BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the technology fields of LED luminaire driving circuits, and more particularly to an LED luminaire driving circuit with high power factor.
2. Description of the Prior Art
Recently, light-emitting diodes (LEDs) are widely applied to be the lighting device in human life. And currently, more and more families replace the traditional fluorescent lamps by LED lamps due to the issue of Energy Conservation and Carbon Reduction is more and more popular. However, since the power formation of the market electricity is AC power and the LED lamps are driven to emit light by DC power, it is necessary to dispose a power converting device between the market electricity and the LED lamps for converting the AC power to DC power.
With reference to FIG. 1, there is shown a circuit framework diagram of a BCM flyback converter with variable frequency control. The BCM (Boundary Conduction Mode) flyback converter with variable frequency control 1a shown by FIG. 1 is a peak-current-mode PWM (pulse width modulation) converter, and the engineers skilled in LED lamp driving circuit field are able to find the following drawbacks of the BCM flyback converter with variable frequency control 1a from the circuit framework of FIG. 1: (1) the voltage-sensing circuit 11a disposed at the input end of the BCM flyback converter with variable frequency control 1a would produce extra power consumption; and (2) the cut-off time of the secondary side current ID—a of the BCM flyback converter with variable frequency control 1a is fully decided by the output diode DO—a, such that the cut-off time of the secondary side current ID—a cannot be precisely predicted and controlled.
Please refer to FIG. 2, there is shown the circuit framework diagram of another BCM flyback converter with variable frequency control. The BCM (Boundary Conduction Mode) flyback converter with variable frequency control 1b shown by FIG. 2 is a constant on-time control converter, and the engineers skilled in LED lamp driving circuit field can find the following drawbacks of the BCM flyback converter with variable frequency control 1b from the circuit framework of FIG. 2: the cut-off time of the secondary side current ID—b of the BCM flyback converter with variable frequency control 1b is fully decided by the output diode DO—b, so the cut-off time of the secondary side current ID—b cannot be precisely predicted and controlled.
Referring to FIG. 3, which illustrates the circuit framework diagram of a DCM flyback converter with constant frequency control. The DCM (Discontinuous Conduction Mode) flyback converter with constant frequency control 1c shown by FIG. 3 is a voltage control converter, and the engineers skilled in LED lamp driving circuit field is able to easily know that the DCM flyback converter with constant frequency control 1c can merely be used for driving low power LED lamps because the DCM flyback converter with constant frequency control 1c includes higher switching current IQ—C under the same working power.
With reference to FIG. 4, there is shown the circuit framework diagram of a COT flyback converter with variable frequency control. The COT (Constant Off-Time) flyback converter with variable frequency control 1d shown by FIG. 4 is a peak-current-mode PWM (pulse width modulation) converter, and the engineers skilled in LED lamp driving circuit field are able to find that the COT flyback converter with variable frequency control 1d can be operated under discontinuous conduction mode, boundary conduction mode or continuous conduction mode (CCM); however, the COT flyback converter with variable frequency control 1d still includes the following drawbacks: the voltage-sensing circuit 11d disposed at the input end of the COT flyback converter with variable frequency control 1d would produce extra power consumption.
Please refer to FIG. 5, which illustrates the circuit framework diagram of a constant-frequency control flyback converter. The constant-frequency control flyback converter 1e shown by FIG. 5 is a current-clamp control converter, and the engineers skilled in LED lamp driving circuit field can easily understand that the constant-frequency control flyback converter 1e carries out the power factor correction by using the constant current (CC) error amplifier 11e, the constant voltage (CV) error amplifier 12e, the opticalcoupler feedback circuit 13e, the triangle compensation signal Vtri, and the power device driving circuit 14e to produce a PWM driving signal to the power transistor QPW′. In spite of that, the constant-frequency control flyback converter 1e still includes the following drawbacks: the entire manufacturing cost of the constant-frequency control flyback converter 1e is too expensive because the disposing of the opticalcoupler feedback circuit 13e.
