Abstract:
A power supply based on resonant converter with or without feedback is used for lamp. The output voltage waveform is high frequency (above 10 kHz) component included in a band envelope without low frequency component. Lamp brightness is proportional to lamp voltage. At low frequency (60 Hz), eye responds to brightness change by shrinking and dilating pupil and crystalline lens 60 times per second and become very tired after several hours. In the long run, the tiredness can cause eye muscles so slack that muscles can&#39;t control crystalline lens and pupil well. Thus myopia is caused and preexistent myopia will be deepened At high frequency (above 10 kHz), Eyes cannot keep pace with such high-speed brightness variation. High frequency will have no impact on people eyes muscle. It doesn&#39;t cause peoples eye tiredness. It prevents people&#39;s eyes from myopia or from myopia deepening for long run. It has dimming function.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to U.S. patent application Ser. No. 11/351,625 filed on Feb. 11, 2006, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND  
       [0002]     The following disclosure relates to electrical circuits and signal processing.  
         [0003]     Power supplies are used to power many types of electronic devices, for example, lamps. Conventional power supplies (e.g., for halogen lamps) typically include a converter. A converter is a power supply switching circuit.  
         [0004]     Lamps have two categories:  
         [0005]     First category uses ballast to strike the lamp to start. Most of them use gas to create light such as Fluorescent, HID, Compact, metal halide lamp etc. Bulbs need ballast because they use gas to create light. When the gas is excited by electricity, it emits invisible ultraviolet light that hits the white coating inside the bulb. The coating changes the ultraviolet light into light you can see. It needs a very high voltage strike to startup the operation of the lamp. But my invention is not applied directly to this category. The invention must be combined with second stage ballast to drive the lamp.  
         [0006]     Second category doesn&#39;t need ballast to start the lamp. Most of them use heat generated by filament or diode etc to create light. Such as Halogen, Incandescent, LED, PAR lamp, miniature sealed beam lamp, Projection lamp, automotive lamp, some stage and studio lamp, DC fluorescent lamp etc.  
         [0007]     My patent can be used directly on second category lamp.  
         [0008]     Because Halogen lamp is the typical lamp of second category (filament or diode etc), all the discussion starts from the application of the power supply on Halogen lamp. For example, 20 W 12V Halogen Lamp, resistance=7.2 ohm at 12 volt; resistance=1.8 ohm at 2 volt.  
         [0009]      FIG. 1  shows a conventional half bridge converter  100  that receives AC sinusoidal voltage from a power source Vin. Converter  100  includes transistors Q 1 , Q 2 , transformer T 11 , Coupled inductor T 1 A, T 1 B and T 1 C; DC blocking Capacitor C 4 , C 5 ; Timing circuit C 2 , R 2  and C 3 , R 3 ; startup circuit D 5 , R 4 , Q 3 ; R 1 , C 1 ; bridge rectifier D 1 , D 2 , D 3  and D 4 ; AC power source 120 Vac 60 Hz sinusoidal (or 220 Vac 50 Hz) and Halogen lamp. (low voltage, for example 12 v)  
         [0010]     Q 1  and Q 2  complementary on/off with 50% duty cycle. Output voltage waveform is 120 Hz low frequency envelope with high switching frequency square waveform in it. As shown in  FIG. 2  and  FIG. 3 .  
         [0011]     Vo=60*(4/3.14159)*ns/np (np is primary turns and ns is secondary turns.)  
         [0012]     Dimming is realized by applying phase cut dimmer in the converter in trailing edge mode. This means that at the beginning of the line voltage half cycle, the switch inside the dimmer is closed and mains voltage is supplied to the converter allowing the converter to operate normally. At some point during the half cycle, the switch inside the dimmer is opened and voltage is no longer applied. The DC bus inside the converter almost immediately drops to 0 V and the output is no longer present. In this way, bursts of high frequency output voltage are applied to the lamp. The RMS voltage across the lamp will naturally vary depending on the phase angle at which the dimmer switch switches off. In this way the lamp brightness may easily be varied from zero to maximum output as shown in  FIGS. 5 and 6 .  
         [0013]     Advantage:  
         [0000]     This typical low-voltage halogen-lamp converter  100  is simple without IC controller.  
         [0014]     Disadvantage: 
    1. Lamp brightness is proportional to the voltage on lamp. Output voltage has low frequency (120 Hz) envelope, voltage on lamp changes from valley to peak 120 times per second, so the brightness of lamp also changes from valley to peak 120 times per second. People eyes pupil will widen (mydriasis) when the brightness become dark and eyes pupil will contract when the brightness is bright (miosis). The eye muscles for controlling pupil and crystalline lens shrink and dilate 120 times per second and become very tired after reading books for several hours. In the long run, the tiredness can cause eye muscles slack and can&#39;t control crystalline lens and pupil well. Thus myopia is caused and preexistent myopia will be deepened.     2.Dimming needs external dimmer based on turn on/off line voltage. So cost increases.     3.Lamp filament behaves likes short circuit when low voltage apply on that. Inrush current during dimmer turn on/off input voltage at dimming is high and shortens the lamp life. Power factor is very low during dimming at low voltage.    
 
