Low-PF silicon controlled rectifier dimming circuit and lighting circuit
By obtaining the voltage at the connection node between the load switch and the LED through an adaptive adjustment circuit, and generating an adjustment voltage to control the LED current, the problem of unstable LED current caused by undervoltage of the input capacitor in the low PF SCR dimming circuit is solved, and the stability of LED current and dimming compatibility are achieved.
Patent Information
- Application Number
- CN202510376979.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-27
- Publication Date
- 2026-02-06
AI Technical Summary
In low power factor (PF) thyristor dimming circuits, undervoltage of the input capacitor causes LED current instability and flickering. Existing technologies cannot effectively control the LED current.
The voltage at the connection point between the load switch and the LED is obtained through an adaptive adjustment circuit, which generates an adjustable voltage to control the LED current and avoids undervoltage of the input capacitor. The adaptive adjustment circuit adjusts the LED current according to voltage changes.
This achieves stability of LED current when the conduction angle of the SCR dimmer changes, avoids input capacitor undervoltage and LED flicker, and improves dimming compatibility and efficiency.
Smart Images
Figure CN121487066A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power electronics, and in particular to a low power factor (PF) silicon controlled rectifier (SCR) dimming circuit and lighting circuit. Background Technology
[0002] In a thyristor dimming circuit, the thyristor regulator achieves dimming through phase control, that is, by changing the conduction phase angle to adjust the output current to achieve dimming. In an existing high-PF dimming scheme, such as... Figure 1 As shown, the bus voltage VBUS output by the rectifier circuit powers the LED and charges the capacitor C0. The capacitor C0 is connected in parallel with the LED. When the bus voltage is insufficient to power the LED, the capacitor C0 continues to power the LED. By detecting the conduction angle of the thyristor dimmer, a dimming reference voltage is generated based on the size of the conduction angle to control the magnitude of the LED current.
[0003] In low-PF SCR dimming solutions, such as Figure 2 As shown, the AC input VAC is rectified to generate a bus voltage VBUS. This bus voltage charges the input capacitor Cin through diode D0. One end of the input capacitor Cin is connected to the positive terminal of the LED, and the other end is grounded. The LED is powered by the voltage across the input capacitor Cin. If the LED current control scheme in the high-PF dimming scheme is still used, that is, the LED current is controlled based on the dimming reference voltage generated by the conduction angle, the following problems will occur: When the conduction angle is small, the energy stored in the input capacitor Cin is small. If the output energy, i.e., the LED current, is not controlled and further reduced, the voltage VIN on the input capacitor will experience an undervoltage phenomenon. That is, the voltage VIN is insufficient to fully turn on the load switch M1 in the LED path. The load switch M1 operates in a linear conduction state. At this time, the LED current is no longer controlled by the dimming reference voltage but is determined by the magnitude of the voltage VIN. This will cause the LED current to be unstable and the LED to flicker. See [link to relevant documentation]. Figure 3 .
[0004] Reference Figure 3 According to the waveform of the bus voltage VBUS, when the conduction angle is small, as the input capacitor voltage VIN decreases, the LED current ILED is no longer in a constant current state, but decreases as the input capacitor voltage VIN decreases, and the LED current is unstable. Summary of the Invention
[0005] The purpose of this invention is to provide a low-PF silicon controlled rectifier dimming circuit and lighting circuit. This invention can adaptively adjust the LED current to avoid undervoltage of the input capacitor, which would cause unstable output and LED flickering.
[0006] This invention also provides a low-PF thyristor dimming circuit, wherein the AC power supply voltage is converted into a phase-cut bus voltage by a thyristor dimmer and a rectifier circuit, characterized in that it includes:
[0007] A diode and an input capacitor are provided. The positive terminal of the diode receives the bus voltage, the negative terminal of the diode is connected to the positive terminal of the LED, the first terminal of the input capacitor is connected to the common connection terminal of the diode and the LED, the second terminal of the input capacitor is grounded, and the input capacitor provides the power supply voltage for the LED.
[0008] A load switch is connected in series with the LED;
[0009] An adaptive adjustment circuit acquires a first voltage characterizing the voltage at the connection node between the load switch and the LED, generates an adjustment voltage based on the first voltage, and uses the adjustment voltage to control the switching state of the load switch in order to control the current of the LED.
[0010] Optionally, the adjusted voltage is positively correlated with the first voltage.
[0011] Optionally, the adjustment voltage is generated based on the difference between the first voltage and the first reference voltage. When the difference is greater than zero, the adjustment voltage is positively correlated with the difference. When the difference is less than zero, the adjustment voltage is negatively correlated with the absolute value of the difference.
