Abstract: A power driver having a power transistor (15) uses a disable unit (17) to disable the transistor (15) upon sensing a short circuit condition. No current sense resistors are used. The base-emitter voltage of the transistor (15) is compared by a comparator (14) with a reference signal provided by a reference signal unit (16) to determine the existence or absence of a short circuit condition. In the presence of a short circuit, the comparator (14) provides a fault detected signal to the disable unit (17). The disable unit functions to deny the control signal to the transistor (15) and to ground the base of the power transistor (15) to thereby doubly ensure disablement. In addition, the disable unit (17) has memory and will disable the transistor (15) until the control signal recycles.

Abstract: A discriminating metal detector that can compensate for ground minerals includes an oscillator circuit having at least two attenuation coils physically located in a probe of the metal detector for ground control. The probe also includes a resonant LC circuit having an inductive coil on the same plane as the attenuation coils but on a different axis than the attenuation coils. The attenuation coils of the oscillator circuit have no magnetic effect on the inductive coil or on the natural response of the inductive coil to metal objects. The attenuation coils of the oscillator operate at a substantially higher frequency than the inductive coil of the resonant LC circuit. As the resonant frequency of the discriminating LC circuit varies due to mineral changes in the ground the oscillator frequency shifts likewise proportionally in order to maintain a constant separation between the two frequencies.