CN108124341B

CN108124341B - LED driver and LED lighting device

Info

Publication number: CN108124341B
Application number: CN201611081245.7A
Authority: CN
Inventors: 陈忠; 王新胜; 陈亮; 邬秋峰
Original assignee: SHANGHAI MINGSHI OPTOELECTRONIC TECHNOLOGY Co Ltd
Current assignee: SHANGHAI MINGSHI OPTOELECTRONIC TECHNOLOGY Co Ltd
Priority date: 2016-11-30
Filing date: 2016-11-30
Publication date: 2020-02-11
Anticipated expiration: 2036-11-30
Also published as: CN108124341A

Abstract

An LED driver and an LED lighting device, the LED driver comprising: the bridge circuit comprises first to fourth bridge arms, a first node is arranged between the first bridge arm and the second bridge arm, a second node is arranged between the second bridge arm and the third bridge arm, a third node is arranged between the third bridge arm and the fourth bridge arm, a fourth node is arranged between the fourth bridge arm and the first bridge arm, direct-current voltage is input between the fourth node and the second node, the first bridge arm comprises a first transistor, the second bridge arm comprises a second transistor, and the first transistor and the second transistor are controlled to be alternately conducted; the parallel resonant circuit is coupled between the first node and the third node and comprises a resonant inductor and a resonant capacitor which are connected in parallel, and the parallel resonant circuit is suitable for driving the LED load; an excitation source circuit adapted to provide an excitation current to the parallel resonant circuit; and the starting circuit is suitable for controlling the conduction of the second transistor after the direct-current voltage is established, so that the parallel resonant circuit starts to start oscillation. The LED driver has excellent load regulation rate and higher driving efficiency.

Description

LED driver and LED lighting device

Technical Field

The invention relates to the field of light source driver design, in particular to an LED driver and an LED lighting device.

Background

In the field of lighting, a fluorescent lamp is a conventional light source, which is a low-pressure gas discharge lamp, and exhibits a negative resistance characteristic during operation, and a matched electronic ballast is mostly required during operation. The LED light source has shown a wide application prospect due to its advantages of high light efficiency, long service life, low cost, etc. In an increasing number of application scenarios, it is more desirable to replace conventional fluorescent lamps with LED light sources.

In the prior art, when replacing a fluorescent lamp with an LED light source, the LED light source compatible with the electronic ballast can be directly selected without detaching the electronic ballast, so that the light source can be updated only by simply removing the old fluorescent lamp and replacing the LED light source. Such applications are popular with users due to their simplicity and convenience. However, the electronic ballast is designed to match the fluorescent lamp, and the power of the LED light source replacing the fluorescent light is much lower than that of the fluorescent light at the same luminous flux output, and is usually only about 50% of the fluorescent light. Therefore, when the LED light source is matched with the electronic ballast, the electronic ballast may cause a phenomenon of "carriage is pulled by a large horse", so that power is not matched, driving efficiency is low, and generally, driving efficiency can only reach 83-85%, so that lighting effect of the whole lighting system is also low, and it is difficult to reach the gold medal standard for efficacy standard in lamp design alliance (DLC) 4.0. The purpose of replacing the conventional fluorescent lamp with the LED light source is to save energy, and therefore, it is necessary to improve the driving efficiency to the DLC4.0 standard. Moreover, when the electronic ballast drives the LED light source, the impedance characteristics of the LED light source and the fluorescent lamp are not consistent, which may also cause the electronic ballast to have unstable working state, and have severe high-frequency oscillation, resulting in noise and electromagnetic compatibility. In addition, the load adjustment rate of the electronic ballast driving the LED light source is also poor, for example, when an electronic ballast driving four by four (a power supply with four light bars) drives an LED light source with 4 light bars and an LED light source with 3 light bars, the amount of change of the current flowing through each light bar exceeds 20%.

In the prior art, there is a scheme of an LED driver, which converts a commercial ac voltage with an amplitude of 200V and a frequency of 50Hz into a stable dc voltage (about 311V), and then steps down the converted dc signal to about 60V through a step-down (Buck) circuit for constant current output, for example, to satisfy a rated driving voltage of an LED light source, and the constant current voltage signal obtained by step-down can be directly used for driving the LED light source. Because the scheme comprises two-stage voltage conversion, the driving efficiency is not high, generally only 85-87%, the gold plate standard of DLC4.0 energy efficiency is difficult to achieve, and the requirement of the market on energy conservation of the LED driver cannot be met.

In the prior art, an LED driver with high driving efficiency is also provided, in which a series resonant circuit is used to connect an LED light source load in parallel to an inductor of series resonance. The driving efficiency of this solution is high, and there is very little high frequency oscillation in the resonant tank, but the load regulation rate of this solution is very poor, for example, the designed LED driver is a one-to-two (one power supply with two light bars), when driving an LED light source load including only one light bar, the load current will double, which may cause the LED light source load to be damaged by overheating.

