CN114466482A - LED constant current source circuit and control method thereof - Google Patents
LED constant current source circuit and control method thereof Download PDFInfo
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
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- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
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- H05B45/345—Current stabilisation; Maintaining constant current
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Abstract
The invention provides an LED constant current source circuit and a control method thereof, the circuit comprises a first optical coupler, a micro control unit, a first voltage sampling module, a first resistor, a first load access end, a second optical coupler, a second voltage sampling module, a second resistor and a second load access end, wherein a first sampling voltage signal and a second sampling voltage signal are collected through the first sampling module and the second sampling module, the micro control unit outputs PWM (pulse width modulation) signals with different duty ratios according to the first sampling voltage signal and the second sampling voltage signal to enable the first optical coupler and the second optical coupler to change output voltage, and further current of LED loads at the first load access end and the second load access end is kept consistent, so that the brightness is consistent.
Description
Technical Field
The invention relates to the field of LED constant current sources, in particular to an LED constant current source circuit and a control method thereof.
Background
The constant current source can make the current identical when different LEDs are connected only under the ideal condition, and actually, the lower the output voltage of the constant current source is, the larger the output current is. With the application of the double-color temperature constant current source, for the double-color temperature lamp with the load carrier having the common-positive characteristic, because the dummy load of the constant current source has loss, when the constant current source is actually used with different loads, the measured currents of two paths of color temperatures have deviation, and the brightness is inconsistent.
Disclosure of Invention
The invention aims to provide an LED constant current source circuit, which can solve the problem of inconsistent brightness caused by deviation of two paths of color temperature currents of a double-color temperature lamp.
The second purpose of the invention is to provide a control method of the LED constant current source circuit.
In order to achieve the first object, the invention provides a first optical coupler, a micro control unit, a first voltage sampling module, a first resistor, and a first load access end; the input end of the first optical coupler comprises a first input end and a second input end, the first input end is connected with a direct-current power supply, and the second input end is connected with the output end of the micro-control unit; the output end of the first optical coupler comprises a first output end and a second output end, the first output end is connected with the positive end of the first load access end, and the second output end is connected with the negative end of the first load access end; the first resistor is connected between the output end of the first optical coupler and the first load access end in series; the input end of the microcontroller is connected with the first sampling end of the first voltage sampling module; the input end of the microcontroller is used for receiving a first sampling voltage signal from the first sampling end; the first voltage sampling module is connected with the positive end of the first load access end and the negative end of the load access end; the first voltage sampling module is used for sampling a first voltage signal at the positive end of the first load access end and sampling a second voltage signal at the negative end of the first load access end; the output end of the microcontroller is connected with the second input end of the first optical coupler, and the microcontroller is used for outputting a first PWM signal corresponding to a preset current value to the first optical coupler according to the first sampling voltage signal; the first optical coupler is used for outputting a first output voltage signal corresponding to the first PWM signal at the output end of the first optical coupler according to the first PWM signal, so that the current flowing through the first load access end is a preset current value; the LED constant-source circuit further comprises a second optical coupler, a second voltage sampling module, a second resistor and a second load access end; the input end of the second optical coupler comprises a third input end and a fourth input end, the third input end is connected with the direct-current power supply, and the fourth input end is connected with the second output end of the micro-control unit; the output end of the second optical coupler comprises a third output end and a fourth output end, the third output end is connected with the positive end of the second load access end, and the fourth output end is connected with the negative end of the second load access end; the positive end of the second load access end is connected with the positive end of the first load access end; the second resistor is connected between the output end of the second optical coupler and the second load access end in series; the second input end of the microcontroller is connected with the second sampling end of the second voltage sampling module; the input end of the microcontroller is used for receiving a second sampling voltage signal from the second sampling end; the second voltage sampling module is connected with the positive end of the second load access end and the negative end of the load access end; the second voltage sampling module is used for sampling a third voltage signal at the positive end of the second load access end and sampling a fourth voltage signal at the negative end of the load access end; a second output end of the microcontroller is connected with a fourth input end of the optical coupler, and the microcontroller is used for outputting a second PWM signal corresponding to the preset current value to the optical coupler according to the second sampling voltage signal; the second optical coupler is used for outputting a second output voltage signal corresponding to the second PWM signal at the output end of the second optical coupler according to the second PWM signal, so that the current flowing through the second load access end is a preset current value.
