CN114466482B - 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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- CN114466482B CN114466482B CN202111678275.7A CN202111678275A CN114466482B CN 114466482 B CN114466482 B CN 114466482B CN 202111678275 A CN202111678275 A CN 202111678275A CN 114466482 B CN114466482 B CN 114466482B
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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
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
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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
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/32—Pulse-control circuits
- H05B45/325—Pulse-width modulation [PWM]
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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
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/345—Current stabilisation; Maintaining constant current
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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
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
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Abstract
The invention provides an LED constant current source circuit and a control method thereof, wherein the circuit comprises a first optocoupler, a micro control unit, a first voltage sampling module, a first resistor, a first load access end, a second optocoupler, a second voltage sampling module, a second resistor and a second load access end, wherein the first sampling voltage signal and the second sampling voltage signal are acquired through the first sampling module and the second sampling module, and the micro control unit outputs PWM signals with different duty ratios according to the first sampling voltage signal and the second sampling voltage signal so that the output voltage of the first optocoupler and the second optocoupler is changed, and then the currents of LED loads of the first load access end and the second load access end are kept consistent, and 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 only can make the current the same when different LEDs are connected in under ideal conditions, and in fact, the lower the output voltage of the constant current source is, the larger the output current is. With the application of the dual-color temperature constant current source, the load is a dual-color temperature lamp with common positive characteristic, and the loss of the pseudo load of the constant current source leads to the deviation of the measured currents of two color temperatures when the constant current source is actually used with different loads, so that the brightness is inconsistent.
Disclosure of Invention
The first object of the invention is to provide an LED constant current source circuit which can solve the problem that the brightness is inconsistent due to the deviation of the current of two color temperatures of a bicolor lamp.
The second object of the invention is to provide a control method of the LED constant current source circuit.
In order to achieve the first objective, the first optical coupler, the micro control unit, the first voltage sampling module, the first resistor and the first load access terminal provided by the invention; 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 in series between the output end of the first optical coupler and the first load access end; the input end of the microcontroller is connected with a 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 a 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 of the positive end of the first load access end and sampling a second voltage signal of 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 an output end of the first optical coupler according to the first PWM signal, so that the current flowing through a 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 a 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 in series between the output end of the second optical coupler and the second load access end; the second input end of the microcontroller is connected with a 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; the second output end of the microcontroller is connected with the fourth input end of the optical coupler, and the microcontroller is used for outputting a second PWM signal corresponding to a preset current value to the optical coupler according to the second sampling voltage signal; the second optocoupler is used for outputting a second output voltage signal corresponding to the second PWM signal at an output end of the second optocoupler 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 optocoupler, the micro control unit, the voltage sampling module and the like are arranged, the voltage sampling module is used for sampling voltage signals of the LED loads, and the micro control unit is used for outputting PWM signals with different duty ratios to the optocoupler according to the sampling voltage signals, so that output voltage of the optocoupler is changed, currents of the two paths of LED loads are kept consistent, and brightness is kept consistent.
The further scheme is that a first capacitor is connected in parallel between the first optical coupler and the first load access end; a second capacitor is connected in parallel between the second optical coupler and the second load access terminal.
It follows that the switched-in capacitance can act as a filter.
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 in series with the second sampling resistor, and one end of the first sampling resistor, which is far away from the second 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, one end of the third sampling resistor, which is far away from the fourth sampling resistor, is connected with the negative end of the load access end, and one end of the second sampling resistor, which is far away from the first sampling resistor, and one end of the fourth sampling resistor, which is far away from the third 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 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 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, and one end of the sixth sampling resistor, which is far away from the fifth sampling resistor, and one end of the eighth sampling resistor, which is far away from the seventh sampling resistor, are grounded together.
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.
Further, the high-level voltage values of the first PWM signal and the second PWM signal are equal to the voltage value of the dc power supply.
It follows that the output of the optocoupler can be effectively controlled.
