Abstract: A security device for use with audio and video equipment installed in an automobile or other type of vehicle, such as a van or boat. The security device includes a module which is coupled to the equipment to be protected. The security device comprises an encoded security key which is plugged into a key receptacle to disarm and arm the module. The key includes logic for producing an encoded disarming signal and is of a size which can be easily carried on the person of the user. The module can be located at a space in the vehicle which is remote to the key receptacle thereby allowing otherwise inaccessible equipment to be conveniently secured from the passenger compartment of the vehicle for example. Without a proper encoded key, the equipment cannot be operated and is virtually useless if removed from the vehicle. To provide a further deterrent to theft, the module and/or equipment include a warning notice signifying the inoperative nature of the equipment without the key.

Abstract: A composite bridge amplifier has four output transistors in a bridge configuration. The transistor control terminals (gates or bases) are controlled by an input signal which is amplified in a phase splitter and voltage gain stage. The output terminals of the transistors receive a power signal which varies with the input signal at a level sufficient to maintain headroom above the output signal but to reduce power dissipation in the transistors. The power signal is produced by a switch connected between a floating power supply and a filter and operated at e.g. 200 kHz. The switch is operated by a pulse width modulated (pwm) signal derived from the absolute value of the input signal. A proportional integral controller is coupled between the filter output and the pulse width modulator for closed loop feedback. The output is aligned with the input signal by a phase shifter connected to the controller. Since there is no time delay in the input signal (i.e. audio) path, high performance is achieved at reduced cost.

Abstract: A composite bridge amplifier having four output metal oxide semi-conductor field effect transistors (mosfets) in a bridge configuration. The gates of the mosfets are controlled by an input signal which is amplified in a diamond differential amplifier phase splitter and voltage gain stage and then applied to the mosfet gates. The power terminals (sources and drains) of the mosfets receive a power signal which varies with the input signal at a level sufficient to maintain headroom above the output signal but to reduce power dissipation in the mosfets. The power signal is produced by a switch connected between a floating power supply and a filter and operated at e.g. 200 KHz. The switch is operated by a pulse width modulated (pwm) signal derived from the absolute value of the input signal. Because the power signal in effect tracks the output signal, little power is dissipated in the mosfets so that the amplifier can be made very compact.