Importance

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Abstract

A precharge circuit (20, 20′, 20″) charges at least one capacitor (22, 22′, 22″) associated with an electrical device with high capacitance, such as a motor (14) which drives a compressor (16) of the pneumatic system. One end of the at least one capacitor is connected with a high voltage bus (10). The other end of the at least one capacitor is connected by at least one charge limiting resistor (24, 24′, 24″) with a low reference node. When the at least one capacitor is charged at least to a preselected level, a control circuit (28, 28′, 28″) controls a switch (26, 26′, 26″) to bypass the current limiting resistor. In this manner, the current limiting resistors limit the surge current to charge the capacitors. Once the capacitors are charged, the resistors and their associated heat dissipation are removed from the circuit and only ripple current from across the capacitors flows through the switch reducing a required current carrying capacity and needed heat sinking for the switch.

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First Claim