CN103582218B - With the LED drive circuit of index correction dimming function - Google Patents

Abstract

The invention provides the LED drive circuit that a kind of exponential corrects light modulation, comprise: for providing the pierce circuit of operating frequency for pwm signal generative circuit, for generating the pwm signal generative circuit of pwm signal needed for switching transistor that controlled hypotension formula translation circuit comprises, and for generating the Buck conversion circuit lighting electric current needed for LED; This exponential corrects the LED drive circuit of light modulation and also comprises: index correction circuit, for providing for described pwm signal generative circuit and the angle of flow of TRIAC or the peak value comparison method voltage that exponentially changes for the PMW signal dutyfactor of light modulation.The LED drive circuit that exponential of the present invention corrects light modulation makes the scope of effective angle of flow of TRIAC broaden, and the change that LED light is strong is comparatively more obvious when linearity light adjusting.

Description

With the LED drive circuit of index correction dimming function

Technical field

The present invention relates to electronic technology field, particularly relate to a kind of LED drive circuit with index correction dimming function.

Background technology

Recent years, increasing LED(Light Emitting Diode, light-emitting diode) be used in home lighting, the field such as commercial lighting and public lighting.Because LED is than traditional incandescent lamp, fluorescent lamp is more energy-efficient, and unit lumen is stronger, at present by extensive promotion and application.

Traditional lighting dimming equipment is all TRIAC(bidirectional thyristor) add the structure of incandescent lamp, after substituting incandescent lamp with LED, the object regulating LED light line power is reached in order to make traditional TRIAC light adjusting system, current modal solution is the PWM(pulse width modulation produced by TRIAC) ripple converts direct current to, with this Current Control LED, reach the object regulating brightness.Usual this conversion is linear relationship, and as shown in Figure 1, abscissa is the angle of flow of TRIAC, and ordinate is the voltage on electric capacity.As can be seen from Figure 1, voltage on the angle of flow of TRIAC and electric capacity is linear, and when the angle of flow of TRIAC reaches after 135 °, the brightness of LED reaches the upper limit region of human eye sensitivity, no matter how the angle of flow increases for another example, and human eye also can not perceive the increase of light intensity.The shortcoming of this kind of method is the enhancing along with luminous intensity, human eye declines to the susceptibility of light, reach necessarily in the brightness of LED, no matter how to strengthen the angle of flow of TRIAC or the width of PWM, capital sensation light intensity be do not have vicissitudinous, cause the effective range of the dimmer conduction angle of TRIAC to narrow or the duty cycle range of PWM diminishes, the light excursion of LED is narrowed.

Summary of the invention

Main purpose of the present invention is to provide a kind of LED drive circuit with index correction dimming function, LED light is changed by force with the angle of flow of TRIAC or be nonlinear change for the width of the pwm signal of light modulation, expand the effective range of the dimmer conduction angle of TRIAC and the duty ratio for the pwm signal of light modulation.

In order to achieve the above object, the invention provides the LED drive circuit that a kind of exponential corrects light modulation, comprise: for providing the pierce circuit of operating frequency for pwm signal generative circuit, for generating the pwm signal generative circuit of the pwm signal of the switching transistor that controlled hypotension formula translation circuit comprises, and for generating the Buck conversion circuit lighting the electric current that LED needs;

The LED drive circuit that this exponential corrects light modulation also comprises:

Index correction circuit, for providing for described pwm signal generative circuit the peak value comparison method voltage exponentially changed with the angle of flow of TRIAC.

During enforcement, described index correction circuit comprises linear charging block, sample circuit, signed magnitude arithmetic(al) circuit and thyrite circuit, wherein,

Described linear charging block comprises charging resistor and charging capacitor;

Described charging resistor, first end is connected with described thyrite circuit, and the second end is connected with described sample circuit;

Described charging capacitor, be connected to described charging resistor the second end and ground hold between;

Described sample circuit, for sampling to the voltage on described charging capacitor;

Described signed magnitude arithmetic(al) circuit, for carrying out plus and minus calculation to this voltage, generates the positive and negative control voltage that described thyrite circuit needs, and the resistance of described thyrite circuit is exponentially changed along with the voltage on described charging capacitor.

