LED driving power supply

Abstract

An LED driving power supply comprises an average current control loop, a PWM generating unit, a driving unit and a control unit, wherein the control unit comprises a first switch module and a second switch module; the first end of the first switch module is inputted with a first voltage, the second end of the first switch module is coupled with the first end of the second switch module, and the control end of the first switch module is coupled with the first output end of the driving unit; the second end of the second switch module is coupled with the second feedforward voltage module of the PWM generating unit, and the control end of the second switch module is coupled with the second output end of the driving unit; the first end of the first feedforward voltage module of the PWM generating unit is inputted with the first voltage, and the second end of the first feedforward voltage module is coupled with the second end of an LED array; the first end of the second feedforward voltage module is coupled with the first end of the LED array, and the second end of the second feedforward voltage module is coupled with the second end of the LED array. The switching frequency of the LED driving power supply provided in the above scheme is not affected by the outside.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and more particularly to an LED driver power supply. Background Technology

[0002] DC-DC switching power supplies are widely used in LED applications due to their advantages of high efficiency, low heat dissipation requirements, and small size. Depending on different input and output requirements, LED driver power supplies have different power supply topologies, such as buck converters and buck-boost converters.

[0003] The switching frequency of existing LED driver power supplies is easily affected by the power supply voltage and the LED array voltage. Summary of the Invention

[0004] The embodiments of the present invention address the technical problem of inconsistent switching frequency of LED driver power supplies.

[0005] To address the aforementioned technical problems, this invention provides an LED driver power supply, comprising: an average current control loop, a PWM generator unit, a driver unit, and a control unit, wherein: the control unit includes a first switching module and a second switching module; the first switching module has a first terminal receiving a first voltage, a second terminal coupled to the first terminal of the second switching module, and a control terminal coupled to the first output terminal of the driver unit; the second switching module has a second terminal coupled to the second feedforward voltage module of the PWM generator unit, and a control terminal coupled to the second output terminal of the driver unit; the PWM generator unit includes a first feedforward voltage module and a second feedforward voltage module. The module comprises: a first feedforward voltage module, a first voltage input at its first terminal, a second terminal coupled to the second terminal of the LED array, and an output first feedforward voltage, wherein the first feedforward voltage is the difference between the first voltage and the voltage at the second terminal of the LED array; a second feedforward voltage module, a first terminal coupled to the first terminal of the LED array, a second terminal coupled to the second terminal of the LED array, and an output second feedforward voltage, wherein the second feedforward voltage is the voltage difference between the first terminal of the LED array and the second terminal of the LED array; an output terminal of the PWM generating unit coupled to the driving unit, and a current input terminal of the PWM generating unit coupled to the average current control loop.

[0006] Optionally, the control unit further includes a voltage source, an inductor, and a sampling resistor, wherein: the voltage source has a first terminal coupled to a first terminal of the first switching module and a first terminal of the first feedforward voltage module; the inductor has a first terminal coupled to a second terminal of the first switching unit and a first terminal of the second switching unit, and a second terminal coupled to a first terminal of the sampling resistor; the sampling resistor has a first terminal coupled to a first sampling input terminal of the average current control loop, and a second terminal coupled to a second sampling input terminal of the average current control loop and a first terminal of the LED array.

[0007] Optionally, the topology of the LED driver power supply is a buck topology.

[0008] Optionally, the second terminal of the voltage source is also coupled to the second terminal of the LED array and the second terminal of the second switching module.

[0009] Optionally, the topology of the LED driver power supply is a boost-buck topology.

[0010] Optionally, the second terminal of the voltage source is also coupled to the first terminal of the sampling resistor to output the second voltage.

[0011] Optionally, the first switching module includes a first NMOS transistor, wherein: the drain of the first NMOS transistor is a first terminal of the first switching module, the gate is a control terminal of the first switching module, and the source is a second terminal of the first switching module.

[0012] Optionally, the second switching module includes a second NMOS transistor, wherein: the drain of the second NMOS transistor is the first terminal of the second switching module, the gate is the control terminal of the second switching module, and the source is the second terminal of the second switching module.

