LED driver and LED illumination system

Abstract

The present invention provides an LED driver and an LED illumination system. The LED driver is used for driving an LED light source, and comprises a DC-DC converter and a stroboscopic circuit. The stroboscopic circuit is configured to generate a low frequency modulation signal. The DC-DC converter is coupled to the stroboscopic circuit and used for providing adjustable working current for the LED light source on the basis of a DC signal and the low frequency modulation signal, wherein the working current comprises a DC signal and a low-frequency AC signal that respectively correspond to the DC signal and the low frequency modulation signal. The frequency of the low-frequency AC signal is between 25 Hz and 100 Hz, and the current ripple percentage of the difference between the maximum value and the minimum value of the working current to the sum of the maximum value and the minimum value is smaller than 8%.

Description

LED driver and LED lighting system Technical Field

[0001] This case relates to an LED (light-emitting diode) driver and an LED lighting system, and more particularly, to an LED driver and an LED lighting system that enable an LED light source to strobe. Background Art

[0002] Many studies investigating the prevention or treatment of Alzheimer's disease have suggested that irradiating patients with light that flickers at a gamma frequency (hereinafter referred to as gamma stroboscopic light) can improve or delay symptoms. The gamma frequency range is between 25Hz and 100Hz. Currently, light therapy using light that flickers at a frequency of 40Hz is the primary research and application direction. During light therapy, patients can notice the flickering light.

[0003] [Corrected 26.06.2024 in accordance with Rule 26] Figure 1 is a schematic diagram of a conventional LED driver. As shown in Figure 1, the LED driver receives power from the mains and supplies power to the LED light source accordingly. Mains power specifications vary by region. For example, Taiwan Province of China uses 110 / 220V AC, 60Hz; Japan uses 100 / 200 / 242V AC, 50 / 60Hz; Europe uses 220 / 230 / 240V AC, 50Hz; and the United States uses 120 / 277V AC, 60Hz.

[0004] Figure 2 illustrates the output current Iout of the LED driver in Figure 1. In general lighting applications, an LED driver provides DC power to an LED light source. The brightness of the LED light source is proportional to the current flowing through it. Therefore, by controlling the current flowing through the LED light source, the LED driver can adjust the brightness of the LED light source, thereby achieving dimming.

[0005] Since the human eye is more sensitive to light flickering with a frequency below 60Hz, when patients are irradiated with Gamma stroboscopic light, some patients may feel uncomfortable and unable to receive sufficient exposure time, resulting in poor treatment effect.

[0006] Summary of the Invention

[0007] The purpose of this case is to provide an LED driver and an LED lighting system to solve the aforementioned technical problems and reduce user discomfort.

[0008] To achieve the above objectives, the present invention provides an LED driver for driving an LED light source, comprising a DC-DC converter and a strobe circuit. The strobe circuit is configured to generate a low-frequency modulation signal. The DC-DC converter is coupled to the strobe circuit to provide an adjustable operating current to the LED light source based on the DC signal and the low-frequency modulation signal. The operating current comprises a DC current signal and a low-frequency AC current signal, corresponding to the DC signal and the low-frequency modulation signal, respectively. The frequency of the low-frequency AC current signal is between 25 Hz and 100 Hz, and the current ripple percentage (the difference between the maximum and minimum values ​​of the operating current and the sum of the maximum and minimum values) is less than 8%.

[0009] To achieve the above objectives, the present invention further provides an LED lighting system comprising an LED light source and an LED driver. The LED driver is used to drive the LED light source and includes a DC-DC converter and a strobe circuit. The strobe circuit is configured to generate a low-frequency modulation signal. The DC-DC converter is coupled to the strobe circuit to provide an adjustable operating current to the LED light source based on the DC signal and the low-frequency modulation signal, wherein the operating current includes a DC current signal and a low-frequency AC current signal, corresponding to the DC signal and the low-frequency modulation signal, respectively. The frequency of the low-frequency AC current signal is between 25 Hz and 100 Hz, and the current ripple percentage (the difference between the maximum and minimum values ​​of the operating current and the sum of the maximum and minimum values) is less than 8%.

[0010] The present invention prevents the human eye from perceiving light flicker by limiting the flicker percentage of the LED light source. Therefore, using gamma stroboscopic light therapy is less likely to cause discomfort to the patient and can provide a sufficient duration of illumination to achieve the therapeutic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG1 is a schematic diagram of a conventional LED driver;

[0012] FIG2 illustrates an output current of the LED driver of FIG1 ;

[0013] FIG3 is a schematic diagram of the structure of the LED driver according to the first embodiment of the present invention;

[0014] FIG4 illustrates an example of the operating current provided to the LED light source by the LED driver in FIG3 ;

[0015] FIG5 illustrates a brightness variation waveform of the LED light source driven by the LED driver in FIG3 ;

[0016] FIG6 illustrates an embodiment of the stroboscopic circuit of the present invention;

[0017] FIG7 illustrates an embodiment of the timing circuit of FIG6;

[0018] FIG8 is a schematic diagram of the structure of an LED driver according to a second embodiment of the present invention;

[0019] FIG9 illustrates a variation of the LED driver of FIG8 ;

[0020] FIG10 is a schematic diagram of the structure of an LED driver according to a third embodiment of the present invention;

[0021] FIG11 is a schematic diagram of the structure of an LED lighting system according to an embodiment of the present invention;

[0022] FIG12 illustrates a modification of the LED lighting system of FIG11 .

