Abstract: A head antenna for nuclear magnetic resonance examinations has an examination chamber, formed so as to accept the head, and an antenna conductor, formed as a frame antenna, that surrounds the examination chamber in an examination position. The antenna conductor is divided into two curved sub-conductors that respectively have electrical contacts at their ends for detachably electrically connecting the sub-contractors together. The first sub-conductor arrangement is fastened to a holding part which is arranged outside the examination chamber and which is made of an electrically non-conductive, non-ferromagnetic material. For fastening the holding part to a patient support, a first fastening assembly is arranged on the holding part. For fixing the position of the head, a second fastening assembly is arranged on the holding part.

Abstract: The device for energizing a heating element of a window pane from a direct current network of a motor vehicle includes a converting device for converting the d.c. voltage of the direct current network into an alternating current voltage of a predetermined frequency and a resonant circuit connected to the output of the converting device having a Q-factor high enough to produce a low number of harmonics in operation. The resonant circuit has a resonant frequency corresponding to that of the alternating current voltage. The heating element is a part of a resistance of the resonant circuit. The converting device can include a control circuit for producing alternating control signals, a base driving circuit controlled by the control signals and having two outputs connected respectively to a base of a switching transistor. The device can also include a protecting circuit for picking up energy during opening of the respective switching transistors and returning the picked-up energy to the d.c. network.

Abstract: In a circuit arrangement for operating a multiphase synchronous motor (10) on a direct current voltage main current valves (15-18), which are successively actuated via a ring counter (38), are connected in series with the phases (w.sub.1 -w.sub.4) of the armature winding (12) of the motor (10). A ring counter switching device (19) advances the ring counter (38) by pulses derived from the comparison of in voltages dropped across two blocked current valves (15-18). To restrict the self control range of the motor to an angular range which is much smaller than half a period, of the voltage drop decreasing in the course of time is additionally compared with a set voltage (k U.sub.S) by the ring counter switching device (19) and the ring counter advancement is enabled only for as long as this voltage drop is greater than the set voltage value.

Abstract: The same electrical machine geared to the fly-wheel of a vehicle engine serves as the starter and as the generator. This machine is excited by permanent magnets on a rotor and its stator is wound with two phase windings offset from each other by 90.degree. electrical. Half-bridge rectifiers are utilized in a circuit cooperating with the center tap of each winding for charging the battery in generator operation, cooperating with a unit including at least one MOSFET for regulating the charging current. In motor operation the winding center taps are connected to one pole of the battery and the common connection of the MOSFETs is connected to the other pole of the battery so that these devices can operate as d.c. to a.c. converter elements for providing pulses in proper sequence to the erstwhile generator to make it operate as a motor.

Abstract: Commutation of the stator windings of a synchronous motor energized by a d.c. supply is controlled by comparison of voltages induced in two stator windings neither of which is a winding previously energized nor a winding about be energized. For speed control, turning on of the winding next energized can be delayed controllably. Motor current during start-up or overload can be limited by chopping, with a variable keying ratio, the d.c. supply connection to the motor during the first 80% of the period of energization of each stator winding. For reducing delay in starting, the rotor may be brought into a particular position automatically every time the motor is stopped or, in the case of a fuel pump motor for an injection type internal combustion engine, just before starting the engine through a supplementary contact controlled by the ignition key. Starting up can be provided by two initial pulses of commutation provided by means of an oscillator and two transistors.

Abstract: To turn a thyristor, particularly a high-voltage thyristor, ON, and to connect the thyristor and the utilization circuit to a power source, a charge capacitor is connected to a charging circuit to charge the capacitor when the thyristor is blocked or in OFF state. A controlled switch, typically a transistor 20, is connected to the charge capacitor 19 and connects the charge capacitor to the gate electrode of the thyristor, when the controlled switch is turned ON; a control circuit is connected to the controlled switch which includes an opto-coupler 28 to control its conduction. Preferably, a threshold sensitive element such as a Zener diode 25, or a four-layer diode 30, is included in the controlled switch transistor base circuit to provide for sharp turn-on characteristics.