WO2017198126A1

WO2017198126A1 - Linear constant-current drive circuit

Info

Publication number: WO2017198126A1
Application number: PCT/CN2017/084334
Authority: WO
Inventors: 邵蕴奇; 江春成; 张绍军
Original assignee: 上海路傲电子科技有限公司; 上海亚明照明有限公司
Priority date: 2016-05-16
Filing date: 2017-05-15
Publication date: 2017-11-23
Also published as: CN107396481A; CN107396481B

Abstract

A linear constant-current drive circuit, powered by mains power (VAC1) via a bridge rectifier (DB1), having multiple LEDs (LED1, LED2, …, LEDX) sequentially connected in series as a load, and forming one positive node (A0) and multiple LED negative nodes (A1, A2, …, AX). The bridge rectifier has an input end connected to the mains power, and an output positive electrode connected to the positive node. The circuit comprises a switchable constant current source (CCX), a voltage detection circuit (VD), a feedback circuit (FB), and a multiplier (M). The circuit enables a waveform of a mains power current to have a near-sinusoidal shape. If an effective voltage value of the mains power is low, the circuit of the present invention reduces a current flowing through the LEDs to prevent the LEDs from over-current operation. In addition, the present invention enables gradual transition from a constant-power mode to a constant-current mode during a dimming process, and the constant-current mode improves LED brightness variation caused by mains power fluctuation in low-brightness applications.

Description

Linear constant current driving circuit

Technical field

The invention relates to a linear driving circuit, in particular to a linear constant current LED driving circuit and an integrated circuit designed by the same, which is suitable for LED lighting applications.

Background technique

At present, LED lamps have been widely used in lighting applications in various fields. The LED can't be directly connected to the AC, and the corresponding current-limiting drive device needs to be configured. The current LED driver uses the traditional high-frequency switching power supply. This solution requires high-frequency switching circuit, complicated circuit, high cost, and linear constant current drive. The replacement of the switching power supply scheme is a development trend.

At present, the input current waveforms of linear constant current driving schemes on the market are pulse wave, square wave or step waveform, which shows low power factor and large harmonic distortion. It can only be applied in low power lighting products, not suitable for large Power lighting applications.

Therefore, it is necessary to develop a linear LED lighting driving scheme with high power factor and low harmonic distortion.

Summary of the invention

The invention provides a linear constant current driving circuit, which realizes high power factor and low harmonic distortion, overcomes the defects of the above technology, and solves the existing technical problems.

The invention provides a linear constant current driving circuit, which is powered by the mains VAC1 via the rectifier bridge DB1, and the load is a plurality of LEDs connected in series to form an anode node and a plurality of LED cathode nodes; the input end of the rectifier bridge DB1 and the mains VAC1 Connected, the output positive pole is connected to the anode node; and comprises a switching constant current source CCX, a voltage detecting circuit VD, a feedback circuit FB and a multiplier M; wherein the switching constant current source CCX comprises a set switching constant current source current Current setting terminal ISET, a common ground GND, a reaction switching constant current source current detection terminal CS and a plurality of constant current output terminals, a plurality of constant current output terminals respectively connected to a plurality of cathode nodes, the common ground terminal is connected to the ground; the voltage detection circuit detects The utility voltage waveform outputs a voltage detection signal VO that is in phase with the mains voltage waveform; the feedback circuit FB includes a reference signal, at least one feedback terminal and an output terminal FBO, and the feedback circuit FB sums the signals on the at least one feedback terminal Obtaining a feedback signal, the difference between the reference signal and the feedback signal is integrated and output to the output terminal FBO; the current detecting terminal CS is connected to the first feedback terminal IN1 of the feedback circuit FB, and the current signal generated by the current detecting terminal CS is controlled by the feedback circuit FB; The multiplier M comprises two input terminals MI1, MI2 and an output terminal MO. The input terminal MI1 is connected to the voltage detection signal VO, and controls the signal shape of the output terminal MO of the multiplier M. The input terminal MI2 is connected to the output terminal FBO of the feedback circuit FB. Controlling the signal amplitude of the output terminal MO of the multiplier M, the output terminal MO of the multiplier M is connected to the current setting terminal ISET of the switching constant current source CCX, and controls the current shape of the switching constant current source CCX and Degree.

The present invention provides a linear constant current driving circuit, which may further have the following features: a constant power compensation circuit CP; a constant power compensation circuit CP input terminal CI detects the voltage detection signal VO, and generates a voltage detection signal VO The monotonically varying compensation signal CO; the compensation signal CO is connected to the second feedback terminal IN2 of the feedback circuit FB.

The present invention provides a linear constant current driving circuit, which may also have the following features: The constant power compensation circuit CP further includes a control terminal CK.