[0012] Optionally, when the difference is greater than zero, the regulating voltage increases; when the difference is less than zero, the regulating voltage decreases.
[0013] Optionally, the adjustment voltage is used as a dimming reference voltage, the dimming reference voltage controls the current of the LED, and the current of the LED is positively correlated with the dimming reference voltage.
[0014] Optionally, the adjustment voltage is used as a dimming reference voltage. When the difference is greater than zero, the dimming reference voltage controls the current of the LED to increase; when the difference is less than zero, the dimming reference voltage controls the current of the LED to decrease.
[0015] Optionally, the thyristor dimming circuit further includes,
[0016] A conduction angle detection circuit detects the conduction angle of the thyristor dimmer and obtains a conduction angle detection signal characterizing the magnitude of the conduction angle.
[0017] The reference voltage generating circuit generates a first reference voltage based on the conduction angle detection signal. The larger the conduction angle detection signal, the larger the first reference voltage. The first reference voltage is used to control the current of the LED.
[0018] Optionally, when the conduction angle is less than a first threshold angle, the current of the LED is controlled by the regulating voltage;
[0019] When the conduction angle is greater than the first threshold angle, the current of the LED is controlled by the first reference voltage.
[0020] Optionally, a low-voltage selection circuit is also included, which receives the regulated voltage and the first reference voltage, selects the smaller value between the regulated voltage and the first reference voltage, and outputs it to obtain a dimming reference voltage; the dimming reference voltage is used to control the switching state of the load switch in order to control the current of the LED.
[0021] Optionally, the adaptive adjustment circuit includes a first operational amplifier, a first switching transistor, a second switching transistor, and a first capacitor. The first operational amplifier amplifies the error between the first voltage and the first reference voltage to obtain an error amplification signal.
[0022] When the error amplification signal is greater than zero, the error amplification signal drives the first switch to turn on, and the first current flowing through the first switch charges the first capacitor.
[0023] When the error amplification signal is less than zero, the error amplification signal is inverted and drives the second switch to turn on, and the second current flowing through the second switch discharges the first capacitor.
[0024] The regulating voltage is obtained based on the voltage of the first capacitor.
[0025] Optionally, a second operational amplifier is also included, wherein the first input terminal of the second operational amplifier receives the dimming reference voltage, the second input terminal of the second operational amplifier receives a current sampling signal characterizing the LED current, and the output terminal of the second operational amplifier is connected to the control terminal of the load switch.
[0026] Optionally, the supply voltage is obtained, and the first voltage is derived based on the supply voltage and the voltage drop across the LED; or, the first voltage is obtained by sampling the voltage at the connection point between the load switch and the LED.
[0027] The present invention also provides a lighting circuit, including any of the above-mentioned low-PF silicon controlled rectifier dimming circuits.
[0028] Compared with existing technologies, this invention has the following advantages: This invention generates an adjustment voltage based on the first voltage at the drain of the load switch, and adaptively adjusts the LED current based on this adjustment voltage. When the conduction angle of the SCR dimmer is small, the larger the first voltage, the larger the adjustment voltage, and the larger the controlled LED current; conversely, the smaller the first voltage, the smaller the adjustment voltage, and the smaller the controlled LED current. Even when the conduction angle of the SCR dimmer is small, this invention can maintain stable LED current control, preventing undervoltage of the input capacitor, uncontrolled LED current, and LED flickering. Attached Figure Description
[0029] Figure 1 The schematic diagram is of an existing high-PF silicon controlled thyristor dimming circuit.
[0030] Figure 2 Schematic diagram of a low-PF silicon controlled rectifier dimming circuit;
[0031] Figure 3 for Figure 2 Waveform diagram of the working state of the thyristor dimming circuit;
[0032] Figure 4 This is a schematic diagram of Embodiment 1 of the low PF silicon controlled thyristor dimming circuit of the present invention;
[0033] Figure 5 This is a schematic diagram of Embodiment 2 of the low PF silicon controlled thyristor dimming circuit of the present invention;
[0034] Figure 6 For the present invention Figure 4 , Figure 5 Schematic diagram of the adaptive adjustment circuit;
[0035] Figure 7 This is a graph of the dimming reference voltage. Detailed Implementation
[0036] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.
[0037] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.
[0038] The invention is described more specifically in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, in order to facilitate and clearly illustrate the purpose of the embodiments of the invention.
