LED driver and LED lighting system

Abstract

To provide an LED driver and an LED lighting system, capable of reducing the discomfort of users.SOLUTION: An LED driver includes a DC-DC converter 11 and a strobe circuit 12. The strobe circuit generates a low-frequency modulation signal. The DC-DC converter is connected to the strobe circuit and provides an adjustable operating current to an LED light source according to a DC electrical signal and the low-frequency modulation signal. The operating current includes a DC current signal corresponding to the electrical DC signal and a low-frequency AC current signal corresponding to the low-frequency modulation signal. A frequency of the low-frequency AC current signal is 25-100 Hz, and a current ripple factor, equaling a difference of a maximum value and a minimum value of the operating current divided by a sum of the maximum value and the minimum value, is less than 8%.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention 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 strobes an LED light source. [Background technology]

[0002] In many studies on the prevention or treatment of Alzheimer's Disease, it has been proposed that the symptoms of patients can be improved or delayed by irradiating them with light that flickers at a frequency in the gamma frequency band (hereinafter referred to as gamma strobe). The gamma frequency band is a frequency band between 25Hz and 100Hz. Currently, phototherapy is mainly performed using strobe light (flashing light) with a frequency of 40Hz, and patients often clearly feel the flickering of light during the phototherapy process.

[0003] Figure 1 is a structural conceptual diagram of an existing LED driver. As shown in Figure 1, the LED driver receives power from a commercial power source and supplies the power to an LED light source. Power standards vary from country to country; for example, Taiwan uses 110 / 220V, 60Hz AC power, Japan uses 100 / 200 / 242V, 50 / 60Hz AC power, Europe uses 220 / 230 / 240V, 50Hz AC power, and America uses 120 / 277V, 60Hz AC power.

[0004] Figure 2 shows the output current Iout of the LED driver in Figure 1. In general lighting, the LED driver supplies DC current to the LED light source, and the brightness of the LED light source is proportional to the magnitude of the current flowing through the LED light source, so the LED driver can adjust the brightness of the LED light source and achieve dimming function by adjusting the magnitude of the current flowing through the LED light source.

[0005] The human eye is more sensitive to light flicker with frequencies below 60Hz. When patients are exposed to Gamma strobe light, some patients feel uncomfortable and are unable to receive sufficient exposure time, resulting in ineffective treatment. Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an LED driver and an LED lighting system that can solve the above-mentioned technical problems and reduce the discomfort of users. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention provides an LED driver for driving an LED light source, the LED driver comprising: a DC-DC converter and a strobe circuit. The strobe circuit generates a low-frequency modulation signal. The DC-DC converter is connected to the strobe circuit and supplies an adjustable operating current to the LED light source according to the DC electrical signal and the low-frequency modulation signal, the operating current includes a DC current signal corresponding to the DC electrical signal and a low-frequency AC current signal corresponding to the low-frequency modulation signal. The frequency of the low-frequency AC current signal is 25Hz-100Hz, and the current ripple ratio of the difference between the maximum value and the minimum value of the operating current and the sum of the maximum value and the minimum value is less than 8%.

[0008] In order to achieve the above-mentioned object, the present invention provides an LED lighting system, which includes an LED light source and an LED driver. The LED driver is used for driving the LED light source, and includes a DC-DC converter and a strobe circuit. The strobe circuit generates a low-frequency modulation signal. The DC-DC converter is connected to the strobe circuit, and provides an adjustable operating current to the LED light source according to the DC electrical signal and the low-frequency modulation signal, where the operating current includes a DC current signal corresponding to the DC electrical signal and a low-frequency AC current signal corresponding to the low-frequency modulation signal. The frequency of the low-frequency AC current signal is 25Hz-100Hz, and the current ripple ratio of the difference between the maximum value and the minimum value of the operating current and the sum of the maximum value and the minimum value is less than 8%. Effect of the Invention

