Charging and discharging control circuit, charging and discharging control method thereof and LED driving circuit

Abstract

The invention provides a charging and discharging control circuit, a charging and discharging control method thereof and an LED driving circuit. And the charging and discharging control circuit is used for controlling an input capacitor in the LED driving circuit. The charging and discharging control circuit comprises a switching circuit and a driving circuit. The switching circuit comprises a first switching tube and is used for being coupled with the second end of the input capacitor. The driving circuit is used for being coupled to the second end of the input capacitor, the driving circuit is coupled to the switching circuit, and the driving circuit is used for generating a first driving signal according to the detection signal to drive the first switching tube. When the bus voltage is larger than the voltage of the input capacitor, the drive circuit controls the first switching tube to be switched off. When the bus voltage is smaller than the difference value between the voltage of the input capacitor and the first preset voltage, the driving circuit controls the first switching tube to be switched on. According to the charging and discharging control circuit, the charging and discharging control method thereof and the LED driving circuit, the harmonic wave requirement of the new national standard is met while the power factor is improved, and the good system reliability is achieved.

Description

Technical Field

[0001] The invention belongs to the field of power electronics, relates to LED driving technology, and in particular to a charge and discharge control circuit and a charge and discharge control method thereof, and an LED driving circuit. Background Art

[0002] LED lighting is a green, energy-saving and environmentally friendly lighting method, and has become the most mainstream lighting method. Since the LED diodes used in LED lighting require direct current to drive, and the current flowing through the LED diodes is related to the brightness, therefore, a driving circuit is often required between the AC mains and the LED diodes to convert the AC power into direct current and ensure that the current flowing through the LED diodes is constant, so as to ensure the constant brightness of the LED lighting.

[0003] With the continuous development of LED technology, the performance requirements for LED drivers are getting higher and higher. The new national standards put forward the following requirements: (1) Displacement factor DF (i.e. Displacement factor) requires that the input power is between 5W and 10W, DF ≥ 0.5, and the input power is between 10W and 25W, DF ≥ 0.7. (2) Harmonic THD (i.e. Total Harmonic Distortion), the input power is 5W to 25W, the input current waveform meets the requirements of I in> 5% before 60°, I in reaches the peak before 65°, I in> 5% before 90°, the third harmonic current is expressed as a percentage of the fundamental current, not exceeding 86%, and the fifth harmonic current does not exceed 61%.

[0004] However, it is difficult for the existing LED driving circuit to effectively improve the DF value and meet the harmonic requirements. This can be achieved by reducing the capacitance of the input electrolytic capacitor or reducing the electrolytic capacitor and using a valley-filling circuit, which will lead to the reduction of the life of the electrolytic capacitor and the increase of the output LED ripple, resulting in flicker and other problems. Therefore, it is necessary to develop a simpler and more reliable circuit and method to meet the new national standard LED switch driving circuit for input power of 5W to 25W.

[0005] like Figure 1The figure shows a schematic diagram of the circuit structure of an LED driving circuit in the prior art. In a conventional switch-type driving circuit, the input AC power supply is generally connected to a large capacitor C1 after full-wave rectification to obtain a DC voltage with a relatively straight waveform. This circuit is a combination of a nonlinear element and an energy storage element. When the input voltage Vin is greater than the voltage on the capacitor C1, the capacitor C1 is charged. When the input voltage Vin is less than the voltage on the capacitor C1, the charging ends and the cycle repeats. Therefore, although the input AC voltage is sinusoidal, the input AC current waveform is severely distorted and pulse-shaped. As a result of the severe distortion of the input current, the power factor of the LED is less than 0.6 when it is working, and the input current waveform cannot meet the requirements of I in>5% before 60° and I in reaching its peak before 65°. Figure 2 In the waveform above, I in>5% before 90°, and the third harmonic current expressed as a percentage of the fundamental current will exceed 86%, and the fifth harmonic current will exceed 61%. The improvement method is to reduce the electrolytic capacitor C1, which can meet the input current waveform I in>5% before 60° and I in reaches the peak before 65°, such as Figure 2 The waveform is shown below. However, the problem is that the power frequency ripple voltage on the electrolytic capacitor C1 increases, which causes power frequency ripple on the output LED, thus causing flicker. In addition, as the capacitance of the electrolytic capacitor decreases, the ripple current capacity of the electrolytic capacitor decreases, or the ESR (equivalent resistance) of the electrolytic capacitor increases, the loss on the electrolytic capacitor increases, causing the electrolytic capacitor to heat up and reduce its usable life, ultimately resulting in a reduction in the life of the LED lamp.