[0023] Explanation of Figure Numbers

[0024] Iout: output current

[0025] 1: LED driver

[0026] Vac: AC input signal

[0027] Vdc: direct current signal

[0028] Io: operating current

[0029] 11: DC-DC converter

[0030] 12: Lightning Road

[0031] 13: EMI filter

[0032] 14: Rectifier

[0033] Mod: low frequency modulation signal

[0034] Fg: strobe frequency

[0035] Idc: DC current signal

[0036] Ig: low-frequency AC current signal

[0037] ton: the time the operating current is at a higher level

[0038] toff: the time the operating current is at a lower level Iomax: the maximum value of the operating current

[0039] Iomin: minimum operating current

[0040] Lmax: Maximum brightness

[0041] Lmin: minimum brightness

[0042] PF: Flicker Percentage

[0043] CRF: Current ripple percentage

[0044] 121: Modulation signal generation circuit

[0045] CS: Current sensing terminal

[0046] R1, R2: resistors

[0047] S1: switch

[0048] 122: Timing Circuit

[0049] CON: switch control signal

[0050] Vcs: voltage value

[0051] Rcs: resistance value

[0052] Ics: current value

[0053] IR1, IR2: current

[0054] V1: voltage source

[0055] R3, R4, R5, R6, R7: resistors

[0056] C1, C2: capacitors

[0057] D1, D2, D3: diodes

[0058] Q1, Q2: switch

[0059] 1a: LED Driver

[0060] 15: Control circuit

[0061] 16: Dimming circuit

[0062] Idim: dimming signal

[0063] 1b: LED driver

[0064] 1c: LED Driver

[0065] 17: Multi-stage control switch DETAILED DESCRIPTION

[0066] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention can be modified in various ways without departing from the scope of this invention, and the descriptions and illustrations herein are intended to be illustrative in nature and not to limit this invention.

[0067] Figure 3 is a schematic diagram of the architecture of an LED driver according to a first embodiment of the present invention. As shown in Figure 3 , LED driver 1 receives an AC input signal Vac from a power supply and correspondingly generates an operating current Io to drive an LED light source. In the embodiment of Figure 3 , LED driver 1 includes a DC-DC converter (DC-to-DC power converter) 11, a strobe circuit 12, an EMI filter (electromagnetic interference filter) 13, and a rectifier 14. To simplify the diagram and facilitate illustration, other components of LED driver 1 are not shown. EMI filter 13 is coupled to the power supply to reduce or eliminate electromagnetic interference from the AC input signal Vac. Rectifier 14 is coupled to EMI filter 13 to rectify the filtered AC input signal Vac into a DC signal Vdc, which is then provided to DC-DC converter 11. Rectifier 14 can be a bridge rectifier or other suitable rectifier circuit.

[0068] The DC-DC converter 11 can employ a suitable power conversion circuit, such as a buck converter, a boost converter, a buck-boost converter, or a flyback converter. The DC-DC converter 11 converts the DC signal Vdc into the DC voltage required by the LED light source and provides an adjustable operating current Io to the LED light source, thereby adjusting the brightness of the LED light source. The strobe circuit 12 is electrically connected to the DC-DC converter 11 and configured to generate a low-frequency modulation signal Mod. The strobe circuit 12 can employ an astable multivibrator circuit or other suitable analog and / or digital circuit to generate a signal of a desired frequency, such as a sine wave signal, a harmonic signal, a pulse signal, or other suitable format, as the low-frequency modulation signal Mod.

[0069] The DC-DC converter 11 is capable of generating the required operating current Io based on the DC signal Vdc and the low-frequency modulation signal Mod, so that the brightness of the LED light source can be varied at a strobe frequency Fg, which is set to be within the gamma frequency band between 25 Hz and 100 Hz. In one embodiment, the strobe frequency Fg is between 30 Hz and 50 Hz. In another embodiment, the strobe frequency Fg is 40 Hz. In one embodiment, the operating current Io provided by the DC-DC converter 11 based on the DC signal Vdc and the low-frequency modulation signal Mod includes a DC current signal Idc and a low-frequency AC current signal Ig. The frequency of the low-frequency AC current signal Ig is within the gamma frequency band between 25 Hz and 100 Hz. In one embodiment, the frequency of the low-frequency AC current signal Ig is between 30 Hz and 50 Hz. In another embodiment, the frequency of the low-frequency AC current signal Ig is 40 Hz. The DC-DC converter 11 sets the current value of the operating current Io to vary between Idc and Idc+Ig at a strobe frequency Fg, so that the brightness of the LED light source can vary correspondingly at the strobe frequency Fg.

