CN103442484A - Linear switching constant current LED drive circuit and LED lamp - Google Patents

Abstract

The invention relates to a linear switching constant current LED drive circuit and an LED lamp. The LED lamp comprises an alternating current input power, a bridge rectifier, the linear switching constant current LED drive circuit and an LED light. The linear switching constant current LED drive circuit comprises an input sampling module, an output sampling module, a feedback control module, a drive control module and a power control module, wherein the input sampling module is used for acquiring input sampling voltage; the output sampling module is used for acquiring output current information of the LED light; the feedback control module is used for generating and outputting integral voltage according to the output current information, wherein the integral voltage keeps basically constant within a power frequency period; the drive control module is used for generating and outputting a drive control signal according to the input sampling voltage and the integral voltage; the power control module is used for driving the LED light according to the drive control signal, controlling the LED light in a constant-current mode and bearing pressure drop in the circuit. The embodiment of the linear switching constant current LED drive circuit and the LED lamp can realize the constancy of an average output current and average output power of the LED light, improve system efficiency, and effectively lower the operating temperature of the drive circuit.

Description

A kind of linear switch constant current LED drive circuit and LED light fixture

Technical field

The present invention relates to the LED drive circuit technical field, more particularly, relate to a kind of linear switch constant current LED drive circuit and LED light fixture.

Background technology

Under the overall background of global energy-saving and emission-reduction, as LED illuminations green, environmental protection and energy saving, more and more be subject to the favor in market.Be different from traditional lighting system, LED lamp pearl is the incoming transport utility grid directly, but will first electric main be converted into to DC power supply by drive circuit, and then is driven.LED drive circuit can be divided into switch power supply type and the large class of linear constant current mode two by its working method.With respect to switch power supply type, drive, the advantage that linear constant current mode drives is: the EMI problem caused without HF switch; Without electrochemical capacitor, and the electrochemical capacitor life-span bottleneck of LED light fixture just; Without inductance and transformer, peripheral circuit is simple, is convenient to realize that the photoelectricity engine is integrated; Volume is less, and cost is cheaper.These advantages make linear constant current mode be driven into the emphasis that drives area research for illumination LED.

Adopt in the prior art in the LED light fixture of linear constant current LED drive circuit, as shown in Figure 1, it comprises stream input power (civil power) 10, bridge rectifier 20, LED lamp 30, power MOS pipe 40, output current sampling resistor 50, error amplifier 60.Wherein, power MOS pipe 40, output current sampling resistor 50 and error amplifier 60 form feedback control loops, i.e. linear constant current LED drive circuit is used for controlling the output current Io of the LED lamp 30 of flowing through.

Fig. 2 shows the groundwork oscillogram of the linear constant current LED drive circuit in Fig. 1.As shown in Figure 2, in figure, VF is the conduction voltage drop of LED lamp; Vin is the voltage of electric main after the bridge rectifier rectification, and its waveform is sinusoidal wave absolute value; Iin is input current, and Io is the output current of LED lamp of flowing through, and Io equates with Iin; Vref is the reference voltage (being reference voltage) that error amplifier 60 receives.The groundwork principle of this circuit is as follows: system is controlled output current Io automatically according to the variation of Vin sine wave.As Vin during lower than the conduction voltage drop VF of LED (in Fig. 20 to t during), LED is not enough to conducting, and Iin and Io equal zero, and the feedback control loop that power MOS pipe 40, output current sampling resistor 50 and error amplifier 60 form is in holding state; When Vin rises to the conduction voltage drop VF of LED (in Fig. 2, t is constantly), the automatic conducting of LED lamp, feedback control loop is started working Io is adjusted into to steady state value (Vref/Rs); Vin continues by sinusoidal wave the variation (t to t in Fig. 2 ' during), and the pressure drop of LED lamp remains VF, and unnecessary pressure drop (Vin-VF) will be born by high-voltage power metal-oxide-semiconductor 40, and feedback control loop makes Io remain steady state value always during this period; When Vin drops to VF (in Fig. 2, t ' constantly), LED is not enough to conducting, and Iin and Io equal zero, and feedback control loop is in holding state.This course of work will constantly repeat.

Below the average output current of above-mentioned LED light fixture, average output power, efficiency etc. are derived.

