A ripple-free LED circuit powered by half voltage

Abstract

The present invention discloses a ripple-free LED circuit with half-voltage power supply. The device includes a power supply unit, a load unit, an energy storage capacitor, a first constant current regulator, a first sampling resistor, a second constant current regulator, and a second sampling resistor. The LED circuit includes a power supply branch, a charging branch, and a discharging branch. The power supply unit, the load unit, the first constant current regulator, and the first sampling resistor are connected in series in the power supply branch and grounded. The power supply unit, the load unit, the energy storage capacitor, the second constant current regulator, the second sampling resistor, and the first sampling resistor are connected in series in the charging branch and grounded. The energy storage capacitor, the load unit, the first constant current regulator, and the first sampling resistor are connected in series in the discharging branch to form a loop. The power supply branch, the charging branch, and the discharging branch work alternately and cyclically in sequence. The present invention uses the master-slave constant current regulator logic control method and the critical working mode of the energy storage capacitor charging and discharging to achieve a high input power factor, a low output forward voltage value and no ripple, and is compatible with the dimming system.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic drive circuit control, and particularly relates to a ripple-free LED circuit powered by half voltage. Background Art

[0002] As an efficient new light source, LED is widely used in lighting in various fields due to its long lifespan, low energy consumption, energy conservation and environmental protection.

[0003] Currently, there are conflicts between power factor and ripple-free technology in both linear and switching constant current drive power supplies. Ordinary linear constant current drivers have some fatal disadvantages such as high output voltage, high cost of LED loads, and non-common ground working mode of ICs, which seriously affect the connection of intelligent control systems in LED power supply circuits. Summary of the Invention

[0004] In order to overcome the deficiencies in the existing LED linear drive circuit technology, the present invention provides a ripple-free LED circuit powered by half voltage, which realizes input high power factor output ripple-free control technology by using the master-slave constant current logic control method and the critical working mode of capacitor charge and discharge. The technical solution is as follows:

[0005] The present invention provides a first ripple-free LED circuit powered by half voltage. The devices in the LED circuit include a power supply unit, a load unit, an energy storage capacitor, a first constant current device, a first sampling resistor, a second constant current device, and a second sampling resistor. The LED circuit includes a power supply branch, a charging branch, and a discharging branch;

[0006] The power supply unit, the load unit, the first constant current device, and the first sampling resistor are connected in series in the power supply branch and grounded;

[0007] The power supply unit, the load unit, the energy storage capacitor, the second constant current device, the second sampling resistor, and the first sampling resistor are connected in series in the charging branch and grounded;

[0008] The energy storage capacitor, the load unit, the first constant current device, and the first sampling resistor are connected in series in the discharging branch and form a loop;

[0009] As the current in the circuit changes, the first constant current device and the second constant current device work alternately, and the power supply branch, the charging branch, and the discharging branch work alternately and cyclically in sequence.

[0010] Further, the LED circuit provided by the present invention further includes a plurality of diodes for controlling the current flow direction in the charging branch or the discharging branch.

[0011] Further, a first diode is provided between the positive electrode of the energy storage capacitor and one end of the load unit, a second diode is provided between the positive electrode of the energy storage capacitor and the other end of the load unit, a third diode is provided between the negative electrode of the energy storage capacitor and the second constant current device, and a fourth diode is provided between the negative electrode of the energy storage capacitor and the ground. The conduction directions of the first diode and the fourth diode are the conduction directions of the discharge branch, and the conduction directions of the second diode and the third diode are the conduction directions of the charging branch.

[0012] Further, the first constant current device includes a first amplifier and a first power transistor. The output end of the first amplifier is connected to the first power transistor. The positive input end of the first amplifier is connected to a first reference voltage. The negative input end of the first amplifier and the first power transistor are both connected to a first sampling resistor. The first power transistor is used to control the current flowing through the first sampling resistor to be a constant value.

[0013] When the terminal voltage of the first sampling resistor is greater than the first reference voltage, the first amplifier controls the first power transistor to be in a cut-off state.

[0014] Further, the second constant current device includes a second amplifier and a second power transistor. The output end of the second amplifier is connected to the second power transistor. The positive input end of the second amplifier is connected to a second reference voltage. The negative input end of the second amplifier and the second power transistor are both connected to a second sampling resistor. The second power transistor is used to control the current flowing through the second sampling resistor to be a constant value.

