Linear constant-current LED power supply

Abstract

The invention provides a linear constant-current LED power supply which comprises a first capacitor, a second capacitor, a first switch, a second switch and a third switch. The first output end and the second output end of the linear constant-current LED power supply are used for being coupled to the two ends of an LED load, the first end of the first capacitor is coupled to rectified input voltage through the first diode and coupled to the first output end through the third diode, and the second end of the first capacitor is coupled to the ground through the first switch and the first current sensing resistor. The first end of the second capacitor is coupled to the rectified input voltage through the second diode, the second end of the second capacitor is coupled to the ground through the second switch and the first current sensing resistor, and the third switch is coupled between the second end of the first capacitor and the first end of the second capacitor. The first capacitor and the second capacitor are subjected to time-sharing constant-current charging and then are subjected to series discharging, so that the conduction phase angle of the system input current of the LED power supply is increased, and the PF value and the system efficiency of the LED power supply are improved.

Description

Technical Field

[0001] The present invention relates to the field of circuits, and more specifically to a linear constant current light emitting diode (LED) power supply. Background Art

[0002] Linear constant current LED power supplies are widely used in the field of LED lighting due to their simple and reliable structure and low system cost. Figure 1 Figure 2 shows a schematic diagram of the topology of a traditional linear constant current LED power supply. Figure 1 In the linear constant current LED power supply 100 shown, the current sensing resistor Rcs samples the current flowing through the switch tube S1 to generate a load current sampling voltage Vcs representing the current flowing through the LED load; in a steady state, the average current flowing through the output capacitor Co is 0, and the average current flowing through the switch tube S1 is equal to the average current flowing through the LED load. Based on the load current sampling voltage Vcs, the switch tube S1 is controlled to work in a saturated conduction state to ensure that the current flowing through the LED load is constant; only when the rectified input voltage Vin is higher than the output voltage Vo on the LED load, there is a system input current Iin and a current flowing through the switch tube S1, so the conduction phase angle of the system input current Iin is small; in order to improve the system power factor (power In order to adjust the power factor (PF) value, it is necessary to add switch tube S2 and bleeder resistor Rb; when the rectified input voltage Vin is lower than the output voltage Vo on the LED load (that is, no current flows through switch S1), switch S2 is controlled to be in the on state, and a bleeder current is formed on the bleeder resistor Rb, so that the system input current Iin can follow the change of the rectified input voltage Vin.

[0003] Figure 2 Shows Figure 1 The working waveform diagram of the voltage and current signals in the linear constant current LED power supply is shown in FIG. Figure 1 and Figure 2 As shown, when the rectified input voltage Vin is less than the output voltage Vo on the LED load, the system input current Iin flows through the branch where the bleeder resistor Rb is located. This part of energy is completely lost in the bleeder resistor Rb and cannot be transmitted to the LED load, so the system efficiency of the linear constant current LED power supply 100 is low. Summary of the invention

[0004] According to an embodiment of the present invention, a linear constant current LED power supply comprises a first capacitor, a second capacitor, a first switch, a second switch, and a third switch, wherein: the first output terminal and the second output terminal of the linear constant current LED power supply are used to couple two ends of an LED load, the first end of the first capacitor is coupled to the rectified input voltage of the linear constant current LED power supply via a first diode and is coupled to the first output terminal via a third diode, the second end of the first capacitor is coupled to ground via the first switch and a first current sensing resistor, the first end of the second capacitor is coupled to the rectified input voltage via a second diode, the second end of the second capacitor is coupled to ground via a second switch and a first current sensing resistor, and the third switch is coupled between the second end of the first capacitor and the first end of the second capacitor; the first switch, the second switch, and the third switch are configured to: when the rectified input voltage is lower than the output voltage on the LED load but higher than the voltage on at least one of the first capacitor and the second capacitor, the rectified input voltage charges one of the first capacitor and the second capacitor, and when the rectified input voltage is lower than the output voltage on the LED load and lower than the voltage on both the first capacitor and the second capacitor, the series circuit of the first capacitor and the second capacitor discharges to the LED load. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0006] Figure 1 A schematic diagram of the topology of a traditional linear constant current LED power supply is shown.