[0070] Furthermore, the components of the LED driver 1 may be increased or decreased based on different design considerations. For example, in FIG3 , the LED driver 1 includes an EMI filter 13 and a rectifier 14. In another embodiment, when the LED driver is coupled to a DC input power source, the LED driver may not include the EMI filter 13 and the rectifier 14.

[0071] FIG4 illustrates an example of the operating current Io provided to the LED light source by the LED driver 1 in FIG3 . As shown in FIG4 , the current level of the operating current Io varies at a strobe frequency Fg. Within a cycle (1 / Fg), the time the operating current Io is at a high level is represented by ton, and the time the operating current Io is at a low level is represented by toff. The duty cycle of the time the operating current Io is at a high level (hereinafter referred to as the strobe duty cycle) is ton / (ton+toff). Because the frequency of the level variation of the operating current Io is affected by the low-frequency modulation signal Mod, in one embodiment, the duty cycle of the low-frequency modulation signal Mod generated by the strobe circuit 12 can be set to ton / (ton+toff), so that the corresponding strobe duty cycle of the operating current Io generated by the DC-DC converter 11 is ton / (ton+toff). In some embodiments, the strobe duty cycle of the operating current Io generated by the DC-DC converter 11 is less than 50%. In some embodiments, the strobe duty cycle of the operating current Io generated by the DC-DC converter 11 is less than 30%. In some other embodiments, the DC-DC converter 11 generates a strobe duty cycle of the operating current Io that is greater than 10% and less than 50%. In still other embodiments, the DC-DC converter 11 generates a strobe duty cycle of the operating current Io that is between 10% and 30%.

[0072] FIG5 illustrates the brightness variation waveform of the LED light source driven by the LED driver 1 in FIG3. The flicker percentage of the LED light source can be calculated according to equation (1). PF = (Lmax-Lmin) / (Lmax+Lmin)*100% (1)

[0073] Where PF is the flicker percentage, Lmax is the maximum brightness, and Lmin is the minimum brightness. Since the brightness of the LED light source is positively correlated with the operating current Io, a similar formula can be used to define the current ripple percentage CRF, as shown in equation (2). CRF = (Iomax - Iomin) / (Iomax + Iomin) * 100% = (Idc + Ig - Idc) / (Idc + Ig + Idc) * 100% = Ig / (2 * Idc + Ig) * 100% (2)

[0074] Where Iomax is the maximum value of the operating current Io, and Iomin is the minimum value of the operating current Io. The flicker percentage PF of the LED light source is estimated based on the current ripple percentage CRF. For example, the flicker percentage PF of the LED light source can be set equal to the current ripple percentage CRF. This means that by setting the current ripple percentage CRF, the flicker percentage PF of the LED light source can be controlled to be below a desired value. In another embodiment, a function can be set that equals the flicker percentage PF of the LED light source to the current ripple percentage CRF, for example: PF = f(CRF) = A*CRF + B, where A and B are appropriate values. This means that by setting the current ripple percentage CRF, the flicker percentage PF of the LED light source can be controlled to be below a desired value.

[0075] Although each user has different sensitivities to light flicker, to prevent the human eye from perceiving flicker, the LED light source's flicker percentage (PF) must be limited to an appropriate value. In one embodiment, the LED light source's flicker percentage (PF) is set to less than 10%. In another embodiment, if the flicker rate is 40 Hz, according to IEEE standard 1789, the LED light source's flicker percentage (PF) can be set to less than 1% to prevent the human eye from perceiving flicker. Assuming the LED light source's flicker percentage (PF) is less than 1%, by setting the LED light source's flicker percentage (PF) equal to the current ripple percentage (CRF), the formula for the current ripple percentage (CRF) indicates that the maximum operating current (Iomax = Idc + Ig) should be less than approximately 1.02 times the minimum operating current (Iomin = Idc). In other words, the maximum current value of the low-frequency AC current signal (Ig) should be less than approximately 0.02 times the current value of the DC current signal (Idc). In another embodiment, if the flicker rate is 100 Hz, according to the recommendations of IEEE standard 1789, the flicker percentage PF of the LED light source can be set to less than 8%, and the flicker percentage PF of the LED light source can be set equal to the current ripple percentage CRF. Based on the aforementioned current ripple percentage CRF formula, it can be deduced that the maximum value of the operating current Io (Iomax = Idc + Ig) should be less than approximately 1.174 times the minimum value of the operating current Io (Iomax = Idc). In other words, the maximum current value of the low-frequency AC current signal Ig should be less than the current value of the DC current signal Idc, which is approximately 0.174. As a result, the operating current Io generated by the LED driver 1 of this embodiment varies between Iomax and Iomin at a strobe frequency Fg. The illumination light produced by the driven LED light source exhibits, in addition to the relatively stable brightness generated by the DC current signal Idc, brightness variations caused by the low-frequency AC current signal Ig at a strobe frequency Fg. However, by setting the operating current Io generated by the LED driver 1 to a flicker percentage PF below a specific value, the brightness variations at this strobe frequency Fg are imperceptible to the human eye and would not cause discomfort. Therefore, the duration of the low-frequency light therapy achieved in this manner does not need to be limited, as is the case with conventional light therapy sessions. Furthermore, the gamma strobe of this embodiment can be applied to everyday lighting fixtures, providing 24-hour light therapy. In some embodiments, the maximum value of the operating current Io (Iomax=Idc+Ig) generated by the DC-DC converter 11 can be set to be less than approximately 1.105 times the minimum value of the operating current Io (Iomax=Idc), and the flicker percentage PF of the LED light source can be set equal to the current ripple percentage CRF, so that the flicker percentage PF of the LED light source is less than 5%.

