CN105764178A - Stroboflash-free sectional type constant-current LED driving circuit - Google Patents

Abstract

The invention relates to a segmented constant current LED drive circuit without flicker. It includes LC low-pass filter circuit, rectifier filter circuit, bridge inverter circuit, LC resonant filter circuit and segmented constant current LED drive circuit, which makes the segmented constant current LED drive circuit have strong versatility and applicability, thereby improving the The application range of the segmented driving scheme in the field of LED lighting.

Description

A Segmented Constant Current LED Driving Circuit Without Flicker

technical field

The invention belongs to the technical field of LED lighting, and in particular aims at an AC direct drive LED drive circuit, and proposes a segmented constant current LED drive circuit directly driven by AC without flicker.

Background technique

LED is the fourth generation lighting source. LED has the characteristics of energy saving, environmental protection, high efficiency, and safety, so it is widely used in lighting occasions such as landscapes, street lamps, and electronic product backlights. With the application of LED lighting in many occasions, the design of mature and efficient LED driving power is a crucial link in LED lighting.

LED lamps have strict requirements on the driving power supply, and the LED driving circuit uses constant current to drive the LED load to work. Although the traditional two-stage drive circuit scheme can achieve high drive performance, it has the disadvantages of many devices, large size of the drive, and high cost. From the perspective of development prospects, small size, integration and light weight are the common technology development direction of LED drive power supply in the future, and the way of directly supplying power to LED with mains power is the general direction of LED drive power supply development.

At present, the more popular AC direct drive LED method is segmented constant current LED drive method, which is mainly proposed based on the principle of AC voltage tracking, that is, the step-by-step drive method is used to gradually light up the LED load. The LED drive scheme based on this type of method The common structure is shown in Figure 1:

The main circuit of the drive circuit generally includes a rectification circuit, a sampling circuit, a control circuit, a switch circuit and a current control circuit. The sampling circuit provides the required voltage and current signals for the switch control circuit; the switch control circuit controls the opening and closing of each section of LED, and most of the switching devices are high-voltage MOS tubes; the current control circuit controls the change process of the LED current, which can be customized according to the design requirements Realize constant current or variable current in each section. It can be seen that the core of this driving method is to drive the LED loads in groups through the switching devices, so that each group of LED loads can be turned on and off sequentially with the change of the input voltage, and the desired LED current can be obtained through the current control circuit. waveform.

But for the segmented constant current LED drive circuit directly driven by AC, since there is no electrolytic capacitor, the drive current contains twice the AC component of the power frequency, so there is a 100Hz flicker in the LED under 50Hz mains power. Although the 100Hz stroboscopic frequency is higher than the frequency of the human eye's persistence of vision, the human eye cannot perceive the light pulsation of this frequency, but recent studies have found that the human visual system needs to constantly work under such a stroboscopic light source for a long time. To ensure the clarity of the imaging on the retina, this will increase the burden on the human eye and cause eye fatigue, thus restricting the wide application of this type of LED driving scheme.

In order to reduce the harm of stroboscopic flicker, the existing solution is mainly to connect filter capacitors in parallel after the rectifier circuit. This solution uses electrolytic capacitors to absorb part of the AC ripple, but when the ripple is controlled to a certain range (10%), it is difficult to If it is further reduced, the stroboscopic phenomenon cannot be eliminated, and the electrolytic capacitor will increase the size and life of the problem, and it is difficult to meet the requirements of small size, high reliability, and easy integration of the AC direct drive power supply. There are also LED chip manufacturers who propose to use valley-filling technology to store a certain amount of charge in the valley-filling capacitor. When the voltage after full-wave rectification drops to near the zero-crossing point, the valley-filling capacitor discharges the LED light string to ensure that the LED lamps are charged during the entire rectification cycle. The load output light effect is constant, but it only alleviates the stroboscopic phenomenon to a certain extent.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the main purpose of the present invention is to solve the problem of 100HZ flicker in the existing segmented constant current LED driving circuit. Provide a segmented constant current LED drive circuit without flicker, using the bridge inverter circuit to improve the frequency of AC signals, by increasing the operating frequency of the input signal of the segmented constant current LED drive circuit, while maintaining the segmented constant current LED drive On the basis of the circuit characteristics, the function of LED load without flicker is realized, so that the segmented constant current LED drive circuit has strong versatility and applicability, thereby improving the application range of the segmented drive scheme in the field of LED lighting.