[0013] Optionally, the switching frequency of the PWM generating unit is related to the first voltage and the LED voltage.

[0014] Optionally, the PWM generating unit includes: a PWM generator employing a sampling self-adjusting constant on-time scheme; the constant on-time is the on-time of the first switching module, and is proportional to the second feedforward voltage output by the second feedforward voltage module, inversely proportional to the first feedforward voltage output by the first feedforward voltage module, and inversely proportional to the target switching frequency of the LED driving power supply.

[0015] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects:

[0016] The first feedforward voltage of the PWM generator unit is the difference between the first voltage and the voltage at the second terminal of the LED array. The second feedforward voltage of the PWM generator unit is the difference between the voltage at the first terminal of the LED array and the voltage at the second terminal of the LED array. The PWM generator unit is controlled by the first feedforward voltage and the second feedforward voltage, thereby controlling the conduction or disconnection of the first switching module and the second switching module, so that the switching frequency of the LED driver power supply is not affected by the power supply voltage and the LED array voltage. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an LED driver power supply according to an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of another LED driver power supply in an embodiment of the present invention. Detailed Implementation

[0019] As described in the background section above, the switching frequency of existing LED driver power supplies is easily affected by the power supply voltage and the LED array voltage.

[0020] In this embodiment of the invention, the first feedforward voltage of the PWM generating unit is the difference between the first voltage and the voltage at the second end of the LED array, and the second feedforward voltage of the PWM generating unit is the difference between the voltage at the first end of the LED array and the voltage at the second end of the LED array. The PWM generating unit is controlled by the first feedforward voltage and the second feedforward voltage, thereby controlling the conduction or disconnection of the first switching module and the second switching module, so that the switching frequency of the LED driving power supply is not affected by the power supply voltage and the LED array voltage.

[0021] To make the above-mentioned objectives, features and beneficial effects of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0022] This invention provides an LED driver power supply, including: an average current control loop, a PWM generation unit, a driving unit, and a control unit.

[0023] In specific implementation, the control unit includes a first switch module and a second switch module, wherein:

[0024] The first terminal of the first switch module is input with a first voltage, the second terminal of the first switch module is coupled to the first terminal of the second switch module, and the control terminal of the first switch module is coupled to the first output terminal of the drive unit.

[0025] The second terminal of the second switching module is coupled to the second feedforward voltage module of the PWM generator unit, and the control terminal of the second switching module is coupled to the second output terminal of the drive unit.

[0026] In a specific implementation, the PWM generating unit includes a first feedforward voltage module and a second feedforward voltage module; the first terminal of the first feedforward voltage module receives a first voltage, and the second terminal of the first feedforward voltage module is coupled to the second terminal of the LED array; the first feedforward voltage module can output a first feedforward voltage, which is the difference between the first voltage and the voltage at the second terminal of the LED array;

[0027] The first terminal of the second feedforward voltage module is coupled to the first terminal of the LED array, and the second terminal of the second feedforward voltage module is coupled to the second terminal of the LED array; the second feedforward voltage module can output a second feedforward voltage, which is the voltage difference between the first terminal and the second terminal of the LED array.

[0028] The output of the PWM generator unit is coupled to the input of the drive unit, and the PWM signal it generates is output to the drive unit; the current input of the PWM generator unit is coupled to the average current control loop.

[0029] In this embodiment of the invention, the control unit may further include a voltage source, an inductor, and a sampling resistor, wherein:

[0030] The first terminal of the voltage source is coupled to the first terminal of the first switching module and the first terminal of the first feedforward voltage module; the first terminal of the voltage source corresponds to the first potential, and the potential difference between the first potential and ground is the first voltage; the second terminal of the voltage source corresponds to the second potential, and the potential difference between the second potential and ground is the second voltage.

[0031] The first end of the inductor is coupled to the second end of the first switching unit and the first end of the second switching unit, and the second end of the inductor is coupled to the first end of the sampling resistor;

[0032] The first end of the sampling resistor is coupled to the first sampling input of the average current control loop, and the second end of the sampling resistor is coupled to the second sampling input of the average current control loop and the first end of the LED array.