$V_{\mathrm{in}}=\sqrt{2}{V}_{\mathrm{ac}}\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">sin</figure-callout>}2\mathrm{\&pi;ft}---\left(1\right)$

$t=\frac{1}{2\mathrm{\&pi;f}}\arcsin \frac{V_F}{\sqrt{2}{V}_{\mathrm{ac}}}=\frac{1}{2\mathrm{\&pi;f}}\&CenterDot;\mathrm{\&theta;}---\left(2\right)$

$\mathrm{\&theta;}=\arcsin \frac{V_F}{\sqrt{2}{V}_{\mathrm{ac}}}$

$t^{,}=\frac{1}{2f}-t=\frac{1}{2f}-\frac{1}{2\mathrm{\&pi;f}}\&CenterDot;\mathrm{\&theta;}---\left(3\right)$

Average output current in one-period:

${\stackrel{\&OverBar;}{I}}_o=2f\&CenterDot;I_o\&CenterDot;(t^{,}-t)=(1-\frac{2\mathrm{\&theta;}}{\mathrm{\&pi;}})\&CenterDot;\frac{V_{\mathrm{ref}}}{R_s}---\left(4\right)$

Average output power in one-period:

$P_{\mathrm{out}}=2f\&CenterDot;V_F\&CenterDot;I_o\&CenterDot;(t^{,}-t)=(1-\frac{2\mathrm{\&theta;}}{\mathrm{\&pi;}})\&CenterDot;V_F\&CenterDot;\frac{V_{\mathrm{ref}}}{R_s}---\left(5\right)$

Mean Input Power in one-period:

$P_{\mathrm{in}}=2f\&CenterDot;{\&Integral;}_t^{t^{,}}{V}_{\mathrm{in}}\&CenterDot;I_o\mathrm{dt}=2f\&CenterDot;\sqrt{2}{V}_{\mathrm{ac}}\&CenterDot;I_o\&CenterDot;{\&Integral;}_t^{t^{,}}\sin 2\mathrm{\&pi;ftdt}=\frac{2\sqrt{2}{V}_{\mathrm{ac}}\&CenterDot;I_o\&CenterDot;\cos \mathrm{\&theta;}}{\mathrm{\&pi;}}---\left(6\right)$

System effectiveness:

$\mathrm{\&eta;}=\frac{P_{\mathrm{out}}}{P_{\mathrm{in}}}=\frac{V_F}{\sqrt{2}{V}_{\mathrm{ac}}}\&CenterDot;\frac{(\frac{\mathrm{\&pi;}}{2}-\mathrm{\&theta;})}{\cos \mathrm{\&theta;}}---\left(7\right)$

There is following defect in existing linear constant current LED drive circuit:

(1) can't realize the constant of the average output current of LED lamp and average output power.From formula (4) and (5), can find out, average output current in one-period is all relevant with VF and Vac with average output power, therefore, when the conduction voltage drop VF of LED lamp and input voltage Vac change, average output current and average output power also can change thereupon.Therefore, when input voltage is unstable, the brightness meeting of LED lamp changes.

(2) when input voltage is higher, system effectiveness is too low.From formula (7), can find out, system effectiveness and input voltage are inversely proportional to, and after the conducting of LED lamp, unnecessary pressure drop (Vin-VF) will produce useless power consumption, and this part power consumption will reduce system effectiveness.That is to say, the power consumption that linear constant-current LED drives is mainly to be produced by unnecessary pressure drop (Vin-VF), and input voltage is larger, and (Vin-VF) is larger in unnecessary pressure drop, and power consumption is larger, and system effectiveness is lower.

(3) when LED drives chip operation, heating is too high.In existing linear constant current LED drive circuit, after the conducting of LED lamp, unnecessary pressure drop (Vin-VF) is born by the high-voltage power pipe MOSFET of chip internal, and this pressure drop meeting produces a large amount of useless power consumption, this part power consumption the most all is converted into heat energy, therefore the high-voltage power pipe MOSFET of chip internal can produce a large amount of heats, and chip cooling (thermal resistance is larger) limited in one's ability, can generate heat during final chip operation too high in addition.