In order to achieve the above object, design of the present invention is:

The flicker-free segmented constant current LED drive circuit proposed by the present invention converts the mains AC signal into a high-frequency near-sine wave AC signal as a segmented constant current through a bridge inverter circuit and an LC resonant filter circuit after rectification and filtering. The input signal of the LED drive circuit improves the operating frequency of the pulsating current flowing through the LED load, solves the problem of 100HZ flickering of the LED load in the 50HZ AC mains direct drive LED scheme, and realizes no flickering of the LED load.

The output of the high-frequency AC signal (greater than 1KHZ) in the present invention can be generated by a bridge inverter circuit, and the rectified and filtered DC voltage signal is converted into a high-frequency square wave or high frequency by controlling the on and off of the switch tube. The frequency quasi square wave voltage signal is output, and then the high frequency sine wave signal is obtained through the LC resonant filter network. The structure of the high-frequency output sine wave inverter circuit is shown in Figure 2.

The bridge topology includes full-bridge and half-bridge topologies. Since the voltage stress of the switch tubes of the bridge topology is equal to the DC input voltage, the bridge topology is generally used in occasions where the input AC voltage is 220V or higher. Preferably, when the switching tube is a MOSFET, by setting the parameters of the LC resonant filter network reasonably, the zero voltage turn-on of the MOSFET can be realized and the switching loss can be reduced. The LC resonant filter network is a passive filter, including several topologies such as LC series resonance, LC parallel resonance and LC series-parallel resonance. The resonant filter network is designed for the frequency of the required high-frequency AC signal and has a good selection frequency filter effect. Preferably, when the resonant filter network is an LC series-parallel resonant network, the LC for the series resonance of the fundamental wave of the high-frequency square wave and the LC for the parallel resonance of the fundamental wave are used simultaneously, the former makes the voltage drop of the fundamental wave zero, and the LC for the harmonic wave It presents inductive high reactance, the latter makes the sum of the fundamental wave currents of the parallel circuit zero, and presents capacitive low impedance to harmonics, has excellent filtering characteristics, can make the waveform closer to a sine wave, and can realize the softness of the switch tube switch.

For realizing above-mentioned design, the technical scheme that the present invention adopts is:

A segmented constant-current LED drive circuit without flickering, comprising an LC low-pass filter circuit, a rectification filter circuit, a bridge inverter circuit, an LC resonant filter circuit and a segmented constant-current LED drive circuit, characterized in that: the power supply is sequentially passed through the LC Low-pass filter circuit, rectifier filter circuit, bridge inverter circuit, LC resonant filter circuit are connected to segmental constant current LED drive circuit; using bridge inverter circuit can improve the characteristics of AC signal frequency, by improving segmental constant current LED drive circuit The operating frequency of the input signal, on the basis of maintaining the characteristics of the segmented constant current LED drive circuit, realizes the function of LED load without flicker.

The LC low-pass filter circuit 1 is connected to the live wire and the neutral terminal of the AC mains; the rectifier filter circuit 2 has two input terminals and two output terminals, and one input terminal is connected to the LC low-pass filter circuit 1 , and the other input terminal is connected to the neutral line of the AC mains. The two output terminals are connected to the bridge inverter circuit 3; the LC resonant filter circuit 4 is connected in parallel at both ends of the bridge inverter circuit 3; the segmented constant current LED driver circuit 5 is connected to the The two output terminals of the LC resonant filter circuit 4 described above are connected.