[0009] The present invention limits the flicker rate of the LED light source, thereby preventing the human eye from sensing the flicker of light. This means that even when using gamma strobe light therapy, it is less uncomfortable for the patient and can be irradiated for a sufficient treatment time, resulting in a therapeutic effect. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of the structure of an existing LED driver. [Diagram 2] FIG. 2 is a diagram showing an output current of the LED driver of FIG. 1. [Diagram 3] FIG. 2 is a configuration diagram of an LED driver in the first embodiment of the present invention. [Figure 4] 4 is a diagram showing an operating current provided by the LED driver of FIG. 3 to an LED light source. [Diagram 5] 4 is a diagram showing a luminance change waveform of an LED light source driven by the LED driver of FIG. 3. [Figure 6] FIG. 2 illustrates one embodiment of a strobe circuit of the present invention. [Figure 7] FIG. 7 illustrates one embodiment of the timing circuit of FIG. 6. [Figure 8] FIG. 5 is a configuration diagram of an LED driver according to a second embodiment of the present invention. [Figure 9] 9 is a variation of the LED driver of FIG. 8. [Figure 10] FIG. 11 is a configuration diagram of an LED driver according to a third embodiment of the present invention. [Figure 11] 1 is a configuration diagram of an LED lighting system according to an embodiment of the present invention. [Figure 12] This is an example of a variation of the LED lighting system in Figure 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Some exemplary embodiments embodying the features and advantages of the present invention will be described in detail in the following description. The present invention can be modified in different aspects without departing from the scope of the invention. Moreover, the detailed description and the accompanying drawings are used to illustrate the present invention, and are not intended to limit the scope of the present invention.

[0012] FIG. 3 is a configuration diagram of an LED driver in a first embodiment of the present invention. As shown in FIG. 3, the LED driver 1 receives an AC input signal Vac from a power supply, and accordingly generates an operating current Io for driving an LED light source. In the embodiment shown in FIG. 3, the 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. Note that other components of the LED driver 1 are not shown for ease of illustration. The EMI filter 13 is connected to the power supply to reduce or eliminate electromagnetic interference of the AC input signal Vac. The rectifier 14 is connected to the EMI filter 13 and is used to rectify the AC input signal Vac filtered by the EMI filter 13 into a DC electrical signal Vdc, and provide the DC electrical signal Vdc to the DC-DC converter 11. The rectifier 14 can use a bridge rectifier or other suitable rectifier circuit.

[0013] The DC-DC converter 11 may use a suitable power conversion circuit such as a step-down converter, a step-up converter, a step-up / step-down converter, or a flying converter. The DC-DC converter 11 converts the DC electrical signal Vdc into a DC voltage required for the LED light source and supplies an adjustable operating current Io to the LED light source. This allows the light emission brightness of the LED light source to be adjusted. 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 may use an astable multivibrator circuit or other suitable analog and / or digital circuits, and generates a signal with a suitable waveform such as a sine wave signal, a harmonic signal, or a pulse signal of a required frequency. The signal is used as the low-frequency modulation signal Mod.

[0014] The DC-DC converter 11 generates a required operating current Io based on the DC electrical signal Vdc and the low-frequency modulation signal Mod, and can change the brightness of the LED light source at a strobe frequency Fg. The strobe frequency Fg is set to a gamma frequency band between 25 Hz and 100 Hz. In one embodiment, the strobe frequency Fg is 30 Hz to 50 Hz. In another embodiment, the strobe frequency Fg is 40 Hz. In one embodiment, the operating current Io supplied by the DC-DC converter 11 based on the DC electrical signal Vdc and the low-frequency modulation signal Mod includes a DC current signal Idc and a low-frequency AC current signal Ig, and the frequency of the low-frequency AC current signal Ig is in the gamma frequency band between 25 Hz and 100 Hz. In one embodiment, the frequency of the low-frequency AC current signal Ig is 30 Hz to 50 Hz. In another embodiment, the frequency of the low-frequency AC current signal Ig is 40 Hz. The DC-DC converter 11 is set so that the current value of the operating current Io changes between Idc and Idc+Ig at the strobe frequency Fg, thereby making it possible to change the brightness of the LED light source at the strobe frequency Fg.

[0015] Furthermore, the components of LED driver 1 can be increased or decreased according to various design considerations. For example, in Fig. 3, LED driver 1 includes EMI filter 13 and rectifier 14. In another embodiment, the LED driver may not include EMI filter 13 and rectifier 14, for example, when the LED driver is electrically connected to a DC input power source.

[0016] Fig. 4 shows the operating current Io supplied to the LED light source by the LED driver 1 of Fig. 3. As shown in Fig. 4, the current level of the operating current Io changes with the strobe frequency Fg, and the time during which the operating current Io is at a relatively high level (high level) during one cycle (1 / Fg) is ton, the time during which the operating current Io is at a relatively low level (low level) is toff, and the duty ratio during which the operating current Io is at a relatively high level (hereinafter referred to as strobe duty ratio) is ton / (ton+toff). Since the frequency of the level change of the operating current Io is affected by the low-frequency modulation signal Mod, in one embodiment, the duty ratio of the low-frequency modulation signal Mod generated by the strobe circuit 12 is set to ton / (ton+toff), and the strobe duty ratio of the operating current Io generated by the DC-DC converter 11 is ton / (ton+toff). In one embodiment, the strobe duty ratio of the operating current Io generated by the DC-DC converter 11 is less than 50%. In one embodiment, the strobe duty ratio of the operating current Io generated by the DC-DC converter 11 is less than 30%. In another embodiment, the strobe duty ratio of the operating current Io generated by the DC-DC converter 11 is greater than 10% and less than 50%. In one embodiment, the strobe duty ratio of the operating current Io generated by the DC-DC converter 11 is 10% to 30%.

