CN105185297A - Pulse width modulation switching-on method and system of LED display driving - Google Patents
Pulse width modulation switching-on method and system of LED display driving Download PDFInfo
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- CN105185297A CN105185297A CN201510427606.8A CN201510427606A CN105185297A CN 105185297 A CN105185297 A CN 105185297A CN 201510427606 A CN201510427606 A CN 201510427606A CN 105185297 A CN105185297 A CN 105185297A
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Abstract
The invention discloses a pulse width modulation switching-on method and system of LED display driving. The method includes the following steps that: a pulse width modulation period tPMW and the switching-on time tON of an LED in the tPMW are obtained; a difference value time period which is obtained through subtracting tON from tPMW can be obtained; a time point in tPMW is determined as a reference time point, and a target time period from a starting time point to the reference time point of tPMW is calculated; and the ratio x of the target time period to tPMW is calculated; the product of x and the difference value time period is adopted as a first time point; the sum of the product and the switching-on time is adopted as a second time points; after tPMW begins, the output of pulse width modulation is initiated at the first time point, and the output of pulse width modulation is stopped at the second time point; a time period length value from the first time point to the reference time point is equal to the product value of the switching-on time and the ratio, and line output voltage is stabilized before PWM switching on, and therefore, the voltage difference of the line output voltage and column current is stable in the PWM switching-on time, and current flowing through the LED is stable.
Description
Technical field
The present invention relates to technical field of LED display, particularly relate to a kind of pulse-length modulation conduction method and system of LED display driver.
Background technology
Fig. 1 shows the composition structure of dynamic LED display screen, comprising: row address bus 1, row voltage source 2, LED display matrix 3, briliancy input clock (GCLK) 4, data input bus (DIB) 5, row current source 6, data-out bus 7, constitute J capable K row display matrix, this matrix is called LED [J, K], wherein the LED of the capable n row of m is designated LED [m, n].
Fig. 2 shows the output timing diagram of actual pulse width modulation (PWM), and Y [m] is m line output voltage, OUT [n] for n row current source waveform, PWM synchro control be PWM synchronous control signal, td1 for row export the stand-by period, t
oNfor LED ON time within the PWM cycle, t
oFFfor the shut-in time of LED within the PWM cycle, td2 is the row closedown stand-by period, existing PWM mode, its defect is, by the impact of the ascending velocity of row voltage source, Y [m] outputs to operating voltage, need certain rise time, the number that this rise time can be subject to row current source affects, when row electric current is more, the ascending velocity of Y [m] is slower, tr is the rise time of Y [m], td1 is row wait output time, as tr>td1, ts=tr-td1, in ts, by the impact of Y [m] voltage, Y [m] is unstable with the pressure reduction of OUT [n] during ts, also be unstable with regard to result in the electric current flowing through LED, thus the problem of the little luminance nonuniformity of LED display system can be caused, the output point of existing row current source is all start at B point, can increase the time of tr further, at A point, because the conducting simultaneously of row current source causes momentary current maximum, very strong electromagnetic interference (EMI) EMI can be produced.
Summary of the invention
In view of this, fundamental purpose of the present invention is the pulse-length modulation conduction method and the system that provide a kind of LED display driver, and can stablize in guarantee LED current, low briliancy conducting is even.
For achieving the above object, the invention provides a kind of pulse-length modulation conduction method of LED display driver, comprising:
Obtain pulse width modulation period and the ON time of LED in pulse width modulation period;
Calculate the differential time section that described pulse width modulation period deducts described ON time;
Determine that a time point in described pulse width modulation period is reference time point, calculate the object time section put from the start time point of described pulse width modulation period to the described reference time;
Calculate the ratio of described object time section and described pulse width modulation period;
Calculate the product of described ratio and described differential time section, as very first time point;
Calculate described product and described ON time and, as the second time point;
During described very first time point after from described pulse width modulation period, start the output of pulse-length modulation, and from described pulse width modulation period after described second time point time, the output of stop pulse width modulated;
It is equal that product value and the described very first time of described ON time and described ratio put the time period length value that the described reference time puts.
Preferably, when the described very first time after from described pulse width modulation period puts, the output starting pulse-length modulation comprises:
Judge current time be whether from described pulse width modulation period after described very first time point, if so, then trigger pulse width modulation exports.
Preferably, during described second time point after from described pulse width modulation period, the output of stop pulse width modulated comprises:
Judge current time be whether from described pulse width modulation period after described second time point, if so, then close pulse-length modulation and export.