[0007] Figure 2 Shows Figure 1 The schematic diagram of the working waveforms of the voltage and current signals in the linear constant current LED power supply is shown.

[0008] Figure 3 A schematic diagram of the topological structure of a linear constant current LED power supply according to an embodiment of the present invention is shown.

[0009] Figure 4 Shows Figure 3 The schematic diagram of the working waveforms of the voltage and current signals in the linear constant current LED power supply is shown.

[0010] Figure 5 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the first and fifth time periods is shown.

[0011] Figure 6 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the second time period and the fourth time period is shown.

[0012] Figure 7 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the third time period is shown.

[0013] Figure 8 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the sixth time period is shown. DETAILED DESCRIPTION

[0014] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, parts and algorithms without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity to the present invention.

[0015] Given that Figure 1 In order to solve one or more problems existing in the linear constant current LED power supply shown, a linear constant current LED power supply according to an embodiment of the present invention is proposed, which improves the system PF value and system efficiency while increasing the conduction phase angle of the system input current.

[0016] Figure 3 FIG. 2 shows a schematic diagram of a topological structure of a linear constant current LED power supply according to an embodiment of the present invention. Figure 3As shown, the linear constant current LED power supply 300 includes a capacitor C1, a capacitor C2, a switch Sa, a switch Sb, and a switch Sc, wherein: the first output terminal and the second output terminal of the linear constant current LED power supply 300 are used to couple the two ends of the LED load, the first end of the capacitor C1 is coupled to the rectified input voltage Vin via a diode D1 and coupled to the first output terminal via a diode D3, the second end of the capacitor C1 is coupled to the ground via the switch Sa and the current sensing resistor Rcs2, the first end of the capacitor C2 is coupled to the rectified input voltage Vin via the diode D2, the second end of the capacitor C2 is coupled to the ground via the switch Sb and the current sensing resistor Rcs2 Rcs2 is coupled to the ground, and the switch Sc is coupled between the second end of the capacitor C1 and the first end of the capacitor C2; the switch Sa, the switch Sb, and the switch Sc are configured to: when the rectified input voltage Vin is lower than the output voltage Vo on the LED load but higher than the voltage on at least one of the capacitors C1 and C2, the rectified input voltage Vin charges one of the capacitors C1 and C2, and when the rectified input voltage Vin is lower than the output voltage Vo on the LED load and lower than the voltage on both the capacitors C1 and C2, the series circuit of the capacitors C1 and C2 discharges to the LED load. Here, the current sensing resistor Rcs2 is used to sample the sum of the charge / discharge currents of the capacitors C1 and C2 and generate the charge / discharge current sampling voltage Vcs2.

[0017] like Figure 3 As shown, in some embodiments, the linear constant current LED power supply 300 further includes an output capacitor Co, a load switch S1, and a current sensing resistor Rcs, wherein the two ends of the output capacitor Co are respectively coupled to the first output terminal and the second output terminal, and the load switch S1 and the current sensing resistor Rcs are coupled in series between the second output terminal and the ground. Here, the current sensing resistor Rcs is used to sample the current flowing through the load switch S1 (i.e., the current flowing through the LED load) and generate a load current sampling voltage Vcs. It should be noted that the load switch S1, the switch Sa, the switch Sb, and the switch Sc can all be implemented by semiconductor switching devices.

[0018] like Figure 3 As shown, in some embodiments, the linear constant current LED power supply 300 also includes an operational amplifier EA1 and a compensation capacitor Ccompl, wherein the operational amplifier EA1 generates an output loop compensation voltage Vcomp_a on the compensation capacitor Ccompl based on the reference voltage Vref_a and the charge / discharge current sampling voltage Vcs2 on the current sensing resistor Rcs2, and the output loop compensation voltage Vcomp_a is used to control the switch Sa to operate in a fully or saturated conduction state or in an off state.

[0019] like Figure 3As shown, in some embodiments, the linear constant current LED power supply 300 also includes an operational amplifier EA2 and a compensation capacitor Ccomp2, wherein the operational amplifier EA2 generates an output loop compensation voltage Vcomp_b on the compensation capacitor Ccomp2 based on the reference voltage Vref_b (where Vref_a<Vref_b) and the charge / discharge current sampling voltage Vcs2 on the current sensing resistor Rcs2, and the output loop compensation voltage Vcomp_b is used to control the switch Sb to operate in a fully or saturated conduction state or in an off state.