[0017] Figure 5 shows the luminance change waveform of the LED light source driven by the LED driver 1 of Figure 3. According to formula (1), the flicker rate (percent flicker) of the LED light source can be calculated. PF=(Lmax-Lmin) / (Lmax+Lmin)*100% (1) In this equation, PF is the flicker rate, Lmax is the maximum brightness, and Lmin is the minimum brightness. Since the brightness of an LED light source is proportional (positively correlated) to the magnitude of the operating current Io, a similar equation can be used to define the current ripple factor 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) In this formula, Iomax is the maximum value of the operating current Io, and Iomin is the minimum value of the operating current Io. The flicker rate PF of the LED light source is estimated based on the current ripple rate CRF. For example, the flicker rate PF of the LED light source can be set to be equal to the current ripple rate CRF, that is, the flicker rate PF of the LED light source can be controlled to be lower than a required value by setting the current ripple rate CRF. In another embodiment, the flicker rate PF of the LED light source can be set to be equal to a function of the current ripple rate CRF, for example, PF=f(CRF)=A*CRF+B, where A and B are suitable values, that is, the flicker rate PF of the LED light source can be controlled to be lower than a required value by setting the current ripple rate CRF.

[0018] Although each user has different sensitivity to light flicker, in order to prevent the human eye from detecting light flicker, the flicker rate PF of the LED light source should be limited to an appropriate value. In one embodiment, the flicker rate PF of the LED light source is set to less than 10%. In another embodiment, in order to prevent the human eye from detecting light flicker when the flicker frequency is 40Hz, the flicker rate PF of the LED light source is set to less than 1% according to the recommendation of IEEE standard 1789. Under the premise that the flicker rate PF of the LED light source is less than 1%, if the flicker rate PF of the LED light source is set equal to the current ripple rate CRF, according to the above-mentioned formula of the current ripple rate CRF, the maximum value of the operating current Io (Iomax=Idc+Ig) should be less than about 1.02 times the minimum value of the operating current Io (Iomin=Idc), that is, the maximum current value of the low-frequency AC current signal Ig should be less than about 0.02 times the current value of the DC current signal Idc. In another embodiment, when the flicker frequency is 100Hz, the flicker rate PF of the LED light source can be set to be less than 8%, and the flicker rate PF of the LED light source can be set to be equal to the current ripple rate CRF according to the recommendation of IEEE standard 1789. According to the above formula of the current ripple rate CRF, the maximum value of the operating current Io (Iomax=Idc+Ig) should be less than about 1.174 times the minimum value of the operating current Io (Iomax=Idc), that is, the maximum current value of the low-frequency AC current signal Ig should be less than about 0.174 of the current value of the DC current signal Idc. In this way, the operating current Io generated by the LED driver 1 of the present invention changes between Iomax and Iomin at the strobe frequency Fg, and in addition to the relatively stable light beam brightness formed by the DC current signal Idc, the illumination light generated by the driven LED light source also has brightness changes generated at the strobe frequency Fg by the low-frequency AC current signal Ig. However, by setting the operating current Io generated by the LED driver 1, the flicker rate PF of the LED light source is set to a certain value or less, and this brightness change due to the strobe frequency Fg is not noticeable to the human eye and does not cause discomfort, so low-frequency light therapy using this method does not require a treatment time limit like existing light therapy.Furthermore, the Gamma strobe of the present invention can be applied to everyday lighting fixtures to provide 24-hour light therapy. In one embodiment, 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 about 1.105 times the minimum value of the operating current Io (Iomax=Idc), and the flicker rate PF of the LED light source can be set to be equal to the current ripple rate CRF, so that the flicker rate PF of the LED light source is less than 5%.