[0039] like Figure 4The diagram illustrates the schematic of Embodiment 1 of the thyristor dimming circuit of the present invention, including a thyristor dimmer T1, a rectifier circuit, a diode D0, an input capacitor Cin, a load switch M1, an adaptive adjustment circuit O1, and an operational amplifier O2. The AC input voltage VAC is converted to a bus voltage VBUS by the thyristor dimmer T1 and the rectifier circuit. The anode of diode D0 receives the bus voltage, and the cathode of diode D0 is connected to the first terminal of the input capacitor Cin. The second terminal of the input capacitor is connected to ground, and the voltage VIN of the input capacitor supplies power to the LED load. The load switch M1 is connected in series with the LED. Preferably, the load switch is an NMOS transistor. The voltage V1 at the connection point between the load switch M1 and the LED, i.e., the drain voltage of the load switch, can be obtained. Alternatively, the voltage VIN of the input capacitor can be sampled, and the voltage V1 is obtained based on the difference between VIN and the forward voltage drop of the LED. The adaptive adjustment circuit 01 receives voltage V1 and generates adjustment voltage VC based on voltage V1. The adjustment voltage VC serves as the dimming reference voltage for controlling the LED current. The non-inverting input of the operational amplifier 02 receives the dimming reference voltage VC, and the inverting input receives the sampling signal VCS that represents the LED current. The sampling signal can be obtained by acquiring the voltage of the sampling resistor RCS connected in series with the LED. The output of the operational amplifier 02 is connected to the control terminal of the load switch M1.
[0040] When the conduction angle of the SCR dimmer is small, the energy stored in the input capacitor Cin is small, and the voltage VIN of the input capacitor is small. To ensure that the input capacitor does not experience undervoltage (i.e., the load switch operates in a controlled saturation state throughout the entire switching cycle (half-wave cycle), this invention controls the LED current to be small. This prevents excessive energy consumption by the LED and avoids undervoltage of the input capacitor. Furthermore, this invention generates an adjustment voltage VC based on the voltage V1. A larger voltage V1 indicates a larger input capacitor voltage VIN, and the adaptive adjustment circuit generates a larger adjustment voltage VC based on the larger voltage V1 to control a larger LED current and improve dimming efficiency. Conversely, a smaller voltage V1 indicates a smaller input capacitor voltage, and the adaptive adjustment circuit generates a smaller adjustment voltage VC based on the smaller voltage V1 to control a smaller LED current. In short, the control voltage VC is positively correlated with the voltage V1, so that the LED current is positively correlated with the voltage V1. Furthermore, the adjustment voltage is obtained based on the difference between the voltage V1 and the preset reference voltage. When the difference is greater than zero, the control voltage is positively correlated with the difference. When the difference is less than zero, the control voltage is negatively correlated with the absolute value of the difference. Furthermore, if the difference is greater than zero, the control voltage increases; if the difference is less than zero, the control voltage decreases.
[0041] This embodiment of the invention employs an adaptive control method, which adaptively generates and adjusts the voltage VC based on the voltage V1, thereby adaptively controlling the LED current. This invention eliminates the need to sample the conduction angle of the SCR dimmer to control the LED current, resulting in a simpler and lower-cost control method. It also prevents input capacitor undervoltage, avoids LED current instability and LED flickering, and improves dimming compatibility.
[0042] When the conduction angle of the SCR dimmer is large, the bus voltage VBUS is smaller than the minimum input capacitor voltage at the moment the SCR dimmer is turned on. For example, when the conduction angle is close to 180 degrees, the bus voltage is close to 0V at the moment the SCR dimmer is turned on, while the minimum input capacitor voltage is much larger than 0V. If the LED current is still controlled solely by the voltage adjustment voltage V1 / bus voltage VBUS, the dimming curve travel will be affected. At a large conduction angle, voltage V1 will stabilize at a large value, and the LED current will also stabilize at a large value, making it impossible to further reduce the LED current. Furthermore, at a large conduction angle, the capacitance of the input capacitor also affects the dimming travel. A larger input capacitor capacitance results in a larger minimum input capacitor voltage and a shorter dimming curve travel. Therefore, this invention also proposes... Figure 5 The dimming scheme shown.