[0076] The aforementioned formula indicates that the maximum current value of the low-frequency AC current signal Ig must be set to be less than a specific ratio of the current value of the DC current signal Idc in order to keep the LED light source's flicker percentage (PF) below a desired value. Therefore, even if variations in the current value of the DC current signal Idc cause corresponding variations in the brightness of the LED light source, the gamma stroboscopic effect provided by the low-frequency AC current signal Ig can keep the LED light source's flicker percentage (PF) below a desired value without causing user discomfort or perception. In some embodiments, the stroboscopic circuit 12 includes the modulation signal generating circuit 121 of FIG. 6 , which generates the desired low-frequency modulation signal Mod. This allows the DC-DC converter 11 to set the current value of the low-frequency AC current signal Ig to be less than a specific ratio of the current value of the DC current signal Idc based on the low-frequency modulation signal Mod. The modulation signal generating circuit 121 includes a current sensing terminal CS, a switch S1, and resistors R1 and R2. The resistor R1 and the switch S1 are connected in series between the current sensing terminal CS and a ground potential (or other suitable preset potential). The resistor R2 is coupled between the current sensing terminal CS and the ground potential and is connected in parallel with the resistor R1 and the switch S1.

[0077] In the embodiment of FIG6 , the strobe circuit 12 includes a timing circuit 122. The timing circuit 122 can be implemented as a suitable analog and / or digital circuit (e.g., an LM555 circuit) to provide a switch control signal CON to the control terminal of the switch S1, thereby setting the conduction state of the switch S1. The switch control signal CON generated by the timing circuit 122 can be configured to have a pulse signal with a frequency within the gamma band (e.g., 40 Hz) and a duty cycle less than 50% (e.g., 10%) to generate the desired low-frequency modulation signal Mod. In one embodiment, when the voltage Vcs between the current sensing terminal CS and the ground potential is constant, when the timing circuit 122 sets the switch control signal CON to a high level, turning on the switch S1, the resistance Rcs between the current sensing terminal CS and the ground potential is equal to the resistance of the parallel combination of resistors R1 and R2, and the current Ics flowing through the current sensing terminal CS is Vcs / Rcs = Vcs / (R1 / / R2). When the timing circuit 122 sets the switch control signal CON to a low level, turning off the switch S1, the resistance Rcs between the current sensing terminal CS and the ground potential is equal to the resistance of resistor R2, and the current Ics flowing through the current sensing terminal CS is Vcs / Rcs = Vcs / R2. For example, assuming Vcs is set to 0.1V, R1 is set to 10Ω, and R2 is set to 1Ω, when the switch S1 is off, the current Ics flowing through the current sensing terminal CS is Vcs / R2 = 0.1A. When the switch S1 is turned on, the current value Ics flowing through the current sensing terminal CS is Vcs / (R1 / / R2)=0.11A, where the current I flowing through the resistor R1 is R1Vcs / R1 = 0.01A, the current flowing through resistor R2 is I R2 Vcs / R1=0.1A.

[0078] The DC-DC converter 11 is coupled to a current sensing terminal CS and adjusts the current value of the operating current Io according to the current value Ics flowing through the current sensing terminal CS. For example, when the switch S1 is off, the current value Ics = Vcs / R2, and the DC-DC converter 11 generates an operating current Io = Idc according to the current value Ics. When the switch S1 is on, the current value Ics = Vcs / (R1 / / R2), and the DC-DC converter 11 generates an operating current Io = Idc + Ig according to the current value Ics. In one embodiment, the DC-DC converter 11 can set the operating current Io to be proportional to the current value Ics. Therefore, by adjusting the frequency and duty cycle of the switch control signal CON generated by the timing circuit 122, the operating current Io and the strobe frequency Fg and strobe duty cycle of the LED light source can be adjusted accordingly.

