A single-stage non-isolated electrolytic capacitor-free LED drive circuit

Abstract

The present invention discloses a single-stage non-isolated type electrolytic capacitor-free LED driving circuit, comprising an LED driving circuit, wherein the LED driving circuit comprises a digital control chip, a contact K in , contact K cs , contact K io , rectifier diode D R1 , rectifier diode D R3 , inductor L1, inductor L2, auxiliary diode D1, switch tube S1, auxiliary diode D2, switch tube S2, capacitor C0, resistor R f , freewheeling diode D0, auxiliary energy storage capacitor voltage v cs , capacitor C8, main switch tube S m , rectifier diode D R2 , rectifier diode D R4 , drive circuit and power supply, the inductor L1 and the inductor L2 form a transformer T1. The present invention balances the difference between input power and output power by adding an auxiliary power balancing circuit on the basis of the flyback converter, suppresses the twice power frequency ripple of the output current, and reduces the voltage stress of the switch tube; the circuit adopts small-capacity film capacitors to achieve electrolytic capacitor-free, and only a small amount of pulsating power is converted twice, thereby improving the conversion efficiency of the circuit.

Description

Technical Field

[0001] The invention relates to the technical field of LED drive circuits, and in particular to a single-stage non-isolated electrolytic capacitor-free LED drive circuit. Background Art

[0002] In today's environment of advocating environmental protection, compared with traditional lighting sources such as incandescent lamps, LEDs are widely used in various occasions because of their advantages such as long service life, energy saving and high efficiency, environmental protection and harmlessness, and simple control.

[0003] Electrolytic capacitors are used in common LED driver power supplies to balance the twice power frequency pulsating power, but the life of the electrolytic capacitor cannot reach the service life of the LED lamp with a working time of nearly 50,000 hours. In addition, the temperature will seriously affect the working life of the electrolytic capacitor. For every 10°C increase in temperature, the service life of the electrolytic capacitor will be halved accordingly. When the working environment temperature of the LED driver power supply is too high, the internal electrolyte boils, which will cause permanent damage to the electrolytic capacitor. Therefore, in order to give full play to the excellent characteristics of LED lamps, it is necessary to remove the electrolytic capacitor in the LED driver power supply, thereby improving the life and reliability of the LED driver power supply.

[0004] In order to eliminate the influence of electrolytic capacitors on the life of LED driver power supply, the existing technologies can be summarized into two types. One is to improve the control strategy based on the existing circuit; the other is to innovate the topology to balance the pulsating power, thereby removing the electrolytic capacitor and reducing the capacitance by injecting harmonic current on the input side. However, the injection of harmonic current will bring about the problem of reduced power factor, so it is not suitable for occasions with strict requirements on power factor. Based on the characteristic that the LED luminous intensity is independent of the instantaneous current waveform, it is proposed to use a pulsating current to drive the LED on the output side, which effectively reduces the power pulsation between the input and output, reduces the capacitance, and has a high power factor. However, the current flowing through the LED contains twice the industrial frequency component, which will cause flicker and cause visual fatigue to the human eye.

[0005] However, the traditional LED driving circuit has the following disadvantages:

[0006] The current LED drive circuit has improved the circuit efficiency, but the control is relatively complex, which limits its application. Some LED drive circuits have high core utilization and efficiency, but require an additional inductor on the output side to reduce the output current ripple, which increases the circuit cost. Summary of the invention

[0007] The purpose of the present invention is to provide a single-stage non-isolated electrolytic capacitor-free LED driving circuit to solve the problem that the current LED driving circuit proposed in the above background technology has improved the circuit efficiency, but the control is relatively complicated, which limits its application. Some LED driving circuits have high magnetic core utilization and efficiency, but require an additional inductor on the output side to reduce the output current ripple, which increases the circuit cost.

[0008] To achieve the above object, the present invention provides the following technical solution: a single-stage non-isolated electrolytic capacitor-free LED driving circuit, comprising an LED driving circuit, wherein the LED driving circuit comprises a digital control chip, a contact K in , contact K cs , contact K io , rectifier diode D R1 , rectifier diode D R3 , inductor L1, inductor L2, auxiliary diode D1, switch tube S1, auxiliary diode D2, switch tube S2, capacitor C0, resistor R f , freewheeling diode D0, auxiliary energy storage capacitor voltage v cs , capacitor C8, main switch tube S m , rectifier diode D R2 , rectifier diode D R4 , drive circuit and power supply, the inductor L1 and the inductor L2 form a transformer T1, one end of the power supply and the rectifier diode D R4 One end of the rectifier diode D R1 One end of the rectifier diode D is connected R1 The other end is connected to the rectifier diode D R3 One end of the inductor L1, one end of the inductor L2, one end of the capacitor C0 and the resistor R f One end of the rectifier diode D is connected R3 The other end of the power supply and the other end of the rectifier diode D R2 One end of the rectifier diode D is connected R1 With the rectifier diode D R3 The connection point and contact K in The other end of the inductor L1 is connected to one end of the auxiliary diode D1 and the main switch tube S m The other end of the auxiliary diode D1 is connected to one end of the switch tube S1, one end of the switch tube S1 is connected to one end of the auxiliary diode D2, the other end of the auxiliary diode D2 is connected to one end of the switch tube S2, the other end of the switch tube S2 is respectively connected to the other end of the inductor L2 and one end of the freewheeling diode D0, the other end of the freewheeling diode D0, the capacitor C o The other end and resistor R f The other end is connected to the contact Kio connection, the main switch tube S m The other end of capacitor C8 and the auxiliary energy storage capacitor voltage v cs The other end is connected to the contact K cs connect.