The LC low-pass filter can effectively prevent high-frequency current from flowing into the AC input side, and filter out high-order harmonics to reduce harmonic pollution to the power grid; the rectification and filtering circuit includes a bridge rectification circuit and a filter Capacitor, using the unidirectional conductivity of the diode to rectify the AC mains and convert it into a pulsating direct current. The pulsating direct current is filtered by a capacitor to form a smooth direct current voltage; Wave converts the rectified and filtered DC signal into a high-frequency square wave signal; the LC resonant filter circuit converts the high-frequency square wave signal into a high-frequency near-sine wave signal, which is used as the input signal for the segmented constant current LED drive The segmented constant current circuit, according to the voltage change of the input AC signal, realizes segmental lighting of the LED load by controlling the switching device, and adopts linear control technology to ensure that each segment works in a constant current state. Since the input signal of the circuit is a high-frequency near-sine wave signal, the operating frequency of the pulsating current flowing through the LED load is increased, thereby realizing the flicker-free function.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant progress:

1. The present invention adopts the LC resonant filter circuit, the resonant network has good filter characteristics and system stability, and the resonant circuit can realize the soft switching of the bridge inverter circuit, thereby reducing the loss of the power supply and improving the efficiency of the power supply.

2. The present invention can be effectively combined with the segmented LED drive. Compared with the traditional AC direct drive LED scheme, the current operating frequency of the LED load is improved, the stroboscopic phenomenon is eliminated, and the drive efficiency is improved. High power factor, and retains the advantages of the original segmented constant current LED drive.

3. In addition, both the bridge inverter circuit and the segmented constant current LED drive circuit can be controlled by special LED chips, so as to realize the adjustable working frequency of the whole circuit, and the segmented constant current LED drive circuit can also realize dimming function, which is easy Product commercialization.

In summary, the flicker-free segmented constant current LED drive circuit of the present invention solves the problem that the LED load has 100HZ strobe in the existing AC direct drive segmented constant current LED drive scheme, and the overall circuit structure is simple , small size, low cost, easy modularization, generalization, and has broad application prospects.

Description of drawings

Figure 1 Segmented constant current LED drive scheme diagram of existing AC direct drive

Fig. 2 structural block diagram of high-frequency output sine wave inverter circuit of the present invention

Fig. 3 block diagram of segmented constant current LED driving structure without flicker of the present invention

Fig. 4 Structural block diagram of segmented constant current LED drive without flicker in the embodiment of the present invention

FIG. 5 is a schematic diagram of a segmented constant current LED drive circuit without flicker in an embodiment of the present invention.

detailed description

Preferred embodiments of the present invention are described in detail as follows in conjunction with accompanying drawings:

Embodiment one:

Referring to Fig. 3, the non-flicker segmental constant current LED drive circuit includes LC low-pass filter circuit 1, rectification filter circuit 2, bridge inverter circuit 3, LC resonant filter circuit 4 and segmental constant current LED drive circuit 5, It is characterized in that: the power supply is sequentially connected to the segmented constant current LED drive circuit 5 through the LC low-pass filter circuit 1, the rectification filter circuit 2, the bridge inverter circuit 3, and the LC resonant filter circuit 4; the bridge inverter circuit can be used to improve the AC The characteristics of the signal frequency, by increasing the operating frequency of the input signal of the segmented constant current LED drive circuit, on the basis of maintaining the characteristics of the segmented constant current LED drive circuit, the function of LED load without flickering is realized.

Embodiment two:

Referring to Figure 4, the flicker-free segmented constant-current LED drive circuit includes LC low-pass filter circuit 1, rectifier and filter circuit 2, half-bridge inverter circuit 3, LC series-parallel resonant circuit 4 and segmented constant-current LED in series. drive circuit 5.

The LC low-pass filter 1 can prevent high-frequency current from flowing into the AC input side, and filter out high-order harmonics to reduce harmonic pollution to the power grid; the rectification and filtering circuit 2 converts the input AC into a The waveform is relatively smooth DC; the half-bridge inverter circuit 3 converts the DC signal into a high-frequency square wave signal through the chopping of the switching tube; the LC series-parallel resonant circuit 4 has better filtering characteristics, The high-frequency square wave signal can generate a high-frequency near-sine wave signal through the LC series-parallel resonant network; the input signal of the segmented LED drive circuit 5 is a high-frequency near-sine wave AC signal, which is passed through the switch control circuit of the chip It controls the opening and closing of the MOSFET field effect tube, and then turns on the LED load in turn. Since the operating frequency of the input AC signal is increased, the operating frequency of the pulsating current flowing through the LED load is increased, which solves the problem of 100HZ flickering of the LED load in the 50HZ AC mains direct drive segmental constant current LED drive scheme, and realizes The LED load has no flicker.

