CN101610621A - Switching type light emitting diode driving circuit - Google Patents

Abstract

The invention provides a switchable light-emitting diode drive circuit, which includes a pulse width modulation generator, two or more dimming constant current sources and two or more light-emitting diodes (LEDs); The width modulation (PWM) generator outputs n groups of independent periodic pulse width modulation signals, and the cycle T and duty cycle d of each group of PWM signals are the same, but the pulse parts are sequentially connected in time, that is, d= 1/n, each set of PWM signals is output to a dimming constant current source to respectively output constant current driving power with the same timing as the input PWM signal to the LED array, so that two or more LED arrays can generate high-frequency sequential Lighting off, the lighting frequency of each LED array is 1/T Hz, and the overall lighting frequency is n/T Hz. Because the LEDs are not continuously lit, the driving current can be increased to increase the brightness, and the visual persistence of the naked eye can be used Effect to produce continuous high-brightness visual effects.

Description

Switchable LED driver circuit

technical field

This invention relates to light emitting diodes, and more particularly to circuits for driving two or more light emitting diodes.

Background technique

In recent years, the manufacturing and application technology of light-emitting diodes (LEDs) has made great progress. LEDs have gradually replaced traditional light sources due to their durability and power-saving advantages, such as fluorescent lamps (Fluorescent Lamp), incandescent lamps (Incandescent Lamp), Halogen bulbs (Halogen Bulb), traffic lights (Traffic Light) and LCD Panel (LCD Panel) backlight, etc. are no longer listed. Most of the LED lamps are recently developed towards the way of forming LED arrays to improve their brightness.

LED is a semiconductor component with a PN junction, which can emit light when the forward current (Forward Current) passes; LED has an important characteristic, that is, its luminous intensity (Luminous Intensity) is proportional to the forward current, that is, The larger the forward current, the higher the luminous intensity; however, a larger forward current will also generate higher heat. Excessive heat may cause permanent damage to the LED or greatly shorten its life. Therefore, LED manufacturers will determine the average forward current I _avg (Average Forward Current) for continuous use and another peak forward current I _peak ( Peak Pulse Forward Current), the latter must be higher than the former; when the LED is turned off at high frequency, a higher peak forward current can be applied to produce a higher instantaneous luminous intensity (Instantaneous Luminous Intensity); and when the LED is continuously lit When it is bright, only a lower average forward current can be applied, and the luminous intensity produced by it is continuous and consistent, but it must be lower than the instantaneous luminous intensity produced by the peak forward current mentioned above.

The known LED lamps all adopt the operation mode of continuous lighting, so only a lower average forward current can be applied. If the luminous intensity needs to be increased, it can only be solved by replacing a higher power LED, but there is no doubt , this move will consume a considerable purchase cost, and its heat dissipation problem will inevitably be more difficult to solve; on the other hand, the development of LED products is not achieved overnight, and each period has its development restrictions, and it is impossible to have a complete solution in the market. Products that meet the needs of use, such as a single LED above 10W, are not easy to find in the market. Therefore, if the luminous intensity of existing LED products can be increased without causing problems such as increased heat generation and shortened lifespan, there must be a demand for it.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a switchable LED driving circuit, which can save the purchase cost required for using higher power LEDs and avoid the accompanying heat dissipation problem.

To achieve the above purpose, the present invention provides a switchable LED drive circuit, the LED has an average forward current and a peak forward current, the LED drive circuit includes:

The pulse width modulation generator outputs n sets of independent periodic pulse width modulation signals, n is a natural number, and n≥2, and the cycle and duty cycle are the same, the duty cycle is the reciprocal of n, and its pulse part is in sequential in time;

Two or more dimming-type constant current sources each have a pulse width modulation signal input terminal, respectively connected to the pulse width modulation generator to receive the pulse width modulation signal; the dimming type constant current source is The output constant current is synchronously intermittent under the control of the pulse width modulation signal, and the output of the constant current is greater than the average forward current and less than or equal to the peak forward current;

Two or more light-emitting diodes are respectively connected to the dimming constant current source, and are driven by the intermittent constant current output by the dimming constant current source to flicker and turn off.

It can be seen from the above technical solutions that the present invention provides a switchable light-emitting diode driving circuit, which applies a high-frequency switching discontinuous current to two or more LEDs or LED arrays, and makes them light up sequentially, and the current It can be higher than the average forward current, and even reach the upper limit of the peak forward current, so as to increase the luminous intensity of the LED without increasing the heat generation of the LED, which can save the purchase cost required for using higher power LEDs, and can Avoid the ensuing heat dissipation problems.

Description of drawings

Fig. 1 is the circuit block diagram of the switching type light-emitting diode drive circuit of the present invention;

FIG. 2 is a timing diagram of a pulse width modulation (PWM) signal of the switching LED driving circuit of the present invention.

Explanation of reference signs

Pulse Width Modulation Generator 1

Dimming constant current source 2a～2f

LED Array 3a～3f

Detailed ways

The human eye has the characteristic of persistence of vision. For high-frequency flickering illuminants, it will produce the illusion of continuous light emission. For example, if a general fluorescent tube (fluorescent lamp) is driven by a transformer-type ballast, it will inevitably produce a flickering frequency twice the frequency of the AC type. (Because there are two zero-value exchange points in a sine wave cycle), that is, 60Hz mains power will produce a flicker frequency of 120Hz, which can still be detected by the human eye, and even have adverse effects on the human eye, so there is a relatively large High-end lamps use electronic ballasts to convert the power frequency to a high-frequency range of about 10-30kHz, increasing the flicker frequency to 20-60kHz. This high-frequency flicker is beyond the range that the human eye can detect, resulting in A visual effect of continuous light, in other words, for the LED, its flickering dots light up, but for the human eye, it is continuous light.