In order to achieve the second object, the present invention provides a control method of 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 first PWM signal corresponding to the current flowing through the first load access terminal as a preset current value according to the first sampling voltage signal; the micro control unit calculates a second PWM signal corresponding to the current flowing through the second load access terminal as 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 an output end of the first optical coupler according to the first PWM signal, so that the current flowing through a first load access end is a preset current value; the second optocoupler outputs a second output voltage signal corresponding to the second PWM signal at an output end of the second optocoupler 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 of the two ends of the two paths of LED loads are sampled and transmitted to the micro control unit, the micro control unit calculates the duty ratio of the output PWM signals according to the sampling voltage values and outputs the duty ratio to the optocoupler, and the optocoupler controls voltage output so that the currents of the two paths of LED loads are constant and the brightness is kept consistent.
The method comprises the steps that a first voltage sampling module collects first sampling signals of a first load access end and transmits the first sampling signals to a micro-control unit, a second voltage sampling module collects second sampling voltage signals of a second load access end and transmits the second sampling voltage signals to the micro-control unit, and before the first voltage sampling module collects third sampling signals of the first load access end and transmits the third sampling signals to the micro-control unit, the second voltage sampling module collects fourth sampling voltage signals of the second load access end and transmits the fourth sampling voltage signals to the micro-control unit; the micro control unit judges whether the first sampling voltage signal is larger than a preset voltage value 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 larger than a voltage preset value, and if the fourth 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 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 judge whether the voltage of the LED load exceeds the output of the LED constant current source circuit or not, and the LED constant current source circuit plays a role in protection.
The further scheme is that 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, 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 comprises the following steps: the output end of the micro control unit outputs PWM signals with gradually reduced duty ratio 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 of the first load access end works and the second LED load of the second load access end works.
Therefore, when the PWM signal is large, the resistance of the LED load is increased, so that the LED can be conducted more quickly.
According to the further scheme, the micro control unit calculates a first PWM signal corresponding to the current flowing through the first load access terminal as a 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 terminal when the current is a preset current value according to the second voltage signal and the PWM calculation formula.
Drawings
Fig. 1 is a circuit schematic of an LED constant current source circuit of the present invention.
Fig. 2 is a flow chart of a control method of the LED constant current source circuit of the present invention.
The invention is further described below with reference to the drawings and examples.
Detailed Description
The invention is used for LED lamps, in particular to a bicolor temperature lamp with common positive characteristic, the voltage sampling module is used for sampling the voltages at two ends of each path of load, the micro control unit is used for calculating PWM signals according to the voltages at two ends of the load, and outputting the PWM signals to the optocoupler so as to change the voltages at two ends of the load, so that the currents of the loads at each path are equal and the brightness is consistent.
The invention discloses an LED constant current source circuit embodiment:
referring to fig. 1, the LED constant current source circuit of the present embodiment includes a first optocoupler U1, a micro control unit U3, a first voltage sampling module 11, a first resistor R2, a first capacitor C1, a second optocoupler 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 capacitance of the first capacitor C1 is equal to the capacitance of the second capacitor C2, and the resistance of the resistor R1 is equal to the resistance of the resistor R7. Wherein, the resistance plays 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 an LED 1-and an LED2-, the two LED loads share an anode, and the LED+ is connected with a direct-current voltage of 50V to the ground.
The input end of the first optocoupler U1 comprises a first input end 1 and a second input end 2, the first input end 1 is connected with a resistor R1, and the resistor R1 is connected with a direct current power supply, namely a 3.3-volt direct current power supply. The second input end 2 is connected to the micro control unit U3, and in this embodiment, the micro control unit U3 adopts an MCU. The output end of the first optical coupler U1 comprises a first output end 4 and a second output end 3, the first output end 4 is connected with the positive end of the first load access end, namely the LED+ end, and the second output end is connected with the negative end of the first load access end, namely the LED 1-end. The first resistor R2 is connected in series between the output end of the first optical coupler and the first load access end, namely one end of the first resistor R2 is connected between the second output end 3, and the other end of the first resistor R2 is connected with the negative end of the first load access end, namely the LED 1-end.