The present invention provides a linear constant current driving circuit, which may further include a dimming circuit DIM; the input of the dimming circuit DIM is a variable signal DI, and the output includes a dimming signal DO1 and a suppressing signal DO2 The dimming signal DO1 is connected to the third feedback terminal IN3 of the feedback circuit FB; when the variable signal DI is changed, the switching current source CCX is controlled by the dimming signal DO1 The current is changed; the suppression signal DO2 is connected to the control terminal CK of the constant power compensation circuit CP, and the influence of the voltage detection signal VO on the feedback signal is controlled.

The present invention provides a linear constant current driving circuit, which may further include a dimming circuit DIM; the input of the dimming circuit DIM is a variable signal DI, and the output includes a dimming signal DO1; the dimming signal DO1 Connected to the third feedback terminal IN3 of the feedback circuit FB; when the variable signal DI changes, the current change of the switching current source CCX is controlled by the dimming signal DO1.

The present invention provides a linear constant current driving circuit, which may further have the following features: a protection circuit PRO is further included; the protection circuit PRO internally includes a set threshold, and the protection circuit PRO input terminal PI detects the voltage detection signal VO, when the voltage detection signal When the VO average value is lower than the set threshold, the protection circuit outputs the protection signal PO, and the current of the switching current source CCX is controlled to decrease as the voltage detection signal VO decreases.

The present invention provides a linear constant current driving circuit, which may further include a protection circuit PRO; the protection circuit PRO input terminal PI detects the voltage detection signal VO, and generates a limiting ratio proportional to the average value of the voltage detection signal VO. Threshold, the output signal FBO of the control feedback circuit FB does not exceed the limit threshold.

The present invention provides a linear constant current driving circuit, which may further have the following features: an input end of the constant power compensation circuit, a first input end of the multiplier, and an input end of the protection circuit are connected to an output end of a voltage detecting circuit.

The present invention provides a linear constant current driving circuit, which may further have the following features: an input end of the constant power compensation circuit, a first input end of the multiplier, and an input end of the protection circuit are connected to the same output end of a voltage detecting circuit.

The present invention provides a linear constant current driving circuit, which can also have the following features: The switching constant current source CCX includes a plurality of voltage controlled current sources, a plurality of signal bias sources corresponding to the voltage controlled current source, and a current detecting resistor. RCS; each of the plurality of voltage-controlled current sources includes two control terminals and two power terminals, and the first power terminal of each voltage-controlled current source is connected to the current-sense terminal CS, and the current is detected. The terminal CS is connected to the common ground through the current detecting resistor RCS, and the second power terminal is respectively used as a plurality of constant current output terminals, and the first control end of each voltage controlled current source is connected to the current setting terminal ISET, and the second control The terminal is connected to the current detecting terminal CS via a corresponding signal bias source.

The invention provides a linear constant current driving circuit, which can also have the following features: a plurality of signal bias sources make the potential on the second control end different, and the second control terminal has a higher potential voltage control current source. The current output terminal is connected to the cathode node with higher potential, and the constant current output terminal of the voltage control current source with lower potential on the second control terminal is connected to the cathode node with lower potential.

The present invention provides a linear constant current driving circuit, which can also have the following features: The switching constant current source CCX includes a plurality of voltage controlled current sources, a plurality of signal bias sources corresponding to the voltage controlled current source, and a current detecting resistor. RCS; each of the plurality of voltage-controlled current sources includes two control terminals and two power terminals, and the first power terminal of each voltage-controlled current source is connected to the current-sense terminal CS, and the current is detected. The terminal CS is connected to the common ground through the current detecting resistor RCS, and the second power terminal is respectively used as a plurality of constant current output terminals, and the first control end of each voltage controlled current source is connected to the current setting via the corresponding signal bias source. The terminal ISET, the second control terminal is connected to the current detecting terminal CS.

The present invention provides a linear constant current driving circuit, which may also have the following features: a plurality of signal bias sources make the potentials on the first control terminals of the plurality of voltage controlled current sources different, the first The constant current output terminal of the voltage control current source with higher potential on the control terminal is connected to the cathode node with lower potential, and the constant current output terminal of the voltage control current source with lower potential on the first control terminal and the cathode with higher potential Nodes are connected.

The present invention provides a linear constant current driving circuit, which can also have the following features: The switching constant current source CCX includes a plurality of voltage controlled current sources, a plurality of signal bias sources corresponding to the voltage controlled current source, and a current detecting resistor. RCS; each of the plurality of voltage-controlled current sources includes two control terminals and two power terminals, and the first power terminal of each voltage-controlled current source is connected to the current-sense terminal CS, and the current is detected. The terminal CS is connected to the common ground through the current detecting resistor RCS, and the second power terminal is respectively used as a plurality of constant current output terminals; the two control terminals are respectively the current reference signal and the current feedback signal of the voltage controlled current source, and the difference between the two is used. To control the current value of the voltage control current source; the bias signal source makes the current setting value of the voltage control current source different, and the constant current output end corresponding to the voltage control current source with a larger current setting value and the lower potential The cathode node is connected, and the constant current output end corresponding to the voltage control current source with a small current setting value is connected to the cathode node with higher potential.