[0079] Table 1 shows the current I flowing through the resistor R1. R1 , the current I flowing through resistor R2 R2 The DC-DC converter 11 can adjust the operating current Io provided according to the current value Ics, so the current I R1 and I R2 The DC-DC converter 11 can adjust the low-frequency AC current signal Ig and the DC current signal Idc in the working current Io. As shown in Table 1, when the current I R2 When the current I R1 Change in the same proportion, rather than by the same difference. For example, when the current I R2 When the current I R1 From 0.01 to 0.009, it is also reduced by 10%. Therefore, in this embodiment, regardless of the current I R2 What is the size of the current Ics (=I R2 +I R1 ) are the current values ​​Ics (=I R2 In other words, regardless of the magnitude of the DC current signal Idc in the operating current Io, the DC-DC converter 11 can correspondingly set the operating current Io when the switch S1 is conducting to be 110% of the operating current Io when the switch S1 is not conducting.

[0080] [Table 1]

[0081] As previously described, the operating current Io provided by the DC-DC converter 11 includes a DC current signal Idc and a low-frequency AC current signal Ig generated by the strobe circuit 12. When the DC current signal Idc in the operating current Io changes (for example, during dimming), the low-frequency AC current signal Ig in the operating current Io also changes at the same rate to prevent changes in the flicker percentage PF, which could cause the human eye to perceive flicker. Specifically, when the DC current signal Idc in the operating current Io increases or decreases at a specific rate, the low-frequency AC current signal Ig in the operating current Io also increases or decreases at the same rate. Therefore, regardless of the magnitude of the DC current signal Idc in the operating current Io (that is, regardless of the brightness of the LED light source), gamma strobe can be achieved while preventing the human eye from perceiving light flicker.

[0082] In another embodiment, the timing circuit 122 may be configured to generate a switch control signal CON to keep the switch S1 continuously turned on or turned off. In this case, the current flowing through the current sensing terminal CS will remain constant, and the operating current Io provided by the DC-DC converter 11 will remain constant, thereby disabling the gamma strobe function.

[0083] FIG7 illustrates an embodiment of the modulation signal generating circuit 121 and timing circuit 122 of FIG6 . In this embodiment, the timing circuit 122 comprises an astable multivibrator employing a totem pole topology. As shown in FIG7 , the timing circuit 122 comprises a voltage source V1, resistors R3, R4, R5, R6, and R7, capacitors C1 and C2, diodes D1, D2, and D3, and switches Q1 and Q2. The first ends of resistors R3, R4, R5, and R6 are electrically connected to the positive terminal of the voltage source V1. The two ends of capacitor C1 are electrically connected to the second ends of resistors R3 and R4, respectively. The anode of diode D1 is electrically connected to the second end of resistor R5. The first, second, and third ends of switch Q1 are electrically connected to the second end of resistor R3, the cathode of diode D1, and the negative terminal of voltage source V1, respectively. The two terminals of capacitor C2 are electrically connected to the second terminals of resistors R5 and R6, respectively. The anode of diode D2 is electrically connected to the second terminal of resistor R4. The first, second, and third terminals of switch Q2 are electrically connected to the second terminal of resistor R6, the cathode of diode D2, and the negative terminal of voltage source V1, respectively. The cathode of diode D3 is electrically connected to the second terminal of resistor R6, the anode of diode D3 is electrically connected to the first terminal of resistor R7 and modulation signal generating circuit 121 (switch S1), and the second terminal of resistor R7 is electrically connected to the negative terminal of voltage source V1. Resistors R4 and R5 serve as startup resistors for switches Q2 and Q1, respectively. In this embodiment, switches Q1 and Q2 are bipolar junction transistors, whose first, second, and third terminals are collector, base, and emitter, respectively. Switch S1 is a metal oxide semiconductor field effect transistor, whose drain, gate, and source are electrically connected to resistor R1, the anode of diode D3, and the negative terminal of voltage source V1, respectively.