[0033] In this embodiment of the invention, the topology of the LED driver power supply can be either a buck topology or a boost-buck topology.

[0034] The following is combined Figure 1 This paper provides a detailed description of LED driver power supplies with a buck topology.

[0035] In a specific implementation, the first terminal of the first switching module can be coupled to the first terminal of the voltage source, the second terminal of the first switching module can be coupled to the first terminal of the inductor and the first terminal of the second switching module, and the control terminal of the first switching module can be coupled to the first output terminal of the drive unit. Under the drive of the first drive signal output by the drive unit, the first switching module can be turned on or off accordingly with the change in the level of the first drive signal.

[0036] In practical implementation, the first terminal of the second switching module can be coupled to the first terminal of the inductor, meaning that both the second terminal of the first switching module and the first terminal of the second switching module are connected to the first terminal of the inductor. The second terminal of the second switching module can be coupled to the second terminal of the voltage source, and the control terminal of the second switching module can be coupled to the second output terminal of the drive unit. Under the drive of the second drive signal output by the drive unit, the second switching unit can be turned on or off accordingly with the change in the level of the second drive signal.

[0037] It is understood that the first switching module can be an NMOS transistor, a bipolar transistor, or other transistors or circuits capable of performing switching functions, or a switching chip. Correspondingly, the second switching module can also be an NMOS transistor, a bipolar transistor, or other transistors or circuits capable of performing switching functions, or a switching chip. In other words, the specific structure or type of the first and second switching modules in the embodiments of the present invention are not limited to the above examples, and can also be other devices capable of performing switching functions.

[0038] In a specific implementation, the second end of the inductor can be coupled to the first end of the sampling resistor; the first end of the sampling resistor can also be coupled to the first sampling input terminal of the average current control loop; the second end of the sampling resistor can be coupled to the second sampling input terminal of the average control current loop and the first end of the LED array; the second end of the LED array is coupled to the second end of the voltage source.

[0039] In a specific implementation, the PWM generator unit may include two feedforward voltage modules. The first feedforward voltage module can be coupled to the first terminal and the second terminal of the voltage source, respectively. The second feedforward voltage module can be coupled to the first terminal and the second terminal of the LED array, respectively. The output terminal of the PWM generator unit can be coupled to the driving unit, and the current input terminal of the PWM generator unit can be coupled to the average current control loop. The first feedforward voltage of the PWM generator unit can be obtained through the first feedforward voltage module; the first feedforward voltage is the difference between the voltage at the first terminal and the voltage at the second terminal of the voltage source. Similarly, the second feedforward voltage of the PWM generator unit can be obtained through the second feedforward voltage module; the second feedforward voltage is the difference between the voltage at the first terminal and the voltage at the second terminal of the LED array.

[0040] The PWM generation unit can generate a PWM signal and output it to the drive unit, which then drives and amplifies the PWM signal to control the on / off state of the first and second switching modules.

[0041] In this embodiment of the invention, the PWM generating unit may include a PWM generator employing a sampling self-adjusting constant on-time scheme.

[0042] In this embodiment of the invention, the aforementioned driving unit is also a circuit capable of performing driving functions. The driving circuit in this embodiment of the invention can also adopt the structure of an existing driving circuit.

[0043] Since the PWM wave generated by the PWM generation unit is output to the drive unit, and the drive unit drives the PWM wave to control the first switching unit and the second switching unit respectively, it is essentially the PWM wave generated by the PWM generation unit that controls the first switching unit and the second switching unit. In specific implementations, the first drive signal and the second drive signal can be the same signal.

[0044] Reference Figure 1 A schematic diagram of an LED driver power supply according to an embodiment of the present invention is given below. Figure 1 Please provide a detailed explanation.

[0045] In practical implementation, the first terminal of voltage source VIN is the "VIN+" terminal of voltage source VIN, and the corresponding voltage is V(VIN+); the second terminal of voltage source VIN is the "VIN-" terminal of voltage source VIN, and the corresponding voltage is V(VIN-). Voltage source VIN provides the power supply voltage.

