CN102159009B - White light LED (light-emitted diode)-line pulse dimming circuit - Google Patents

Abstract

The invention provides a white light LED (light-emitted diode)-pulse dimming circuit and a dimming method. The white light LED-line pulse dimming circuit comprises a power supply, a pulse control module, a current conversion module and a constant current source driving module, wherein the pulse control module is used for outputting a line pulse sequence; the current conversion module is respectively connected to the power supply and the pulse control module and is used for generating a standard current according to a voltage output by the power supply and generating a voltage which gradually reduces according to the increasing of line pulse by the utilizing of the standard current and the line pulse sequence; and the constant current source driving module is connected to the current conversion module and the white light LED and is used for outputting a driving current which has a fixed proportion relation with the voltage outputted by the current conversion module to the white light LED. The dimming circuit has the advantages that the dimming is realized simply, the working is stable and the precision is high.

Description

White LED one-line pulse dimming circuit

technical field

The invention relates to the technical field of dimming of white light LEDs, in particular to a one-line pulse dimming circuit of white light LEDs.

Background technique

White LED (Light Emitting Diode, Light Emitting Diode) has many advantages that other traditional lighting sources cannot match, such as high luminous efficiency, low power consumption, long life, and environmental protection. At present, white LEDs have been widely used in the backlighting of display screens of various portable electronic devices.

The wavelength of the light emitted by the white LED is significantly affected by the current flowing through the LED, so in order to ensure the color of the emitted light is constant, the current flowing through the LED needs to be kept constant. Therefore, one of the main functions of the white LED driver chip is to provide a constant driving current output for the LED. At the same time, in order to adjust the brightness of the light, it is also necessary to adjust the current flowing through the LED.

Figure 1 is a typical application example of a white light driver chip. The cathodes of the four white LEDs are connected to the drive current output pin of the chip, and the anodes are connected to the power supply. Inside the chip, a constant current drive is generated on the pins of LED1~LED4 so that the current flowing through the white LED can remain constant when the external temperature, power supply voltage, and forward conduction voltage of the LED change. At the same time, the chip controls the gating of the entire chip through the EN terminal, and adjusts the size of the output current, thereby adjusting the brightness of the light.

Among them, the light intensity felt by the human eye can be adjusted by periodically turning on and off the driving current, that is, the light intensity emitted by the average current felt by the human eye can be adjusted by adjusting the duty cycle of the turn-on time. However, this dimming method needs to switch the current at a high frequency, which will cause certain interference to the power supply and other devices. If the frequency is within the audio frequency range, it will also generate noise that can be heard by the human ear. If the switching frequency is not high enough It also causes fluctuations in the emitted light that are perceived by the naked eye.

Contents of the invention

The purpose of the present invention is to provide a white light LED one-line pulse dimming circuit to solve the problems that the existing white light LED dimming method is easy to generate noise and visual fluctuations, and cause interference to power supply and other devices.

Another object of the present invention is to propose a one-line pulse dimming method for white LEDs to solve the problems that existing white LED dimming methods tend to generate noise and visual fluctuations, and cause interference to power supplies and other devices.

The invention proposes a white LED one-line pulse dimming circuit, which includes a power supply, a pulse control module, a current conversion module and a constant current source driving module. The pulse control module is used to output a one-line pulse sequence. The current conversion module is connected with the power supply and the pulse control module respectively, and is used to generate a reference current according to the voltage output by the power supply, and use the reference current and the one-line pulse sequence to generate a voltage that is gradually reduced according to the number of rising edges of one-line pulse. The constant current source driving module is respectively connected with the current conversion module and the white LED, and is used to output a driving current to the white LED with a fixed proportional relationship with the voltage output by the current conversion module.

According to the white LED one-line pulse dimming circuit described in the preferred embodiment of the present invention, the current conversion module further includes a reference current generation circuit, a current mirror, a switch circuit, a two-frequency divider and a voltage output circuit. The reference current generating circuit is connected with the power supply and is used to generate a reference current. The current mirror is connected with the reference current generating circuit, and is used to generate four currents by using the reference current. The switch circuit is connected with the current mirror and is used to control the on-off state of the four currents generated by the current mirror. The two frequency dividers are respectively connected with the pulse control module and the switch circuit, and are used to control the on-off state of the switch circuit by using the one-line pulse sequence output by the pulse control module, so that the four currents generated by the current mirror are all in binary form with the reference current Weight ratio relationship. The voltage output circuit is connected with the switch circuit, and is used for converting the total current of the four currents into a final voltage output.

