Multi-path low-ripple current driving circuit

Abstract

The invention discloses a multi-channel low-ripple current driving circuit which comprises a direct-current power supply Vin, a switch S1, a main inductor Lm, a branch inductor Lb, a capacitor C1, a resonant capacitor Cr, an inductor Lr, a capacitor Co1, a capacitor Co2, a capacitor Co3, an LED1, an LED2 and an LED3, the capacitor Co1 and the LED1 are connected in parallel to form a first circuit, the capacitor Co2 and the LED2 are connected in parallel to form a second circuit, the capacitor Co3 and the LED3 are connected in parallel to form a third circuit, and the first circuit and the second circuit are connected in parallel. One end of the switch S1 is electrically connected with the negative electrode of the direct-current power supply Vin and the positive electrode of the first circuit, the negative electrode of the first circuit is electrically connected with one end of the resonant capacitor Cr and the positive electrode of the second circuit through the series inductor Lr, and the negative electrode of the second circuit is electrically connected with one end of the capacitor C1 and the positive electrode of the third circuit. The negative electrode of the third circuit is electrically connected with the other end of the resonant capacitor Cr, the other end of the switch S1 and one end of a main inductor Lm through a series branch inductor Lb, the other end of the main inductor Lm is electrically connected with the other end of the capacitor C1 and the positive electrode of the direct-current power supply Vin, and current balance and non-stroboscopic dimming are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of LED dimming, in particular to a multi-channel low-ripple current driving circuit. Background Art

[0002] Traditional types of LED-based backlights or studio panel lights require high brightness output, constant brightness, and zero flicker. Therefore, the existing technology is to achieve this through the output of ripple-free current by DC-DC converters (LED drivers). However, due to thermal limitations, the forward current flowing through a single LED is limited. In order to achieve the required brightness, more LEDs need to be connected in series. Any broken LED in the series circuit will cause the entire series circuit to fail. The current method to achieve current balance between parallel LEDs is active current balancing, such as Figure 1 As shown, active devices are connected in series to each LED to regulate the current. The disadvantages of existing active current balancing schemes are mainly: low efficiency and flicker; due to manufacturing tolerances, the current flowing through each LED string in parallel will be different; most importantly, LEDs are negative temperature coefficient devices, which will cause the forward current to increase rapidly during thermal overload and lead to the deterioration of LED life. Summary of the invention

[0003] The object of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a multi-channel low-ripple current driving circuit for realizing flicker-free LED backlight driving.

[0004] A multi-channel low-ripple current driving circuit according to an embodiment of the present invention includes: a DC power supply Vin, a switch S1, a main inductor Lm, a branch inductor Lb, a capacitor C1, a resonant capacitor Cr, an inductor Lr, a capacitor Co1, a capacitor Co2, a capacitor Co3, an LED1, an LED2 and an LED3, wherein the capacitor Co1 is connected in parallel with the LED1 to form a first circuit, the capacitor Co2 is connected in parallel with the LED2 to form a second circuit, and the capacitor Co3 is connected in parallel with the LED3 to form a third circuit, one end of the switch S1 is respectively electrically connected to the negative electrode of the DC power supply Vin and the positive electrode of the first circuit, the negative electrode of the first circuit is respectively electrically connected to one end of the resonant capacitor Cr and the positive electrode of the second circuit via the series inductor Lr, the negative electrode of the second circuit is respectively electrically connected to one end of the capacitor C1 and the positive electrode of the third circuit, the negative electrode of the third circuit is respectively electrically connected to the other end of the resonant capacitor Cr, the other end of the switch S1 and one end of the main inductor Lm via the series branch inductor Lb, and the other end of the main inductor Lm is respectively electrically connected to the other end of the capacitor C1 and the positive electrode of the DC power supply Vin.

[0005] According to some embodiments of the present invention, the switch S1 is a MOS tube, a source of the MOS tube is electrically connected to one end of the main inductor Lm, and a drain of the MOS tube is electrically connected to the positive electrode of the first circuit.

