Abstract:
A method and circuit board arrangement for an intrinsically safe portable device includes two or more circuit boards having a frame structure that forms a contiguous boundary around a space between the circuit boards. In the space there are circuit components mounted on both circuit boards, and a connector that connect the two circuit boards. An encapsulant material fills the space bounded by the frame structure between the circuit boards to exclude airborne material from coming into contact with the encapsulated circuit components.
Abstract:
An intrinsically safe audio power circuit includes redundant electronic fuses disposed between the power input of an audio power amplifier and the battery source of the portable two-way radio device. The electronic fuse circuits are connected in series with each other, and each electronic fuse circuit includes a series switch transistor that can shut off the flow of current between the battery and the audio power amplifier. Each electronic fuse circuit also includes a current sense portion, and when the current through the electronic fuse circuits reaches a current threshold, it will shut off its series switch transistor using an active bias circuit in order to ensure sufficiently rapid shut off.