Present invention also offers a kind of pulse-length modulation conducting system of LED display driver, comprising:
PWM period register, PWM briliancy register, subtracter, offset bit register, shift unit, totalizer and conduction module;
Described PWM period register is for obtaining pulse width modulation period;
Described PWM briliancy register is for obtaining the ON time of LED in pulse width modulation period;
Described subtracter deducts the differential time section of described ON time for calculating described pulse width modulation period;
Described subtracter is for determining that a time point in described pulse width modulation period is reference time point, calculate the object time section put from the start time point of described pulse width modulation period to the described reference time, and calculate the ratio of described object time section and described pulse width modulation period;
Described shift unit for calculating the product of described ratio and described differential time section, as very first time point;
Described totalizer for calculate described product and described ON time and, as the second time point;
When described conduction module is used for the described very first time point after from described pulse width modulation period, start the output of pulse-length modulation, and from described pulse width modulation period after described second time point time, the output of stop pulse width modulated.
Preferably, described conduction module comprises:
First comparer, the second comparer and trigger;
Described first comparer for judge current time be whether from described pulse width modulation period after described very first time point;
Described second comparer for judge current time be whether from described pulse width modulation period after described second time point;
When described trigger is used for the point of the described very first time after described pulse width modulation period starts, trigger pulse width modulation exports, and during described second time point after from described pulse width modulation period, closes pulse-length modulation and export.
Preferably, described trigger is rest-set flip-flop.
Apply pulse-length modulation conduction method and the system of a kind of LED display driver provided by the invention, obtain pulse width modulation period t
pMWand LED is at t
pMWoN time t
oN; Calculate t
pMWdeduct t
oNdifferential time section; Determine t
pMWan interior time point is reference time point, calculates from t
pMWstart time point to the object time section of described reference time point; Calculate described object time section and t
pMWratio x; Calculate the product of x and described differential time section, as very first time point; Calculate described product and described ON time and, as the second time point; From t
pMWthe described very first time after beginning, when putting, starts the output of pulse-length modulation, and from t
pMWduring described second time point after beginning, the output of stop pulse width modulated; X is greater than 0 and is less than 1, it is equal with the product value of described ON time and described ratio that the described very first time puts the time period length value that the described reference time puts, line output voltage is stablized before PWM conducting, stablize with row electric current pressure reduction in PWM ON time like this, flow through the current stabilization of LED, can ensure that low briliancy conducting is even.
Accompanying drawing explanation
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only embodiments of the invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to the accompanying drawing provided.
Fig. 1 is the structural representation of existing dynamic LED display screen;
Fig. 2 is the output timing diagram of actual pulse width modulation (PWM);
Fig. 3 is embodiment one process flow diagram of the pulse-length modulation conduction method of a kind of LED display driver of the present invention;
Fig. 4 is the output voltage wave of embodiment one reality of the pulse-length modulation conduction method of a kind of LED display driver of the present invention;
Fig. 5 is embodiment two structural representation of the pulse-length modulation conducting system of a kind of LED display driver of the present invention.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.
The invention provides a kind of pulse-length modulation conduction method of LED display driver, Fig. 3 shows the process flow diagram of the embodiment 1 of the pulse-length modulation conduction method of LED display driver of the present invention, comprising:
Step S101: obtain pulse width modulation period and the ON time of LED in pulse width modulation period;
Step S102: calculate the differential time section that described pulse width modulation period deducts described ON time;
Step S103: determine that a time point in described pulse width modulation period is reference time point, calculate the object time section put from the start time point of described pulse width modulation period to the described reference time;
Step S104: the ratio calculating described object time section and described pulse width modulation period;
Step S105: the product calculating described ratio and described differential time section, as very first time point;
Step S106: calculate described product and described ON time and, as the second time point;
Step S107: during described very first time point after from described pulse width modulation period, start the output of pulse-length modulation, and from described pulse width modulation period after described second time point time, the output of stop pulse width modulated;
It is equal that product value and the described very first time of described ON time and described ratio put the time period length value that the described reference time puts.
