Constant-voltage output dimming circuit

Abstract

The utility model relates to the technical field of power electronics, in particular to a constant-voltage output dimming circuit, which comprises a voltage conversion unit, a self-adaptive current-limiting control unit and a micro-control unit. The voltage conversion unit comprises a resistor R99 and an MOS tube Q11; the self-adaptive current-limiting control unit is used for receiving dimming current I from a resistor R99, generating a feedback signal and transmitting the feedback signal to the micro-control unit, and then the micro-control unit generates a self-adaptive signal and a dimming PWM signal and transmits the self-adaptive signal and the dimming PWM signal to the self-adaptive current-limiting control unit; if the dimming PWM signal received by the self-adaptive current-limiting control unit is at a low level, a linear signal is generated in a time period t1, so that an MOS tube Q11 works in a linear region, and a saturation signal is generated in a time period t2, so that the MOS tube Q11 works in a saturation region; if the voltage is a high level, namely a t3 time period, a cut-off signal is generated, so that the MOS tube Q11 works in a cut-off region; therefore, according to different overshoot currents, self-adaptive suppression is realized, and a dimming function is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of power electronics, in particular to a constant voltage output dimming circuit. Background Art

[0002] In recent years, LED (light emitting diode) as a green, energy-saving, long-life luminous product, compared with traditional lighting sources, has obvious advantages in small size, durability, long life, and high energy efficiency, so it is widely used in daily LED lighting. Therefore, according to different environments, LED lights need to adjust different brightness to meet the different brightness needs of different people, and the brightness of LED light can be adjusted by adjusting the current flowing through the LED.

[0003] At present, the usual control method of the LED dimming system is to connect a field effect tube in series at the negative output end of the control circuit, and achieve the dimming purpose by controlling the proportion of the field effect tube's conduction time within the cycle, that is, dimming through duty cycle. This dimming technology has good dimming performance and consistency.

[0004] However, each time the field effect tube is turned on, due to the long size of the LED load and the short distance between the lines, the distributed capacitance between the lines is large, resulting in a large overshoot current at the output end in a short time when it is turned on, affecting the working stability and reliability of the dimming circuit; at the same time, part of the overshoot current flows through the LED lamp beads, which has a great impact on the reliability of the LED lamp beads. More importantly, the output current of the constant voltage power supply is not fixed, but a range value, so when the output current is different, the limit point of the overshoot current is also different, and the current overshoot current suppression circuit cannot adaptively adjust the corresponding limit point. Utility Model Content

[0005] In view of the above-mentioned defects, the purpose of the utility model is to provide a constant voltage output dimming circuit, which adaptively suppresses and realizes the dimming function according to different overshoot currents.

[0006] To achieve this purpose, the utility model adopts the following technical solutions:

[0007] A constant voltage output dimming circuit comprises a voltage conversion unit, an adaptive current limiting control unit and a micro control unit; the voltage conversion unit comprises a common mode inductor LF4, a resistor R99 and a MOS tube Q11; one end of the resistor R99 is electrically connected to the negative output end of the voltage conversion unit, the other end of the resistor R99 and the collection end of the adaptive current limiting control unit are electrically connected to the source of the MOS tube Q11, the drain of the MOS tube Q11 is electrically connected to the pin 3 of the common mode inductor LF4, the pin 2 of the common mode inductor LF4 is electrically connected to the positive output end of the voltage conversion unit, the control end of the adaptive current limiting control unit is electrically connected to the gate of the MOS tube Q11, and the dimming input end, adaptive input end and feedback end of the adaptive current limiting control unit are electrically connected to the dimming output end, adaptive output end and feedback input end of the micro control unit respectively;

[0008] The adaptive current limiting control unit is used to receive the dimming current I from the resistor R99, generate a feedback signal and transmit it to the micro control unit; after the micro control unit receives the feedback signal, it generates an adaptive signal and transmits it to the adaptive current limiting control unit;

[0009] The micro control unit is used to generate a dimming PWM signal and transmit it to the adaptive current limiting control unit;

[0010] When the adaptive current limiting control unit receives the dimming PWM signal and the adaptive signal, if the dimming PWM signal is at a low level, a linear signal is generated in the time period t1, and a saturation signal is generated in the time period t2; if the dimming PWM signal is at a high level, that is, in the time period t3, a cutoff signal is generated;

[0011] When the MOS transistor Q11 receives the linear signal, the saturation signal or the cut-off signal, it works in the linear region, the saturation region or the cut-off region respectively.

