LED driving circuit and LED lighting circuit comprising the same

Abstract

A driving circuit for LED is proposed which comprising an arrangement (32) to provide a driving power; an output to be connected to a LED load; a voltage biasing component (C3) adapted to provide a bias voltage, a series connection of the output and the voltage biasing component (C3) is across the arrangement to receive the driving power; and a bidirectional converter (30) coupled with the voltage biasing component (C3) and adapted to regulate the bias voltage for regulating a power over the output, wherein said bidirectional converter (30) is adapted to switch between a first direction mode of injecting energy into the voltage biasing component (C3) thereby increasing the bias voltage and a second direction mode of drawing energy away from the voltage biasing component (C3) thereby decreasing the bias voltage, wherein said bidirectional converter (30) is adapted to switch between the two modes according to an operation condition. The regulation can be used for either smoothing the power over the output especially when the driving fluctuates, or fast changing the power over the output especially when the driving power maintains or slowly changes.

Description

[0001] LED driving circuit and LED lighting circuit comprising the same

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of electrical circuits, and in particular, to LED driving circuit.

[0004] BACKGROUND OF THE INVENTION

[0005] For low power LED lamps or luminaries, it is much harder to achieve high energy efficacy compared to mid / high power lamps or luminaires. The low driver efficiency for low power LED lamps or luminaires is one of the key roadblocks. Figures la and lb show two typical traditional low power drivers, wherein Figure la shows single stage boost or buck topology and Figure lb shows a linear current source CS typically implemented by a transistor such as BJT or MOSFET operating in linear region. SMPS driver solution has high voltage power conversion with low power which always leads to poor efficiency due to the large switching loss. And linear current source LED driver also has low efficiency due to large power consumption.

[0006] In order to avoid power loss in a linear current source solution, there have been proposed some switching mode replacement of the linear current source. Figure 2 shows an example. The essence of such technology is using a capacitor in series with the LED across the bus voltage, and using a switching converter to regulate a voltage on the capacitor, such that the bus voltage and the capacitor voltage together make a voltage / current on the LED meet a desired value. More specifically, the switch SW1, diode DI, and the inductor LI form a buck converter to draw energy away from the capacitor C3 so as to adjust the voltage on the capacitor C3. The output of the buck converter is connected to another capacitor Cl and powers a load such as MCU, or a sensor. US2018026521A1 discloses such a technology wherein the switching converter can work selectively in a buck mode or a boost mode to draw energy from a capacitor in series with the LED. SUMMARY OF THE INVENTION

[0007] There is also another implementation of the above switching mode replacement, wherein the switching converter injects, not drawing away, power into the series capacitor. One such implementation is disclosed by US2017 / 0288557A1.

[0008] The two patent documents are based on PFC architecture, wherein the LED, the capacitor in series with the LED and the switching converter are connected to an output of a PFC stage. The output voltage of a PFC stage superimposes with the capacitor voltage and the ripple component of the output voltage of the PFC stage is reduced by a ripple voltage on the capacitor voltage, such that the LED does not undertake ripple voltage and its current is also smooth. In such topologies, the output voltage of the PFC stage, though having a ripple component, has a major large DC / constant component, thus the voltage on the capacitor is also relatively stable. However, if using the non-PFC architecture as shown in figure 2, the output of the rectifier varies over a wide range, making the bus voltage vary over a wide range, thus the capacitor voltage needs also vary over a wide range to compensate the bus voltage. The switching converter in the known technologies is not able to regulate the voltage on the capacitor to such a wide range. For example, in the prior art in figure 2, if the voltage on the capacitor is no sufficient and needs to have a high voltage, it is not easy to make the load not absorb energy.

[0009] An essence of the invention is using a bi-directional converter to implement the switching converter, enabling a dynamic selection of injecting energy into and drawing energy away from the concerned capacitor. Thus the voltage on the concerned capacitor can be regulated fast and in a wide range to balance the voltage on the bus and the voltage on the LED that generates the desired LED current / voltage.