Therefore, summarizing, the LED driver according to the related art has a technical problem that the low driving efficiency and the poor load regulation cannot be simultaneously achieved.

Disclosure of Invention

The invention solves the technical problem of how to simultaneously consider the driving efficiency and the load regulation rate of an LED driver.

To solve the above technical problem, an embodiment of the present invention provides an LED driver, including: the bridge circuit comprises a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm, wherein a first node is arranged between the first bridge arm and the second bridge arm, a second node is arranged between the second bridge arm and the third bridge arm, a third node is arranged between the third bridge arm and the fourth bridge arm, the fourth bridge arm and the first bridge arm are provided with a fourth node, direct-current voltage is input between the fourth node and the second node, the first bridge arm comprises a first transistor, the second bridge arm comprises a second transistor, and the first transistor and the second transistor are controlled to be alternately conducted; a parallel resonant circuit coupled between the first node and a third node, comprising a resonant inductor and a resonant capacitor connected in parallel, the parallel resonant circuit being adapted to drive the LED load non-isolatedly; an excitation source circuit adapted to provide an excitation current to the parallel resonant circuit; and the starting circuit is suitable for controlling the second transistor to be conducted after the direct-current voltage is established, so that the parallel resonant circuit starts to start oscillation.

Optionally, the LED driver further comprises: and the high-frequency oscillation eliminating circuit is connected in series in a loop formed by coupling the parallel resonant circuit and the LED load, and is suitable for inhibiting parasitic oscillation.

Optionally, the high-frequency oscillation elimination circuit comprises a first inductor and a first resistor which are connected in parallel.

Optionally, the resonant inductor includes a second inductor and a third inductor connected in series, a first end of the second inductor is coupled to the third node, a second end of the third inductor is coupled to the first node, and a second end of the second inductor and a first end of the third inductor are coupled to a fifth node; the LED driver further includes: a first protection circuit coupled between the fifth node and a fourth node and adapted to clamp a voltage between the fifth node and the fourth node; a second protection circuit coupled between the fifth node and the second node and adapted to clamp a voltage between the fifth node and the second node.

Optionally, the first protection circuit comprises a first diode, an anode of the first diode is coupled to the fifth node, and a cathode of the first diode is coupled to the fourth node; the second protection circuit comprises a second diode, wherein the anode of the second diode is coupled to the second node, and the cathode of the second diode is coupled to the fifth node.

Optionally, the excitation source circuit comprises: a first ballast inductor connected in series between the first transistor and a first node; and the second ballasting inductor is connected between the second transistor and the first node in series.

Optionally, the LED driver further comprises: and the first capacitor is connected with the first ballasting inductor and the second ballasting inductor which are connected in series in parallel.

The excitation source circuit includes: a third ballast inductor connected in series between the first transistor and a fourth node, wherein a first terminal of the third ballast inductor is coupled to the fourth node; a fourth ballasting inductor connected in series between the second transistor and a second node, wherein a first terminal of the fourth ballasting inductor is coupled to the second node.

Optionally, the LED driver further comprises: a second capacitor coupled between a second terminal of the third ballast inductor and a second terminal of the fourth ballast inductor.

Optionally, the LED load comprises a single LED unit or a plurality of parallel LED units coupled between the first node and a third node.

In order to solve the above technical problem, an embodiment of the present invention further provides an LED lighting device, including the LED driver and the LED load.

Compared with the prior art, the technical scheme of the embodiment of the invention has the following beneficial effects:

the embodiment of the invention provides an LED driver, which can comprise a bridge circuit, a parallel resonant circuit, a drive source circuit and a starting circuit. The bridge circuit comprises first to fourth bridge arms which are connected end to end, a first node is arranged between the first bridge arm and the second bridge arm, a second node is arranged between the second bridge arm and the third bridge arm, a third node is arranged between the third bridge arm and the fourth bridge arm, a fourth node is arranged between the fourth bridge arm and the first bridge arm, the first bridge arm comprises a first transistor, the second bridge arm comprises a second transistor, and the first transistor and the second transistor are controlled to be alternately conducted; a direct current voltage is input between the fourth node and the second node; the starting circuit is suitable for controlling the conduction of the second transistor after the direct-current voltage is established, so that the parallel resonant circuit starts to start oscillation; the parallel resonant circuit is coupled between the first node and the third node and comprises a resonant inductor and a resonant capacitor which are connected in parallel, and the parallel resonant circuit is suitable for driving the LED load in a non-isolated mode; the excitation source circuit is adapted to provide an excitation current to the parallel resonant circuit. In the embodiment of the invention, a parallel resonance scheme is adopted, and compared with a scheme adopting series resonance in the prior art, in the parallel resonance scheme, the voltage at two ends of the resonance inductor is smaller, and the voltage difference between the voltage at two ends of the resonance inductor and two ends of the LED load (namely the voltage of a parasitic series capacitor of the LED load or the voltage of a current-limiting capacitor externally connected in series with the LED load) is limited within a smaller range, so that the LED driver of the embodiment has an excellent load regulation rate. Further, the parallel resonant circuit drives the LED load in a non-isolated manner, compared with a conventional electronic ballast, the parallel resonant circuit in this embodiment does not need to be coupled through the middle of a step-up transformer when driving the LED load, and does not have loss and high-frequency oscillation caused by an isolation winding (i.e., the step-up transformer), so that the driving efficiency can be greatly improved, and the rated driving voltage requirement of the LED load can be met.