[0012] Further, the adaptive current limiting control unit includes an adaptive current limiting circuit and a switch circuit; the collection end of the adaptive current limiting circuit is used as the collection end of the adaptive current limiting control unit, the control end of the adaptive current limiting circuit is used as the control end of the adaptive current limiting control unit, the feedback end of the adaptive current limiting circuit is used as the feedback end of the adaptive current limiting control unit, the adaptive input end of the adaptive current limiting circuit is used as the adaptive input end of the adaptive current limiting control unit, and the dimming input end of the switch circuit is used as the dimming input end of the adaptive current limiting control unit;

[0013] The switch end of the adaptive current limiting circuit is electrically connected to the output end of the switch circuit;

[0014] The adaptive current limiting circuit is used to receive the dimming current I from the resistor R99, generate the feedback signal and transmit it to the micro control unit; after the micro control unit receives the feedback signal, it generates the adaptive signal and transmits it to the adaptive current limiting circuit;

[0015] The switch circuit is used for turning off the adaptive current limiting circuit when the dimming PWM signal received is at a low level, and turning on the adaptive current limiting circuit when the dimming PWM signal received is at a high level;

[0016] When the adaptive current limiting circuit receives the adaptive signal and is cut off, the linear signal is generated in the t1 time period, and the saturation signal is generated in the t2 time period; if the adaptive current limiting circuit is turned on, that is, in the t3 time period, the cutoff signal is generated.

[0017] Further, the adaptive current limiting circuit includes a resistor R93, a resistor R94, a resistor R95, a resistor R98, a resistor R100, a resistor R101, a transistor Q13, a capacitor C28, a capacitor C50, an operational amplifier U9A and an operational amplifier U9B; the negative input terminal of the operational amplifier U9A is used as a feedback terminal of the adaptive current limiting circuit, one end of the resistor R95 is used as an adaptive input terminal of the adaptive current limiting circuit, the collector of the transistor Q13 is used as a collection terminal of the adaptive current limiting circuit, the emitter of the transistor Q13 is used as a control terminal of the adaptive current limiting circuit, and the base of the transistor Q13 is used as a switch terminal of the adaptive current limiting circuit;

[0018] One end of the resistor R101 and the positive input end of the operational amplifier U9B are electrically connected to the collector of the transistor Q13, the other end of the resistor R101 and one end of the resistor R93 are electrically connected to the emitter of the transistor Q13, one end of the resistor R98 and one end of the resistor R100 are electrically connected to the negative input end of the operational amplifier U9B, the other end of the resistor R100 and the output end of the operational amplifier U9B are electrically connected to the negative input end of the operational amplifier U9A, and the resistor R101 is electrically connected to the collector of the transistor Q13. The other end of R95 and one end of the capacitor C28 are electrically connected to one end of the resistor R94, the other end of the resistor R94 is electrically connected to the positive input end of the operational amplifier U9A, the other end of the resistor R93 is electrically connected to the output end of the operational amplifier U9A, the positive power supply end of the operational amplifier U9A and one end of the capacitor C50 are connected to the power supply, and the other end of the capacitor C50, the other end of the capacitor C28, the other end of the resistor R98 and the negative power supply end of the operational amplifier U9A are grounded;

[0019] When the transistor Q13 is turned off, the adaptive current limiting circuit is turned on; when the transistor Q13 is turned on, the adaptive current limiting circuit is turned off.

[0020] Further, the feedback signal: Iout_SENSE=I*R99*N;

[0021] The duty cycle of the adaptive signal: SHOOT_PWM=Iout_SENSE / [(1-a)*V], that is, SHOOT_PWM=I*R99*N / [(1-a)*V];

[0022] Wherein I is the dimming current I, R99 is the resistance value of the resistor R99, N is the amplification factor of the operational amplifier U9B, a is the peak reserved margin of the dimming current I, and V is the voltage when the dimming output end of the micro control unit outputs a high level.

[0023] Furthermore, the value of the peak reserve margin a of the dimming current I is 0.1.

[0024] Furthermore, the switch circuit includes a resistor R102, a resistor R103, a resistor R104 and a MOS tube Q12; one end of the resistor R103 is used as a dimming input end of the switch circuit, and one end of the resistor R104 is used as an output end of the switch circuit;

[0025] The other end of the resistor R104 is electrically connected to the drain of the MOS transistor Q12, the other end of the resistor R103 and one end of the resistor R102 are electrically connected to the gate of the MOS transistor Q12, and the other end of the resistor R102 and the emitter of the MOS transistor Q12 are grounded.

[0026] Furthermore, it also includes a dimming signal receiving unit and a power factor correction unit; the input end of the dimming signal receiving unit is externally connected to the dimming AC signal, and the output end of the dimming signal receiving unit is electrically connected to the input end of the micro control unit;

[0027] The input end of the power factor correction unit is externally connected to a single-phase alternating current, and the output end of the power factor correction unit is electrically connected to the input end of the voltage conversion unit;

[0028] The dimming signal receiving unit is used to optically isolate the external dimming AC signal, convert it into a dimming DC signal and transmit it to the micro control unit; when the micro control unit receives the dimming DC signal, it generates the dimming PWM signal;

[0029] The power factor correction unit is used to improve the power factor of the single-phase alternating current and generate a constant voltage to be transmitted to the voltage conversion unit;

[0030] When the voltage conversion unit receives the constant voltage, it generates the dimming current I and a dimming signal.