[0010] In a basic aspect of the invention, it is proposed a driving circuit comprising an arrangement to provide a driving power; an output to be connected to a LED load; a voltage biasing component adapted to provide a bias voltage, a series connection of the output and the voltage biasing component is across the arrangement to receive the driving power; and a bidirectional converter coupled with the voltage biasing component and adapted to regulate the bias voltage for regulating a power over the output, wherein said bidirectional converter is adapted to switch between a first direction mode of injecting energy into the voltage biasing component thereby increasing the bias voltage and a second direction mode of drawing energy away from the voltage biasing component thereby decreasing the bias voltage, wherein said bidirectional converter is adapted to switch between the two modes according to an operation condition. In this aspect, since the voltage biasing component can either receive or release energy and change the bias voltage, it can provide the bias voltage over a wide voltage range in a fast speed so as to balance the voltage from the arrangement and the LED voltage. The LED voltage can be regulated to generate a desired power / current on the LED. This provides a low power loss and more dynamic regulation on the LED power in the operation.

[0011] In one embodiment, the driving circuit comprises an AC mains input to receive an AC input power AC with an AC frequency ripple, the power from the arrangement varies in a wide voltage range, the arrangement comprises a rectifier to provide the driving power with the AC frequency ripple and the driving circuit is decoupled with a power factor correction circuit. The driving circuit working with AC mains input but without a power factor correction circuit intends to have unstable output. The present application uses a low cost and small power bidirectional converter to regulate the bias voltage biasing so as to stabilize the output on the LED load at least partially being unaffected by said AC frequency ripple, and the added cost is still much less than the cost of a power factor correction circuit.

[0012] In one embodiment, said operation condition comprises a relationship among an instantaneous voltage amplitude of the driving power, the forward voltage of the LED load generating a desired current and the bias voltage. In this embodiment, the direction of the bidirectional converter is switched to ensure a proper voltage generating a desired LED current is applied across the LED load, so as to smooth the LED current and reduce / remove light ripple.

[0013] In one further embodiment, the bidirectional converter is adapted to switch in the first direction mode when the instantaneous voltage amplitude of the driving power is larger than a voltage sum of the forward voltage of the LED load generating a desired current and the bias voltage so as to equalize the instantaneous voltage amplitude and the voltage sum by increasing the bias voltage. In this embodiment, when the instantaneous voltage amplitude of the driving power is high, meaning that the output current would probably increases, the bidirectional converter switches in the first direction of injecting energy into the voltage biasing component and increases the bias voltage so as to at least partially counteract the high instantaneous voltage amplitude of the driving power, so the LED voltage and current are probably maintained.

[0014] Alternatively, when the instantaneous voltage amplitude of the driving power is smaller than a voltage sum of the forward voltage of the LED load generating a desired current and the bias voltage, meaning that the driving power is not sufficient to generate the desired current on the LED, said bidirectional converter is adapted to switch in the second direction mode so as to equalize the instantaneous voltage amplitude and the voltage sum by decreasing the bias voltage. By decreasing the bias voltage, more portion of the driving power can be applied on the LED load and maintains the LED voltage / current.

[0015] In one embodiment, the bidirectional converter comprises a current control loop to detect a current through the output and adapted to select the first or the second direction mode to match the detected current and the desired current. Using current control loop is easy to implement. More specifically, the current control loop can switch in the first direction mode when the detected current is larger than the desired current, and switch in the second direction mode when the detected current is smaller than the desired current. Additionally, the current control loop may also adjust the duty cycle of the bidirectional converter in the selected mode according to the detected current and the desired current.

[0016] Alternatively, the driving circuit can also use a voltage control loop to sense and compare the instantaneous voltage amplitude of the driving power and the voltage sum and switch the direction mode according to the comparison.

[0017] In another embodiment, the driving power may not vary substantially but it is the power requirement of the LED load that varies substantially, and this requires / leads to a substantial and fast change in the LED voltage. The present application can also handle this situation. More specifically, the direction mode of the bidirectional converter can be dynamically changed to adapt the LED voltage, wherein said operation condition comprises a current through the output is adapted to be changed. This embodiment can provide dynamic load regulation in a high efficiency manner.