Furthermore, the embodiment of the present invention further includes a high-frequency oscillation cancellation circuit adapted to suppress parasitic oscillation, which is connected in series in a loop formed by coupling the parallel resonant circuit and the LED load, and the high-frequency oscillation cancellation circuit includes a first inductor and a first resistor connected in parallel, and can effectively change the frequency characteristic of the parasitic oscillation and reduce the amplitude of the parasitic oscillation by increasing the inductance in the resonant loop, respectively, so as to accomplish suppression of the parasitic oscillation, thereby improving the driving efficiency of the LED driver and improving the circuit EMC.

Further, the LED driver further includes: a first protection circuit adapted to clamp a voltage between the fifth node and a fourth node; a second protection circuit adapted to clamp a voltage between the fifth node and the second node to protect the first transistor and the second transistor from breakdown.

Drawings

Fig. 1 is a schematic block diagram of an LED driver in the prior art.

Fig. 2 is a schematic structural block diagram of an LED driver according to a first embodiment of the present invention.

Fig. 3 is a schematic block diagram of an LED driver according to a second embodiment of the present invention.

Fig. 4 is a schematic structural block diagram of an LED driver according to a third embodiment of the present invention.

Fig. 5 is a circuit diagram of an LED driver according to a fourth embodiment of the present invention.

Fig. 6 is a schematic structural block diagram of an LED driver according to a fifth embodiment of the present invention.

Detailed Description

As described in the background section, the LED driver capable of driving the LED light source in the prior art cannot satisfy both the driving efficiency and the load regulation rate, and cannot meet the market demand.

The inventor of the present application has analyzed an LED driver using a series resonance scheme in the prior art.

Fig. 1 is a schematic block diagram of an LED driver in the prior art. As shown in fig. 1, the LED driver 100 in the prior art may include a half-bridge circuit composed of a capacitor C2A, a capacitor C2B, a switching tube Q1 and a switching tube Q2, an electrolytic capacitor C1, current limiting resistors R1 and R2, a driving circuit, a capacitor C3 and an inductor T4A forming a series resonant circuit, an LED load (not shown) connected in parallel across the inductor T4A, and current limiting capacitors C4A and C4B. The LED load shown in fig. 1 includes two LED units, for example, the LED units may be light bars, and a current-limiting capacitor is connected in series on a branch where each light bar is located. The electrolytic capacitor C1 has a dc voltage (not shown) input to its two ends, where the dc voltage may be obtained by rectifying the ac voltage of the mains supply, and the electrolytic capacitor C1 is a filter capacitor. After the dc voltage is established, the driving circuit may drive the switching tube Q2 to be turned on, the dc voltage forms a current loop via the capacitor C2A, the series resonant circuit, and the switching tube Q2, so that the series resonant circuit starts to start oscillating, and after the oscillation starts, current starts to flow through the light bars in the two LED units. After the driving circuit controls the switching tube Q2 to be turned off, the switching tube Q1 is controlled to be turned on, at this time, the dc voltage forms a current loop via the switching tube Q1, the series resonant circuit and the capacitor C2A, and at this time, the current direction in the inductor T4A is opposite to the current direction when the switching tube Q2 is turned on. Then, under the action of the driving circuit, the switching tubes Q1 and Q2 are alternately turned on, so that the series resonant circuit continuously oscillates to maintain the current supplied to the LED load.

Compared with the traditional electronic ballast, the scheme has higher efficiency; however, since the series resonance belongs to the voltage resonance, the voltage across the resonance capacitor (i.e., the capacitor C3) and the resonance inductor (i.e., the inductor T4A) reaches the maximum when the resonance point is reached. When the number of the light bars is increased or decreased, the LED load driven by the series resonant circuit affects the resonant parameters of the series resonant circuit, and since the voltage across the resonant inductor (i.e., the inductor T4A) is very high, the difference between the voltage across the LED load actually coupled to the LED load and the voltage across the resonant inductor (i.e., the inductor T4A) is very large, resulting in a poor load regulation rate. In addition, the driving circuit of the scheme needs to use a control chip, so that the control cost is higher.

