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This paper presents a solution for battery-less power management circuits for micro-power energy converters, allowing energy harvesting systems to operate under continuous and intermittent conditions. The proposed trigger circuit is a fully passive, normally open, single pole, single throw, analog switch driven by a nano-power CMOS control unit. The trigger circuit starts in an OPEN state until the voltage, at its input terminal, reaches a high threshold, when it toggles to the CLOSED state. Once the input voltage drops below a low threshold, the trigger circuit returns to the OPEN state. In the CLOSED state, the trigger circuit creates a low resistance path between the input and output terminals, while at the OPEN state the input is isolated from the output. A first prototype was breadboarded by using discrete components for the sake of performance evaluation. Low threshold voltages (2.15 V and 1.15 V), sub-ohm CLOSED-state resistance, and power consumption requirements (in the order of 55.9 and 167.7 nW), coupled with relatively high energy extraction capabilities are confirmed by experimental results. These features put our proposed circuit among the best of its kind in the state-of-the-art circuits. To prove the effectiveness of the proposed trigger circuit, we have included it into a custom battery-less power management circuit for a piezoelectric energy harvesting system. The system was proven to work even under intermittent operating conditions, and lock-up phenomena, related to current surge effect, were avoided. [ABSTRACT FROM AUTHOR]