[0015] When the sum of the terminal voltages of the first sampling resistor and the second sampling resistor is greater than the second reference voltage, the second amplifier controls the second power transistor to be in a cut-off state.

[0016] Further, the load unit includes one or more series-connected LED loads, and the forward voltage of the load unit is lower than half of the peak value of the input voltage of the power supply unit.

[0017] Further, the first constant current device and the second constant current device operate in a common ground connection manner to be capable of accessing a dimming control system.

[0018] Further, the power supply unit includes an AC mains supply, a fuse, and a rectifier.

[0019] Further, the energy storage capacitor includes one capacitor or multiple capacitors connected in parallel.

[0020] Further, the first power transistor is an NMOS transistor MN101, and the second power transistor is an NMOS transistor MN201.

[0021] The beneficial effects brought by the technical solution provided by the present invention are as follows:

[0022] 1) By using the master-slave constant current logic control method and the critical working mode of energy storage capacitor charging and discharging, high input power factor, low output LED forward voltage value and no ripple are achieved.

[0023] 2) The ICs of the first constant current regulator and the second constant current regulator work in a common ground connection mode, making the circuit of the present invention compatible with the intelligent dimming control system. Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is a circuit schematic diagram of a ripple-free LED circuit with half-voltage power supply provided by an embodiment of the present invention;

[0026] Figure 2 It is a connection schematic diagram of the common ground working mode of the first constant current regulator and the second constant current regulator provided by an embodiment of the present invention;

[0027] Figure 3 It is a schematic diagram of connecting the ripple-free LED circuit with half-voltage power supply provided by an embodiment of the present invention to the dimming control system;

[0028] Figure 4 It is a waveform diagram of the input voltage and current of the ripple-free LED circuit with half-voltage power supply provided by an embodiment of the present invention;

[0029] Figure 5 It is a real-time status diagram of the terminal voltage and the flowing current of the LED load provided by an embodiment of the present invention;

[0030] Figure 6 It is a topology diagram of the first constant current regulator provided by an embodiment of the present invention;

[0031] Figure 7 It is a topology diagram of the second constant current regulator provided by an embodiment of the present invention.

[0032] Among them, the reference numerals include: 1 - load unit, 2 - energy storage capacitor, 3 - first constant current regulator, 31 - first amplifier, 32 - first power transistor, 4 - first sampling resistor, 5 - second constant current regulator, 51 - second amplifier, 52 - second power transistor, 6 - second sampling resistor, 71 - first diode, 72 - second diode, 73 - third diode, 74 - fourth diode. Detailed Embodiments

[0033] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, device, product or equipment comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or equipment.

[0035] In an embodiment of the present invention, a ripple-free LED circuit with half-voltage power supply is provided. Refer to Figure 1 , the LED circuit includes a power supply unit, a load unit 1, an energy storage capacitor 2, a first constant current regulator 3, a first sampling resistor 4, a second constant current regulator 5, and a second sampling resistor 6. As Figure 1 shown, the load unit 1 includes one or more series-connected LED loads. The LED circuit includes a power supply branch ( Figure 1 branch I in Figure 1 ), a charging branch ( Figure 3 branch II in Figure 1 ), and a discharging branch ( Figure 1 branch III in Figure 1 ). Refer to branch I in

[0036] Figure 1 : The power supply unit, the load unit 1, the first constant current regulator 3, and the first sampling resistor 4 are connected in series in the power supply branch and grounded; Refer to branch II in Figure 1 : The power supply unit, the load unit 1, the energy storage capacitor 2, the second constant current regulator 5, the second sampling resistor 6, and the first sampling resistor 4 are connected in series in the charging branch and grounded; Refer to branch III in Figure 1 : The energy storage capacitor 2, the load unit 1, the first constant current regulator 3, and the first sampling resistor 4 are connected in series in the discharging branch and form a loop.