[0018] More specifically, said bidirectional converter is adapted to switch in the first direction mode when a current through the output is adapted to be reduced so as to reduce a voltage over the output by increasing the bias voltage. In this embodiment, increasing the bias voltage can effectively reduce the voltage portion of the driver power on the LED load and reduces the LED current.

[0019] Also, said bidirectional converter is adapted to switch in the second direction mode when a current through the output is adapted to be increased so as to increase a voltage over the output by reducing the bias voltage. In this embodiment, decreasing the bias voltage can effectively increase the voltage portion of the driver power on the LED load and increases the LED current.

[0020] To implement the above mode switching, said bidirectional converter comprises a current control loop to receive a command to change the current through the output and adapted to switch in the first or second direction mode according to the command. Additionally, the current control loop may also adjust the duty cycle of the bidirectional converter in the selected mode according to the detected current and the desired current.

[0021] In one embodiment, the voltage biasing component comprises a capacitor. It could also be implemented by a super capacitor, a battery, and a similar component which can provide a voltage depending on the energy stored therein.

[0022] In one embodiment, the driving circuit further comprises an energy buffering component, and said bidirectional converter is adapted to store in the energy buffering component the energy voltage away from the voltage biasing component in the second direction mode and draw energy from the energy buffering component and inject into the voltage biasing component in the first direction mode. In this embodiment, the power stored in the second direction mode is used in the first direction mode thus the energy is self- contained / cycled and this further reduces energy consumption of the driving circuit.

[0023] In one embodiment, said energy buffering component is also connected across the arrangement. In this embodiment, the energy buffering component’s voltage, the voltage of the driving power from the arrangement, and the voltage sum of the LED load and the voltage biasing component are dynamically balanced.

[0024] In one embodiment, the driving circuit further comprises a charging circuit connected between the AC mains input and the energy buffering component and adapted to charge said energy buffering component from the AC mains input. In a real product, the power stored in the second direction mode may not be sufficient for being used in the first direction mode. This embodiment draws energy directly from the AC mains input to provide extra energy in the energy buffering component when the energy in the energy buffering component is not enough.

[0025] In a further aspect of the application, it is provided a LED lighting circuit comprises a driving circuit of the above basic aspect, and a LED load connected at the output of the driving circuit. In still a further aspect of the application, it is provided a LED lighting apparatus comprising the LED lighting circuit of the further aspect.

[0026] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0028] Figures la, lb and 2 show known driving circuits for LED;

[0029] Figure 3 shows a new driving circuit for LED according to an embodiment of the invention;

[0030] Figure 4 shows a current control loop to select the direction mode of the driving circuit in figure 3;

[0031] Figure 5 shows two direction modes of the bidirectional converter in figure 3; and

[0032] Figure 6 shows a voltage waveform with time indications.

[0033] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The invention will be described with reference to the Figures.

[0035] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0036] Basically shown in figure 3, the application proposes a driving circuit comprising an arrangement 32 to provide a driving power; an output to be connected to a LED load LED; a voltage biasing component C3 adapted to provide a bias voltage, a series connection of the output and the voltage biasing component C3 is across the arrangement to receive the driving power; and a bidirectional converter 30 coupled with the voltage biasing component C3 and adapted to regulate the bias voltage for regulating a power over the output, wherein said bidirectional converter 30 is adapted to switch between a first direction mode of injecting energy derived from the AC mains input to the voltage biasing component C3 thereby increasing the bias voltage and a second direction mode of drawing energy away from the voltage biasing component C3 thereby decreasing the bias voltage, wherein said bidirectional converter 30 is adapted to switch between the two modes according to an operation condition.

[0037] The arrangement can be as simple as a diode rectifier. Preferably the driver circuit is decoupled with a power factor correction (PFC) circuit thus the arrangement does preferably not include such a PFC circuit.

[0038] In one embodiment, the voltage Vin / bus voltage Vbus is a rectified version of AC mains voltage and it has a double of the 60Hz AC ripple. In order to keep the ripple current over the LED being zero, an equivalent result is keeping the ripple voltage over the LED being zero or as low as possible, and a ripple should be produced on the voltage biasing component C3 so as to at least partially counteract the ripple voltage on Vin / Vbus.