[0009] As a preferred technical solution of the present invention, the contact K in The other end, contact K cs The other end and contact K in The other end of each of the two switches is connected to one end of the digital control chip, the other end of the digital control chip is connected to one end of the drive circuit, and the other end of the drive circuit is respectively connected to one end of the switch tube S1, one end of the switch tube S2 and the main switch tube S m one end.

[0010] As a preferred technical solution of the present invention, the digital control chip includes input voltage sampling, energy storage capacitor voltage average value collection, output current sampling, power size judgment, capacitor C8 average voltage control, output constant current control, switch Q m , switch Q1 and switch Q2, the two ends of the input voltage sampling are respectively connected to the power size judgment and contact K in The energy storage capacitor voltage average value is collected and connected to the capacitor C8 average voltage control and contact K cs connection, the output current sampling is respectively connected with the output constant current control and the contact K io The average voltage control end of the capacitor C8 is connected to one end of the switch Q1 and one end of the switch Q2 respectively, and the output constant current control end is connected to the switch Q m one end of the .

[0011] As a preferred technical solution of the present invention, the switch Q1 is connected to the switch tube S1 through a driving circuit, and the switch Q2 is connected to the switch tube S2 through a driving circuit. m Through the driving circuit and the main switch tube S m connect.

[0012] As a preferred technical solution of the present invention, the power size judgment includes P in >P o and P in and P o .

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. On the basis of the flyback converter, an auxiliary power balancing circuit is added to balance the difference between input power and output power, and the voltage spike caused by the transformer leakage inductance is absorbed, thereby suppressing the twice power frequency ripple of the output current and reducing the voltage stress of the switch tube;

[0015] 2. The circuit uses small-capacity film capacitors to replace electrolytic capacitors, thus achieving electrolytic capacitor-free operation. Since only a small amount of pulsating power needs to be converted twice through the auxiliary power balancing circuit, the conversion efficiency of the circuit is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a control block diagram of a single-stage electrolytic capacitor-free LED drive circuit of the present invention;

[0017] Figure 2 C of the present invention s The maximum, average, minimum value of the voltage across the two terminals and its capacitance

[0018] Size relationship curve graph;

[0019] Figure 3 This is a diagram of an experimental prototype of a single-stage electrolytic capacitor-free LED driving circuit of the present invention;

[0020] Figure 4 This is the main experimental waveform diagram of the electrolytic capacitor-free LED driving circuit of the present invention;

[0021] Figure 5 The switch tube driving waveform and capacitor voltage v of the present invention are cs Experimental waveform diagram of

[0022] Figure 6 This is the main working waveform diagram of the present invention when Pin>Po;

[0023] Figure 7 This is the main working waveform diagram of the present invention when Pin<Po. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] See also Figure 1-7 The present invention provides a single-stage non-isolated electrolytic capacitor-free LED driving circuit, including an LED driving circuit, the LED driving circuit including a digital control chip, a contact K in , contact K cs, contact K io , rectifier diode D R1 , rectifier diode D R3 , inductor L1, inductor L2, auxiliary diode D1, switch tube S1, auxiliary diode D2, switch tube S2, capacitor C0, resistor R f , freewheeling diode D0, auxiliary energy storage capacitor voltage v cs , capacitor C8, main switch tube S m , rectifier diode D R2 , rectifier diode D R4 , drive circuit and power supply, inductor L1 and inductor L2 form transformer T1, one end of the power supply and rectifier diode D R4 One end of the rectifier diode D R1 One end of the rectifier diode D R1 The other end is connected to the rectifier diode D R3 One end of the inductor L1, one end of the inductor L2, one end of the capacitor C0 and the resistor R f One end of the rectifier diode D R3 The other end of the power supply and the other end of the rectifier diode D R2 One end of the rectifier diode D R1 With the rectifier diode D R3 The connection point and contact K in The other end of the inductor L1 is connected to one end of the auxiliary diode D1 and the main switch tube S m The other end of the auxiliary diode D1 is connected to one end of the switch tube S1, one end of the switch tube S1 is connected to one end of the auxiliary diode D2, the other end of the auxiliary diode D2 is connected to one end of the switch tube S2, the other end of the switch tube S2 is respectively connected to the other end of the inductor L2 and one end of the freewheeling diode D0, the other end of the freewheeling diode D0, the capacitor C o The other end and resistor R f The other end is connected to the contact K io Connection, main switch tube S m The other end of capacitor C8 and the auxiliary energy storage capacitor voltage v cs The other end is connected to the contact K cs connect.

