A circuit capable of providing stable timing clock includes: a step-down clamping circuit, an oscillating circuit, and a voltage potential-conversing circuit. The step-down clamping circuit that step down the input first voltage potential, and clamp to output second voltage, the oscillating circuit is coupled to the clamping circuit and is an oscillating circuit that takes the second voltage as a operating voltage to generate a first timing clock signal, which has a lower voltage potential. The voltage potential-conversing circuit is coupled to the oscillating circuit to convert the first timing clock signal into a second timing clock signal, which has a higher voltage potential. And it is a stable timing clock signal available for other system circuit.

A digital hearing aid comprises a microphone (2), an output transducer (3), a digital signal processor (5) interconnected between the microphone and the output transducer, and a power source (7) including a standard hearing aid battery for the supply of operation voltage for the digital signal processor. At least one of the integrated circuit signal processing parts is designed to operate at a reduced unstabilized operation voltage substantially below a nominal voltage of the battery. A switched step-down voltage converter is connected between the power source and such signal processing parts for lowering the battery voltage to provide the reduced operation voltage.

A brushless motor drive circuit supplies power to a brushless motor by soft switching and prevents saturation of power supply transistors under any conditions. The brushless motor drive circuit includes, for respective phases, a first set of transistors for driving output transistors connected to the side of a DC power supply; a second set of transistors which constitute current mirror circuits in combination with the first set, respectively; a reference voltage generating device is connected to the second set of transistors respectively, for generating voltages proportional to currents flowing in the second set. A current feedback circuit, which, when potential differences between the inputs and outputs of the first set of transistors reach values close to the voltages generated by the reference voltage device, are turned on, causing voltage drops nearly equal to voltages generated by the second set of transistors, so as to partly feed back output currents of the first set of transistors to stages preceding the reference voltage generating device so that input currents to the first transistor are reduced. This results in an avoidance of saturation of the output transistors and also avoids the adverse reliance on circuit values.

An output voltage of a solar cell is supplied to a voltage converter. The voltage converter converts the input voltage into a predetermined voltage, and supplies it to a capacitor. The capacitor is charged by the output current of the voltage converter. The capacitor has a relatively large capacitance. A second voltage converter converts an input voltage from the capacitor into a voltage which is lower than the charged voltage of the capacitor and higher than a minimum operating voltage of a load. The load performs a predetermined operation using the output voltage of the second voltage converter.

The power generated by a power generating means (1) of a power-generating type electronic clock is measured by a first power generating sensing means (101) and a second power generating sensing means (102). The power generation level required when the operation is changed from a normal mode to a power-saving mode and the power generation level required when the operation is changed from the power-saving mode back to the normal mode are made different to prevent the phenomenon that the operation changes frequently by imparting hysteresis characteristics to the power generation level which causes a change in the mode, thereby improving the power-saving effect.