[0006] According to some embodiments of the present invention, the device further includes a diode D1, a diode D2, and a diode D3. The diode D1 is connected between the resonant capacitor Cr and the inductor Lr, and the positive electrode of the diode is electrically connected to the inductor Lr. The negative electrode of the diode D2 is electrically connected to the positive electrode of the second circuit, the positive electrode of the diode D2 is electrically connected to the resonant capacitor Cr, and the diode D3 is connected between the branch inductor Lb and the switch S1, and the positive electrode of the diode D3 is electrically connected to the branch inductor Lb.

[0007] According to some embodiments of the present invention, the switching period of the switch S1 is T s , switching period T s It includes a continuous first period τ1, a second period τ2, a third period τ3 and a fourth period τ4, wherein τ1 and τ2 are the on time, and τ3 and τ4 are the off time. In the first period τ1, the switch S1 is turned on, and the current i of the main inductor Lm is Lm (t) and the circuit i of the branch inductance Lb Lb (t) satisfies the following formula:

[0008] The inductor Lr and the resonant capacitor Cr form a resonant circuit. The current flows from the resonant capacitor Cr through the inductor Lr and then outputs through LED1. The voltage of the inductor Lr is v Cr (t)-v LED1 , the average voltage across the resonant capacitor Cr and the current i through the inductor Lr Lr The maximum values ​​are:

[0009] At the end of the first period τ1, the resonance of the resonant capacitor Cr and the inductor Lr ends.

[0010] According to some embodiments of the present invention, in the second period τ2, the switch S1 continues to be turned on, and the current i Lr (t) and the current i of the resonant capacitor Cr Cr (t) are all zero, and the voltage v on the resonant capacitor Cr cr Keep constant; at the end of the second period τ2, the current i of the main inductor Lm Lm The maximum value of the branch inductance Lb and the current i Lb The maximum values ​​of (t) are:

[0011]

[0012] According to some embodiments of the present invention, in the third time period τ3, the switch S1 is turned off, the diode D2 and the diode D3 are turned on, the capacitor C1 is discharged, and the voltage v cr is a constant voltage, then iLm (t), i Lb (t) are decreased as follows:

[0013]

[0014] when i Lb When (t) decreases to 0, diode D3 is turned off. Lb When it becomes zero, it enters the fourth working period.

[0015] According to some embodiments of the present invention, in the fourth time period τ4, the switch S1 is turned off, i Lm Continue to decline, when i Lm When it drops to 0, diode D1, diode D2 and diode D3 are all turned off.

[0016] According to some embodiments of the present invention, in a switching cycle T a In order to make all currents reach a balanced state in each branch, the charge stored in the resonant capacitor Cr and the capacitor C1 needs to be equal to the charge released from the resonant capacitor Cr and the capacitor C1. Therefore, Q r-charge =Q r-discharge , Q 1-charge =Q 1-discharge ; and the average current of LED1 I LED1 、The average current of LED2 I LED2 、The average current of LED3 I LED3 Between: I LED1 -I LED2 -I LED3 .

[0017] The multi-channel low-ripple current driving circuit according to the embodiment of the present invention has at least the following beneficial effects: the dimming circuit adopts passive devices and has only one switch S1. The circuit structure combines a buck-boost-buck converter and a passive current balancing circuit. The current output by each LED is achieved by the ampere-second balance of the storage capacitor C1 and the resonant capacitor Cr, so that the currents of multiple LEDs are balanced. Therefore, the dimming efficiency is high and there is no flicker, and the influence of the manufacturing tolerance of active devices can be avoided, so that the current of each LED is balanced.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings;

[0020] Figure 1 It is a circuit schematic diagram of a multi-channel low ripple current drive circuit;

[0021] Figure 2 It is the waveform diagram of each passive device during the switching cycle;