[0031] Furthermore, the duty cycle of the dimming signal is (t1+t2) / (t1+t2+t3).

[0032] Furthermore, the voltage conversion unit further includes an isolation transformer T1, and the isolation transformer T1 isolates the constant voltage from the dimming signal.

[0033] The technical solution provided by the utility model may include the following beneficial effects: the adaptive current limiting control unit collects the dimming current I output by the voltage conversion unit in real time through the resistor R99, and forms a feedback signal (Iout_SENSE) that can be recognized by the microcontroller unit (such as MCU) after being processed by the internal circuit of the adaptive current limiting control unit, and feeds it back to the microcontroller unit, so that the microcontroller unit generates an adaptive signal (SHOOT_PWM) according to the received feedback signal and transmits it to the adaptive current limiting control unit; when the adaptive current limiting control unit receives the dimming PWM signal (DIM_PWM) and the adaptive signal (SHOOT_PWM), if the dimming PWM signal is at a low level, it means that the dimming current is to be adjusted. To control the MOS tube Q11 to be turned on, a linear signal is first generated in the t1 time period to make the MOS tube Q11 work in the linear region to over-conduct the overshoot current, and then a saturation signal is generated in the t2 time period to make the MOS tube Q11 work in the saturation region and be fully turned on; if the dimming PWM signal is at a high level, it means that the MOS tube Q11 is to be turned off, that is, the cut-off time period is set to the t3 time period, and a cut-off signal is generated to make the MOS tube Q11 work in the cut-off region; thereby, the overshoot current phenomenon caused by the conduction of the MOS tube Q11 is suppressed by adapting to the dimming current I in real time, and the logic of the dimming control of the lamp is kept unchanged by following the dimming PWM signal, so as to realize the dimming function and improve the working stability and reliability of the dimming circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The utility model is a schematic diagram of a constant voltage output dimming circuit in one embodiment of the utility model.

[0035] Figure 2 Yes Figure 1 The signal principle diagram of a constant voltage output dimming circuit is shown.

[0036] Figure 3 Yes Figure 1 The circuit diagram of the voltage conversion unit and the adaptive current limiting control unit is shown.

[0037] Among them: voltage conversion unit 1, adaptive current limiting control unit 2, micro control unit 3, common mode inductor LF4, resistor R99, MOS tube Q11, adaptive current limiting circuit 21, switch circuit 22, resistor R93, resistor R94, resistor R95, resistor R98, resistor R100, resistor R101, transistor Q13, capacitor C28, capacitor C50, operational amplifier U9A, operational amplifier U9B, resistor R102, resistor R103, resistor R104, MOS tube Q12, dimming signal receiving unit 4, power factor correction unit 5, isolation transformer T1. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0039] In the description of the embodiments of the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0041] Combine the following Figures 1 to 3 , describing a constant voltage output dimming circuit of an embodiment of the utility model.

[0042] A constant voltage output dimming circuit comprises a voltage conversion unit 1, an adaptive current limiting control unit 2 and a micro control unit 3; the voltage conversion unit 1 comprises a common mode inductor LF4, a resistor R99 and a MOS tube Q11; one end of the resistor R99 is electrically connected to the negative output end of the voltage conversion unit 1, the other end of the resistor R99 and the collection end of the adaptive current limiting control unit 2 are both electrically connected to the source of the MOS tube Q11, the drain of the MOS tube Q11 is electrically connected to the pin 3 of the common mode inductor LF4, the pin 2 of the common mode inductor LF4 is electrically connected to the positive output end of the voltage conversion unit 1, the control end of the adaptive current limiting control unit 2 is electrically connected to the gate of the MOS tube Q11, and the dimming input end, the adaptive input end and the feedback end of the adaptive current limiting control unit 2 are electrically connected to the dimming output end, the adaptive output end and the feedback input end of the micro control unit 3 respectively;

[0043] The adaptive current limiting control unit 2 is used to receive the dimming current I from the resistor R99, generate a feedback signal and transmit it to the micro control unit 3; when the micro control unit 3 receives the feedback signal, it generates an adaptive signal and transmits it to the adaptive current limiting control unit 2;

[0044] The micro control unit 3 is used to generate a dimming PWM signal and transmit it to the adaptive current limiting control unit 2;

[0045] When the adaptive current limiting control unit 2 receives the dimming PWM signal and the adaptive signal, if the dimming PWM signal is at a low level, a linear signal is generated in the t1 period, and a saturation signal is generated in the t2 period; if the dimming PWM signal is at a high level, that is, in the t3 period, a cutoff signal is generated;

[0046] When the MOS transistor Q11 receives a linear signal, a saturation signal or a cutoff signal, it operates in a linear region, a saturation region or a cutoff region respectively.