As shown in Figure 4, be the output voltage wave of the present embodiment reality, at a PWM cycle t
pWMin, namely in the AC time period, B point is a bit in AC time shaft, i.e. reference point, x=t (A, B)/t (A, C), 0<x<1; The pulsewidth of PWM cycle conducting OUT [n] is t
oN, with B point for reference point, by t
oNbe divided into two parts, i.e. t (E, B)=x*t
oN, t (B, F)=(1 – x) * t
oN, the starting point that PWM exports is E, t (E, F) is PWM output ON time t
oN; At PWM cycle t
pWMin, meet t (E, B)/t (A, B)=t (B, F)/t (B, C)=t
oN/ t
pWM; PWM exports with B point for reference point, extends to both sides, and form complete PWM and export, E is very first time point, and F is the second time point.
Start with the starting point A in PWM cycle, first calculate the time span of very first time point t (A, E), t (A, E)=x* (t
pWM– t
oN), after time delay t (A, E), PWM exports conducting; With the starting point that E point exports for PWM, time delay t
oNin the cycle, to the second time point F, PWM has exported.
Because the ON time of each LED is determined by the content of the PWM register of correspondence, therefore the starting point of conducting is only relevant with the content of PWM Cycle Length and corresponding register, after LED display system configures, the PWM cycle is fixing, therefore the opening point of row current source only can be relevant to corresponding content of registers, will not necessarily can open at all row current sources of A point so simultaneously simultaneously, there is no the concentrated dash current of A point under traditional approach, after the dispersion of firing point time, start-up point energy spectrometer can be made, the energy frequency spectrum diffusion of EMI, reduce the EMI interference of system.
For low briliancy PWM, Y [m] when E point, export and stablize, like this within the EF time period, the pressure reduction between Y [m] and OUT [n] is stable, and the electric current flowing through LED [m, n] is exactly stable, and low briliancy conducting is even.
The pulse-length modulation conduction method of a kind of LED display driver that application the present embodiment provides obtains pulse width modulation period t
pMWand LED is at t
pMWoN time t
oN; Calculate t
pMWdeduct t
oNdifferential time section; Determine t
pMWan interior time point is reference time point, calculates from t
pMWstart time point to the object time section of described reference time point; Calculate described object time section and t
pMWratio x; Calculate the product of x and described differential time section, as very first time point; Calculate described product and described ON time and, as the second time point; From t
pMWthe described very first time after beginning, when putting, starts the output of pulse-length modulation, and from t
pMWduring described second time point after beginning, the output of stop pulse width modulated; X is greater than 0 and is less than 1, it is equal with the product value of described ON time and described ratio that the described very first time puts the time period length value that the described reference time puts, line output voltage is stablized before PWM conducting, stablize with row electric current pressure reduction in PWM ON time like this, flow through the current stabilization of LED, can ensure that low briliancy conducting is even.
Present invention also offers a kind of pulse-length modulation conducting system of LED display driver, the embodiment one of present system specifically comprises:
PWM period register, PWM briliancy register, subtracter, offset bit register, shift unit, totalizer and conduction module;
Described PWM period register is for obtaining pulse width modulation period;
Described PWM briliancy register is for obtaining the ON time of LED in pulse width modulation period;
Described subtracter deducts the differential time section of described ON time for calculating described pulse width modulation period;
Described subtracter is for determining that a time point in described pulse width modulation period is reference time point, calculate the object time section put from the start time point of described pulse width modulation period to the described reference time, and calculate the ratio of described object time section and described pulse width modulation period;
Described shift unit for calculating the product of described ratio and described differential time section, as very first time point;
Described totalizer for calculate described product and described ON time and, as the second time point;
When described conduction module to be used for after from described pulse width modulation period to described very first time point, start the output of pulse-length modulation, and from described pulse width modulation period after to described second time point time, the output of stop pulse width modulated.
The pulse-length modulation conducting system of the LED display driver that application the present embodiment provides, line output voltage is stablized before PWM conducting, stablizes like this, flow through the current stabilization of LED in PWM ON time with row electric current pressure reduction, can ensure that low briliancy conducting is even.
Fig. 5 shows the structural representation of the pulse-length modulation conducting system embodiment two of LED display driver of the present invention, and corresponding to above-described embodiment, described conduction module comprises:
First comparer, the second comparer and trigger;
Described first comparer for judge current time be whether from described pulse width modulation period after described very first time point;
Described second comparer for judge current time be whether from described pulse width modulation period after described second time point;
When described trigger to be used for after described pulse width modulation period starts to described very first time point, trigger pulse width modulation exports, and after from described pulse width modulation period to described second time point time, close pulse-length modulation and export.