[0022] Figure 3 It is the circuit schematic diagram in the first period;

[0023] Figure 4 This is the circuit schematic during the second period;

[0024] Figure 5 This is the circuit schematic in the third period;

[0025] Figure 6 This is the circuit schematic in the fourth period. DETAILED DESCRIPTION

[0026] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0027] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0028] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0029] Reference Figures 1 to 6The present invention provides a multi-channel low-ripple current driving circuit, comprising: a DC power supply Vin, a switch S1, a main inductor Lm, a branch inductor Lb, a capacitor C1, a resonant capacitor Cr, an inductor Lr, a capacitor Co1, a capacitor Co2, a capacitor Co3, an LED1, an LED2 and an LED3, wherein the capacitor Co1 is connected in parallel with the LED1 to form a first circuit, the capacitor Co2 is connected in parallel with the LED2 to form a second circuit, and the capacitor Co3 is connected in parallel with the LED3 to form a third circuit, one end of the switch S1 is respectively electrically connected to the negative electrode of the DC power supply Vin and the positive electrode of the first circuit, the negative electrode of the first circuit is respectively electrically connected to one end of the resonant capacitor Cr and the positive electrode of the second circuit via the series inductor Lr, the negative electrode of the second circuit is respectively electrically connected to one end of the capacitor C1 and the positive electrode of the third circuit, the negative electrode of the third circuit is respectively electrically connected to the other end of the resonant capacitor Cr, the other end of the switch S1 and one end of the main inductor Lm via the series branch inductor Lb, and the other end of the main inductor Lm is respectively electrically connected to the other end of the capacitor C1 and the positive electrode of the DC power supply Vin.

[0030] In some embodiments, the switch S1 is a MOS tube, a source of the MOS tube is electrically connected to one end of the main inductor Lm, and a drain of the MOS tube is electrically connected to the positive electrode of the first circuit.

[0031] like Figure 1 In some embodiments, it also includes a diode D1, a diode D2, and a diode D3. The diode D1 is connected between the resonant capacitor Cr and the inductor Lr, and the anode of the diode is electrically connected to the inductor Lr. The cathode of the diode D2 is electrically connected to the anode of the second circuit. The anode of the diode D2 is electrically connected to the resonant capacitor Cr. The diode D3 is connected between the branch inductor Lb and the switch S1, and the anode of the diode D3 is electrically connected to the branch inductor Lb.

[0032] The switching period of switch S1 is T s , switching period T s It includes a first time period τ1, a second time period τ2, a third time period τ3 and a fourth time period τ4, wherein τ1 and τ2 are the on time, and τ3 and τ4 are the off time; Figure 2 and Figure 3 , first in the first period, the switch S1 is turned on, and the current i of the main inductor Lm Lm (t) and the circuit i of the branch inductance Lb Lb (t) satisfies the following formula: The inductor Lr and the resonant capacitor Cr form a resonant circuit. The current flows from the resonant capacitor Cr through the inductor Lr and then outputs through LED1. The voltage of the inductor Lr is v Cr (t)-v LED1 , the average voltage across the resonant capacitor Cr and the current i through the inductor Lr Lr The maximum values ​​are:

[0033] At the end of the first period, the resonance of the resonant capacitor Cr and the inductor Lr ends.

[0034] like Figure 2 and Figure 4 Then, the second period begins, the switch S1 continues to conduct, and the current i Lr (t) and the current i of the resonant capacitor Cr Cr (t) are all zero, and the voltage v on the resonant capacitor Cr cr Keep constant; at the end of the second period, the current i of the main inductor Lm Lm The maximum value of the branch inductance Lb and the current i Lb The maximum values ​​of (t) are:

[0035] like Figure 2 and Figure 5 Then, in the third period, switch S1 is turned off, diodes D2 and D3 are turned on, capacitor C1 is discharged, and the voltage v cr is a constant voltage, then i Lm (t), i Lb (t) are decreased as follows:

[0036]

[0037] when i Lb When (t) decreases to 0, diode D3 is turned off. Lb When it becomes zero, it enters the fourth working period.