Accordingly, in view of the conventional LED lamps driving circuits all include drawbacks and shortcomings, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided an LED luminaire driving circuit with high power factor.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to provide an LED luminaire driving circuit with high power factor, which especially integrated with a zero current detecting unit, a feedback unit and an error amplifier unit without using any input-end voltage detecting signal. The LED luminaire driving circuit can be used for driving high power LED lamps, and work without producing any extra power consumption.
The another objective of the present invention is to provide an LED luminaire driving circuit with high power factor, which integrated with a zero current detecting unit, a feedback unit and an error amplifier unit. Particularly, the LED luminaire driving circuit proposed by the present invention does not include any optocoupler feedback circuits, so it is able to effectively reduce the entire circuit manufacturing cost of this LED luminaire driving circuit. Moreover, this LED luminaire driving circuit can selectively work under CCM operation or DCM operation with high power factor (PF˜1), and provide stable output voltage signal and output current signal to load end. In addition, this LED luminaire driving circuit performs excellent stability and current modulation error rate (<+3%).
Accordingly, to achieve the primary objective of the present invention, the inventor of the present invention provides an LED luminaire driving circuit with high power factor, comprising:
a filter unit, coupled to an input source for receiving an AC signal;
a rectifier unit, coupled to the filter unit for receiving the AC signal via the filter unit, and then treats the AC signal with a rectifying process so as to output an input signal;
a transformer unit, coupled to the rectifier unit for receiving the input signal, and then transforms the input signal having a peak input voltage to an output signal having a peak output voltage, so as to output the output signal to an LED lighting unit for making the LED lighting unit emit light;
a power switch unit, coupled between the rectifier unit and the transformer unit and used for treating the input signal with switching control;
a zero current detecting unit, being coupled to the transformer unit and used for treating the output signal with a zero current detection, so as to output a zero current detection signal;
a feedback unit, being coupled to the zero current detecting unit and the power switch unit, wherein the feedback unit receives a power switch current and the zero current detection signal, and outputting a feedback signal according to the power switch current and the zero current detection signal;
an error amplifier unit, being coupled to the zero current detecting unit and the feedback unit for receiving the feedback signal, and then outputs an error amplification signal according to the feedback signal; and
a power switch driving unit, being coupled to the power switch unit and the error amplifier unit for receiving the error amplification signal, and then outputs a driving signal to the power switch unit according to the error amplification signal, so as to drive the power switch unit to treat the input signal with switching control.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention as well as a preferred mode of use and advantages thereof will be best understood by referring to the following detailed description of an illustrative embodiment in conjunction with the accompanying drawings, wherein:
FIG. 1 is a circuit framework diagram of a BCM flyback converter with variable frequency control;
FIG. 2 is a circuit framework diagram of another BCM flyback converter with variable frequency control;
FIG. 3 is a circuit framework diagram of a DCM flyback converter with constant frequency control;
FIG. 4 is a circuit framework diagram of a COT flyback converter with variable frequency control;
FIG. 5 is a circuit framework diagram of a constant-frequency control flyback converter;
FIG. 6 is a circuit block diagram of an LED luminaire driving circuit with high power factor according to the present invention;
FIG. 7 is a circuit framework diagram of the LED luminaire driving circuit with high power factor according to the present invention;
FIG. 8 shows signal waveforms of the LED luminaire driving circuit working under DCM operation;
FIG. 9 is a plot of an input current as a function of the conduction angle;
FIG. 10 shows signal waveforms of the LED luminaire driving circuit working under CCM operation;
FIG. 11 shows curves of the input current and the conduction angle;
FIG. 12 is a plot of the input current as a function of the conduction angle;
FIG. 13A and FIG. 13B show simulated signal waveforms of the LED luminaire driving circuit working under CCM operation; and
FIG. 14A and FIG. 14B show simulated signal waveforms of the LED luminaire driving circuit working under DCM operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
To more clearly describe an LED luminaire driving circuit with high power factor according to the present invention, embodiments of the present invention will be described in detail with reference to the attached drawings hereinafter.