         [0018]      FIG. 4  shows another way to drive the halogen lamp. A low frequency transformer is connected directly to the halogen lamp.  
         [0000]     Advantage: Component is only one transformer and cost is less.  
         [0000]     Disadvantage:  
         [0000]    
       
          1.Output voltage has low frequency (60 Hz or 50 Hz) sinusoidal waveform, thus muscles to control eyes pupil and crystalline lens will shrink and dilate 60 or 50 times and feel tired. In the long run, the tiredness can cause eye muscles slack and can&#39;t control crystalline lens and pupil well. Thus myopia is caused and preexistent myopia will be deepened.  
          2.Variation output voltage for No Feedback;  
          3.Dimming needs external dimmer based on turn on/off line voltage, so the Power factor is very low during dimming, Inrush current during turn on is high and shorten the lamp life.  
          4.Transformer is too big and heavy for low frequency use.  
       
     
       SUMMARY  
       [0023]     In general, in one aspect, this specification describes new block diagram for Halogen lamp converter as  FIGS. 7,8  and  9  as well as topology in FIGS.  12 , 13 , 14 , 15 , 19 ,  20 , 21 , 22  and  23 .  
         [0024]     Implementations can include one or more of the following advantages. 
    1.Output voltage is high frequency component in band envelope as shown in FIGS.  17 , 18 , 25  and  26 . The high frequency is above 10 kHz. At that frequency, people eyes cannot keep pace with this high-speed brightness variation. High frequency will have no effect on people eyes muscle. There is almost no low frequency component or we can say low frequency component is trivia compared to  FIG. 2 . It doesn&#39;t cause peoples eye tiredness. It prevents people&#39;s eyes from myopia or from myopia deepening to maximum extent protection.     2.Output voltage can have feedback control or no feedback control.     3. Dimming is realized by changing switching frequency to change magnitude. No need for external dimmer and save cost. Dimming does not turn on/off input line voltage and does not cause inrush current. So lamp&#39;s life is prolonged.     4.Power factor correction circuit can be included or not included.     5.Input voltage source can be AC sinusoidal or DC substantially constant.    
 
         [0030]     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0031]      FIG. 1 : typical low-voltage halogen-lamp converter based on conventional half bridge converter  100 .  
         [0032]      FIG. 2 : Output voltage waveform of typical halogen lamp converter  100  is high frequency square waveform contained in low frequency (120 Hz) envelope. 
    Top graph: Blue or red curve-rms voltage of output voltage; Red shade-output voltage Bottom table:     VP 1 -Peak value of output voltage=17 v; SQRT(AVG-rms value of output voltage.12 v      
         [0035]      FIG. 3 : Output high frequency square waveform in the low frequency envelope of typical halogen lamp converter  100 . 
    Top: Red waveform-high frequency square waveform in output voltage     Bottom: rms value of output voltage      
         [0038]      FIG. 4 : The halogen lamp converter driven directly by a big low frequency transformer and output voltage on the lamp.  
         [0039]     Top table:  
                                                   V2-peak voltage value of output voltage = 16.9 v;           SQRT(AVG-rms value of output voltage = 12 v.           Top waveform: red-sinusoidal output voltage; blue-rms value of           output voltage           Bottom waveform: red-rms value of output voltage                      
 