Summary of the invention

The technical problem to be solved in the present invention is, can't realize the constant of the average output current of LED lamp and average output power for the linear constant current LED drive circuit of prior art, when input voltage is higher, system effectiveness is too low, and the LED too high defect of generating heat while driving chip operation, a kind of linear switch constant current LED drive circuit and LED light fixture are provided, can make the average output current of LED lamp and average output power and its input voltage irrelevant, thereby realize the constant of the average output current of LED lamp and average output power, simultaneously, can improve system effectiveness and reduce the working temperature that drives chip.

The technical solution adopted for the present invention to solve the technical problems is: construct a kind of linear switch constant current LED drive circuit, for the LED lamp is carried out to constant current control, wherein, described linear switch constant current LED drive circuit comprises:

The input sample module, for the Gather and input sampled voltage;

The output sampling module, for gathering the output current information of described LED lamp;

Feedback control module, be connected with described output sampling module, for according to described output current information, generating and export, keeps substantially invariable integral voltage in a power frequency period;

Drive control module, be connected with described feedback control module with described input sample module respectively, for according to described input sample voltage and described integral voltage, generating and export drive control signal;

Power control module, be connected with described drive control module, controls described LED lamp for drive also constant current according to described drive control signal, and bear the pressure drop in circuit.

Preferably, described feedback control module comprises reference voltage maker, mutual conductance error amplifier and integrating capacitor; The in-phase input end of described mutual conductance error amplifier connects described reference voltage maker to obtain reference voltage, the inverting input of described mutual conductance error amplifier connects described output sampling module to obtain described output current information, and the output of described mutual conductance error amplifier is by described integrating capacitor ground connection; Described mutual conductance error amplifier is discharged and recharged described integrating capacitor for described output current information and described reference voltage are compared to rear output gain electric current, to generate described integral voltage.

Preferably, described power control module comprises the first metal-oxide-semiconductor and current-limited power resistance; The grid of described the first metal-oxide-semiconductor connects the output of described drive control module, the source electrode of described the first metal-oxide-semiconductor connects described output sampling module, the drain electrode of described the first metal-oxide-semiconductor connects the first end of described current-limited power resistance, and the second end of described current-limited power resistance connects described LED lamp; Described current-limited power resistance is for bearing the pressure drop of circuit.

Preferably, described input sample module comprises the first resistance and the second resistance; Ground connection after described the first resistance and described the second resistance series connection, an end of described the first resistance connects the input power of described LED lamp, and the tie point of described the first resistance and described the second resistance is as the output of described input sample module.

Preferably, described drive control module comprises drive circuit and comparator; The in-phase input end of described comparator connects the output of described feedback control module to obtain described integral voltage, the inverting input of described comparator connects the output of described input sample module to obtain described input sample voltage, the output of described comparator connects the input of described drive circuit, and the output of described drive circuit connects the grid of described the first metal-oxide-semiconductor.

Preferably, described output sampling module comprises sampling resistor; The first end of described sampling resistor connects respectively the source electrode of described the first metal-oxide-semiconductor and the inverting input of described mutual conductance error amplifier, the second end ground connection of described sampling resistor.

Preferably, described reference voltage maker, described mutual conductance error amplifier, described the first metal-oxide-semiconductor, described drive circuit and described comparator are integrated in chip piece.

Preferably, described power control module also comprises the second metal-oxide-semiconductor be connected between described the first metal-oxide-semiconductor and described current-limited power resistance; The grid of described the second metal-oxide-semiconductor connects high level, and the source electrode of described two metal-oxide-semiconductors connects the drain electrode of described the first metal-oxide-semiconductor, and the drain electrode of described two metal-oxide-semiconductors connects the first end of described current-limited power resistance.

Preferably, the appearance value scope of described integrating capacitor is 1 microfarad to 10 microfarad.

Another technical scheme that the present invention solves its technical problem employing is, construct a kind of LED light fixture, comprise alternating current input power supplying, rectifier bridge, linear switch constant current LED drive circuit and LED lamp, wherein, described linear switch constant current LED drive circuit adopts above-mentioned linear switch constant current LED drive circuit.

