On increasing the power available to an intrinsically safe wireless HART adapter

A wireless HART adapter is a self-powered device that harvests power from the 4 .. 20mA current loop. It wirelessly transmits the digital information present on the loop. Such adapters can be retrofitted to in-place current loops if the voltage loss induced by harvesting is small enough. This paper presents two techniques that more than double the power available to the adapter for a given induced voltage loss. Conversely, these techniques can be used to minimise the voltage loss for a given required power. More precisely, the first technique proposes a new topology for the coupling between HART modulation (AC) and energy harvesting (DC); the power efficiency is increased by 30% compared to a previously used topology. The second technique proposes and power-efficient transistor-based reverse-current blocking barrier. The proposed barrier performs much better in terms of power efficiency (up to 50%) than the conventional diode-based barrier; it is thus a valuable substitute in any low-voltage and low-power electronics that involves compliance with intrinsic safety requirements.