According to the scheme, the LED load driving circuit is provided with the optical coupler, the micro control unit, the voltage sampling module and the like, wherein the voltage sampling module is used for sampling the sampling voltage signals of the LED load, and the micro control unit is used for outputting PWM signals with different duty ratios to the optical coupler according to the sampling voltage signals so that the output voltage of the optical coupler is changed, the currents of two paths of LED loads are kept consistent, and the brightness is kept consistent.
A first capacitor is connected in parallel between the first optical coupler and the first load access end; and a second capacitor is connected in parallel between the second optical coupler and the second load access end.
Therefore, the accessed capacitor can play a role in filtering.
The first voltage sampling module comprises a first sampling resistor group and a second sampling resistor group, the first sampling resistor group comprises a first sampling resistor and a second sampling resistor, the first sampling resistor and the second sampling resistor are connected in series, and one end, far away from the second sampling resistor, of the first sampling resistor is connected with the positive end of a first load access section; the second sampling resistor group comprises a third sampling resistor and a fourth sampling resistor, the third sampling resistor is connected with the fourth sampling resistor in series, one end, far away from the fourth sampling resistor, of the third sampling resistor is connected with the negative end of the load access end, and one end, far away from the first sampling resistor, of the second sampling resistor and one end, far away from the third sampling resistor, of the fourth sampling resistor are grounded together.
The second voltage sampling module comprises a third sampling resistor group and a fourth sampling resistor group, the third sampling resistor group comprises a fifth sampling resistor and a sixth sampling resistor, the fifth sampling resistor is connected with the sixth sampling resistor in series, and one end of the fifth sampling resistor, which is far away from the sixth sampling resistor, is connected with the positive end of the second load access section; the fourth sampling resistor group comprises a seventh sampling resistor and an eighth sampling resistor, the seventh sampling resistor is connected with the eighth sampling resistor in series, one end, far away from the eighth sampling resistor, of the seventh sampling resistor is connected with the negative end of the second load access end, and one end, far away from the fifth sampling resistor, of the sixth sampling resistor and one end, far away from the seventh sampling resistor, of the eighth sampling resistor are grounded.
The first sampling end comprises a first end and a second end, the first end is arranged between the first sampling resistor and the second sampling resistor, and the second end is arranged between the third sampling resistor and the fourth sampling resistor; the second sampling end comprises a third end and a fourth end, the third end is arranged between the fifth sampling resistor and the sixth sampling resistor, and the second end is arranged between the seventh sampling resistor and the eighth sampling resistor.
In a further scheme, the voltage value of the high level of the first PWM signal and the second PWM signal is equal to the voltage value of the direct current power supply.
Thus, the output of the optical coupler can be effectively controlled.
In order to achieve the second object, the present invention provides a method for controlling an LED constant current source circuit, including: the first voltage sampling module collects a first sampling voltage signal of a first load access end and transmits the first sampling voltage signal to the micro control unit; the second voltage sampling module collects a second sampling voltage signal of a second load access end and transmits the second sampling voltage signal to the micro control unit; the micro control unit calculates a corresponding first PWM signal when the current flowing through the first load access end is a preset current value according to the first sampling voltage signal; the micro control unit calculates a corresponding second PWM signal when the current flowing through the second load access end is a preset current value according to the second sampling voltage signal; the first optical coupler outputs a first output voltage signal corresponding to the first PWM signal at the output end of the first optical coupler according to the first PWM signal, so that the current flowing through the first load access end is a preset current value; the second optical coupler outputs a second output voltage signal corresponding to the second PWM signal at the output end of the second optical coupler according to the second PWM signal, so that the current flowing through the second load access end is a preset current value.
According to the scheme, the sampling voltage values at two ends of the two LED loads are sampled and transmitted to the micro control unit, the micro control unit calculates the duty ratio of the output PWM signal according to the sampling voltage values and outputs the duty ratio to the optical coupler, and the optical coupler controls voltage output so that the currents of the two LED loads are constant and the brightness is kept consistent.
