Abstract:
The present invention relates to an LED luminaire driving circuit with high power factor, comprising: a filter unit, a rectifier unit, a transformer unit, a power switch unit, a zero current detecting unit, a feedback unit, an error amplifier unit, and a power switch driving 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 (&lt;±3%).

Description:
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  1   a  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  1   a  from the circuit framework of  FIG. 1 : (1) the voltage-sensing circuit  11   a  disposed at the input end of the BCM flyback converter with variable frequency control  1   a  would produce extra power consumption; and (2) the cut-off time of the secondary side current I D     —     a  of the BCM flyback converter with variable frequency control  1   a  is fully decided by the output diode D O     —     a , such that the cut-off time of the secondary side current I D     —     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  1   b  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  1   b  from the circuit framework of  FIG. 2 : the cut-off time of the secondary side current I D     —     b  of the BCM flyback converter with variable frequency control  1   b  is fully decided by the output diode D O     —     b , so the cut-off time of the secondary side current I D     —     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  1   c  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  1   c  can merely be used for driving low power LED lamps because the DCM flyback converter with constant frequency control  1   c  includes higher switching current I Q     —     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  1   d  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  1   d  can be operated under discontinuous conduction mode, boundary conduction mode or continuous conduction mode (CCM); however, the COT flyback converter with variable frequency control  1   d  still includes the following drawbacks: the voltage-sensing circuit  11   d  disposed at the input end of the COT flyback converter with variable frequency control  1   d  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  1   e  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  1   e  carries out the power factor correction by using the constant current (CC) error amplifier  11   e , the constant voltage (CV) error amplifier  12   e , the opticalcoupler feedback circuit  13   e , the triangle compensation signal V tri , and the power device driving circuit  14   e  to produce a PWM driving signal to the power transistor Q PW ′. In spite of that, the constant-frequency control flyback converter  1   e  still includes the following drawbacks: the entire manufacturing cost of the constant-frequency control flyback converter  1   e  is too expensive because the disposing of the opticalcoupler feedback circuit  13   e.    
     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 (&lt;+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 V S  for receiving an AC signal. The filter unit  10  consists of a first capacitor C X1 , a common mode chock winding L CM  and a second capacitor C X2 , wherein the first capacitor C X1  is connected across the two input terminals of the common mode chock winding L CM , and the second capacitor C X2  is connected across the two output terminals of the common mode chock winding L CM . 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 V in . 
     The transformer unit  12  is coupled to the rectifier unit  11  and has a primary winding coil N p , a secondary winding coil N S  and an auxiliary winding coil N a . In the present invention, the transformer unit  12  is used for receiving the input signal V in , and then transforming the input signal V in  having a peak input voltage to an output signal V O  having a peak output voltage, so as to output the output signal V O  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 V O  to the LED lighting unit  14 . As shown in  FIG. 7 , the output unit  13  is consisted of an output diode D O  and an output capacitor C O , wherein the output diode D O  is coupled to the one terminal of the primary winding coil N p  by one end thereof, and the output capacitor C O  is coupled to the other end of the output diode D O  by one end thereof, moreover the other end of the output capacitor C O  is coupled to other terminal of the primary winding coil N p  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 R S . The power switch unit  15  is coupled between the rectifier unit  11  and the transformer unit  12  and used for treating the input signal V in  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 V O  via a signal detecting unit  16   a  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  16   a  has at least one resistor (R dect1 , R dect2 ), wherein one end of the resistor (R dect1 , R dect2 ) is coupled to one terminal of the auxiliary winding coil N a , and the other end of the resistor is coupled to the other terminal of the auxiliary winding coil N a  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 Z CD  after receiving a detection signal V ded  from the signal detecting unit  16   a.    