The present invention provides a linear constant current driving circuit, and may also have the following feature: the input terminal VI of the voltage detecting circuit VD detects the positive voltage signal of the rectifier bridge DB1.

The present invention provides a linear constant current driving circuit, which may also have the following feature: the input terminal VI of the voltage detecting circuit VD detects the voltage signal of the cathode node having the highest potential.

The role and effect of the invention

The linear constant current driving circuit realized by the invention can make the main current waveform appear close to the shape of a sine wave, and has the advantages of high power factor and low harmonic distortion; in addition, the solution provided by the invention can be used when the mains voltage fluctuates. Input work is achieved by changing the current flowing through the LED The rate is basically constant, and when the rms voltage is low, the current flowing through the LED is reduced to avoid the LED overcurrent operation. Thirdly, the solution provided by the invention can achieve good dimming performance, and is lowered. During the brightness process, the drive circuit gradually transitions from constant power mode to constant current mode. Since the human eye is more sensitive to low-brightness light, the constant current mode improves the LED brightness variation caused by grid fluctuations in low-brightness applications.

DRAWINGS

1 is a schematic diagram showing the principle of a linear constant current driving circuit of the first embodiment.

2 is a circuit diagram of a switching constant current source CCX of the first embodiment.

Fig. 3 is a circuit diagram of a voltage detecting circuit VD of the first embodiment.

4 is a circuit diagram of a feedback circuit FB of the first embodiment.

Fig. 5 is a circuit diagram of a constant power compensation circuit CP of the first embodiment.

Fig. 6 is a circuit diagram of a dimming circuit DIM of the first embodiment.

Fig. 7 is a circuit diagram of a protection circuit PRO of the first embodiment.

Fig. 8 is a circuit diagram of a protection circuit PRO of the second embodiment.

Fig. 9 is a circuit diagram of a switching constant current source CCX of the third embodiment.

Fig. 10 is a circuit diagram of a switching constant current source CCX of the fourth embodiment.

Figure 11 is a circuit diagram of a switching constant current source CCX of the fifth embodiment.

detailed description

The present invention will be further described below in conjunction with the drawings and specific embodiments.

Embodiment 1

As shown in Figure 1, LED1, LED2, and LEDX are connected in series to form a load to form an anode. Node A0 and a plurality of cathode nodes A1, A2 and AX, the input end of the rectifier bridge DB1 is connected to the mains VAC1, the output positive pole is connected to the anode node A0, and the output negative pole is grounded. The driving circuit comprises: switching constant current source CCX, voltage detecting circuit VD, feedback circuit FB, multiplier M, constant power compensation circuit CP, protection circuit PRO and dimming circuit DIM.

The switching constant current source CCX includes a current setting terminal ISET for setting a switching constant current source current, a common ground GND, a current detecting terminal CS for reacting the switching constant current source current, and a plurality of constant current output terminals OUT1, OUT2 and OUTX. OUT1, OUT2, and OUTX are connected to a plurality of cathode nodes A1, A2, and AX, respectively, and the common ground terminal GND is grounded.

The input terminal VI of the voltage detecting circuit VD is connected to the output positive pole of the rectifier bridge DB1 or to the cathode node A1 having the highest potential for detecting the mains waveform, and generating a voltage detecting signal VO which is in phase with the mains voltage waveform.

The feedback circuit FB includes feedback terminals IN1, IN2, IN3 and an output terminal FBO. The feedback circuit FB sums the signals on the feedback terminals IN1, IN2 and IN3 to obtain a feedback signal, and is integrated with the internal reference signal for error integration and then connected to the output terminal FBO.

The current signal generated by the current-sense terminal CS of the switching constant current source CCX reflects the currents of the LEDs 1, LED2 and LEDX, and is connected to the first feedback terminal IN1 of the feedback circuit FB, and the current signal of the current-sense terminal CS is controlled by the feedback circuit FB.

The multiplier M comprises two input terminals MI1, MI2 and an output terminal MO. The first input terminal MI1 is connected to the voltage detection signal VO, controls the signal shape of the multiplier output terminal MO, and the second input terminal MI2 and the feedback circuit FB The output terminal FBO is connected to control the signal amplitude of the multiplier output terminal MO, and the multiplier output terminal MO is connected to the current setting terminal ISET of the switching constant current source CCX to control the current shape and amplitude of the switching constant current source CCX.

The input terminal CI of the constant power compensation circuit CP is connected to the voltage detection signal VO to generate a compensation signal CO that monotonically changes as the voltage detection signal VO changes. The compensation signal CO is connected as an output to the second feedback terminal IN2 of the feedback circuit FB.

When the average value of the mains VAC1 increases, the compensation signal CO controls the current of the switching current source CCX to be reduced via the feedback circuit FB, and the average value of the current flowing through the mains VAC1 also decreases; conversely, when the average value of the mains VAC1 decreases The compensation signal CO controls the current average value of the switching current source CCX to be increased via the feedback circuit FB, and the current average value flowing through the commercial power VAC1 also increases, so that the input power is relatively constant when the commercial power voltage changes.