[0046] In a specific implementation, the first switching module may include a first NMOS transistor MN1. Specifically, the drain of the first NMOS transistor MN1 can be the first terminal of the first switching module, the gate of the first NMOS transistor MN1 can be the control terminal of the first switching module, and the source of the first NMOS transistor MN1 can be the second terminal of the first switching module.

[0047] That is, the drain of the first NMOS transistor MN1 is coupled to the first terminal of the voltage source VIN, the gate of the first NMOS transistor MN1 is coupled to the driving unit, and the source of the first NMOS transistor MN1 is coupled to the first terminal of the inductor L. Under the control of the first driving signal output by the driving unit, the first NMOS transistor MN1 is turned on / off accordingly with the high / low level of the first driving signal.

[0048] In a specific implementation, the second switching module may include a second NMOS transistor MN2. Specifically, the drain of the second NMOS transistor MN2 can be the first terminal of the second switching module, the gate of the second NMOS transistor MN2 can be the control terminal of the second switching module, and the source of the second NMOS transistor MN2 can be the second terminal of the second switching module.

[0049] That is, the drain of the second NMOS transistor MN2 is coupled to the source of the first NMOS transistor MN1 and the first terminal of the inductor L; the gate of the second NMOS transistor MN2 is coupled to the driving unit; and the source of the second NMOS transistor MN2 is coupled to the second terminal of the voltage source VIN. Under the control of the second driving signal output by the driving unit, the second NMOS transistor MN2 is turned on / off accordingly with the high / low level of the second driving signal.

[0050] In practical implementation, the first terminal of inductor L ( Figure 1 The L+ terminal of inductor L is coupled to the source of the first NMOS transistor MN1 and the drain of the second NMOS transistor MN2, respectively. Figure 1 The L- terminal of the sampling resistor RS is coupled to the first terminal of the sampling resistor RS. The second terminal of the sampling resistor RS is coupled to the first terminal LED+ of the LED array. The first sampling input terminal (RS+) of the average current control loop is coupled to the first terminal of the sampling resistor RS, and the second sampling input terminal (RS-) of the average current control loop is coupled to the second terminal of the sampling resistor RS, thereby sampling the voltage at the first terminal of the sampling resistor RS and the voltage at the second terminal of the sampling resistor RS, respectively.

[0051] In specific implementation, the first feedforward module of the PWM generation unit includes two input terminals: one input terminal is coupled to the first terminal of the voltage source VIN, corresponding to the voltage V(VIN+); the other input terminal is coupled to the second terminal of the voltage source VIN, corresponding to the voltage V(LED-). The second feedforward module of the PWM generation unit also includes two input terminals: one input terminal is coupled to the first terminal LED+ of the LED array, corresponding to the voltage V(LED+); the other input terminal is coupled to the second terminal LED- of the LED array, corresponding to the voltage V(LED-).

[0052] In this embodiment of the invention, combined with Figure 1 It can be seen that the voltage at the second terminal of the voltage source VIN is actually equal to the voltage at the second terminal of the LED array, that is, V(VIN-) = V(LED-).

[0053] The present invention will now be described in detail. Figure 1 The working principle of the provided LED driver power supply is explained.

[0054] For the PWM generator unit, its corresponding first feedforward voltage is: V1 = V(VIN+) - V(LED-); its corresponding second feedforward voltage is: V2 = V(LED+) - V(LED-).

[0055] When the PWM generation unit is a COT scheme PWM generator, its corresponding TON = K × V2 / V1 / FSTARGET, where: K is a fixed parameter of the PWM generator, and FSTARGET is the target frequency.

[0056] Therefore, the actual switching frequency is FS = 1 / (TON + TOFF).

[0057] Furthermore, combined with Figure 1 and Figure 2 The provided LED driver power supply yields FS = 1 / (TON + TON*(V1-V2) / V2) = 1 / TON*V2 / V1 = FSTARGET / K. It is evident that the final switching frequency is independent of the output voltage of the voltage source VIN and the voltage of the LED array.

[0058] In other words, the switching frequency of the final LED driver power supply is fixed and unaffected by external factors.