With reference to FIG. 6, there is shown a circuit block diagram of an LED luminaire driving circuit with high power factor according to the present invention. As shown in FIG. 6, the LED luminaire driving circuit 1 of the present invention includes: a filter unit 10, a rectifier unit 11, a transformer unit 12, an output unit 13, a power switch unit 15, a zero current detecting unit 16, a feedback unit 17, an error amplifier unit 18, and a power switch driving unit 19.
Referring to FIG. 6 again, and please simultaneously refer to FIG. 7, which shows a circuit framework diagram of the LED luminaire driving circuit with high power factor. As shown in FIG. 6 and FIG. 7, the filter unit 10 is coupled to an input source VS for receiving an AC signal. The filter unit 10 consists of a first capacitor CX1, a common mode chock winding LCM and a second capacitor CX2, wherein the first capacitor CX1 is connected across the two input terminals of the common mode chock winding LCM, and the second capacitor CX2 is connected across the two output terminals of the common mode chock winding LCM. The rectifier unit 11 is a bridge rectifier, which is coupled to the filter unit 10 for receiving the AC signal via the filter unit 10, and then treats the AC signal with a rectifying process so as to output an input signal Vin.
The transformer unit 12 is coupled to the rectifier unit 11 and has a primary winding coil Np, a secondary winding coil NS and an auxiliary winding coil Na. In the present invention, the transformer unit 12 is used for receiving the input signal Vin, and then transforming the input signal Vin having a peak input voltage to an output signal VO having a peak output voltage, so as to output the output signal VO to an LED lighting unit 14 for making the LED lighting unit 14 emit light.
Inheriting to above description, the output unit 13 is coupled between the transformer unit 12 and the LED lighting unit 14 for outputting the output signal VO to the LED lighting unit 14. As shown in FIG. 7, the output unit 13 is consisted of an output diode DO and an output capacitor CO, wherein the output diode DO is coupled to the one terminal of the primary winding coil Np by one end thereof, and the output capacitor CO is coupled to the other end of the output diode DO by one end thereof, moreover the other end of the output capacitor CO is coupled to other terminal of the primary winding coil Np and the LED lighting unit 14.
The power switch unit 15 is a Power Metal-Oxide-Semiconductor Field-Effect Transistor (power MOSFET), and the source terminal of the power MOSFET Q is coupled with a source resistor RS. The power switch unit 15 is coupled between the rectifier unit 11 and the transformer unit 12 and used for treating the input signal Vin with switching control. Particularly, the LED luminaire driving circuit 1 of the present invention includes a zero current detecting unit 16, which is able to detect the output signal VO via a signal detecting unit 16a coupled between the transformer unit 12 and the zero current detecting unit 16. As shown in FIG. 6 and FIG. 7, the signal detecting unit 16a has at least one resistor (Rdect1, Rdect2), wherein one end of the resistor (Rdect1, Rdect2) is coupled to one terminal of the auxiliary winding coil Na, and the other end of the resistor is coupled to the other terminal of the auxiliary winding coil Na and the ground of the LED luminaire driving circuit 1. Thus, the zero current detecting unit 16 is able to output a zero current detection signal ZCD after receiving a detection signal Vded from the signal detecting unit 16a.
The zero current detecting unit 16 consists of a comparator 161, an adder 162, an inverter 163, and a Set/Reset flip flop 164, wherein the comparator 161 is coupled to the signal detecting unit 16a for receiving the detection signal Vdec. The an adder 162 is coupled between a first input end and an output end of the comparator 161, moreover the adder 162 is further coupled with a reference signal VREF1. Besides, the inverter 163 is coupled to the output end of the comparator 161, and the Set/Reset flip flop 164 is respectively coupled to the invertor 163 and the power switch unit 15 by one reset end and one set end thereof.