During enforcement, when the control voltage of described thyrite circuit is maximum and the minimum value of described charging capacitor voltage, the resistance of described thyrite circuit is identical, is minimum value;

When described control voltage be described charging capacitor voltage peak two/for the moment, the resistance of thyrite is maximum;

When described control voltage is remaining charging capacitor magnitude of voltage, the resistance of described thyrite circuit changes according to exponential relationship.

During enforcement, described pierce circuit comprises charge and discharge capacitance, for the current source of this charge and discharge capacitance charging, provide the discharge transistor of discharge path for this charge and discharge capacitance, and the voltage on this charge and discharge capacitance and reference voltage are compared and export the voltage comparator of frequency of oscillation waveform.

During enforcement, the LED drive circuit that exponential of the present invention corrects light modulation also comprises:

Abnormity protection circuit, comprises undervoltage lockout circuit, thermal-shutdown circuit and NOR gate;

The output of described undervoltage lockout circuit and the output of thermal-shutdown circuit are connected with two inputs of described NOR gate respectively, and the output of described NOR gate is connected with described pwm signal generative circuit.

During enforcement, described pwm signal generative circuit comprises buffer circuit, latch, peak current comparator, lead-edge-blanking circuit, the first transistor, inverter, two inputs and door and driver, wherein,

Described buffer circuit, for carrying out shaping for this frequency of oscillation waveform;

Described latch, set end is connected with the output of described buffer circuit, and reset terminal is connected with the output of described peak current comparator, and positive output end and described two inputs and is connected with an input of door;

Described two inputs are connected with the output of this NOR gate with another input of door;

Described driver, input and described two inputs and is connected with the output of door, and output is connected with the grid of this switching transistor;

Described inverter, input and described two inputs and is connected with the output of door, and output is connected with one end of the described lead-edge-blanking circuit for eliminating interference;

The other end of described lead-edge-blanking circuit is connected with the grid of described the first transistor;

Described peak current comparator, normal phase input end is respectively by described the first transistor ground connection and be connected with the source electrode of described switching transistor, and inverting input is connected with the charging capacitor of described index correction circuit.

During enforcement, described Buck conversion circuit comprises switching transistor, sampling resistor, inductance, fly-wheel diode and filter capacitor, wherein,

Described filter capacitor is parallel to LED string two ends;

Described filter capacitor, first end is by the described inductance connected successively, described switching transistor and described sampling resistor ground connection;

Described fly-wheel diode, anode is connected between described inductance and described switching transistor, and negative electrode is connected with the second end of described filter capacitor.

Compared with prior art, the LED drive circuit that exponential of the present invention corrects light modulation makes the scope of effective angle of flow of switching transistor broaden, more obvious during the strong change linearity light adjusting of LED light.

Accompanying drawing explanation

Fig. 1 is the dimming curve of existing linearity light adjusting system;

Fig. 2 is the structured flowchart that exponential described in first embodiment of the invention corrects the LED drive circuit of light modulation;

Fig. 3 is the structured flowchart that exponential described in second embodiment of the invention corrects the LED drive circuit of light modulation;

Fig. 4 is the circuit diagram that exponential described in third embodiment of the invention corrects the LED drive circuit of light modulation;

Fig. 5 is the index dimming curve adopting exponential of the present invention to correct the LED drive circuit of light modulation;

Fig. 6 is that typical dimming curve contrasts schematic diagram with the index dimming curve adopting exponential of the present invention to correct the LED drive circuit of light modulation.

Embodiment

Expressing for making the object, technical solutions and advantages of the present invention clearly clear, below in conjunction with drawings and the specific embodiments, the present invention being further described in detail again.

The mode of specific embodiment of the invention is not limited only to description below, existing in addition further instruction by reference to the accompanying drawings.