In addition, both the conventional electronic ballast and the LED driver scheme adopting the two-stage buck circuit in the prior art cannot simultaneously consider the driving efficiency and the load regulation rate of the LED driver, so that the LED driver capable of driving the LED light source in the prior art cannot meet the market demand.

In view of the above technical problems, embodiments of the present invention provide an LED driver, which has high driving efficiency and an excellent load regulation rate when driving an LED load.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

As shown in fig. 2, in the LED driver 200 according to the first embodiment of the present invention, the LED driver 200 may include a bridge circuit (not shown), a parallel resonant circuit 20, a driving source circuit 30, and a start circuit 40.

The bridge circuit comprises a first bridge arm 101, a second bridge arm 102, a third bridge arm 103 and a fourth bridge arm 104 which are sequentially connected end to end, a first node A is arranged between the first bridge arm 101 and the second bridge arm 102, a second node B is arranged between the second bridge arm 102 and the third bridge arm 103, a third node C is arranged between the third bridge arm 103 and the fourth bridge arm 104, a fourth node D is arranged between the fourth bridge arm 104 and the first bridge arm 101, a direct current voltage Udc is input between the fourth node D and the second node B, the first bridge arm 101 comprises a first transistor Q1, the second bridge arm 102 comprises a second transistor Q2, and the first transistor Q1 and the second transistor Q2 are controlled to be alternately conducted.

The first transistor Q1 and the second transistor Q2 may be MOS transistors or triodes, and this embodiment is not particularly limited, and in this embodiment, the first transistor Q1 and the second transistor Q2 are illustrated as triodes.

The dc voltage Udc may be obtained by rectifying a 50Hz 220V commercial ac voltage through a rectifier bridge and filtering the rectified ac voltage through a rectifier filter, but is not limited thereto, and may also be directly supplied by a dc voltage source, such as a high voltage battery.

It should be noted that the bridge circuit in the embodiment of the present invention may be a full bridge circuit or a half bridge circuit, and therefore the circuit configurations of the third arm 103 and the fourth arm 104 are not limited. The third arm 103 and the fourth arm 104 may be transistors, and may be controlled to cooperate with the first transistor Q1 and the second transistor Q2 to form a full bridge circuit, or may be other elements such as a capacitor or a resistor, and form a half bridge circuit with the first transistor Q1 and the second transistor Q2.

The parallel resonant circuit 20 is coupled between the first node a and the third node C, and may include a resonant inductor Lh and a resonant capacitor Ch connected in parallel, and the parallel resonant circuit 20 is adapted to drive the LED load 201.

Since the parallel resonance is a current resonance mode, the excitation source circuit 30 is required to supply an excitation current to the parallel resonance circuit 20. In a specific implementation, the driver source circuit 30 may be divided into two parts, one part is disposed between the first node a and the first transistor Q1, and the other part is disposed between the first node a and the second transistor Q2. In the present embodiment, the position of the excitation source circuit 30 is not particularly limited, and fig. 2 only illustrates one of the possible embodiments.

The LED load 201 may include a single LED unit or a plurality of parallel LED units (not shown), between the first node a and the third node C. Optionally, each LED unit in the LED load 201 may be connected in series with a current-limiting capacitor, where the current-limiting capacitor is adapted to limit the current flowing through the LED unit, and the magnitude of the current flowing through the LED unit may be set by setting the magnitude of the capacitance of the current-limiting capacitor. However, without being limited thereto, each LED unit in the LED load 201 may not be connected in series with the current limiting capacitor, for example, the impedance of each LED unit in the LED load 201 is relatively large, or a current limiting capacitor is integrated in each LED unit inside the LED load 201.

The start-up circuit 40 is adapted to operate in a start-up phase of the LED driver 200, and after the dc voltage Udc is established, controls the second transistor Q2 to be turned on, so that the dc voltage Udc forms a current loop (set as a first resonant loop) via the fourth leg 104, the parallel resonant circuit 20, the first node a and the second transistor Q2, so that the parallel resonant circuit 20 starts to start oscillation, so as to generate a driving current to drive the LED load 201.

After the second transistor Q2 is controlled to be turned off, the first transistor Q1 is controlled to be turned on, the dc voltage Udc may form a current loop (set as a second resonant loop) via the first transistor Q1, the first node a, the parallel resonant circuit 20, the third node C and the third bridge arm 103, so that the parallel resonant circuit 20 resonates again, and the direction of the current flowing through the resonant inductor Lh is opposite to that when the second transistor Q2 is turned on, and the LED driver 200 completes the oscillation.

