Abstract: A magnetic detector, such as is used in a frequency generator, for detecting the rotational rate of a motor includes magnetic resistance elements and an operational amplifier. The magnetic resistance elements have a predetermined resistance ratio and are connected serially between a power source and ground. The common node between the two magnetic resistance elements serves as an output terminal for providing an output voltage. The output voltage from the output terminal being supplied to one of the two input terminals of the amplifier. The voltage from a resistance voltage divider disposed between the power source and ground is supplied to the other input terminal of the amplifier. A change of the resistance ratio between the two magnetic resistance elements is effected by a resistor disposed in series with the elements or in parallel with one of the elements.

Abstract: The negative temperature dependency of the torque ripple correction capability of a known drive circuit is offset by making the amplitude of input voltage signals applied to a m-differential amplifier of the drive circuit positively temperature-dependent to improve the overall torque ripple correction capability of the circuit so that deteriorated torque ripples at low temperature and increase in the level of reactive currents at high temperature may be effectively eliminated. Moreover, since temperature induced deformation of waveforms of electric currents to be carried to soft switching coils of the drive circuit is minimized, a too rapid switching speed at low temperature is avoided to suppress generation of electric as well as mechanical noises, while too dull waveforms of electric currents at high temperature are also eliminated.

Abstract: The present invention concerns a current amplifier which is formed by a transistor, with a view to preventing oversaturation of the transistor. The transistor saturation preventing circuit, according to the invention, includes a second transistor (Q.sub.2) which constitutes a current mirror circuit with respect to a first transistor (Q.sub.1) forming the current amplifier, a saturation detecting element (R.sub.1) connected to the second transistor (Q.sub.2) to detect saturation of the first transistor (Q.sub.1), and a current feedback element (D.sub.1), so as to decrease the base current of the first transistor (Q.sub.1).

Abstract: 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.

Abstract: A three-phase sine wave signal synthesizing circuit comprises a pair of detectors for respectively generating substantially sinusoidal wave output signals having a phase difference of 120.degree. in terms of electric angle upon detecting a two-phase sine wave output generated by a signal generator and a pair of amplifiers for amplifying the output signals from the pair of detectors and transmitting the non-inverted output signals as a first-phase output signal and a second-phase output signal as well as an inverted signal. Terminals for transmitting the inverted signals from the pair of amplifiers are mutually short-circuited and a third-phase, non-inverted output signal is transmitted from the point of the short-circuit. Such circuit does not require a synthesizer to obtain a third-phase output signal and consequently can be significantly simplified to reduce its manufacturing cost. Moreover, such circuit can enhance the accuracy of three-phase sine wave output signals it transmits.

Abstract: The coil middle point voltage of a brushless motor drive circuit is kept to a proper level and, therefore, brings forth stable and improved torque ripple correction effects even when the electric current gain of the source side and that of the sink side of the drive coils of the circuit are not well balanced.

Abstract: A brushless motor drive circuit having a position detection output signal in the form of an m-phase sine wave with a signal composing circuit to flatten the inflection points of the sine wave by logarithmic compression. Switching elements control the rate of the current to the drive coil in response to the signal composing circuit. Simultaneously, the switching elements having the same phase are switched on to supply a resistive feedback element with reactive current during the periods when no current is to be supplied to the drive coil.

Abstract: A drive circuit for driving a brushless motor includes a rotor magnet with m (m=integer) different phases for rotatatively driving the rotor magnet. A total of k (k=integer) locating devices, such as Hall elements, are employed for detecting the rotary position of the rotor magnet and for generating output signals representing the detected position. A total of m controlling and multiplying circuits are included, each responsive to the output signal from the corresponding one of the k locating devices at one of its input terminals. The drive circuit includes m output amplifiers, each for receiving the output signal from the corresponding one of the m controlling and multiplying circuits to provide m output voltage to drive the drive coils. M repetitive multipliers are included for repetitively multiplying each of the output voltages by itself until the sum of the powers of the output voltages reaches a given value. The exponent of the repetitive multiplication is an even number.

Abstract: A brushless motor drive circuit comprises a stator having m-phase drive coils, a rotor having magnetic poles, a position detecting element for generating m-phase output signals in accordance with the positional relationship between the rotor and the stator, electric current capable of flowing through the m-phase drive coils of the stator in either direction, a plurality of switching devices for switching the current being supplied to the m-phase drive coils in accordance with the output signals from the position detecting element, a current control circuit for controlling the level of the current being supplied to the drive coils utilizing the group of switching devices and a brake circuit for braking the rotor by feeding back the counter electromotive voltage generated when the current being supplied to the drive coils is interrupted so as to suppress the voltage to about half of the power source voltage for the drive circuit.

Abstract: A drive circuit for a three-phase brushless motor in which two Hall detectors are spaced 120.degree. apart in electrical angle near the rotors to detect magnetic flux signals for two phases. Their outputs are summed and inverted to form the third phase signal. The three phase signals drive the respective coils on the stator. The three phase signals are also separately squared and then added to adjust, in a feedback fashion, the current through the Hall detectors, whereby torque ripple is reduced.