METHOD AND APPARATUS FOR CALCULATING AN AVERAGE VALUE OF AN INACCESSIBLE CURRENT FROM AN ACESSIBLE CURRENT

摘要

In a power converter, a circuit determines an average value of an inaccessible current from an average value of an accessible current and a value of the operating duty cycle of the converter. A method of measuring an average value of an inaccessible current from a measured value of a current in a power converter by a duty cycle of a pulse width modulation (PWM) signal representing a duty cycle of the power converter. Coupling a voltage representing the measured value to an input of a low pass filter during a time period (D) and coupling the input of the low pass filter to a reference voltage during a time period (1−D).

主权项

1. In a switching power converter for driving an LED at a constant current comprising:
a circuit for regulating the converter so that the input current equals a constant times the duty cycle D of the converter, the circuit comprising: a main switch coupled to an input voltage source and being controlled by a Pulse Width Modulated (PWM) signal; an LED coupled between the input voltage source and the main switch; a current measuring device for measuring current through the main switch; a current amplifier coupled to the current measuring device and having an output coupled to a PWM signal generator, an output of the PWM signal generator being coupled to a control electrode of the main switch and a first node; a first switch coupled between the output of the PWM signal generator and a second node; a second switch coupled between the second node and a reference voltage; a current reference being coupled to the first node; an input to the current amplifier being coupled to the second node; the first switch being controlled by the PWM signal; the second switch being controlled by an inverse of the PWM signal, whereby the current through the LED can be maintained substantially constant.