According to the white light LED one-line pulse dimming circuit described in the preferred embodiment of the present invention, the two-frequency divider includes four D flip-flops, and the four D flip-flops are connected in stages, and the clock signal terminal of the first-stage D flip-flops is connected to Pulse control module, the reverse output terminals of the D flip-flops of the first three stages are connected to the data signal input terminals, and at the same time connected to the clock signal terminal of the D flip-flops of the next stage as the trigger signal of the next stage, and the D flip-flops of the fourth stage The negative output terminals of the flip-flops are connected with the data signal input terminals, and the forward output terminals of the four D flip-flops are connected with the switch circuits to control the on-off states of the four currents.

According to the white LED one-line pulse dimming circuit described in the preferred embodiment of the present invention, the reference current generating circuit includes an operational amplifier and a reference resistor, and the reference resistor is connected to an output terminal of the operational amplifier.

According to the white LED one-line pulse dimming circuit described in the preferred embodiment of the present invention, the voltage output circuit includes an operational amplifier and a resistor, and the resistor is connected between the output terminal of the operational amplifier and an input terminal.

According to the white LED one-line pulse dimming circuit described in the preferred embodiment of the present invention, the four currents generated by the current mirror are respectively 1, 2, 4 and 8 times the reference current.

According to the white LED one-line pulse dimming circuit described in the preferred embodiment of the present invention, the power supply is a bandgap reference voltage source.

The present invention further proposes a one-line pulse dimming method for a white LED, which includes the following steps: (1) generating a reference current according to a power supply voltage. (2) Using the reference current and a one-line pulse sequence to generate four currents in a binary weight proportional relationship with the reference current. (3) Convert the total current of the four currents into a voltage that decreases step by step according to the number of rising edges of the one-line pulse. (4) Output the drive current with a fixed proportional relationship with the voltage to the white light LED.

According to the white light LED one-line pulse dimming method described in the preferred embodiment of the present invention, it specifically uses the logic output of four D flip-flops connected in the form of a two-frequency divider to control the four channels and the reference current to form a binary weight ratio The current of the relationship, and convert the four currents into a voltage output.

According to the white LED one-line pulse dimming method described in the preferred embodiment of the present invention, the four currents are respectively 1, 2, 4 and 8 times the reference current.

Compared with the prior art, the beneficial effects of the present invention are: the present invention has the advantages of simple implementation, stable operation and high precision, and the circuit adopted in the present invention does not require a high switching frequency, effectively avoiding noise, visual The generation of fluctuations will not cause interference to other devices.

Description of drawings

FIG. 1 is a schematic diagram of an existing white light driver chip;

Fig. 2 is a structure diagram of an embodiment of a white LED one-line pulse dimming circuit of the present invention;

Fig. 3 is a circuit diagram of an embodiment of the current conversion module of the present invention;

Fig. 4 is a relation diagram between the logic state of ports b0-b3 and the logic level state of CLK signal;

Fig. 5 is a schematic diagram of the driving current change of the white LED of the present invention;

FIG. 6 is a flow chart of an embodiment of a one-line pulse dimming method for a white light LED according to the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings. Wherein, the "connection" between modules and circuits in the present invention is a direct or indirect electrical connection.

Please refer to FIG. 2 , which is a structural diagram of an embodiment of a white LED one-line pulse dimming circuit of the present invention, which includes a bandgap reference voltage source 21 , a pulse control module 22 , a current conversion module 23 and a constant current source driving module 24 . Both the gap reference voltage source 21 and the pulse control module 22 are connected to the current conversion module 23, and the current conversion module 23 is connected to the constant current source driving module 24 after passing through an amplifying circuit, and the constant current source driving module 24 is connected to four white LEDs.

Among them, the bandgap reference voltage source 21 is a relatively mature technology, which is not affected by the ambient temperature, and outputs a fixed bandgap reference voltage. The output of the pulse control module 22 is a one-line pulse sequence, which can be used to control the voltage output of the current conversion module 23 . The input of the current conversion module 23 is composed of a bandgap reference voltage source 21 and a pulse control module 22, which outputs a voltage that decreases step by step according to the number of rising edges of a line pulse. The constant current source drive module 24 is a functional module that provides constant current source drive for four white LEDs (LED1, LED2, LED3, LED4). The output drive current maintains a certain proportional relationship with the internally set current, and its The internal current is generated by the output voltage of the current conversion module 23 through a resistor.

Therefore, the driving current output by the constant current source driving module 24 can be changed through a one-line pulse sequence, and the light intensity emitted by each white LED can be adjusted. Since the dimming scheme of the present invention does not require a very high switching frequency, the generation of noise and visual fluctuations is effectively avoided, and at the same time, it does not cause interference to other devices.

