U.S. Philips Corporation

Johannes P Bahlmann

Henricus M Van Hout

Wilhelmus A Zwijsen

Johannes P Inghels

A motor drive circuit for driving an electromotor having a permanent magnet rotor and a stator comprising one or more stator windings. When the supply voltage of the motor drive circuit fails, an emergency signal is generated by a signal generator. This emergency control signal activates an auxiliary power supply circuit for extracting electric energy from the motor and supplying the extracted energy to an auxiliary circuit. The auxiliary power supply circuit comprises a rectifier circuit formed by the fly back diodes bridging the switches of an electronic commutation circuit. The drive circuit comprises short-circuit switches bridging the stator windings. In response to the emergency control signal a short-circuit apparatus causes the stator windings to be temporarily intermittently short-circuited. As a result, a capacitor is charged. The energy stored in the capacitor is used for temporarily energizing the auxiliary circuit once the power supply to the drive circuit has failed. If the drive circuit is used with a hard disc drive, the energy supplied by the auxiliary power supply circuit can be used for moving the magnetic head to an idle position.

Motor drive circuit with emergency auxiliary power supply energized by

An integrated circuit having a unit for controlling a load of an inductive nature, which unit includes a first output transistor having a first control electrode and a first main current path, a second output transistor having a second control electrode and a second main current path, a control stage coupled to the control electrodes and adapted to control the output transistors. An output terminal is coupled between the main current paths and adapted to connect the load. In order to limit a voltage transient appearing on the output terminal, as a result of an interruption of a current flowing through the load, the control stage is coupled to the output terminal and is adapted to detect a first voltage transient on the output terminal, to turn on the second transistor in response to the first voltage transient, to detect a second voltage transient on the output terminal, which second voltage transient is opposed to the first voltage transient, and to turn off the second transistor in response to the second voltage transient.

Integrated circuit comprising a unit for controlling a load of an

A receiver for use in a remote control system in which clock pulse-modulated information pulses are transmitted in a wireless mode to the receiver. The receiver is intended for use in hearing aids energized with supply voltages of approximately 1 V. The receiver includes a receiving device (1) for the conversion of the wirelessly transmitted information pulses into an electric signal and a cascade arrangement of first and second selective amplifier circuits (2) and (4), each of which have their highest gain factor at a frequency which is approximately equal to the frequency of the clock pulses. This cascade arrangement is connected to the output of the receiver device and supplies a first output signal to a mean value detector (5) which produces a rough version of the information pulses, which in turn are shaped in a pulse shaper (6).

Receiver for use in a remote control system

A transistor output stage including an output transistor having its base coupled to the emitter of a driver transistor is driven into saturation by a current source which is connected to the base of the driver transistor. When a small output current is flowing through the load connected to the collector of the output transistor, the surplus of the current from the current source is drained from the base of the driver transistor to the collector of the output transistor via the collector-emitter path of a limiting transistor having its base connected to the base of the output transistor. This reduces the power dissipation in the driver transistor and improves the power efficiency of the transistor output stage.

Output circuit with drive current limitation

An output transistor (T.sub.1) is to be protected from damage due to excessive currents. This transistor supplies a current (I.sub.o) to a load (3) and is driven by a driver transistor (T.sub.2). The base-emitter junction of a current-sensing trnsistor (T.sub.3) is connected in parallel with that of the output transistor (T.sub.1). The collector current of transistor (T.sub.3) is a measure of the current (I.sub.o) of the output transistor (T.sub.1). A current generator (5) supplying a reference current (I.sub.ref) is coupled to the collector of the current-sensing transistor (T.sub.3). If the collector current of the current-sensing transistor exceeds the reference current (I.sub.ref) the protection circuit is activated so that the driver transistor is bottomed via an emitter-follower (T.sub.4). The base current of transistor T.sub.1 is thereby limited. Thus, the output current of the output transistor is limited to a maximum value which is substantially equal to the product of the reference current (I.sub.ref) and the ratio between the emitter areas of the output transistor (T.sub.1) and the current-sensing transistor (T.sub.3).

Transistor protection circuit

An arrangement suitable for producing pulse-shaped signals whose amplitude is determined by a control voltage in an electronic musical instrument. The arrangement comprises a first transistor having a control electrode to which the control voltage is applied and a main electrode connected to a point of fixed potential via an impedance. The arrangement further comprises means for transferring the output current of the first transistor, which current is determined by the control voltage, to an output in a pulse-shaped fashion. In order to convert the unipolar current pulses into bipolar current pulses the arrangement includes a second transistor whose input circuit is connected in parallel with the input circuit of the first transistor. The output current of this second transistor is subtracted from the output current of the first transistor by means of a current amplifier, the result being available at the output.

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Eindhoven, Netherlands

Johannes P Bahlmann