[0006] like Figure 3 As shown in FIG. 1 , the prior art provides another circuit structure diagram of an LED driving circuit. Figure 1 The capacitor C1 in Figure 3The three diodes D1, D2, D3 and two equal-value capacitors C1 and C2 shown in the figure can be replaced to greatly improve the distortion of the input current. The valley-filling passive PFC circuit composed of diodes D1 to D3, capacitors C1 and C2 is also called a partial or incomplete filtering circuit. When the AC line voltage is high, capacitors C1 and C2 are charged in series due to the connection of diode D1. As long as the AC voltage is higher than the voltage on C1 and C2, the line current will pass through the load. Once the line voltage amplitude drops below the charging voltage [VAC(PEAK) / 2] on each capacitor, diode D1 is reverse biased, while diodes D2 and D3 are turned on, and C1 and C2 are discharged through the load in parallel. At this time, the AC current no longer supplies power to the load. The output voltage (Vo) waveform of this incomplete filtering valley-filling circuit is pulsating and extremely unsmooth, but the power frequency input current is trimmed, and the conduction angle reaches 120°, that is, it increases from 30° to 150°, and from 210° to 330°. The use of valley-filling circuits can make the line power factor higher than 0.9, the 3rd and 5th harmonic currents are reduced to below 20% and 16% respectively, and the total harmonic distortion (THD) is reduced to 30%. When the valley-filling circuit is used in LED lamps, although the line power factor can reach above 0.8 and the harmonic current is greatly attenuated, the DC output voltage it generates is extremely uneven, so there is also power frequency ripple on the output LED, causing flicker, and the circuit is relatively complex, with an additional electrolytic capacitor C2 and three diodes D1, D2, and D3, and the cost of this solution is relatively high.

[0007] In view of this, it is necessary to provide a new structure or control method to solve at least part of the above problems. Summary of the invention

[0008] In view of one or more problems in the prior art, the present invention provides a charge and discharge control circuit and a charge and discharge control method thereof and an LED drive circuit.

[0009] According to one aspect of the present invention, a charge and discharge control circuit is disclosed. The charge and discharge control circuit is used to control the input capacitance in the LED drive circuit. The charge and discharge control circuit includes:

[0010] A switch circuit includes a first switch tube, a first end of which is used to couple to the second end of the input capacitor, and a second end of which is used to couple to the ground; and

[0011] A driving circuit, whose input end is used to couple the second end of the input capacitor, and whose output end is coupled to the switching circuit, is used to generate a first driving signal to drive the first switching tube according to a detection signal representing the difference between the bus voltage and the voltage of the input capacitor; when the bus voltage is greater than the voltage of the input capacitor, the driving circuit controls the first switching tube to turn off and charge the input capacitor; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the driving circuit controls the first switching tube to turn on and enable the input capacitor to power the LED driving circuit.

[0012] In a preferred embodiment, the switch circuit comprises:

[0013] A first diode, an anode of which is coupled to the second end of the input capacitor, and a cathode of which is coupled to the ground; and

[0014] The first switch tube has a first end coupled to the anode of the first diode, a second end coupled to the cathode of the first diode, and a control end coupled to the output end of the driving circuit.

[0015] In a preferred embodiment, the first end of the first switch tube is used to couple the anode of the first diode, the second end of the first switch tube is used to couple the cathode of the first diode, and the control end of the first switch tube is coupled to the output end of the driving circuit; or,

[0016] The drain of the first switch tube is coupled to the ground, the source of the first switch tube is coupled to the second end of the input capacitor, and the control end of the first switch tube is coupled to the output end of the driving circuit.

[0017] In a preferred embodiment, the drive circuit includes a comparison circuit, which is used to generate a first drive signal based on a detection signal; when the bus voltage is greater than the voltage of the input capacitor, the drive circuit controls the first switch tube to be turned off; when the bus voltage is less than the difference between the voltage of the input capacitor and a preset voltage, the drive circuit controls the first switch tube to be turned on.