First, technical term involved in the present invention is described:

MOSFET:Metal Oxide Semiconductor Field Effect Transistor, NMOS N-channel MOS N field-effect transistor;

PWM:Pulse Width Modulation, pulse width modulation;

LED:Light Emitting Diode, light-emitting diode;

BUCK circuit: Buck conversion circuit;

TRIAC: TRIAC;

UVLO:Under Voltage Lock Out, under-voltage locking.

As shown in Figure 2, the LED drive circuit that exponential described in first embodiment of the invention corrects light modulation comprises: for providing the pierce circuit 21 of operating frequency for pwm signal generative circuit 22, for generating the pwm signal generative circuit 22 of the pwm signal of the switching transistor that controlled hypotension formula translation circuit 23 comprises, and for generating the Buck conversion circuit 23 lighting the electric current that LED needs;

The LED drive circuit that this exponential corrects light modulation also comprises index correction circuit 24, for providing for described pwm signal generative circuit 22 the peak value comparison method voltage exponentially changed with the angle of flow of TRIAC.

The LED drive circuit that exponential described in first embodiment of the invention corrects light modulation by index correction circuit 24 for described pwm signal generative circuit 22 provides the peak value comparison method voltage exponentially changed with the angle of flow of TRIAC, thus make the angle of flow of LED light Strength Changes and TRIAC or the width of PWM be nonlinear change, expand the effective range of the PWM duty ratio of TRIAC dimmer conduction angle and light modulation.

Fig. 3 is the circuit diagram that exponential described in second embodiment of the invention corrects the LED drive circuit of light modulation.Exponential described in second embodiment of the invention corrects the LED drive circuit of light modulation based on the LED circuit described in first embodiment of the invention.

As shown in Figure 3; the LED drive circuit that exponential described in second embodiment of the invention corrects light modulation also comprises abnormity protection circuit 25; it is connected with described pwm signal generative circuit 22; there is provided protection time when LED drive circuit for correcting light modulation at exponential works when operating voltage and working temperature abnormity, be against any misfortune and occur and expand further.

Fig. 4 is the circuit diagram that exponential described in third embodiment of the invention corrects the LED drive circuit of light modulation.Exponential described in third embodiment of the invention corrects the LED drive circuit of light modulation based on the LED circuit described in second embodiment of the invention.

As shown in Figure 4, correct in the LED drive circuit of light modulation at the exponential described in third embodiment of the invention,

Described index correction circuit 24 comprises linear charging block 241, sample circuit 242, signed magnitude arithmetic(al) circuit 243 and thyrite circuit 244, wherein,

Described linear charging block 241 comprises charging resistor R1 and charging capacitor C1;

Described charging resistor R1, first end is connected with described thyrite circuit 244, and the second end is connected with described sample circuit 242;

Described charging capacitor C1, be connected to described charging resistor R1 the second end and ground hold between;

Described sample circuit 242, for sampling to the voltage on described charging capacitor C1;

Described signed magnitude arithmetic(al) circuit 243, for carrying out plus and minus calculation to this voltage, generates the positive and negative control voltage that described thyrite circuit 244 needs, and the resistance of described thyrite circuit 244 is exponentially changed along with the voltage on described charging capacitor;

When the control voltage of described thyrite circuit 244 is maximum and the minimum value of described charging capacitor C1 voltage, the resistance of described thyrite circuit 244 is identical, is minimum value;

When described control voltage be described charging capacitor C1 voltage peak two/for the moment, the resistance of thyrite circuit 244 is maximum;

When described control voltage is remaining charging capacitor C1 magnitude of voltage, the resistance of described thyrite circuit 244 changes according to exponential relationship;

The control voltage of thyrite is:

$V_{\mathrm{CTRL}+}=V_{\mathrm{CAP}}+\frac{V_{\mathrm{CAP}}+R_{107}}{R_{108}}---\left(1\right)$

With

$V_{\mathrm{CTRL}-}=V_{\mathrm{CAP}}\frac{V_{\mathrm{CAP}}\×R_{107}}{R_{108}}---\left(2\right)$

The resistance of thyrite is:

