LED Lighting Driver and Driving Method

Abstract

Embodiments of the present disclosure relate to an LED lighting driver and a driving method. The LED lighting driver has a switched-mode power supply that generates an auxiliary power supply. The auxiliary power supply circuit has a first power inductor and a second power inductor connected in series with each other. The second power inductor is selectively switched into or disconnected from the auxiliary power supply circuit, thereby changing the turns ratio for a main energy storage inductor. The switching can be based on whether it is in a light output mode or a standby mode during operation. Further, the standby mode enables more efficient generation of the auxiliary power supply voltage.

Description

[0001] This application is a divisional application of a patent application for an invention titled "LED Lighting Driver and Driving Method", with an international filing date of April 5, 2018, entering the Chinese national phase on October 12, 2019, and a Chinese national application number of 201880024877.0. Technical Field

[0002] The present invention relates to LED lighting, and particularly to an LED lighting driver. Background Art

[0003] Solid-state lighting units, especially LED (modified)-based lamps, are increasingly being used in home buildings and offices. In addition to their high efficiency, they also attract consumers due to new design features, different color temperatures, dimming capabilities, etc.

[0004] To adapt LED lighting to existing mains lighting fixtures, each LED lamp unit utilizes a converter circuit for converting an AC power supply into a DC drive signal and also for reducing the voltage level.

[0005] The converter circuit typically includes a rectifier and a switched-mode power converter.

[0006] There are various possible designs for the switched-mode power converter. A low-cost switched-mode power converter is a single-stage converter, such as a buck converter or a buck-boost converter. In both cases, there is a main inductor that controls the energy delivery to the load. The main power switch controls the energy supply from the input to the main inductor.

[0007] The timing (especially the duty cycle) of the operation of the main power switch controls the energy delivery. A flyback choke converter (RCC) is a typical self-oscillating converter where the cyclic operation of the switch is self-controlled and is widely used as a low-cost LED driver. Alternatively, an IC-based converter has control over the main power switch using the IC. The IC can then implement additional functions, such as dimming control.

[0008] Due to the limited PCB space within the LED lamp unit and for cost reduction, it is desirable to reduce the size or number of components within the driver circuit. For dimmable LEDs, a local control circuit is also required.

[0009] To reduce the cost of dimming solutions, the integration of an auxiliary power supply with the already required switched-mode power converter has been proposed. A flyback auxiliary power supply can be used to generate the auxiliary power supply.

[0010] One way to generate a stable auxiliary power supply is to provide a controlled voltage for the auxiliary power supply and a controlled voltage for the main load. However, this is not the cheapest and most efficient implementation for the connected lamps. Especially for single-stage, single-string LED implementations, current control is required for the LED load and voltage control is required for the auxiliary power supply.

[0011] High efficiency is desired at all dimming levels and during the standby (off) state. However, in low-cost switched converters such as buck converters, the combination of LED current control and an auxiliary power supply that remains efficient even during standby is not straightforward. In the standby state, the LEDs should be turned off, so the output voltage of the switched-mode power supply should be low, but the auxiliary power supply (for the microcontroller unit, MCU) should remain at the same level. If the transformer of the auxiliary power supply achieves this, it means that in the on state, the voltage of the auxiliary power supply is likely to be too high.

[0012] Therefore, the turns ratio of the auxiliary power supply is not ideal for both states. In the standby mode, the output voltage is ideally less than half of the LED forward voltage. This means that the auxiliary power supply output voltage doubles during normal operation compared to during the standby mode. This results in significant losses. The capacitive load on the main output also makes the control of the auxiliary power supply difficult.

[0013] Therefore, a low-cost driver architecture is needed that enables the efficient generation of an integrated auxiliary power supply during all operating modes of the main LED lighting load.

[0014] US 2014 / 0239829 discloses an LED driver that includes: a first auxiliary winding and a second auxiliary winding connected in series with each other; a first rectifying device coupled to the terminals of the first auxiliary winding and the other terminal coupled to the second auxiliary winding; a second rectifying device coupled to the terminals of the second auxiliary winding; a first voltage regulator coupled to the first rectifying device; a unidirectional conduction device having a positive terminal and a negative terminal; and a DC output terminal coupled to the negative terminal of the unidirectional conduction device and configured to provide the required DC power to a control circuit in the LED driver. The LED driver can ensure that the Vcc voltage provided in the heavy load state or the light load state can always meet the DC power supply requirements of the corresponding control devices in the driver, while reducing losses. Summary of the Invention

[0015] The present invention is defined by the claims.

