TWI649006B - Method and system for eliminating LED flicker - Google Patents

Abstract

The invention relates to a method and a system for eliminating LED flicker. Provided is a system for eliminating LED flicker: including: an LED driving circuit, one end of which is connected to an AC power source through a rectifying filter element, and one end connected to an LED load; and a strobe canceling circuit, which includes three ports, The first port is connected to the LED load; the second port is connected to the ground through a filter capacitor; the third port is connected to the ground, where the strobe cancellation circuit includes: a power transistor, a gate driving unit, and a drain sensing unit; wherein the gate driving unit is connected Input to the gate and gate driving unit of the power transistor and input a first signal to the gate driving unit, and the gate driving unit is configured to output a driving signal to drive the power transistor, wherein the driving signal is driven by the gate The unit is generated based at least in part on the first signal.

Description

Method and system for eliminating LED strobe

Certain embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a method and system for eliminating LED flicker.

As a new type of energy-saving light source, light-emitting diodes (LEDs) are widely used in various lighting applications such as landscapes, street lights, home lighting, and commercial lighting due to their high efficiency, environmental protection, and safety.

According to the load characteristics of LEDs, LED drive circuits generally use a constant current drive method. Traditional LED drivers include LED drivers and output capacitors. Figure 1 shows a conventional LED linear constant current control system. As shown in Figure 1. The LED driver rectifies the AC mains power and converts it into DC current to provide the LED load. However, the DC current converted in this way contains AC current ripple that is twice the mains frequency; for LED drivers with high PF (Power Factor, power factor), the AC current ripple proportion is even greater. Such ripples can cause flicker that can be perceived by the human eye or can be captured by camera equipment. Therefore, an LED driving system needs a circuit capable of eliminating LED flicker.

Certain embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a method and system for eliminating LED flicker. By way of example only, some embodiments of the invention are applied to the field of LEDs. However, it will be recognized that the invention has a wider scope of applicability.

The invention discloses a method and a circuit for eliminating LED frequency flicker (strobe). The circuit for eliminating LED flicker is applied to an LED driving circuit. When the load connected to the LED driver has a constant current characteristic, the current flowing through the load is a direct current without AC components. Current, but its output voltage contains a small amount of AC ripple components. Therefore, the present invention provides a constant DC current without an AC component to the load of the LED driver through a controllable circuit, and uses a filter control circuit to filter out the AC ripple component of the output voltage to eliminate LED flicker. At the same time, the strobe cancellation circuit provides a self-adjusting voltage adjustment function to improve the system's working efficiency; and a current limiting function is set to ensure the reliability of the circuit application.

According to an embodiment, a system for eliminating LED flicker is provided, including: an LED driving circuit, one end of which is connected to an AC power source through a rectifying and filtering element, and one end connected to an LED load; and a flicker canceling circuit, a flicker canceling circuit It includes three ports. The first port is connected to the LED load. The second port is grounded through a filter capacitor. The third port is grounded. The strobe cancellation circuit includes: a power transistor, a gate drive unit, a drain sensing unit and others. Optional module; where the gate drive unit is connected to the gate of the power transistor and the gate drive unit input and a first signal is input to the gate drive unit, and the gate drive unit is configured to output a drive signal to drive power The transistor, wherein the driving signal is generated by the gate driving unit based at least in part on the first signal.

According to yet another embodiment, an LED luminaire for a system for eliminating LED flicker according to an embodiment of the present invention is provided.

According to an embodiment, one or more benefits may be obtained. These benefits and the various additional objects, features, and advantages of the present invention will be thoroughly understood with reference to the detailed description and drawings that follow.

M1‧‧‧ Power Transistor

Vd‧‧‧Drain voltage

Vg‧‧‧Gate voltage

Vth‧‧‧Threshold voltage

Rs‧‧‧sense resistor

M2, M3‧‧‧ switch tube

D1‧‧‧diode

Gm‧‧‧ Transconductance Amplifier

M4‧‧‧ sensor tube

M5, M6 ‧‧‧ modulation tube

V _out ‧‧‧ voltage

Vref‧‧‧ Internal Reference Voltage

Vc‧‧‧Filter capacitor voltage

Figure 1 shows a conventional LED linear constant current control system.

FIG. 2 is a schematic diagram of a system for eliminating LED flicker according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a circuit for eliminating LED flicker according to an embodiment of the present invention.

Figure 4A is a drain sensing of a circuit for eliminating LED flicker according to an embodiment of the present invention A schematic implementation of the unit.

FIG. 4B is another schematic implementation of a drain sensing unit of a circuit for eliminating LED flicker according to an embodiment of the present invention.