$R_{\mathrm{CTRL}}=R_{102}+R_{101}$

$=R_{102}+\frac{1}{(K_{+}\×V_{\mathrm{CTRL}+}+K_{-}\×V_{\mathrm{CTRL}-})+(K_{+}+K_{-})\×(V_{\mathrm{IN}}-V_{\mathrm{CAP}})}---\left(3\right)$

In formula (1), V _cTRL+for the positive controling voltage of thyrite;

V in formula (2) _cTRL-for the negative control voltage of thyrite;

V in formula (3) _iNfor input voltage, V _cAPfor the voltage on electric capacity;

Described sample circuit 242 comprises amplifier 2421 and sampling transistor TC;

Described signed magnitude arithmetic(al) circuit 243 comprises the first computing resistance R21, the second computing resistance R22, the 3rd computing resistance R23 and the 4th computing resistance R24;

Described thyrite circuit 244, first end access pwm signal, second end is connected with described linear charging block 241, and three-terminal link is between described first computing resistance R21 and the second computing resistance R22, and the 4th end is connected between described 3rd computing resistance R23 and the 4th computing resistance R24;

Described signed magnitude arithmetic(al) circuit 243, include but not limited to signed magnitude arithmetic(al) circuit that signed magnitude arithmetic(al) circuit, MOSFET and mosfet transistor that signed magnitude arithmetic(al) circuit, amplifier and MOSFET or BIPOLAR transistor that amplifier and resistance are formed are formed form, signed magnitude arithmetic(al) circuit that BIPOLAR and BIPOLAR transistor is formed, or the signed magnitude arithmetic(al) circuit that MOSFET and BIPOLAR transistor is formed;

The inverting input of described amplifier 2421, is connected with described pwm signal generative circuit 22 respectively, is connected with described thyrite circuit 244 by described charging resistor R1, and by described charging capacitor C1 ground connection;

Described amplifier 2421, normal phase input end is connected with the source electrode of described sampling transistor TC, and output is connected with the grid of described sampling transistor TC;

Described amplifier 2421 includes but not limited to MOSFET and BIPOLAR(bipolarity) the transistor single transistor amplifier, the RAIL2RAIL(track to track that form) operational amplifier of structure, FOLDEDCASCODE(be Origami cascaded) operational amplifier of structure or OTA(mutual conductance) operational amplifier of structure;

Described amplifier 104, its type of attachment includes but not limited to the negative feedback structure that the follower configuration that amplifier out and reverse input end connect and compose or amplifier and MOSFT or BIPOLAR mutually combine and form;

The drain electrode of described sampling transistor TC is connected with power end with the first computing resistance R11 by the second computing resistance R22 connected successively;

The source electrode of described sampling transistor TC is by the 3rd computing resistance R23 that connects successively and the 4th computing resistance R24 ground connection;

Described pierce circuit 21 comprise charge and discharge capacitance C2, for charge to this charge and discharge capacitance C2 current source 211, provide the discharge transistor T of discharge path for this charge and discharge capacitance C2, and the voltage on this charge and discharge capacitance C2 and reference voltage are compared and export the voltage comparator 212 of frequency of oscillation waveform;

Described current source 211 is connected with the normal phase input end of described voltage comparator 222 respectively, by described discharge transistor T ground connection, by described charge and discharge capacitance C2 ground connection;

Described voltage comparator 212, inverting input access reference voltage, output is connected with described pwm signal generative circuit 22;

Described abnormity protection circuit 25, comprises undervoltage lockout circuit 251, thermal-shutdown circuit 252 and NOR gate 253;

The output of described undervoltage lockout circuit 251 is connected with two inputs of described NOR gate 253 respectively with the output of thermal-shutdown circuit 252, and the output of described NOR gate 253 is connected with described pwm signal generative circuit 22;

Described pwm signal generative circuit 22 comprises buffer circuit 221, latch 222, peak current comparator 223, lead-edge-blanking circuit 224, the first transistor T1, inverter 225, two input and door 226 and driver 227, wherein,

Described buffer circuit 221, for carrying out shaping for this frequency of oscillation waveform;

Described latch 222, set end is connected with the output of described buffer circuit 221, and reset terminal is connected with the output of described peak current comparator 223, and positive output end and described two inputs and is connected with an input of door 226;