[0059] In embodiments of the present invention, the topology of the LED driver power supply can also be a boost-buck topology. In the following embodiments of the present invention, an LED driver power supply with a boost-buck topology is also provided. (Refer to...) Figure 2 This invention provides another LED driving power supply in an embodiment of the invention.

[0060] In a specific implementation, the first terminal of the first switching module can be coupled to the first terminal of the voltage source, the second terminal of the first switching module can be coupled to the first terminal of the inductor and the first terminal of the second switching module, and the control terminal of the first switching module can be coupled to the first output terminal of the drive unit. Under the drive of the first drive signal output by the drive unit, the first switching module can be turned on or off accordingly with the change in the level of the first drive signal.

[0061] In practical implementation, the first terminal of the second switching module can be coupled to the first terminal of the inductor, meaning that both the second terminal of the first switching module and the first terminal of the second switching module are connected to the first terminal of the inductor. The second terminal of the second switching module can be coupled to the second terminal of the voltage source, and the control terminal of the second switching module can be coupled to the second output terminal of the drive unit. Under the drive of the second drive signal output by the drive unit, the second switching unit can be turned on or off accordingly with the change in the level of the second drive signal.

[0062] It is understood that the first switching module can be an NMOS transistor, a bipolar transistor, or other transistors or circuits capable of performing switching functions, or a switching chip. Correspondingly, the second switching module can also be an NMOS transistor, a bipolar transistor, or other transistors or circuits capable of performing switching functions, or a switching chip. In other words, the specific structure or type of the first and second switching modules in the embodiments of the present invention are not limited to the above examples, and can also be other devices capable of performing switching functions.

[0063] In a specific implementation, the second end of the inductor can be coupled to the first end of the sampling resistor and the second end of the voltage source; the first end of the sampling resistor can also be coupled to the first sampling input terminal of the average current control loop; the second end of the sampling resistor can be coupled to the second sampling input terminal of the average control current loop and the first end LED+ of the LED array; the second end LED- of the LED array is coupled to the second end of the second switching module.

[0064] In a specific implementation, the PWM generator unit may include two feedforward voltage modules. The first feedforward voltage module can be coupled to the first terminal of the voltage source and the second terminal LED- of the LED array, respectively. The second feedforward voltage module can be coupled to the first terminal LED+ and the second terminal LED- of the LED array, respectively. The output terminal of the PWM generator unit can be coupled to the driving unit, and the current input terminal of the PWM generator unit can be coupled to the average current control loop. The first feedforward voltage of the PWM generator unit can be obtained through the first feedforward voltage module; the first feedforward voltage is the difference between the voltage at the first terminal of the voltage source and the voltage at the second terminal of the LED array. Similarly, the second feedforward voltage of the PWM generator unit can be obtained through the second feedforward voltage module; the second feedforward voltage is the difference between the voltage at the first terminal of the LED array and the voltage at the second terminal of the LED array.

[0065] The PWM generation unit can generate a PWM signal and output it to the drive unit, which then drives and amplifies the PWM signal to control the on / off state of the first and second switching modules.

[0066] In this embodiment of the invention, the PWM generating unit may include a PWM generator employing a sampling self-adjusting constant on-time scheme.

[0067] In this embodiment of the invention, the aforementioned driving unit is also a circuit capable of performing driving functions. The driving circuit in this embodiment of the invention can also adopt the structure of an existing driving circuit.

[0068] Since the PWM wave generated by the PWM generation unit is output to the drive unit, and the drive unit drives the PWM wave to control the first switching unit and the second switching unit respectively, it is essentially the PWM wave generated by the PWM generation unit that controls the first switching unit and the second switching unit. In specific implementations, the first drive signal and the second drive signal can be the same signal.

[0069] Reference Figure 2 A schematic diagram of another LED driver power supply in an embodiment of the present invention is provided. In an embodiment of the present invention, Figure 2 The LED driver power supply shown has a boost-buck topology.

[0070] In practical implementation, the first terminal of voltage source VIN is the "VIN+" terminal of voltage source VIN, and the corresponding voltage is V(VIN+); the second terminal of voltage source VIN is the "VIN-" terminal of voltage source VIN, and the corresponding voltage is V(VIN-). Voltage source VIN provides the power supply voltage.