FIG. 5A is a schematic implementation manner of a drain voltage self-adjusting adjusting unit of a circuit for eliminating LED flicker according to an embodiment of the present invention.

FIG. 5B is another schematic implementation of a drain voltage self-adjusting adjusting unit of a circuit for eliminating LED flicker according to an embodiment of the present invention.

FIG. 6 is a schematic implementation of a current sensing and current limiting unit of a circuit for eliminating LED flicker according to an embodiment of the present invention.

FIG. 7 is a schematic implementation of a gate driving unit of a circuit for eliminating LED flicker according to an embodiment of the present invention.

Features and exemplary embodiments of various aspects of the invention will be described in detail below. Numerous specific details are set forth in the following detailed description in order to provide a thorough understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely for providing a better understanding of the present invention by showing examples of the present invention. The invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

Preferably, the control method of the present invention can be applied to the field of LED lighting with linear constant current control mode of high PF or TRIodes AC switch (TRAIC) dimming.

This application proposes a method and circuit for eliminating LED flicker to suppress or remove the output current ripple of the LED driver; to improve the system's working efficiency through self-adjusting and adjusting functions; and to ensure the reliability of circuit applications through the current limiting function.

FIG. 2 is a diagram of a system for eliminating LED flicker according to an embodiment of the present invention. Schematic illustration. Among them, the strobe cancellation circuit has three ports. The first port is connected to the LED load; a filter capacitor is connected between the second port and the ground; and the third port is connected to the ground.

FIG. 3 is a schematic diagram of a circuit for eliminating LED flicker according to an embodiment of the present invention. The strobe cancellation circuit contains five functional modules, as shown in Figure 3, which are rectified power metal-oxide semiconductor field effect transistors (MOSFETs), hereinafter referred to as power transistors; Drain sensing is the drain voltage sensing circuit of power transistor M1; the minimum drain limit is the drain voltage self-adjusting adjustment unit of power transistor M1; Over Current Protection (OCP) is the current sensing and Current limiting unit; gate drive unit for gate drive power transistor M1. An external capacitor is used to filter the gate voltage of power transistor M1.

The strobe cancellation circuit sets the power transistor M1 to work in the saturation region to achieve the constant current demand of the LED load. In addition, through the drain sensing, the drain voltage of the power transistor M1 is sensed, the gate voltage of the power transistor M1 is adjusted, and finally the current through the LED load is adjusted to eliminate the AC current component therein, thereby realizing the elimination of the LED. Strobe. When the LED driver has high PF characteristics, the output voltage ripple is usually relatively large. At this time, the drain voltage of the power transistor M1 fluctuates greatly, and its average value is also high. Under the condition of the rated LED load current, the higher the average drain voltage of the power transistor M1 is, the larger the power loss and heat loss generated by the strobe cancellation circuit are. Drain sensing also has the function of pulling the lowest value of the drain voltage fluctuation of the power transistor M1 to the boundary between its saturation region and linear region.

During the fluctuation of the drain voltage of the power transistor M1, in order to ensure that the power transistor M1 can always work in the saturation region and not enter the linear region because the drain voltage is too low, the minimum drain limit circuit always The drain voltage of M1 is sensed. When the drain voltage of power transistor M1 satisfies Vd <Vg-Vth (where Vd, Vg, and Vth are the drain voltage, gate voltage, and threshold voltage of power transistor M1, respectively), the minimum drain limit circuit will reduce the gate Voltage to satisfy the condition that the power transistor M1 operates in the saturation region Vd> Vg-Vth.

In order to improve the reliability of eliminating the strobe circuit and prevent the circuit from working in a high voltage and high current state, OCP provides a current sensing function and adjusts the power transistor M1 according to the detection result. The gate voltage limits the maximum on-current of power transistor M1.

The gate driver collects and processes the control signals of other circuit modules to complete the gate driving of the power transistor M1.

FIG. 4A is a schematic implementation of a drain sensing unit of a circuit for eliminating LED flicker according to an embodiment of the present invention. The forward diode connected between the drain and gate of the power transistor M1 provides the starting path; the adjustment resistor directly connected between the drain and gate of the power transistor M1 is used to adjust the minimum value of the drain voltage fluctuation . The circuit always senses the drain voltage of the power transistor M1 and adjusts its gate voltage.

FIG. 4B is another schematic implementation of a drain sensing unit of a circuit for eliminating LED flicker according to an embodiment of the present invention. In the initial stage of startup, the switch M2 is turned on and forms a low-impedance path with the diode D1 to quickly charge the gate capacitor of the power transistor M1; when its potential rises to the threshold of the switch M3, the switch M3 is turned on , Turn off the fast-start path of the switch M2 to avoid current overshoot. In order to further improve the response capability of the strobe circuit, the startup speed is provided.

