LED driving power supply and control method thereof

Abstract

The present invention discloses an LED driving power supply and a control method thereof, belonging to the field of LED driving power supply; the driving circuit of the present invention comprises a PFC converter, a power decoupling converter and a half-bridge LLC converter connected in sequence; the control unit comprises a PFC converter control module and a power decoupling converter control module, the PFC converter control module obtains a PWM signal according to a sampling current and a sampling voltage through reset integral comparison to control the switch tube of the PFC converter, and the power decoupling converter control module obtains a driving signal according to an instantaneous value of a voltage at an output terminal of the PFC converter and a given value to control the switch tube of the power decoupling converter. The present invention reduces the number of conducting devices, improves system efficiency, realizes electrolytic capacitor-free operation without affecting the power factor correction effect, and improves the service life of the whole machine.

Description

Technical Field

[0001] The present invention relates to the field of LED driving power supplies, and in particular to an LED driving power supply and a control method thereof. Background Art

[0002] In recent years, LED technology has developed rapidly. It is deeply loved by the public for its advantages of energy saving, long life and high light efficiency, and has become a new generation of lighting source. In traditional LED driver power supplies, large electrolytic capacitors are usually used to balance the power at the input end and the PFC output end. However, the service life of electrolytic capacitors is about 5000 hours, and its service life decreases with the increase of temperature. The service life of LEDs is 80,000-100,000 hours, and the service life of the two is seriously mismatched. In addition, the volume of electrolytic capacitors is large, which increases the volume of the system. Therefore, it is very important to study an electrolytic capacitor-free LED driver power supply that matches the service life of LEDs.

[0003] In the application of high-power LEDs, a two-stage drive circuit is usually used. The front stage usually uses a Boost PFC converter. By controlling the converter, the input current changes with the input voltage to achieve power factor correction. The power factor is approximately 1, and the drive circuit is simple and efficient. However, in order to maintain a stable output voltage, a large electrolytic capacitor is usually connected in parallel at the output end. The use of electrolytic capacitors not only increases the volume of the system but also limits the service life of the system and reduces the reliability of the system. The back-stage DC / DC converter usually uses a half-bridge LLC resonant converter. The LLC resonant converter is a resonant circuit that achieves a constant output voltage by controlling the switching frequency. Its advantages are that it can achieve zero voltage turn-on (ZVS) of the primary switch tube and zero current turn-off (ZCS) of the secondary rectifier diode, can achieve high-efficiency DC-DC conversion, simple circuit topology, and the voltage stress of the secondary rectifier diode body can be minimized to approximately twice the output voltage. The selectivity of the components is high, and the two resonant inductors can be combined on a transformer core. The transformer leakage inductance and excitation inductance can be used as resonant components, and the volume of the resonant component can be greatly reduced. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide an LED driving power supply and a control method thereof, which reduces the number of conducting devices, improves the system efficiency, realizes the electrolytic capacitor-free operation without affecting the power factor correction effect, and increases the service life of the whole machine.

[0005] To achieve the above object, the present invention provides an LED driving power supply, comprising:

[0006] A driving circuit, comprising a PFC converter, a power decoupling converter and a half-bridge LLC converter connected in sequence;

[0007] The sampling unit includes a current sampling circuit and a voltage sampling circuit to collect the output voltage of the bridgeless PFC and the current flowing through the input current detection resistor R s The current;

[0008] The control unit includes a PFC converter control module and a power decoupling converter control module. The PFC converter control module obtains a PWM signal according to a sampling current and a sampling voltage through reset integration comparison to control the switch tube of the PFC converter. The power decoupling converter control module obtains a driving signal according to an instantaneous value of a voltage at an output terminal of the PFC converter and a given value to control the switch tube of the power decoupling converter.

[0009] Furthermore, the PFC converter is a dual-diode bridgeless PFC converter.

[0010] Furthermore, the power decoupling converter is a step-up bidirectional Buck / boost power decoupling converter.

[0011] Furthermore, the PFC converter control module includes: a current amplifier, a voltage error amplifier, an integrator with reset, a comparator and a PWM controller.

