When both terminal voltage IO, R<4> of the resistor R4 exceeds the threshold of the transistor Q1, the transistor Ql is turned on and a current IS3 flows, and voltage V9 suddenly lowers by voltage induced in the feedback winding L3 and the FET 1 is turned off. Consequently, no excess current IP flows even at the time of transition. Accordingly, oscillation can be maintained stably. |