FIG. 5A is a schematic implementation manner of a drain voltage self-adjusting adjusting unit of a circuit for eliminating LED flicker according to an embodiment of the present invention. The circuit senses the drain voltage of the power transistor M1, and the difference between the drain voltage of the power transistor M1 and the internal reference voltage Vref outputs a signal for unidirectionally adjusting the gate voltage of the power transistor M1 through the transconductance amplifier Gm. When the drain voltage of the power transistor M1 is greater than the internal reference voltage Vref, the transconductance amplifier Gm does not output an adjustment signal; otherwise, when the drain voltage of the power transistor M1 is less than the internal reference voltage Vref, the transconductance amplifier Gm outputs an adjustment signal , Reducing the gate voltage of the power transistor M1 and weakening the current capability of the power transistor M1, so that the drain voltage of the power transistor M1 is forced to be raised, thereby avoiding that the drain voltage is too low and the power transistor M1 enters the linear region.

FIG. 5B is another schematic implementation of a drain voltage self-adjusting adjusting unit of a circuit for eliminating LED flicker according to an embodiment of the present invention. When the partial voltage of the drain voltage of the power transistor M1 is lower than the threshold voltage of the sensing tube M4, the sensing tube M4 is turned off; the modulation tube M5 starts to work, and extracts the charge of the gate extreme capacitance of the power transistor M1 to reduce its gate Electricity The voltage can also achieve the function of reducing the current capability of the power transistor M1, so that the power transistor M1 always works in the saturation region.

FIG. 6 is a schematic implementation of a current sensing and current limiting unit of a circuit for eliminating LED flicker according to an embodiment of the present invention. The unit includes a sense resistor Rs and a second power transistor M6 connected in series between the source and the ground of the power transistor M1, and a gate terminal of the second power transistor M6 receives a voltage signal on the sense resistor Rs. . When the on-current of the power transistor M1 is too large, the voltage signal on the sensing resistor Rs exceeds the threshold voltage of the second power transistor M6, the second power transistor M6 starts to work, and the gate extreme capacitance of the power transistor M1 is extracted (not shown). Eq.), By reducing its gate voltage, it limits its current capability.

FIG. 7 is a schematic implementation of a gate driving unit of a circuit for eliminating LED flicker according to an embodiment of the present invention. The resistor parallel circuit constitutes an adder to adjust the output impedance and the control voltage to the power transistor M1.

According to an embodiment of the present invention, a system for eliminating LED flicker is provided. The system may include: an LED driving circuit, one end of which is connected to an AC power source through a rectifying filter element, and one end connected to an LED load; The flash cancellation circuit includes three ports, the first port is connected to the LED load, the second port is grounded through a filter capacitor, and the third port is grounded. The strobe cancellation circuit includes: a power transistor, a gate drive unit, and a drain sensor. Unit and other optional modules; wherein the gate driving unit is connected to the gate of the power transistor, and the gate driving unit is configured to receive a first signal output from the drain sensing unit and output a driving signal to A driving power transistor, wherein the driving signal is generated by the gate driving unit based at least in part on the first signal.

According to an embodiment of the present invention, the strobe cancellation circuit may further include: a current sensing and current limiting unit; the current sensing and current limiting unit is configured to sense a current flowing through the power transistor, and output a second signal based on the detection result To the gate driving unit, wherein the driving signal is generated by the gate driving unit based at least in part on the first signal and the second signal.

According to an embodiment of the present invention, the stroboscopic elimination circuit further includes: a drain voltage self-adjusting adjustment unit, and the drain voltage self-adjusting adjustment unit is configured to sense a power transistor. The drain voltage, the gate voltage, and the threshold voltage, and output a third signal to the gate driving unit, wherein when the drain voltage self-adjusting and adjusting unit senses that the drain voltage is less than the difference between the gate voltage and the threshold voltage, A third signal is generated indicative of reducing the gate voltage of the power transistor, wherein the driving signal is generated by the gate driving unit based at least in part on the first signal, the second signal, and the third signal.

According to an embodiment of the present invention, the drain sensing unit may include: a forward diode, a positive electrode of the forward diode is connected to a drain of the power transistor, a negative electrode is connected to a gate of the power transistor, and a resistor is adjusted. The adjusting resistor is connected in parallel with the forward diode between the drain and the gate of the power transistor.

According to the embodiment of the present invention, the drain sensing unit may further include a first switching tube and a second switching tube, wherein the drain of the first switching tube is connected to the negative electrode of the diode, and the source is connected to the gate of the second switching tube. The gate is connected to the adjustment resistor; the gate of the second switch is connected to the source of the second switch, the drain is connected to the adjustment resistor, and the source is grounded.