[0026] Contact K in The other end, contact K cs The other end and contact K in The other end of each is connected to one end of the digital control chip, the other end of the digital control chip is connected to one end of the drive circuit, and the other end of the drive circuit is respectively connected to one end of the switch tube S1, one end of the switch tube S2 and the main switch tube S m one end.

[0027] The digital control chip includes input voltage sampling, energy storage capacitor voltage average value collection, output current sampling, power size judgment, capacitor C8 average voltage control, output constant current control, switch Q m , switch Q1 and switch Q2, the two ends of the input voltage sampling are respectively connected to the power size judgment and contact K in The average voltage of the energy storage capacitor is collected and connected to the average voltage control of capacitor C8 and contact K cs Connection, output current sampling and output constant current control and contact K io The average voltage control end of capacitor C8 is connected to one end of switch Q1 and one end of switch Q2 respectively, and the output constant current control end is connected to switch Q m one end of the .

[0028] The switch Q1 is connected to the switch tube S1 through the driving circuit, and the switch Q2 is connected to the switch tube S2 through the driving circuit. m Through the driving circuit and the main switch tube S m connect.

[0029] Power size judgment includes P in >P o and P in and P o .

[0030] In the present invention, in conjunction with the specification Figure 2 , assuming that the power factor and efficiency of the LED driver are both 1, when the output power P o When the value is constant, the auxiliary energy storage capacitor capacity C is derived according to the relationship between instantaneous input power and output power. s And the output power P o The relationship between the auxiliary energy storage capacitor voltage v cs The relationship over time is:

[0031]

[0032] Where: ΔV cs is the capacitance, C s Voltage ripple value; V cs_max is the capacitance C s The maximum voltage; then the auxiliary energy storage capacitor C s The minimum and average voltages are:

[0033]

[0034] P in >P o Situation: To ensure that the circuit always works in DCM mode, the duration of each stage in the switching cycle should satisfy the following relationship:

[0035] Δt1+Δt2+Δt3<T s ,

[0036] The primary inductor L1 must meet the following conditions:

[0037]

[0038] P in <P o In order to ensure that the circuit always works in DCM mode, the duration of each stage in the switching cycle should satisfy the following relationship:

[0039] Δt1+Δt2+Δt3+Δt4<T s ,

[0040] The primary inductor L1 must meet the following conditions:

[0041]

[0042] Where A(t) is expressed as:

[0043]

[0044] In conjunction with the instruction manual Figure 3 The main parameters of the prototype are shown in Table 1. The parameter design meets the circuit working in DCM mode and the constraints. The main components are selected as follows: the main switch tube Sm, auxiliary switch tubes S1 and S2 are FQPF10N60C; auxiliary diodes D1 and D2, freewheeling diode D o And the rectifier diode D R 1-D R4 HER506 was used in all cases;

[0045] Table 1 Main parameters of the prototype

[0046]

[0047]

[0048] In conjunction with the instruction manual Figure 4 , input voltage v in 、Input current i in , auxiliary energy storage capacitor voltage v cs And the output current i o The experimental waveform shows that the input voltage and input current are basically in phase, and the circuit has a high power factor. When the input voltage changes in the range of 90-135V, the auxiliary energy storage capacitor C sThe voltage at both ends is in the form of pulsating voltage, and the average voltage is stable, which balances the difference between input power and output power. The low-frequency ripple of the output current is reduced to less than 20%, which is consistent with the theoretical analysis.

