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Light-emitting diode driver and its control method

A light-emitting diode and driver technology, which is applied in the direction of electroluminescence light source, light source, electric light source, etc., can solve the problem of reducing switching frequency and so on

Active Publication Date: 2016-04-27
ANALOG DEVICES INT UNLTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In Figure 3, it is assumed that the rising ramp increases the switching frequency, but in other types of systems, the rising ramp decreases the switching frequency

Method used

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  • Light-emitting diode driver and its control method
  • Light-emitting diode driver and its control method
  • Light-emitting diode driver and its control method

Examples

Experimental program
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Embodiment Construction

[0033] Figure 4 Illustrating the conventional system of FIG. 1 , but where the SSC signal is synchronized with the PWM pulses used to dim the LED 14 . The circuit can be referred to as an LED driver using SSFM with controllable dimming.

[0034] Converter 12 comprises a conventional controllable oscillator such as that shown in Figure 2, the frequency of which varies with a variable input voltage. In another embodiment, the frequency can be varied under the control of any variable signal, such as current. Converter 12 may generate a regulated current or a regulated voltage.

[0035]The SSC ramp generator 30 generates a ramp signal. The ramp signal can self-oscillate, but can be reset to the starting level by the reset signal. For example the ramp generator may comprise a capacitor charged with a fixed current source to generate a ramp up voltage until the voltage reaches a limit. The current source may be internal to converter 12 . When the upper limit is detected, eg us...

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PUM

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Abstract

The invention relates to a light emitting diode driver and a control method thereof. A technique for eliminating perceived flicker of LEDs dimmed by PWM pulses is disclosed. A controllable oscillator controls the switching frequency of a converter for supplying a regulated current or a regulated voltage. The converter controls the first switch at the switching frequency. A spread spectrum control (SSC) circuit generates a variable second signal level for controlling the oscillator to vary the switching frequency during operation. A PWM dimming circuit generates a PWM pulse train that controls a switch in series with the LED. The SSC circuit is synchronized with the PWM pulses to generate the same second signal level at the beginning of each PWM pulse, thereby forcing the switching frequency of the converter to be substantially the same at the beginning of each PWM pulse with a constant pulse width. Repetitive drive current waveforms eliminate perceivable flickering of the LEDs.

Description

technical field [0001] The present invention relates to dimming light emitting diodes (LEDs) using pulse width modulation (PWM) and in particular to a technique for reducing flickering of LEDs when using spread spectrum frequencies to control switching of switch mode regulators. Background technique [0002] Figure 1 illustrates a known type of system for driving and dimming LEDs. Many different types of systems are known. [0003] A conventional DC-DC converter 12 receives an input voltage Vin. The converter 12 typically boosts the voltage to slightly above the combined forward voltage of the series connected LEDs 14 , such as 40 volts, in order to cause a predetermined regulated current to flow through the LEDs 14 . Any type of converter can be used, such as a flyback converter. Other types of converters, such as buck converters, can be used depending on the relationship between the input voltage and the required drive voltage. [0004] Converter 12 adjusts the duty cy...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H05B37/02H05B44/00
CPCH05B45/10Y02B20/30H05B45/38
Inventor 齐昕埃里克·S·杨基思·D·索露莎
Owner ANALOG DEVICES INT UNLTD