Pulse width modulation (PMW) modulator circuit

Abstract

The invention discloses a pulse width modulation (PMW) modulation circuit which specifically comprises a first transmission door, a first current comparer, a first alternative selector, a reset set (RS) trigger, two input nor gates, a phase inverter, a first N-channel metal oxide semiconductor (NMOS) tube, an error accumulation capacitor and a comparer with the selection function. The PMW modulator circuit can certainly modulate external input PWM signals according to current actually flowing through a light-emitting diode (LED), the duty ratio is adjusted, the duty ratio of the PWM signals actually participating in dimming in the circuit can be dynamically and correspondingly modulated as actual current change of the LED, and a signal driving switch of the LED is controlled to enable the luminance of the LED in all digital pulse periods to be equal to a preset value to improve PME dimming accuracy.

Description

technical field [0001] The invention belongs to the field of integrated circuits and specifically designs a PWM modulation circuit, which is used in LED backlight chips to improve the precision of PWM dimming. Background technique [0002] As an important dimming method of LED backlight chips, PWM dimming has the advantages of simple application and high efficiency. In addition, compared with analog dimming, PWM dimming has the advantages of high precision, good linearization, and no color shift. . But the traditional PWM dimming has the following problems: [0003] (1) In the application of multiple strings of LEDs, due to the differences in the characteristics of the LEDs, the current on each string of LEDs is different, resulting in a deviation in the brightness of the LED light strings in each dimming cycle. [0004] (2) Since the establishment of the system loop takes a certain amount of time (such as figure 1 As shown: where the output signal COMP of the error ampli...

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Problems solved by technology

[0003] (1) In the application of multiple strings of LEDs, due to the difference in the characteristics of the LEDs, the current on each string of LEDs is different, resulting in a deviation in the brightness of the LED light strings in each dimming cycle

[0004] (2) Since the establishment of the system loop takes a certain amount of time (such as figure 1 As shown: where the output signal COMP of the error amplifier represents the establishment process of the system loop), then the loss of brightness will inevitably be introduced when the LED is turned on, resulting in a decrease in PWM dimming accuracy

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