The constant power compensation circuit CP further includes a control terminal CK for changing the transfer coefficient of the voltage detection signal VO to the compensation signal CO.

The input of the dimming circuit DIM is a variable signal DI, and the output includes a dimming signal DO1 and a suppressing signal DO2. The dimming signal DO1 is connected to the third feedback terminal IN3 of the feedback circuit FB. When the variable signal DI is changed, the feedback signal of the feedback circuit FB is controlled by the dimming signal DO1 to control the current change of the switching current source CCX; the suppression signal DO2 is connected to The control terminal CK of the constant power compensation circuit CP controls the influence of the voltage detection signal VO on the feedback signal. When the variable signal DI controls the current of the switching current source CCX to gradually decrease, the influence of the voltage detection signal VO on the feedback signal is gradually weakened, and vice versa. When the variable signal DI controls the current of the switching current source CCX to gradually increase, the influence of the voltage detection signal VO on the feedback signal is gradually enhanced.

The input terminal PI of the protection circuit PRO is connected to the voltage detection signal VO for detecting the voltage detection signal VO. When the average value of the voltage detection signal VO is lower than the internal set threshold, the protection circuit PRO outputs the protection signal PO, and the protection circuit PRO Output PO and multiplier M The input terminal MI2 is connected, so that the current of the switching current source CCX is controlled to decrease as the voltage detection signal VO decreases.

As shown in FIG. 2, the switching constant current source CCX includes: a plurality of voltage-controlled current sources VCCS1, VCCS2, and VCCSX, a plurality of signal bias sources VOS1, VOS2, and VOSX corresponding to the voltage-controlled current source, and a current-sense resistor. RCS.

Each voltage-controlled current source includes two power terminals and two control terminals. The first power terminal of each voltage-controlled current source is connected to the current-sense terminal CS, and the current-sense terminal CS is connected to the common through the current-sense resistor RCS. At ground GND, the current sense terminal CS generates a current signal. The second power terminal acts as a number of constant current output terminals OUT1, OUT2 and OUTX, respectively.

The first control terminal of each voltage controlled current source is connected to the current setting terminal ISET. The second control terminal is respectively connected to one end of a plurality of signal bias sources VOS1, VOS2 and VOSX, and the other ends of the plurality of signal bias sources VOS1, VOS2 and VOSX are connected in parallel to receive feedback of the current signal on the current detecting terminal CS.

The signal amplitudes of several signal bias sources VOS1, VOS2 and VOSX are different. The signal output source VOS1 with the largest offset frequency is connected to the constant current output terminal OUT1 and the cathode node A1 with the highest potential. The constant current output terminal OUT2 controlled by the source VOS2 is connected to the cathode node A2 of the second potential, and so on, the constant current output terminal OUTX controlled by the signal bias source VOSX having the smallest offset amplitude is connected to the cathode node AX having the lowest potential. When the instantaneous value of the VAC1 sine wave voltage is lower, when there is lower than the conduction threshold of LED1, no current flows through all the voltage-controlled current sources; when the instantaneous value of the VAC1 sine wave voltage reaches the conduction gate of LED1 Limited time, LED1 and voltage-controlled current source VCCS1 have current flowing; when the city VAC1 sine wave When the instantaneous value reaches the conduction threshold of LED2, current flows through LED1, LED2 and voltage-controlled current source VCCS2, and VCCS1 is turned off because the offset of signal bias source VOS1 is greater than signal bias source VOS2; and so on, When the instantaneous value of the VAC1 sinusoidal voltage reaches the conduction threshold of LEDX, current flows through LED1, LED2, LEDX and voltage-controlled current source VCCSX, and VCCS1 and VCCS2 have greater offset than signal bias sources VOS1 and VOS2. The signal is biased off by the source VOSX.

In the present invention, the voltage-controlled current sources VCCS1, VCCS2, and VCCSX all have higher gains, so the signal difference between the two control terminals of the voltage-controlled current sources VCCS1, VCCS2, and VCCSX is close to zero, and the signal at the current setting terminal ISET is close. The signal of the sine wave makes the signal amplitude of VOS1, VOS2 and VOSX much smaller than the signal amplitude of the current setting terminal ISET, and the presence of VOS1, VOS2 and VOSX hardly affects the signal of the current setting terminal ISET to the current detecting terminal CS. The control accuracy is almost negligible for the waveform distortion caused by the CS at the current detecting end, so the waveform of the CS at the current detecting end is close to a sine wave, and the commercial current is also close to a sine wave.

As shown in FIG. 3, the voltage detecting circuit VD includes a resistor RH and a resistor RL. One end of the resistor RH and the resistor RL in series is connected to the input terminal VI, the other end is connected to the ground, and the intersection of the resistor RH and the resistor RL serves as the output terminal VO of the voltage detecting circuit VD.

