LED lighting circuit and LED lamp comprising same

Abstract

There is provided an LED lighting circuit comprising: a current regulator (I1) adapted to provide a regulated current (I); an LED string comprising at least two LED units (D1, D3) connected in series for receiving the regulated current (I); a switch (S1) connected in parallel with one LED unit (D1) of the at least two LED units (D1, D3), said switch (S1) being adapted to be controlled to be closed to bypass the regulated current (I) away from one LED unit (D1) or to be opened to allow the regulated current (I) to enter one LED unit (D1); an output capacitor (C1) connected in series and in parallel with the LED; and a control unit coupled to the switch (S1) and adapted to operate the switch (S1) on or off; characterised in that the control circuit is further adapted to operate said switch (D1) in a current regulation mode to conduct a current (I ') having a certain deviation from the regulated current (I) so as to regulate the voltage on the output capacitor (C1) before operating said switch (S1) to be closed or open.

Description

Technical Field

[0001] The invention relates to the field of LED lighting circuits. Background Art

[0002] Figure 1 A common topology of a driving device for LEDs is shown. An overall current regulator / current source I1 generates a current I to power an LED string including LED units D1 and D3 connected in series. The current regulator / current source may be a single PFC stage or a hysteresis-controlled DC-DC stage, so the current I1 is not a 100% constant current but has a certain ripple. A relatively large output capacitor is placed in parallel with the LED string to smooth the ripple. At least one LED unit D1 (which may include one or more LED chips) in the LED string is connected in parallel with a switch M2 (referred to as a shunt switch), and the shunt switch selectively closes by entering a saturation mode or opens by entering a cutoff mode to selectively bypass or not bypass the parallel LED unit D1 so as to adjust whether the current I1 flows into the LED unit D1 or the shunt switch. By doing so, the output of the LED unit D1 can be changed dynamically, while the remaining LED units D3 (which may include one or more LED chips) are not affected and are always powered by the current I. In Figure 1 In FIG. 1 , the current regulator I1 is floated from ground, and the shunt switch M2 and LED D1 are connected to the positive output of the current regulator I1. The shunt switch M2 is a PMOS transistor. A ground control circuit / gate driver for the PMOS transistor M2 is provided. The control circuit includes a resistor R2, a resistor R1, and an NMOS transistor M1, connected between the positive output of the floating current regulator and ground. The interconnection of resistor R2 and resistor R1 is connected to the gate of the PMOS transistor M2. In an alternative embodiment where the current regulator I1 is grounded, an NMOS can be used to implement the shunt switch. Note that Figure 1 This is just an example and alternatively the current regulator may be grounded / not floating. DE 10 2017 200 490 B3 discloses such a topology.

[0003] The problem with this topology is that the voltage on the output capacitor C1 will be different from the effective voltage of the LED string when some LEDs are shunted or restored to a non-shunted state. Specifically, assume that switch M2 is first opened to allow both LED unit D1 and LED unit D3 to be powered by current I1. Therefore, the voltage on capacitor C1 is equal to the sum of the forward voltages of LED unit D1 and LED unit D3. When PMOS M2 is closed to shunt / disable LED unit D1, the voltage on capacitor C1 is much higher than the forward voltage of the remaining LED unit D3, so a surge current passes through PMOS switch M2 and the remaining LED unit D3. The surge current is much higher than the original current and will cause LED D3 to flicker. Figure 2 shows a current curve where the original current of 280 mA rises to about 370 mA. Figure 3 As shown, when the shunt switch PMOS M2 is turned off, the current drops. Assume that the switch M2 is turned off first, bypassing the LED unit D1 and allowing only the LED unit D3 to be powered by the current I1. Therefore, the voltage on the capacitor C1 is equal to the forward voltage of the LED unit D3. When the PMOS M2 is turned off to enable / not shunt the LED unit D1, the voltage on the capacitor C1 is much lower than the sum of the forward voltages of the LED unit D1 and the LED unit D3 (unbalanced), and the two LED units D1 and D3 are difficult to disconnect, and the LED current drops from 280mA to only 30mA. When the voltage across the capacitor C1 reaches the sum of the forward voltages of the LED unit D1 and the LED unit D3, the current returns to I1. The LED unit D3 has flicker in its light output. If the LED unit D1 and the LED unit D3 have different lighting functions or are spatially displaced from each other, this flicker is visible to people and is not desirable.