[0016] According to an example of one aspect of the present invention, there is provided an LED lighting driver including:

[0017] A switching power supply having a storage inductor for delivering energy to an LED lighting load; and

[0018] An auxiliary power supply circuit including a power inductor device magnetically coupled to the storage inductor and a rectifier diode device for delivering a rectified voltage to an auxiliary load,

[0019] wherein the power inductor device includes a first power inductor and a second power inductor,

[0020] wherein the auxiliary power supply circuit further includes a switching circuit for selectively switching the second power inductor to or from the auxiliary power supply circuit, thereby changing the turns ratio of the storage inductor,

[0021] and wherein the LED lighting driver further includes a controller for controlling the switching circuit according to a desired lighting level.

[0022] The driver controls the lighting load and generates an auxiliary power supply. To make the generation of the auxiliary power supply efficient, a switchable turns ratio is implemented. This means that the voltage across the lighting load can be reduced (to turn off the lighting) while maintaining the desired power delivery to the auxiliary power supply circuit, such that a desired auxiliary power supply voltage can be generated in an efficient manner.

[0023] For example, the controller is adapted to: control the switching circuit to connect the second power inductor to the auxiliary power supply circuit when the LED lighting is in a standby mode, and disconnect the second storage inductor from the auxiliary power supply circuit when the LED lighting is in a light output mode.

[0024] Thus, the power inductor device can be configured as a single inductor or two inductors in series. With a constant inductor on the switching power supply side, the turns ratio can then be controlled between two values. A turns ratio based on a larger number of turns on the secondary side enables the generation of a sufficient auxiliary power supply voltage from a smaller voltage drop across the main storage inductor. This corresponds to a smaller turns ratio (e.g., 4:2 instead of 4:1).

[0025] The switching circuit can include:

[0026] A first diode between a reference terminal and a first end of the second power inductor, at the first end of the second power inductor, the first diode being connected to the first power inductor; and

[0027] A second diode between the reference terminal and a second end of the second power inductor; and

[0028] A switch in series with the second diode.

[0029] The switch is used to control whether the second power inductor is in the circuit. When the switch is closed, the two power inductors are operable in the circuit, and this has the automatic effect of reverse-biasing the first diode. Therefore, the second diode serves as the rectifying diode for the auxiliary power switched-mode power supply. When the switch is open, only the first power inductor is operable in the circuit, and the first diode serves as the rectifying diode for the switched-mode power supply.

[0030] The driver may also include a pre-load at the output of the driver, which is used to deliver sufficient and (controlled) stable standby power and voltage. In the standby mode, the main output does not deliver power (the LEDs of the lighting load are off), but the stored energy is required during the on-time of the switch in the main inductor. Therefore, a pre-load is provided to store energy in the main inductor. In the flyback mode, this energy is delivered to the auxiliary power supply during the off-time of the switch.

[0031] Preferably, a switching circuit is provided for controlling the electrical connection and disconnection of the pre-load to the output of the driver. This is used to reduce the losses in the circuit. A switch can be used because in the normal operating mode, the LEDs are on, and thus there is energy stored in the inductor.

[0032] Therefore, the losses can be controlled according to the operating mode.

[0033] The controller may also be adapted to provide control of the switched-mode power supply to provide constant voltage control of the auxiliary power supply voltage when the LED lighting is in the standby mode. The inductor configuration ensures that the LED load remains off, and this means that the switched-mode power supply can be controlled to generate the auxiliary power supply in the most efficient manner.

[0034] The switched-mode power supply preferably also includes a main switch for controlling the current through the energy storage inductor.

[0035] The switched-mode power supply includes, for example, a single-stage buck converter or a single-stage buck-boost converter. The switched-mode power supply includes, for example, a non-isolated converter. In this way, the main energy storage inductor supplies power directly to the output load without passing through a transformer. These are low-cost and thus low-performance drivers.

[0036] The present invention also provides an LED lighting circuit:

[0037] A driver as defined above;

[0038] An LED lighting load driven by the driver; and

[0039] An auxiliary load, driven by an auxiliary power supply circuit.

[0040] The auxiliary load can be a microcontroller unit (MCU) that implements a dimming function. It can be an IC that also controls the main switch of the switched-mode power supply.