Implement linear switch constant current LED drive circuit of the present invention and LED light fixture, by utilizing " integration constant current " mode to realize the constant of the average output current of LED lamp and average output power, the average output current of LED lamp and average output power and input voltage are irrelevant, therefore, when line voltage changes, the average output current of LED lamp and average output power can not change thereupon, and the brightness of LED lamp can remain unchanged.Simultaneously, the present invention also can solve the conventional linear constant-current LED and drive the too low problem of chip efficiency when input voltage is higher.Circuit structure of the present invention has improved system effectiveness when input voltage is higher, and, when unnecessary pressure drop is larger, efficiency improves more obviously.The present invention also can solve when the conventional linear constant-current LED drives chip operation the too high problem of generating heat.Can bear unnecessary pressure drop by current-limited power resistance, effectively reduce the working temperature of chip circuit.

The accompanying drawing explanation

Below in conjunction with drawings and Examples, the invention will be further described, in accompanying drawing:

Fig. 1 is the circuit theory diagrams of the linear switch constant current LED drive circuit of prior art;

Fig. 2 is the working waveform figure of the linear switch constant current LED drive circuit shown in Fig. 1;

Fig. 3 is the circuit theory diagrams of linear switch constant current LED drive circuit the first embodiment of the present invention;

Fig. 4 is the working waveform figure of the linear switch constant current LED drive circuit shown in Fig. 3;

Fig. 5 is the circuit theory diagrams of linear switch constant current LED drive circuit the second embodiment of the present invention.

Embodiment

In order to make purpose of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.

Fig. 3 is the circuit theory diagrams of linear switch constant current LED drive circuit the first embodiment of the present invention.As shown in Figure 3, the linear switch constant current LED drive circuit comprises output sampling module 100, feedback control module 200, drive control module 300, power control module 400 and input sample module 500.Wherein, input sample module 500 is connected between the input power and drive control module 300 of LED lamp, output sampling module 100 is connected with power control module 400 with feedback control module 200 respectively, feedback control module 200 is connected with drive control module 300, and drive control module 300 is connected with power control module 400.Input sample module 500 is for the Gather and input sampled voltage; Output sampling module 100 is for gathering the output current information of LED lamp D1; Feedback control module 200 keeps substantially invariable integral voltage for according to this output current information, generating and export in a power frequency period; Drive control module 300 is for generating and export drive control signal according to input sample voltage and integral voltage; Power control module 400 is for driving according to this drive control signal and LED lamp D1 is controlled in constant current, and bears the pressure drop in circuit, poor as input voltage vin and LED conduction voltage drop VF: Vin-VF, i.e. unnecessary pressure drop.

In the present embodiment, input sample module 500 comprises the first resistance R 1 and the second resistance R 2; Output sampling module 100 comprises sampling resistor Rs; Feedback control module 200 comprises reference voltage maker 201, mutual conductance error amplifier 202 and integrating capacitor C1; Drive control module 300 comprises drive circuit 301 and comparator 302; Power control module 400 comprises the first metal-oxide-semiconductor M1 and current-limited power resistance R p.

Alternating current input power supplying AC and bridge rectifier provide input voltage vin for the LED lamp.Ground connection after the first resistance R 1 and described the second resistance R 2 series connection, an end of the first resistance R 1 connects the input power of LED lamp, connects the output of bridge rectifier, and the tie point of the first resistance R 1 and the second resistance R 2 is as the output of input sample module 500.Certainly, those skilled in the art can know, input sample module 500 of the present invention also can adopt the electronic components such as transformer to realize.

The grid of the first metal-oxide-semiconductor M1 connects the output of drive circuit 301, the drain electrode of the first metal-oxide-semiconductor M1 connects the first end of current-limited power resistance R p, the second end of current-limited power resistance R p connects the LED lamp, the source electrode of the first metal-oxide-semiconductor M1 connects the first end of sampling resistor Rs, the second end ground connection of sampling resistor Rs.The output current of the LED lamp sampling resistor Rs that flows through draws above-mentioned output current information, and this output current information is CS=Io * Rs.

The in-phase input end of mutual conductance error amplifier 202 connects reference voltage maker 201 to obtain reference voltage Vref 1, the inverting input of mutual conductance error amplifier 202 connects the first end of sampling resistor RS to obtain output current information, and the output of mutual conductance error amplifier 202 is by integrating capacitor C1 ground connection.Mutual conductance error amplifier 202 compares rear output gain electric current by obtained output current information and reference voltage Vref 1 integrating capacitor C1 is discharged and recharged, thus formation product component voltage Vcomp.Preferably, the appearance value scope of integrating capacitor C1 is 1 microfarad to 10 microfarad.Certainly, the present invention is not limited to this, and the appearance value of integrating capacitor C1 also can be got other value.

