Apparatus, dimmable light emitting diode driver and control method
地域：
Hangzhou, ZheJiang Province
摘要
An apparatus can include: a linear drive circuit configured to control a drive current flowing through an LED load; a control circuit configured to acquire a conduction angle signal of a silicon-controlled rectifier dimmer and control the linear drive circuit; and the control circuit being configured to control the drive current to be decreased to reduce a current ripple and to maintain the silicon-controlled rectifier dimmer in a turn-on state when the conduction angle signal is less than a predetermined value.
說明書
This application claims the benefit of Chinese Patent Application No. 201711460088.5, filed on Dec. 28, 2017, which is incorporated herein by reference in its entirety.
The present invention generally relates to the field of power electronics, and more particularly to an LED driver and associated circuits and methods.
A switched-mode power supply (SMPS), or a “switching” power supply, can include a power stage circuit and a control circuit. When there is an input voltage, the control circuit can consider internal parameters and external load changes, and may regulate the on/off times of the switch system in the power stage circuit. Switching power supplies have a wide variety of applications in modern electronics. For example, switching power supplies can be used to drive light-emitting diode (LED) loads.
權利要求
What is claimed is:1. An apparatus, comprising:a) a linear drive circuit comprising a first transistor connected in series with a light emitting diode (LED) load, wherein the linear drive circuit is configured to control the transistor to operate in a linear mode to generate a drive current flowing through the first transistor and the LED load; b) a control circuit configured to acquire a conduction angle signal representing conduction angle information of a silicon-controlled rectifier dimmer, and to control the linear drive circuit based on the conduction angle signal; and c) the control circuit being configured to decrease the drive current through the linear drive circuit to reduce a current ripple flowing through the LED load when the conduction angle signal is less than a predetermined value. 2. The apparatus of claim 1 , wherein the control circuit is configured to control the drive current to be decreased to a current corresponding to the conduction angle signal when the conduction angle signal is less than the predetermined value. 3. The apparatus of claim 1 , wherein the control circuit is configured to decrease a reference voltage based on the conduction angle signal in order to decrease the drive current. 4. The apparatus of claim 3 , wherein the control circuit is configured to adjust the reference voltage based on the conduction angle signal and a predetermined reference voltage curve. 5. The apparatus of claim 1 , wherein the control circuit is configured to decrease a compensation signal based on the conduction angle signal to control the linear drive circuit to generate the current, and wherein the compensation signal represents an error between a predetermined reference voltage and a current sampling signal of the drive current. 6. The apparatus of claim 1 , wherein the control circuit is configured to acquire the conduction angle signal in accordance with a detection signal representing a direct current bus voltage. 7. The apparatus of claim 6 , wherein the control circuit comprises a detection circuit configured to detect a time period during which the direct current bus voltage is greater than a first threshold and less than a second threshold to acquire the conduction angle signal. 8. The apparatus of claim 7 , wherein the detection circuit comprises:a) a first capacitor, wherein a voltage across the first capacitor serves as the conduction angle signal; b) a charge and discharge circuit configured to charge the first capacitor in a first state and discharge the first capacitor in a second state; and c) a state controller configured to control the charge and discharge circuit to switch to the first state when it is detected that the direct current bus voltage rises to a voltage greater than the first threshold, and to control the charge and discharge circuit to switch to the second state when it is detected that the direct current bus voltage decreases to a voltage less than the second threshold. 9. The apparatus of claim 1 , wherein the control circuit is configured to detect the drive current to acquire the conduction angle signal. 10. The apparatus of claim 9 , wherein the control circuit comprises a detection circuit configured to acquire a signal indicating a time period during which the drive current is continuously greater than a third threshold to acquire the conduction angle signal. 