[0020] like Figure 3 As shown, in the linear constant current LED power supply 300, the switch Sa and the switch Sb control the charging current of the capacitor C1 and the capacitor C2 respectively; when the switch Sa works in the saturated conduction state under the control of the output loop compensation voltage Vcomp_a, the charging current of the capacitor C1 is constant; when the switch Sb works in the saturated conduction state under the control of the output loop compensation voltage Vcomp_b, the charging current of the capacitor C2 is constant; due to Vref_a<Vref_b, the charging current of the capacitor C1 is less than the charging current of the capacitor C2, and the voltage on the capacitor C1 is less than the voltage on the capacitor C2.

[0021] like Figure 3 As shown, in the linear constant current LED power supply 300, when the rectified input voltage Vin is lower than the output voltage Vo on the LED load, higher than the voltage on the capacitor C1, and lower than the voltage on the capacitor C2, the constant current loop of the operational amplifier EA1 works, and the switch Sa works in a saturated conduction state under the control of the output loop compensation voltage Vcomp_a, the charging current of the capacitor C1 is constant, and the charging current sampling voltage Vcs2 on the current sensing resistor Rcs2 is Vref_a; since Vref_a<Vref_b, Vcs2<Vref_b, the operational amplifier EA2 works in an open loop state, the output loop compensation voltage Vcomp_b reaches the maximum, and the switch Sb works in a fully on state; since the rectified input voltage Vin is lower than the voltage on the capacitor C2, even if the switch Sb is in a fully on state, the charging current of the capacitor C2 is zero.

[0022] like Figure 3As shown, in the linear constant current LED power supply 300, when the rectified input voltage Vin is lower than the output voltage Vo on the LED load, higher than the voltage on the capacitor C1, and higher than the voltage on the capacitor C2, the constant current loop of the operational amplifier EA2 works, the switch Sb works in a saturated conduction state under the control of the output loop compensation voltage Vcomp_b, the charging current of the capacitor C2 is constant, and the charging current sampling voltage Vcs2 on the current sensing resistor Rcs2 is Vref_b; since Vref_a<Vref_b, Vcs2>Vref_a, the operational amplifier EA1 works in an open loop state, the output loop compensation voltage Vcomp_a reaches the minimum, the switch Sa is in an off state, and the charging current of the capacitor C1 is zero.

[0023] Figure 4 Shows Figure 3 Schematic diagram of working waveforms of voltage and current signals in the linear constant current LED power supply shown in the figure, wherein Vo represents the output voltage on the LED load, Vin represents the rectified input voltage, Vcs represents the load current sampling voltage generated by the current sensing resistor Rcs sampling the current flowing through the LED load, ISa represents the current flowing through the switch Sa, ISb represents the current flowing through the switch Sb, Iin represents the system input current, Sa_gate represents the control voltage for controlling the switch Sa, Sb_gate represents the control voltage for controlling the switch Sb, and Sc_gate represents the control voltage for controlling the switch Sc.

[0024] like Figure 3 and Figure 4 As shown, the working process of the linear constant current LED power supply 300 is as follows:

[0025] During the time periods t0-t1 and t4-t5: when the rectified input voltage Vin is lower than the output voltage Vo on the LED load, lower than the voltage on the capacitor C2, and higher than the voltage on the capacitor C1, the rectified input voltage Vin charges the capacitor C1 with a constant current via the diode D1 and the switch Sa, and the current flowing through the LED load is provided by the output capacitor Co. Figure 5 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the time periods t0-t1 and t4-t5 shown in FIG. 1 is shown in FIG. 2 , wherein the current flows as indicated by the arrows. Figure 5As shown, during the time periods t0-t1 and t4-t5, the switch Sc is in the off state; the switch Sa operates in the saturated conduction state under the control of the output loop compensation voltage Vcomp_a; since the rectified input voltage Vin is lower than the voltage on the capacitor C2 and higher than the voltage on the capacitor C1, the charging current of the capacitor C2 is zero, the system input current Iin is equal to the charging current of the capacitor C1, the current sensing resistor Rcs2 only samples the charging current of the capacitor C1 to generate the charging current sampling voltage Vcs2, and Vcs2=Vref_a; since Vref_a<Vref_b, Vcs2<Vref_b, the operational amplifier EA2 operates in the open-loop state, and the switch Sb operates in the fully on state.