[0004] WO2021 / 198349A1 proposes a solution to address this voltage imbalance during shunt switching. WO2021 / 198349A1 has a dedicated circuit, including a switch, a capacitor and a resistor, for discharging a capacitor in parallel with all LEDs when some LEDs are shunted. US20120299489A1 also discloses a topology including an output capacitor, a string of LEDs and a bypass switch connected in parallel with each LED. US20120299489A1 also has a dedicated capacitor charging constant current part, connected in series with the capacitor, for charging and discharging the capacitor. Summary of the invention

[0005] The invention is defined by the claims.

[0006] The applicant found that WO2021 / 198349A1 requires a dedicated circuit to discharge the capacitor, which increases the number of components and costs. In addition, the energy released from the output capacitor is dissipated by the resistor in the circuit, which increases the power loss.

[0007] The basic idea of ​​the present application is to reuse the shunt switch (and the remaining LED units) to discharge or charge the output capacitor before operating the shunt switch to enter a closed state or an open state to shunt / not shunt the LED units in the LED string, so as to adjust the voltage on the output capacitor from the original effective voltage of the LED string to the target effective voltage of the LED string. The shunt switch is operated in an active (linear) mode, in which a control circuit is provided to actively control the shunt switch to conduct a switch current different from the output current of the current regulator, the differential current between the switch current and the output current is related to the output capacitor, and the voltage on the output capacitor is adjusted to reach the target voltage.

[0008] Based on the above basic idea, the first aspect of the present invention provides an LED lighting circuit, comprising: a current regulator, suitable for providing a regulated current; an LED string, comprising at least two LED units connected in series to receive the regulated current; a switch, connected in parallel with one of the at least two LED units, the switch being suitable for being controlled to be closed to bypass the regulated current from one LED unit, or being controlled to be open to allow the regulated current to enter one LED unit; an output capacitor, connected in parallel with the LED string; and a control unit, coupled to the switch and suitable for operating the switch to be closed or open; it is characterized in that the control circuit is also suitable for operating the switch in a current regulation mode to conduct a current that has a certain deviation from the regulated current, so as to adjust the voltage on the output capacitor before operating the switch to be closed or open.

[0009] Reusing the shunt switch to regulate the voltage on the output capacitor alleviates the need for a dedicated circuit to discharge the output capacitor in the above-mentioned prior art and reduces the complexity / cost of the LED lighting circuit. In addition, the shunt switch conducts current to the remaining LED units, so the remaining LED units help consume the energy in the output capacitor to regulate the voltage, thereby wasting less energy and improving efficiency compared to the above-mentioned prior art.

[0010] In another embodiment, the switch is a semiconductor transistor, and the control circuit is suitable for operating the switch in a current regulation mode in an active mode to conduct a current that has a certain deviation from the regulated current, operating the switch in a saturation mode to be closed, and operating the switch in a cut-off mode to be open.

[0011] Semiconductor transistors are common and low-cost components for implementing the three modes. In addition, it is also simple and low-cost to implement a control circuit for driving the semiconductor transistor in the three modes. Therefore, this embodiment has the advantage of low cost.

[0012] In another embodiment, the control circuit is suitable for changing the voltage of the output capacitor from the original effective forward voltage of the LED string before the switch is operated to the target effective forward voltage of the LED string, and then operating the switch to close or open.

[0013] In this embodiment, the voltage of the output capacitor is adjusted to match the new effective forward voltage of the LED string driven by the output capacitor when the switch is closed or opened. Voltage imbalance is alleviated because the voltage across the output capacitor gradually changes to the voltage of the LED string after the switch changes its state, and it prevents a surge or drop in current. Here, if the operation of the switch changes from closed to open or vice versa, the target effective forward voltage results in a new sum of the forward voltages of the (multiple) LED units to be driven by the current, excluding the LED units to be shunted by the switch.

[0014] Preferably, a voltage sensing circuit is provided to sense the voltage on the output capacitor, and a comparison circuit is provided to compare the voltage on the output capacitor with a pre-stored value of the target effective forward voltage. If the difference is less than the threshold, i.e., the voltage on the output capacitor has been regulated to be substantially the same as the future forward voltage, the control circuit operates the switch to exit the active mode to the saturated conduction mode or the cut-off mode, and continue the normal shunt / non-shunt function.

