LOAD DRIVING APPARATUS RELATING TO LIGHT-EMITTING-DIODES

摘要

A load driving apparatus relating to light-emitting-diodes (LEDs) is provided. In the invention, a compensation voltage on a compensation pin (CMP) of a control chip does not change in response to (or with) the variation (i.e. enabling and disabling) of a pulse-width-modulation (PWM) signal for dimming. In other words, regardless of whether the PWM signal for dimming is enabled or disabled, the compensation voltage on the compensation pin of the control chip maintains unchanged. Therefore, an LED string at the current switching transient does not have the generation of over-shoot current. Furthermore, by detecting the compensation voltage on the compensation pin of the control chip, the control chip would enter into a shutdown status in response to the detected compensation voltage being greater than a predetermined threshold voltage for a predetermined counting time in case that the LED string is failure.

主权项

1. A load driving apparatus, comprising:
a power conversion circuit configured to provide a DC output voltage to a light emitting diode string; a dimming circuit connected in series with the light emitting diode string, and configured to adjust a luminance of the light emitting diode string; a control chip coupled to the power conversion circuit and the dimming circuit, and configured to:
generate a gate pulse-width-modulation signal in response to a comparison between a compensation voltage and a ramp signal to control operation of the power conversion circuit;generate a dimming output pulse-width-modulation signal in response to a dimming input pulse-width-modulation signal and the gate pulse-width-modulation signal to control operation of the dimming circuit;transfer the compensation voltage to a compensation pin of the control chip in response to an enabling of the dimming input pulse-width-modulation signal; and a compensation circuit coupled to the compensation pin, and configured to store the compensation voltage and compensate the compensation voltage so that the power conversion circuit stably provides the DC output voltage, wherein the control chip is further configured to stop transferring the compensation voltage to the compensation pin in response to a disabling of the dimming input pulse-width-modulation signal, such that the compensation voltage stored by the compensation circuit does not change with variation of the dimming output pulse-width-modulation signal, wherein the control chip enters into a shutdown status in response to the compensation voltage being greater than a predetermined threshold voltage for a predetermined counting time, so as to stop generating the gate pulse-width-modulation signal.