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 with the second sampling resistor R5 in series, and one end of the first sampling resistor R3 far away from the second sampling resistor R5 is connected with the positive end of the 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 with the fourth sampling resistor R6 in series, one end, far away from the fourth sampling resistor R6, of the third sampling resistor R4 is connected with the negative end of the first load access end, namely the LED 1-end, one end, far away from the first sampling resistor R3, of the second sampling resistor R5 is grounded, and one end, far away from the third sampling resistor R4, of the fourth sampling resistor R6 is grounded. The first sampling end of the first sampling voltage module 11 includes a first end and a second end, the first end is Vsen1, and is disposed between the first sampling resistor R3 and the second sampling resistor R5, the second end is vsen1+ and is disposed between the third sampling resistor R4 and the fourth sampling resistor R6, the Vsen1 and vsen1+ are connected to the input end of the micro control unit U3, that is, the first input end Vsen1 and the vsen1+ of the micro control unit U3 are respectively connected, and the micro control unit U3 can calculate the voltage between the led+ and the LED 1-by receiving the potentials of the two points Vsen1 and vsen1+, that is, the second voltage signal and the first sampling voltage signal, and combining the resistance values of the first sampling resistor R3, the second sampling resistor R5, the third sampling resistor R4 and the fourth sampling resistor R6.
The input end of the second optocoupler U2 includes a third input end 5 and a fourth input end 6, the first input end 1 is connected to a resistor R7, and the resistor R7 is connected to a dc power supply, i.e., a 3.3 v dc power supply. The third input 5 is connected to the micro control 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 end of the second optical coupler and the second load access end, i.e. one end of the second resistor R8 is connected with the third output end 7, and the other end is connected with the negative end of the first load access end, i.e. the LED 2-end. A first capacitor C2 is connected in parallel between the second optical coupler U2 and the second load access terminal.
The second voltage sampling module 12 comprises a third sampling resistor group and a fourth sampling resistor group, the third sampling resistor group comprises 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 far away from the sixth sampling resistor R11 is connected with the positive end of the second load access section, namely an 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 with the eighth sampling resistor R12 in series, one end of the seventh sampling resistor R10 far away from the eighth sampling resistor R12 is connected with the negative end of the second load access end, namely the LED 2-end, and one end of the sixth sampling resistor R11 far away from the fifth sampling resistor R9 and one end of the eighth sampling resistor R12 far away from the seventh sampling resistor R10 are grounded. The second sampling end of the first sampling voltage module 11 includes a third end and a fourth end, namely Vsen2, which are disposed between the fifth sampling resistor R9 and the sixth sampling resistor R11, the fourth end, namely vsen2+, is disposed between the seventh sampling resistor R10 and the eighth sampling resistor R12, the Vsen2 and vsen2+ are connected to the input end of the micro-control unit U3, namely, the second input end Vsen2 and the vsen2+ of the micro-control unit U3, and the micro-control unit U3 can calculate the voltage between the led+ and the LED 2-by receiving the potentials of the two points Vsen2 and vsen2+, namely, the fourth voltage signal and the third voltage signal, and combining the resistances of the fifth sampling resistor R9, the sixth sampling resistor R11, the seventh sampling resistor R10, and the eighth sampling resistor 12.