[0015] In a specific embodiment, in order to balance the capacitor voltage in a non-shunt state and the LED string voltage in a shunt state, the control circuit is suitable for operating the switch to conduct a current greater than the regulated current, thereby discharging the output capacitor so as to reduce the voltage on the output capacitor before operating the switch to close, preferably to the forward voltage of the LED unit connected in series with the switch.

[0016] In this embodiment, since the current through the switch is greater than the current from the current regulator, the output capacitor must discharge to provide the differential current, and in turn the voltage on the output capacitor decreases. This embodiment provides an efficient way to reduce the voltage and match it to the forward voltage of the LED string in the shunt state.

[0017] In another specific embodiment, in order to balance the capacitor voltage in the shunt state and the LED string voltage in the non-shunt state, the control circuit is suitable for operating the switch to conduct a current less than the regulated current, thereby charging the output capacitor so as to increase the voltage on the output capacitor before operating the switch to be opened, preferably to the forward voltage of at least two LED units.

[0018] In this embodiment, since the current through the switch is less than the current from the current regulator, the differential current flows into the output capacitor and charges the output capacitor, and in turn the voltage on the output capacitor increases. This embodiment provides an effective way to increase the capacitor voltage and match the voltage with the forward voltage of the two LED units in the non-shunting state.

[0019] In a specific implementation, the certain deviation is 5% to 30% of the magnitude of the regulated current.

[0020] In this implementation, a difference of at least 5% timely adjusts the voltage on the output capacitor, and a difference of at most 30% prevents human-visible flicker on the LED units that are still operating. This range can achieve a balance between fast response and low flicker.

[0021] In another embodiment, the LED lighting circuit further comprises an interface adapted to receive a light setting command, and the control circuit is adapted to operate the switch according to the light setting command.

[0022] In a specific embodiment, the at least two LED units have different lighting functions, and the light setting command is adapted to select one or two of the at least two LED units to operate.

[0023] In another specific embodiment, the LED unit connected in parallel with the switch is used for lighting, and the LED unit connected in series with the switch is used for generating ambient light.

[0024] These embodiments apply the present invention to scene / function switchable lighting so that flickering during lighting scene / function switching can be avoided.

[0025] In a second aspect, an LED lamp is provided, comprising the LED lighting circuit according to the above aspects and embodiments.

[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 effected, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0028] Figure 1 An LED lighting circuit is shown having two LED units and a shunt switch connected in parallel with one of the LED units;

[0029] Figure 2 shows the LED current waveform when the shunt switch is closed;

[0030] Figure 3 The LED current waveform when the shunt switch is turned off is shown;

[0031] Figure 4 An LED lighting circuit according to aspects of the present application is shown;

[0032] Figure 5a shows that the shunt switch is closed to shunt an LED unit Figure 4 Equivalent circuit of LED lighting circuit;

[0033] Figure 5b shows the shunt switch closed when Figure 4 Equivalent circuit of LED lighting circuit;

[0034] Figure 6 Shows Figure 5a and Figure 5b LED current waveform;

[0035] Figure 7a shows that the shunt switch will be disconnected to not shunt an LED unit, Figure 4 The equivalent circuit of the LED lighting circuit in;

[0036] Figure 7b shows when the shunt switch has been opened Figure 4 Equivalent circuit of LED lighting circuit;

[0037] Figure 8 Shows Figure 7a and Figure 7b LED current waveform; and

[0038] Fig. 9 Shows Figure 4 The implementation method of the LED lighting circuit in. DETAILED DESCRIPTION

[0039] The present invention will be described with reference to the accompanying drawings.

[0040] It should be understood that the detailed description and specific examples are intended to be illustrative only while indicating exemplary embodiments of the apparatus, system and method, and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the apparatus, system and method of the present invention will become better understood through the following description, the appended claims and the accompanying drawings. It should be understood that these figures are merely schematic and not drawn to scale. It should also be understood that in these figures, the same reference numerals are used to indicate the same or similar components.