Inheriting to above description, the feedback unit 17 is coupled to the zero current detecting unit 16 and the power switch unit 15. In the present invention, the feedback unit 17 is used for receiving a power switch current IQ of the power switch unit 15 and the zero current detection signal ZCD, and then outputting a feedback signal VFB according to the power switch current IQ and the zero current detection signal ZCD. As shown in FIG. 6 and FIG. 7, the feedback unit 17 includes a low pass filter 171 and a multiplexer 172, wherein the low pass filter 171 is coupled to power switch unit 15 for receiving the power switch current IQ, so as to treat the power switch current IQ with a low pass filtering process. The multiplexer 172 is coupled to the low pass filter 171 and the zero current detecting unit 16 for receiving the zero current detection signal ZCD and the low-pass-filtered power switch current IQ, so as to output the feedback signal VFB. Moreover, the feedback unit 17 further includes a relay coupled between the multiplexer 172 and the error amplifier unit 18.
The error amplifier unit 18 is coupled to the zero current detecting unit 16 and the feedback unit 17 for receiving the feedback signal VFB, and then outputs an error amplification signal Vea according to the feedback signal VFB. In addition, the power switch driving unit 19 is coupled to the power switch unit 15 and the error amplifier unit 18 for receiving the error amplification signal Vea, so as to output a driving signal VG to the power switch unit 15 according to the error amplification signal Vea; therefore, the power switch unit 15 is able to treat the input signal Vin with switching control according to the driving signal VG.
As shown in FIG. 6 and FIG. 7, the error amplifier unit 18 consists of a proportional-integral (PI) compensator 181 and a multiplexer 182, wherein the PI compensator 181 is coupled to the feedback unit 17 for receiving the feedback signal VFB, and the multiplexer 182 is coupled to the power switch driving unit 19 for receiving the driving signal VG. Moreover, the multiplexer 182 is further coupled with a reference current signal IREF, such that the multiplexer 182 is able to output a reference voltage signal VREF to the PI compensator 181 according to the driving signal VG and the reference current signal IREF, and then the PI compensator 181 may output the error amplification signal Vea to a subtractor 191 of the power switch driving unit 19 according to the reference voltage signal VREF and the feedback signal VFB.
Besides the error amplification signal Vea, the subtractor 191 coupled to the error amplifier unit 18 simultaneously receiving the a ripple signal Vrip, therefore the subtractor 191 outputs a conversion signal Vcon to a comparator 192 of the power switch driving unit 19 according to the ripple signal Vrip and the error amplification signal Vea. The comparator 192, coupled to the subtractor 191 and the power switch unit 15, is used for respectively receiving the conversion signal Vcon and a power switch voltage signal VCS of the power switch unit 15; therefore, the comparator 192 would output a comparison signal according to the power switch voltage signal VCS and the conversion signal Vcon. As shown in FIG. 6 and FIG. 7, the power switch driving unit 19 further includes a Set/Reset flip flop 193, which is coupled to the output end of the comparator 193 by one reset end thereof; moreover, one set end of the Set/Reset flip flop 193 is coupled with a clock signal CLK, such that the Set/Reset flip flop 193 is able to output the driving signal VG to the power switch unit 15 according the clock signal CLK and the comparison signal received from the comparator 193.
Therefore, above descriptions have been introduce the detailed circuit framework of the LED luminaire driving circuit 1 proposed by the present invention; Next, in order to prove the practicability and performance of the LED luminaire driving circuit 1, a variety of circuit simulation are completed and the related simulation data are recorded. Please refer to FIG. 8, which shows signal waveforms of the LED luminaire driving circuit working under DCM (Discontinuous Conduction Mode) operation. From the signal waveforms, it is able to derive the following formula (1): Vcon=Vea−maTon=m1Ton. In above-mentioned formula (1), Vcon is the conversion signal outputted by the subtractor 191 of the power switch driving unit 19, Vea is the error amplification signal Vea outputted by the PI compensator 181 of the error amplifier unit 18, and Ton is the conduction time of the power switch unit 15, ma is the slope of the ripple signal Vrip, and m1 is the slope of the ripple signal VCS of the power MOSFET Q of the power switch unit 15. Moreover, the ID marked in FIG. 8 means the diode current of the output diode DO of the output unit 13.