[0084] In the circuit shown in Figure 7, when voltage source V1 provides a voltage (e.g., 5V), either switch Q1 or Q2 turns on. Specifically, if the voltage across capacitor C2 is charged to 0.7V, switch Q1 turns on and simultaneously provides a reverse voltage to turn off switch Q2, and the voltage across capacitor C1 is charged to 5V. Conversely, if the voltage across capacitor C1 is charged to 0.7V, switch Q2 turns on and simultaneously provides a reverse voltage to turn off switch Q1, and the voltage across capacitor C2 is charged to 5V. Thus, switches Q1 and Q2 alternately turn on and off, thereby providing an oscillation at a frequency in the gamma band (e.g., 40Hz). Furthermore, when switch Q2 turns on, the gate voltage of switch S1 discharges, turning switch S1 off. When switch Q2 is off, the voltage across resistors R6 and R7 establishes a gate voltage, turning switch S1 on. When the switch S1 is on, the resistance Rcs between the current sensing terminal CS and the ground potential is the resistance of the resistors R1 and R2 in parallel, and the current Ics flowing through the current sensing terminal CS is Vcs / Rcs=Vcs / (R1 / / R2); and when the switch S1 is not conducting, the resistance Rcs between the current sensing terminal CS and the ground potential is the resistance of the resistor R2, and the current Ics flowing through the current sensing terminal CS is Vcs / Rcs=Vcs / R2. For example, Vcs is set to 0.1V, R1 is set to 10Ω, and R2 is set to 1Ω. When the switch S1 is not conducting, the current Ics flowing through the current sensing terminal CS is Vcs / R2=0.1A. When the switch S1 is on, the current Ics flowing through the current sensing terminal CS is Vcs / (R1 / / R2)=0.11A, where the current I flowing through the resistor R1 is R1 Vcs / R1 = 0.01A, the current flowing through resistor R2 is I R2 Vcs / R1=0.1A.

[0085] The DC-DC converter 11 is coupled to the current sensing terminal CS and adjusts the current value of the operating current Io according to the current value Ics flowing through the current sensing terminal CS. For example, when the switch S1 is off, the current value Ics = Vcs / R2, and the DC-DC converter 11 generates the operating current Io = Idc according to the current value Ics. When the switch S1 is on, the current value Ics = Vcs / (R1 / / R2), and the DC-DC converter 11 generates the operating current Io = Idc + Ig according to the current value Ics. In one embodiment, the DC-DC converter 11 can set the operating current Io to be proportional to the current value Ics. Therefore, by setting the frequency and duty cycle of the timing circuit 122 to drive the switch S1 to operate, the operating current Io and the strobe frequency Fg and strobe duty cycle of the LED light source can be adjusted accordingly.

[0086] Possible implementations of the DC-DC converter 11 and the strobe circuit 12 of the present invention are not limited to those described above. Provided that the DC-DC converter 11 has a DC-DC conversion function and the strobe circuit 12 can cause the operating current provided by the DC-DC converter 11 to include a low-frequency pulse signal, an appropriate implementation method may be selected based on actual needs.

[0087] Figure 8 is a schematic diagram of the architecture of an LED driver according to a second embodiment of the present invention. In Figure 8 , components similar to those in the first embodiment shown in Figure 3 are denoted by the same reference numerals and are not further described here. Compared to the LED driver 1 of the first embodiment shown in Figure 3 , the LED driver 1a of the second embodiment shown in Figure 8 further includes a control circuit 15 and a dimming circuit 16 . The control circuit 15 receives a dimming control signal and controls the dimming circuit 16 accordingly to provide a dimming signal Idim to the DC-DC converter 11. The control circuit 15 can be implemented using a microcontroller or other suitable circuit. The dimming circuit 16 is electrically connected to the DC-DC converter 11. The DC-DC converter 11 adjusts the operating current Io supplied to the LED light source based on the dimming signal Idim, thereby adjusting the brightness of the LED light source. In one embodiment, the strobe circuit 12 may include a microcontroller unit, which utilizes the microcontroller unit to provide a PWM (pulse width modulation) dimming signal. In one embodiment, the strobe circuit 12 may also integrate the control circuit 15 or the dimming circuit 16, and employ a microcontroller unit to provide a combined dimming signal and a low-frequency modulation signal to the DC-DC converter 11. For example, the microcontroller unit of the strobe circuit 12 generates a 1.25kHz PWM dimming signal. In one cycle (e.g., 0.025 seconds, corresponding to a frequency of 40Hz), 90% of the PWM dimming signal has an 80% PWM duty cycle, while the remaining 10% of the PWM dimming signal has an 88% PWM duty cycle. The DC-DC converter 11 adjusts the maximum and minimum values ​​of the operating current Io based on the 90% and 10% PWM duty cycles, respectively. In this case, the strobe duty cycle of the LED light source is 10%, and the flicker percentage PF = (88-80) / (88+80)*100% to = 4.7%. Consequently, the LED light source can generate gamma strobe with a flicker percentage PF below 5%.

[0088] In the aforementioned embodiment, the strobe circuit 12 continuously generates a signal with a frequency in the gamma band, but the present invention is not limited thereto. In other embodiments, the strobe circuit 12 can also be controlled to enable or disable the function of generating a signal with a frequency in the gamma band. FIG9 illustrates a variation of the LED driver of FIG8 . As shown in FIG9 , in this LED driver 1b, a control circuit 15 is further electrically connected to the strobe circuit 12 to control the operation of the strobe circuit 12. Based on a received control signal (e.g., from a user or other circuit), the control circuit 15 controls the strobe circuit 12 to generate or stop generating a signal with a frequency in the gamma band (e.g., by setting the switch S1 in FIG6 or FIG7 to a continuously conductive or continuously non-conductive state using the switch control signal CON).

