Abstract: A fluorescent lamp driver circuit has regulator (SR); primary circuit of transformer (TF); electronic switches (TR2A and TR2B) and current sensing device (Rsense) connected successively in series across power supply (PSF). Controller (CTRL) is connected to create a feed back loop. The secondary circuit of transformer (TF) is coupled to fluorescent lamps (U10 and U11) via ballast capacitors (C1 and C2). Diode (D1) creates unidirectional current flow, so current sensing device (Rsense) indicates only energy input to lamps (U10 and U11). Capacitors (C1 and C2) are placed physically very close to their respective lamps, enabling good matching of currents through lamps (U10 and U11). Pulse width modulator (PM) with predetermined input is connected to regulator (SR) and, via delay circuit (TD) to controller (CTRL), thus permitting a larger dimming ratio, and further control of input power.

Abstract: A self contained hand held fetal detector comprises an ultrasonic receiver and transmitter (23). Selectively actuable ultrasonic receiving and transmitting circuits (25,21) are connected to the ultrasonic receiver and transmitter (23) with a controller (24) for actuating either the ultrasonic receiving circuit (25) or the ultrasonic transmitting circuit and a loudspeaker (29) connected to the ultrasonic receiving circuit (25) for generating an audio output signal. The detector comprises a single unit (13) and the controller (24) modifies at least one of the transmitted and received signals, to prevent interference in the received ultrasound.