[0071] In a specific implementation, the first switching module may include a first NMOS transistor MN1. Specifically, the drain of the first NMOS transistor MN1 can be the first terminal of the first switching module, the gate of the first NMOS transistor MN1 can be the control terminal of the first switching module, and the source of the first NMOS transistor MN1 can be the second terminal of the first switching module.

[0072] That is, the drain of the first NMOS transistor MN1 is coupled to the first terminal of the voltage source VIN, the gate of the first NMOS transistor MN1 is coupled to the driving unit, and the source of the first NMOS transistor MN1 is coupled to the first terminal of the inductor. Under the control of the first driving signal output by the driving unit, the first NMOS transistor MN1 is turned on / off accordingly with the high / low level of the first driving signal.

[0073] In a specific implementation, the second switching module may include a second NMOS transistor MN2. Specifically, the drain of the second NMOS transistor MN2 can be the first terminal of the second switching module, the gate of the second NMOS transistor MN2 can be the control terminal of the second switching module, and the source of the second NMOS transistor MN2 can be the second terminal of the second switching module.

[0074] That is, the drain of the second NMOS transistor MN2 is coupled to the source of the first NMOS transistor MN1 and the first terminal of the inductor; the gate of the second NMOS transistor MN2 is coupled to the driving unit; and the source of the second NMOS transistor MN2 is coupled to the second terminal of the voltage source VIN. Under the control of the second driving signal output by the driving unit, the second NMOS transistor MN2 is turned on / off accordingly with the high / low level of the second driving signal.

[0075] In practical implementation, the first end of the inductor ( Figure 1 The L+ terminal of the inductor is coupled to the source of the first NMOS transistor MN1 and the drain of the second NMOS transistor MN2, respectively. Figure 1 The L- terminal of the sampling resistor RS is coupled to the first terminal of the sampling resistor RS and the second terminal of the voltage source VIN. The second terminal of the sampling resistor RS is coupled to the first terminal LED+ of the LED array. The first sampling input terminal (RS+) of the average current control loop is coupled to the first terminal of the sampling resistor RS, and the second sampling input terminal (RS-) of the average current control loop is coupled to the second terminal of the sampling resistor RS, thereby sampling the voltage at the first terminal of the sampling resistor RS and the voltage at the second terminal of the sampling resistor RS, respectively.

[0076] In specific implementation, the first feedforward module of the PWM generation unit includes two input terminals: one input terminal is coupled to the first terminal of the voltage source VIN, corresponding to a voltage of V(VIN+); the other input terminal is coupled to the second terminal of the LED array LED-, corresponding to a voltage of V(LED-). The second feedforward module of the PWM generation unit also includes two input terminals: one input terminal is coupled to the first terminal of the LED array LED+, corresponding to a voltage of V(LED+); the other input terminal is coupled to the second terminal of the LED array LED-, corresponding to a voltage of V(LED-).

[0077] The present invention will now be described in detail. Figure 2 The working principle of the provided LED driver power supply is explained.

[0078] For the PWM generator unit, its corresponding first feedforward voltage is: V1 = V(VIN+) - V(LED-); its corresponding second feedforward voltage is: V2 = V(LED+) - V(LED-).

[0079] When the PWM generation unit is a COT scheme PWM generator, its corresponding TON = K × V2 / V1 / FSTARGET, where: K is a fixed parameter of the PWM generator, and FSTARGET is the target frequency.

[0080] Therefore, the actual switching frequency is FS = 1 / (TON + TOFF).

[0081] Furthermore, combined with Figure 2 The provided LED driver power supply yields FS = 1 / (TON + TON*(V1-V2) / V2) = 1 / TON*V2 / V1 = FSTARGET / K. It is evident that the final switching frequency is independent of the output voltage of the voltage source VIN and the voltage of the LED array.

[0082] In other words, for boost-buck type LED driver power supplies, the final switching frequency is fixed and unaffected by external factors.