The method comprises the following steps that a first voltage sampling module collects a first sampling signal of a first load access end and transmits the first sampling signal to a micro control unit, a second voltage sampling module collects a second sampling voltage signal of a second load access end and transmits the second sampling voltage signal to the micro control unit, the first voltage sampling module collects a third sampling signal of the first load access end and transmits the third sampling signal to the micro control unit, and the second voltage sampling module collects a fourth sampling voltage signal of the second load access end and transmits the fourth sampling voltage signal to the micro control unit; the micro control unit judges whether the first sampling voltage signal is larger than a preset voltage value or not according to the third sampling voltage signal and the fourth sampling voltage signal, and if the third sampling voltage signal is larger than the preset voltage value, the micro control unit outputs a PWM signal with the duty ratio of 100% to the second input end; the micro control unit also judges whether the fourth voltage signal is greater than a preset voltage value, and if the fourth sampling voltage signal is greater than the preset voltage value, the micro control unit outputs a PWM signal with a duty ratio of 100% to the fourth input end.
Therefore, the LED constant current source circuit can judge whether the LED load is connected or not, so that the PWM signal is controlled to reduce loss, and whether the voltage of the LED load exceeds the output of the LED constant current source circuit or not is judged, and the protection effect is achieved.
The further scheme is that after a first voltage sampling module collects a first sampling voltage signal of a first load access end and transmits the first sampling voltage signal to the micro control unit, a second voltage sampling module collects a second sampling voltage signal of a second load access end and transmits the second sampling voltage signal to the micro control unit, the method further executes: and the output end of the micro control unit respectively outputs PWM signals with the duty ratio gradually reduced to the second input end of the first optical coupler and the fourth input end of the second optical coupler until a first LED load at the first load access end works and a second LED load at the second load access end works.
Therefore, when the PWM signal is large, the resistance of the LED load is increased, and the LED can be conducted more quickly.
The method comprises the following steps that a micro control unit calculates a first PWM signal corresponding to a preset current value of current flowing through a first load access end according to a first sampling voltage signal and a PWM calculation formula; and the micro control unit calculates a corresponding second PWM signal when the current flowing through the second load access end is a preset current value according to the second voltage signal and a PWM calculation formula.
Drawings
Fig. 1 is a circuit schematic of the LED constant current source circuit of the present invention.
Fig. 2 is a flowchart of a control method of the LED constant current source circuit of the present invention.
The invention is further explained with reference to the drawings and the embodiments.
Detailed Description
The invention is used for LED lamps, in particular to a double-color temperature lamp with a common-anode characteristic, the voltage sampling module is used for sampling the voltage at two ends of each load, the micro control unit calculates PWM signals according to the voltage at two ends of the load, and outputs the PWM signals to the optical coupler to change the voltage at two ends of the load, so that the load currents of all paths are equal, and the brightness is consistent.
The embodiment of the LED constant current source circuit of the invention comprises the following steps:
referring to fig. 1, the LED constant current source circuit of this embodiment includes a first optical coupler U1, a micro control unit U3, a first voltage sampling module 11, a first resistor R2, a first capacitor C1, a second optical coupler U2, a second voltage sampling module 12, a second resistor R8, a second capacitor C2, a resistor R1, and a resistor R7. The resistance of the first resistor R2 is equal to the resistance of the second resistor D8, the capacitances of the first capacitor C1 and the second capacitor C2 are equal, and the resistances of the resistor R1 and the resistor R7 are equal. Wherein, the resistors all play a role in current limiting. The first load access end and the second load access end are both connected to the wiring terminal J1, the positive end of the first load access end is an LED + end, the negative end of the first load access end is an LED 1-end, and the positive end of the second load access end is connected with the positive end of the first load access end, namely the positive end of the second load access end is connected to the LED + end, namely the positive end of the second load access end is an LED + end, and the negative end of the second load access end is an LED 2-end. The wiring terminal is connected with two LED loads (not shown in the figure), the positive ends of the two LED loads are connected to the LED + end, the negative ends of the two LED loads are respectively connected with the LED 1-and the LED2-, the two LED loads share the anode, and the LED + is connected with a direct-current voltage of 50V to the ground.