Then, the first transistor Q1 and the second transistor Q2 are controlled to be turned on alternately, so that the parallel resonant circuit 20 oscillates continuously, and the LED driver 200 enters a normal operation state to maintain the supply of the driving current to the LED load 201. With the alternating conduction of the first transistor Q1 and the second transistor Q2, the output end of the half-bridge circuit (i.e., the first node a) forms a unidirectional half sine wave, and a sine wave resonant voltage is generated across the resonant inductor Lh, which has a fixed proportional relationship with the dc voltage Udc, and if the dc voltage Udc is a fixed value, the voltage across the resonant inductor Lh is also a fixed value.

In the embodiment of the invention, a parallel resonance scheme is adopted, and the LED load 201 is connected in parallel to the resonance inductor Lh. Taking the example that the LED load 201 includes two LED units, it is assumed that each LED unit is connected in series with a current limiting capacitor. Compared with the LED driver 100 adopting the series resonance scheme shown in fig. 1, in the parallel resonance scheme of this embodiment, the voltage across the resonance inductor Lh is small, the voltage variation across the resonance inductor Lh is also small, and the voltage difference between the voltage across the resonance inductor Lh and the voltage across the LED load 201 (that is, the voltage across the parasitic series capacitor of the LED load 201 or the voltage across the current-limiting capacitor externally connected in series to the LED load 201) is limited in a small range, so that the LED driver of this embodiment has an excellent load regulation rate.

In a specific implementation, the parallel resonant circuit 20 drives the LED load 201 non-isolatedly.

Compared with the conventional electronic ballast, the parallel resonant circuit 20 in this embodiment does not need to be coupled through the middle of the step-up transformer when driving the LED load 201, and does not have loss and high-frequency oscillation caused by the isolation winding (i.e., the step-up transformer), so that the driving efficiency can be greatly improved, and the rated driving voltage requirement of the LED load 201 can be met.

Referring to fig. 3, fig. 3 shows an LED driver 300 according to a second embodiment of the present invention, compared to the LED driver 200 shown in fig. 2, the LED driver 300 may further include a high frequency oscillation cancellation circuit 50 on the basis of the bridge circuit, the parallel resonant circuit 20, the excitation source circuit 30 and the start-up circuit 40.

Since the LED driver has a long external lead and a parasitic inductance is provided on the lead, coupling with parasitic parameters (i.e. parasitic inductance and parasitic capacitance) in the resonant circuit (refer to the first and second resonant circuits) can generate parasitic oscillation, and the parasitic oscillation will affect the electromagnetic Compatibility (EMC) of the circuit and also generate loss in the resonant circuit, which affects the driving efficiency.

The high frequency oscillation elimination circuit 50 is connected in series in a loop formed by coupling the parallel resonant circuit 20 and the LED load 201, and is adapted to suppress parasitic oscillation, so as to improve the driving efficiency of the LED driver 300 and improve the circuit EMC.

In a specific implementation, the high-frequency oscillation elimination circuit 50 may include a first inductor and a first resistor (not shown in the figure) connected in parallel. The first inductor is suitable for increasing the inductive reactance in the resonant tank and effectively changing the frequency characteristic of the parasitic oscillation, and the first resistor is suitable for effectively reducing the amplitude of the parasitic oscillation so as to complete the suppression of the parasitic oscillation.

For more information on the bridge circuit, the parallel resonant circuit 20 and the start circuit 40, reference is made to the related description of the foregoing embodiments, and details are not repeated here.

Referring to fig. 4, fig. 4 shows an LED driver 400 according to a third embodiment of the present invention, compared to the LED driver 200 shown in fig. 2, the LED driver 400 may further include a first protection circuit 60 and a second protection circuit 70 on the basis of the bridge circuit, the parallel resonant circuit 20, the excitation source circuit 30 and the start circuit 40. The resonant inductor Lh may include a second inductor L2 and a third inductor L3 connected in series, wherein a first terminal of the second inductor L2 is coupled to the third node C, a second terminal of the third inductor L3 is coupled to the first node a, and a second terminal of the second inductor L2 and a first terminal of the third inductor L3 are coupled to a fifth node E.

The first protection circuit 60 is coupled between the fifth node E and the fourth node D, and is adapted to clamp a voltage between the fifth node E and the fourth node D. The second protection circuit 70 is coupled between the fifth node E and the second node B, and is adapted to clamp a voltage between the fifth node E and the second node B.

In an implementation, the first protection circuit 60 may include a first diode (not shown), an anode of the first diode is coupled to the fifth node E, and a cathode of the first diode is coupled to the fourth node D. The second protection circuit 70 includes a second diode (not shown), an anode of the second diode is coupled to the second node B, and a cathode of the second diode is coupled to the fifth node E.