The resistor RH and the resistor RL constitute a voltage dividing resistor network, and the waveform of the output terminal VO is identical to the signal shape of the input terminal VI, and the input terminal VI is connected to the anode of the rectifier bridge DB1 or to the cathode node A1 having the highest potential, and can be realized. The waveform of the output VO is consistent with the phase of the mains voltage waveform, and the shape is similar.

The output terminal VO reflects both the voltage waveform of the mains VAC1 and the electricity of the mains VAC1. The average value.

4 is a circuit diagram of a feedback circuit FB of the first embodiment.

As shown in FIG. 4, the feedback circuit FB includes an error amplifier AMP4, a filter F4, an adder SUM4, and a voltage reference V4.

The non-inverting terminal of the error amplifier AMP4 is grounded via a voltage reference V4, the inverting terminal is connected to the output of the adder SUM4, the input of the adder SUM4 is connected to the three feedback terminals IN1, IN2 and IN3 of the feedback circuit FB, and the AMP4 of the error amplifier The output is filtered by filter F4 and connected to the output FBO of feedback circuit FB.

The error amplifier AMP4 and the filter F4 constitute an error integration circuit, and integrate the difference between the output signal of the adder SUM4 and the voltage reference V4. According to the negative feedback principle, the output average of the control adder SUM4 is equal to the voltage reference V4. . According to different feedback terminals, the feedback circuit FB has the following working modes:

When the first feedback terminal IN1 is used in the three input terminals of the feedback circuit FB, IN1 is connected to the current signal of the current detecting terminal CS, and the feedback circuit FB controls the current signal to be constant, that is, the current of the switching constant current source CCX is controlled to be constant.

When the second feedback terminal IN2 of the feedback circuit FB is connected to the output of the constant power compensation circuit CP, the current of the switching constant current source CCX is affected by the output of the constant power compensation circuit CP, and the function of the constant power compensation circuit CP is realized in the city. The input power is relatively constant as the electrical voltage changes.

When the third feedback terminal IN3 is connected to the output of the dimming circuit DIM, the current of switching the constant current source CCX will be affected by the DIM circuit, and the function of the dimming circuit DIM is to achieve adjustment of the brightness of the LED.

The three feedback terminals of the feedback circuit FB can be selectively selected for different performance requirements. use. When the stability of the LED brightness is high, only the first feedback terminal IN1 can be used, and the feedback circuit FB controls the current of the switching constant current source CCX to be constant, the system operates in the constant current mode; when the input power to the driving power is stable When the requirement is high, the access of the second feedback terminal IN2 can make the system work in the constant power mode; when the external signal is required to adjust the brightness of the LED, it is necessary to access the third feedback terminal IN3 to make the system work in dimming. mode.

As shown in FIG. 5, the constant power compensation circuit CP is a multiplier. The input terminals of the multiplier M5 are the input terminal CI and the control terminal CK of the constant power compensation circuit CP, respectively, and the output terminal is the compensation signal CO.

The input terminal CI is connected to the voltage detection signal VO, the control terminal CK is connected to the dimming circuit DIM, and the output terminal CO is connected to the second feedback terminal IN2 of the feedback circuit FB.

When the amplitude of the control terminal CK signal is constant, the compensation signal CO monotonously changes with the change of the voltage detection signal VO. When the average value of the commercial power VAC1 increases, the compensation signal CO controls the current of the switching current source CCX via the feedback circuit FB. The average current flowing through the mains VAC1 is also reduced; conversely, when the mains VAC1 average value is decreased, the compensation signal CO is controlled by the feedback circuit FB to control the current value of the switching current source CCX to increase, flowing through the mains VAC1 The current average is also increased to achieve a relatively constant input power when the mains voltage changes.

When the amplitude of the control terminal CK signal decreases, the transmission coefficient of the input terminal CI to the compensation signal CO decreases. Conversely, when the amplitude of the control terminal CK signal increases, the transmission coefficient of the input terminal CI to the compensation signal CO increases. By changing the signal amplitude of the control terminal CK, the influence of the voltage detection signal VO on the feedback signal of the feedback circuit FB can be changed.

Fig. 6 is a circuit diagram of a dimming circuit DIM of the first embodiment.

As shown in FIG. 6, the dimming circuit DIM has an input signal DI and two output signals. The two output signals are a dimming signal DO1 and a suppression signal DO2, respectively. The dimming circuit DIM internally contains two amplifiers AMP5, AMP6 and a voltage reference V6. The input end of the amplifier AMP5 is connected to the input signal DI, and the output signal is the suppression signal DO2. The non-inverting input of the amplifier AMP6 is connected to the positive pole of the voltage reference V6, the negative pole of the voltage reference V6 is grounded, the inverting input of the amplifier AMP6 is connected to the input signal DI, and the output signal is the dimming signal DO1.

The input signal DI is externally connected to a variable signal.

The dimming signal DO1 is connected to the third feedback terminal IN3 of the feedback circuit FB. When the variable signal is increased, the dimming signal DO1 is decreased, and the current of the switching current source CCX is increased; conversely, when the variable signal is decreased, The dimming signal DO1 is increased, and the current for controlling the switching current source CCX is decreased.