[0018] In a preferred embodiment, the driving circuit comprises:

[0019] A first comparator, wherein a non-inverting input terminal of the comparator is coupled to the ground, an inverting input terminal of the comparator is coupled to the positive electrode of a first reference source, a negative electrode of the first reference source is coupled to the second end of the input capacitor, and the first reference source is used to provide a first voltage;

[0020] A second comparator, whose non-inverting input terminal is coupled to the second end of the input capacitor, whose inverting input terminal is coupled to the positive electrode of a second reference source, whose negative electrode is coupled to the ground, and the second reference source is used to provide a second voltage;

[0021] A third comparator, whose non-inverting input terminal is coupled to the second terminal of the input capacitor, whose inverting input terminal is coupled to the positive electrode of a third reference source, whose negative electrode is coupled to the ground, and the third reference source is used to provide a third voltage;

[0022] A first trigger, a set terminal of which is coupled to the output terminal of the second comparator, and a reset terminal of which is coupled to the output terminal of the first comparator;

[0023] an AND gate, a first input terminal of which is coupled to the output terminal of the third comparator, and a second input terminal of which is coupled to the output terminal of the first trigger; and

[0024] The second trigger has a set end coupled to the output end of the first comparator, a reset end coupled to the output end of the AND gate, and an output end coupled to the first switch tube.

[0025] In a preferred embodiment, in the preliminary stage of the charge and discharge cycle of the input capacitor, the drive circuit controls the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, the drive circuit controls the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is less than the preset current, the drive circuit controls the first switch tube to turn off; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the drive circuit controls the first switch tube to turn on.

[0026] In a preferred embodiment, the first switch tube is an N-type metal oxide semiconductor field effect tube.

[0027] According to another aspect of the present invention, an LED driving circuit is disclosed, the LED driving circuit comprising the charging and discharging control circuit as described in any one of the above items, the charging and discharging control circuit being used to control the charging and discharging of an input capacitor.

[0028] According to another aspect of the present invention, a charge and discharge control method is disclosed. The charge and discharge control method is used to control a charge and discharge control circuit. The charge and discharge control circuit includes a switch circuit and a drive circuit. The switch circuit includes a first switch tube. The first end of the switch circuit is used to couple to the second end of the input capacitor. The second end of the switch circuit is used to couple to the ground. The output end of the drive circuit is coupled to the switch circuit. The charge and discharge control method includes:

[0029] Acquire a detection signal representing a difference between a bus voltage and a voltage of an input capacitor;

[0030] A first drive signal is generated according to the detection signal to drive the first switch tube; when the bus voltage is greater than the voltage of the input capacitor, the first switch tube is controlled to be turned off and the input capacitor is charged; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the first switch tube is controlled to be turned on and the input capacitor supplies power to the LED drive circuit.

[0031] In a preferred embodiment, the step of generating a first drive signal according to a detection signal to drive the first switch tube specifically includes: in a preliminary stage of the charge and discharge cycle of the input capacitor, controlling the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than a preset current, controlling the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, controlling the first switch tube to turn off; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, controlling the first switch tube to turn on.

[0032] The present invention proposes a charge and discharge control circuit and a charge and discharge control method thereof and an LED driving circuit. The charge and discharge control circuit is used to control the input capacitor in the LED driving circuit. The charge and discharge control circuit includes a switch circuit and a driving circuit. The switch circuit includes a first switch tube, the first end of the switch circuit is used to couple the second end of the input capacitor, and the second end of the switch circuit is used to couple to the ground. The input end of the driving circuit is used to couple the second end of the input capacitor, the output end of the driving circuit is coupled to the switch circuit, and the driving circuit is used to generate a first drive signal to drive the first switch tube according to a detection signal representing the difference between the bus voltage and the voltage of the input capacitor. When the bus voltage is greater than the voltage of the input capacitor, the driving circuit controls the first switch tube to turn off and charge the input capacitor. When the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the driving circuit controls the first switch tube to turn on and the input capacitor supplies power to the LED driving circuit. The charge and discharge control circuit and the charge and discharge control method thereof and the LED driving circuit proposed by the present invention meet the harmonic requirements of the new national standard while improving the power factor, and have good system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are used to provide a further understanding of the present invention and are used together with the description to explain the embodiments of the present invention, but do not constitute a limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 A circuit structure schematic diagram of a LED driving circuit in the prior art is shown;

[0035] Figure 2 A signal waveform schematic diagram of an LED driving circuit in the prior art is shown;

[0036] Figure 3 Another circuit structure schematic diagram of an LED driving circuit in the prior art is shown;

[0037] Figure 4 A circuit structure schematic diagram of an LED driving circuit according to an embodiment of the present invention is shown;

[0038] Figure 5A circuit structure schematic diagram of an LED driving circuit according to another embodiment of the present invention is shown;

[0039] Figure 6 A circuit structure schematic diagram of a charge and discharge control circuit according to an embodiment of the present invention is shown;

[0040] Figure 7 A schematic diagram of signal waveforms of an LED driving circuit according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0041] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0042] The description in this section is only for several typical embodiments, and the present invention is not limited to the scope of the embodiments. The combination of different embodiments, the mutual replacement of some technical features in different embodiments, and the mutual replacement of the same or similar prior art means with some technical features in the embodiments are also within the scope of the description and protection of the present invention.