Start counting with briliancy input clock GCLK in the present embodiment, the first comparer compares value and the x* (t of PWM counter
pWM– t
oN), when both are equal, trigger PWM and export; Second comparer compares value and the x*t of PWM counter
pWM+ (1-x) * t
oN, when both are equal, close PWM and export, PWM exports ON time t
oN, described trigger can be rest-set flip-flop.
It should be noted that, each embodiment in this instructions all adopts the mode of going forward one by one to describe, and what each embodiment stressed is the difference with other embodiments, between each embodiment identical similar part mutually see.
Finally, also it should be noted that, in this article, the such as relational terms of first and second grades and so on is only used for an entity or operation to separate with another entity or operational zone, and not necessarily requires or imply the relation that there is any this reality between these entities or operation or sequentially.And, term " comprises ", " comprising " or its any other variant are intended to contain comprising of nonexcludability, thus make to comprise the process of a series of key element, method, article or equipment and not only comprise those key elements, but also comprise other key elements clearly do not listed, or also comprise by the intrinsic key element of this process, method, article or equipment.When not more restrictions, the key element limited by statement " comprising ... ", and be not precluded within process, method, article or the equipment comprising described key element and also there is other identical element.
Be described in detail method and system provided by the present invention above, apply specific case herein and set forth principle of the present invention and embodiment, the explanation of above embodiment just understands method of the present invention and core concept thereof for helping; Meanwhile, for one of ordinary skill in the art, according to thought of the present invention, all will change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention.
Claims (6)
1. a pulse-length modulation conduction method for LED display driver, is characterized in that, comprising:
Obtain pulse width modulation period and the ON time of LED in pulse width modulation period;
Calculate the differential time section that described pulse width modulation period deducts described ON time;
Determine that a time point in described pulse width modulation period is reference time point, calculate the object time section put from the start time point of described pulse width modulation period to the described reference time;
Calculate the ratio of described object time section and described pulse width modulation period;
Calculate the product of described ratio and described differential time section, as very first time point;
Calculate described product and described ON time and, as the second time point;
During described very first time point after from described pulse width modulation period, start the output of pulse-length modulation, and from described pulse width modulation period after described second time point time, the output of stop pulse width modulated;
It is equal that product value and the described very first time of described ON time and described ratio put the time period length value that the described reference time puts.
2. the pulse-length modulation conduction method of LED display driver according to claim 1, is characterized in that, when the described very first time after from described pulse width modulation period puts, the output starting pulse-length modulation comprises:
Judge current time be whether from described pulse width modulation period after described very first time point, if so, then trigger pulse width modulation exports.
3. the pulse-length modulation conduction method of LED display driver according to claim 2, is characterized in that, during described second time point after from described pulse width modulation period, the output of stop pulse width modulated comprises:
Judge current time be whether from described pulse width modulation period after described second time point, if so, then close pulse-length modulation and export.
4. a pulse-length modulation conducting system for LED display driver, is characterized in that, comprising:
PWM period register, PWM briliancy register, subtracter, offset bit register, shift unit, totalizer and conduction module;
Described PWM period register is for obtaining pulse width modulation period;
Described PWM briliancy register is for obtaining the ON time of LED in pulse width modulation period;
Described subtracter deducts the differential time section of described ON time for calculating described pulse width modulation period;
Described subtracter is for determining that a time point in described pulse width modulation period is reference time point, calculate the object time section put from the start time point of described pulse width modulation period to the described reference time, and calculate the ratio of described object time section and described pulse width modulation period;
Described shift unit for calculating the product of described ratio and described differential time section, as very first time point;
Described totalizer for calculate described product and described ON time and, as the second time point;
When described conduction module is used for the described very first time point after from described pulse width modulation period, start the output of pulse-length modulation, and from described pulse width modulation period after described second time point time, the output of stop pulse width modulated.
5. the pulse-length modulation conducting system of LED display driver according to claim 4, it is characterized in that, described conduction module comprises:
First comparer, the second comparer and trigger;
Described first comparer for judge current time be whether from described pulse width modulation period after described very first time point;
Described second comparer for judge current time be whether from described pulse width modulation period after described second time point;
When described trigger is used for the point of the described very first time after described pulse width modulation period starts, trigger pulse width modulation exports, and during described second time point after from described pulse width modulation period, closes pulse-length modulation and export.
6. the pulse-length modulation conducting system of LED display driver according to claim 5, is characterized in that, described trigger is rest-set flip-flop.
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