The first output end PWM1 end of the microcontroller U3 is connected with the second input end 2 of the first optical coupler U1, and the second output end PWM2 end of the microcontroller U3 is connected with the fourth input end 6 of the second optical coupler U2. The microcontroller U3 outputs a first PWM signal corresponding to a preset current value to the first optocoupler U1 according to the first sampling voltage signal, and the first optocoupler U1 is used for outputting a first output voltage signal corresponding to the first PWM signal at the output end of the first optocoupler 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 a preset current value to the second coupler U2 according to the second sampling voltage signal, and the second optical coupler U2 is used for outputting a second output voltage signal corresponding to the second PWM signal at the output end of the second optical coupler U2 according to the second PWM signal, so that the current flowing through the second load access end is the preset current value; 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, namely, the voltage value of the first PWM signal and the second PWM signal is 3.3 volts when the high level is the high level, and the voltage value of the low level is 0. The specific process is that, for the first sampled voltage signal, it is assumed that the first sampled voltage signal is U1, and according to the formula d1=1+i R/U1-U2I R/U1-U2 (1-D2)/U1, where I is a preset current value, U2 is a reference voltage value, D2 is a duty ratio when the optocoupler output voltage is the reference voltage value, and R is a resistance value of a resistor connected in series between the optocoupler output end and the load access end. The duty ratio D1 of the first PWM signal is calculated, and outputting the PWM1 signal with the duty ratio D1 may change 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, since preset current values of two paths corresponding to the first optocoupler U1 and the second optocoupler U2 are equal, it is set as I; the resistance value of the first resistor R1 is equal to that of the second resistor R8, and R is set; the total power consumed by the power of the LED load at the first load access end and the first resistor R1 is P1, the total power consumed by the power of the LED load at the second load access end and the second load R8 is P2, and p1=p2=p can be obtained:
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 is required to be determined, namely a preset current I, a corresponding sampling voltage signal U2 and the duty ratio D2 of PWM at the moment are determined, 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 duty ratio of the PWM signal which is required to be output by the micro control unit when the current passing through the LED load is a preset value, the optocoupler adjusts the output voltage according to the PWM signal, the current passing through the LED load is the preset current value, the effect of constant current is achieved, and as the LED loads of each path calculate the duty ratio corresponding to the PWM signal by the same reference point, the current of each path of LED load is consistent, and the brightness of the LED loads is consistent.
It can be understood that for one path of LED load or multiple paths of LED load, the effect that the current passing through the LED load is a preset value can be achieved by the LED constant current source circuit of the present invention.
The invention relates to a control method of an LED constant current source circuit, which comprises the following steps:
referring to fig. 2, the voltage acquisition module acquires a third sampling voltage signal and a fourth sampling voltage signal of the load access terminal and transmits the third sampling voltage signal and the fourth sampling voltage signal to the micro control unit, i.e. executes step S1.
The micro control unit determines whether the third sampling voltage signal and the fourth sampling voltage signal are greater than a preset voltage value, and then step S2 is executed. If the third sampling signal is greater than the preset voltage value, the fourth sampling signal is greater than the preset voltage value, which means that at this time, the first load access end and the second load access end are empty, or the voltage at both ends of the first LED load accessed by the first load access end and the voltage at both ends of the second LED load accessed by the second load access end are greater than the nominal voltage of the LED constant current source circuit, in order to reduce the no-load loss or as protection, the micro control unit needs to execute S4, i.e. outputs a PWM signal with a duty ratio of 100% to the input end of the optocoupler, outputs a PWM signal of 100%, so that the first optocoupler and the second optocoupler are cut off, thereby reducing no-load loss or protecting the LED constant current source circuit, and then returns to step S1, repeats the judgment process, and monitors the load condition in real time. If the third sampling voltage signal and the fourth sampling voltage signal are smaller than the preset voltage value, the fact that the first LED load and the second LED load which are connected at the moment meet the constant current condition is indicated, and S3 can be continuously executed.
The micro control unit outputs PWM signals with gradually reduced duty ratio to the input end of the optical coupler until the LED load works, namely, step S3 is executed, and the output end of the micro control unit outputs PWM signals with gradually reduced duty ratio to the second input end of the first optical coupler and the fourth input end of the second optical coupler respectively until the first LED load of the first load access end works and the second load of the second LED load access end works, so that the LED load can be conducted rapidly.
And then executing step S5, wherein the voltage acquisition module acquires a first sampling voltage signal and a second sampling voltage of the load access terminal and transmits the first sampling voltage signal and the second sampling voltage 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.
