Abstract: A power source adaptor employing a small switch to securely and positively turn on and off the power source, and which can be detachably connected to an electrical apparatus. To avoid the cost and excessive size associated with prior art power source adaptors, the adaptor can include an auxiliary switch element provided for the control section of an electrical switching element to selectively start and stop a switching operation. A switch operating button on an adaptor housing operates the auxiliary switch element. An insulated coupling bar is also provided through which the switch operating button is mechanically coupled to the power on/off operating button on the apparatus body.

Abstract: A variable resistance circuit comprises first and second transistor pairs, first and second load circuits connected to respective collector sides of the first and second transistor pairs, and first and second constant current sources connected to respective common connected emitters of the first and second transistor pairs. Each of the load circuits supplies collectors of each transistor pair with currents having same current values with each other. Each of the constant current sources supplies the common connected emitters of each transistor pairs with a constant current. Respective base and collector of one transistors of the first and second transistor pairs are connected to each other and connected to first and second terminals, respectively. Bases of the other transistors of the first and second transistor pairs are connected to the second and first terminals, respectively.

Abstract: A protection circuit for a switching power amplifier comprises a first detection circuit which detects a current flowing through an output stage switching circuit, a second detection circuit which detects an output voltage of the output stage switching circuit, and an amplitude limitation circuit which limits the amplitude of an input signal to the output stage switching circuit in accordance with both the first and second detection. Thus the switching circuit is surely protected from destruction.