The suppression signal DO2 is used to control the transfer coefficient of the constant power compensation circuit CP. When the current of the variable signal control switching current source CCX is gradually decreased, the influence of the voltage detection signal VO on the feedback signal is gradually weakened, and the system is from the constant power mode to the constant current. The mode gradually transitions; conversely, when the variable signal control switching current source CCX gradually increases, the influence of the voltage detection signal VO on the feedback signal gradually increases, and the system gradually transitions from the constant current mode to the constant power mode.

As shown in FIG. 7, the protection circuit PRO includes a filter F7, an amplifier AMP7, a voltage reference V7, and a transistor Q7. The input of the filter F7 is connected to the input terminal PI of the protection circuit PRO, the output terminal is connected to the inverting input terminal of the amplifier AMP7, the non-inverting input terminal of the amplifier AMP7 is grounded via the voltage reference V7, and the output terminal is connected to the gate of the transistor Q7. The source of the transistor Q7 is grounded, and the drain is connected to the output terminal PO of the protection circuit PRO.

The input terminal PI of the protection circuit PRO is connected to the voltage detection signal VO for detecting the voltage The detection signal VO is connected to the output terminal FBO of the feedback circuit FB. When the voltage detection signal VO is filtered by the filter F7 and the signal output is lower than the voltage reference V7, the amplifier AMP7 drives the transistor Q7 to control the output terminal FBO voltage of the feedback circuit FB to fall. The lower the voltage detection signal VO, the output terminal FBO of the feedback circuit FB The lower the voltage, the higher the current of the switching current source CCX is as the voltage detection signal VO decreases. This causes the current flowing through the LED to decrease when the average value of the mains voltage is low, avoiding the LED overcurrent operation.

The effect and effect of the embodiment: the mains current waveform can be approximated to the shape of a sine wave, and has the advantages of high power factor and low harmonic distortion; when the mains voltage fluctuates, the input power is realized by changing the current flowing through the LED. Basically constant characteristics, and reduce the current flowing through the LED when the average value of the mains voltage is low, to avoid the LED overcurrent operation; in the dimming application, the driving circuit is from constant power mode to constant during the process of reducing the brightness The gradual transition of the flow mode suppresses changes in LED brightness caused by grid fluctuations in low-light applications.

Embodiment 2

In the second embodiment, except for the structure of the protection circuit PRO and the implementation one, the other circuit structures and working principles are the same, and the description will not be repeated.

As shown in FIG. 8, the protection circuit PRO includes a filter F8, an amplifier AMP8, and a transistor Q8. The input of the filter F8 is connected to the input terminal PI of the protection circuit PRO, the output terminal is connected to the inverting input terminal of the amplifier AMP8, the output terminal of the amplifier AMP8 is connected to the gate of the transistor Q8, the source of the transistor Q8 is grounded, and the amplifier The non-inverting input of AMP8 and the drain of transistor Q8 are both connected to the output PO of protection circuit PRO.

The input terminal PI of the protection circuit PRO is connected to the voltage detection signal VO for detecting the voltage The detection signal VO is connected to the output terminal FBO of the feedback circuit FB. When the voltage detection signal VO is filtered by the filter F8 and the signal output is lower than the signal of the output terminal FBO of the feedback circuit FB, the amplifier AMP8 drives the transistor Q8 to control the output terminal FBO voltage of the feedback circuit FB does not exceed the output signal of the filter F8, the voltage The lower the detection signal VO, the lower the FBO voltage at the output of the feedback circuit FB, and finally the current of the switching current source CCX decreases as the voltage detection signal VO decreases. This causes the current flowing through the LED to decrease when the average value of the mains voltage is low, avoiding the LED overcurrent operation.

Embodiment 3

In the third embodiment, except that the switching constant current source CCX structure is different from the implementation one, the other circuit structures and working principles are the same, and the description will not be repeated.

As shown in FIG. 9, the second control end of each of the voltage-controlled current sources in the switching constant current source CCX circuit shown in FIG. 2 is connected to one end of a plurality of signal bias sources VOS1, VOS2, and VOSX, respectively. The other ends of the signal bias sources VOS1, VOS2, and VOSX are connected to the current setting terminal ISET, and the same function as that of FIG. 2 can be realized.

Embodiment 4

In the fourth embodiment, except that the switching constant current source CCX structure is different from the implementation one, the other circuit structures and working principles are the same, and the description will not be repeated.

As shown in FIG. 10, the signal bias sources VOS1, VOS2, and VOSX in the switching constant current source CCX circuit shown in FIG. 2 are sequentially connected in series and then connected to the first control terminals of the voltage control current sources VCCS1, VCCS2, and VCCSX, respectively. The same function as in Fig. 2 can be realized.

Embodiment 5

In the fifth embodiment, except that the switching constant current source CCX structure is different from the implementation one, the other circuit structures and working principles are the same, and the description will not be repeated.