[0049] In conjunction with the instruction manual Figure 5 , under power frequency, the auxiliary energy storage capacitor voltage v cs And the switch tube S m , driving voltage u of S1 and S2 gsm 、u gs1 and u gs2 The experimental waveform shows that P in >P o When the main switch tube S m , the auxiliary switch tube S1 is turned on, the auxiliary switch tube S2 remains off, and the capacitor C s Charging, storing excess input energy, P in <P o When the main switch tube S m , the auxiliary switch tube S2 is turned on, the auxiliary switch tube S1 remains off, and the capacitor C s Release energy to the load. It can be seen that when S1 and S2 are switched, the capacitor voltage peaks and valleys occur. Since the switching moment is when the input instantaneous power is equal to the output power, the grid-side current i in There is no transient current fluctuation, which is consistent with the theoretical analysis;

[0050] In conjunction with the instruction manual Figure 6 And the instruction manual Figure 7 , respectively P in >Po、P in Experimental waveforms of key points of the circuit at the switching frequency when <Po, including u gsm 、u gs1 and u gs2 And the transformer primary inductance current i p , secondary current i s , diode D1, current i D1 and diode D2 current i D2 It can be seen that when Pin>Po, after the main switch tube Sm is turned off, the auxiliary switch tube S2 remains on for a period of time. p Decline, i D1 with i p Equal in size, capacitor C s Stores excess input energy; when P in >P o When the main switch tube S m After shutdown, i p Linearly decreases to 0, the auxiliary switch tube S2 is turned on, and during this period, ip rises linearly, i D2 with i sEqual in size, capacitor C s Energy is released and the output current ripple is compensated. In both modes, the circuit works in discontinuous mode. The experimental results are consistent with the theoretical analysis.

[0051] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A single-stage non-isolated electrolytic capacitor-free LED driving circuit, comprising an LED driving circuit, characterized in that: The LED driving circuit includes a digital control chip, a contact K in , contact K cs , contact K io , rectifier diode D R1 , rectifier diode D R3 , inductor L1, inductor L2, auxiliary diode D1, switch tube S1, auxiliary diode D2, switch tube S2, capacitor C0, resistor R f , freewheeling diode D0, auxiliary energy storage capacitor voltage v cs , capacitor C8, main switch tube S m , rectifier diode D R2 , rectifier diode D R4 , drive circuit and power supply, the inductor L1 and the inductor L2 form a transformer T1, one end of the power supply and the rectifier diode D R4 One end of the rectifier diode D R1 One end of the rectifier diode D is connected R1 The other end is connected to the rectifier diode D R3 One end of the inductor L1, one end of the inductor L2, one end of the capacitor C0 and the resistor R f One end of the rectifier diode D is connected R3 The other end of the power supply and the other end of the rectifier diode D R2 One end of the rectifier diode D is connected R1 With the rectifier diode D R3 The connection point and contact K in The other end of the inductor L1 is connected to one end of the auxiliary diode D1 and the main switch tube S m The other end of the auxiliary diode D1 is connected to one end of the switch tube S1, one end of the switch tube S1 is connected to one end of the auxiliary diode D2, the other end of the auxiliary diode D2 is connected to one end of the switch tube S2, the other end of the switch tube S2 is respectively connected to the other end of the inductor L2 and one end of the freewheeling diode D0, the other end of the freewheeling diode D0, the capacitor C o The other end and resistor R f The other end is connected to the contact K io connection, the main switch tube S m The other end of capacitor C8 and the auxiliary energy storage capacitor voltage v cs The other end is connected to the contact K cs connect.

2. A single-stage non-isolated electrolytic capacitor-free LED drive circuit according to claim 1, characterized in that: The contact K in The other end, contact K cs The other end and contact K in The other end of each of the two switches is connected to one end of the digital control chip, the other end of the digital control chip is connected to one end of the drive circuit, and the other end of the drive circuit is respectively connected to one end of the switch tube S1, one end of the switch tube S2 and the main switch tube S m one end.

3. The single-stage non-isolated electrolytic capacitor-free LED driving circuit according to claim 1, characterized in that: The digital control chip includes input voltage sampling, energy storage capacitor voltage average value collection, output current sampling, power size judgment, C8 average voltage control, output constant current control, switch Q m , switch Q1 and switch Q2.

4. The single-stage non-isolated electrolytic capacitor-free LED driving circuit according to claim 3, characterized in that: The two ends of the input voltage sampling are respectively connected to the power size judgment and contact K in The energy storage capacitor voltage average value is collected and connected to the C8 average voltage control and contact K cs connect.

5. The single-stage non-isolated electrolytic capacitor-free LED driving circuit according to claim 3, characterized in that: The output current sampling is respectively connected to the output constant current control and the contact K io The average voltage control end of C8 is connected to one end of switch Q1 and one end of switch Q2 respectively, and the output constant current control end is connected to switch Q m one end of the .

6. The single-stage non-isolated electrolytic capacitor-free LED driving circuit according to claim 3, characterized in that: The switch Q1 is connected to the switch tube S1 through a driving circuit, and the switch Q2 is connected to the switch tube S2 through a driving circuit. m Through the driving circuit and the main switch tube S m connect.

7. The single-stage non-isolated electrolytic capacitor-free LED driving circuit according to claim 3, characterized in that: The power size determination includes P in >P o and P in and P o .

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