Abstract: A molded electronic circuit device including a printed circuit board having an electronic circuit in a synthetic resin, the electronic circuit including heat-radiating electronic elements such as a power transistor and contained within a case holding the printed circuit board. According to the present invention, the synthetic resin material fills the case between the electronic elements so as to conduct heat away from the electronic elements, the synthetic resin material comprising a silicon carbide or a silicon carbide compound mixed as a major constituent in an epoxy resin and having a metal oxide added to the resultant mixture.

Abstract: A pulse absorbing circuit is disclosed for a power source circuit for absorbing an abnormal pulse when an input current at a primary winding of an output transformer in a switching power source is cut off. The pulse absorbing circuit includes a capacitor, one end of which is connected to a secondary winding output terminal of a transformer in a phase opposite to a primary winding input terminal thereof. A first rectifying element is provided, an anode of which is connected to the other end of the capacitor and a cathode of which is connected to an output terminal of a rectifying circuit arranged at a secondary winding side of the transformer. A second rectifying element is provided, a cathode of which is connected to a junction between the first rectifying element and the capacitor. A conductor is inserted between a ground terminal and the second rectifying element. The conductor has, for example, a coil for absorbing and effectively reutilizing abnormal pulse energy.

Abstract: A switching power source circuit intermittently switches a current at a primary winding of a transformer in accordance with the repeated switching of a bipolar transistor so as to rectify and smooth a voltage induced at a secondary winding of the transformer, thereby obtaining an output voltage. A capacitor is charged by a voltage induced by a feedback winding of the transformer. The base-emitter path of the bipolar transistor is reverse biased by this charge voltage so as to perform high-speed switching, so that a compact transformer and capacitor can be used and the switching power source circuit becomes low in cost.The application of the reverse bias voltage is performed by a transistor which is turned on when an emitter (grounded through a resistor) voltage of the bipolar transistor is increased to a predetermined level (threshold). A switching period of the bipolar transistor is determined by a period determining circuit consisting of a timing capacitor and a resistor.