Since the operating state of the parallel resonant circuit 20 is unstable at the initial stage of establishment of the dc voltage Udc, a high voltage is generated between the emitters and the collectors of the first transistor Q1 and the second transistor Q2, which may cause the transistors to break down if not suppressed. The unstable operating condition of the parallel resonant circuit 20 is caused by the unstable voltage across the second inductor L2 and the third inductor L3, and the voltage at the fifth node E can be clamped by dividing the resonant inductor Lh into two parts and providing a diode between the node where the two are connected (i.e., the fifth node E) and the collector of the first transistor Q1, and between the fifth node E and the emitter of the second transistor Q2, so as to clamp the voltage across the second inductor and the third inductor, and clamp the voltage between the input terminal and the output terminal of the transistor within a safe voltage range, so as to protect the first transistor Q1 and the second transistor Q2.

It should be noted that the second inductor L2 and the third inductor L3 may belong to the same transformer, and the turns ratio of the second inductor L2 and the third inductor L3 is not limited in this embodiment as long as the sum of the inductive reactance of the two inductors is equal to the resonant inductor Lh.

Referring to fig. 5, fig. 5 shows an LED driver 500 according to a fourth embodiment of the invention. In the fourth embodiment of the present invention, the LED driver 500 may include a bridge circuit, a parallel resonant circuit, a start circuit, a high frequency oscillation elimination circuit, a first protection circuit, and a second protection circuit, which are not shown in the figure.

The bridge circuit may include first to fourth legs (not shown), the first leg includes a first transistor Q1, and the second leg includes a second transistor Q2; the parallel resonant circuit may include a resonant capacitor Ch, a second inductor L2, and a third inductor L3; the high-frequency oscillation elimination circuit can comprise a first inductor L1 and a first resistor (not shown in the figure, and referring to resistors R1-1 and R1-2 connected in parallel); the first protection circuit may include a first diode D1; the second protection circuit may include a second diode D2. In addition, each LED unit in the LED load (not shown) may be connected in series with a current limiting capacitor (refer to capacitor Cl1 and capacitor Cl 2).

For further description of the bridge circuit, the parallel resonant circuit, the start circuit, the high-frequency oscillation cancellation circuit, the first protection circuit and the second protection circuit, reference is made to the related description of the foregoing embodiments, and further description is omitted here.

In the fourth embodiment of the present invention, the driver circuit may include a first ballast inductor Lb1 and a second ballast inductor Lb 2. Wherein the first ballasting inductor Lb1 is connected in series between the first transistor and a first node, and the second ballasting inductor Lb2 is connected in series between the second transistor and the first node; both are adapted to convert a direct voltage source, i.e. the direct voltage Udc, into an excitation current for exciting the parallel resonant circuit.

In a specific implementation, the LED driver 500 further includes a first capacitor C1 connected in parallel with the first ballast inductor Lb1 and the second ballast inductor Lb2 after being connected in series. Wherein the first capacitor C1 is adapted to freewheel the first and second ballast inductors Lb1, Lb2 when the first and second transistors Q1, Q2 are turned off at the same time, i.e. corresponding to the dead time of the two transistors.

In the fourth embodiment of the present invention, the LED driver 500 may further include a switch control circuit (not shown), which is coupled to the parallel resonant circuit and adapted to control the first transistor Q1 and the second transistor Q2 to be alternately turned on according to an output signal of the parallel resonant circuit.

Because the switch control circuit in this embodiment is coupled to the parallel resonant circuit, the first transistor Q1 and the second transistor Q2 may be indirectly controlled by the resonance state of the parallel resonant circuit to be alternately turned on, so that a dedicated control chip may be eliminated, and the control cost is greatly saved.

In a specific implementation, the switch control circuit may include a fourth inductor L4 and a fifth inductor L5. The fourth inductor L4 is coupled to the resonant inductor (i.e., the second inductor L2 and the third inductor L3 connected in series), and is coupled between the control terminal and the input terminal of the first transistor Q1; the fifth inductor L5 is coupled to the resonant inductor, and is coupled between the control terminal and the input terminal of the second transistor Q2, and two terminals of the fifth inductor L5 and two terminals of the fourth inductor L4 are opposite in phase to the control signal coupled from the resonant inductor.

Specifically, the fourth inductor L4 and the fifth inductor L5 may belong to the same transformer as the resonant inductor, and are wound on the same core bobbin. Wherein, the inductance coil of the resonance inductance is used as a main winding, and the fourth inductance L4 and the fifth inductance L5 are used as secondary windings.

In a specific implementation, the first transistor Q1 and the second transistor Q2 may be both transistors, and the control terminal of the transistor is the base thereof, and the input terminal of the transistor is the emitter thereof.