[0038] like Figure 2 and Figure 6 At the beginning of the fourth period, the switch S1 is turned off, the diodes D1 and D3 are turned off, the diode D2 is turned on, and i Lm (t) continues to decrease at the same slope as in the third stage. At the end of the fourth period, i Lm When the voltage drops to zero, diodes D1, D2 and D3 are all turned off, thus completing a conversion cycle.

[0039] In a switching cycle T a In order to make all currents reach a balanced state in each branch, the charge stored in the resonant capacitor Cr and the capacitor C1 needs to be equal to the charge released from the resonant capacitor Cr and the capacitor C1. Therefore, Q r-charge =Q r-discharge , Q 1-charge =Q 1-discharge The resonant capacitor Cr stores charge in the third and fourth time periods, i Cr (t) = iLm (t)+i Lb (t); the resonant capacitor Cr releases charge in the first period and the second period, i Cr (t) = i Lr (t); Capacitor C1 stores charge in the first period and the second period, i c1 (t) = i Lb (t); Capacitor C1 releases charge in the third and fourth time periods, i Lb (t) = i Lm (t); therefore the average current satisfies the following formula:

[0040]

[0041] Where Q r-dis , Q 1-dis They are the charges released by the resonant capacitor Cr and the capacitor C1, Q r-ch , Q 1-ch For a switching cycle T s The charge stored in the resonant capacitor Cr and capacitor C1; the current I LED1 is a switching cycle T s The average current flowing through the inductor Lr, the LED2 current I LED2 = ... LED3 Equal to one switching period T s The average current flowing through the branch inductor Lb is, therefore, the average currents of the three LEDs are:

[0042]

[0043] The relationship between the three LED currents can be obtained by solving the above equation:

[0044] I LED1 =I LED2 =I LED3 .

[0045] That is, the dimming circuit uses passive devices and has only one switch S1. The circuit structure combines a buck-boost-buck converter and a passive current balancing circuit. The current output by each LED is achieved through the ampere-second balance of the storage capacitor C1 and the resonant capacitor Cr, so that the currents of multiple LEDs are balanced. Therefore, the dimming efficiency is high and there is no flicker, and the influence of the manufacturing tolerance of active devices can be avoided, so that the current of each LED is balanced.

[0046] In some embodiments, a controller is further included, wherein the controller is designed to make the main inductor current i LmZero current base (ZCB) conduction is achieved during the switching cycle. When zero current is detected on the main inductor Lm, the switch S1 is turned on, and the on-time is mapped to a current error value by comparing the LED current with the input reference current value i ref The maximum on-time in any case is limited to 50μs, because the operating frequency at any time must not be in the audible range, lower than 20kHz, and the minimum on-time must be greater than 3 seconds, where the minimum on-time is determined by half a cycle of the resonant period of the resonant capacitor Cr and the inductor Lr.

[0047] It is easy for those skilled in the art to understand that the above preferred embodiments can be freely combined and superimposed without conflict.

[0048] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or directly or indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A multi-channel low ripple current drive circuit, characterized in that: include: A DC power supply Vin, a switch S1, a main inductor Lm, a branch inductor Lb, a capacitor C1, a resonant capacitor Cr, an inductor Lr, a capacitor Co1, a capacitor Co2, a capacitor Co3, an LED1, an LED2 and an LED3, wherein the capacitor Co1 is connected in parallel with the LED1 to form a first circuit, the capacitor Co2 is connected in parallel with the LED2 to form a second circuit, and the capacitor Co3 is connected in parallel with the LED3 to form a third circuit. One end of the switch S1 is respectively electrically connected to the negative electrode of the DC power supply Vin and the positive electrode of the first circuit, the negative electrode of the first circuit is respectively electrically connected to one end of the resonant capacitor Cr and the positive electrode of the second circuit via the series inductor Lr, the negative electrode of the second circuit is respectively electrically connected to one end of the capacitor C1 and the positive electrode of the third circuit, the negative electrode of the third circuit is respectively electrically connected to the other end of the resonant capacitor Cr, the other end of the switch S1 and one end of the main inductor Lm via the series branch inductor Lb, and the other end of the main inductor Lm is respectively electrically connected to the other end of the capacitor C1 and the positive electrode of the DC power supply Vin.