[0019] From the above formula, it can be seen that in order to make the flicker rate PF of the LED light source less than a required value, the maximum current value of the low-frequency AC current signal Ig should be set lower than a certain ratio of the current value of the DC current signal Idc. Therefore, even if the lighting brightness of the LED light source changes correspondingly due to the change in the magnitude of the current value of the DC current signal Idc, the flicker rate PF of the LED light source can be suppressed to less than a required value due to the Gamma strobe effect of the low-frequency AC current signal Ig, and the user will not feel uncomfortable. In one embodiment, the strobe circuit 12 includes a modulation signal generating circuit 121 of FIG. 6 for generating a required low-frequency modulation signal Mod so that the DC-DC converter 11 can set the current value of the low-frequency AC current signal Ig to less than a certain ratio of the current value of the DC current signal Idc according to 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, and the resistor R1 and the switch S1 are connected in series between the current sensing terminal CS and a ground potential (or other suitable set potential). The resistor R2 is connected between the current sensing terminal CS and the ground potential, and is connected in parallel with the resistor R1 and the switch S1.

[0020] In the embodiment of FIG. 6, the strobe circuit 12 includes a timer circuit 122. The timer circuit 122 can use an appropriate analog circuit and / or digital circuit (e.g., a circuit such as LM555) and can provide a switch control signal CON to the control end of the switch S1 to set the conductive state of the switch S1. The switch control signal CON generated by the timer circuit 122 can be set to a pulse signal with a frequency of a gamma frequency band (e.g., 40 Hz) to generate a required low-frequency modulation signal Mod, and the duty ratio of the pulse signal can be set to less than 50% (e.g., 10%). In one embodiment, when the voltage value Vcs between the current sensing end CS and the ground potential is fixed, when the timer circuit 122 sets the switch control signal CON to a high level to turn on (conduct) the switch S1, the resistance value Rcs between the current sensing end CS and the ground potential is the resistance value of resistors R1 and R2 connected in parallel, and the current value Ics flowing through the current sensing end CS is Vcs / Rcs=Vcs / (R1 / / R2). When the timer circuit 122 sets the switch control signal CON to a low level to turn the switch S1 off (non-conductive), 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, if Vcs is 0.1 V, R1 is 10 Ω, and R2 is 1 Ω, when the switch S1 is off (non-conductive), the current Ics flowing through the current sensing terminal CS is Vcs / R2=0.1 A, and when the switch S1 is on (conductive), the current Ics flowing through the current sensing terminal CS is Vcs / (R1 / / R2)=0.11 A, of which the current I flowing through the resistor R1 is R1 is Vcs / R1=0.01A, and the current I R2 is Vcs / R1=0.1A.

[0021] The DC-DC converter 11 is connected 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 not turned on, the current value is Ics=Vcs / R2, and the DC-DC converter 11 generates the operating current Io=Idc according to the current value Ics. On the other hand, when the switch S1 is turned on, the current value is 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. This allows the operating current Io, the strobe frequency Fg of the LED light source, and the strobe duty ratio to be adjusted accordingly by setting the frequency and duty ratio of the switch control signal CON generated by the timer circuit 122.

[0022] Table 1 shows the current I R1 , the current I flowing through resistor R2 R2 and a fluctuation Iripple according to the current value Ics flowing through the current sensing terminal CS. The DC-DC converter 11 can adjust the operating current Io supplied according to the current value Ics, so the current I R1 and I R2 This allows the DC-DC converter 11 to adjust the low-frequency AC current signal Ig and the DC current signal Idc in the operating current Io, respectively. As shown in Table 1, the current I R2 When changes occur, the current I R1 changes at the same rate (proportional) rather than changing by the same difference value. For example, the current I R2 When changes from 0.1 to 0.09 (a 10% decrease), the current I R1 changes from 0.01 to 0.009, which is also a 10% decrease. Therefore, in this embodiment, the current I R2 Regardless of the magnitude of I, when switch S1 is on, the current Ics (=I R2 +I R1 ) is the current value Ics (=I R2In other words, regardless of the magnitude of the DC current signal Idc in the operating current Io, the DC-DC converter 11 can set the operating current Io when the switch S1 is on to 110% of the operating current Io when the switch S1 is off.

[0023] JPEG2025043268000002.jpg156165

[0024] As described above, the operating current Io provided by the DC-DC converter 11 includes the DC current signal Idc and the 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, when dimming), the low-frequency AC current signal Ig in the operating current Io also changes at the same rate (proportional) to prevent the human eye from perceiving a strobe-like flicker due to a change in the flicker rate PF. Specifically, when the DC current signal Idc in the operating current Io increases or decreases at a certain 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 (i.e., regardless of the magnitude of the luminance of the LED light source), the Gamma strobe is effectively maintained and the human eye does not feel discomfort due to the flicker of light (flicker).