The in-phase input end of comparator 302 connects the output (being the ungrounded end of integrating capacitor C1) of feedback control module 200 to obtain integral voltage Vcomp, the inverting input of comparator 302 connects the output (i.e. tie point between the first resistance R 1 and the second resistance R 2) of input sample module 500 to obtain input sample voltage Vin-sen, the output of comparator 302 connects the input of drive circuit 301, and the output of drive circuit 301 connects the grid of the first metal-oxide-semiconductor M1.Comparator 302 compares rear output pwm signal by input sample voltage and integral voltage and controls conducting or the cut-off of the first metal-oxide-semiconductor M1 to drive circuit 301, thereby controls the LED lamp.Therefore, the pwm signal here can be understood as the conducting control signal of LED.

In the present embodiment, the first metal-oxide-semiconductor M1 is mainly used to do switch use, and current-limited power resistance R p, for bearing unnecessary pressure drop (Vin-VF), shares unnecessary pressure drop (Vin-VF) with the form of dividing potential drop.

Preferably, in the present embodiment, reference voltage maker 201, mutual conductance error amplifier 202, the first metal-oxide-semiconductor M1, drive circuit 301 and comparator 302 are integrated in chip piece.And current-limited power resistance R p is placed on chip exterior, to avoid the chip internal excess Temperature.Sampling resistor Rs generally is also placed in chip exterior, because sampling resistor Rs needs very high precision, integrated resistor does not reach this precision, and sampling resistor Rs can adjust power output in addition, is placed on chip exterior and is convenient to adjust power output according to different application.Because the appearance value of capacitor C 1 is larger, generally be also placed in chip exterior.And the first resistance R 1 and the second resistance R 2 all can be integrated in chip, also can be placed on outside chip.Certainly, this is preferred embodiment of the present invention, and the present invention is not limited to this.

The operation principle of the linear switch constant current LED drive circuit of first embodiment of the invention is described below in conjunction with Fig. 4.The working waveform figure of the linear switch constant current LED drive circuit that Fig. 4 shows the present embodiment in a power frequency period (i.e. half electric main cycle T/2=1/2f, f is ac power frequency).As shown in Figure 4, Vin is the voltage of electric main after the bridge rectifier rectification, and its waveform is sinusoidal wave absolute value; The conduction voltage drop that VF is LED; Iin is input current, and Io is the output current of LED lamp of flowing through, and Io equates with Iin; Vin-sen is input sample voltage, and Vcomp is the output signal (being integral voltage) of mutual conductance error amplifier 202; PWM is LED conduction ratio control signal, the on off state of this signal controlling the first metal-oxide-semiconductor.

The circuit working principle of the present embodiment is as follows: during 0-t1, input voltage vin is lower than the conduction voltage drop VF of LED, and LED is not enough to conducting, and Iin and Io equal zero, and Vin_sen is lower than Vcomp, and PWM is high level, and the first metal-oxide-semiconductor M1 is in conducting state; At t1 constantly, Vin rises to the conduction voltage drop VF of LED, the automatic conducting of LED lamp, and Iin and Io start to rise; During t1-t2, Vin continues to rise by sinusoidal wave, Iin and Io are also along with rising, and the pressure drop of LED lamp remains VF, and unnecessary pressure drop (Vin-VF) will be born by current-limited power resistance R p (because the resistance of Rp is probably left and right, 1K Europe, and the conducting resistance of M1 is 20 left and right, Europe, the resistance of Rs is 10 left and right, Europe, so the pressure drop of the relative Rp of pressure drop of M1 and Rs is very little, can ignore), during this period, the first metal-oxide-semiconductor M1 keeps conducting state; At t2 constantly, Vin rises to and makes its sampled signal Vin_sen surpass Vcomp, and PWM becomes low level, the first metal-oxide-semiconductor M1 cut-off, and Iin and Io equal zero; When Vin descends, process is just contrary.