[0041] like Figure 4 As shown, the first aspect of the present invention provides an LED lighting circuit, comprising: a current regulator I1, suitable for providing a regulated current I; an LED string, comprising at least two LED units D1 and D3 connected in series, for receiving the regulated current I; a switch S1, connected in parallel with one LED unit D1 of the at least two LED units, the switch S1 being suitable for being controlled to be closed to bypass the regulated current I from one LED unit D1, or being controlled to be open to allow the regulated current I to enter one LED unit D1; an output capacitor C1, connected in parallel with the LED string; and a control unit (not shown), coupled to the switch S1 and suitable for operating the switch S1 to be open or closed; it is characterized in that the control circuit is also suitable for operating the switch S1 in a current regulation mode, in other words, as a current regulator / current source I2, to conduct a current I' having a certain deviation from the regulated current I, so as to adjust the voltage on the output capacitor C1 before operating the switch S1 to be closed or open.

[0042] More specifically, in the transition state between not shunting and shunting one LED unit, the control circuit operates the switch S1 to obtain the current I' so as to change the voltage of the output capacitor C1 from the original effective forward voltage of the LED string before the switch is operated to the target effective forward voltage of the LED string when the switch has been operated, and then the control circuit operates the switch S1 to shunt or not shunt the LED unit D1. Therefore, when the shunt switch S1 is operated, the capacitor voltage has been adjusted to be close to the effective LED string voltage, and when the shunt switch connects the output capacitor to the LED unit in the target state, there is less flicker in the LED current.

[0043] Now, the description will be Figure 7a , Figure 5a , Figure 5b and Figure 6 To explain how the embodiment works in the transition from non-dividing to dividing.

[0044] Assume that the switch S1 is open in order not to shunt the LED unit D1 at the beginning. The current regulator I1 outputs the desired current I. The capacitor C1 has been charged to the effective forward voltage of the LED string, that is, the sum of the forward voltages of the LED unit D1 and the LED unit D3. All the current I flows through the LED unit D1 and the LED unit D3. Figure 7b The diagram illustrates this situation.

[0045] The light setting command is sent to the LED lighting circuit to turn off the LED unit D1, preferably via an interface of the LED lighting circuit. The control circuit operates the switch S1 in active mode / current regulation mode and makes the switch S1 a current regulator I2 to obtain a current I' greater than the current I. This can be obtained from Figure 6 The current I' can be seen in the small rising portion 62 of the curve 60 of the current of the LED unit D3 in FIG. The current I' can be 1.05 to 1.3 times the current I. The embodiment uses 1.1 as an example. Figure 5a As shown, the differential current of the switch current 1.1*I and the output current I from the current regulator I1 is 0.1*I, and the output capacitor must provide this differential current. For ΔU=ΔQ / C, where ΔU is the voltage change on the capacitor, C is the capacitance of the capacitor, and ΔQ is the charge change on the capacitor, the voltage on the capacitor C1 will drop by 0.1*I*t / C, where t is the discharge time for the switch to obtain the 1.1*I current. Figure 6 Curve 64 in shows the voltage across capacitor C1 and the downslope 66 shows the voltage drop due to the discharge of switch S1.

[0046] In the above embodiment, with a 0.1*I current released from the capacitor, the capacitor can be discharged to a sufficiently low voltage in only about 100ms. Moreover, the slight increase in the current of the LED unit D3 is only 10% and does not cause uncomfortable flickering to the user. Please note that this parameter is only an example and is not the only applicable parameter, and those skilled in the art can design different parameters to achieve a good balance between low flicker and fast voltage regulation.

[0047] When the capacitor voltage drops to a value close to the forward voltage of the LED unit D3, the control unit can operate the switch S1 to enter the saturation mode, and the conduction current I' is equal to I, as shown in FIG. Figure 5b shown.

[0048] Now, the description will be Figure 5b , Figure 7a , Figure 7b and Figure 8Let's explain how the embodiment works in the transition from shunting to non-shunting. Assume that in order to shun the LED unit D1 at the beginning, the switch S1 is closed. The current regulator I1 outputs the desired current I. The capacitor C1 has been charged to the effective forward voltage of the LED string, that is, the forward voltage of only the LED unit D3. All the current I flows through the LED unit D3. This is consistent with Figure 5b The diagram is very similar.