[0043] "Coupled" or "connected" in the specification includes both direct connection and indirect connection. Indirect connection is a connection through an intermediate medium, such as a connection through an electrically conductive medium such as a conductor, wherein the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or a connection through an intermediate circuit or component described in the embodiments in the specification; an indirect connection may also include a connection through other active or passive devices on the basis of achieving the same or similar functions, such as a connection through circuits or components such as switches, signal amplification circuits, and follower circuits. "Multiple" or "many" means two or more. In addition, in the present invention, words such as first and second are mainly used to distinguish one technical feature from another technical feature, and do not necessarily require or imply that there is a certain actual relationship or order between these technical features.

[0044] like Figure 4As shown, an embodiment of the present invention discloses an LED driving circuit. The LED driving circuit includes a rectifier circuit, an input capacitor C1, a charge and discharge control circuit 1 and a switch type driving circuit 2. The first end of the input capacitor C1 is coupled to the rectifier circuit, one end of the charge and discharge control circuit 1 is coupled to the second end of the input capacitor C1, and the other end of the charge and discharge control circuit 1 is coupled to the ground. The charge and discharge control circuit is used to control the charge and discharge process of the input capacitor C1 in the LED driving circuit. The first end of the switch type driving circuit 2 is coupled to the first end of the input capacitor C1, and the second end of the switch type driving circuit 2 is coupled to the ground. The switch type driving circuit 2 is coupled to the LED load, and the switch type driving circuit 2 is used to control the operation of the LED load. The charge and discharge control circuit 1 includes a switch circuit and a driving circuit. The switch circuit includes a first switch tube, the first end of the switch circuit is used to couple to the second end of the input capacitor C1, and the second end of the switch circuit is used to couple to the ground. The input end of the driving circuit is used to couple to the second end of the input capacitor C1, and the output end of the driving circuit is coupled to the switch circuit. The driving circuit is used to generate a first driving signal to drive the first switch tube according to the detection signal, and the detection signal represents the difference between the bus voltage and the voltage of the input capacitor. When the bus voltage is greater than the voltage of the input capacitor, the driving circuit controls the first switch tube to turn off and charge the input capacitor. When the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the driving circuit controls the first switch tube to turn on and the input capacitor supplies power to the LED driving circuit.

[0045] In one embodiment, if Figure 5 As shown, the charge and discharge control circuit 1 includes a switching circuit and a driving circuit 11. The switching circuit includes a first diode D1 and a first switch tube Q1. The anode of the first diode D1 is used to couple the second end of the input capacitor C1, and the cathode of the first diode D1 is used to couple to the ground. The first end of the first switch tube Q1 is coupled to the anode of the first diode D1, and the second end of the first switch tube Q1 is coupled to the cathode of the first diode. The input end of the driving circuit 11 is used to couple the second end of the input capacitor C1, and the output end of the driving circuit 11 is coupled to the control end of the first switch tube Q1. The driving circuit 11 is used to generate a first driving signal according to a detection signal to control the switching state of the first switch tube Q1. In a specific embodiment, the detection signal is the difference between the bus voltage V_bus and the input capacitor voltage V_cap. When the bus voltage is greater than the voltage of the input capacitor, the driving circuit controls the first switch tube to turn off and charges the input capacitor. When the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the driving circuit controls the first switch tube to turn on and enables the input capacitor to power the LED driving circuit. As shown Figure 5As shown, the detection signal is the voltage at the second terminal of the input capacitor C1. In another embodiment, the detection signal is the voltage divided by the difference between the bus voltage V_bus and the voltage V_cap of the input capacitor. In yet another embodiment, the detection signal is a signal obtained by calculating or processing the difference between the bus voltage V_bus and the voltage V_cap of the input capacitor. In one embodiment of the present invention, the drive circuit includes a comparison circuit, which is used to generate a first drive signal based on the detection signal. If the conduction voltage drop of the first diode is ignored, when the bus voltage is greater than the voltage of the input capacitor, the drive circuit controls the first switch tube to turn off. When the bus voltage is less than the difference between the voltage of the input capacitor and the preset voltage, the drive circuit controls the first switch tube to turn on. In the LED drive circuit based on the present invention, the current width is increased, the effective power is increased, and thus the power factor PF is improved, while also meeting the sub-harmonic requirements of the new national standard.