[0039] The operation condition comprises a relationship among an instantaneous voltage amplitude of the driving power, the forward voltage of the LED load corresponding to a desired current and the bias voltage. In order to generate a ripple voltage over the voltage biasing component C3 which is preferably a capacitor, the present application proposes to use a bidirectional converter to actively inject energy into the capacitor to increase the capacitor voltage, and actively draw energy away from the capacitor to decrease the capacitor voltage.

[0040] More specifically, assuming at the present moment the voltage of the driving power has been equivalized to a sum of the voltage on the capacitor C3 and the LED load’s voltage corresponding to a desired LED current. In a next moment, the AC input voltage goes up such as ascending in t2 to t3 of figure 6, in order to keep the LED load voltage / current unchanged, the voltage on the capacitor C3 should be increased synchronously. Therefore the bidirectional converter is switched in the first direction mode to inject energy derived from the AC mains input into the capacitor C3.

[0041] Even more, working in the first direction mode is a macro-view / general way of working along with the AC input voltage going up. In micro-view, the input voltage and the voltage on the capacitor C3 may be so dynamic that during the above regulation, the input voltage may suddenly become less than the sum of the voltage on the capacitor C3 and the LED load’ s voltage corresponding to a desired LED current. For example, the AC input voltage may have uprising spikes, or the bidirectional converter may over charge the capacitor C3. In this case, the bidirectional converter may quickly stop buck converting and stop injecting the energy into the capacitor C3, or even temporarily switch to the second direction mode to draw energy away from the capacitor C3 so as to lower the voltage on the capacitor C3 in order to balance those voltages and provide the desired LED current.

[0042] Similarly, assuming at the present moment the voltage of the driving power has been equivalized to a sum of the voltage on the capacitor C3 and the LED load’s voltage corresponding to a desired LED current. In a next moment, the AC input voltage goes down such as descending in tl to t2 of the AC mains, in order to keep the LED load voltage / current unchanged, the voltage on the capacitor C3 should be decreased synchronously. Therefore the bidirectional converter is switched in the second direction mode to draw energy derived from the AC mains input into the capacitor C3.

[0043] Even more, working in the second direction mode is a macro-view / general way of working along with the AC input voltage going down. In micro-view, the input voltage and the voltage on the capacitor C3 may be so dynamic that during the above regulation, the input voltage may suddenly become more than the sum of the voltage on the capacitor C3 and the LED load’ s voltage corresponding to a desired LED current. For example, the AC input voltage may have downward dips, or the bidirectional converter may over discharge the capacitor C3. In this case, the bidirectional converter may quickly stop boost converting and stop drawing the energy away from the capacitor C3, or even temporarily switch to the first direction mode to inject energy into the capacitor C3 so as to increase the voltage on the capacitor C3 in order to balance those voltages and provide the desired LED current.

[0044] To sense the increasing or decreasing of the instantaneous voltage of the driving power, one implementation is sensing and comparing these voltages. An alternative implementation is sensing an output current at the LED since the output current can reflect the increasing or decreasing of the instantaneous voltage of the driving power: if the instantaneous voltage amplitude of the driving power increases, the LED current would exceed the desired value; otherwise if the instantaneous voltage amplitude of the driving power decreases, the LED current would drop below the desired value. Therefore by sensing the output current and comparing it with the desired value, the direction mode of the bidirectional converter can be selected accordingly.

[0045] As shown in figure 3, the bidirectional converter 30 comprises a current control loop shown by the block CC control which detects a current through the output as CS and adapted to select the first or the second direction mode to match the detected current and the desired current. More specifically, the current control loop is adapted to switch in the first direction mode when the detected current is larger than the desired current, and switch in the second direction mode when the detected current is smaller than the desired current. Figure 4 shows the current control loop in more detail. The sensed current is compared with a reference signal Vref corresponding to the desired current by the comparator U1. If the detected current is smaller than the reference signal, meaning the bias voltage is too large, the EN input is a high potential and the control block would switch to the second direction mode to decrease the bias voltage. Otherwise if the detected current is larger than the reference signal, meaning the bias voltage is too small, the EN input is a low potential and the control block would switch to the first direction mode to decrease the bias voltage. Moreover, after the direction mode has been switched, if need to fine tune the LED current, a state-of-art negative current feedback control based on the detected current and desired current can be employed in either one of the two direction mode, and this negative current feedback control can be via tuning the PWM duty cycle of the switches.