According to an embodiment of the present invention, the current sensing and current limiting unit includes a sensing resistor and a second power transistor connected in series between the source and the ground of the power transistor, and the second power transistor receives the sensing resistor. When the voltage signal is greater than the threshold voltage of the second power transistor, the second power transistor extracts the charge of the capacitor connected to the gate of the power transistor.

According to an embodiment of the present invention, the drain voltage self-adjusting and adjusting unit is a transconductance amplifier, and is configured not to output a third signal when the detected drain voltage is greater than an internal reference voltage, otherwise, outputting a third signal indicates a decrease in power. The gate voltage of the crystal.

According to an embodiment of the present invention, the gate driving unit includes a series diode to form a translation circuit; and a resistor parallel circuit to form an adder.

According to one example, an LED luminaire for a system for eliminating LED flicker is provided according to an embodiment of the present disclosure.

For example, using one or more software elements, one or more hardware elements, and / or one or more combinations of software and hardware elements, some or all of the various embodiments of the invention Each of the component elements is implemented individually and / or in combination with at least another element. In another example, some or all of the elements of various embodiments of the present invention are each implemented individually and / or in combination with at least another element, such as one or more analog circuits and / or one or more digits In one or more circuits. In another example, various embodiments and / or examples of the invention may be combined.

Although specific embodiments of the invention have been described, those skilled in the art will understand that there are other embodiments that are equivalent to the described embodiments. It is understood, therefore, that this invention is not limited to the particular embodiments shown, but is only limited by the scope of the appended claims.

Claims (7)

A system for eliminating LED flicker includes: an LED driving circuit, one end of which is connected to an AC power source through a rectifying filter element, and one end connected to an LED load; and a strobe canceling circuit, which includes three Port, the first port is connected to the LED load; the second port is grounded through a filter capacitor; and the third port is grounded, wherein the strobe cancellation circuit includes a power transistor, a gate driving unit, a drain sensing unit, and Drain voltage self-adjusting adjustment unit; wherein the gate driving unit is connected to the gate of the power transistor, and the gate driving unit is configured to receive a first signal output from the drain sensing unit And output a driving signal to drive the power transistor, wherein the driving signal is generated by the gate driving unit based at least in part on the first signal, and the drain voltage self-adjusting adjusting unit is configured to detect A drain voltage of the power transistor, and outputting a third signal to the gate driving unit, wherein when the drain voltage is self-adjusting and adjusting the unit When it is detected that the drain voltage is less than a difference between a gate voltage of the power transistor and a threshold voltage of the power transistor, a third signal is generated indicating that the gate voltage of the power transistor is reduced, wherein The driving signal is generated by the gate driving unit based at least in part on the first signal and the third signal. The system according to item 1 of the patent application scope, wherein the strobe cancellation circuit further comprises: a current sensing and current limiting unit; the current sensing and current limiting unit is configured to sense the current flowing through the power transistor And a second signal is output to the gate driving unit based on a detection result, wherein the driving signal is based at least in part on the first signal, the second signal, and the gate driving unit. The third signal is generated. The system according to item 1 of the patent application scope, wherein the drain sensing unit comprises: a forward diode, the anode of the forward diode is connected to the drain of the power transistor, and the anode is connected to the drain of the power transistor. A gate connection of the power transistor; and an adjustment resistor connected in parallel with the forward diode between a drain and a gate of the power transistor. The system according to item 3 of the patent application scope, wherein the drain sensing unit further comprises a first switch tube and a second switch tube, wherein the drain of the first switch tube and the forward diode The negative electrode is connected, the source is connected to the gate of the second switching tube, and the gate is connected to the adjusting resistor; and the gate of the second switching tube is connected to the source of the second switching tube, The drain is connected to the adjustment resistor, and the source is grounded. The system according to item 2 of the patent application scope, wherein the current sensing and current limiting unit comprises a sensing resistor and a second power transistor connected in series between a source and a ground of the power transistor, said A gate terminal of a second power transistor receives a voltage signal on the sensing resistor. When the voltage signal is greater than a threshold voltage of the second power transistor, the second power transistor extracts a voltage signal from the power transistor. The gate of the crystal is connected to the capacitor's charge. The system of claim 1, wherein the drain voltage self-adjusting adjustment unit includes a transconductance amplifier and is configured not to output the sensed drain voltage when the sensed drain voltage is greater than an internal reference voltage. A third signal, otherwise outputting the third signal instructs to reduce the gate voltage of the power transistor. The system according to item 1 of the patent application range, wherein the gate driving unit comprises a resistor parallel circuit to form an adder.