What specify is, in the present invention, when system has just been started working also unsettled the time, if the sampled signal CS(CS=Io*Rs of the output current of LED lamp, be foregoing output current information) mean value less than reference voltage Vref 1, in a power frequency period, the charge volume of 202 couples of integrating capacitor C1 of mutual conductance error amplifier can be more than discharge capacity, therefore Vcomp can constantly rise, conduction ratio also can increase thereupon, the integrated value of output current in a power frequency period also can increase thereupon, finally make the mean value of CS increase that (mean value of CS equals the integrated value of output current in a power frequency period and is multiplied by Rs, then divided by the power frequency period time), if the mean value of the sampled signal CS of output current is larger than reference voltage Vref 1, in a power frequency period, the charge volume of 202 couples of integrating capacitor C1 of mutual conductance error amplifier can be fewer than discharge capacity, therefore Vcomp can constantly descend, conduction ratio also can reduce thereupon, the integrated value of output current in a power frequency period also can reduce thereupon, finally makes the mean value of CS reduce.Under the effect of this negative feedback mechanism, when system reaches while stablizing, the mean value of the sampled signal CS of output current finally can keep constant and equal Vref1, thereby in a power frequency period, the charge volume of 202 couples of integrating capacitor C1 of mutual conductance error amplifier equates with discharge capacity, therefore Vcomp keeps constant, and it is constant that conduction ratio keeps, so the mean value of output current also can keep constant and equal Vref1/Rs.If capacitor C 1 is enough large, the fluctuating range of Vcomp in a power frequency period is very little, and this fluctuation can be ignored, and therefore, after system stability, can think, it is constant that Vcomp keeps.In the present embodiment, system can be according to different input voltage effective values, LED conduction voltage drop and current-limited power resistance R p, automatically adjusts the mean value that Vcomp and conduction ratio make output current and remains on constant set point (Vref1/Rs) always.This employing mutual conductance error amplifier and an integrating capacitor make the mean value of output current reach constant mode, and we are referred to as " integration constant current " mode.

For the advantage of linear switch constant current LED drive circuit the first embodiment of the present invention is described more easily, below will be derived to the average output current of this circuit, average output power etc.

Front mentions, and when system reaches while stablizing, in a power frequency period, the variable quantity of Vcomp is zero, therefore can draw:

${\mathrm{\&Delta;V}}_{\mathrm{comp}}=\frac{1}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">C</figure-callout>}1}{\&Integral;}_0^{1/2f}{G}_m\&CenterDot;(V_{\mathrm{ref}1}-I_o\&CenterDot;R_s)\&CenterDot;\mathrm{dt}=0$

$\&DoubleRightArrow;2f\&CenterDot;{\&Integral;}_0^{1/2f}{I}_o\&CenterDot;\mathrm{dt}=\frac{V_{\mathrm{ref}1}}{R_s}\&DoubleRightArrow;2f\&CenterDot;({\&Integral;}_{t1}^{t2}{I}_o\&CenterDot;\mathrm{dt}+{\&Integral;}_{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">t</figure-callout>}2}^{\&prime;}}^{{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">t</figure-callout>}1}^{\&prime;}}{I}_o\&CenterDot;\mathrm{dt})=\frac{V_{\mathrm{ref}1}}{R_s}$

An interior average output current of power frequency period is:

${\stackrel{\&OverBar;}{I}}_o=2f\&CenterDot;({\&Integral;}_{t1}^{t2}{I}_o\&CenterDot;\mathrm{dt}+{\&Integral;}_{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">t</figure-callout>}2}^{\&prime;}}^{{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">t</figure-callout>}1}^{\&prime;}}{I}_o\&CenterDot;\mathrm{dt})=\frac{V_{\mathrm{ref}1}}{R_s}---\left(8\right)$

An interior average output current of power frequency period is:

$P_{\mathrm{out}}=2f\&CenterDot;V_F\&CenterDot;({\&Integral;}_{t1}^{t2}{I}_o\&CenterDot;\mathrm{dt}+{\&Integral;}_{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">t</figure-callout>}2}^{\&prime;}}^{{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000366912160000031.png"\; state="\{\{state\}\}">t</figure-callout>}1}^{\&prime;}}{I}_o\&CenterDot;\mathrm{dt})=V_F\&CenterDot;\frac{V_{\mathrm{ref}1}}{R_s}---\left(9\right)$

Therefore, the advantage of the linear switch constant current LED drive circuit of the present embodiment comprises:

(1) realize the constant of the average output current of LED lamp and average output power.From above-mentioned formula (8) and (9), can find out, the average output current of LED lamp and average output power and input voltage are irrelevant, and therefore, when line voltage changes, the brightness of LED lamp can remain unchanged.Especially, the resistance Rs of the conduction voltage drop VF of LED, reference voltage Vref 1, sampling resistor is chosen as a particular value usually.