The input end of the first optocoupler U1 includes a first input end 1 and a second input end 2, the first input end 1 is connected with a resistor R1, and a resistor R1 is connected with a dc power supply, that is, a 3.3 v dc power supply. The second input end 2 is connected to a micro control unit U3, in this embodiment, the micro control unit U3 is an MCU. The output end of the first optical coupler U1 includes a first output end 4 and a second output end 3, the first output end 4 is connected to the positive end of the first load input end, i.e., the LED + end, and the second output end is connected to the negative end of the first load input end, i.e., the LED 1-end. The first resistor R2 is connected in series between the output terminal of the first optocoupler and the first load connection terminal, i.e. one end of the first resistor R2 is connected between the second output terminal 3, and the other end is connected to the negative terminal of the first load connection terminal, i.e. the LED 1-terminal.
A first capacitor C1 is connected in parallel between the first optocoupler U1 and the first load access terminal.
The first voltage sampling module 11 comprises a first sampling resistor group and a second sampling resistor group, the first sampling resistor group comprises a first sampling resistor R3 and a second sampling resistor R5, the first sampling resistor R3 is connected in series with the second sampling resistor R5, and one end, far away from the second sampling resistor R5, of the first sampling resistor R3 is connected with the positive end of a first load access section, namely an LED + end; the second sampling resistor group comprises a third sampling resistor R4 and a fourth sampling resistor R6, the third sampling resistor R4 is connected in series with the fourth sampling resistor R6, one end, far away from the fourth sampling resistor R6, of the third sampling resistor R4 is connected with the negative end, namely an LED 1-end, of the first load access end, one end, far away from the first sampling resistor R3, of the second sampling resistor R5 and one end, far away from the third sampling resistor R4, of the fourth sampling resistor R6 are connected to the common ground. The first sampling end of the first sampling voltage module 11 includes a first end and a second end, the first end is Vsen1, the first end is disposed between the first sampling resistor R3 and the second sampling resistor R5, the second end is Vsen1+, the second end is disposed between the third sampling resistor R4 and the fourth sampling resistor R6, the Vsen1 and the Vsen1+ are connected to the input end of the micro-control unit U3, that is, the input end is respectively connected to the Vsen1 end and the Vsen1+ end of the micro-control unit U3, the micro-control unit U3 receives potentials of two points, namely, a second voltage signal and a first sampling voltage signal, of the Vsen1 and the Vsen1+, and combines the first sampling resistor R3, the second sampling resistor R5, the third sampling resistor R4 and the fourth sampling resistor R6, and the resistance values of the resistors can calculate the voltage between the LED + and the LED 1-.
The input end of the second optocoupler U2 comprises a third input end 5 and a fourth input end 6, the first input end 1 is connected with a resistor R7, and a resistor R7 is connected with a direct current power supply, namely a 3.3-volt direct current power supply. The third input 5 is connected to a microcontroller unit U3. The output end of the first optical coupler U2 includes a third output end 8 and a fourth output end 7, the third output end 8 is connected to the positive end of the second load access end, i.e., the LED + end, and the third output end is connected to the negative end of the second load access end, i.e., the LED 2-end. The second resistor R8 is connected in series between the output terminal of the second optocoupler and the second load connection terminal, i.e. one end of the second resistor R8 is connected to the third output terminal 7, and the other end is connected to the negative terminal of the first load connection terminal, i.e. the LED 2-terminal. A first capacitor C2 is connected in parallel between the second optocoupler U2 and the second load connection terminal.