[0047] In a preferred embodiment of a constant voltage output dimming circuit proposed by the utility model, as Figure 1 As shown, the dimming current I used to dim the lamp is output from the positive and negative output terminals of the voltage conversion unit 1, and connected to the lamp through the pins 1 and 4 of the common mode inductor LF4. The resistor R99 is connected in series at the negative output terminal of the common mode inductor LF4 in front of the output terminal as a sampling resistor, and the MOS tube Q11 is connected in series to control the output of the dimming current I, so that the PWM waveform for adjusting the brightness of the lamp is formed with the on time and off time of the MOS tube Q11. Therefore, the measure to suppress the overcurrent generated when the MOS tube Q11 is turned on can be to control the MOS tube Q11 to enter the linear region transition first when it is turned on, and then enter the saturation region to suppress the overshoot current at the moment of the MOS tube Q11 turning on. Because the dimming current I output by the voltage conversion unit 1 is not constant, the process of adaptive dimming current I is as follows:

[0048] The adaptive current limiting control unit 2 collects the dimming current I output by the voltage conversion unit 1 in real time through the resistor R99, and forms a feedback signal (Iout_SENSE) that can be recognized by the micro control unit 3 (such as MCU) through the internal circuit processing of the adaptive current limiting control unit 2, and feeds back to the micro control unit 3, so that the micro control unit 3 generates an adaptive signal (SHOOT_PWM) according to the received feedback signal and transmits it to the adaptive current limiting control unit 2; when the adaptive current limiting control unit 2 receives the dimming PWM signal (DIM_PWM) and the adaptive signal (SHOOT_PWM), if the dimming PWM signal is low, it means that the MOS tube Q11 is to be controlled to be turned on, then a linear signal is first generated in the t1 time period to make the MOS tube Q11 work in the linear region to pass the overshoot current at the moment of turn-on, and then a saturation signal is generated in the t2 time period to make the MOS tube Q11 work in the saturation region and be fully turned on; if the dimming PWM signal is high, it means that the MOS tube Q11 is to be controlled to be turned off, that is, the cut-off time period is set to the t3 time period, and a cut-off signal is generated to make the MOS tube Q11 work in the cut-off region, such as Figure 2 As shown; thereby, the overshoot current phenomenon caused by the conduction of the MOS tube Q11 is suppressed by adapting to the dimming current I in real time, and the logic of the dimming control of the lamp is kept unchanged by following the dimming PWM signal, so as to realize the dimming function and improve the working stability and reliability of the dimming circuit.

[0049] Further, the adaptive current limiting control unit 2 includes an adaptive current limiting circuit 21 and a switch circuit 22; the acquisition end of the adaptive current limiting circuit 21 is used as the acquisition end of the adaptive current limiting control unit 2, the control end of the adaptive current limiting circuit 21 is used as the control end of the adaptive current limiting control unit 2, the feedback end of the adaptive current limiting circuit 21 is used as the feedback end of the adaptive current limiting control unit 2, the adaptive input end of the adaptive current limiting circuit 21 is used as the adaptive input end of the adaptive current limiting control unit 2, and the dimming input end of the switch circuit 22 is used as the dimming input end of the adaptive current limiting control unit 2;

[0050] The switch end of the adaptive current limiting circuit 21 is electrically connected to the output end of the switch circuit 22;

[0051] The adaptive current limiting circuit 21 is used to receive the dimming current I from the resistor R99, generate a feedback signal and transmit it to the micro control unit 3; when the micro control unit 3 receives the feedback signal, it generates an adaptive signal and transmits it to the adaptive current limiting circuit 21;

[0052] The switch circuit 22 is used to turn off the adaptive current limiting circuit 21 when the dimming PWM signal received is at a low level, and turn on the adaptive current limiting circuit 21 when the dimming PWM signal received is at a high level;

[0053] When the adaptive current limiting circuit 21 receives the adaptive signal and is turned off, a linear signal is generated in the time period t1 and a saturation signal is generated in the time period t2; if the adaptive current limiting circuit 21 is turned on, that is, in the time period t3, a cutoff signal is generated.