[0012] A second aspect of the present invention provides a method for controlling an LED driving power supply, comprising:

[0013] S1, get the input current i of the bridgeless PFC in and the output voltage of the bridgeless PFC;

[0014] S2, set the clock frequency of the PWM controller. When the PWM controller clock arrives, PWM is at a high level, driving the switch tubes S1 and S2 to turn on;

[0015] S3, obtaining a PWM signal according to the sampling current and the sampling voltage through reset integration comparison to control the switching tubes S1 and S2 of the PFC converter to turn off;

[0016] Step S3 specifically includes:

[0017] S31, the input current i of the bridgeless PFC in The input current is amplified in the input current amplifier and then connected to the input current detection resistor R of the bridgeless PFC converter. s Multiply them to get R s i in ;

[0018] S32, based on the output voltage of the sampled bridgeless PFC and the reference voltage U ref Get the voltage error U m ;

[0019] S33, the voltage error U m Divided into two paths, one path is voltage error U m With R s i in After difference is taken, it is input into the comparator;

[0020] Another voltage error U m By integrating the integrator, we get And input the integration result into the comparator;

[0021] S34, establish the following comparison equation, and determine whether the two sides of the comparison equation are equivalent. When the two sides of the comparison equation are equal, the output value of the comparator is flipped, the switch tubes S1 and S2 are controlled to be turned off, and then the integrator is reset; when the two sides of the comparison equation are not equal, execute step S2;

[0022]

[0023] S4, obtaining a driving signal according to the instantaneous value of the voltage at the output terminal of the PFC converter and a given value, so as to control the switch tube of the power decoupling converter;

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The bridgeless PFC circuit is adopted in the driving circuit of the present invention so that the input current follows the input voltage, the two are in phase and sinusoidal, which effectively suppresses the distortion of the input current and reduces harmonic pollution. In addition, the bridgeless PFC circuit replaces the rectifier bridge circuit in the traditional driving circuit, reduces the number of conducting devices and the switching loss of the switch tube, and improves the system efficiency of the system during operation.

[0026] 2. The step-up bidirectional Buck / Boost power decoupling converter adopted by the present invention absorbs the double frequency ripple power, greatly reduces the capacitance of the filter capacitor, realizes the electrolytic capacitor-free operation without affecting the power factor correction effect, and improves the service life of the whole machine. In addition, film capacitors are used instead of electrolytic capacitors to achieve electrolytic capacitor-free operation.

[0027] 3. The present invention processes the input voltage from the bridgeless PFC converter through the LLC resonant converter to provide a stable direct current for the LED load, thereby achieving high-efficiency LED lamp driving.

[0028] 4. The present invention has a high power factor and small input current distortion, and can effectively suppress the low-frequency ripple of the output voltage of the bridgeless PFC circuit and reduce the capacitance value at the output end of the bridgeless PFC circuit.

[0029] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the circuit structure of an LED driving power supply according to a specific embodiment of the present invention;

[0031] Figure 2 It is a control principle block diagram of a bridgeless PFC converter according to a specific embodiment of the present invention;

[0032] Figure 3 It is a control principle block diagram of a power decoupling circuit according to a specific embodiment of the present invention.

[0033] Figure 4 1 is an output voltage pulsating waveform of different filter capacitors when no power decoupling circuit is added in a specific embodiment of the present invention. Figure 4 a is the PFC output voltage pulsation waveform when the output filter capacitor is 220uF. Figure 4 b is the PFC output voltage pulsation waveform when the F is 40uF.

[0034] Figure 5 This is a PFC output voltage pulsation waveform with different output filter capacitors when a power decoupling circuit is added to a specific embodiment of the present invention. Figure 5 a is the PFC output voltage pulsation waveform when the output filter capacitor is 220uF. Figure 5 b is the PFC output voltage pulsation waveform when the F is 40uF.

[0035] Figure 6 1 is an output voltage waveform of a half-bridge LLC resonant converter according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0037] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0038] While some exemplary embodiments of the present invention have been described for the purpose of illustration, it should be understood that the present invention may be implemented in other ways not specifically shown in the drawings.

[0039] In a specific embodiment, there is provided an LED driving power supply, including a driving circuit, a sampling unit and a control unit;

[0040] like Figure 1 As shown, the driving circuit includes a PFC converter 2, a power decoupling converter 3 and a half-bridge LLC converter 4 connected in sequence, the PFC converter is connected to a single-phase input power supply 1, the power decoupling converter is connected to the PFC converter, the half-bridge LLC resonant converter is connected to the power decoupling converter, and the half-bridge LLC resonant converter is connected to an LED load 5.

[0041] The PFC converter is a dual-diode bridgeless PFC converter, including a diode D1, a diode D2, a diode D3, a diode D4, a switch tube S1, a switch tube S2, an inductor L1 and an inductor L2, wherein the cathode of the diode D3 and one end of the inductor L1 are connected to one end of the input power supply, the cathode of the diode D4 and one end of the inductor L2 are connected to the other end of the input power supply, the anodes of the diodes D3 and D4 are connected to the source electrodes of the switch tube S1 and the switch tube S2, the drain of the switch tube S1 is connected to the anode of the diode D1 and the other end of the inductor L1, the drain of the switch tube S2 is connected to the anode of the diode D2 and the other end of the inductor L2. The cathode of the diode D1 is connected to the cathode of the diode D2.