[0083] In practice, the brightness of an LED array is typically achieved by controlling its average current. The average current control loop employs a negative feedback principle, collecting the current of the LED array as a negative feedback signal to form a negative feedback system and outputting a control signal.

[0084] In this embodiment of the invention, the current of the LED array is determined by collecting the voltage across the sampling resistor, and a control signal is output to the PWM generation unit. The output current of the LED driver power supply is adjusted by controlling the switching of the first and second switching modules. When the negative feedback loop reaches stability, the output current of the LED driver power supply also achieves the goal of matching the control current target. Furthermore, the on-time of the first switching module is controlled by an adaptive constant on-time scheme, and the off-time is controlled by the output control signal of the average current control loop.

[0085] It is understandable that the specific implementation and principle of the average current control loop can be referred to existing technologies, and will not be elaborated here.

[0086] In summary, whether it is a buck LED driver or a boost-buck driver, the resulting switching frequency is stable and unaffected by external factors.

[0087] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An LED driving power supply, characterized by, include: The system comprises an average current control loop, a PWM generator unit, a drive unit, and a control unit, including: The control unit includes a first switch module and a second switch module; the first switch module has a first terminal that receives a first voltage, a second terminal that is coupled to the first terminal of the second switch module, and a control terminal that is coupled to the first output terminal of the drive unit; the second switch module has a second terminal that is coupled to the second feedforward voltage module of the PWM generator unit, and a control terminal that is coupled to the second output terminal of the drive unit. The PWM generating unit includes a first feedforward voltage module and a second feedforward voltage module. The first feedforward voltage module receives a first voltage at its first terminal and is coupled to the second terminal of the LED array, outputting a first feedforward voltage, which is the difference between the first voltage and the voltage at the second terminal of the LED array. The second feedforward voltage module is coupled to the first terminal of the LED array and to the second terminal of the LED array, outputting a second feedforward voltage, which is the voltage difference between the first terminal and the second terminal of the LED array. The output terminal of the PWM generating unit is coupled to the driving unit, and the current input terminal of the PWM generating unit is coupled to the average current control loop. The PWM generating unit includes a PWM generator employing a sampling self-adjusting constant on-time scheme; the constant on-time is the on-time TON of the first switching module, and is directly proportional to the second feedforward voltage V2 output by the second feedforward voltage module, inversely proportional to the first feedforward voltage V1 output by the first feedforward voltage module, and inversely proportional to the target switching frequency of the LED driving power supply, and satisfies the following relationship: TON=K×V2 / V1 / FSTARGET, where K is a fixed parameter of the PWM generator, and FSTARGET is the target switching frequency.

2. The LED driving power supply according to claim 1, wherein The control unit also includes a voltage source, an inductor, and a sampling resistor, wherein: The voltage source has its first terminal coupled to the first terminal of the first switching module and the first terminal of the first feedforward voltage module. The inductor has a first end coupled to the second end of the first switching module and the first end of the second switching module, and its second end coupled to the first end of the sampling resistor. The sampling resistor has a first end coupled to the first sampling input terminal of the average current control loop, and a second end coupled to the second sampling input terminal of the average current control loop and the first end of the LED array.

3. The LED driver power supply as described in claim 2, characterized in that, The LED driver power supply has a buck topology.

4. The LED driver power supply as described in claim 3, characterized in that, The voltage source is also coupled at its second end to the second end of the LED array and the second end of the second switching module.

5. The LED driver power supply as described in claim 2, characterized in that, The LED driver power supply has a boost-buck topology.

6. The LED driver power supply as described in claim 5, characterized in that, The voltage source has its second terminal also coupled to the first terminal of the sampling resistor.

7. The LED driver power supply as described in claim 2, characterized in that, The first switching module includes a first NMOS transistor, wherein: The first NMOS transistor has its drain as the first terminal of the first switching module, its gate as the control terminal of the first switching module, and its source as the second terminal of the first switching module.

8. The LED driver power supply as described in claim 2, characterized in that, The second switching module includes a second NMOS transistor, wherein: The second NMOS transistor has its drain as the first terminal of the second switching module, its gate as the control terminal of the second switching module, and its source as the second terminal of the second switching module.

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