The LED driver 500 may further include: a second resistor R2 coupled between the control terminal and the input terminal of the first transistor Q1; a third resistor R3 is coupled between the control terminal and the input terminal of the second transistor Q2. The second resistor R2 and the third resistor R3 are current limiting circuits for limiting the current flowing through the bases of the first transistor Q1 and the second transistor Q2.

In addition, the LED driver may further include a sixth diode D6 connected in parallel with the second resistor R2 and a seventh diode D7 connected in parallel with the third resistor R3, for accelerating the speed of the first transistor Q1 and the second transistor Q2 when turned off, respectively.

When the first transistor Q1 and the second transistor Q2 are both triodes, the LED driver 500 may further include a freewheel circuit 80 adapted to provide a freewheel path for the parallel resonant circuit when the first transistor Q1 and the second transistor Q2 are simultaneously turned off.

In a particular implementation, the freewheel circuit 80 may include a third diode D3 and a fourth diode D4. Wherein the third diode D3 is coupled between the input and output of the first transistor Q1; the fourth diode D4 is coupled between the input and the output of the second transistor Q2.

In all the above embodiments, the bridge circuit may be a half-bridge circuit, the third leg of the bridge circuit may include, but is not limited to, a third capacitor C3, and the fourth leg of the bridge circuit may include, but is not limited to, a fourth capacitor C4. The third capacitor C3 and the fourth capacitor C4 may form a bridge arm of the half-bridge circuit, and may also perform a filtering function.

The LED driver 500 may further comprise an electrolytic capacitor C6 to filter the direct voltage Udc.

In the fourth embodiment of the present invention, the starting circuit may include a charging and discharging circuit (not shown), a diac DB1 and a fifth diode D5.

Wherein the charging and discharging circuit is adapted to be charged by the dc voltage Udc, and when the diac DB1 is charged to be activated, the control terminal (i.e., base) of the second transistor Q2 can be discharged via the diac DB1, so that the second transistor Q2 is turned on after the dc voltage Udc is established. The anode of the fifth diode D5 is coupled to the output terminal of the charge and discharge circuit, the cathode of the fifth diode D5 is coupled to the output terminal of the second transistor Q2, and the unidirectional conduction characteristic of the fifth diode D5 enables the charge and discharge circuit to be discharged by the second transistor Q2 after the second transistor Q2 is turned on, and cannot be recharged by the dc voltage Udc to a voltage that can trigger the diac DB1, that is, the start-up circuit 40 is enabled only in the start-up phase of the LED driver.

In a specific implementation, the charge and discharge circuit may include: a fourth resistor (not shown, refer to resistors R4-1 and R4-2) coupled between the fourth node D and the third node C; a fifth resistor (not shown, refer to resistors R5-1 and R5-2) having a first terminal coupled to the third node C; a sixth resistor R6, having a first terminal coupled to the second terminal of the fifth resistor and a second terminal coupled to the second node B; a fifth capacitor C5, a first terminal of which is coupled to the second terminal of the fifth resistor and the diac DB1, and a second terminal of which is coupled to the second node B. Wherein the fourth resistor and the series-connected fifth and sixth resistors R6 can be used to balance the amplitudes across the third and fourth capacitors C4 and C4.

The specific scheme of fig. 5 for the first leg, the second leg, the third leg, the fourth leg, and the start-up circuit is also applicable to the first to third embodiments of the present invention.

Referring to fig. 6, in a fifth embodiment of the present invention, the LED driver 600 may include a bridge circuit (not shown) which may include first to fourth legs (not shown) and first to fourth nodes. The first leg includes a first transistor Q1 and the second leg includes a second transistor Q2. For more information on the bridge circuit, reference is made to the related description of the foregoing embodiments, and further description is omitted here.

In the fifth embodiment of the present invention, the driver circuit may include a third ballast inductor Lb3 and a fourth ballast inductor Lb 4.

Wherein the third ballast inductor Lb3 is connected in series between the first transistor Q1 and a fourth node D, wherein a first terminal of the third ballast inductor Lb3 is coupled to the fourth node D; a fourth ballast inductor connected in series between the second transistor Q2 and a second node B, wherein a first terminal of the fourth ballast inductor Lb4 is coupled to the second node B; both are adapted to convert a direct voltage source, i.e. the direct voltage Udc, into an excitation current for exciting the parallel resonant circuit.

In a specific implementation, the LED driver 600 may further include: a second capacitor C2 coupled between the second terminal of the third ballast inductor Lb3 and the second terminal of the fourth ballast inductor Lb 4. The second capacitor C2 is adapted to freewheel the third and fourth ballast inductors Lb3 and Lb4 when the first and second transistors Q1 and Q2 are turned off at the same time.