It is worth noting that the current conversion module 23 is the core part of the present invention, which realizes the purpose of adjusting the voltage output by a one-line pulse sequence, thereby adjusting the final output driving current. The current conversion module 23 is described in detail here, please Referring to FIG. 3 , it is a circuit diagram of an embodiment of the current conversion module of the present invention. The current conversion module 23 includes a reference current generation circuit 31 , a current mirror 32 , a switch circuit 33 , a frequency divider 34 and a voltage output circuit 35 .

The reference current generating circuit 31 is connected to the bandgap reference voltage source 21, and includes an operational amplifier A4 and a reference resistor R1 for generating a reference current. The current mirror 32 is connected to the reference current generating circuit 31, which includes four mirror channels connected in parallel, and the currents on the four mirror channels are 1, 2, 4 and 8 times of the reference current respectively. The bias circuit 36 is connected to the current mirror 32 and is used to provide a cascode bias for the current mirror 32 . The switch circuit 33 is composed of four switch tubes, which are respectively connected in series to the four mirror channels of the current mirror 32 to control the opening and closing of the four currents. The voltage output circuit 35 is connected to the switch circuit 33 and includes an operational amplifier A5 and a resistor R2 for converting the total current of the four currents into a final voltage output.

The two frequency divider 34 is respectively connected with the pulse control module 22 and the switch circuit 33, which includes four D flip-flops B0 to B3, and the four D flip-flops are connected step by step, and the first-stage D flip-flop (D flip-flop B0) The clock signal terminal of the clock signal is connected to the pulse control module 22, and the reverse output terminals of the D flip-flops (D flip-flop B0, D flip-flop B1, D flip-flop B2) of the first three stages are connected to the data signal input terminal, and connected to the next stage The clock signal end of the D flip-flop is used as the trigger signal of the next stage. The reverse output end of the fourth-stage D flip-flop (D flip-flop B3) is connected to the data signal input end, and the positive Connect the four switch tubes of the switch circuit 33 to the output terminals b0~b3 to control the on-off state of the four currents, that is, the port b0 corresponds to the opening and closing of 1 times the reference current, and the port b1 corresponds to the opening and closing of 2 times the reference current And shutdown, and so on, port b2 controls 4 times the reference current, port b3 controls 8 times the reference current, the logic is high, the current is turned on, and the logic is low, the current is turned off.

The operating principle of this current conversion module 23 is:

First, a reference current is generated by the combination of operational amplifier A4 and R1, whose value is:

Iref=Vrefin/R1,

Wherein, Vrefin is the bandgap reference voltage output by the bandgap reference voltage source 21 .

The 1-times, 2-times, 4-times, and 8-times currents mirrored by the current mirror 32 are respectively recorded as I0, I1, I2, and I3. The logic bits of the four ports b0, b1, b2, and b3 respectively control the opening and closing of the four currents. The relationship between the logic state of each port b0 - b3 and the logic level state of the CLK signal is shown in FIG. 4 , where the CLK signal is a one-line pulse sequence output by the pulse control module 22 .

It can be seen from Figure 4 that the relationship between the change of the logic state of each port b0~b3 and the arrival of each rising edge of CLK is shown in Table 1:

Table 1

It can be found that if the combination of the logic states of b0~b3 is converted into decimal, it is exactly the count of the rising edge of the CLK pulse. Since the weight ratio between the current controlled by b0~b3 and the reference current is consistent with its weight in binary, the proportional relationship between the sum of the four currents and the reference current is the count of the rising edge of the CLK pulse. Let the sum of the four currents be Io, and the final output voltage of the operational amplifier A5 be Vo:

Io=I0+I1+I2+I3,

From the connection of operational amplifier A5 and resistor R2, we know:

Vo＝Vrefin－Io*R2

＝Vrefin－N*Iref*R2

= Vrefin - N*Vrefin/R1*R2,

Among them, N is the count of the rising edge of CLK pulse. If the design makes R2=16*R1, then there is: Vo=Vrefin-N/16*Vrefin, so when the rising edge of the first CLK pulse arrives, Vo becomes 15/16*Vrefin, when the second CLK After the rising edge of the pulse arrives, Vo becomes 14/16*Vrefin, and so on, the value of Vo decreases step by step, and the step size of each step is 1/16*Vrefin. When the number of CLK pulse rising edges exceeds 15, Vo returns to Vrefin, and then decreases step by step, as shown in Figure 5. Since the voltage value of Vo and the final output driving current are in a fixed proportional relationship, the purpose of dimming through the one-line pulse sequence of CLK is realized in this way.