And step S6, the micro control unit outputs a PWM signal to the optical coupler according to the sampling 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 terminal is a preset current value according to a PWM calculation formula calculated by the first sampling voltage signal; and the micro control unit calculates a second PWM signal corresponding to the current flowing through the second load access terminal when the current is a preset current value according to the second sampling voltage signal and the PWM calculation formula. The specific process is the same as that of the embodiment of the LED constant current source circuit, and will not be described herein.
Finally, step S7 is executed, where the optocoupler changes the output terminal voltage of the optocoupler according to the PWM signal. Specifically, the first optocoupler outputs a first output voltage signal corresponding to the first PWM signal at an output end of the first optocoupler according to the first PWM signal, so that the current flowing through the first load access end is a preset current value; the second optocoupler outputs a second output voltage signal corresponding to the second PWM signal at an output end of the second optocoupler 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 collect the first sampling voltage signal and the second sampling voltage signal, and the micro control unit outputs PWM signals with different duty ratios according to the first sampling voltage signal and the second sampling voltage signal so that the first optocoupler and the second optocoupler change output voltage, and then the currents of LED loads of the first load access end and the second load access end are kept consistent, and brightness is further consistent.
Claims (10)
1. An LED constant current source circuit, comprising:
the device 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 in series between the output end of the first optical coupler and the first load access end;
the input end of the micro control unit is connected with the first sampling end of the first voltage sampling module; the input end of the micro control unit 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 of the positive end of the first load access end and sampling a second voltage signal of the negative end of the first load access end;
the output end of the micro control unit is connected with the second input end of the first optical coupler, and the micro control unit 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 configured to output 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 a 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 in series between the output end of the second optical coupler and the second load access end;
the second input end of the micro control unit is connected with the second sampling end of the second voltage sampling module; the input end of the micro control unit 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;
the second output end of the micro control unit is connected with the fourth input end of the optical coupler, and the micro control unit 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 optocoupler is configured to output a second output voltage signal corresponding to the second PWM signal at an output end of the second optocoupler according to the second PWM signal, so that a current flowing through the second load access end is the preset current value.
2. The 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. The 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 in series with the second sampling resistor, and one end of the first sampling resistor far away from the second sampling resistor is connected with the positive end of the first load access end; 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 is grounded together with one end, far away from the third sampling resistor, of the fourth sampling resistor.
4. The 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 in series with the sixth sampling resistor, 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 end; 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 in common.
5. The 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. The LED constant current source circuit according to any one of claims 1 to 5, wherein:
the high-level voltage values of the first PWM signal and the second PWM signal are equal to the voltage value of the direct current power supply.
7. A control method for applying the LED constant current source circuit according to any one of claims 1 to 6, comprising:
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; 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 micro control unit calculates a first PWM signal corresponding to the current flowing through the first load access terminal as the preset current value according to the first sampling voltage signal; the micro control unit calculates a second PWM signal corresponding to the current flowing through the second load access terminal as the 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 an 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 second optocoupler outputs a second output voltage signal corresponding to the second PWM signal at an output end of the second optocoupler according to the second PWM signal, so that the current flowing through the second load access end is the preset current value.
8. The control method of an LED constant current source circuit according to claim 7, wherein:
before the first voltage sampling module collects the first sampling voltage signal of the first load access end and transmits the first sampling voltage signal to the micro control unit, the second voltage sampling module collects the second sampling voltage signal of 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 voltage signal of the first load access end and transmits the third sampling voltage 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 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 larger than a voltage preset value, and if the fourth 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 fourth input end.
9. The control method of the LED constant current source circuit according to claim 8, wherein:
after the first voltage sampling module collects the first sampling voltage signal of the first load access end and transmits the first sampling voltage signal to the micro control unit, the second voltage sampling module collects the 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 comprises the following steps:
and the output end of the micro control unit outputs PWM signals with gradually reduced duty ratios 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 of the first load access end works and the second LED load of the second load access end works.
10. The control method of an LED constant current source circuit according to claim 9, wherein:
the micro control unit calculates a first PWM signal corresponding to the current flowing through the first load access terminal as 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 terminal as the preset current value according to the second voltage signal and the PWM calculation formula.
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