[0046] In one embodiment, in the LED driving circuit, when the bus voltage V_bus is greater than the voltage V_cap of the input capacitor C1, the charge and discharge control circuit charges the input capacitor C1 through the diode in the LED driving circuit, and controls the first switch tube Q1 to be turned off at the same time. When the bus voltage V_bus is less than the voltage V_cap of the input capacitor C1, the charge and discharge control circuit controls the first switch tube Q1 to remain in the off state. Since the input capacitor C1 cannot provide energy to the switch-type driving circuit, the switch-type driving circuit obtains energy from the input voltage VAC, so the input current I in generates a tail. When the bus voltage V_bus is less than the difference between the voltage of the input capacitor C1 and the first preset voltage, the charge and discharge control circuit controls the switch tube Q1 to be turned on, and the input capacitor C1 provides energy to the switch-type driving circuit to achieve a flicker-free function.

[0047] In another embodiment, the LED driver chip includes a charge and discharge control circuit, the LED driver chip is provided with a ground pin GND, and a first diode is externally connected in series between the input capacitor C1 and the ground pin GND. The switch circuit includes a first switch tube, the first end of the first switch tube is used to couple the anode of the first diode, the second end of the first switch tube is used to couple the cathode of the first diode, and the control end of the first switch tube is coupled to the output end of the drive circuit. In another embodiment, the switch circuit includes a first switch tube, the drain of the first switch tube is used to couple to the ground, the source of the first switch tube is used to couple the second end of the input capacitor, and the control end of the first switch tube is coupled to the output end of the drive circuit. The parasitic diode of the first switch tube can provide a charging path for the input capacitor C1 and can prevent the discharge of the input capacitor C1, so there is no need to set up a diode separately.

[0048] In one embodiment of the present invention, Figure 6As shown, the charge and discharge control circuit includes a switch circuit and a drive circuit 11. The switch circuit includes a first diode D1 and a first switch tube Q1. The drive circuit 11 includes a first comparator U1, a second comparator U2, a third comparator U3, a first trigger U4, an AND gate U5, a second trigger U6, and a driver U7. The non-inverting input terminal of the first comparator U1 is coupled to the ground, the inverting input terminal of the first comparator U1 is coupled to the positive electrode of the first reference source V1, the negative electrode of the first reference source V1 is used to couple to the second end of the input capacitor C1, and the first reference source V1 is used to provide a first voltage V1. The non-inverting input terminal of the second comparator U2 is used to couple to the second end of the input capacitor C1, the inverting input terminal of the second comparator U2 is coupled to the positive electrode of the second reference source V2, the negative electrode of the second reference source V2 is used to couple to the ground, and the second reference source V2 is used to provide a second voltage V2. The non-inverting input terminal of the third comparator U3 is coupled to the second terminal of the input capacitor C1, the inverting input terminal of the third comparator U3 is coupled to the positive terminal of the third reference source V3, the negative terminal of the third reference source V3 is coupled to the ground, and the third reference source V3 is used to provide a third voltage V3. The set terminal of the first trigger U4 is coupled to the output terminal of the second comparator U2, and the reset terminal of the first trigger U4 is coupled to the output terminal of the first comparator U1. The first input terminal of the AND gate U5 is coupled to the output terminal of the third comparator U3, and the second input terminal of the AND gate U5 is coupled to the output terminal of the first trigger U4. The set terminal of the second trigger U6 is coupled to the output terminal of the first comparator U1, the reset terminal of the second trigger U6 is coupled to the output terminal of the AND gate U5, the output terminal of the second trigger U6 is coupled to the input terminal of the driver U7, and the output terminal of the driver U7 is coupled to the control terminal of the first switch tube Q1. In a preferred embodiment, the first switch tube Q1 is an N-type metal oxide semiconductor field effect transistor (NMOS tube for short). A drain of the first switch tube Q1 is coupled to the ground, a source of the first switch tube Q1 is coupled to the second end of the input capacitor C1 , and a gate of the first switch tube Q1 is coupled to the output end of the driving circuit.