[0036] As the current in the circuit changes, the first constant current device 3 and the second constant current device 5 work alternately, and the power supply branch (branch I), the charging branch (branch II) and the discharging branch (branch III) work alternately and cyclically in sequence. It should be noted that during the alternating operation of the first constant current device 3 and the second constant current device 5, there is a stage where the first constant current device 3 and the second constant current device 5 work simultaneously, including: (during the process of switching the power supply branch to the charging branch) the first constant current device 3 gradually cuts off while the second constant current device 5 gradually saturates and conducts, or (during the process of switching the charging branch to the power supply branch) the second constant current device 5 gradually cuts off while the first constant current device 3 gradually saturates and conducts. The specific working principle and process are as follows:

[0037] In a preferred embodiment of the present invention, the forward voltage V of the load unit 1 F is lower than half of the input voltage peak value (220V * 1.414) of the power supply unit, that is, half - voltage power supply is achieved to achieve ripple - free. For example, the forward voltage V of the load unit is set F to 150V. Starting from connecting to the mains, the mains is rectified to supply power to the load unit 1. At this time, the current passes through the power supply branch (branch I), and the voltage waveform is shown in Figure 4 , starting from the zero point of a waveform, the current increases as the voltage rises until the voltage rises to the forward voltage set value (150V). At this time, the power supply branch (branch I) is switched to the charging branch (branch II). After that, the current flowing through the load unit 1 is a constant value. The switching from the power supply branch (branch I) to the charging branch (branch II) is achieved by cutting off the first constant current device 3 and conducting the second constant current device 5 simultaneously. For the power supply branch (branch I) and the charging branch (branch II), the whole switching process includes that when the input voltage is between 150V and V 1 (V 1 is greater than 150V, V 1 is less than the peak value V p ), the current of the power supply branch (branch I) changes from strong to weak, and the current of the charging branch (branch II) changes from weak to strong. At the V 1 node, the first constant current device 3 cuts off and the second constant current device 5 saturates and conducts;

[0038] When the input voltage is between V 1 and V p , the leakage current of the power supply branch (branch I) is small and can be ignored. The current of the charging branch (branch II) remains constant under the control of the second constant current device 5. The working principle of the first constant current device 3 is specifically described as follows; as mentioned above, the process of the current flowing through the charging branch (branch II) is the process of the voltage waveform continuing to rise. Preferably, after crossing the peak, the voltage drops by a certain amplitude (drops to V 1) This process is the operation of the charging branch (branch II). During this process, the second constant current device 5 makes the current flowing through the load unit 1 a constant value;

[0039] until the input voltage drops from V 1 and continues to decrease (to 150V). During this process, the current of the charging branch (branch II) weakens from strong, and the current of the discharging branch (branch III) strengthens from weak. During this process, the first constant current device 3 and the second constant current device 5 jointly make the current flowing through the load unit 1 a constant value. At the 150V node, the second constant current device 5 cuts off (specifically explained by the following operating principle of the second constant current device), and the first constant current device 3 is saturated and conducting. The leakage current of the charging branch (branch II) is small and can be ignored;

[0040] When the input voltage continues to drop from 150V to 0, the current of the discharging branch (branch III) weakens from strong (not zero), and the current of the power supply branch (branch I) strengthens from weak. During this process, the first constant current device 3 makes the current flowing through the load unit 1 a constant value.

[0041] The above is one cycle, and then the next cycle starts from the zero point of a waveform. In the embodiment of the present invention, the energy storage capacitor 2 operates in a critical charge-discharge working mode, that is, during charging, the energy storage capacitor 2 is not saturatedly charged; during discharging, the energy storage capacitor 2 does not completely discharge its power.

[0042] In order to switch the power supply branch (branch I) to the charging branch (branch II), first, the first constant current device 3 must be in a cut-off state. Second, the current flow direction after switching the branch is controlled to be the direction of the charging branch (branch II). Therefore, the LED circuit provided by the present invention further includes a plurality of diodes for controlling the current flow direction in the charging branch or the discharging branch. In a preferred embodiment, a first diode 71 is provided between the positive electrode of the energy storage capacitor 2 and one end of the load unit 1, a second diode 72 is provided between the positive electrode of the energy storage capacitor 2 and the other end of the load unit 1, a third diode 73 is provided between the negative electrode of the energy storage capacitor 2 and the second constant current device 5, and a fourth diode 74 is provided between the negative electrode of the energy storage capacitor 2 and the ground. As Figure 1 shown, the conduction directions of the first diode 71 and the fourth diode 74 are the conduction directions of the discharging branch, and the conduction directions of the second diode 72 and the third diode 73 are the conduction directions of the charging branch. That is, after the first constant current device is in a cut-off state, under the reverse blocking action of the first diode 71 and the fourth diode 74, the current can only flow through the charging branch; similarly, after the second constant current device is in a cut-off state, under the reverse blocking action of the second diode 72 and the third diode 73, the current can only flow through the discharging branch.