[0025] In another embodiment, the timer circuit 122 may be configured to generate a switch control signal CON for the switch S1 to be in a continuously conductive state or a continuously non-conductive state, so that the current value flowing through the current sensing terminal CS is maintained constant, the operating current Io provided by the DC-DC converter 11 is maintained at a constant value, and the Gamma strobe function can be turned off.

[0026] FIG. 7 shows one embodiment of the modulation signal generating circuit 121 and the timing circuit 122 of FIG. 6. In this embodiment, the timing circuit 122 includes an astable multivibrator using a totem pole topology. As shown in FIG. 7, the timing circuit 122 includes a voltage source V1, resistors R3, R4, R5, R6, R7, capacitors C1, C2, diodes D1, D2, D3, and switches Q1, Q2. The first terminals of the resistors R3, R4, R5, R6 are connected to the positive terminal of the voltage source V1. Both ends of the capacitor C1 are respectively connected to the second terminals of the resistors R3, R4, the anode of the diode D1 is connected to the second terminal of the resistor R5, and the first, second and third terminals of the switch Q1 are respectively connected to the second terminal of the resistor R3, the cathode of the diode D1 and the negative terminal of the voltage source V1. Both ends of the capacitor C2 are connected to the second terminals of the resistors R5 and R6, the anode of the diode D2 is connected to the second terminal of the resistor R4, and the first, second and third terminals of the switch Q2 are connected to the second terminal of the resistor R6, the cathode of the diode D2 and the negative terminal of the voltage source V1, respectively. The cathode of the diode D3 is connected to the second terminal of the resistor R6, the anode of the diode D3 is connected to the first terminal of the resistor R7 and the modulation signal generating circuit 121 (switch S1), and the second terminal of the resistor R7 is connected to the negative terminal of the voltage source V1. The resistors R4 and R5 are start-up resistors of the switches Q2 and Q1, respectively. In this embodiment, the switches Q1 and Q2 are bipolar junction transistors whose first, second and third terminals are the collector, base and emitter, respectively. The switch S1 is a metal oxide semiconductor field effect transistor having a drain, a gate, and a source connected to a resistor R1, an anode of a diode D3, and a cathode of a voltage source V1, respectively.

[0027] In the circuit shown in FIG. 7, when the voltage source V1 supplies a voltage (for example, 5V), the switch Q1 or Q2 turns on. Specifically, when the voltage of the capacitor C2 is charged to 0.7V, the switch Q1 turns on, and at the same time, a reverse voltage is supplied to turn off the switch Q2, and the voltage of the capacitor C1 is charged to 5V. On the other hand, when the voltage of the capacitor C1 is charged to 0.7V, the switch Q2 turns on, and at the same time, a reverse voltage is supplied to turn off the switch Q1, and the voltage of the capacitor C2 is charged to 5V. Therefore, by opening and closing the conductive and non-conductive states of the switches Q1 and Q2, it is possible to provide oscillation (oscillation current) at a frequency (for example, 40Hz) of the gamma frequency band. Also, when the switch Q2 is on, the gate voltage of the switch S1 is discharged, and the switch S1 turns off. When the switch Q2 is off, the voltages of the resistors R6 and R7 become the gate voltage, and the switch S1 turns on. When the switch S1 is on, the resistance value Rcs between the current sensing terminal CS and the ground potential is the resistance value when the resistors R1 and R2 are connected in parallel, and the current value Ics flowing through the current sensing terminal CS is Vcs / Rcs=Vcs / (R1 / / R2). When the switch S1 is off, the resistance value Rcs between the current sensing terminal CS and the ground potential is the resistance value of the resistor R2, and the current value Ics flowing through the current sensing terminal CS is Vcs / Rcs=Vcs / R2. For example, Vcs is set to 0.1 V, R1 to 10 Ω, and R2 to 1 Ω. When the switch S1 is off, the current value Ics flowing through the current sensing terminal CS is Vcs / R2=0.1 A. When the switch S1 is on, the current value Ics flowing through the current sensing terminal CS is Vcs / (R1 / / R2)=0.11 A, and the current I R1 is Vcs / R1=0.01A, and the current I R2 is Vcs / R1=0.1A.

[0028] The DC-DC converter 11 is connected 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 not on, the current value is Ics=Vcs / R2, and the DC-DC converter 11 generates the operating current Io=Idc based on the current value Ics. When the switch S1 is on, the current value is Ics=Vcs / (R1 / / R2), and the DC-DC converter 11 generates the operating current Io=Idc+Ig based on 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, and thus the operating current Io and the strobe frequency Fg and strobe duty ratio of the LED light source can be adjusted by setting the frequency and duty ratio at which the timer circuit 122 drives the operation of the switch S1.