11. The apparatus of claim 9 , wherein the detection circuit comprises:a) a second capacitor, wherein a voltage across the second capacitor serves as the conduction angle signal; b) a charge and discharge circuit configured to charge the second capacitor in a first state and discharge the second capacitor in a second state; and c) a state controller configured to control the charge and discharge circuit to switch to the first state when the drive current is greater than the third threshold, and to control the charge and discharge circuit to switch to the second state when the drive current is decreased to a current less than the third threshold. 12. The apparatus of claim 1 , wherein the linear drive circuit comprises:a) an output port coupled to the LED load; and b) an output capacitor coupled in parallel with the LED load. 13. The apparatus of claim 12 , wherein the linear drive circuit further comprises a unidirectional conductive circuit coupled between a direct current bus and the output port. 14. The apparatus of claim 1 , wherein the linear drive circuit comprises:a) an output port coupled to the LED load; b) an output capacitor coupled in parallel with the LED load; and c) a second transistor coupled between the LED load and a ground terminal, wherein the second transistor is configured to clamp a current flowing through the second transistor. 15. The apparatus of claim 14 , wherein the linear drive circuit further comprises a unidirectional conductive circuit connected between a direct current bus and the output port. 16. The apparatus of claim 14 , wherein the control circuit is configured to:a) control the linear drive circuit based on a first predetermined reference voltage when the conduction angle signal is greater than a first angle threshold; b) control the linear drive circuit based on a second predetermined reference voltage when the conduction angle signal is less than a second angle threshold; and c) control the linear drive circuit based on a reference voltage changing with the conduction angle signal when the conduction angle signal is not greater than the first angle threshold and not less than the second angle threshold. 17. The apparatus of claim 1 , wherein the control circuit is configured to:a) control the linear drive circuit to cause the drive current to change with the conduction angle signal when the conduction angle signal is greater than a third angle threshold; and b) control the linear drive circuit to cause the drive current to be not less than a clamp current when the conduction angle signal is not greater than the third angle threshold. 18. The apparatus of claim 1 , wherein the control circuit is configured to:a) control the linear drive circuit to cause the drive current to be equal to a current corresponding to the conduction angle signal when the conduction angle signal is not less than the predetermined value; and b) control the linear drive circuit to cause the drive current to be less than a current corresponding to the conduction angle signal when the conduction angle signal is less than the predetermined value. 19. The apparatus of claim 1 , wherein the control circuit is configured to:a) control the linear drive circuit to cause the drive current to be equal to a current corresponding to the conduction angle signal when the conduction angle signal is not less than the predetermined value; and b) control the linear drive circuit to cause the drive current to be less than a current corresponding to the conduction angle signal and not less than a holding current of the silicon-controlled rectifier dimmer when the conduction angle signal is less than the predetermined value. 20. A dimmable light-emitting diode (LED) drive circuit, comprising the apparatus of claim 1 , and further comprising:a) a rectification circuit coupled to the silicon-controlled rectifier dimmer, wherein the rectification circuit is configured to generate a direct current bus voltage and b) a bleeder circuit coupled to output terminals of the rectification circuit, and being configured to sink a bleeder current. 21. The drive circuit of claim 20 , further comprising:a) a first sensing resistor; b) a second sensing resistor coupled in series with the first transistor and between the first transistor and ground; and c) wherein said bleeder circuit comprises a bleeding transistor having a first power terminal coupled to a direct current bus of the rectification circuit, and a second power terminal coupled to a common node between the first and second sensing resistors. 22. The drive circuit of claim 20 , wherein the control circuit is configured to control at least one of the linear drive circuit and the bleeder circuit in order to maintain the silicon-controlled rectifier dimmer in a conduction state. 23. The apparatus of claim 1 , wherein the control circuit is configured to control the drive current to be decreased at a greater rate when the conduction angle signal is less than the predetermined value than a rate when the conduction angle signal is not less than the predetermined value. 24. The apparatus of claim 1 , wherein the control circuit is configured to control the drive current when the conduction angle signal is less than the predetermined value to be less than the drive current when the conduction angle signal is not less than the predetermined value.
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