Described two inputs are connected with the output of this NOR gate 253 with another input of door 226;

Described two inputs are connected with the grid of described discharge transistor T with the output of door 226;

Described driver 227, input and described two inputs and is connected with the output of door 226, and output is connected with the grid of this switching transistor;

Described inverter 225, input and described two inputs and is connected with the output of door 226, and output is connected with one end of the described lead-edge-blanking circuit 224 for eliminating interference;

The other end of described lead-edge-blanking circuit 224 is connected with the grid of described the first transistor T1;

Described peak current comparator 223, normal phase input end is respectively by described the first transistor T1 ground connection and be connected with the source electrode of described switching transistor, and inverting input is connected with the charging capacitor C2 of described index correction circuit 24;

Described Buck conversion circuit 23 comprises switching transistor T2, sampling resistor R2, inductance L, sustained diode and filter capacitor C3, wherein,

Described filter capacitor C3 is parallel to LED string (being made up of to LED 141n the LED 141a connected successively) two ends;

Described filter capacitor C3, first end is by the described inductance L connected successively, described switching transistor T2 and described sampling resistor R2 ground connection;

Described sustained diode, anode is connected between described inductance L and described switching transistor T2, and negative electrode is connected with second end of described filter capacitor C3.

Correct in the LED drive circuit of light modulation at the exponential described in third embodiment of the invention, described index correction circuit 24 provides peak value comparison method voltage for pwm signal generative circuit 22; The charging capacitor C1 of index correction circuit 24 is connected with the negative input end of peak current comparator 223, the output of peak current comparator 223 is connected with the reset terminal of latch 222, when the voltage of sampling resistor R2 arrives the deboost of peak current, reset latch, by driver 227 closing switch transistor T2, after switching transistor T2 closes, provide LED string 141a to the 141n electric current needed by inductance L through sustained diode, maintain the conducting of LED string; The output of comparator 212 is connected with buffer 221, the output waveform of oscillator is after buffer shaping, output to the set end of latch 222, after the voltage of charge and discharge capacitance C2 arrives 1.2V, comparator 212 exports asserts signal, export through latch 222, being exported by driver 227, control switch transistor T2 conducting, is inductance L charging, the electric current that LED string 141a to 141n needs is provided simultaneously, maintains the conducting of LED string; Abnormity protection circuit 25 provides UVLO protection and overheat protector, ensures the normal work of circuit, and after also preventing circuit abnormality, disaster generates further and expands simultaneously.

Fig. 5 is the index dimming curve adopting exponential of the present invention to correct the LED drive circuit of light modulation; Fig. 6 is that typical dimming curve contrasts schematic diagram with the index dimming curve adopting exponential of the present invention to correct the LED drive circuit of light modulation, and in Fig. 5, Fig. 6, abscissa is the angle of flow of TRIAC, and ordinate is the voltage on electric capacity.

As shown in Figure 5, when the angle of flow of switching transistor is less than 45 °, widely used light adjusting system and the present invention control by force basically identical to LED light, be greater than after 45 ° at the TRIAC angle of flow, the present invention presents the angle of flow and capacitance voltage exponentially relationship change, dimming scope of the present invention is broadened, and the increase that LED light is strong slows down than during linearity light adjusting.

Fig. 6 compared for linearity light adjusting curve and index dimming curve of the present invention, obviously can see, the invention enables the scope of effective angle of flow of switching transistor to broaden from both contrasts, more obvious during the strong change linearity light adjusting of LED light.

The embodiment of the present invention can complete the process according to exponential curve light modulation, and effective angle of flow of TRIAC is broadened, and the increase of LED light line strength is than more obvious during linearity light adjusting.More than illustrate just illustrative for the purpose of the present invention; and nonrestrictive, those of ordinary skill in the art understand, when not departing from the spirit and scope that claims limit; many amendments, change or equivalence can be made, but all will fall within the scope of protection of the present invention.