[0029] The possible embodiments of the DC-DC converter 11 and the strobe circuit 12 of the present invention are not limited to those described above. On the premise that the DC-DC converter 11 has a DC-DC conversion function, and the working current provided by the DC-DC converter 11 includes a low-frequency pulse signal, the strobe circuit 12 can select an appropriate mode according to actual needs.

[0030] FIG. 8 is a configuration diagram of an LED driver in a second embodiment of the present invention. In FIG. 8, the same components as those in the first embodiment of FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. Compared with the LED driver 1 in the first embodiment shown in FIG. 3, the LED driver 1a in the second embodiment shown in FIG. 8 further includes a control circuit 15 and a dimming circuit 16. The control circuit 15 receives a dimming control signal, controls the dimming circuit 16 accordingly, and provides (transmits) 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, and 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 an embodiment, the strobe circuit 12 includes a microcontroller unit and uses the microcontroller unit to provide a PWM (pulse width modulation) dimming signal. In one embodiment, the strobe circuit 12 can be combined with a control circuit 15 or a dimming circuit 16, which can provide the combined (combined / mixed) dimming signal and low-frequency modulation signal to the DC-DC converter 11 through a microcontroller unit. For example, the microcontroller unit of the strobe circuit 12 generates a 1.25kHz PWM dimming signal, and within one period (e.g., 0.025 seconds, corresponding to a frequency of 40Hz), the 90% PWM dimming signal has a PWM signal duty ratio of 80%, and the remaining 10% PWM dimming signal has a PWM signal duty ratio of 88%. The DC-DC converter 11 adjusts the maximum and minimum values ​​of the operating current Io according to the PWM signal duty ratios of the 90% and 10% PWM dimming signals, respectively. In this case, the strobe duty ratio of the LED light source is 10%, and the flicker rate PF=(88-80) / (88+80)*100%=4.7%, and the LED light source can generate a Gamma strobe with a flicker rate PF of less than 5%.

[0031] In the above-described embodiment, the strobe circuit 12 continuously generates a signal with a frequency in the gamma frequency band, but the present invention is not limited thereto. In another embodiment, the strobe circuit 12 may be configured to have a function that enables or disables the generation of a signal with a frequency in the gamma frequency band (the strobe circuit 12 can be controlled to generate and stop generating a signal with a frequency in the gamma frequency band). FIG. 9 shows a modified example of the LED driver of FIG. 8. As shown in FIG. 9, in the LED driver 1b, the control circuit 15 is also electrically connected to the strobe circuit 12 to control the operation of the strobe circuit 12. Based on a received control signal (e.g., received from a user or another circuit), the control circuit 15 controls the strobe circuit 12 so that the strobe circuit 12 generates or stops generating a signal with a frequency in the gamma frequency band (e.g., the switch S1 in FIG. 6 or FIG. 7 is set to a state in which it is continuously conducting or continuously non-conducting by the switch control signal CON).

[0032] FIG. 10 is a configuration diagram of an LED driver in a third embodiment of the present invention. In FIG. 10, the same components as those in the first embodiment shown in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. Compared with the LED driver 1 in the first embodiment shown in FIG. 3, the LED driver 1c in the third embodiment shown in FIG. 10 further includes a multi-stage control switch 17, which is connected between the power supply and the EMI filter 13 to provide a dimming function. The multi-stage control switch 17 can receive power from the power supply and selectively switch and provide different output powers. Thereby, the LED driver 1c can adjust the DC current signal Idc in the operating current Io accordingly, and set the corresponding low-frequency AC current signal Ig by the strobe circuit 12 to realize the dimming and Gamma strobe functions. The switching of the multi-stage control switch 17 can be realized by, for example, a mechanical switch, but the present invention is not limited thereto. In an embodiment, the LED driver 1c can selectively operate in three different modes based on the switching of the multi-stage control switch 17. For example, when the multi-step control switch 17 operates in the first mode, the LED driver 1c supplies 100% output to the LED light source, and the main light of the LED light source operates at maximum brightness. When the multi-step control switch 17 operates in the second mode, the LED driver 1c supplies 65% output to the LED light source, and the main light of the LED light source operates at a relatively low brightness. When the multi-step control switch 17 operates in the third mode, the LED light source is turned off.

[0033] As can be seen from the above-mentioned embodiments, the LED driver of the present invention can make the LED light source brighter during the remaining (100-X)% of the time in one cycle compared to X% of the time, where X% is, for example, less than 50% or less than 30%, or between 10% and 30%. The low frequency AC current signal of the operating current is 30Hz to 50Hz (for example, 40Hz), and accordingly, the LED driver can set the LED light source at this frequency to appear brighter during X% of the time in one cycle.

