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 would not be changed in response to (or with) the variation (i.e. enabling and disabling) of a pulse-width-modulation (PWM) signal for dimming. In other words, the compensation voltage on the compensation pin (CMP) of the control chip would be maintained in unchanging regardless of whether the PWM signal for dimming is enabled or disabled. Therefore, an LED string at the current switching transient does not have the generation of over-shoot current.

主权项

1. A load driving apparatus, comprising:
a power conversion circuit configured to provide a direct current (DC) output voltage to a light emitting diode (LED) string in response to a high frequency component of a complex driving signal; a dimming circuit connected in series with the LED string, and configured to adjust a brightness of the LED string in response to a low frequency component of the complex driving signal; a control chip coupled to the power conversion circuit and the dimming circuit, and configured to:
generate a high frequency gate pulse-width-modulation signal in response to a comparison between a compensation voltage and a ramp signal;generate the complex driving signal in response to an “AND” operation of a low frequency dimming input pulse-width-modulation signal and the high frequency gate pulse-width-modulation signal to control operation of the power conversion circuit and the dimming circuit; andtransfer the compensation voltage to a compensation pin of the control chip in response to an enabling of the low frequency 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 low frequency dimming input pulse-width-modulation signal, such that the compensation voltage stored by the compensation circuit does not change with variation of the low frequency dimming input pulse-width-modulation signal.