As shown in FIG. 11, the signal bias sources VOS1, VOS2, and VOSX in the switching constant current source CCX circuit shown in FIG. 2 are sequentially connected in series and then connected to the second control terminals of the voltage control current sources VCCS1, VCCS2, and VCCSX, respectively. The same function as in Fig. 2 can be realized.

In the end, the signal bias source still has other connection modes. In all connection modes, the signal bias source functions to make the current setting values of each of the voltage control current sources VCCS1, VCCS2 and VCCSX different. The constant current output terminal of the voltage control current source with a larger current setting value is connected to the cathode node having a lower potential, and the constant current output terminal of the voltage control current source having a smaller current setting value is connected to the cathode node having a higher potential when the current is When a current flows through the constant current output terminal of the voltage control current source with a large setting value, the constant current output terminal of the voltage control current source with a small current setting value is turned off.

The above specific embodiments only describe the main features and innovations of the present solution. Those skilled in the art will appreciate that the present solution is not limited by the above embodiments. Without departing from the scope of this innovation and protection, there will be various changes to the program, and these changes and improvements will fall within the scope of this program. The scope of the claims is defined by the appended claims and their equivalents.

It is to be noted that the above-described embodiments are intended to be illustrative, not limiting, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude those elements or steps that are different from those listed in the claims. The presence of a component or step. The word "a" or "an" preceding an element does not exclude the existence of a plurality of such elements. In the enumeration of several circuit claims, several of these devices can be represented by one, and the hardware items are the same, simply because of The methods are described in the different dependent claims and do not indicate that combinations of these methods are not used for profit.

It should be noted that, in this context, relational terms such as first and second are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of between such entities or operations. Any such actual relationship or order, and the terms "comprising", "including", or any other variations are intended to encompass a non-exclusive inclusion, such that a process, method, article, or device comprising a plurality of elements includes those elements. , and includes those elements that are explicitly listed, or elements that are inherent to such a process, method, article, or device, the terms "connected," "connected," "connected to," or other variant, not only It consists only of connecting two entities directly, as well as indirectly connecting through other entities with beneficial improvements.

Claims

A linear constant current driving circuit is powered by the mains VAC1 via the rectifier bridge DB1, and the load is a plurality of LEDs connected in series to form an anode node and a plurality of LED cathode nodes; the input end of the rectifier bridge DB1 is connected to the mains VAC1, and the output is The positive pole is connected to the anode node, and the output negative pole is grounded;

The utility model is characterized in that it comprises a switching constant current source CCX, a voltage detecting circuit VD, a feedback circuit FB and a multiplier M;

The switching constant current source CCX includes a current setting terminal ISET for setting a switching constant current source current, a common ground GND, a current detecting terminal CS for reacting the switching constant current source current, and a plurality of constant current output terminals, and several The constant current output ends are respectively connected to a plurality of cathode nodes, and the common ground ends are connected to the ground;

The voltage detecting circuit detects the mains voltage waveform, and outputs a voltage detecting signal VO that is in phase with the mains voltage waveform;

The feedback circuit FB includes a reference signal, at least one feedback terminal and an output terminal FBO. The feedback circuit FB sums the signals on the at least one feedback terminal to obtain a feedback signal, and the difference between the reference signal and the feedback signal is integrated and output to the output end. FBO;

The current detecting terminal CS is connected to the first feedback terminal IN1 of the feedback circuit FB, and the current signal generated by the current detecting terminal CS is controlled by the feedback circuit FB;

The multiplier M comprises two input terminals MI1, MI2 and an output terminal MO. The input terminal MI1 is connected to the voltage detection signal VO, and controls the signal shape of the output terminal MO of the multiplier M. The input terminal MI2 is connected to the output terminal FBO of the feedback circuit FB. , controlling the output of the multiplier M The signal amplitude, the output terminal MO of the multiplier M is connected to the current setting terminal ISET of the switching constant current source CCX, and controls the current shape and amplitude of the switching constant current source CCX.
The linear constant current driving circuit according to claim 1, further comprising a constant power compensation circuit CP;

The constant power compensation circuit CP input terminal CI detects the voltage detection signal VO, and generates a compensation signal CO that monotonically changes as the voltage detection signal VO changes;

The compensation signal CO is connected to the second feedback terminal IN2 of the feedback circuit FB.
The linear constant current driving circuit according to claim 2, wherein the constant power compensation circuit CP further comprises a control terminal CK.
The linear constant current driving circuit according to claim 3, further comprising a dimming circuit DIM;

The input of the dimming circuit DIM is a variable signal DI, and the output comprises a dimming signal DO1 and a suppressing signal DO2;

The dimming signal DO1 is connected to the third feedback terminal IN3 of the feedback circuit FB; when the variable signal DI is changed, the current change of the switching current source CCX is controlled by the dimming signal DO1;

The suppression signal DO2 is connected to the control terminal CK of the constant power compensation circuit CP, and controls the influence of the voltage detection signal VO on the feedback signal.
The linear constant current driving circuit according to claim 1, further comprising a dimming circuit DIM;