[0054] In this embodiment, Figure 3 As shown, the adaptive current limiting control unit 2 is composed of an adaptive current limiting circuit 21 and a switch circuit 22, wherein the adaptive current limiting circuit 21 is used to receive the dimming current I to generate a feedback signal (Iout_SENSE) to feed back to the micro control unit 3, and the micro control unit 3 analyzes and obtains an adaptive signal (SHOOT_PWM) to match different dimming currents I to drive the MOS tube Q11 to work in the linear region and the saturation region; and the switch circuit 22 is controlled by the dimming PWM signal (DIM_PWM) to turn on or off the adaptive current limiting circuit 21, ensuring that the adaptive current limiting circuit 21 is turned off to suppress the overshoot current when the dimming PWM signal (DIM_PWM) controls the MOS tube Q11 to turn on, otherwise the switch circuit 22 turns on the adaptive current limiting circuit 21 to keep the MOS tube Q11 in the cut-off region.

[0055] Further, the adaptive current limiting circuit 21 includes a resistor R93, a resistor R94, a resistor R95, a resistor R98, a resistor R100, a resistor R101, a transistor Q13, a capacitor C28, a capacitor C50, an operational amplifier U9A and an operational amplifier U9B; the negative input terminal of the operational amplifier U9A is used as a feedback terminal of the adaptive current limiting circuit 21, one end of the resistor R95 is used as an adaptive input terminal of the adaptive current limiting circuit 21, the collector of the transistor Q13 is used as a collection terminal of the adaptive current limiting circuit 21, the emitter of the transistor Q13 is used as a control terminal of the adaptive current limiting circuit 21, and the base of the transistor Q13 is used as a switch terminal of the adaptive current limiting circuit 21;

[0056] One end of the resistor R101 and the positive input end of the operational amplifier U9B are electrically connected to the collector of the transistor Q13, the other end of the resistor R101 and one end of the resistor R93 are electrically connected to the emitter of the transistor Q13, one end of the resistor R98 and one end of the resistor R100 are electrically connected to the negative input end of the operational amplifier U9B, the other end of the resistor R100 and the output end of the operational amplifier U9B are electrically connected to the negative input end of the operational amplifier U9A, the other end of the resistor R95 and one end of the capacitor C28 are electrically connected to one end of the resistor R94, the other end of the resistor R94 is electrically connected to the positive input end of the operational amplifier U9A, the other end of the resistor R93 is electrically connected to the output end of the operational amplifier U9A, the positive power supply end of the operational amplifier U9A and one end of the capacitor C50 are connected to the power supply, and the other end of the capacitor C50, the other end of the capacitor C28, the other end of the resistor R98 and the negative power supply end of the operational amplifier U9A are grounded;

[0057] When the transistor Q13 is turned off, the adaptive current limiting circuit 21 is turned on; when the transistor Q13 is turned on, the adaptive current limiting circuit 21 is turned off.

[0058] In this embodiment, the resistor R101 in the adaptive current limiting circuit 21 is a discharge resistor, which is used to be pulled down by the switch circuit 22 when the dimming PWM signal (DIM_PWM) is at a high level, and quickly discharge the gate-source voltage Vgs of the MOS switch Q11, so that the MOS tube Q11 is in the cut-off region; the operational amplifier U9B, the resistor R98 and the resistor R100 constitute an amplifier circuit, which is used to amplify the small voltage (i.e., the dimming current I) collected on the resistor R99, that is, to obtain a feedback signal (Iout_SENSE), and transmit the feedback signal to the operational amplifier U9A and feed it back to the micro control unit 3 at the same time; the resistor R94 is a current limiting resistor, which prevents the input current from being too large to damage the positive electrode of the operational amplifier U9A, and the resistor R95 and the capacitor C28 constitute an RC filter circuit, which is used to feed back the micro control unit 3 The adaptive signal (SHOOT_PWM) coming from the output is filtered into a stable DC signal to provide a reference voltage signal for the operational amplifier U9A. The capacitor C50 is a decoupling capacitor, which is used to filter out the high-frequency noise of the operational amplifier U9A to ensure that the operational amplifier U9 operates in a normal working state. Finally, the operational amplifier U9A compares the positive adaptive signal (SHOOT_PWM) with the negative feedback signal (Iout_SENSE), and outputs the corresponding voltage drive signal to the gate of the MOS tube Q11 for current limiting. The voltage drive signal output after the comparison of the two signals in different time periods t1 and t2 completes the process of adaptively suppressing overshoot current, so that the MOS tube Q1 works in the linear region in the t1 time period and in the saturation region in the t2 time period, thereby completing the conduction process.

[0059] Further, the feedback signal: Iout_SENSE = I*R99*N;

[0060] Duty cycle of adaptive signal: SHOOT_PWM = Iout_SENSE / [(1-a)*V], that is, SHOOT_PWM = I*R99*N / [(1-a)*V];

[0061] Wherein I is the dimming current I, R99 is the resistance value of the resistor R99, N is the gain of the operational amplifier U9B, a is the peak reserve margin of the dimming current I, and V is the voltage when the dimming output terminal of the micro control unit 3 outputs a high level.