(2) improved system effectiveness, solved the conventional linear constant-current LED and driven the too low problem of chip efficiency when input voltage is higher.In the present embodiment, owing to having increased input sample module 500 and correspondingly having adopted different drive control module 300 and power control module 400, make the first metal-oxide-semiconductor M1 be turned off (when unnecessary pressure drop (Vin-VF) is larger) during t2-t2 ', now, the output current Io vanishing of LED, power consumption is also zero, thereby has improved system effectiveness.So relatively traditional structure (as the circuit structure of Fig. 1), the linear switch constant current LED drive circuit of the present embodiment has improved system effectiveness when input voltage is higher, and (Vin-VF) is larger in unnecessary pressure drop, and efficiency improves more obvious.

(3) solve when the conventional linear constant-current LED drives chip operation the too high problem of generating heat.In the present embodiment, unnecessary pressure drop (Vin-VF) is born by the current-limited power resistance R p of chip exterior, and non-traditional structure is born by the power MOSFET of chip internal like that, thermal source is transferred to chip exterior by chip internal, thereby effectively reduced the working temperature of chip, and heat-sinking capability also can not be subject to the restriction of chip package thermal resistance.

Fig. 5 is the circuit theory diagrams of linear switch constant current LED drive circuit the second embodiment of the present invention.The main distinction of the present embodiment and linear switch constant current LED drive circuit the first embodiment of the present invention is power control module 400, and remaining circuit module and linear switch constant current LED drive circuit the first embodiment of the present invention are basic identical, do not repeat them here.

In the present embodiment, power control module 400 also comprises the second metal-oxide-semiconductor M2 be connected between the first metal-oxide-semiconductor M1 and current-limited power resistance R p.The grid of the second metal-oxide-semiconductor M2 meets fixedly high level Vcc, and the source electrode of two metal-oxide-semiconductor M2 connects the drain electrode of the first metal-oxide-semiconductor M1, and the drain electrode of two metal-oxide-semiconductor M2 connects the first end of current-limited power resistance R p.Different its type of drive that are of the present embodiment and the first embodiment of the present invention.In the present embodiment, the grid of the first metal-oxide-semiconductor M1 connects the drive control signal of the output of driver module 300, the on off state of the second metal-oxide-semiconductor M2 is controlled by its source signal (i.e. the drain signal of the first metal-oxide-semiconductor M1), and therefore, what the present embodiment adopted is " source drive " mode.And, in the first embodiment of the present invention, only adopt a metal-oxide-semiconductor (i.e. the first metal-oxide-semiconductor M1), and the on off state of M1 is directly controlled by its signal, and therefore, what it adopted is " grid driving " mode.Except the type of drive difference, the operation principle of the present embodiment is identical with the first embodiment of the present invention, does not repeat them here.

Implement linear switch constant current LED drive circuit of the present invention and LED light fixture, by the mode of utilizing " integration constant current ", realize the constant of the average output current of LED lamp and average output power.When line voltage changes, the brightness of LED lamp can remain unchanged.In addition, the present invention has also solved the conventional linear constant-current LED and has driven the too low problem of chip efficiency when input voltage is higher, improve system effectiveness, and solved when the conventional linear constant-current LED drives chip operation the too high problem of generating heat, effectively reduced the working temperature of chip.

Although the present invention describes by specific embodiment, it will be appreciated by those skilled in the art that, without departing from the present invention, can also carry out various conversion and be equal to alternative the present invention.Therefore, the present invention is not limited to disclosed specific embodiment, and should comprise the whole execution modes that fall in the claims in the present invention scope.