The input of the dimming circuit DIM is a variable signal DI, and the output comprises a dimming signal DO1;

The dimming signal DO1 is connected to the third feedback terminal IN3 of the feedback circuit FB; when the variable signal DI is changed, the current change of the switching current source CCX is controlled by the dimming signal DO1.
The linear constant current driving circuit according to claim 1, further comprising a protection circuit PRO;

The protection circuit PRO internally includes a set threshold, and the protection circuit PRO input terminal PI detects the voltage detection signal VO. When the average value of the voltage detection signal VO is lower than the set threshold, the protection circuit outputs a protection signal PO to control the current of the switching current source CCX. It decreases as the voltage detection signal VO decreases.
The linear constant current driving circuit according to claim 1, further comprising a protection circuit PRO;

The protection circuit PRO input terminal PI detects the voltage detection signal VO, generates a clipping threshold proportional to the average value of the voltage detection signal VO, and controls the output signal FBO of the feedback circuit FB not to exceed the clipping threshold.
The linear constant current driving circuit according to any one of claims 1 to 7, characterized in that the input end of the constant power compensation circuit, the first input end of the multiplier and the input end of the protection circuit are connected to a voltage detecting circuit. Output.
The linear constant current driving circuit according to any one of claims 1 to 7, characterized in that the input end of the constant power compensation circuit, the first input end of the multiplier and the input end of the protection circuit are connected to a voltage detecting circuit. The same output.
The linear constant current driving circuit according to any one of claims 1 to 7, wherein the switching constant current source CCX comprises a plurality of voltage controlled current sources and a plurality of signal bias sources corresponding to the voltage controlled current sources. And a current-sense resistor RCS;

Each of the plurality of voltage-controlled current sources includes two control terminals and two power terminals, and the first power terminal of each of the voltage-controlled current sources is connected to the current-sense terminal CS, and the current is detected. The terminal CS is connected to the common ground through the current detecting resistor RCS, and the second power terminal is respectively used as a plurality of constant current output terminals, and the first control end of each of the voltage controlled current sources is connected to the current setting terminal ISET, and the second The control terminals are connected to the current detecting terminal CS via corresponding signal bias sources.
The linear constant current driving circuit according to claim 10, wherein said plurality of signal bias sources make the potential on said second control terminal different, and the second control terminal has a higher potential voltage control The constant current output terminal of the current source is connected to the cathode node with higher potential, and the constant current output terminal of the voltage control current source with lower potential on the second control terminal is connected to the cathode node with lower potential.
The linear constant current driving circuit according to any one of claims 1 to 7, wherein the switching constant current source CCX comprises a plurality of voltage controlled current sources and a plurality of signal bias sources corresponding to the voltage controlled current sources. And a current-sense resistor RCS;

Each of the plurality of voltage-controlled current sources includes two control terminals and two power terminals, and the first power terminal of each of the voltage-controlled current sources is connected to the current-sense terminal CS, and the current is detected. The terminal CS is connected to the common ground through the current detecting resistor RCS, and the second power terminal is respectively used as a plurality of constant current output terminals, and the first control end of each of the voltage controlled current sources is connected to the current through a corresponding signal bias source. The terminal ISET is set, and the second control terminal is connected to the current detecting terminal CS.
The linear constant current driving circuit according to claim 12, wherein said plurality of signal bias sources cause different potentials on said first control terminal of said plurality of voltage controlled current sources, and said first control terminal The constant current output terminal of the voltage-controlled current source with higher potential is connected to the cathode node with lower potential, and the constant current output terminal of the voltage-controlled current source with lower potential on the first control terminal is connected with the cathode node with higher potential. .
The linear constant current driving circuit according to any one of claims 1 to 7, wherein the switching constant current source CCX comprises a plurality of voltage controlled current sources and a plurality of signal bias sources corresponding to the voltage controlled current sources. And a current-sense resistor RCS;

Each of the plurality of voltage controlled current sources includes two control terminals and two power terminals, and the first power terminal of each of the voltage control current sources is connected to the current detecting terminal CS, the current detecting terminal CS is connected to the common ground through the current detecting resistor RCS, and the second power end is respectively used as a plurality of constant current output terminals;

The two control terminals are respectively a current reference signal and a current feedback signal of the voltage control current source, and the difference between the two is used to control the current value of the voltage control current source;

The bias signal source causes the current setting values of the voltage control current source to be different, and the constant current output end corresponding to the voltage control current source with a large current setting value is connected to the cathode node with a lower potential, and the current is set. The constant current output corresponding to the smaller voltage controlled current source is connected to the cathode node with higher potential.
The linear constant current driving circuit according to claim 1, wherein the input terminal VI of the voltage detecting circuit VD detects the positive voltage signal of the rectifier bridge DB1.
The linear constant current driving circuit according to claim 1, wherein the input terminal VI of the voltage detecting circuit VD detects the voltage signal of the cathode node having the highest potential.