[0043] The working principles of the first constant current source and the second constant current source will be described separately as follows:

[0044] Referring to Figure 6 it can be seen that the first constant current source 3 includes a first amplifier 31 and a first power transistor 32. The output terminal of the first amplifier 31 is connected to the first power transistor 32. The positive input terminal of the first amplifier 31 is connected to the first reference voltage V ref1 . The negative input terminal of the first amplifier 31 and the first power transistor 32 are both connected to the first sampling resistor 4. The first power transistor 32 is used to control the current flowing through the first sampling resistor 4 to be a constant value. Preferably, the first power transistor 32 is an NMOS transistor MN101. When the terminal voltage of the first sampling resistor 4 is greater than the first reference voltage V ref1 , the first amplifier 31 controls the first power transistor 32 to be in the cut-off state. As Figure 6 shown, the first reference voltage V ref1 is a fixed preset value (assumed to be 0.5V), and the first sampling resistor 4 should satisfy that when the input voltage is 150V, the terminal voltage of the first sampling resistor 4 is equal to V ref1 (assumed to be 0.5V).

[0045] Referring to Figure 7 it can be seen that the second constant current source 5 includes a second amplifier 51 and a second power transistor 52. The output terminal of the second amplifier 51 is connected to the second power transistor 52. The positive input terminal of the second amplifier 51 is connected to the second reference voltage V ref2 . The negative input terminal of the second amplifier 51 and the second power transistor 52 are both connected to the second sampling resistor 6. The second power transistor 52 is used to control the current flowing through the second sampling resistor 6 to be a constant value. Preferably, the second power transistor 52 is an NMOS transistor MN201. When the sum of the terminal voltages of the first sampling resistor 4 and the second sampling resistor 6 is greater than the second reference voltage V ref2 , the second amplifier 51 controls the second power transistor 52 to be in the cut-off state. It can be seen that the preset value of the second reference voltage V ref2 is not limited to a certain value, but can float within a suitable range (as long as after the energy storage capacitor 2 is charged for a period of time, and there is volatility in the charging, when the input voltage drops to 150V, the sum of the terminal voltages of the second sampling resistor 6 and the first sampling resistor 4 in the charging branch). Specifically, referring to Figure 7 , the working principle of the second constant current source 5 is as follows: The second sampling resistor 6 is the sampling resistor of the second constant current source 5. The reference voltage between the positive input terminal of the second amplifier 51 and the second sampling resistor is a fixed value (assumed to be 0.5V), and the total reference voltage is the fixed value plus the floating ground reference, and the floating ground reference is the voltage across the first sampling resistor 4.

[0046] In a preferred embodiment of the present invention, the first constant current source 3 and the second constant current source 5 operate in a common ground connection mode, as Figure 2 shown, so as to be conveniently connected to the intelligent dimming control system, as Figure 3 shown.

[0047] In an embodiment of the present invention, the power supply unit includes an AC mains (220V AC), a fuse (FU1) and a rectifier (DB1). Preferably, the energy storage capacitor 2 includes one capacitor (see the accompanying drawings of the specification) or multiple capacitors connected in parallel (not shown).

[0048] In the present invention, during the switching of the three branches in the LED circuit, the first constant current source 3 and the second constant current source also alternately operate in terms of current strength. Under the constant current action of the first constant current source 3 or the second constant current source 5, except for a certain initial period after the power is turned on, the current flowing through the load unit 1 in the circuit is a constant value at other times. See Figure 5 which enables the LED load to have constant voltage and constant current during operation, achieving ripple-free light source.

[0049] In the existing LED lighting industry, there is a conflict between the power factor and ripple-free. In order to overcome the deficiencies of the existing LED linear drive circuit technology, the present invention provides a master-slave constant current source logic control method and a critical working mode of energy storage capacitor charge and discharge to achieve a high input power factor, a low LED forward voltage value and ripple-free output; at the same time, a special application circuit is adopted to make the IC (the first constant current source and the second constant current source) work in a common ground connection mode to facilitate the connection of the intelligent control system.

