Lag mode LED driver with accurate average current and method

Abstract

The invention relates to a lag mode LED driver which is used for providing a driving current to an LED. The lag mode LED driver is characterized by comprising a power level, a first sensor, a first signal source, a lag comparison circuit, a second signal source and a feedback loop, wherein the power level is used for providing the driving current; the first sensor is coupled with the power level and used for sensing the driving current to generate a first sensing signal; the first signal source provides a first reference signal; the lag comparison circuit is connected with the power level, the first sensor and the first signal source and generates a control signal to the power level according to the first sensing signal and the first reference signal so as to control a peak value and a valley value of the driving current; the second signal source provides a second reference signal; and the feedback loop is connected with the first signal source and the second signal source and generates a feedback signal to the first signal source according to a second sensing signal related to the driving current and the second reference signal so as to regulate the first reference signal.

Description

technical field [0001] The invention relates to an LED driver, in particular to a hysteretic mode LED driver. Background technique [0002] Such as figure 1 As shown, the hysteretic mode LED driver 10 is used to provide the driving current IL to the LED 12 . In the hysteretic mode LED driver 10, the power stage 13 provides the driving current IL to the LED 12 in response to the control signal Sc, and the sensor 14 senses the driving current IL to generate an induction signal Ic. The reference signal Vref1 controls the duty cycle ratio (duty) of the control signal Sc, and further controls the peak and valley values ​​of the driving current IL to control the average value of the driving current IL. The power stage 13 includes an inductor L, a switch MN and a diode D1, wherein the inductor L is connected between the cathode of the LED 12 and the switch MN, and the diode D1 is connected between the inductor L and the power input terminal VIN. The hysteresis comparator circuit...

AI Technical Summary

Problems solved by technology

However, due to the delay caused by the comparator 18, when the sensing signal Vcomp rises to be greater than the reference signal Vref1, it takes a while for the switch MN to close, as shown in the waveform 56, so the actual driving current IL will have a larger peak value, As shown in waveform 50, this causes the actual average current to be greater than the ideal average current, as shown in waveforms 52 and 60

[0005] Therefore, there are above-mentioned inconveniences and problems in the known hysteretic mode LED driver.

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