Abstract: A switching power device uses a non-capacitor flyback converter circuit not provided with a smoothing input capacitor having a large capacity. Therefore, a power harmonic can be suppressed and a rush current preventing element is not required. A fluctuation in an output current to be supplied to a load is fed back to the non-capacitor flyback converter circuit by a feedback circuit at a lower speed than an input AC frequency. Therefore, it is possible to improve a power factor by causing an input AC current to be proportional to an input AC voltage. A voltage control circuit controls an output voltage so as to have a constant voltage, and the output voltage is dropped in proportion to an output current when the output current exceeds a threshold. Therefore, it is possible to have the same output characteristic as a power device comprising a low frequency power transformer.

Abstract: A switching power device uses a non-capacitor flyback converter circuit not provided with a smoothing input capacitor having a large capacity. Therefore, a power harmonic can be suppressed and a rush current preventing element is not required. A fluctuation in an output current to be supplied to a load is fed back to the non-capacitor flyback converter circuit by a feedback circuit at a lower speed than an input AC frequency. Therefore, it is possible to improve a power factor by causing an input AC current to be proportional to an input AC voltage. A voltage control circuit controls an output voltage so as to have a constant voltage, and the output voltage is dropped in proportion to an output current when the output current exceeds a threshold. Therefore, it is possible to have the same output characteristic as a power device comprising a low frequency power transformer.

Abstract: An amplifier circuit comprises a differential or operational amplifier having a first input connected to receive an input signal, and a transistor having its base connected to the output of the differential amplifier, its collector connected to a first power supply terminal through a constant current source and connected to a second input of the differential amplifier through a DC negative feedback circuit, and its emitter connected to a second power supply terminal through a resistor and connected to the first input of the differential amplifier through an AC negative feedback circuit. A load such as a recording head is connected between the collector of the transistor and circuit ground. With this circuit, an output signal current including no DC component and proportional to an input signal voltage flows through the load.

Abstract: A plurality of parallel branch paths are connected in an intermediate frequency or high frequency amplifying circuit of a radio receiver for the purpose of switching the bandwidth. Between an intermediate point of each branch path and the ground is connected output electrodes of a transistor, and the base electrode of the transistor is selectively connected to a source of control voltage via a transfer switch to render the selected transistor conductive.