[0049] In one embodiment, in the preliminary stage of the charge and discharge cycle of the input capacitor C1, the drive circuit controls the first switch tube to turn on. When the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, the drive circuit controls the first switch tube to turn on; in this process, a large current is ensured to pass through to achieve stable charging of the input capacitor. When the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is less than the preset current, the drive circuit controls the first switch tube to turn off. When the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the drive circuit controls the first switch tube to turn on.

[0050] In one embodiment, in combination Figure 6, the principle of the charge and discharge control circuit is as follows: in the first stage of the charge and discharge cycle of the input capacitor C1, the first switch tube Q1 is pre-operated in the open state, and the on-resistance of the first switch tube Q1 is Rdson. When the bus voltage V_bus is greater than the voltage V_Cap of the input capacitor, and when the voltage of the first switch tube (IQ1*Rdson) is greater than the second voltage V2 and less than the third voltage V3, after the comparison processing of the second comparator U2, the output signal U2_OUT of the second comparator is high, and the output signal U3_OUT of the third comparator U3 is low, and the output signal U4_OUT of the first trigger U4 is high. Among them, IQ1 is the current flowing through the first switch tube Q1. Since the two input signals of the AND gate U5 do not satisfy the two signals being high at the same time, the output signal of the AND gate U5 is low. The second trigger U6 maintains a high level and does not flip, so the Gate signal output by the driver U7 is high, so the first switch tube Q1 maintains an open state. The first voltage V1 is much larger than the second voltage V2 and the third voltage V3, and the third voltage V3 is larger than the second voltage V2. The second voltage V2 and the third voltage V3 are set to increase hysteresis and enhance the robustness of the logic for closing the first switch tube Q1.

[0051] In the second stage of the charge and discharge cycle of the input capacitor C1, when the voltage of the first switch tube (IQ1*Rdson) is greater than the third voltage V3, the output signal U3_OUT of the third comparator U3 is high, and at this time the output signal U4_OUT of the first trigger is high, and the two input signals of the AND gate U5 are both high, so the output signal of the AND gate U5 is flipped to a high level, so that the second trigger U6 is reset, and the output signal U6_OUT of the second trigger U6 is low, so the Gate signal is low, and the drive circuit controls the first switch tube Q1 to be turned off.

[0052] In the third stage of the charge and discharge cycle of the input capacitor C1, although the first switch tube Q1 is in the off state, since there is still a first diode D1 path, the input continues to charge the input capacitor C1 until the voltage of the input capacitor C1 is greater than or equal to the bus voltage V_bus. Since the first switch tube Q1 is still in the off state, the energy on the input capacitor C1 has no discharge path, so the energy stored in the input capacitor C1 is neither charged nor discharged, and the energy required by the switch type drive circuit comes from the input voltage VAC, so Figure 7 As shown, the input current I in during the Td1 period is maintained as a constant current. Figure 7 The figure also provides a schematic diagram of the signal waveforms of the Gate signal, the bus voltage V_bus, and the input capacitor voltage V_cap.

[0053] In the fourth stage of the charge and discharge cycle of the input capacitor C1, since the first switch tube Q1 is in the off state at the beginning, the bus voltage V_bus follows the input voltage to drop, V_source = V_bus-V_cap, so the second terminal voltage V_source of the input capacitor is reduced to a negative voltage. When the terminal voltage V_source drops to V_source+V1<0, the output signal U1_OUT of the first comparator U1 is high, and the second trigger U6 outputs a high level. At this time, U7 provides a high level Gate signal to drive the first switch tube Q1 to turn on, and the input capacitor C1 provides energy to the drive switch. When the drive circuit controls the opening of the first switch tube Q1 through the Gate signal, the Vsource voltage generates a large voltage mutation dv / dt, which will generate EMI interference, so the drive signal is required to provide a very slowly rising voltage to turn on the first switch tube Q1 and slow down the dv / dt of the terminal voltage Vsource. In one embodiment, the above four stages of the charge and discharge cycle of the input capacitor C1 follow the power frequency cycle to cycle back and forth.

[0054] Another embodiment of the present invention further discloses an LED driving circuit, the LED driving circuit comprising the charging and discharging control circuit as described in any one of the above items, the charging and discharging control circuit is used to control the charging and discharging process of the input capacitor. The charging and discharging control circuit and the LED driving circuit proposed by the present invention improve the power factor while meeting the harmonic requirements of the new national standard and having good system reliability.