The second voltage sampling module 12 includes a third sampling resistor group and a fourth sampling resistor group, the third sampling resistor group includes a fifth sampling resistor R9 and a sixth sampling resistor R11, the fifth sampling resistor R9 is connected in series with the sixth sampling resistor R11, and one end of the fifth sampling resistor R9, which is far away from the sixth sampling resistor R11, is connected with the positive end of the second load access section, i.e., the LED + end; the fourth sampling resistor group comprises a seventh sampling resistor R10 and an eighth sampling resistor R12, the seventh sampling resistor R10 is connected in series with the eighth sampling resistor R12, one end, far away from the eighth sampling resistor R12, of the seventh sampling resistor R10 is connected with the negative end of the second load access end, namely the LED 2-end, and one end, far away from the fifth sampling resistor R9, of the sixth sampling resistor R11 and one end, far away from the seventh sampling resistor R10, of the eighth sampling resistor R12 are grounded in common. The second sampling end of the first sampling voltage module 11 includes a third end and a fourth end, the third end is Vsen2, the third end is disposed between the fifth sampling resistor R9 and the sixth sampling resistor R11, the fourth end is Vsen2+, the fourth end is disposed between the seventh sampling resistor R10 and the eighth sampling resistor R12, the Vsen2 and the Vsen2+ are connected to the input end of the micro-control unit U3, that is, the second input end Vsen2 and the Vsen2+ of the micro-control unit U3, the micro-control unit U3 receives potentials of two points, namely, the fourth voltage signal and the third voltage signal, of the Vsen2 and the Vsen2+, so as to obtain a third sampling voltage signal, and the voltage between the LED + and the LED 2-can be calculated by combining resistance values of the fifth sampling resistor R9, the sixth sampling resistor R11, the seventh sampling resistor R10, and the eighth sampling resistor 12.
A first output PWM1 of the microcontroller U3 is connected to the second input 2 of the first optocoupler U1, and a second output PWM2 of the microcontroller U3 is connected to the fourth input 6 of the second optocoupler U2. The microcontroller U3 outputs a first PWM signal corresponding to a preset current value to the first optical coupler U1 according to the first sampling voltage signal, and the first optical coupler U1 is used for outputting a first output voltage signal corresponding to the first PWM signal at the output end of the first optical coupler U1 according to the first PWM signal, so that the current flowing through the first load access end is the preset current value; the microcontroller U3 outputs a second PWM signal corresponding to the preset current value to the second coupler U2 according to the second sampling voltage signal, and the second optical coupler U2 is configured to output a second output voltage signal corresponding to the second PWM signal at an output end of the second optical coupler U2 according to the second PWM signal, so that the current flowing through the second load connection end is the preset current value; the high level voltage value of the first PWM signal and the second PWM signal is equal to the voltage value of the dc power supply, i.e., the first PWM signal and the second PWM signal are 3.3 v at the high level and 0 at the low level. Specifically, for the first sampled voltage signal, assuming that the first sampled voltage signal is U1, according to a formula D1 ═ 1+ I × R/U1-U2 × I × R/U1/U1-U2 × U2 (1-D2)/U1/U1, where I is a preset current value, U2 is a reference voltage value, and D2 is a duty ratio when the output voltage of the optical coupler is the reference voltage value, and R is a resistance value of a resistor connected in series between the optical coupler output terminal and the load access terminal. The duty ratio D1 of the first PWM signal is calculated, and outputting the PWM1 signal with the duty ratio D1 changes the voltage output by the first optocoupler U1, so that the current flowing through the LED load is a preset current value. The derivation process of the formula is: referring to fig. 1, two paths of preset current values corresponding to the first optical coupler U1 and the second optical coupler U2 are equal and are set as I; the resistance values of the first resistor R1 and the second resistor R8 are equal and are set as R; the total power consumed by the power of the LED load at the first load connection end and the first resistor R1 is P1, the total power consumed by the power of the LED load at the second load connection end and the second load R8 is P2, and P1 is P2 is P, so that:
P1＝U1*I+U1*U1*(1-D1)/R1；
P2＝U2*I+U2*U2*(1-D2)/R3；
P1＝U1*I+U1*U1*(1-D1)/R1＝P2＝U2*I+U2*U2*(1-D2)/R3；
U1*I+U1*U1*(1-D1)/R＝U2*I+U2*U2*(1-D2)/R；
when the LED constant current source circuit is set, a reference point needs to be determined, namely, a preset current I is determined, the reference point corresponds to a sampling voltage signal U2, and the duty ratio D2 of PWM at the moment, namely, the functional relation between D1 and the sampling voltage signal of the current LED load can be obtained, when different LED loads are connected, the micro control unit can calculate the current passing through the LED load as the preset value, the duty ratio of the PWM signal which the micro control unit should output is the duty ratio of the PWM signal, the optical coupler adjusts the output voltage according to the PWM signal, so that the current passing through the LED load is the preset current value, and the constant current effect is achieved.