[0062] In this embodiment, according to the circuit analysis, the feedback signal is calculated by the formula Iout_SENSE=I*R99*N; after the micro control unit 3 receives the feedback signal, the adaptive signal obtained by internally programming the adaptive feedback signal can be calculated by the formula SHOOT_PWM=Iout_SENSE / [(1-a)*V], which can be simplified as: SHOOT_PWM=I*R99*N / [(1-a)*V]; thus, after receiving the feedback signal generated by the dimming current I circuit, the micro control unit 3 can adaptively generate an adaptive signal, and the operational amplifier U9A compares the dynamic feedback signal and the adaptive signal, and constantly outputs a voltage driving signal that can make the MOS tube Q11 work in the linear region in the t1 time period and work in the saturation region in the t2 time period, thereby making the MOS tube Q11 not work at the peak value (reduced by a) in the t1 time period when it is turned on, to prevent the generation of overshoot current, and then transition to the t2 time period when it is turned on and work in the saturation region, thereby reducing the loss of the MOS tube Q11.

[0063] Furthermore, the value of the peak reserve margin a of the dimming current I is 0.1.

[0064] In this embodiment, considering that the conduction working area of ​​the MOS tube Q11 will affect the final effect of the dimming function, in order to avoid the Vgs voltage in the t1 time period when the MOS tube Q11 is turned on being too small, the peak reserve margin a of the dimming current I is preferably set to 0.1, i.e. 10%, which can basically eliminate the overshoot current.

[0065] Furthermore, the switch circuit 22 includes a resistor R102, a resistor R103, a resistor R104 and a MOS tube Q12; one end of the resistor R103 is used as a dimming input end of the switch circuit 22, and one end of the resistor R104 is used as an output end of the switch circuit 22;

[0066] The other end of the resistor R104 is electrically connected to the drain of the MOS transistor Q12, the other end of the resistor R103 and one end of the resistor R102 are electrically connected to the gate of the MOS transistor Q12, and the other end of the resistor R102 and the emitter of the MOS transistor Q12 are grounded.

[0067] In this embodiment, the main functions of the switch circuit 22 are: first, to ensure that the adaptive current limiting circuit 21 follows the dimming control logic of the dimming PWM signal (DIM_PWM); second, to ensure that the MOS tube Q11 works in the cut-off region during the t3 period when the dimming PWM signal (DIM_PWM) is at a high level; therefore, the switch circuit 22 is composed of the MOS tube Q12 and its peripheral circuits, and when the dimming PWM signal (DIM_PWM) is at a low level, the triode Q13 is cut off, and the MOS tube Q11 is controlled by the adaptive current limiting circuit 21, and when the dimming PWM signal (DIM_PWM) is at a high level, the triode Q13 is turned on, and the MOS tube Q11 is pulled down, and the gate voltage of the MOS tube Q11 is quickly discharged by the resistor R101, and works in the cut-off region.

[0068] Furthermore, it also includes a dimming signal receiving unit 4 and a power factor correction unit 5; the input end of the dimming signal receiving unit 4 is externally connected to the dimming AC signal, and the output end of the dimming signal receiving unit 4 is electrically connected to the input end of the micro control unit 3;

[0069] The input end of the power factor correction unit 5 is externally connected to a single-phase alternating current, and the output end of the power factor correction unit 5 is electrically connected to the input end of the voltage conversion unit 1;

[0070] The dimming signal receiving unit 4 is used to optically isolate the external dimming AC signal, convert it into a dimming DC signal and transmit it to the micro control unit 3; when the micro control unit 3 receives the dimming DC signal, it generates a dimming PWM signal;

[0071] The power factor correction unit 5 is used to improve the power factor of the single-phase AC power and generate a constant voltage to be transmitted to the voltage conversion unit 1;

[0072] When the voltage conversion unit 1 receives the constant voltage, it generates a dimming current I and a dimming signal.

[0073] In this embodiment, when the dimming PWM signal (DIM_PWM) of the dimming circuit is generated by the microcontroller unit 3 external circuit drive, there is a dimming signal receiving unit 4 for converting the dimming AC signal transmitted from the outside into a dimming DC signal recognizable by the microcontroller unit 3, and the dimming signal receiving unit 4 uses an optical coupler (photocoupler) to isolate the AC signal and the DC signal to improve the stability of the dimming circuit; and the voltage conversion unit 1 needs to be driven by a high power factor constant voltage provided by the power factor correction unit 5 to generate a dimming current I for realizing the dimming function, reducing the impact of voltage fluctuations on the dimming function, and using the resistor R99 and the MOS tube Q11 to cooperate with the adaptive current limiting control unit 2 to generate the final dimming signal for stably and reliably realizing the dimming function. It should be noted that there are many circuit structures in the prior art that can realize the functions of the dimming signal receiving unit 4 and the power factor correction unit 5, so their circuit structures are not limited here.