     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  16   a  for receiving the detection signal V dec . 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 V REF1 . 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 I Q  of the power switch unit  15  and the zero current detection signal Z CD , and then outputting a feedback signal V FB  according to the power switch current I Q  and the zero current detection signal Z CD . 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 I Q , so as to treat the power switch current I Q  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 Z CD  and the low-pass-filtered power switch current I Q , so as to output the feedback signal V FB . 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 V FB , and then outputs an error amplification signal Vea according to the feedback signal V FB . 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 V ea , so as to output a driving signal V G  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 V G . 
     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 V FB , and the multiplexer  182  is coupled to the power switch driving unit  19  for receiving the driving signal V G . Moreover, the multiplexer  182  is further coupled with a reference current signal I REF , such that the multiplexer  182  is able to output a reference voltage signal V REF  to the PI compensator  181  according to the driving signal V G  and the reference current signal I REF , and then the PI compensator  181  may output the error amplification signal V ea  to a subtractor  191  of the power switch driving unit  19  according to the reference voltage signal V REF  and the feedback signal V FB . 
     Besides the error amplification signal V ea , the subtractor  191  coupled to the error amplifier unit  18  simultaneously receiving the a ripple signal V rip , therefore the subtractor  191  outputs a conversion signal V con  to a comparator  192  of the power switch driving unit  19  according to the ripple signal V rip  and the error amplification signal V ea . The comparator  192 , coupled to the subtractor  191  and the power switch unit  15 , is used for respectively receiving the conversion signal V con  and a power switch voltage signal V CS  of the power switch unit  15 ; therefore, the comparator  192  would output a comparison signal according to the power switch voltage signal V CS  and the conversion signal V con . 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 V G  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): V con =V ea −m a T on =m 1 T on . In above-mentioned formula (1), V con  is the conversion signal outputted by the subtractor  191  of the power switch driving unit  19 , V ea  is the error amplification signal V ea  outputted by the PI compensator  181  of the error amplifier unit  18 , and T on  is the conduction time of the power switch unit  15 , m a  is the slope of the ripple signal V rip , and m 1  is the slope of the ripple signal V CS  of the power MOSFET Q of the power switch unit  15 . Moreover, the I D  marked in  FIG. 8  means the diode current of the output diode D O  of the output unit  13 . 
     Since m 1 =(R S *V S )/L P  and I pk =(T on *m 1 )/R S , the T on  can be calculated by the formula of T on =V ea /(m 1 +m a ). Herein L p  means the self-inductance of the transformer unit  12  and I pk  means the peak value of the power switch current I Q . Moreover, because input current I S  is equal to the average value of the power switch current I Q  in a switching period, the input current I S  can be calculated by using the formula of I S =(I pk *T on )/2T S ; wherein T S  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): I S =(V ea   2 /2R S T S )*[m 1 /(m 1 +m a ) 2 ]. Eventually, after letting m a =K S M 1,max =K S R S (V sm /L p ) and substituting different slope compensating parameter K S  and slope m a  into above-mentioned formula (2), a plot of the input current I S  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 K S  is set, the less distortion the input current I S  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): ΔI pk =(m 1 *T on )/R S . Because input current I S  is equal to the average value of the power switch current I Q  in a switching period, the input current I S  can be calculated by using the following formula (4): I S =I a (T on /T S )+(ΔI pk T on )/2T S , wherein the LED luminaire circuit  1  of the present invention would work under DCM operation when I a &lt;I pk . Moreover, as  FIG. 11  shows, when the conduction angle is ranged between θ 0  and π−θ 0  and different slope compensating parameter K S  is substituted into above-mentioned formula (4), a plot of the input current I S  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 K S  is set, the less distortion the input current I S  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 V O  and output current signal I O , and simultaneously performs excellent stability and current modulation error rate (&lt;±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., V S =110V rms ) reaches to 0.991, and the working current I LED  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 V O  and output current signal I O , and simultaneously performs excellent stability and current modulation error rate (&lt;±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., V S =220V rms ) reaches to 0.953, and the working current I LED  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.