[0042] The power decoupling converter is a step-up bidirectional Buck / boost power decoupling converter, as shown in the figure, including a switch tube S3, a switch tube S4, a decoupling inductor Ls and a decoupling capacitor Cs, one end of the decoupling inductor Ls is connected to the cathode of the diode D2 and one end of the capacitor C1, the other end of the decoupling inductor Ls is connected to the drain of the switch tube S3 and the source of the switch tube S4, the drain of the switch tube S4 is connected to one end of the decoupling capacitor Cs, the other end of the decoupling capacitor Cs is connected to the source of the switch tube S3 and the other end of the capacitor C1, and the source of the switch tube S3 is connected to the source of the switch tube S2. The decoupling capacitor Cs and the first capacitor C1 are both thin film capacitors.

[0043] The half-bridge LLC resonant converter is composed of a switch tube S5, a switch tube S6, and a diode D S5 、Diode D S6 , capacitor C S5 , C S6, a resonant capacitor Cr, a resonant inductor Lr, an excitation inductor Lm, a transformer T, a diode D5, a diode D6 and a capacitor C2. The drain of the switch tube S5 is connected to one end of the capacitor C1, the source of the switch tube S6 is connected to the other end of the capacitor C1, the source of the switch tube S5 and the drain of the switch tube S6 are connected together, and the capacitor C S5 Connected in parallel at both ends of the switch tube S5, the capacitor C S6 Connected in parallel at both ends of the switch tube S6, the diode D S5 Anti-parallel connection at both ends of the switch tube S5, that is, diode D S5 The cathode of the switch tube S5 is connected to the drain of the diode D S5 The anode of the switch tube S5 is connected to the source of the diode D S6 Anti-parallel connection at both ends of the switch tube S6, that is, diode D S6 The cathode of the switch tube S6 is connected to the drain of the diode D S6 The anode of the switch tube S6 is connected to the source of the switch tube S6. The resonant inductor Lr and the resonant capacitor Cr are connected in series and connected between the drain of the switch tube S5 and one end of the primary side of the transformer. The other end of the primary side of the transformer is connected to the source of the switch tube S6, and the excitation inductor Lm is connected in parallel to the primary side of the transformer. The diodes D5 and D6 are reversely connected in series to the secondary side of the transformer T, one end of the capacitor C2 is connected to the cathode of the diodes D5 and D6, and the other end is connected to the secondary side of the transformer T. The load is connected in parallel to both ends of the capacitor C2.

[0044] The sampling unit includes a current sampling circuit and a voltage sampling circuit to collect the output voltage of the bridgeless PFC and the current flowing through the input current detection resistor R s The current;

[0045] The control unit includes a PFC converter control module and a power decoupling converter control module. The PFC converter control module obtains a PWM signal according to a sampling current and a sampling voltage through reset integration comparison to control the switch tube of the PFC converter. The power decoupling converter control module obtains a driving signal according to an instantaneous value of a voltage at an output terminal of the PFC converter and a given value to control the switch tube of the power decoupling converter.

[0046] like Figure 2 As shown, the PFC converter control module of this embodiment includes a current amplifier, a voltage error amplifier, an integrator with reset, a comparator and a PWM controller. The sampled current is input into the current amplifier as an input signal, and the sampled voltage is subtracted from the reference voltage to obtain a voltage error U m, the voltage error is used as the input signal of the voltage error amplifier; the voltage error amplified by the voltage error amplifier is used as the input signal of the integrator with reset, and the comparator obtains the closing and opening instructions of the switch tube according to the comparison result of the following formula:

[0047]

[0048] Among them, i in is the input current of the bridgeless PFC, R s is the input current detection resistor of the bridgeless PFC converter, and DT is the conduction time of the switch tube in one cycle.

