Abstract: A high power semiconductor heat sink assembly comprising a semiconductor slice or chip and a heat sink structure. The heat sink structure comprises two spaced apart thermally and electrically conductive plates of for example aluminum between which the slice or chip is clamped. A device such as an O-ring is sandwiched between the plates so as to extend around the slice or chip and define a sealed compartment within which the slice or chip is located. An electrically non-conductive thermally conductive material such as a resin comprising alumina fills the space between the plates outside the compartment.

Abstract: To control the energization of an electric motor pulses of current are supplied to the motor from a power source, and the pulse mark/space ratio and the motor field strength are controlled to determine the output speed and torque of the motor. Means are provided for deriving information representative of the speed of the motor and the torque required to be developed by the motor at that speed, and means are provided for determining information representative of the pulse mark/space ratio and the motor field strength necessary to provide the required torque at the said derived speed such that power losses are minimized. This makes it possible to control the motor field strength and mark/space ratio in accordance with the determined information to achieve optimum efficiency.

Abstract: A field weakening circuit for an electric motor comprises a switching circuit the impedance of which is variable connected in parallel with a field winding of the motor. The switching circuit impedance is variable in dependence upon motor speed and current, either continuously or in a plurality of discrete steps, to control the current through the field winding.

Abstract: A control arrangement is described for dynamically braking a vehicle driven by an electric motor having a single field winding. The control arrangement comprises means for controlling the supply of power to the motor, a permanent magnet generator for mechanically coupling to the motor, and circuit closure means arranged to complete a circuit between the output of the generator and the field winding to dynamically brake the motor when the motor is de-energized by the controlling means.

Abstract: A controller for a series electric motor is described of the type comprising means for applying D.C. pulses to the motor and means for controlling the mark/space ratio of the pulses applied to the motor. The current through the motor is sensed and the maximum mark/space ratio which may be applied to the motor is reduced when the motor current is below a predetermined limit to avoid overspeed in light load conditions.