[0046] In the above embodiment, it is the ripple of driving power output by the arrangement that needs to be counteracted and the operation condition is about the relationship between the instantaneous voltage amplitude of the driving power and the voltage of the LED load and the voltage biasing capacitor. It should be noted that other operation condition is also possible and the present application is applicable. For example, the application can be used to dynamically change / regulate the LED power / current, regardless of whether the driving power varies or not. The principle behind this function is by adjusting the bias voltage, the voltage taken by the LED load can be regulated and the LED power / current can be changed.

[0047] More specifically, the bidirectional converter 30 is adapted to switch in the first direction mode when a current through the output is adapted to be reduced so as to reduce a voltage over the output by increasing the bias voltage. And said bidirectional converter 30 is adapted to switch in the second direction mode when a current through the output is adapted to be increased so as to increase a voltage over the output by reducing the bias voltage.

[0048] As shown in figure 3, said bidirectional converter 30 comprises a current control loop to receive a command CMD to change the current through the output and adapted to switch in the first or second direction mode according to the command.

[0049] In case that the driving power voltage is also changing simultaneously, the bias voltage should be determined by considering all voltages together and eventually it should either be maintained, increased, or decreased. When it is to be increased or decreased, the first direction mode or the second direction mode can be employed. This can also be implemented by the current control loop since the detected current would reflect how the present current deviates from the desired current and this can be used in selecting the proper mode. In the above embodiment, the arrangement is no longer necessarily a rectifier to receive an AC mains voltage, but could be a DC-DC converter or a PFC converter. In the later case, it should be noted that the DC-DC or PFC converter should till take the main role of load regulation in the long term, and the bidirectional converter kicks in just for making a fast response. After the bidirectional kicks in, the DC-DC converter or the PFC converter may be adapted to change the driving power to meet the desired LED current, and then the bidirectional converter’s regulation may be weakened and let the DC-DC or PFC converter gradually takes back the main role of load regulation. This is beneficial especially for a PFC converter which is typically slow responsive.

[0050] In a preferable embodiment, the driving circuit further comprising an energy buffering component Cl, and said bidirectional converter 30 is adapted to store in the energy buffering component Cl the energy voltage away from the voltage biasing component C3 in the second direction mode and draw energy from the energy buffering component Cl and inject into the voltage biasing component C3 in the first direction mode.

[0051] In one specific embodiment, as shown in figure 3, said energy buffering component Cl is also connected across the arrangement 32.

[0052] Sometimes the energy stored in the capacitor Cl to discharge the capacitor C3 and the energy released from the capacitor Cl to charge the capacitor C3 are not equal. In order to prevent that the energy in capacitor Cl is totally consumed, the driving circuit further comprises a charging circuit formed by for example diodes DI, D2 and switch SW3 connected between the AC mains input and the energy buffering component Cl and adapted to charge said energy buffering component Cl from the AC mains input. Preferably, the charging circuit is activated when the AC mains input is slightly higher than the voltage on the capacitor Cl, and the power loss in the charging circuit can be minimized.

[0053] Figure 5 shows the two direction modes of the bidirectional converter 30. The upper schematic in figure 5 shows the first direction mode wherein the bidirectional converter 30 operates as a buck converter, preferably a synchronous buck converter. The lower schematic in figure 5 shows the second direction mode wherein the bidirectional converter 30 operates as a boost converter, preferably a synchronous boost converter. It should be noted that there also exists other kind of bidirectional converter which only has one inductor and has switches to allow power conversion in both directions. Moreover, the bidirectional converter can also be implemented by two sub -converters each of which only handles power conversion in one direction, and the two sub -converters have different power inductor and / or power switches. Such an implementation also falls into the scope of bidirectional converter in the claims. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims.

[0054] 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.

[0055] 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.