[0055] Based on the LED driving circuit of the present invention, the input capacitor with a larger capacitance value can be maintained without affecting the life of the capacitor due to the reduction of the capacitance. In addition, compared with the valley filling circuit, the input ripple of the present invention is smaller, and the number of devices is less than the valley filling circuit. In addition, taking the first switch tube as an NMOS tube as an example, the source of the first switch tube of the present invention is not coupled to the reference ground like the conventional coupling method, but is coupled to the second end of the input capacitor. The voltage of the second end of the input capacitor is lower than the reference ground, so that the withstand voltage of the control end of the first switch tube is limited to 60V, which can reduce the withstand voltage of the first switch tube, reduce Rdson, thereby reducing the conduction loss, improving efficiency and reducing the chip area. In addition, the input capacitor C1 continues to maintain the charging loop. When a lightning surge is input, the input capacitor C1 can absorb energy well, reduce the impact of high-voltage devices, have better system reliability, and reduce the cost of lightning surge protection.

[0056] Another embodiment of the present invention further discloses a charge and discharge control method, which is used to control a charge and discharge control circuit, wherein the charge and discharge control circuit includes a switch circuit and a drive circuit, wherein the switch circuit includes a first switch tube, wherein the first end of the switch circuit is used to couple to the second end of the input capacitor, the second end of the switch circuit is used to couple to the ground, and the output end of the drive circuit is coupled to the switch circuit. The charge and discharge control method includes the following steps:

[0057] Acquire a detection signal representing a difference between a bus voltage and a voltage of an input capacitor;

[0058] A first drive signal is generated according to the detection signal to drive the first switch tube; when the bus voltage is greater than the voltage of the input capacitor, the first switch tube is controlled to be turned off and the input capacitor is charged; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the first switch tube is controlled to be turned on and the input capacitor supplies power to the LED drive circuit.

[0059] In another embodiment, the drive circuit obtains a detection signal representing the difference between the bus voltage and the voltage of the input capacitor. The drive circuit generates a first drive signal according to the detection signal to drive the first switch tube. When the bus voltage is greater than the voltage of the input capacitor, the drive circuit controls the first switch tube to turn off and charge the input capacitor. When the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the drive circuit controls the first switch tube to turn on and the input capacitor to power the LED drive circuit.

[0060] In one embodiment, the step of generating a first drive signal according to a detection signal to drive the first switch tube specifically includes: in a preliminary stage of the charge and discharge cycle of the input capacitor, controlling the first switch tube to turn on. When the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than a preset current, controlling the first switch tube to turn on. When the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, controlling the first switch tube to turn off. And when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, controlling the first switch tube to turn on.

[0061] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "non-inverting input terminal" and "inverting input terminal" in the logic controls involved in the specification or drawings can be interchanged or changed with each other, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic controls.

[0062] The description and application of the present invention here are illustrative, and it is not intended to limit the scope of the present invention to the above-mentioned embodiments. The effects or advantages involved in the specification may not be reflected in the actual experimental examples due to the uncertainty of specific condition parameters or other factors, and the effects or advantages are not used to limit the scope of the invention. The deformation and change of the embodiments disclosed here are possible, and the replacement of the embodiments and the various equivalent parts are well known to those of ordinary skill in the art. It should be clear to those skilled in the art that the present invention can be implemented in other forms, structures, arrangements, proportions, and with other components, materials and parts without departing from the spirit or essential features of the present invention. Other deformations and changes can be made to the embodiments disclosed here without departing from the scope and spirit of the present invention.

Claims

1. A charge and discharge control circuit for controlling the input capacitance in an LED drive circuit, characterized in that: The charge and discharge control circuit comprises: A switch circuit includes a first switch tube, a first end of which is used to couple to the second end of the input capacitor, and a second end of which is used to couple to the ground; and A driving circuit, whose input end is used to couple the second end of the input capacitor, and whose output end is coupled to the switching circuit, is used to generate a first driving signal to drive the first switching tube according to a detection signal representing the difference between the bus voltage and the voltage of the input capacitor; when the bus voltage is greater than the voltage of the input capacitor, the driving circuit controls the first switching tube to turn off and charge the input capacitor; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the driving circuit controls the first switching tube to turn on and enable the input capacitor to power the LED driving circuit.