Since m1=(RS*VS)/LP and Ipk=(Ton*m1)/RS, the Ton can be calculated by the formula of Ton=Vea/(m1+ma). Herein Lp means the self-inductance of the transformer unit 12 and Ipk means the peak value of the power switch current IQ. Moreover, because input current IS is equal to the average value of the power switch current IQ in a switching period, the input current IS can be calculated by using the formula of IS=(Ipk*Ton)/2TS; wherein TS is the switching period of the power MOSFET Q of the power switch unit 15. Subsequently, it is able to derive the following formula (2): IS=(Vea2/2RSTS)*[m1/(m1+ma)2]. Eventually, after letting ma=KSM1,max=KSRS(Vsm/Lp) and substituting different slope compensating parameter KS and slope ma into above-mentioned formula (2), a plot of the input current IS as a function of the conduction angle can be obtained and shown as FIG. 9. From the plot of FIG. 9, it is able to observe that the greater value the slope compensating parameter KS is set, the less distortion the input current IS shows.
Continuously referring to FIG. 10, which shows signal waveforms of the LED luminaire driving circuit working under CCM (continuous conduction mode) operation. From FIG. 10, it is able to derive the following formula (3): ΔIpk=(m1*Ton)/RS. Because input current IS is equal to the average value of the power switch current IQ in a switching period, the input current IS can be calculated by using the following formula (4): IS=Ia(Ton/TS)+(ΔIpkTon)/2TS, wherein the LED luminaire circuit 1 of the present invention would work under DCM operation when Ia<Ipk. Moreover, as FIG. 11 shows, when the conduction angle is ranged between θ0 and π−θ0 and different slope compensating parameter KS is substituted into above-mentioned formula (4), a plot of the input current IS as a function of the conduction angle can be obtained and shown as FIG. 12. From the plot of FIG. 12, it is able to observe that the greater value the slope compensating parameter KS is set, the less distortion the input current IS shows.
Please refer to FIG. 13A and FIG. 13B, there are shown simulated signal waveforms of the LED luminaire driving circuit working under CCM operation. The simulated signal waveforms shown by FIG. 13A and FIG. 13B have been proved that the LED luminaire driving circuit 1 proposed by the present invention can provide stable output voltage signal VO and output current signal IO, and simultaneously performs excellent stability and current modulation error rate (<±3%). In addition, from FIG. 13A, it can find that the power factor (PF) of the LED luminaire driving circuit 1 working under CCM operation (i.e., VS=110Vrms) reaches to 0.991, and the working current ILED of the LED lighting unit 14 oppositely reaches to 519 mA.
Moreover, please refer to FIG. 14A and FIG. 14B, there are shown simulated signal waveforms of the LED luminaire driving circuit working under DCM operation. The simulated signal waveforms shown by FIG. 14A and FIG. 14B have been proved that the LED luminaire driving circuit 1 proposed by the present invention can provide stable output voltage signal VO and output current signal IO, and simultaneously performs excellent stability and current modulation error rate (<±3%). In addition, from FIG. 14A, it can find that the power factor (PF) of the LED luminaire driving circuit 1 working under DCM operation (i.e., VS=220Vrms) reaches to 0.953, and the working current ILED of the LED lighting unit 14 oppositely reaches to 501 mA. Therefore, the simulated signal waveforms of FIG. 13A, FIG. 13B, FIG. 14A, and FIG. 14B proves that the LED luminaire driving circuit 1 proposed by the present invention can indeed works under different mode (CDM or DCM) operation with high power factor.
The above description is made on embodiments of the present invention. However, the embodiments are not intended to limit scope of the present invention, and all equivalent implementations or alterations within the spirit of the present invention still fall within the scope of the present invention.