Abstract: A rare earth sintered magnet is prepared by a method comprising the steps of melting raw materials to form an alloy, pulverizing the alloy into a fine powder, shaping the fine powder into a compact, and sintering the compact. The pulverizing step includes a coarse pulverizing step including hydrogen decrepitation and a fine pulverizing step, and further includes the step of adding a lubricant. The sintering step includes an atmosphere heat treatment including heating the compact at a temperature from the lubricant decomposition temperature to the sintering temperature and holding at the temperature for a time, in an inert gas atmosphere, and a vacuum heat treatment. The sintered magnet has a low impurity concentration and a narrow carbon concentration distribution.

Abstract: In a synchronous rectifying circuit comprising a main transformer, a primary circuit, a secondary circuit, and a control circuit, the secondary circuit includes a synchronous rectifier which comprises not only a second series circuit comprising first and second synchronous rectifying elements but also first and second impedance circuits. The first impedance circuit is inserted between an end of a secondary winding of the main transformer and a first control terminal of the first synchronous rectifying element. The second impedance circuit is inserted between another end of the secondary winding of the main transformer and a second control terminal of the second synchronous rectifying element. Each of the first and the second impedance circuits may consist of a parallel circuit comprising a resistor and a diode. Each of the first and the second impedance circuits may a capacitor.

Abstract: A DC-DC converter comprises a switching pulse generator for generating a plurality of switching pulse signals for operating a primary switch and a synchronized-rectifying circuit. The switching pulse generator generates the respective switching pulse signals having different pulse widths based on different control voltages which are generated by a voltage divider comprising a variable-impedance device. The pulse width of each switching pulse signal is set according to the differences between the control voltages. The switching pulse generator comprises a first control circuit for the primary switch and a second control circuit for the synchronized-rectifying circuit. Switching timing of the synchronized-rectifying circuit is deviated from that of the primary switch by a period corresponding to the difference between a certain control voltage and each of the other control voltages.