[0089] Figure 10 is a schematic diagram of the architecture of an LED driver according to a third embodiment of the present invention. In Figure 10 , components similar to those in the first embodiment shown in Figure 3 are denoted by the same reference numerals and are not further described here. Compared to the LED driver 1 of the first embodiment shown in Figure 3 , the LED driver 1c of the third embodiment shown in Figure 10 further includes a multi-level control switch 17 , electrically connected between the power supply and the EMI filter 13 , to provide a dimming function. The multi-level control switch 17 receives power and selectively switches to provide several different power levels, allowing the LED driver 1c to adjust the DC current signal Idc within the operating current Io accordingly. The strobe circuit 12 then generates a corresponding low-frequency AC current signal Ig, achieving both dimming and gamma strobe functions. The switching of the multi-level control switch 17 can be achieved, for example, but not limited to, via a mechanical switch. In some embodiments, the LED driver 1c can selectively operate in three different modes based on the switching of the multi-level control switch 17 . For example, when the multi-stage control switch 17 operates in the first mode, the LED driver 1c provides 100% output to the LED light source, so that the main light of the LED light source operates at full brightness; when the multi-stage control switch 17 operates in the second mode, the LED driver 1c provides 65% output to the LED light source, so that the main light of the LED light source operates at a lower brightness; when the multi-stage control switch 17 operates in the third mode, the LED light source is turned off.

[0090] As can be seen from the aforementioned embodiments, the LED driver of this embodiment can make the LED light source brighter for X% of the time within a cycle than for the remaining (100-X)% of the time. X% can be, for example, less than 50% or 30%, or between 10% and 30%. The low-frequency AC current signal of the operating current is between 30Hz and 50Hz (e.g., 40Hz), so that the LED driver correspondingly sets the LED light source to be brighter for X% of the time within a cycle.

[0091] Furthermore, the operating current generated by the LED driver during the brighter periods of the LED light source (i.e., during X% of a cycle) is less than Y% of the operating current generated during the dimming period of the LED light source (i.e., during (100-X)% of a cycle), thereby preventing the human eye from perceiving flickering while the LED light source performs gamma strobing. Y% is less than 120% (e.g., 110%), thereby reducing the flicker percentage (PF) to less than 5%.

[0092] In addition, the amplitude of the low-frequency AC current signal of the operating current during the period when the LED light source is brighter (i.e., X% of the time within a cycle) is proportional to the magnitude of the DC current signal of the operating current during the period when the LED light source is darker (i.e., (100-X)% of the time within a cycle). Therefore, regardless of the brightness of the LED light source, a certain flicker percentage PF is maintained to prevent the human eye from perceiving light flicker.

[0093] Furthermore, when using PWM dimming, the PWM signal duty cycle Z1 during the brighter LED light source period (i.e., X% of the time within a cycle) is less than the PWM signal duty cycle Z2 during the darker LED light source period (i.e., (100-X)% of the time within a cycle), by W%. This allows the LED light source to perform gamma strobing while preventing the human eye from perceiving flickering. W% is less than 120% (e.g., 110%), so that the flicker percentage PF (=(Z1-Z2) / (Z1+Z2)*100%) is less than 5%.

[0094] In one embodiment, the LED lighting system shown in FIG11 includes an LED driver 1 and an LED light source. The LED light source includes a plurality of LED light modules. A DC-DC converter 11 is coupled to all of the LED light modules of the LED light source, enabling the DC-DC converter 11 to drive all of the LED light modules to simultaneously provide both lighting and gamma strobe functions. In another embodiment, the LED lighting system shown in FIG12 includes an LED driver 1 and an LED light source. The LED light source includes a plurality of LED light modules. The DC-DC converter 11 is coupled to a portion of the LED light modules of the LED light source, enabling all of the LED light modules of the LED light source to provide lighting, and the portion of the LED light modules driven by the DC-DC converter 11 to simultaneously provide both lighting and gamma strobe functions. Therefore, the LED light source does not require dedicated LED light modules for gamma strobe functions or their placement, resulting in a more uniform lighting effect. Furthermore, since the LED light modules can simultaneously provide both lighting and gamma strobe functions, fewer LED light modules are required to achieve the same brightness, further enhancing environmental protection and energy conservation. 11 and 12 take the LED driver 1 shown in FIG. 3 as an example, but the present invention is not limited thereto. This embodiment is applicable to any LED driver of the present invention (eg, LED drivers 1a, 1b, and 1c in FIG. 8, 9, and 10).

