A pulse width modulation conduction method and system for LED display driving

Abstract

The invention discloses a pulse width modulation conduction method and system for LED display drive, which obtains the pulse width modulation period tPMW and the conduction time tON of the LED at tPMW; calculates the difference time period of tPMW minus tON; A time point is a reference time point, calculate the target time period from the starting time point of tPMW to the reference time point; calculate the ratio x of the target time period and tPMW; the product of x and the difference time period, As the first time point; the sum of the product and the conduction time is used as the second time point; at the first time point after the start of tPMW, the output of the pulse width modulation is started until the second time At the point, the output of the pulse width modulation is stopped; the time period length value from the first time point to the reference time point is equal to the product value of the conduction time and the ratio, and the row output voltage is before the PWM conduction has been stabilized, so that the voltage difference between the column current and the column current is stable during the PWM on-time, and the current flowing through the LED is stable.

Description

technical field [0001] The invention relates to the technical field of LED display, in particular to a pulse width modulation conduction method and system for LED display driving. Background technique [0002] figure 1 Shows the structure of the dynamic LED display, including: row address bus 1, row voltage source 2, LED display matrix 3, luminance input clock (GCLK) 4, data input bus 5, column current source 6, data output bus 7. A display matrix with J rows and K columns is formed. This matrix is ​​called LED[J, K], and the LEDs with m rows and n columns are identified as LED[m, n]. [0003] figure 2 It shows the output timing diagram of the actual pulse width modulation PWM, Y[m] is the output voltage of m rows, OUT[n] is the current source waveform of n columns, the PWM synchronous control is the PWM synchronous control signal, td1 is the column output waiting time, t ON is the conduction time of the LED in the PWM cycle, t OFF is the turn-off time of the LED in th...

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Problems solved by technology

[0003] figure 2 It shows the output timing diagram of the actual pulse width modulation PWM, Y[m] is the output voltage of m rows, OUT[n] is the current source waveform of n columns, the PWM synchronous control is the PWM synchronous control signal, td1 is the column output waiting time, t ON is the conduction time of the LED in the PWM cycle, t OFF is the turn-off time of the LED in the PWM cycle, and td2 is the row turn-off waiting time; the defect of the existing PWM mode is that, affected by the rising speed of the row voltage source, Y[m] output to the working voltage requires a certain Rise time, this rise time will be affected by the number of column current sources, when the column current is more, the rise rate of Y[m] will be slower, tr is the rise time of Y[m], td1 is the column waiting output time, When tr>td1, ts=tr-td1, within ts, affected by the voltage of Y[m], the voltage difference between Y[m] and OUT[n] is unstable during ts, which leads to flow The current through the LED is unstable, which will lead to the problem of uneven brightness of the LED display system; the output points of the existing column current sources all start at point B, which will further increase the time of tr; at point A , because the column current sources are turned on at the same time, resulting in the maximum instantaneous current, which will generate strong electromagnetic interference EMI

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