Claims (10)

1. a linear switch constant current LED drive circuit, for the LED lamp is carried out to constant current control, is characterized in that, described linear switch constant current LED drive circuit comprises:

Input sample module (500), for the Gather and input sampled voltage;

Output sampling module (100), for gathering the output current information of described LED lamp;

Feedback control module (200), be connected with described output sampling module (100), for according to described output current information, generating and export, keeps substantially invariable integral voltage in a power frequency period;

Drive control module (300), be connected with described feedback control module (200) with described input sample module (500) respectively, for according to described input sample voltage and described integral voltage, generating and export drive control signal;

Power control module (400), be connected with described drive control module (300), controls described LED lamp for drive also constant current according to described drive control signal, and bear the pressure drop in circuit.

2. linear switch constant current LED drive circuit according to claim 1, is characterized in that, described feedback control module (200) comprises reference voltage maker (201), mutual conductance error amplifier (202) and integrating capacitor (C1); The in-phase input end of described mutual conductance error amplifier (202) connects described reference voltage maker (201) to obtain reference voltage, the inverting input of described mutual conductance error amplifier (202) connects described output sampling module (100) to obtain described output current information, and the output of described mutual conductance error amplifier (202) is by described integrating capacitor (C1) ground connection; Described mutual conductance error amplifier (202) is discharged and recharged described integrating capacitor (C1) for described output current information and described reference voltage are compared to rear output gain electric current, to generate described integral voltage.

3. linear switch constant current LED drive circuit according to claim 2, is characterized in that, described power control module (400) comprises the first metal-oxide-semiconductor (M1) and current-limited power resistance (Rp); The grid of described the first metal-oxide-semiconductor (M1) connects the output of described drive control module (300), the source electrode of described the first metal-oxide-semiconductor (M1) connects described output sampling module (100), the drain electrode of described the first metal-oxide-semiconductor (M1) connects the first end of described current-limited power resistance (Rp), and the second end of described current-limited power resistance (Rp) connects described LED lamp; Described current-limited power resistance (Rp) is for bearing the pressure drop of circuit.

4. linear switch constant current LED drive circuit according to claim 3, is characterized in that, described input sample module (500) comprises the first resistance (R1) and the second resistance (R2); Ground connection after described the first resistance (R1) and described the second resistance (R2) series connection, one end of described the first resistance (R1) connects the input power of described LED lamp, and the tie point of described the first resistance (R1) and described the second resistance (R2) is as the output of described input sample module (500).

5. linear switch constant current LED drive circuit according to claim 4, is characterized in that, described drive control module (300) comprises drive circuit (301) and comparator (302); The in-phase input end of described comparator (302) connects the output of described feedback control module (200) to obtain described integral voltage, the inverting input of described comparator (302) connects the output of described input sample module (500) to obtain described input sample voltage, the output of described comparator (302) connects the input of described drive circuit (301), and the output of described drive circuit (301) connects the grid of described the first metal-oxide-semiconductor (M1).

6. linear switch constant current LED drive circuit according to claim 5, is characterized in that, described output sampling module (100) comprises sampling resistor (Rs); The first end of described sampling resistor (Rs) connects respectively the source electrode of described the first metal-oxide-semiconductor (M1) and the inverting input of described mutual conductance error amplifier (202), the second end ground connection of described sampling resistor (Rs).

7. linear switch constant current LED drive circuit according to claim 6, it is characterized in that, described reference voltage maker (201), described mutual conductance error amplifier (202), described the first metal-oxide-semiconductor (M1), described drive circuit (301) and described comparator (302) are integrated in chip piece.

8. linear switch constant current LED drive circuit according to claim 7, is characterized in that, described power control module (400) also comprises the second metal-oxide-semiconductor (M2) be connected between described the first metal-oxide-semiconductor (M1) and described current-limited power resistance (Rp); The grid of described the second metal-oxide-semiconductor (M2) connects high level, and the source electrode of described two metal-oxide-semiconductors (M2) connects the drain electrode of described the first metal-oxide-semiconductor (M1), and the drain electrode of described two metal-oxide-semiconductors (M2) connects the first end of described current-limited power resistance (Rp).

9. linear switch constant current LED drive circuit according to claim 2, is characterized in that, the appearance value scope of described integrating capacitor (C1) is 1 microfarad to 10 microfarad.

10. a LED light fixture, comprise alternating current input power supplying, rectifier bridge, linear switch constant current LED drive circuit and LED lamp, it is characterized in that, described linear switch constant current LED drive circuit adopts linear switch constant current LED drive circuit as described as claim 1-9 any one.

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