[0034] Also, the operating current generated by the LED driver during the period when the LED light source is relatively bright (i.e., during X% of the time in one cycle) is less than Y% of the operating current generated during the period when the LED light source is relatively dark (i.e., during (100-X)% of the time in one cycle). This can prevent the human eye from perceiving light flickering while the LED light source is performing Gamma strobe. Since Y% is less than 120% (e.g., 110%), the flicker rate PF is less than 5%.

[0035] In addition, since the amplitude of the low-frequency AC current signal of the operating current during the period when the LED light source is relatively bright (i.e., within X% of one cycle) is proportional to the magnitude of the DC current signal of the operating current during the period when the LED light source is relatively dark (i.e., within (100-X)% of one cycle), a constant flicker rate PF is maintained so that the human eye does not perceive light flicker regardless of the brightness of the LED light source.

[0036] Also, when dimming using a PWM signal, the PWM signal duty ratio Z1 during the period when the LED light source is relatively bright (i.e., within X% of one cycle) is smaller than W% of the PWM signal duty ratio Z2 during the period when the LED light source is relatively dark (i.e., within (100-X)% of one cycle). This can prevent the human eye from perceiving light flicker while the LED light source is performing Gamma strobe. Since W% is less than 120% (e.g., 110%), the flicker rate PF (=(Z1-Z2) / (Z1+Z2)*100%) is less than 5%.

[0037] In one embodiment, the LED lighting system shown in FIG. 11 includes an LED driver 1 and an LED light source. The LED light source includes a plurality of LED light-emitting modules. The DC-DC converter 11 is connected to all the LED light-emitting modules of the LED light source, and the DC-DC converter 11 can drive all the LED light-emitting modules of the LED light source to simultaneously realize (provide) the lighting and Gamma strobe functions. In another embodiment, the LED lighting system shown in FIG. 12 includes an LED driver 1 and an LED light source. The LED light source includes a plurality of LED light-emitting modules. The DC-DC converter 11 is connected to a portion of the LED light-emitting modules of the LED light source, and enables all the LED light-emitting modules of the LED light source to provide the lighting function, and the portion of the LED light-emitting modules driven by the DC-DC converter 11 can simultaneously realize (provide) the lighting and Gamma strobe functions. Therefore, the LED light source does not need to be equipped with a special LED light-emitting module for realizing the Gamma strobe function, and the arrangement is not specially designed, and a uniform lighting effect can be achieved. In addition, since the LED light-emitting module can provide both illumination and Gamma strobe functions at the same time, a similar brightness can be achieved with a relatively small number of LED light-emitting modules, which is energy-saving and environmentally friendly. Note that, although the LED driver 1 shown in FIG. 3 is given as an example in FIG. 11 and FIG. 12, the present invention is not limited thereto. This embodiment is applicable to any LED driver of the present invention (for example, the LED drivers 1a, 1b, and 1c in FIG. 8, FIG. 9, and FIG. 10).

[0038] The above description describes the preferred embodiment of the present invention, and the present invention is not limited to the above embodiment, and the scope of the present invention is determined by the claims. The present invention can be modified, revised, and improved in various ways by those skilled in the art, and all such modifications, revisions, and improvements do not deviate from the scope of the claims of this application and are all included. [Explanation of symbols]

[0039] Iout: Output current 1: LED driver Vac: AC input signal (AC input signal) Vdc: DC electrical signal (direct current signal) Io: Operating current 11: DC-DC converter 12: Strobe circuit 13: EMI filter 14: Rectifier Mod: Low frequency modulating signal Fg: Strobe frequency Idc: DC current signal Ig: Low frequency AC current signal ton: Time during which the operating current is at a relatively high level toff: Time during which the operating current is at a relatively low level Iomax: Maximum operating current Iomin: Minimum operating current Lmax: maximum luminance Lmin: Minimum luminance PF: Flicker rate CRF: Current ripple factor 121: Modulation signal generating circuit CS: Current sensing end R1, R2: Resistance S1: Switch 122: Timing circuit CON: Switch control signal Vcs: Voltage value Rcs: Resistance value Ics: Current value I R1 , I R2 :Current V1: Voltage source R3, R4, R5, R6, R7: Resistance C1, C2: Capacitors D1, D2, D3: Diodes Q1, Q2: Switch 1a: LED driver 15: Control circuit 16: Dimming circuit Idim: Dimming signal 1b:LED driver 1c:LED driver 17: Multi-stage control switch