It can be understood that for one-way LED load or multiple-way LED loads, the effect that the current passing through the LED load is a preset value can be achieved through the LED constant current source circuit.
The invention discloses a control method of an LED constant current source circuit, which comprises the following steps:
referring to fig. 2, the voltage acquisition module acquires the third sampled voltage signal and the fourth sampled voltage signal at the load input end and transmits the signals to the micro control unit, that is, step S1 is executed.
The micro control unit determines whether the third sampled voltage signal and the fourth sampled voltage signal are greater than the predetermined voltage value, i.e., executes step S2. If the third sampling signal is greater than the preset voltage value and the fourth sampling signal is greater than the preset voltage value, it indicates that the first load access end and the second load access end are idle at this time, or the voltage across the first LED load accessed by the first load access end and the voltage across the second LED load accessed by the second load access end are both greater than the nominal voltage of the LED constant current source circuit, in order to reduce idle loss or serve as protection, S4 needs to be executed, the micro control unit outputs a PWM signal with a duty ratio of 100% to the input end of the optical coupler, outputs a PWM signal with a duty ratio of 100%, and can cut off the first optical coupler and the second optical coupler, thereby reducing idle loss or protecting the LED constant current source circuit, and then returns to step S1, repeats the determination process, and monitors the load condition in real time. If the third sampled voltage signal and the fourth sampled voltage signal are smaller than the preset voltage value, it indicates that the first LED load and the second LED load connected at this time satisfy the constant current condition, and S3 may be continuously executed.
The micro control unit outputs the PWM signal with the duty ratio gradually decreasing to the input end of the optical coupler until the LED load operates, that is, step S3 is executed, the output end of the micro control unit outputs the PWM signal with the duty ratio gradually decreasing to the second input end of the first optical coupler and the fourth input end of the second optical coupler until the first LED load at the first load connection end operates and the second load at the second LED load connection end operates, so that the LED load can be rapidly turned on.
Then, step S5 is executed, and the voltage acquisition module acquires the first sampling voltage signal and the second sampling voltage signal at the load access end and transmits the first sampling voltage signal and the second sampling voltage signal to the micro control unit. Specifically, a first voltage sampling module collects a first sampling voltage signal of a first load access end and transmits the first sampling voltage signal to a micro control unit; the second voltage sampling module collects a second sampling voltage signal of the second load access end and transmits the second sampling voltage signal to the micro control unit.
Continuing to step S6, the mcu outputs a PWM signal to the optocoupler according to the sampled voltage signal and the PWM calculation formula. Specifically, the micro control unit calculates a corresponding first PWM signal when the current flowing through the first load access end is a preset current value according to a first sampling voltage signal calculation PWM calculation formula; and the micro control unit calculates a corresponding second PWM signal when the current flowing through the second load access end is a preset current value according to the second sampling voltage signal and a PWM calculation formula. The specific process is the same as the embodiment of the LED constant current source circuit, and is not described herein again.
Finally, step S7 is executed, and the optocoupler changes the output voltage of the optocoupler according to the PWM signal. Specifically, the first optical coupler outputs a first output voltage signal corresponding to the first PWM signal at an output end of the first optical coupler according to the first PWM signal, so that the magnitude of the current flowing through the first load access end is a preset current value; the second optical coupler outputs a second output voltage signal corresponding to the second PWM signal at the output end of the second optical coupler according to the second PWM signal, so that the current flowing through the second load access end is a preset current value.
In summary, the first sampling module and the second sampling module are used for acquiring the first sampling voltage signal and the second sampling voltage signal, and the micro control unit outputs the PWM signals with different duty ratios according to the first sampling voltage signal and the second sampling voltage signal, so that the first optical coupler and the second optical coupler change the output voltage, and further the current of the LED loads at the first load access end and the second load access end can be kept consistent, and further the brightness is consistent.
