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EP-4475630-B1 - LED DRIVING CIRCUIT

EP4475630B1EP 4475630 B1EP4475630 B1EP 4475630B1EP-4475630-B1

Inventors

  • LAI, HONGBIN

Dates

Publication Date
20260513
Application Date
20240531

Claims (13)

  1. An LED driving circuit, comprising an LED load (25), a rectifier circuit (11), an electrolytic capacitor (EC4, EC5), an auxiliary power supply circuit (22), a dimming control circuit (23), and a linear driving circuit (24), wherein the electrolytic capacitor (EC4, EC5) is connected between two outputs of the rectifier circuit (11); the auxiliary power supply circuit (22) configured as a switch-mode power converter comprises two inputs connected to two terminals of the electrolytic capacitor (EC4, EC5), respectively, and is configured to convert a voltage of the electrolytic capacitor (EC4, EC5) into a power supply voltage at an output to at least power the dimming control circuit (23), wherein the dimming control circuit (23) is connected the output of the auxiliary power supply circuit (22) and configured to receive the power supply voltage and generate a dimming control signal (Vrefi); and the linear driving circuit (24) is configured to control a driving current flowing through the LED load (25) based on the dimming control signal (Vrefi), wherein a series connection of the linear driving circuit (24) and the LED load (25) is coupled in parallel with the electrolytic capacitor (EC4, EC5).
  2. The LED driving circuit according to claim 1, wherein a first terminal of the electrolytic capacitor (EC4, EC5) is connected to a first output of the rectifier circuit (11), and a second terminal of the electrolytic capacitor (EC4, EC5) is connected to a second output of the rectifier circuit (11) and a ground terminal.
  3. The LED driving circuit according to claim 1, wherein the LED driving circuit further comprises a voltage regulation circuit (36), and the voltage regulation circuit (36) is configured to control the voltage of the electrolytic capacitor (EC4, EC5), and decrease a difference between the voltage of the electrolytic capacitor (EC4, EC5) and a load voltage of the LED load (25).
  4. The LED driving circuit according to claim 3, wherein the voltage regulation circuit (36) is configured to control the voltage of the electrolytic capacitor (EC4, EC5) based on a voltage sampling signal (Vs) indicating a difference between the voltage of the electrolytic capacitor (EC4, EC5) and the load voltage of the LED load (25), such that the voltage of the electrolytic capacitor (EC4, EC5) closely matches the load voltage of the LED load (25).
  5. The LED driving circuit according to claim 4, wherein the voltage regulation circuit (36) is configured to compare the voltage sampling signal (Vs) with a threshold voltage (Vdsth) and control the voltage of the electrolytic capacitor (EC4, EC5), wherein when the voltage sampling signal (Vs) is greater than the threshold voltage (Vdsth), the voltage regulation circuit (36) is configured to decrease the voltage of the electrolytic capacitor (EC4, EC5).
  6. The LED driving circuit according to claim 4, wherein the voltage regulation circuit (36) is configured to compare the voltage sampling signal (Vs) with a threshold voltage (Vdsth) and control the voltage of the electrolytic capacitor (EC4, EC5), wherein when the voltage sampling signal (Vs) is less than the threshold voltage (Vdsth), the voltage regulation circuit (36) is configured to increase the voltage of the electrolytic capacitor (EC4, EC5).
  7. The LED driving circuit according to claim 3, wherein the voltage regulation circuit (36) is connected in series with the electrolytic capacitor (EC4, EC5) between the two outputs of the rectifier circuit (11).
  8. The LED driving circuit according to claim 7, wherein the electrolytic capacitor (EC4, EC5) is connected to a first output of the rectifier circuit (11), and the voltage regulation circuit (36) is connected to a second output of the rectifier circuit (11), wherein the second output of the rectifier circuit (11) is a ground terminal.
  9. The LED driving circuit according to claim 7, wherein the electrolytic capacitor (EC4, EC5) is connected to a second output of the rectifier circuit (11), and the voltage regulation circuit (36) is connected to a first output of the rectifier circuit (11), wherein a common node of the voltage regulation circuit (36) and the electrolytic capacitor (EC4, EC5) is a ground terminal.
  10. The LED driving circuit according to claim 4, wherein the voltage regulation circuit (36) comprises: a first control signal generation circuit (361), configured to receive the voltage sampling signal (Vs) and a threshold voltage (Vdsth) to obtain a first control signal (V COMPV ); and a voltage control circuit (362), configured to receive the first control signal (V COMPV ) and control the voltage of the electrolytic capacitor (EC4, EC5) based on the first control signal (V COMPV ); wherein the electrolytic capacitor (EC4, EC5) is connected in series with the voltage control circuit (362), or connected to an output of the voltage control circuit (362).
  11. The LED driving circuit according to claim 10, wherein a variation trend of the first control signal (V COMPV ) is opposite to a variation trend of the voltage sampling signal (Vs), and is consistent with a variation trend of the voltage of the electrolytic capacitor (EC4, EC5).
  12. The LED driving circuit according to claim 10, wherein the voltage control circuit (362) comprises a transistor (Q1, Q2), and the transistor (Q1, Q2) is connected in series with the electrolytic capacitor (EC4, EC5); wherein the voltage control circuit (362) controls a charging current or a discharging current of the electrolytic capacitor (EC4, EC5) by a current flowing through the transistor (Q1, Q2) to adjust the voltage of the electrolytic capacitor (EC4, EC5).
  13. The LED driving circuit according to claim 1, wherein the electrolytic capacitor (EC4, EC5) is configured as an input capacitor of the auxiliary power supply circuit (22).