[0049] The light setting command is sent to the LED lighting circuit to turn off the LED unit D1. The control circuit operates the switch S1 in active mode and makes it a current regulator I2 to obtain a current I' that is less than the current I, such as Figure 8 The small descending portion 82 of the curve 80 of the current of the LED unit D3 in FIG. The current I' may be 0.7 to 0.95 times the current I. The embodiment uses 0.9 as an example. Figure 7a As shown, the differential current between the switch current 0.9*I and the output current I from the current regulator I1 is 0.1*I, and this differential current must flow into the output capacitor C1 and charge it. For ΔU=ΔQ / C, where ΔU is the voltage change on the capacitor, C is the capacitance of the capacitor, and ΔQ is the charge change on the capacitor, the voltage on the capacitor C1 will increase by 0.1*I*t / C, where t is the time the switch conducts the 0.9*I current. Figure 8 Curve 84 in shows the voltage across capacitor C1 and the upslope 86 shows the voltage increase due to charging.

[0050] In the above embodiment, with a current of 0.1*I into the capacitor C1, the capacitor C1 can be charged to a sufficient voltage in only about 100ms. Moreover, the slight drop in the current of the LED unit D3 is only 10% and does not cause uncomfortable flickering to the user. Please note that this parameter is not the only applicable parameter, and those skilled in the art can design different parameters to achieve a good balance between low flicker and fast voltage regulation.

[0051] When the capacitor voltage increases to a value close to the sum of the forward voltages of the LED units D1 and D3, the control circuit can operate the switch S1 to enter the cut-off mode. The conduction current I' is zero, the current regulator I1 only drives the LED units D1 and D3 connected in series, and the switch S1 can be effectively ignored, as shown in FIG. Figure 7b shown.

[0052] In one embodiment, in order to monitor the voltage on the output capacitor C1 and control the switch S1 accordingly, a voltage sensing circuit is provided to sense the voltage on the output capacitor, and a comparison circuit is provided to compare the voltage on the output capacitor with a target value (i.e., the sum of the forward voltage of the LED unit D3 in the case of shunting or the forward voltage of the LED unit D1 in the case of non-shunting). If the difference is less than the threshold, meaning that the voltage on the output capacitor C1 has been adjusted to be substantially close to the forward voltage in the new state, the control circuit can control the switch to change from the active mode to the closed mode for normal shunting function or the cut-off mode for non-shunting function.

[0053] The switch S1 is preferably a transistor, where the closed / saturated conduction mode means that the transistor does not limit the current through it and only conducts any current provided by the upstream power supply. The cut-off mode means that the transistor is open and does not conduct any current. The active mode means that the current through the transistor is controlled by the signal applied to the base / gate in a linear relationship, and the active mode can also be regarded as a linear mode.

[0054] The transistor is preferably a MOSFET transistor. Controlling the MOSFET in active mode and in closed (saturated conduction) mode and cut-off mode can be achieved by controlling the gate voltage of the MOSFET. Fig. 9 Give an example. The current source consists of M1, R1 and C2. The current through R1 and M1 is adjusted by the voltage across C1. The level shifter consists of R2, R3, C3, D2, R4 and M2. The C2 voltage is controlled by the PWM duty. When the PWM duty is 0 (M2 is always open), the C2 voltage is zero. Moreover, the PWM duty is 1 (M1 is always closed), and the C2 voltage is clamped by D2 (Vd2). Moreover, the PWM duty is between 0 and 1, and the C2 voltage is also correspondingly between 0 and Vd2. For the current source, there is a threshold of PMOS (Vpmos). When the C2 voltage is lower than Vpmos, the PMOS operates in cutoff mode. No current is bypassed by the current source. When the C2 voltage is higher than Vpmos and the voltage of D1 is higher than the C2 voltage, the PMOS operates in adjustable resistance mode / active mode. The D1 current is bypassed by the current source, and the current is set by the PWM duty. When the voltage of C2 is higher than Vpmos and the voltage of D1 is lower than the voltage of C2, the PMOS operates in saturation mode. D1 is short-circuited by the PMOS.

[0055] In another example, the switch S1 can also be implemented by a BJT transistor. Controlling the BJT transistor in the active mode and in the closed / saturated conduction mode and the open / cutoff mode can be achieved by controlling the base current of the BJT transistor. For those skilled in the art, circuits designed to control the base current of the BJT transistor to achieve the three modes are well known, and the description will not give additional details.

[0056] In an implementation of scene-switchable LED lighting, the at least two LED units have different lighting functions, the LED lighting circuit also includes an interface suitable for receiving a light setting command, and the control circuit is suitable for operating the switch according to the light setting command to select one or two LED units of the at least two LED units to operate, thereby activating different operating scenes of the LED lighting.