[0056] If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "circuit", and vice versa.

[0057] Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A driving circuit comprising an arrangement (32) to provide a driving power; an output to be connected to a LED load; a voltage biasing component (C3) adapted to provide a bias voltage, a series connection of the output and the voltage biasing component (C3) is across the arrangement to receive the driving power; and a bidirectional converter (30) coupled with the voltage biasing component (C3) and adapted to regulate the bias voltage for regulating a power over the output, wherein said bidirectional converter (30) is adapted to switch between a first direction mode of injecting energy into the voltage biasing component (C3) thereby increasing the bias voltage and a second direction mode of drawing energy away from the voltage biasing component (C3) thereby decreasing the bias voltage, wherein said bidirectional converter (30) is adapted to switch between the two modes according to an operation condition.

2. The driving circuit of claim 1, further comprising an AC mains input to receive an AC input power (AC) with an AC frequency ripple, wherein said arrangement is to provide the driving power with the AC frequency ripple, said bidirectional converter (30) is adapted to regulate the bias voltage for smoothing a power over the output at least partially being unaffected by said AC frequency ripple, and said operation condition comprises a relationship among an instantaneous voltage amplitude of the driving power, the forward voltage of the LED load corresponding to a desired current and the bias voltage.

3. The driving circuit of claim 2, wherein said bidirectional converter (30) is adapted to switch in the first direction mode when the instantaneous voltage amplitude of the driving power is larger than a voltage sum of the forward voltage of the LED loadcorresponding to the desired current and the bias voltage so as to equalize the instantaneous voltage amplitude and the voltage sum by increasing the bias voltage.

4. The driving circuit of claim 2 or 3, wherein said bidirectional converter (30) is adapted to switch in the second direction mode when the instantaneous voltage amplitude of the driving power is smaller than a voltage sum of the forward voltage of the LED load corresponding to the desired current and the bias voltage so as to equalize the instantaneous voltage amplitude and the voltage sum by decreasing the bias voltage.

5. The driving circuit of claim 3 or 4, wherein the bidirectional converter (30) comprises a current control loop to detect a current through the output and adapted to select the first or the second direction mode to match the detected current to the desired current.

6. The driving circuit of claim 5, wherein the current control loop is adapted to switch in the first direction mode when the detected current is larger than the desired current, and switch in the second direction mode when the detected current is smaller than the desired current.

7. The driving circuit of claim 1, wherein said operation condition comprises that a current through the output is adapted to be changed and said bidirectional converter is adapted to regulate the bias voltage for changing the power over the output so as to change the current.

8. The driving circuit of claim 7, wherein said bidirectional converter (30) is adapted to switch in the first direction mode when the current through the output is adapted to be reduced so as to reduce a voltage over the output by increasing the bias voltage.

9. The driving circuit of claim 7 or 8, wherein said bidirectional converter (30) is adapted to switch in the second direction mode when the current through the output is adapted to be increased so as to increase a voltage over the output by reducing the bias voltage.

10. The driving circuit of claim 8 or 9, wherein said bidirectional converter (30) comprises a current control loop to receive a command to change the current through the output and adapted to switch in the first or second direction mode according to the command.

11. The driving circuit of claim 1, wherein said arrangement (32) comprises a rectifier, said voltage biasing component (C3) comprises a capacitor, and said driving circuit is decoupled with a power factor correction circuit.

12. The driving circuit of claim 1, further comprising an energy buffering component (Cl), and said bidirectional converter is adapted to store in the energy buffering component (Cl) the energy drawn away from the voltage biasing component (C3) in the second direction mode, and draw energy from the energy buffering component (Cl) and inject into the voltage biasing component (C3) in the first direction mode.

13. The driving circuit of claim 12, wherein said energy buffering component (Cl) is also connected across the arrangement (32).

14. The driving circuit of claim 12, further comprising a charging circuit (DI, D2, SW3) connected between an AC mains input and the energy buffering component (Cl) and adapted to charge said energy buffering component (Cl) from the AC mains input.

15. A LED lighting circuit comprises a driving circuit of any one of claims 1 to 14, and a LED load connected at the output of the driving circuit.

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