Low dissipation current sensing system for a switched DC power supply

摘要

A system and method for measuring the load current in a power supply driven by switched transformer or the like. Rectified rectangular waveform input voltage pulses are interrupted to exhibit a less than 100 percent duty cycle with an off state value approaching zero volts. A filtering inductor is situated in normal manner between the input voltage pulses and the load. Preferably, a capacitor is connected across the load. A freewheeling diode and sensing resistor are connected across the less than 100 percent duty cycle rectangular input voltage. The peak values of the current pulses through the sensing resistor have been determined to be related to the load current of the power supply. The voltage drop across the resistor is amplified, detected and used to regulate the magnitude of the limited duty cycle input voltage. The voltage drop across the resistor may be used to limit the power supply output current or to balance current in parallel configurations of multiple power supplies. The placement of the sensing resistor in the path of the freewheeling diode allows load current measurement with minimum power dissipation.