Avoid audio noise of a LED driver during PWM dimming
AssigneeRichtek Technology Corporation
InventorsTsung-Wei Huang, Shui-Mu Lin, Huan-Chien Yang, Nang-Ching Yeung, Ti-Ti Liu
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Abstract
A LED driver using a PWM signal for dimming control includes a power converter and a current regulator. The power converter provides an output voltage and a load current for a plurality of LEDs. The current regulator provides a load current dependent signal for the power converter to speed up load transient response caused by variation of the load current, to reduce the ripple of the output voltage, and thereby to avoid audio noise during PWM dimming.
Claims17
A LED driver using a PWM signal for dimming control, the LED driver comprising:
- a power converter providing an output voltage and a load current for a plurality of LEDs, the power converter comprising:
- an operational amplifier amplifying a difference between a reference voltage and a feedback signal related to the output voltage to thereby generate a compensation voltage;
- and
- a PWM logic circuit connected to the operational amplifier and configured to generate a control signal according to the compensation voltage and a ramp signal, the control signal having a duty ratio for regulating the output voltage;
- and
- a current regulator having a plurality of control terminals connected to the plurality of LEDs respectively, and configured to be responsive to the PWM signal to adjust a plurality of LED currents which flow through the plurality of control terminals respectively and determine the load current, and to generate a sense signal related to the load current, the sense signal being applied to the power converter to adjust the duty ratio.
A method for a LED driver using a PWM signal for dimming control, the method comprising the steps of:
- A.) providing an output voltage and a load current for a plurality of LEDs;
- B.) detecting the output voltage to generate a feedback signal;
- C.) amplifying a difference between a reference voltage and the feedback signal to thereby generate a compensation voltage;
- D.) according to the compensation voltage and a ramp signal, generating a control signal having a duty ratio for regulating the output voltage;
- E.) responsive to the PWM signal, adjusting a plurality of LED currents which flow through the plurality of LEDs respectively and determine the load current;
- and
- F.) generating a sense signal related to the load current to adjust the duty ratio.
Dependencies are inferred from the claim text.