[0041] An example according to another aspect of the present invention provides an LED lighting method, which includes:

[0042] Delivering energy to an LED lighting load using a switched-mode power supply having a storage inductor;

[0043] Generating an auxiliary power supply using an auxiliary power supply circuit and providing an auxiliary power supply output voltage to an auxiliary load, the auxiliary power supply circuit having a first power inductor and a second power inductor and a rectifier diode device, the second power inductor being in series with the first power inductor, and the first power inductor and the second power inductor being magnetically coupled to the storage inductor; and

[0044] Selectively switching the second power inductor into or out of the auxiliary power supply circuit, thereby changing the turns ratio of the storage inductor.

[0045] The method provides a controlled turns ratio such that a suitable auxiliary power supply can be generated even when a low voltage is required across the main output load.

[0046] For example, when the LED lighting is in the standby mode, the second power inductor is connected to the switched-mode power supply circuit, and when the LED lighting is in the light output mode, the second power inductor is disconnected from the switched-mode power supply circuit.

[0047] The method may further include controlling the electrical connection of a preload at the output of the driver. This can be used to improve the overall circuit efficiency by reducing losses.

[0048] The method may include: when the LED lighting is in the standby mode, controlling the switched-mode power supply to provide constant voltage control of the auxiliary power supply voltage.

[0049] Delivering energy to the LED lighting load may include: using a single-stage non-isolated buck converter or a single-stage non-isolated buck-boost converter. Description of the Drawings

[0050] Examples of the present invention will now be described in detail with reference to the drawings, in which:

[0051] Figure 1 The layout of a standard single-stage non-isolated buck converter is shown;

[0052] Figure 2 An auxiliary power supply circuit according to the present invention is shown;

[0053] Figure 3shows a control circuit for controlling a switched-mode power supply during regulation of an auxiliary power supply voltage; and

[0054] Figure 4 shows an LED lighting driving method according to the present invention. Detailed Description

[0055] The present invention provides an LED lighting driver having a switched-mode power supply that generates an auxiliary power supply. The auxiliary power supply circuit has a first power inductor and a second power inductor connected in series with each other. The second power inductor is selectively switched into or disconnected from the auxiliary power supply circuit, thereby changing the turns ratio for a main energy storage inductor of the switched-mode power supply. The switching can be based on whether it is a light output mode or a standby mode during operation. Further, the standby mode enables more efficient generation of the auxiliary power supply voltage.

[0056] The present invention particularly focuses on low-cost switched-mode power supplies, where buck converters and buck-boost converters are the most common examples.

[0057] Figure 1 shows a buck converter (step-down converter) having an inductor L2 as a main energy storage element.

[0058] The buck converter has the current in inductor L2 controlled by two switches, which are a main power switch in the form of transistor M main and a freewheeling diode D free . The load of the circuit is represented by inductor Z load , and inductor Z load includes an LED "LED" in parallel with a resistive pre-load PL. The main power switch, the inductor, and the load are in series, and the freewheeling diode D free is connected in parallel across the series combination of the inductor and the load.

[0059] In the transistor off state, the current in the circuit is initially zero. When the transistor first conducts, the current will start to increase, and the inductor will generate an opposing voltage across its terminals in response to the changing current. This voltage drop cancels the voltage at the input, and thus reduces the net voltage across the load. As time progresses, the rate of change of the current decreases, and in turn the voltage across the inductor decreases, thereby increasing the voltage at the load. During this time, the inductor stores energy in the form of a magnetic field. When the current is still changing, the transistor is turned off, such that there is always a voltage drop across the inductor, and the net voltage at the load will always be less than the input voltage source.

[0060] The inductor alternately acts as a current source to the load and a current absorber from the input.

[0061] Figure 1It is shown that the main inductor L2 can also be used to generate an auxiliary power supply. As shown, the auxiliary power supply includes an inductor L1 and a rectifier diode D rect , and the inductor L1 is magnetically coupled to the main inductor L2. This delivers the rectified auxiliary power supply to an auxiliary load represented by a capacitor C aux .

[0062] In the case of a lighting circuit, the main load Z load is LED lighting, and the pre-load and the auxiliary load C aux can be, for example, a controller for controlling the operation timing of the main switch M main . This controller implements a dimming function, for example.

[0063] The present invention provides a modification to the auxiliary power supply circuit, as Figure 2 shown.