In particular, the half-bridge inverter circuit described in this example is one of the bridge inverter circuits described, and is not limited to the specific implementation in this example; the LC series-parallel resonant network is the LC A type of resonant filter network is not limited to the specific implementation manner given in the present invention. The segmented LED drive may be a general AC direct drive segmented LED drive, and is not limited to the specific implementation manner given in the present invention.

The specific working principle of the flicker-free segmented constant current LED drive circuit is shown in Figure 5. The LC low-pass filter circuit 1 includes an inductor L1 and a capacitor C1, wherein the inductor L1 is directly connected to the AC input terminal, and the capacitor C1 One end is connected to the AC input end, one end is connected to the inductor L1, and the common end of the two is connected to the anode of the D1 diode in the rectification filter circuit 2; the half-bridge inverter circuit includes two resistors R1 and R2, two Capacitors C3, C4 and C5, a fast recovery diode D5, two MOSFET field effect transistors Q1 and Q2, where resistor R1 and capacitor C3 are connected in series, and the common end of the two is connected to the VCC pin of the driver chip IR2153; resistor R2 and capacitor CT is connected in series, one end of the resistor R2 is connected to the RT terminal of the driver chip IR2153, the common terminal of the resistor R2 and the capacitor C4 is connected to the CT pin of the driver chip IR2153; the diode D5 and the capacitor C5 are connected in series between the VCC pin and the VS pin of the driver chip Between; field effect transistors Q1 and Q2 are respectively connected to the HO and LO pins of the driver chip IR2153, and the common end of the two is connected to the VS pin of the driver chip. The LC series-parallel resonant circuit includes two inductors L2 and L3, two capacitors C6 and C7, wherein the inductor L2 is connected to the VS pin of the drive chip, the inductor L2 and the capacitor C6 are connected in series, the inductor L3 and the capacitor C7 are connected in parallel, and output high frequency Sinusoidal AC signal. The segmented constant current circuit driving circuit is composed of five diodes D6-D10, nine resistors R3-R11, one capacitor, four MOSFET switch tubes Q3-Q6 and a driver chip CL2012, and the diodes D6-D9 form a rectifier circuit, reducing The piezoresistor R9 and C1 are connected in series, the common end of the two is connected to the VCC pin of the driver chip, the resistors R7-R10 form a resistor network, the G1-G4 pins of the driver chip are respectively connected to the G terminals of the MOSFET switch tubes Q3-Q6, and the resistor R3 -R6 is connected in series, where resistor R3 is connected to chip pin S1, the common end of resistor R3 and R4 is connected to chip pin S2, the common end of resistor R4 and R5 is connected to chip pin S3, and the common end of resistor R5 and R6 is connected to chip pin S4.

Specific work process

The example of the present invention is connected to the 50HZ industrial frequency AC mains according to the accompanying drawing 5, and after passing through the low-pass filter 1 composed of the inductance L1 and the capacitor C1, the high-order harmonics can be effectively filtered out, and the harmonic pollution to the power grid can be reduced. After eliminating the interference, the AC power is converted into a smooth DC bus voltage through the rectification and filtering circuit 2;

The DC bus voltage charges the power supply capacitor C3 of the driver chip 3 through the step-down resistor R1. When the terminal voltage of the capacitor C3 exceeds the undervoltage lock release threshold of the driver chip 3, the chip will start automatically. After the driver chip 3 starts working, the output signals of the high-end HO pin and the low-end output LO pin control the switching on and off of the MOSFET switch tubes, and the duty ratios of the two switch tubes are both 0.5, and they are turned on alternately and complementary. Among them, R2 and C4 determine the switching frequency of the drive switch tube (greater than or equal to 1KHZ). After the DC bus voltage is chopped by the MOSFET switch tubes Q1 and Q2, the VS pin of the drive chip 3 outputs a high-frequency square wave voltage whose operating frequency is equal to the switching frequency;

The high-frequency square wave voltage passes through the series-parallel resonant filter network 4 formed by the inductors L2 and L3, and the capacitors C6 and C7 to obtain a high-frequency near-sinusoidal AC voltage. The resonant angular frequency of the series branch composed of inductor L2 and capacitor C6 is approximately equal to the switching frequency, and the resonant frequency of the parallel branch composed of inductor L3 and capacitor C7 is slightly higher than the switching frequency, making the entire resonant network inductive to realize MOS switching The zero voltage of the tube S is turned on, thereby reducing the switching loss and improving the switching efficiency frequency.