Claims (10)
1. An LED constant current source circuit, comprising:
the circuit comprises a first optical coupler, a micro control unit, a first voltage sampling module, a first resistor and a first load access end;
the input end of the first optical coupler comprises a first input end and a second input end, the first input end is connected with a direct-current power supply, and the second input end is connected with the output end of the micro-control unit;
the output end of the first optical coupler comprises a first output end and a second output end, the first output end is connected with the positive end of the first load access end, and the second output end is connected with the negative end of the first load access end;
the first resistor is connected between the output end of the first optical coupler and the first load access end in series;
the input end of the microcontroller is connected with the first sampling end of the first voltage sampling module; the input end of the microcontroller is used for receiving a first sampling voltage signal from the first sampling end;
the first voltage sampling module is connected with the positive end of the first load access end and the negative end of the load access end; the first voltage sampling module is used for sampling a first voltage signal at the positive end of the first load access end and sampling a second voltage signal at the negative end of the first load access end;
the output end of the microcontroller is connected with the second input end of the first optical coupler, and the microcontroller is used for outputting a first PWM signal corresponding to a preset current value to the first optical coupler according to the first sampling voltage signal; the first optical coupler is used for outputting a first output voltage signal corresponding to the first PWM signal at the output end of the first optical coupler according to the first PWM signal, so that the current flowing through the first load access end is the preset current value;
the LED constant-source circuit further comprises a second optical coupler, a second voltage sampling module, a second resistor and a second load access end;
the input end of the second optical coupler comprises a third input end and a fourth input end, the third input end is connected with the direct-current power supply, and the fourth input end is connected with the second output end of the micro-control unit;
the output end of the second optical coupler comprises a third output end and a fourth output end, the third output end is connected with the positive end of the second load access end, and the fourth output end is connected with the negative end of the second load access end;
the positive end of the second load access end is connected with the positive end of the first load access end;
the second resistor is connected between the output end of the second optical coupler and the second load access end in series;
the second input end of the microcontroller is connected with the second sampling end of the second voltage sampling module; the input end of the microcontroller is used for receiving a second sampling voltage signal from a second sampling end;
the second voltage sampling module is connected with the positive end of the second load access end and the negative end of the load access end; the second voltage sampling module is used for sampling a third voltage signal of the positive end of the second load access end and sampling a fourth voltage signal of the negative end of the load access end;
a second output end of the microcontroller is connected with a fourth input end of the optical coupler, and the microcontroller is used for outputting a second PWM signal corresponding to the preset current value to the optical coupler according to the second sampling voltage signal; the second optical coupler is used for outputting a second output voltage signal corresponding to the second PWM signal at the output end of the second optical coupler according to the second PWM signal, so that the current flowing through the second load access end is the preset current value.
2. An LED constant current source circuit according to claim 1, wherein:
a first capacitor is connected in parallel between the first optical coupler and the first load access end;
and a second capacitor is connected in parallel between the second optical coupler and the second load access end.
3. An LED constant current source circuit according to claim 2, wherein:
the first voltage sampling module comprises a first sampling resistor group and a second sampling resistor group, the first sampling resistor group comprises a first sampling resistor and a second sampling resistor, the first sampling resistor is connected with the second sampling resistor in series, and one end, far away from the second sampling resistor, of the first sampling resistor is connected with the positive end of the first load access section; the second sampling resistor group comprises a third sampling resistor and a fourth sampling resistor, the third sampling resistor is connected with the fourth sampling resistor in series, the third sampling resistor is far away from one end of the fourth sampling resistor and is connected with the negative end of the load access end, and the second sampling resistor is far away from one end of the first sampling resistor and one end of the fourth sampling resistor are grounded together.