[0064] Figure 1 The power supply inductor L1 of

[0065] is replaced by a first power supply inductor L1a and a second power supply inductor L1b connected in series with the first power supply inductor. These two inductors thus replace the coupled inductor L1 for auxiliary power supply generation. Figure 1 A switching circuit is used to set two different configurations of the two inductors. In particular, the inductor operating within the auxiliary power supply circuit can include only the first inductor L1a, or it can include both inductors L1a and L1b. Thus, the second power supply inductor can be switched into or disconnected from the auxiliary power supply circuit. This changes the turns ratio of the main energy storage inductor L2 (shown in

[0066] ). The energy storage inductor L2 is magnetically coupled to both inductors L1a and L1b such that the connection of one or both inductors in the secondary side circuit (i.e., the auxiliary power supply circuit) effectively changes the turns ratio with the primary side circuit (i.e., the switched-mode power supply circuit).

[0067] The transistor Q2 also forms part of the auxiliary power supply circuit. The transistor Q2 is connected in series with the second diode D1b, such that the second inductor L1b can be coupled to ground through the diode D1b, or it can be isolated from the circuit.

[0068] The controller 20 controls the switching circuit according to the desired lighting level. The controller 20 controls the base voltage to the transistor Q2 through another control transistor Q1. The voltage to the base of the transistor Q1 is controlled by the controller 20, and this in turn controls whether the base of the transistor Q2 is pulled high (to turn it on) or left open (to turn it off).

[0069] When the transistor Q2 is conducting, the diode D1a is automatically blocked due to the positive voltage at the cathode.

[0070] After being regulated by a low-dropout voltage regulator, the power supply to the switching circuit "3V3" is the auxiliary power supply.

[0071] By changing the inductor configuration, the turns ratio is changed. This means that the voltage across the auxiliary power supply can be reduced (relative to the main switched-mode converter circuit) during normal operation mode, and increased during standby mode, so as to maintain the desired power delivery to the auxiliary power supply circuit, such that the desired auxiliary power supply voltage can be generated in an efficient manner.

[0072] When two inductors are used for the standby mode, the large effective number of turns (and the corresponding turns ratio) on the auxiliary power supply side means that even when the voltage across the primary-side inductor is low, such as approximately half of the forward voltage of the LED (the LED is thus turned off), a suitable auxiliary power supply voltage can be enabled with high efficiency.

[0073] When one inductor is used for the normal operation mode, there is a relatively small effective number of turns (and the corresponding turns ratio) on the auxiliary power supply side, thus preventing an excessive auxiliary power supply voltage. Therefore, if the full turns ratio (using two inductors) is suitable for generating the auxiliary power supply from a low standby voltage, then conversely when in the normal operation mode, the auxiliary power supply will be too high. The inductor switching makes it possible to prevent this. Conversely, when in the standby mode, the increased number of turns still enables the generation of a sufficient auxiliary power supply voltage.

[0074] The reduction in the number of turns on the secondary side corresponds to an increase in the turns ratio (e.g., 4:1 instead of 4:2).

[0075] The transformer formed by the inductor is a step-down transformer, for example, gradually reducing from the forward voltage of the LED string, which is usually in the tens of volts, to the desired auxiliary power supply voltage, such as 5V.

[0076] Thus, by providing different turns ratios, this device reduces steady-state (normal operation) losses. In nominal and standby operations, the auxiliary power supply can be optimized for minimum losses.

[0077] As described above, the driver can also include a switchable preload PL at the output of the driver. This is used to reduce losses in the circuit. In particular, this enables further reduction of losses by adopting a switchable method for the preload. Under nominal operating conditions, the preload is reduced, resulting in reduced losses.

[0078] The use of a preload is known for dual-output single-stage converters, and in buck converters, such a preload is particularly needed.

[0079] The preload is switched according to the circuit mode (specifically, standby mode or normal operation mode). This can also be used in the deep dimming mode where the lighting load is reduced. Figure 1 A switch SW in series with the parallel preload PL is shown.

[0080] During the standby mode, the inductor configuration allows a low output voltage, such as less than half of the forward string voltage of the LED device, so that the control of the switched-mode power supply can be used to provide a constant voltage at the output of the auxiliary power supply.

[0081] Figure 3 A circuit for generating a control signal "IC control" for an IC controller is shown, and the IC controller in turn controls the main switch M when in the standby mode main to provide a regulated auxiliary power supply voltage.

[0082] VCC_3V3 is the low-dropout regulator output of the auxiliary power supply. Thus, the current flowing through the transistor depends on the voltage level, providing feedback control. The VCC_3V3 signal from the linear regulator is used as a reference for controlling the standby voltage.