Claims (6)

1. the LED drive circuit of an exponential correction light modulation, comprise: for providing the pierce circuit of operating frequency for pwm signal generative circuit, for generating the pwm signal generative circuit of the pwm signal of the switching transistor needs that controlled hypotension formula translation circuit comprises, and for generating the Buck conversion circuit lighting the electric current that LED needs;

It is characterized in that, the LED drive circuit that this exponential corrects light modulation also comprises:

Index correction circuit, for providing for described pwm signal generative circuit the peak value comparison method voltage exponentially changed with the angle of flow of TIRAC;

Described index correction circuit comprises linear charging block, sample circuit, signed magnitude arithmetic(al) circuit and thyrite circuit, wherein,

Described linear charging block comprises charging resistor and charging capacitor;

Described charging resistor, first end is connected with described thyrite circuit, and the second end is connected with described sample circuit;

Described charging capacitor, be connected to described charging resistor the second end and ground hold between;

Described sample circuit, for sampling to the voltage on described charging capacitor;

Described signed magnitude arithmetic(al) circuit, for carrying out plus and minus calculation to this voltage, generates the positive and negative control voltage that described thyrite circuit needs, and the resistance of described thyrite circuit is exponentially changed along with the voltage on described charging capacitor.

2. exponential as claimed in claim 1 corrects the LED drive circuit of light modulation, it is characterized in that,

When the control voltage of described thyrite circuit is maximum and the minimum value of described charging capacitor voltage, the resistance of described thyrite circuit is identical, is minimum value;

When described control voltage be described charging capacitor voltage peak two/for the moment, the resistance of thyrite is maximum;

When described control voltage is remaining charging capacitor magnitude of voltage, the resistance of described thyrite circuit changes according to exponential relationship.

3. exponential as claimed in claim 1 or 2 corrects the LED drive circuit of light modulation, it is characterized in that,

Described pierce circuit comprises charge and discharge capacitance, for the current source of this charge and discharge capacitance charging, provide the discharge transistor of discharge path for this charge and discharge capacitance, and the voltage on this charge and discharge capacitance and reference voltage are compared and export the voltage comparator of frequency of oscillation waveform.

4. exponential as claimed in claim 3 corrects the LED drive circuit of light modulation, it is characterized in that, also comprises:

Abnormity protection circuit, comprises undervoltage lockout circuit, thermal-shutdown circuit and NOR gate;

The output of described undervoltage lockout circuit and the output of thermal-shutdown circuit are connected with two inputs of described NOR gate respectively, and the output of described NOR gate is connected with described pwm signal generative circuit.

5. exponential as claimed in claim 4 corrects the LED drive circuit of light modulation, it is characterized in that,

Described pwm signal generative circuit comprises buffer circuit, latch, peak current comparator, lead-edge-blanking circuit, the first transistor, inverter, two inputs and door and driver, wherein,

Described buffer circuit, for carrying out shaping for this frequency of oscillation waveform;

Described latch, set end is connected with the output of described buffer circuit, and reset terminal is connected with the output of described peak current comparator, and positive output end and described two inputs and is connected with an input of door;

Described two inputs are connected with the output of this NOR gate with another input of door;

Described driver, input and described two inputs and is connected with the output of door, and output is connected with the grid of this switching transistor;

Described inverter, input and described two inputs and is connected with the output of door, and output is connected with one end of the described lead-edge-blanking circuit for eliminating interference;

The other end of described lead-edge-blanking circuit is connected with the grid of described the first transistor;

Described peak current comparator, normal phase input end is respectively by described the first transistor ground connection and be connected with the source electrode of described switching transistor, and inverting input is connected with the charging capacitor of described index correction circuit.

6. exponential as claimed in claim 5 corrects the LED drive circuit of light modulation, and it is characterized in that, described Buck conversion circuit comprises switching transistor, sampling resistor, inductance, fly-wheel diode and filter capacitor, wherein,

Described filter capacitor is parallel to LED string two ends;

Described filter capacitor, first end is by the described inductance connected successively, described switching transistor and described sampling resistor ground connection;

Described fly-wheel diode, anode is connected between described inductance and described switching transistor, and negative electrode is connected with the second end of described filter capacitor.