[0057] Preferably, in a large luminaire, the LED unit D1 connected in parallel with the switch S1 is used for lighting and is placed in the center of the luminaire, and the LED unit D3 connected in series with the switch S1 is used for generating ambient light and is placed at the edge of the luminaire. Thus, the lighting function can be selectively activated and disabled, while the ambient lighting is always on. Moreover, by using the above-described embodiments of the present invention, visible flicker in the ambient lighting during scene switching can be avoided.

[0058] In the above embodiment, LED unit D1 has only one shunt switch. This should not limit the scope of the present application. LED unit D1 and LED unit D3 may each have two shunt switches, wherein each of the two shunt switches can be operated as described above to adjust the capacitor voltage.

[0059] The LED unit D1 and the LED unit D3 are only intended to distinguish between LEDs controlled (shunted) by the switch S1 and LEDs not controlled (shunted) by the switch S1. Each of the LED unit D1 and the LED unit D3 may include one or more LED chips.

[0060] By studying the drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments while practicing the claimed invention. 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.

[0061] 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.

[0062] If the term "suitable for" is used in the claims or the specification, it is noted that the term "suitable for" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or the specification, it is noted that the term "arrangement" is intended to be equivalent to the term "system" and vice versa.

[0063] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An LED lighting circuit, comprising: a current regulator (I1) adapted to provide a regulated current (I); an LED string comprising at least two LED units (D1, D3) connected in series, wherein the LED string is adapted to receive the regulated current (I); a switch (S1) connected in parallel with one LED unit (D1) of the at least two LED units (D1, D3), wherein the switch (S1) is adapted to be controlled to be closed to bypass the regulated current (I1) from leaving the one LED unit (D1), or to be controlled to be open to allow the regulated current (I1) to enter the one LED unit (D1); an output capacitor (C1) connected in parallel with the LED string; as well as a control circuit coupled to the switch (S1) and adapted to operate the switch (S1) to be closed or open; Features The control circuit is further adapted to operate the switch (D1) in a current regulation mode to conduct a current (I') that is deviated from the regulated current (I) so as to adjust the voltage across the output capacitor (C1) before operating the switch (S1) to close or open.

2. The LED lighting circuit according to claim 1, wherein the switch is a semiconductor transistor, and The control circuit is suitable for: operating the switch (S1) in the current regulation mode in the active mode to conduct the current (I') having the certain deviation from the regulated current (I), operating the switch (S1) closed in saturation mode, and In the cut-off mode, the switch (S1) is operated to be open.

3. The LED lighting circuit according to claim 1, wherein the control circuit is adapted to: The voltage of the output capacitor (C1) is changed from the original effective forward voltage of the LED string before the switch is operated to the target effective forward voltage of the LED string when the switch is set to be closed or open, and then The switch (S1) is operated to be closed or opened.

4. The LED lighting circuit according to claim 1, wherein the control circuit is adapted to operate the switch (S1) to conduct the current (I') greater than the regulated current (I), whereby the output capacitor (C1) is discharged so as to reduce the voltage across the output capacitor (C1) to a forward voltage of an LED unit (D3) connected in series with the switch (S1) before operating the switch (S1) to close.

5. The LED lighting circuit according to claim 1, wherein the control circuit is adapted to operate the switch (S1) to conduct the current (I') less than the regulated current (I), whereby the output capacitor (C1) is charged so as to increase the voltage on the output capacitor (C1) to the forward voltage of the at least two LED units (D1, D3) before operating the switch (S1) to be opened.

6. The LED lighting circuit according to claim 4 or 5, wherein the certain deviation is 5% to 30% of the amplitude of the regulated current (I).

7. The LED lighting circuit according to claim 1, further comprising: An interface is provided, the interface being adapted to receive a light setting command, and the control circuit being adapted to operate the switch (S1) according to the light setting command.

8. The LED lighting circuit according to claim 7, wherein the at least two LED units (D1, D3) have different lighting functions, and the light setting command is suitable for selecting one or two of the at least two LED units (D1, D3) to operate.

9. The LED lighting circuit according to claim 8, wherein the LED unit (D1) connected in parallel with the switch (S1) is used for lighting, and the LED unit (D3) connected in series with the switch (S1) is used for generating ambient light.

10. An LED lamp, comprising the LED lighting circuit according to any one of claims 1 to 9.

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