2. The charge and discharge control circuit according to claim 1, characterized in that: The switch circuit comprises: A first diode, an anode of which is coupled to the second end of the input capacitor, and a cathode of which is coupled to the ground; and The first switch tube has a first end coupled to the anode of the first diode, a second end coupled to the cathode of the first diode, and a control end coupled to the output end of the driving circuit.

3. The charge and discharge control circuit according to claim 1, characterized in that: The first end of the first switch tube is used to couple to the anode of the first diode, the second end of the first switch tube is used to couple to the cathode of the first diode, and the control end of the first switch tube is coupled to the output end of the driving circuit; or, The drain of the first switch tube is coupled to the ground, the source of the first switch tube is coupled to the second end of the input capacitor, and the control end of the first switch tube is coupled to the output end of the driving circuit.

4. The charge and discharge control circuit according to claim 1, characterized in that: The driving circuit includes a comparison circuit, which is used to generate a first driving signal according to a detection signal; when the bus voltage is greater than the voltage of the input capacitor, the driving circuit controls the first switch tube to be turned off; when the bus voltage is less than the difference between the voltage of the input capacitor and a preset voltage, the driving circuit controls the first switch tube to be turned on.

5. The charge and discharge control circuit according to claim 1, characterized in that: The driving circuit comprises: A first comparator, wherein a non-inverting input terminal of the comparator is coupled to the ground, an inverting input terminal of the comparator is coupled to the positive electrode of a first reference source, a negative electrode of the first reference source is coupled to the second end of the input capacitor, and the first reference source is used to provide a first voltage; A second comparator, whose non-inverting input terminal is coupled to the second end of the input capacitor, whose inverting input terminal is coupled to the positive electrode of a second reference source, whose negative electrode is coupled to the ground, and the second reference source is used to provide a second voltage; A third comparator, whose non-inverting input terminal is coupled to the second terminal of the input capacitor, whose inverting input terminal is coupled to the positive electrode of a third reference source, whose negative electrode is coupled to the ground, and the third reference source is used to provide a third voltage; A first trigger, a set terminal of which is coupled to the output terminal of the second comparator, and a reset terminal of which is coupled to the output terminal of the first comparator; an AND gate, a first input terminal of which is coupled to the output terminal of the third comparator, and a second input terminal of which is coupled to the output terminal of the first trigger; and The second trigger has a set end coupled to the output end of the first comparator, a reset end coupled to the output end of the AND gate, and an output end coupled to the first switch tube.

6. The charge and discharge control circuit according to claim 1, characterized in that: In the preliminary stage of the charge and discharge cycle of the input capacitor, the drive circuit controls the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, the drive circuit controls the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is less than the preset current, the drive circuit controls the first switch tube to turn off; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the drive circuit controls the first switch tube to turn on.

7. The charge and discharge control circuit according to claim 3, characterized in that: The first switch tube is an N-type metal oxide semiconductor field effect tube.

8. An LED driving circuit, characterized in that: The LED driving circuit comprises the charge and discharge control circuit as claimed in any one of claims 1 to 7, and the charge and discharge control circuit is used to control the charge and discharge of the input capacitor.

9. A charge and discharge control method for controlling a charge and discharge control circuit, characterized in that: The charge and discharge control circuit includes a switch circuit and a drive circuit, the switch circuit includes a first switch tube, the first end of the switch circuit is used to couple to the second end of the input capacitor, the second end of the switch circuit is used to couple to the ground, and the output end of the drive circuit is coupled to the switch circuit; The charge and discharge control method comprises: obtaining a detection signal representing a difference between a bus voltage and a voltage of an input capacitor; A first drive signal is generated according to the detection signal to drive the first switch tube; when the bus voltage is greater than the voltage of the input capacitor, the first switch tube is controlled to be turned off and the input capacitor is charged; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, the first switch tube is controlled to be turned on and the input capacitor supplies power to the LED drive circuit.

10. The charge and discharge control method according to claim 9, characterized in that: The step of generating a first drive signal according to the detection signal to drive the first switch tube specifically includes: in the preliminary stage of the charge and discharge cycle of the input capacitor, controlling the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, controlling the first switch tube to turn on; when the bus voltage is greater than the voltage of the input capacitor and the current flowing through the first switch tube is greater than the preset current, controlling the first switch tube to turn off; when the bus voltage is less than the difference between the voltage of the input capacitor and the first preset voltage, controlling the first switch tube to turn on.

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