[0095] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the embodiment described. The scope of the present invention is determined by the appended claims. Furthermore, the present invention is subject to various modifications as conceived by those skilled in the art, without departing from the scope of the appended claims.

Claims

1. An LED driver for driving an LED light source, comprising: a strobe circuit configured to generate a low frequency modulation signal; and A DC-DC converter, coupled to the flash circuit, for providing an adjustable working current to the LED light source according to the DC signal and the low-frequency modulation signal, wherein the working current comprises a DC current signal and a low-frequency AC current signal, corresponding to the DC signal and the low-frequency modulation signal, respectively; The frequency of the low-frequency AC current signal is between 25 Hz and 100 Hz, and the current ripple percentage of the difference between the maximum value and the minimum value of the working current and the sum of the maximum value and the minimum value is less than 8%.

2. The LED driver according to claim 1, wherein the strobe circuit comprises: A modulation signal generating circuit, comprising a current sensing terminal, a switch, a first resistor and a second resistor, wherein the first resistor and the switch are connected in series between the current sensing terminal and a ground potential, and the second resistor is coupled between the current sensing terminal and the ground potential and connected in parallel with the first resistor and the switch; as well as A timing circuit coupled to the modulation signal generating circuit and providing a switch control signal to the switch, wherein the switch control signal is used to set the conduction state of the switch so that the modulation signal generating circuit generates the low-frequency modulation signal; The DC-DC converter is coupled to the current sensing end, and adjusts the operating current accordingly according to the current value flowing through the current sensing end.

3. The LED driver according to claim 1 further comprises a control circuit and a dimming circuit, wherein the control circuit receives a dimming control signal and controls the dimming circuit to provide a dimming signal to the DC-DC converter, and the DC-DC converter adjusts the operating current according to the dimming signal. 4 . The LED driver according to claim 3 , wherein the control circuit is further coupled to the strobe circuit, and controls the strobe circuit to generate or stop generating the low-frequency modulation signal.

5. The LED driver according to claim 1, further comprising a multi-stage control switch electrically connected to the DC-DC converter, wherein the multi-stage control switch can be selectively switched to provide a plurality of different powers so that the LED driver can correspondingly adjust the DC current signal of the operating current.

6. The LED driver according to claim 1, wherein the strobe circuit comprises a microcontroller unit, the microcontroller unit provides a PWM (pulse width modulation) dimming signal to the DC-DC converter, the PWM dimming signal consists of a first part and a second part in one cycle, a first duty cycle of the PWM dimming signal in the first part is less than 120% of a second duty cycle in the second part, and the DC-DC converter adjusts the maximum value and the minimum value of the operating current according to the first duty cycle and the second duty cycle respectively. 7 . The LED driver according to claim 6 , wherein the first duty cycle of the PWM dimming signal in the first portion is less than 110% of the second duty cycle in the second portion. 8 . The LED driver according to claim 1 , wherein the maximum value of the operating current and the minimum value of the operating current are in a fixed ratio, and the fixed ratio is less than 120%. 9 . The LED driver according to claim 8 , wherein the fixed ratio is less than 110%.

10. The LED driver of claim 1, wherein the frequency of the low-frequency AC current signal is between 30 Hz and 50 Hz. 11 . The LED driver according to claim 10 , wherein the frequency of the low-frequency AC current signal is 40 Hz. 12 . The LED driver according to claim 1 , wherein the operating current is at the maximum value for less than 50% of the time in one cycle.

13. The LED driver according to claim 12, wherein the time proportion is less than 30%. The LED driver according to claim 13 , wherein the time proportion is greater than 10%.

15. The LED driver according to claim 1, wherein the current ripple percentage is less than 5%.

16. The LED driver according to claim 1, wherein the current ripple percentage is less than 1%.

17. An LED lighting system, comprising: LED light source; and An LED driver, used to drive the LED light source, comprises: A strobe circuit configured to generate a low frequency modulation signal; and A DC-DC converter, coupled to the strobe circuit and the LED light source, for providing an adjustable working current to the LED light source according to the DC signal and the low-frequency modulation signal, wherein the working current comprises a DC current signal and a low-frequency AC current signal, corresponding to the DC signal and the low-frequency modulation signal, respectively; in, The frequency of the low-frequency AC current signal is between 25 Hz and 100 Hz, and the current ripple percentage of the difference between the maximum value and the minimum value of the working current and the sum of the maximum value and the minimum value is less than 8%. 18 . The LED lighting system according to claim 17 , wherein the LED light source comprises a plurality of LED light emitting modules, and the DC-DC converter is coupled to the plurality of LED light emitting modules to provide the operating current to the plurality of LED light emitting modules.

19. The LED lighting system according to claim 17, wherein the LED light source comprises a plurality of LED light-emitting modules, and the DC-DC converter is coupled to a portion of the LED light-emitting modules to provide the operating current to the portion of the LED light-emitting modules.

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