[0043] like Figure 5 The diagram illustrates the principle of Embodiment 2 of the thyristor dimming circuit of the present invention. Based on Embodiment 1, it is necessary to control the LED current according to the conduction angle of the thyristor dimmer. Therefore, Embodiment 2 further includes a conduction angle detection circuit 03, a reference voltage generation circuit 04, and a low-voltage selection circuit 05. The conduction angle detection circuit detects the conduction angle of the thyristor dimmer T1 and outputs a signal A1 representing the magnitude of the conduction angle. The reference voltage generation circuit 04 receives the signal A1 and generates a first reference voltage VREF1. The larger the conduction angle represented by the signal A1, the larger the first reference voltage VREF1, i.e., the first reference voltage VREF1 is positively correlated with the conduction angle of the thyristor dimmer. The low-voltage selection circuit 05 receives the adjustment voltage VC and the first reference voltage VREF1, and selects the lower value as the dimming reference voltage output. For example, when the adjustment voltage VC is less than the first reference voltage VREF1, the low-voltage selection circuit selects the adjustment voltage VC as the dimming reference voltage output. The non-inverting input of op-amp 02 is connected to the output of the low-voltage selection circuit, and its inverting output receives the sampling voltage VCS from the sampling resistor RCS. Its control terminal is connected to the control terminal of the load switch M1.
[0044] Embodiment 2 of the present invention controls the LED current based on both the voltage V1 and the conduction angle. This solves the problem of undervoltage of the input capacitor when the conduction angle is small, as the dimming reference voltage is fixed and the LED current cannot be further reduced. It also solves the problem of poor dimming compatibility and short dimming travel when the conduction angle is large, as the voltage V1 is large and the LED current is large, preventing further reduction of the LED current. However, Embodiment 2 requires sampling the conduction angle of the thyristor dimmer, which increases the complexity, cost, and the impact of external interference such as common-mode interference.
[0045] like Figure 6 As shown, the present invention is illustrated. Figure 4 , 5 The schematic diagram of an embodiment of the adaptive adjustment circuit includes operational amplifier 101, switching transistors K1 and K2, current sources I1 and I2, inverter 102, and capacitor C1. Operational amplifier 101 amplifies the error between voltage V1 and reference voltage VREF0, and the output is used to drive the switching transistors K1 and K2 to turn on and off. When voltage V1 is greater than the reference voltage VREF0, operational amplifier 101 outputs a high-level signal to control switching transistor K1 to turn on, and the current source I1 outputs current through switching transistor K1 to charge capacitor C1, and the voltage of capacitor C1, i.e., the adjustment voltage VC, gradually increases. When voltage V1 is less than the reference voltage VREF0, operational amplifier 101 outputs a low-level signal, which, after passing through inverter 102, controls switching transistor K2 to turn on, and the output current of current source I2 flows through switching transistor K2 to discharge capacitor C1, and the voltage on capacitor C1 decreases.
[0046] When the conduction angle is small, the voltage VIN of the input capacitor is small, and the drain voltage V1 of the switching transistor M1 is small. If the voltage V1 is less than the reference voltage VREF0, the switching transistor K2 turns on, and the capacitor C1 discharges through the switch K2. The regulating voltage VC on the capacitor C1 decreases. Figure 3 For example, based on the virtual short characteristic of the op-amp, the sampling voltage VCS decreases, thereby reducing the LED current and the energy consumed by the load. This prevents the input capacitor voltage from dropping too low and causing an undervoltage state. In practice, the voltage V1 gradually decreases following the voltage VIN, and VC also gradually decreases. The LED current is not completely constant, but the fluctuation of the LED current is not large and is acceptable. The situation described in the background technology, where the input capacitor is undervoltage and the LED current suddenly drops, will not occur. Similarly, when the conduction angle is large, the input capacitor voltage VIN is large. If the voltage V1 is greater than the reference voltage VREF0, the switch K1 turns on, and capacitor C1 is charged through the switch K1. The regulating voltage VC on capacitor C1 increases, thereby controlling the LED current to increase.
[0047] Although the adaptive adjustment circuit of this invention is only given Figure 6The schematic diagram is shown in one embodiment. However, based on the above analysis, the present invention can obtain the adjustable voltage in a variety of ways. As long as the adjustment circuit obtained according to the design method of the present invention can solve the problems proposed by the present invention, it should be within the protection scope of the present invention.
[0048] like Figure 7 The diagram illustrates the dimming reference voltage curves. Curves ①, ②, and ③ represent the dimming reference voltage Vref set based on voltage V1, with corresponding input capacitor values C1, C2, and C3, respectively, where C1 > C2 > C3. Curve ④ represents the dimming reference voltage Vref set solely based on the conduction angle. As can be seen from the diagram, when the conduction angle is small, the dimming reference voltages corresponding to curves ①, ②, and ③ are less than those corresponding to curve ④. Therefore, setting the dimming reference voltage based on voltage V1 can further control the LED current, preventing undervoltage at the input capacitor and ensuring stable LED current. When the conduction angle is large, setting the dimming reference voltage based on the conduction angle can prevent the LED current from becoming too small, further improving dimming efficiency and dimming travel.