[0083] The VCC_5V signal is the auxiliary power supply before the LDO. Thus, both the signals VCC_3V3 and VCC_5V will vary together, but the circuit still provides a suitable feedback signal. The feedback controls the main switch duty cycle to control the 5V output. The 3.3V output is used as a reference voltage.

[0084] The switched-mode power supply includes, for example, a single-stage buck converter or a single-stage buck-boost converter.

[0085] The single-stage converter is, for example, a single-stage circuit with power factor correction and other functions such as an auxiliary power supply and a dimming function.

[0086] Switching power supplies, for example, include non-isolated converters. These are low-cost and thus low-performance drivers, and flicker can be an issue due to imperfect decoupling between the auxiliary power supply and the main circuit load.

[0087] The present invention also provides an LED lighting circuit, comprising:

[0088] A driver as defined above;

[0089] An LED lighting load driven by the driver; and

[0090] An auxiliary load driven by an auxiliary power supply circuit.

[0091] The auxiliary load can be a microcontroller unit (MCU) that implements a dimming function. It can be an IC that also controls the main switch of the switching power supply.

[0092] The present invention particularly focuses on a single-string, single-stage buck implementation with switchable flyback control having a constant voltage auxiliary power supply. The use of a pre-load allows for high-efficiency operation with current control for the main load and voltage control for the auxiliary power supply.

[0093] Low-cost controllers widely used in the market can be used to control single-stage converters.

[0094] Figure 4 There is shown Figure 2 a method of circuit operation.

[0095] In step 30, a switching power supply having a main energy storage inductor is used to deliver energy to the LED lighting load.

[0096] In step 32, a power inductor device is used to generate an auxiliary power supply, the power inductor device comprising a first power inductor L1a and a second power inductor L1b, the first power inductor L1a and the second power inductor L1b being connected in series and coupled to the main energy storage inductor.

[0097] In step 34, the auxiliary power supply is provided to the auxiliary load.

[0098] In step 36, the second power inductor is selectively switched into or disconnected from the auxiliary power supply circuit, thereby changing the turns ratio of the main energy storage inductor.

[0099] The present invention focuses on lighting systems with an integrated power architecture. Of particular interest is a single-stage, single-string LED lighting method having an integrated microcontroller using an auxiliary power supply, especially for low-cost connected lamps.

[0100] Only one example of the inductor switching circuit is shown above. However, the same core functionality can be implemented in different ways. For example, any suitable switching circuit can be used to generate a configurable inductor circuit.

[0101] In the example above, there are two possible turns ratios. However, this can be increased to three or more by having additional inductors within the switching circuit, thereby achieving efficiency optimization at different drive levels or operating modes. The system can also generate multiple auxiliary power voltage levels. In addition, the first and second power inductors can be placed in parallel rather than in series. The switching circuit can then select one of the power inductors to be coupled to the auxiliary load.

[0102] Those skilled in the art, when practicing the claimed invention, can understand and realize other variations of the disclosed embodiments by studying the drawings, the present disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An LED lighting driver having a light output mode and an optional standby mode, the LED lighting driver comprising: - An input; - An output for coupling to an LED lighting load (Zload); - Switching power supply, having a storage inductor (L2) and a main power switch (M main ), the storage inductor (L2) being adapted to be electrically connected to the LED lighting load (Zload) and to deliver energy to the LED lighting load (Zload), the main power switch (M main ) electrically connecting the input and the storage inductor (L2), and the main power switch (M main ) being adapted to control the energy supply from the input to the storage inductor (L2); And - An auxiliary power circuit, comprising: Power inductor means (L1a, L1b) magnetically coupled to the energy storage inductor (L2), The LED lighting driver further comprises: - A switchable pre-load (PL) at the output of the driver, the switchable pre-load (PL) being electrically connected to the energy storage inductor (L2), Wherein the switchable pre-load (PL): Is reduced during nominal operation; and is switched in the standby mode such that the output does not deliver power, but during the off-time of the main power switch (M main ), energy is delivered to the auxiliary power supply circuit in a flyback mode.