4. An LED constant current source circuit according to claim 3, wherein:
the second voltage sampling module comprises a third sampling resistor group and a fourth sampling resistor group, the third sampling resistor group comprises a fifth sampling resistor and a sixth sampling resistor, the fifth sampling resistor is connected with the sixth sampling resistor in series, and one end, far away from the sixth sampling resistor, of the fifth sampling resistor is connected with the positive end of the second load access section; the fourth sampling resistor group comprises a seventh sampling resistor and an eighth sampling resistor, the seventh sampling resistor is connected with the eighth sampling resistor in series, one end of the seventh sampling resistor, which is far away from the eighth sampling resistor, is connected with the negative end of the second load access end, one end of the sixth sampling resistor, which is far away from the fifth sampling resistor, is connected with one end of the eighth sampling resistor, which is far away from the seventh sampling resistor, and is connected with the common ground.
5. An LED constant current source circuit according to claim 4, wherein:
the first sampling end comprises a first end and a second end, the first end is arranged between the first sampling resistor and the second sampling resistor, and the second end is arranged between the third sampling resistor and the fourth sampling resistor;
the second sampling end comprises a third end and a fourth end, the third end is arranged between the fifth sampling resistor and the sixth sampling resistor, and the second end is arranged between the seventh sampling resistor and the eighth sampling resistor.
6. An LED constant current source circuit according to any one of claims 1 to 5, wherein:
the voltage values of the high levels of the first PWM signal and the second PWM signal are equal to the voltage value of the direct current power supply.
7. The control method of the LED constant current source circuit applied to any one of the above claims 1 to 6, is characterized by comprising the following steps:
the first voltage sampling module collects a first sampling voltage signal of the first load access end and transmits the first sampling voltage signal to the micro control unit; a second voltage sampling module collects a second sampling voltage signal of the second load access end and transmits the second sampling voltage signal to the micro control unit; the micro control unit calculates a corresponding first PWM signal when the current flowing through the first load access end is the preset current value according to the first sampling voltage signal; the micro control unit calculates a second PWM signal corresponding to the preset current value of the current flowing through the second load access end according to the second sampling voltage signal;
the first optical coupler outputs a first output voltage signal corresponding to the first PWM signal at the output end of the first optical coupler according to the first PWM signal, so that the current flowing through the first load access end is the preset current value; and the second optical coupler outputs a second output voltage signal corresponding to the second PWM signal at the output end of the second optical coupler according to the second PWM signal, so that the current flowing through the second load access end is the preset current value.
8. The method of claim 7 wherein the LED constant current source circuit comprises:
before the first voltage sampling module collects a first sampling signal at the first load access end and transmits the first sampling signal to the micro control unit, the second voltage sampling module collects a second sampling voltage signal at the second load access end and transmits the second sampling voltage signal to the micro control unit,
the first voltage sampling module collects a third sampling signal of the first load access end and transmits the third sampling signal to the micro control unit, and the second voltage sampling module collects a fourth sampling voltage signal of the second load access end and transmits the fourth sampling voltage signal to the micro control unit;
the micro control unit judges whether the first sampling voltage signal is greater than a preset voltage value or not according to the third sampling voltage signal and the fourth sampling voltage signal, and if the third sampling voltage signal is greater than the preset voltage value, the micro control unit outputs a PWM signal with a duty ratio of 100% to the second input end;
the micro control unit also judges whether the fourth voltage signal is greater than a preset voltage value, and if the fourth sampling voltage signal is greater than the preset voltage value, the micro control unit outputs a PWM signal with a duty ratio of 100% to the fourth input end.
9. The method of claim 8 for controlling an LED constant current source circuit, wherein:
after the first voltage sampling module collects a first sampling voltage signal of the first load access end and transmits the first sampling voltage signal to the micro control unit, and the second voltage sampling module collects a second sampling voltage signal of the second load access end and transmits the second sampling voltage signal to the micro control unit, the method further executes:
and the output end of the micro control unit respectively outputs PWM signals with duty ratio gradually reduced to the second input end of the first optical coupler and the fourth input end of the second optical coupler until a first LED load at the first load access end works and a second LED load at the second load access end works.
10. The method of claim 9 for controlling an LED constant current source circuit, wherein:
the micro control unit calculates a corresponding first PWM signal when the current flowing through the first load access end is the preset current value according to the first sampling voltage signal and a PWM calculation formula; and the micro control unit calculates a second PWM signal corresponding to the current flowing through the second load access end when the current is the preset current value according to the second voltage signal and the PWM calculation formula.
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