[0026] During the time periods t1-t2 and t3-t4: when the rectified input voltage Vin is lower than the output voltage Vo on the LED load, higher than the voltage on the capacitor C1, and higher than the voltage on the capacitor C2, the rectified input voltage Vin charges the capacitor C2 with a constant current via the diode D2 and the switch Sb, and the current flowing through the LED load is provided by the output capacitor Co. Figure 6 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the time periods t1-t2 and t3-t4 shown in FIG. 1 shows the current flow direction as shown by the arrows. Figure 6 As shown, during the time periods t1-t2 and t3-t4, the switch Sc is in the off state; the switch Sa is in the off state under the control of the output loop compensation voltage Vcomp_a; the switch Sb operates in the saturated conduction state under the control of the output loop compensation voltage Vcomp_b; the system input current Iin is equal to the charging current of the capacitor C2, the charging current of the capacitor C1 is zero, the current sensing resistor Rcs2 only samples the charging current of the capacitor C2 to generate the charging current sampling voltage Vcs2, and Vcs2=Vref_b; since Vref_a<Vref_b, Vref_a<Vcs2, the operational amplifier EA1 operates in the open-loop state, and the switch Sa is in the off state.

[0027] During the t2-t3 period: when the rectified input voltage Vin is higher than the output voltage Vo on the LED load, the current flowing through the LED load is provided by the rectified input voltage Vin, the current flowing through the load switch S1 is equal to the system input current Iin, and the switches Sa, Sb, and Sc are all in the off state. Figure 7 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the period t2-t3 shown in FIG. 1 is shown in FIG. 1 , in which the current flows as indicated by the arrows. Figure 7As shown, during the time period t2-t3, the rectified input voltage Vin provides current to the LED load via the load switch S1 and the current sensing resistor Rcs while charging the output capacitor Co; the load current sampling voltage Vcs generated by sampling the current flowing through the load switch S1 based on the current sensing resistor Rcs controls the current flowing through the load switch S1, so that the load switch S1 operates in a saturated conduction state.

[0028] During the period t5-t6: when the rectified input voltage Vin is lower than the output voltage Vo on the LED load, lower than the voltage on the capacitor C1, and lower than the voltage on the capacitor C2, the rectified input voltage Vin can neither provide current to the LED load nor charge the capacitors C1 or C2, the system input current Iin is zero, and the capacitors C1 and C2 are connected in series to discharge to the LED load. Figure 8 Shows Figure 3 The linear constant current LED power supply shown in Figure 4 The equivalent circuit diagram during the period t5-t6 shown in FIG. 1 is shown in FIG. 1 , in which the current flows as indicated by the arrows. Figure 8 As shown, during the time period t5-t6, the switch Sb and the switch Sc operate in a fully on state, the load switch S1 operates in a saturated on state, and the switch Sa is in an off state; the current flowing through the load switch S1 is controlled based on the load current sampling voltage Vcs, thereby controlling the discharge current of the capacitor C1 and the capacitor C2 (i.e., the current flowing through the LED load); the current sensing resistor Rcs2 samples the discharge current of the capacitor C1 and the capacitor C2 to generate a discharge current sampling voltage Vcs2.

[0029] In the switching power supply system 300 according to the embodiment of the present invention, by charging the capacitor C1 and the capacitor C2 with a constant current in a time-sharing manner and then discharging the capacitor C1 and the capacitor C2 in series, the conduction phase angle of the system input current Iin is increased and the system PF value and system efficiency are improved. When the rectified input voltage Vin is so low that it can neither provide current to the LED load nor charge the capacitor C1 or C2, the capacitor C1 and the capacitor C2 are connected in series to discharge the LED load, and the charging energy is discharged to the LED load, which can improve the system efficiency while achieving low total harmonic distortion (THD). Specifically, the larger the charging current of the capacitor C1 and the capacitor C2, the lower the THD, and the lower the system efficiency; the smaller the charging current of the capacitor C1 and the capacitor C2, the higher the THD, and the higher the system efficiency.