[0074] Furthermore, the duty cycle of the dimming signal is (t1+t2) / (t1+t2+t3).

[0075] In this embodiment, because the adaptive current limiting control unit 2 suppresses the generation of overshoot current by controlling the MOS tube Q11 to work in the linear region, the saturation region, and the cut-off region, and it is necessary to keep the time when the MOS tube Q11 works in the linear region and the saturation region corresponding to the low level of the dimming PWM signal, and the time when the MOS tube Q11 works in the cut-off region corresponds to the high level of the dimming PWM signal, so as to keep the logic of the dimming control of the lamp unchanged, when the voltage conversion unit 1 receives a constant voltage, after generating the dimming current I, the adaptive current limiting control unit 2 controls the MOS tube Q11 to adaptively suppress the overshoot current, and the duty cycle of the dimming signal finally generated should be (t1+t2) / (t1+t2+t3), wherein (t1+t2+t3) is the time of one cycle, and (t1+t2) is the conduction time (i.e., the high level time); the dimming signal can realize stable and reliable dimming of the subsequent lamp.

[0076] Furthermore, the voltage conversion unit 1 further includes an isolation transformer T1, and the isolation transformer T1 isolates the constant voltage and the dimming signal.

[0077] In this embodiment, the power factor correction unit 5 is transmitted to the primary side of the isolation transformer T1 of the voltage conversion unit 1 for voltage conversion, and the dimming current I is generated by electromagnetic induction on the secondary side of the isolation transformer T1, and then the dimming signal is generated by the dimming current I, thereby isolating the constant voltage and the dimming signal to avoid the high voltage side from affecting the dimming signal, thereby affecting the dimming effect.

[0078] Other structures and operations of a constant voltage output dimming circuit according to an embodiment of the utility model are known to ordinary technicians in the field and will not be described in detail here.

[0079] In the description of this specification, the description with reference to the terms "embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0080] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A constant voltage output dimming circuit, characterized in that: It includes a voltage conversion unit, an adaptive current limiting control unit and a micro control unit; the voltage conversion unit includes a common mode inductor LF4, a resistor R99 and a MOS tube Q11; one end of the resistor R99 is electrically connected to the negative output end of the voltage conversion unit, the other end of the resistor R99 and the collection end of the adaptive current limiting control unit are electrically connected to the source of the MOS tube Q11, the drain of the MOS tube Q11 is electrically connected to the pin 3 of the common mode inductor LF4, the pin 2 of the common mode inductor LF4 is electrically connected to the positive output end of the voltage conversion unit, the control end of the adaptive current limiting control unit is electrically connected to the gate of the MOS tube Q11, and the dimming input end, the adaptive input end and the feedback end of the adaptive current limiting control unit are electrically connected to the dimming output end, the adaptive output end and the feedback input end of the micro control unit respectively; The adaptive current limiting control unit is used to receive the dimming current I from the resistor R99, generate a feedback signal and transmit it to the micro control unit; after the micro control unit receives the feedback signal, it generates an adaptive signal and transmits it to the adaptive current limiting control unit; The micro control unit is used to generate a dimming PWM signal and transmit it to the adaptive current limiting control unit; When the adaptive current limiting control unit receives the dimming PWM signal and the adaptive signal, if the dimming PWM signal is at a low level, a linear signal is generated in the time period t1, and a saturation signal is generated in the time period t2; if the dimming PWM signal is at a high level, that is, in the time period t3, a cutoff signal is generated; When the MOS transistor Q11 receives the linear signal, the saturation signal or the cut-off signal, it works in the linear region, the saturation region or the cut-off region respectively.

2. The constant voltage output dimming circuit according to claim 1, characterized in that: The adaptive current limiting control unit comprises an adaptive current limiting circuit and a switch circuit; the collection end of the adaptive current limiting circuit is used as the collection end of the adaptive current limiting control unit, the control end of the adaptive current limiting circuit is used as the control end of the adaptive current limiting control unit, the feedback end of the adaptive current limiting circuit is used as the feedback end of the adaptive current limiting control unit, the adaptive input end of the adaptive current limiting circuit is used as the adaptive input end of the adaptive current limiting control unit, and the dimming input end of the switch circuit is used as the dimming input end of the adaptive current limiting control unit; The switch end of the adaptive current limiting circuit is electrically connected to the output end of the switch circuit; The adaptive current limiting circuit is used to receive the dimming current I from the resistor R99 and generate the feedback signal to be transmitted to the micro control unit; After receiving the feedback signal, the micro control unit generates the adaptive signal and transmits it to the adaptive current limiting circuit; The switch circuit is used for turning off the adaptive current limiting circuit when the dimming PWM signal received is at a low level, and turning on the adaptive current limiting circuit when the dimming PWM signal received is at a high level; When the adaptive current limiting circuit receives the adaptive signal and is cut off, the linear signal is generated in the t1 time period, and the saturation signal is generated in the t2 time period; if the adaptive current limiting circuit is turned on, that is, in the t3 time period, the cutoff signal is generated.