The white light LED one-line pulse dimming circuit of the present invention has the advantages of simple realization, stable operation and high precision. Corresponding to the above circuit, the present invention also proposes a white LED one-line pulse dimming method, as shown in Figure 6, which includes the following steps:

S601. Generate a reference current according to a power supply voltage. The power supply preferably adopts a bandgap reference voltage source.

S602, using the reference current and a one-line pulse sequence to generate four currents in a binary weight proportional relationship with the reference current.

A better implementation method is to use a current mirror to mirror the reference current into four currents, and then use the logic output of four D flip-flops connected in the form of a frequency divider to control the on-off state of the four currents, so that There is a binary weight proportional relationship between the four currents and the reference current.

S603, converting the total current of the four currents into a voltage gradually reduced according to the number of rising edges of one line of pulses.

The optimal binary weight proportional relationship between the four-way current and the reference current is 1 times, 2 times, 4 times, and 8 times, so that the proportional relationship between the sum of the four-way currents and the reference current is the count of the rising edge of the first-line pulse, combined with The combination of the operational amplifier circuit and the resistor can convert the total current of the four currents into a voltage that decreases step by step according to the number of rising edges of the one-line pulse. For specific principles and calculation processes, please refer to FIGS. 3 to 5 and corresponding descriptions, and details are not repeated here.

S604, outputting a driving current with a fixed proportional relationship with the voltage to the white LED.

Since the driving current decreases step by step corresponding to the number of rising edges of the one-line pulse, the purpose of dimming the white LED through the one-line pulse sequence can be realized.

The above disclosures are only several specific embodiments of the present invention, but the present invention is not limited thereto, and any changes that those skilled in the art can think of, as long as they do not exceed the scope described in the appended claims, should fall within the scope of the appended claims. within the protection scope of the present invention.

Claims (6)

1. white light LEDs one a line pulse light modulation circuit, is characterized in that, comprising:

One power supply;

One pulse control module is used for one line pulse train of output;

One current conversion module, be connected with this power supply and this pulse control module respectively, be used for generating a reference current according to the voltage of this power supply output, and utilize this reference current and this line pulse train to generate a voltage that reduces step by step according to a line rising edge of a pulse number;

One constant-current source driver module is connected with this current conversion module and white light LEDs respectively, is used for becoming with this voltage of this current conversion module output to white light LEDs output a drive current of fixed proportion relation;

This current conversion module further comprises again:

One reference current generating circuit is connected with this power supply, is used for generating a reference current;

One current mirror is connected with this reference current generating circuit, is used for utilizing this reference current to generate four road electric currents;

One switching circuit is connected with this current mirror, be used for to control the on off operating mode of four road electric currents that this current mirror produces;

One two-divider, be connected with this pulse control module and this switching circuit respectively, control the on off operating mode of this switching circuit for this line pulse train of utilizing this pulse control module output, so that four road electric currents that this current mirror produces all become the binary weights proportionate relationship with this reference current;

One voltage follower circuit is connected with this switching circuit, is used for converting the total current of four road electric currents to final Voltage-output.

2. white light LEDs one line pulse light modulation circuit as claimed in claim 1, it is characterized in that, this two-divider comprises four d type flip flops, four d type flip flops connect step by step, the clock signal terminal of the d type flip flop of the first order connects this pulse control module, the inverse output terminal of the d type flip flop of first three grade is connected with the data-signal input, the clock signal terminal that connects simultaneously the next stage d type flip flop, with the triggering signal as next stage, the inverse output terminal of the d type flip flop of the fourth stage is connected with the data-signal input, and the forward output of four d type flip flops is connected with this switching circuit, to control the on off operating mode of four road electric currents.

3. white light LEDs one line pulse light modulation circuit as claimed in claim 1, is characterized in that, this reference current generating circuit comprises an operational amplifier and a reference resistance, and this reference resistance is connected with an input of this operational amplifier.

4. white light LEDs one line pulse light modulation circuit as claimed in claim 1, is characterized in that, this voltage follower circuit comprises an operational amplifier and a resistance, and this resistance is connected between the output and input of this operational amplifier.

5. white light LEDs one line pulse light modulation circuit as claimed in claim 1, is characterized in that, four road electric currents that this current mirror produces are respectively 1 times, 2 times, 4 times, 8 times of this reference current.

6. white light LEDs one line pulse light modulation circuit as described in claim 1～5 any one, is characterized in that, this power supply is bandgap voltage reference.

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