2. The multi-channel low ripple current driving circuit according to claim 1, characterized in that: The switch S1 is a MOS tube, a source of the MOS tube is electrically connected to one end of the main inductor Lm, and a drain of the MOS tube is electrically connected to the positive electrode of the first circuit.

3. The multi-channel low ripple current driving circuit according to claim 1, characterized in that: It also includes a diode D1, a diode D2, and a diode D3. The diode D1 is connected between the resonant capacitor Cr and the inductor Lr, and the anode of the diode is electrically connected to the inductor Lr. The cathode of the diode D2 is electrically connected to the anode of the second circuit. The anode of the diode D2 is electrically connected to the resonant capacitor Cr. The diode D3 is connected between the branch inductor Lb and the switch S1, and the anode of the diode D3 is electrically connected to the branch inductor Lb.

4. The multi-channel low ripple current driving circuit according to claim 1, characterized in that: The switching period of switch S1 is T s , switching period T s It includes a continuous first period τ1, a second period τ2, a third period τ3 and a fourth period τ4, wherein τ1 and τ2 are the on time, and τ3 and τ4 are the off time. In the first period τ1, the switch S1 is turned on, and the current i of the main inductor Lm is Lm (t) and the circuit i of the branch inductance Lb Lb (t) satisfies the following formula: The inductor Lr and the resonant capacitor Cr form a resonant circuit. The current flows from the resonant capacitor Cr through the inductor Lr and then outputs through LED1. The voltage of the inductor Lr is v Cr (t)-v LED1 , the average voltage across the resonant capacitor Cr and the current i through the inductor Lr Lr The maximum values ​​are: At the end of the first period τ1, the resonance of the resonant capacitor Cr and the inductor Lr ends.

5. The multi-channel low ripple current driving circuit according to claim 4, characterized in that: In the second period τ2, the switch S1 continues to be turned on, and the current i Lr (t) and the current i of the resonant capacitor Cr Cr (t) are all zero, and the voltage v on the resonant capacitor Cr cr Keep constant; at the end of the second period τ2, the current i of the main inductor Lm Lm The maximum value of the branch inductance Lb and the current i Lb The maximum values ​​of (t) are:

6. The multi-channel low ripple current driving circuit according to claim 5, characterized in that: In the third period τ3, switch S1 is turned off, diodes D2 and D3 are turned on, capacitor C1 is discharged, and the voltage v cr is a constant voltage, then i Lm (t), i Lb (t) are decreased as follows: when i Lb When (t) decreases to 0, diode D3 is turned off. Lb When it becomes zero, it enters the fourth working period.

7. The multi-channel low ripple current driving circuit according to claim 6, characterized in that: In the fourth period τ4, the switch S1 is turned off, i Lm Continue to decline, when i Lm When it drops to 0, diode D1, diode D2 and diode D3 are all turned off.

8. The multi-channel low ripple current driving circuit according to claim 7, characterized in that: In a switching cycle T s In order to make all currents reach a balanced state in each branch, the charge stored in the resonant capacitor Cr and the capacitor C1 needs to be equal to the charge released from the resonant capacitor Cr and the capacitor C1. Therefore, Q r-charge =Q r-discharge , Q 1-charge =Q 1-discharge ; and the average current of LED1 I LED1 、The average current of LED2 I LED2 、The average current of LED3 I LED3 Between: I LED1 =I LED2 =I IED3 .

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