[0030] The present invention can be implemented in other specific forms without departing from its spirit and essential features. For example, the algorithms described in the specific embodiments can be modified, and the system architecture does not depart from the basic spirit of the present invention. Therefore, the current embodiments are regarded as exemplary and non-restrictive in all aspects, and the scope of the present invention is defined by the appended claims rather than the above description, and all changes falling within the meaning and equivalent scope of the claims are thus included in the scope of the present invention.

Claims

1. A linear constant current LED power supply, comprising a first capacitor, a second capacitor, a first switch, a second switch, and a third switch, wherein: The first output terminal and the second output terminal of the linear constant current LED power supply are used to couple two ends of the LED load, the first end of the first capacitor is coupled to the rectified input voltage of the linear constant current LED power supply via a first diode and is coupled to the first output terminal via a third diode, the second end of the first capacitor is coupled to the ground via the first switch and the first current sensing resistor, the first end of the second capacitor is coupled to the rectified input voltage via a second diode, the second end of the second capacitor is coupled to the ground via the second switch and the first current sensing resistor, and the third switch is coupled between the second end of the first capacitor and the first end of the second capacitor; The first switch, the second switch, and the third switch are configured to: when the rectified input voltage is lower than the output voltage on the LED load but higher than the voltage on at least one of the first capacitor and the second capacitor, the rectified input voltage charges one of the first capacitor and the second capacitor, and when the rectified input voltage is lower than the output voltage on the LED load and lower than the voltage on both the first capacitor and the second capacitor, the series circuit of the first capacitor and the second capacitor discharges to the LED load.

2. The linear constant current LED power supply according to claim 1, wherein: When the rectified input voltage is higher than the output voltage on the LED load, the first switch, the second switch, and the third switch are configured to be in an off state, so that the rectified input voltage powers the LED load via the first diode and the third diode.

3. The linear constant current LED power supply according to claim 1, wherein: When the rectified input voltage is lower than the output voltage on the LED load but higher than the voltage on both the first capacitor and the second capacitor, the first switch and the third switch are configured to be in an off state, and the second switch is configured to operate in a saturated on state, so that the rectified input voltage charges the second capacitor.

4. The linear constant current LED power supply according to claim 1, wherein: When the rectified input voltage is lower than the output voltage on the LED load and the voltage on the second capacitor but higher than the voltage on the first capacitor, the first switch is configured to operate in a saturated conduction state, the second switch is configured to operate in a fully on state, and the third switch is configured to be in an off state, so that the rectified input voltage charges the first capacitor.

5. The linear constant current LED power supply according to claim 1, wherein: When the rectified input voltage is lower than the output voltage on the LED load and lower than the voltage on both the first capacitor and the second capacitor, the first switch is configured to be in an off state, and the second switch and the third switch are configured to operate in a fully on state, so that the series circuit of the first capacitor and the second capacitor discharges to the LED load via the third diode.

6. The linear constant current LED power supply according to claim 1, further comprising a first operational amplifier and a first compensation capacitor, wherein: The first operational amplifier generates a first output loop compensation voltage on the first compensation capacitor based on the output generated by the first reference voltage and the charging or discharging current sampling voltage on the first current sensing resistor. The first output loop compensation voltage is used to control the first switch to operate in a fully or saturated conduction state or in an off state.

7. The linear constant current LED power supply according to claim 6, further comprising a second operational amplifier and a second compensation capacitor, wherein: The second operational amplifier generates a second output loop compensation voltage on the second compensation capacitor based on the output generated by the second reference voltage and the charging or discharging current sampling voltage on the first current sensing resistor. The second output loop compensation voltage is used to control the second switch to operate in a fully or saturated conduction state or in an off state. The second reference voltage is greater than the first reference voltage.

8. The linear constant current LED power supply according to claim 1 further includes an output capacitor, a load switch, and a second current sensing resistor, wherein the two ends of the output capacitor are respectively coupled to the first output terminal and the second output terminal, and the load switch and the second current sensing resistor are coupled in series between the second output terminal and ground.

9. The linear constant current LED power supply according to claim 8, wherein: When the rectified input voltage is lower than the output voltage across the LED load but higher than a voltage across at least one of the first capacitor and the second capacitor, the output capacitor discharges to the LED load.

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