Description

FIELD OF THE INVENTION The present disclosure relates to the technical field of power electronics, and in particularly, to an LED driving circuit. BACKGROUND OF THE INVENTION Light-emitting diode (LED) lighting finds widespread application in various fields such as furniture, offices, outdoor lighting, and stage illumination. Dimming technology allows for adjustable brightness of LED loads, thereby enhancing the practical applications and user experience of LED lighting. In current dimmable LED driving circuits, a rectifier circuit 11, an auxiliary power supply circuit 12, a dimming control circuit 13, and a linear driving circuit 14 are usually comprised. The rectifier circuit 11 is used to convert alternate currents (AC) into direct currents (DC), which are then output to a DC bus. The linear driving circuit 14 is connected in series with an LED load 15. By controlling a transistor Q1 to operate in the linear state, a current flowing through the LED load 15 is constant and controllable. An electrolytic capacitor EC1 is connected in parallel with the LED load 15 and in series with the linear driving circuit 14. The dimming control circuit 13 generates a dimming control signal Vrefi based on a dimming signal. Based on the dimming control signal Vrefi, the linear driving circuit 14 generates a driving current for the LED load 15. The dimming control circuit 13 is powered by the auxiliary power supply circuit 12, which is typically a switch-mode power converter. Due to the high switching frequency of the auxiliary power supply circuit 12, an electromagnetic interference (EMI) filter 16 is necessary for filtering. The EMI filter includes a diode D1, an inductor L1, and capacitors EC2 and EC3. However, this approach increases system costs and the number of components, which is not ideal for highly integrated designs. Known LED driving circuits are disclosed in US 2010/148691 A1, US 2017/318639 A1 and CN 113 766 701 A. SUMMARY OF THE INVENTION In view of the above-mentioned shortcomings, the present disclosure provides an LED driving circuit, which helps to improve the power density of the system. The present invention relates an LED driving circuit as disclosed in the appended claim 1. Further features of the claimed LED driving circuit are disclosed in the appended dependent claims. By sharing a large capacitor between the auxiliary power supply circuit and the LED load, the LED driving circuit of the present disclosure has a simple structure without a separate filtering circuit for the auxiliary power supply circuit. Specifically, the auxiliary power supply circuit is connected in parallel with the electrolytic capacitor of the LED driving circuit, and the LED load is connected in series with the linear driving circuit and then in parallel with the electrolytic capacitor. Furthermore, the LED driving circuit adaptively controls the voltage across the electrolytic capacitor, ensuring it closely matches the load voltage of the LED load, minimizing the potential difference of the linear driving circuit, allowing the LED driving circuit to operate at a relatively higher or the highest efficiency. BRIEF DESCRIPTION OF DRAWINGS In order to further clarify the technical solutions in the embodiments of the present disclosure or the prior art, a brief introduction will be made to the drawings necessary for describing the embodiments or the prior art. Obviously, the drawings described below are merely examples of the present disclosure, and people with ordinary skills in the art can obtain other drawings without creative work based on the provided drawings. FIG. 1 shows a schematic diagram of an LED driving circuit in the prior art;FIG. 2 shows a schematic diagram of an LED driving circuit according to a first embodiment of the present disclosure;FIG. 3 shows a schematic diagram of an LED driving circuit according to a second embodiment of the present disclosure;FIG. 4 shows a schematic structural diagram of the LED driving circuit according to the second embodiment of the present disclosure;FIG. 5 shows an operating waveform diagram of the LED driving circuit according to the second embodiment of the present disclosure; andFIG. 6 shows a schematic diagram of an LED driving circuit according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION The following describes the present disclosure based on embodiments, but the present disclosure is not merely limited to these embodiments. The detailed descriptions of the present disclosure in the following elaborate on some specific details. Those skilled in the art can fully understand the present disclosure without the description of more details. Well-known methods, procedures, processes, components and circuits are not described in detail to avoid obscuring the essence of the present disclosure. In addition, those skilled in the art should understand that the accompanying drawings are only for the purpose of illustration and are not necess