The high-frequency sinusoidal AC voltage is converted into high-frequency pulsating direct current through the rectifier circuit 5, and through the sampling circuit and switch control circuit inside the driver chip 6, the driver chip 6 controls the conduction and shutdown of the MOSFET switch tubes Q3-Q6, thereby controlling The LED loads are grouped to achieve the effect that the LED loads of each group light up and go out sequentially with the change of the input voltage, and the desired LED current waveform is obtained through the current control circuit inside the driver chip 6 . The current flowing through each section of LED load is set by the resistors R3-R6, and the G1-G4 pins of the driver chip control the MOSFET switch tubes Q3-Q6 to work alternately in the fully on, linear constant current, and completely off states. Since the input AC signal is a high-frequency AC signal, the operating frequency of the pulsating current flowing through the LED load is increased, and the problem of 100HZ flickering of the LED load in the segmented constant current LED drive scheme directly driven by 50HZ AC mains is solved. The LED load has no flicker.

The flicker-free segmented constant-current LED drive of the present invention has been described in detail above, and a circuit diagram of the flicker-free segmented constant-current LED drive circuit has been provided. Those of ordinary skill in the art can realize the corresponding Segmented constant current LED drive circuit without flicker. The flicker-free segmented constant-current LED drive circuit of the present invention solves the problem of 100 Hz flicker in the LED load in the scheme of directly driving the LED with 50 Hz AC mains, and realizes the flicker-free LED load.

Claims (5)

1. the stagewise constant current LED drive circuit without stroboscopic, including LC low-pass filter circuit (1), current rectifying and wave filtering circuit (2), bridge inverter main circuit (3), LC resonator filter circuit (4) and stagewise constant current LED drive circuit (5), it is characterised in that: power supply is successively through LC low-pass filter circuit (1), current rectifying and wave filtering circuit (2), bridge inverter main circuit (3), LC resonator filter circuit (4) is connected to stagewise constant current LED drive circuit (5)；Utilize bridge inverter main circuit can improve the feature of AC signal frequency, by improving the operating frequency of the input signal of stagewise constant current LED drive circuit, possessing, the basis of stagewise constant current LED drive circuit feature realizes the LED load function without stroboscopic.

2. a kind of stagewise constant current LED drive circuit without stroboscopic according to claim 1, it is characterized in that: described LC low-pass filter circuit (1) includes an an inductance L1 and electric capacity C1, described inductance L1 is directly connected with ac input end, electric capacity C1 one end is connected with ac input end, the other end is connected with inductance L1, and the common port of inductance L1 and electric capacity C1 is connected to stream filter circuit (2)；Adopt LC low pass filter, can effectively prevent high frequency electric from flowing into exchange input side, and filter higher hamonic wave, reduce the harmonic pollution to electrical network.

3. a kind of stagewise constant current LED drive circuit without stroboscopic according to claim 1, it is characterized in that: adopt bridge inverter main circuit, by the copped wave of switching tube, direct current signal after rectifying and wave-filtering is converted to the square-wave signal of high frequency, improves the operating frequency of integrated circuit.

4. a kind of stagewise constant current LED drive circuit without stroboscopic according to claim 1, it is characterized in that: adopt LC resonator filter circuit, resonant network has good filtering characteristic and system stability, and resonance circuit can realize the Sofe Switch of bridge inverter main circuit, thus reducing the loss of power supply, improve the efficiency of power supply.

5. a kind of stagewise constant current LED drive circuit without stroboscopic described in claim 1, it is characterized in that: adopt stagewise constant current LED drive circuit, the drive circuit change in voltage according to input ac voltage signal, the segmentation realizing LED load by controlling switching device is lighted, and each section is operated in constant current state to adopt linear control technique to ensure, there is topology simple, the feature that power factor is high.