[0050] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A ripple-free LED circuit powered by half voltage, characterized in that, the devices in the LED circuit include a power supply unit, a load unit (1), an energy storage capacitor (2), a first constant current regulator (3), a first sampling resistor (4), a second constant current regulator (5) and a second sampling resistor (6), and the LED circuit includes a power supply branch, a charging branch and a discharging branch; the power supply unit, the load unit (1), the first constant current regulator (3), and the first sampling resistor (4) are connected in series in the power supply branch and grounded; the power supply unit, the load unit (1), the energy storage capacitor (2), the second constant current regulator (5), the second sampling resistor (6), and the first sampling resistor (4) are connected in series in the charging branch and grounded; the energy storage capacitor (2), the load unit (1), the first constant current regulator (3), and the first sampling resistor (4) are connected in series in the discharging branch and form a loop; as the current in the circuit changes, the first constant current regulator (3) and the second constant current regulator (5) work alternately, and the power supply branch, the charging branch and the discharging branch work alternately and cyclically in sequence; the first constant current regulator (3) and the second constant current regulator (5) work in a common ground connection mode to be able to access a dimming control system; the power supply unit includes an AC mains, a fuse and a rectifier; a first diode (71) is provided between the positive electrode of the energy storage capacitor (2) and one end of the load unit (1), a second diode (72) is provided between the positive electrode of the energy storage capacitor (2) and the other end of the load unit (1), a third diode (73) is provided between the negative electrode of the energy storage capacitor (2) and the second constant current regulator (5), and a fourth diode (74) is provided between the negative electrode of the energy storage capacitor (2) and the ground. The conduction directions of the first diode (71) and the fourth diode (74) are the conduction directions of the discharging branch, and the conduction directions of the second diode (72) and the third diode (73) are the conduction directions of the charging branch; the first constant current regulator (3) includes a first amplifier (31) and a first power transistor (32). The output end of the first amplifier (31) is connected to the first power transistor (32). The positive input end of the first amplifier (31) is connected to a first reference voltage. The negative input end of the first amplifier (31) and the first power transistor (32) are both connected to the first sampling resistor (4). The first power transistor (32) is used to control the current flowing through the first sampling resistor (4) to be a constant value; when the terminal voltage of the first sampling resistor (4) is greater than the first reference voltage, the first amplifier (31) controls the first power transistor (32) to be in a cut-off state; The second constant current device (5) includes a second amplifier (51) and a second power transistor (52). The output terminal of the second amplifier (51) is connected to the second power transistor (52). The positive input terminal of the second amplifier (51) is connected to a second reference voltage. The negative input terminal of the second amplifier (51) and the second power transistor (52) are both connected to a second sampling resistor (6). The second power transistor (52) is used to control the current flowing through the second sampling resistor (6) to be a constant value; When the sum of the terminal voltages of the first sampling resistor (4) and the second sampling resistor (6) is greater than the second reference voltage, the second amplifier (51) controls the second power transistor (52) to be in a cut-off state; The load unit includes one or more series-connected LED loads, and the forward voltage of the load unit is lower than one-half of the peak value of the input voltage of the power supply unit; The first constant current device (3) and the second constant current device (5) work alternately, and the energy storage capacitor (2) works in a critical charge-discharge working mode. During charging, the energy storage capacitor (2) is not saturated. During discharging, the energy storage capacitor (2) does not completely discharge; The first reference voltage is a fixed preset value. The first sampling resistor (4) satisfies that when the input voltage is the forward voltage of the load unit (1), the terminal voltage of the first sampling resistor (4) is equal to the first reference voltage; The reference voltage between the positive input terminal of the second amplifier (51) and the second sampling resistor (6) is a fixed value, and the total reference voltage is the sum of the reference voltage between the positive input terminal of the second amplifier (51) and the second sampling resistor (6) and the floating ground reference. The floating ground reference is the voltage across the first sampling resistor (4).

2. The LED circuit according to claim 1, characterized in that, It further includes a plurality of diodes for controlling the current flow direction in the charging branch or the discharging branch.

3. The LED circuit according to claim 1, characterized in that, The energy storage capacitor (2) includes one capacitor or a plurality of capacitors connected in parallel.

4. The LED circuit according to claim 3, characterized in that, The first power transistor (32) is an NMOS transistor MN101, and the second power transistor (52) is an NMOS transistor MN201.

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