Please refer to Fig. 1, which is a circuit block diagram of a switchable light-emitting diode drive circuit of the present invention, mainly consisting of a pulse width modulation (PWM) generator 1, two or more dimming constant current sources (Dimming Constant Current Source) 2a ~ 2f and two or more LED arrays 3a ~ 3f, in which the number of dimming constant current sources 2a ~ 2f is the same as that of LED arrays 3a ~ 3f, and they are configured one-to-one. As shown in Fig. 1, six Group configuration is taken as an example, of course, it can also be any number of groups except one. On the other hand, it is described here that six LED arrays 3a-3f form a larger array. For example, if each LED array 3a-3f 3f is composed of 10 LEDs, then six LED arrays 3a-3f will form a larger array with 60 LEDs, of course, the single LED arrays 3a-3f can also be composed of a single LED, and Figure 1 uses six LEDs form an LED array as an example. In addition, the so-called dimming constant current sources 2a-2f refer to a DC constant current source with a PWM signal input terminal, the constant current output of the constant current source can be controlled by the PWM signal to generate synchronous interruption, such as Macroblock (Macroblock ) of the MBI6650 model DC/DC Converter integrated circuit, the dimming control terminal (DIM, Dimming Control Terminal) of the second pin of the DC-DC converter integrated circuit can be used as the PWM signal input terminal .

The PWM signal input terminals of the dimming constant current sources 2a-2f are respectively connected to the PWM signal output terminals of the PWM generator 1, and the constant currents output by the dimming constant current sources 2a-2f are controlled by the PWM signals. synchronous intermittent, and the output of the constant current is greater than the average forward current of the light-emitting diode, and less than or equal to the peak forward current of the light-emitting diode; the PWM generator 1 can generate the same number of PWM signals as the dimming constant current source, The PWM generator 1 outputs n sets of independent periodic PWM signals, n is a natural number, and n≥2, and outputs the PWM signals to the dimming constant current source respectively, and the timing of the PWM signals is shown in FIG. 2; A group of PWM signals are all periodic signals, and their cycle T and duty cycle d are the same, that is, the pulse period τ of each PWM signal is the same. Assuming that the number of driven LED arrays 3a-3f is n, the duty cycle d is the reciprocal of n, that is, d=1/n, and the pulses of the LED arrays are sequentially followed in time, that is, the first pulse received by the LED array 1 The pulse of a PWM signal is closely followed by the pulse of the second PWM signal received by the LED array 2. When the pulse of the first PWM signal ends, the pulse of the second PWM signal occurs, as shown in Figure 2, and the rest of the LED array 3 And so on to the LED array 6; assuming the pulse period τ=1ms, and n=6, then the cycle T of each group of PWM signals is equal to 6ms, and the duty cycle d=1/6≈16.67%.

Each group of PWM signals is output to the corresponding dimming-type constant current sources 2a-2f, so that the dimming-type constant current sources 2a-2f respectively output constant-current driving power with the same time sequence as the input PWM signals to each LED array 3a ~ 3f, make the LED arrays 3a ~ 3f produce the same high-frequency sequential lighting as in Fig. 2, that is, the lighting frequency of each single LED array 3a ~ 3f is 1/THz, and the overall lighting of all LED arrays 3a ~ 3f The extinguishing frequency is n/THz. As the figures illustrated above combined with Fig. 2, if τ=1ms, n=6, T=6ms, then the extinguishing frequency of each single LED array 3a-3f is 166.7Hz, and the overall point The off frequency is 1kHz, if the pulse period τ of each PWM signal is set to 0.1ms, the overall off frequency will rise to 10kHz; if τ=0.05ms, the overall off frequency will rise to 20kHz; if τ=0.0286ms , the overall flickering frequency will rise to 35kHz.

In the present invention, two or more LED arrays 3a-3f are extinguished with high-frequency cycles, and a driving current higher than the rated average forward current of the LEDs is applied to increase the instantaneous luminous intensity. The retention characteristics make the above-mentioned instantaneous luminous intensity form a visual effect equivalent to continuous luminous intensity, that is, to achieve the effect of improving the overall brightness.

The above descriptions are only specific illustrations of preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Equivalent transformations made by other persons familiar with the art shall be covered within the scope of the claims.

Claims (2)

1, a kind of switchover type light emitting diode (LED) drive circuit is characterized in that, this light-emitting diode has mean forward current and peak forward current, and this LED driving circuit comprises:

Pulse-width modulation generator, output n group be pulse-width modulation signal periodically independently, and n is a natural number, and n 〉=2, and its cycle and work period are all identical, and the work period is the inverse of n, and its segment pulse continues in time in regular turn;

Two or more light adjusting type constant current sources have the pulse-width modulation signal input part respectively, are connected to this pulse-width modulation generator respectively, receive this pulse-width modulation signal; This light adjusting type constant current source is exported decides that electric current is subjected to the control of this pulse-width modulation signal and interrupted synchronously, and the described output of deciding electric current is greater than described mean forward current, and is less than or equal to described peak forward current;

Two or more light-emitting diodes are connected to described light adjusting type constant current source respectively, and be subjected to that the light adjusting type constant current source exported intermittently decide current drives and point of scintillation is gone out.

2, switchover type light emitting diode (LED) drive circuit as claimed in claim 1 is characterized in that, described light-emitting diode is formed light emitting diode matrix.

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