[0049] Although the embodiments are described and illustrated separately above, some common technologies are involved. Those skilled in the art can replace and integrate them between the embodiments. If there is any content not explicitly described in one embodiment, then another embodiment that is described can be referred to.
[0050] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.
Claims
1. A low-PF thyristor dimming circuit, wherein the AC power supply voltage is converted into a phase-cut bus voltage by a thyristor dimmer and a rectifier circuit, characterized in that, include: A diode and an input capacitor are provided. The positive terminal of the diode receives the bus voltage, the negative terminal of the diode is connected to the positive terminal of the LED, the first terminal of the input capacitor is connected to the common connection terminal of the diode and the LED, the second terminal of the input capacitor is grounded, and the input capacitor provides the power supply voltage for the LED. A load switch is connected in series with the LED; An adaptive adjustment circuit acquires a first voltage characterizing the voltage at the connection node between the load switch and the LED, generates an adjustment voltage based on the first voltage, and uses the adjustment voltage to control the switching state of the load switch in order to control the current of the LED.
2. The thyristor dimming circuit according to claim 1, characterized in that: The adjusted voltage is positively correlated with the first voltage.
3. The thyristor dimming circuit according to claim 1, characterized in that: The adjustment voltage is generated based on the difference between the first voltage and the first reference voltage. When the difference is greater than zero, the adjustment voltage is positively correlated with the difference. When the difference is less than zero, the adjustment voltage is negatively correlated with the absolute value of the difference.
4. The thyristor dimming circuit according to claim 3, characterized in that: When the difference is greater than zero, the regulating voltage increases; when the difference is less than zero, the regulating voltage decreases.
5. The thyristor dimming circuit according to claim 2 or 3, characterized in that: The adjustment voltage serves as the dimming reference voltage, which controls the current of the LED. The current of the LED is positively correlated with the dimming reference voltage.
6. The thyristor dimming circuit according to claim 4, characterized in that: The adjustment voltage serves as the dimming reference voltage. When the difference is greater than zero, the dimming reference voltage controls the current of the LED to increase; when the difference is less than zero, the dimming reference voltage controls the current of the LED to decrease.
7. The thyristor dimming circuit according to any one of claims 2, 3, or 4, characterized in that: It also includes, A conduction angle detection circuit detects the conduction angle of the thyristor dimmer and obtains a conduction angle detection signal characterizing the magnitude of the conduction angle. The reference voltage generating circuit generates a first reference voltage based on the conduction angle detection signal. The larger the conduction angle detection signal, the larger the first reference voltage. The first reference voltage is used to control the current of the LED.
8. The thyristor dimming circuit according to claim 7, characterized in that: When the conduction angle is less than the first threshold angle, the current of the LED is controlled by the adjustment voltage; When the conduction angle is greater than the first threshold angle, the current of the LED is controlled by the first reference voltage.
9. The thyristor dimming circuit according to claim 7, characterized in that: It also includes a low-voltage selection circuit that receives the regulated voltage and the first reference voltage, selects the smaller value between the regulated voltage and the first reference voltage for output, and obtains a dimming reference voltage; the dimming reference voltage is used to control the switching state of the load switch in order to control the current of the LED.
10. The thyristor dimming circuit according to claim 1, characterized in that: The adaptive adjustment circuit includes a first operational amplifier, a first switching transistor, a second switching transistor, and a first capacitor. The first operational amplifier amplifies the error between the first voltage and the first reference voltage to obtain an error amplification signal. When the error amplification signal is greater than zero, the error amplification signal drives the first switch to turn on, and the first current flowing through the first switch charges the first capacitor. When the error amplification signal is less than zero, the error amplification signal is inverted and drives the second switch to turn on, and the second current flowing through the second switch discharges the first capacitor. The regulating voltage is obtained based on the voltage of the first capacitor.
11. The thyristor dimming circuit according to any one of claims 6 or 9, characterized in that: It also includes a second operational amplifier, the first input terminal of which receives the dimming reference voltage, the second input terminal of which receives a current sampling signal characterizing the LED current, and the output terminal of which is connected to the control terminal of the load switch.
12. The thyristor dimming circuit according to claim 1, characterized in that: Obtain the power supply voltage, and get the first voltage based on the power supply voltage and the voltage drop of the LED; or, sample the voltage at the connection node between the load switch and the LED to get the first voltage.
13. A lighting circuit, characterized in that, The thyristor dimming circuit includes any one of claims 1-12.