[0049] In a specific embodiment, a method for controlling an LED driving power supply is provided, comprising the following steps:

[0050] S1, get the input current i of the bridgeless PFC in and the output voltage of the bridgeless PFC;

[0051] S2, set the clock frequency of the PWM controller. When the PWM controller clock arrives, PWM is at a high level, driving the switch tubes S1 and S2 to turn on;

[0052] S3, obtaining a PWM signal based on the sampling current and the sampling voltage through reset integration comparison to control the switching tubes S1 and S2 of the PFC converter to turn off, specifically including:

[0053] S31, the input current i of the bridgeless PFC in The input current is amplified in the input current amplifier and then connected to the input current detection resistor R of the bridgeless PFC converter. s Multiply them to get R s i in ;

[0054] S32, based on the output voltage of the sampled bridgeless PFC and the reference voltage U ref Get the voltage error U m ;

[0055] S33, the voltage error U m Divided into two paths, one path is voltage error U m With R s i in After the difference is made, it is input into the comparator. At this time, the inductor stores energy, the inductor current increases linearly, and the difference between the two decreases linearly.

[0056] Another voltage error U m By integrating the integrator, we get Through integration, its value gradually increases, and the integration result is input into the comparator;

[0057] S34, establish the following comparison equation, and determine whether the two sides of the comparison equation are equivalent. When the two sides of the comparison equation are equal, the output value of the comparator is flipped, the switch tubes S1 and S2 are controlled to be turned off, and then the integrator is reset; when the two sides of the comparison equation are not equal, execute step S2;

[0058]

[0059] Through the above method, the duty cycle D of the switch tubes S1 and S2 is controlled.

[0060] S4, obtaining a driving signal according to the instantaneous value of the voltage at the output terminal of the PFC converter and a given value, so as to control the switch tubes S3 and S4 of the power decoupling converter;

[0061] The output power and input power of the PFC converter satisfy the following relationship:

[0062] P o (t) = P in (t)-P o cos(2ωt).

[0063] Where P o is the output power, P in is the input power. It can be seen from the above formula that the low-frequency ripple on the DC side of the PFC converter is generated because the output instantaneous power contains a ripple power of twice the power frequency. Therefore, the ripple power is processed by the boost bidirectional Buck / Boost converter to reduce the low-frequency ripple of the DC output voltage.

[0064] In this embodiment, since the bidirectional Buck / Boost converter usually works in an under-compensated state, the power decoupling capacitor C s The output filter capacitor of the bridgeless PFC only needs to handle a small amount of ripple power. The voltage fluctuation required by the decoupling capacitor is consistent with the output voltage waveform of the bridgeless PFC, so the duty cycle of the decoupling circuit is directly controlled by the output voltage of the bridgeless PFC. First, the instantaneous value of the output voltage u o With the given value U ref After the difference is made, it passes through the voltage error amplifier and then with the DC bias D s The modulated signal is summed and compared with the triangular wave carrier to generate a drive signal, which is superimposed with a DC bias D sTo avoid the duty cycle of switch tube S3 being less than 0. The compensation capacitor voltage increases with the increase of duty cycle, and the duty cycle is proportional to the output voltage, so when the output voltage increases, the power handled by the decoupling capacitor increases, which reduces the output voltage fluctuation of the bridgeless PFC converter. The same is true when the output voltage of the bridgeless PFC converter decreases. It can be seen that through this control strategy, the bidirectional Buck / Boost circuit compensates for the output voltage fluctuation caused by the reduction of the capacitor value in the bridgeless PFC converter, thereby completing power decoupling and realizing electrolytic capacitor-free.

[0065] S4, adjusting the duty cycle of the switch tube in the half-bridge LLC resonant converter, inserting a fixed dead time during the period when the switch tube is turned on and off, and outputting a stable voltage through frequency regulation.

[0066] The switch tube S5 and the switch tube S6 in this embodiment provide two driving signals with a duty cycle of 50% and a phase difference of 180 degrees, and a fixed dead time is inserted between the turn-on and turn-off periods of the upper and lower switches to ensure the realization of soft switching and safe operation under high-frequency working conditions. A stable output voltage is maintained by adjusting the working frequency. In this embodiment, the half-bridge LLC resonant converter uses L6599 as the control chip, and L6599 is a double-ended controller for the half-bridge LLC resonant converter.

[0067] Figure 4 When the power decoupling circuit is not added, the filter capacitor at the output of the bridgeless PFC converter is changed. It can be observed that when the capacitor C o =220uF, the output voltage fluctuation is ±5V, and the voltage ripple coefficient γ = 1.25%; when the capacitor C o =40uF, the output voltage fluctuation reaches ±27V, and the voltage ripple coefficient γ=6.75%, which cannot meet the circuit requirements.

[0068] Figure 5 After adding the power decoupling circuit, the filter capacitor at the output of the bridgeless PFC converter is changed. It can be observed that when the capacitor C o =220uF, the output voltage fluctuation is ±3V, and the voltage ripple coefficient γ = 0.75%; when the capacitor C o =40uF, the output voltage fluctuation is only ±3V, and the voltage ripple coefficient γ = 0.75%. Figure 4 and Figure 5 It can be seen that the addition of the power decoupling circuit reduces the capacitance value of the capacitor, and the use of film capacitors instead of electrolytic capacitors solves the disadvantage of shortening the service life of the entire machine due to the short life of electrolytic capacitors.