For more information on the starting circuit 40, the current capacitors Cl1 and Cl2, the third capacitor C3, the fourth capacitor C4, the electrolytic capacitor C6, the resonant inductor Lh, the resonant capacitor Ch, the third diode D3, the fourth diode D4, the second resistor R2, the third resistor R3, the sixth diode D6, the seventh diode D7, the fourth inductor L4, and the fifth inductor L5 shown in fig. 6, reference is made to the related description of the foregoing embodiments, and no further description is provided herein.

It should be noted that the embodiment of the present invention does not limit the specific location and structure of the excitation source circuit, and only the LED driver 500 shown in fig. 5 and the LED driver 600 shown in fig. 6 are taken as examples, but not limited to this, and the excitation source circuit may also adopt other implementable manners, and this embodiment is not exemplified.

It should be further noted that, in the embodiment of the present invention, specific implementation forms of all the resistance, inductance, and capacitance elements may be implemented by using a single element, or may be implemented by using equivalent elements obtained by connecting resistance, inductance, and capacitance elements in series and/or in parallel, and this embodiment is not particularly limited.

Embodiments of the present invention also disclose an LED lighting device, which may include the LED driver 200/300/400/500/600 and the LED load shown in fig. 2 to 6 above. The LED lighting device provided by the embodiment of the invention has higher driving efficiency and excellent load regulation rate.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An LED driver, comprising:

the bridge circuit comprises a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm, wherein a first node is arranged between the first bridge arm and the second bridge arm, a second node is arranged between the second bridge arm and the third bridge arm, a third node is arranged between the third bridge arm and the fourth bridge arm, the fourth bridge arm and the first bridge arm are provided with a fourth node, direct-current voltage is input between the fourth node and the second node, the first bridge arm comprises a first transistor, the second bridge arm comprises a second transistor, and the first transistor and the second transistor are controlled to be alternately conducted;

the parallel resonant circuit is coupled between the first node and the third node and comprises a resonant inductor and a resonant capacitor which are connected in parallel, and the parallel resonant circuit drives the LED load in a non-isolated manner without intermediate coupling of the boosting transformer;

an excitation source circuit adapted to provide an excitation current to the parallel resonant circuit;

the starting circuit is suitable for controlling the second transistor to be conducted after the direct-current voltage is established, so that the parallel resonant circuit starts to start oscillation;

when the parallel resonant circuit drives the LED load, the parallel resonant circuit does not pass through the intermediate coupling of the step-up transformer.

2. The LED driver of claim 1, further comprising: and the high-frequency oscillation eliminating circuit is connected in series in a loop formed by coupling the parallel resonant circuit and the LED load, and is suitable for inhibiting parasitic oscillation.

3. The LED driver of claim 2, wherein the high frequency ringing cancellation circuit comprises a first inductor and a first resistor connected in parallel.

4. The LED driver of claim 1, wherein the resonant inductor comprises a second inductor and a third inductor connected in series, a first terminal of the second inductor is coupled to the third node, a second terminal of the third inductor is coupled to the first node, and a second terminal of the second inductor and a first terminal of the third inductor are coupled to a fifth node;

the LED driver further includes:

a first protection circuit coupled between the fifth node and a fourth node and adapted to clamp a voltage between the fifth node and the fourth node;

a second protection circuit coupled between the fifth node and the second node and adapted to clamp a voltage between the fifth node and the second node.

5. The LED driver of claim 4, wherein the first protection circuit comprises a first diode, an anode of the first diode is coupled to the fifth node, and a cathode of the first diode is coupled to the fourth node;

the second protection circuit comprises a second diode, wherein the anode of the second diode is coupled to the second node, and the cathode of the second diode is coupled to the fifth node.

6. The LED driver according to any of claims 1 to 5, wherein the excitation source circuit comprises:

a first ballast inductor connected in series between the first transistor and a first node;

and the second ballasting inductor is connected between the second transistor and the first node in series.

7. The LED driver of claim 6, further comprising: and the first capacitor is connected with the first ballasting inductor and the second ballasting inductor which are connected in series in parallel.

8. The LED driver according to any of claims 1 to 5, wherein the excitation source circuit comprises:

a third ballast inductor connected in series between the first transistor and a fourth node, wherein a first terminal of the third ballast inductor is coupled to the fourth node;

a fourth ballasting inductor connected in series between the second transistor and a second node, wherein a first terminal of the fourth ballasting inductor is coupled to the second node.

9. The LED driver of claim 8, further comprising: a second capacitor coupled between the second terminal of the third ballast inductor and the second terminal of the fourth ballast inductor.

10. The LED driver according to any of claims 1 to 5, wherein the LED load comprises a single LED unit or a plurality of parallel LED units coupled between the first node and a third node.

11. An LED lighting device comprising the LED driver of any one of claims 1 to 10 and an LED load.