2. The LED lighting driver according to claim 1, wherein the power inductor means (L1a, L1b) comprises a first power inductor (L1a) and a second power inductor (L1b), and the auxiliary power circuit further comprises a rectifier diode means and a switch circuit (Q1, Q2), the rectifier diode means for delivering a rectified voltage to an auxiliary load (Caux), the switch circuit (Q1, Q2) for selectively switching the second power inductor (L1b) into or out of the auxiliary power circuit, thereby changing the turns ratio of the energy storage inductor (L2), The LED lighting driver further comprises a controller (20) for controlling the switch circuit according to a desired lighting level, the controller (20) being adapted to control the switch circuit to connect the second power inductor (L1b) to the auxiliary power circuit when the LED lighting driver is in the standby mode and to disconnect the second power inductor (L1b) from the auxiliary power circuit when the LED lighting driver is in the light output mode.

3. The LED lighting driver according to claim 2, wherein the switch circuit comprises: A first diode (D1a) between a reference terminal and a first end of the second power inductor (L1b), at the first end, the first diode (D1a) being connected to the first power inductor (L1a); A second diode (D1b) between the reference terminal and a second end of the second power inductor (L1b); and A switch (Q2) in series with the second diode.

4. The LED lighting driver according to any one of the preceding claims, comprising a further switch circuit (SW) for controlling the electrical connection and disconnection of the pre-load to the output of the driver, wherein the pre-load is adapted to: store energy in the energy storage inductor during the on-time of the main power switch by being in series with the input, the main power switch and the energy storage inductor.

5. The LED lighting driver according to any one of claims 1 to 3, wherein the controller is further adapted to provide control of the switched-mode power supply to provide constant voltage control of the auxiliary power supply output when the LED lighting driver is in the standby mode.

6. The LED lighting driver according to any one of claims 1 to 3, wherein the switching power supply further includes a main switch (M main ), and the main switch (M main ) is used to control the current flowing through the energy storage inductor.

7. The LED lighting driver according to any one of claims 1 to 3, wherein the switched-mode power supply comprises a single-stage buck converter or a single-stage buck-boost converter.

8. The LED lighting driver according to any one of claims 1 to 3, wherein the switched-mode power supply comprises a non-isolated converter.

9. An LED lighting circuit, comprising: a driver according to any one of the preceding claims; an LED lighting load (Zload) driven by the driver; and An auxiliary load (C aux ) driven by the auxiliary power supply circuit.

10. A driving method for an LED lighting driver having a light output mode and an optional standby mode, the driving method comprising: (30) Use a switched-mode power supply to deliver energy to an LED lighting load at an output for coupling to an LED lighting load (Zload), the switched-mode power supply having the output, an input, a storage inductor, and a main power switch (M main ), the main power switch (M main ) being used to control the supply of energy from the input to the storage inductor (L2); and (32) generating an auxiliary power supply using an auxiliary power supply circuit and providing an auxiliary power supply output voltage to an auxiliary load, the auxiliary power supply circuit having a power inductor device (L1a, L1b) magnetically coupled to the energy storage inductor (L2); The driving method further comprises: controlling the electrical connection of a pre-load at the output of the driver, and controlling the electrical connection of the pre-load at the output of the driver includes: reducing the pre-load during nominal operation; and Switch the preload in the standby mode so that the output does not deliver power, but during the off-time of the main power switch (M main ), energy is delivered to the auxiliary power supply in a flyback mode.

11. The method according to claim 10, wherein the power supply inductor device (L1a, L1b) comprises a first power supply inductor (L1a) and a second power supply inductor (L1b), the second power supply inductor (L1b) is connected in series with the first power supply inductor, the auxiliary power supply circuit further comprises a rectifier diode device (D1a, D1b), and the method comprises: selectively switching the second power inductor (L1b) into or out of the auxiliary power supply circuit by connecting the second power inductor (L1b) to the auxiliary power supply circuit when the LED lighting driver is in the standby mode and disconnecting the second power inductor (L1b) from the auxiliary power supply circuit when the LED lighting driver is in the light output mode, (36) thereby changing the turns ratio of the energy storage inductor.

12. The method according to claim 10 or 11, wherein switching the preload comprises: Switching the pre-load to be in series with the input, the main power switch, and the energy storage inductor to store energy in the energy storage inductor during the on-time of the main power switch.

13. The method according to claim 10 or 11, comprising: Providing control of the switched-mode power supply to provide constant voltage control of the auxiliary power supply output voltage when the LED lighting driver is in the standby mode.

14. The method according to claim 10 or 11, wherein delivering energy to the LED lighting load comprises: Using a single-stage non-isolated buck converter or a single-stage non-isolated buck-boost converter.

Images