[0069] The volt-ampere characteristics of LEDs require that their drivers have constant voltage and constant current output characteristics. Figure 6It is a stable DC voltage output by the half-bridge LLC resonant converter, which reduces the light decay of the LED and improves the working performance of the LED.

[0070] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for controlling an LED driving power supply, characterized in that: The LED driving power supply comprises: The driving circuit includes a dual-diode bridgeless PFC converter, a boost bidirectional Buck / boost power decoupling converter and a half-bridge LLC converter connected in sequence; the sampling unit includes a current sampling circuit and a voltage sampling circuit to collect the output voltage of the bridgeless PFC and the current flowing through the input current detection resistor R s The control unit includes a PFC converter control module and a power decoupling converter control module. The PFC converter control module obtains a PWM signal based on the sampled current and the sampled voltage through reset integration comparison to control the switch tube of the PFC converter. The PFC converter control module includes a current amplifier, a voltage error amplifier, an integrator with reset, a comparator and a PWM controller. The power decoupling converter control module obtains a driving signal based on the instantaneous value of the voltage at the output terminal of the PFC converter and a given value to control the switch tube of the power decoupling converter. The dual-diode bridgeless PFC converter comprises a diode D1, a diode D2, a diode D3, a diode D4, a switch tube S1, a switch tube S2, an inductor L1 and an inductor L2, wherein the cathode of the diode D3 and one end of the inductor L1 are connected to one end of the input power supply, the cathode of the diode D4 and one end of the inductor L2 are connected to the other end of the input power supply, the anodes of the diode D3 and the diode D4 are connected to the source of the switch tube S1 and the switch tube S2, the drain of the switch tube S1 is connected to the anode of the diode D1 and the other end of the inductor L1, the drain of the switch tube S2 is connected to the anode of the diode D2 and the other end of the inductor L2, and the cathode of the diode D1 is connected to the cathode of the diode D2; The step-up bidirectional Buck / boost power decoupling converter includes a switch tube S3, a switch tube S4, a decoupling inductor Ls and a decoupling capacitor Cs. One end of the decoupling inductor Ls is connected to the cathode of the diode D2 and one end of the capacitor C1, and the other end of the decoupling inductor Ls is connected to the drain of the switch tube S3 and the source of the switch tube S4. The drain of the switch tube S4 is connected to one end of the decoupling capacitor Cs, and the other end of the decoupling capacitor Cs is connected to the source of the switch tube S3 and the other end of the capacitor C1. The source of the switch tube S3 is connected to the source of the switch tube S2. The decoupling capacitor Cs and the first capacitor C1 are both thin film capacitors. The control method comprises: S1, get the input current i of the bridgeless PFC in and the output voltage of the bridgeless PFC; S2, set the clock frequency of the PWM controller. When the PWM controller clock arrives, PWM is at a high level, driving the switch tubes S1 and S2 to turn on; S3, obtaining a PWM signal based on the sampling current and the sampling voltage through reset integration comparison to control the switching tubes S1 and S2 of the PFC converter to turn off, specifically including: S31, the input current i of the bridgeless PFC in The input current is amplified in the input current amplifier and then connected to the input current detection resistor R of the bridgeless PFC converter. s Multiply them to get R s i in ; S32, based on the output voltage of the sampled bridgeless PFC and the reference voltage U ref Get the voltage error U m ; S33, the voltage error U m Divided into two paths, one path is voltage error U m With R s i in After difference is taken, it is input into the comparator; Another voltage error U m By integrating the integrator, we get , and input the integral result into the comparator, where i in is the input current of the bridgeless PFC, R s is the input current detection resistor of the bridgeless PFC converter, DT is the conduction time of the switch tube in one cycle; S34, establish the following comparison equation, and determine whether both sides of the comparison equation are equal. When both sides of the comparison equation are equal, the output value of the comparator is flipped, the switch tubes S1 and S2 are controlled to be turned off, and then the integrator is reset; when both sides of the comparison equation are not equal, execute step S2; ； S4. After the instantaneous value of the output voltage of the PFC converter is subtracted from the given value, it passes through the voltage error amplifier and then is summed with the DC bias to obtain a modulation signal, which is compared with the triangular wave carrier to generate a drive signal to control the switch tube of the power decoupling converter.

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