3. The constant voltage output dimming circuit according to claim 2, characterized in that: The adaptive current limiting circuit includes a resistor R93, a resistor R94, a resistor R95, a resistor R98, a resistor R100, a resistor R101, a transistor Q13, a capacitor C28, a capacitor C50, an operational amplifier U9A and an operational amplifier U9B; the negative input end of the operational amplifier U9A is used as a feedback end of the adaptive current limiting circuit, one end of the resistor R95 is used as an adaptive input end of the adaptive current limiting circuit, the collector of the transistor Q13 is used as a collection end of the adaptive current limiting circuit, the emitter of the transistor Q13 is used as a control end of the adaptive current limiting circuit, and the base of the transistor Q13 is used as a switch end of the adaptive current limiting circuit; One end of the resistor R101 and the positive input end of the operational amplifier U9B are electrically connected to the collector of the transistor Q13, the other end of the resistor R101 and one end of the resistor R93 are electrically connected to the emitter of the transistor Q13, one end of the resistor R98 and one end of the resistor R100 are electrically connected to the negative input end of the operational amplifier U9B, the other end of the resistor R100 and the output end of the operational amplifier U9B are electrically connected to the negative input end of the operational amplifier U9A, and the resistor R101 is electrically connected to the collector of the transistor Q13. The other end of R95 and one end of the capacitor C28 are electrically connected to one end of the resistor R94, the other end of the resistor R94 is electrically connected to the positive input end of the operational amplifier U9A, the other end of the resistor R93 is electrically connected to the output end of the operational amplifier U9A, the positive power supply end of the operational amplifier U9A and one end of the capacitor C50 are connected to the power supply, and the other end of the capacitor C50, the other end of the capacitor C28, the other end of the resistor R98 and the negative power supply end of the operational amplifier U9A are grounded; When the transistor Q13 is turned off, the adaptive current limiting circuit is turned on; when the transistor Q13 is turned on, the adaptive current limiting circuit is turned off.

4. The constant voltage output dimming circuit according to claim 3, characterized in that: The feedback signal: Iout_SENSE=I*R99*N; The duty cycle of the adaptive signal: SHOOT_PWM=Iout_SENSE / [(1-a)*V], that is, SHOOT_PWM=I*R99*N / [(1-a)*V]; Wherein I is the dimming current I, R99 is the resistance value of the resistor R99, N is the amplification factor of the operational amplifier U9B, a is the peak reserved margin of the dimming current I, and V is the voltage when the dimming output end of the micro control unit outputs a high level.

5. The constant voltage output dimming circuit according to claim 4, characterized in that: The value of the peak reserve margin a of the dimming current I is 0.

1.

6. The constant voltage output dimming circuit according to claim 2, characterized in that: The switch circuit includes a resistor R102, a resistor R103, a resistor R104 and a MOS tube Q12; one end of the resistor R103 is used as a dimming input end of the switch circuit, and one end of the resistor R104 is used as an output end of the switch circuit; The other end of the resistor R104 is electrically connected to the drain of the MOS transistor Q12, the other end of the resistor R103 and one end of the resistor R102 are electrically connected to the gate of the MOS transistor Q12, and the other end of the resistor R102 and the emitter of the MOS transistor Q12 are grounded.

7. The constant voltage output dimming circuit according to claim 1, characterized in that: It also includes a dimming signal receiving unit and a power factor correction unit; the input end of the dimming signal receiving unit is externally connected to the dimming AC signal, and the output end of the dimming signal receiving unit is electrically connected to the input end of the micro control unit; The input end of the power factor correction unit is externally connected to a single-phase alternating current, and the output end of the power factor correction unit is electrically connected to the input end of the voltage conversion unit; The dimming signal receiving unit is used to optically isolate the external dimming AC signal, convert it into a dimming DC signal and transmit it to the micro control unit; when the micro control unit receives the dimming DC signal, it generates the dimming PWM signal; The power factor correction unit is used to improve the power factor of the single-phase alternating current and generate a constant voltage to be transmitted to the voltage conversion unit; When the voltage conversion unit receives the constant voltage, it generates the dimming current I and a dimming signal.

8. The constant voltage output dimming circuit according to claim 7, characterized in that: The duty cycle of the dimming signal is (t1+t2) / (t1+t2+t3).

9. The constant voltage output dimming circuit according to claim 7, characterized in that: The voltage conversion unit further includes an isolation transformer T1, and the isolation transformer T1 isolates the constant voltage from the dimming signal.

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