Claims

1. 1. An LED driver for driving an LED light source, comprising: A strobe circuit and a DC-DC converter are provided. The strobe circuit generates a low frequency modulated signal; the DC-DC converter is connected to the strobe circuit and provides an adjustable operating current to the LED light source based on a DC electrical signal and the low-frequency modulation signal, the operating current including a DC current signal corresponding to the DC electrical signal and a low-frequency AC current signal corresponding to the low-frequency modulation signal; The frequency of the low-frequency AC current signal is 25 Hz to 100 Hz, and a current ripple rate of a difference between a maximum value and a minimum value of the operating current and a sum of the maximum value and the minimum value is less than 8%.

2. the strobe circuit includes a modulation signal generating circuit and a timing circuit; the modulation signal generating circuit includes a current sensing terminal, a switch, a first resistor, and a second resistor, the first resistor and the switch being connected in series between the current sensing terminal and a ground potential, the second resistor being connected between the current sensing terminal and the ground potential and being connected in parallel to the first resistor and the switch; the timer circuit is connected to the modulation signal generating circuit and supplies a switch control signal to the switch, the switch control signal being used to set the conductive state of the switch so that the modulation signal generating circuit generates the low-frequency modulation signal; 2. The LED driver as claimed in claim 1, wherein the DC-DC converter is connected to the current sensing terminal, and adjusts the operating current correspondingly according to a current value flowing through the current sensing terminal.

3. 2. The LED driver of claim 1, further comprising: a control circuit and a dimming circuit, wherein the control circuit receives a dimming control signal, and correspondingly controls the dimming circuit to provide a dimming signal to the DC-DC converter, and the DC-DC converter adjusts the working current according to the dimming signal.

4. 4. The LED driver of claim 3, wherein the control circuit is further connected to the strobe circuit, and controls the strobe circuit to generate or stop generating the low-frequency modulated signal.

5. 2. The LED driver of claim 1, further comprising a multi-stage control switch coupled to the DC-DC converter, the multi-stage control switch selectively switching to provide different power outputs such that the LED driver correspondingly adjusts the DC current signal of the operating current.

6. 2. The LED driver of 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 being composed of a first part and a second part in one cycle, a first duty ratio of the first part of the PWM dimming signal is smaller than 120% of a second duty ratio of the second part of the PWM dimming signal, and the DC-DC converter adjusts the maximum value and the minimum value of the operating current based on the first duty ratio and the second duty ratio, respectively.

7. 7. The LED driver of claim 6, wherein the first duty ratio of the first portion of the PWM dimming signal is less than 110% of the second duty ratio of the second portion of the PWM dimming signal.

8. 2. The LED driver of claim 1, wherein a ratio between the maximum value of the operating current and the minimum value of the operating current is a constant value, and the constant value is less than 120%.

9. 2. The LED driver of claim 1, wherein the frequency of the low-frequency AC current signal is between 30 Hz and 50 Hz.

10. 10. The LED driver of claim 9, wherein the frequency of the low frequency AC current signal is 40 Hz.

11. 2. The LED driver of claim 1, wherein the operating current is at the maximum value less than 50% of the time during one period.

12. 12. The LED driver of claim 11, wherein the percentage of time is between 10% and 30%.

13. 2. The LED driver of claim 1, wherein the current ripple rate is less than 5%.

14. An LED lighting system comprising an LED light source and an LED driver, the LED driver drives the LED light source and includes a strobe circuit and a DC-DC converter; The strobe circuit generates a low frequency modulated signal; the DC-DC converter is connected to the strobe circuit and the LED light source, and supplies an adjustable operating current to the LED light source based on a DC electrical signal and the low-frequency modulation signal, the operating current including a DC current signal corresponding to the DC electrical signal and a low-frequency AC current signal corresponding to the low-frequency modulation signal; The frequency of the low-frequency AC current signal is 25 Hz to 100 Hz, and a current ripple rate of a difference between a maximum value and a minimum value of the operating current and a sum of the maximum value and the minimum value is less than 8%.

15. 15. The LED lighting system according to claim 14, wherein the LED light source comprises a plurality of LED light-emitting modules, and the DC-DC converter is connected to the plurality of LED light-emitting modules and supplies the operating current to the plurality of LED light-emitting modules.

16. 15. The LED lighting system according to claim 14, wherein the LED light source comprises a plurality of LED light-emitting modules, and the DC-DC converter is connected to a portion of the LED light-emitting modules and supplies the operating current to the portion of the LED light-emitting modules.

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