Circuits for sensing current levels within a lighting apparatus incorporating a voltage converter

摘要

Circuits for sensing current levels within an apparatus are disclosed. In specific cases, a constant voltage power supply is used to power an LED lighting apparatus in which there are uncertainties within the forward voltages of the LEDs, which in turn creates uncertainty with respect to the current level flowing through the LEDs. To manage these uncertainties, the current flowing through the LEDs is measured by determining a voltage level across a known resistor and calculating the current level. To prevent the known resistor from causing a significant reduction in the efficiency of the overall light engine, the circuit includes one or more transistors in parallel with the known resistor to reduce the effective resistance in the LED circuit during times that the current is not being sensed.

主权项

1. A circuit comprising:
a voltage converter operable to receive an input voltage and generate an output voltage defined between a high voltage rail and a low voltage rail coupled to the output of the voltage converter; a current sense circuit coupled to the voltage converter at a node to receive a sense current, the current sense circuit comprising a resistor coupled in parallel with at least one transistor, the at least one transistor being activated during a first state of the current sense circuit to reduce the resistance of the current sense circuit and being deactivated during a second state; and a current determination apparatus coupled to the current sense circuit and operable to sample a current sense voltage at the node during the second state; wherein the voltage converter is operable to receive a voltage control signal to selectively allow the sense current to flow to the current sense circuit and the current determination apparatus is operable to sample the current sense voltage when the voltage converter is set to allow the sense current to flow to the current sense circuit.