         [0040]      FIG. 5 : input bus voltage and lamp output voltage waveform during dimming with external dimmer for typical Halogen lamp converter  100 .  
                                                       Left: trailing edge dimming   Right: Leading edge dimming                        
         [0041]      FIG. 6 : Output voltage and current during dimming of typical halogen lamp converter  100 .  
         [0042]      FIG. 7 : Block diagram of my invention, Power Supply  200 , power supply based on resonant converter for Lamp without feedback. 
    (a) Voltage source  210  comes from AC sinusoidal power line     (b) Voltage source  220  comes from DC substantially constant voltage      
         [0045]      FIG. 8 . Block diagram of my invention, Power Supply  200 , power supply based on resonant converter for Lamp with feedback sampling signal coming from interior component in converter 
    (a) Voltage source  210  comes from AC sinusoidal power line     (b) Voltage source  220  comes from DC substantially constant voltage      
         [0048]      FIG. 9 . Block diagram of my invention, Power Supply  200 , power supply based on resonant converter for Lamp with feedback sampling signal coming directly from lamp. 
    (a) Voltage source  210  comes from AC sinusoidal power line     (b) Voltage source  220  comes from DC substantially constant voltage      
         [0051]      FIG. 10  Voltage waveform across B and B′ on block diagram FIGS.  7 ( a ), 8 ( a ) and  9 ( a ) when voltage source  210  comes from 120 volt AC sinusoidal line voltage.  
         [0052]      FIG. 11 . Voltage waveform across C and C′ on block diagram FIGS.  7 ( a ), 7 ( b ),  8 ( a ),  8 ( b ),  9 ( a ) and  9 ( b ).  
         [0053]      FIG. 12 . Implementation 1 of power supply  200  for lamp: 
    Half-bridge secondary series resonant converter for converter  206  in  FIG. 7      1.(1) Without feedback     (a) Power source V 1  comes from AC sinusoidal power line     (b) Power source comes from DC constant voltage      
         [0058]      FIG. 13 . Implementation 1 of power supply  200  for lamp: Half-bridge secondary series resonant converter for converter  206  in  FIG. 8      1.(2) With feedback (feedback signal comes from secondary of transformer coupled with lamp)     (a) Power source V 1  comes from AC sinusoidal power line     (b) Power source VDC 1  is DC constant voltage      
         [0062]      FIG. 14 . Implementation 1 of power supply  200  for lamp: Half-bridge secondary series resonant converter for converter  206  in  FIG. 8      1.(3) With feedback (feedback signal comes from current sense resistor)     (a) Power source V 1  comes from AC sinusoidal power line     (b) Power source VDC 1  comes from DC constant voltage      
         [0066]      FIG. 15 . Implementation 1 of power supply  200  for lamp: Half-bridge secondary series resonant converter for converter  206  in  FIG. 9      1.(4) with feedback (feedback signal comes directly from lamp) 
        (a) Power source V 1  comes from AC sinusoidal power line     (b) Voltage source comes from DC constant voltage    
         
         [0070]      FIG. 16  Lamp voltage rms value vs. switching frequency calculation for power supply  200  based on half bridge secondary series resonant converter of FIGS.  12 , 13 , 14  and  15 .  
         [0071]      FIG. 17 . Normal operation output voltage waveform simulation and rms value measurement for circuit in FIGS.  12 , 13 , 14  and  15 . (implementation 1 of power supply  200 ) 
    (In one implementation, lamp resistance=7.2 ohm at normal operation; switching frequency=60 kHz, C 3 =259 nf, L 1 =27 uh,turns ratio (primary:secondary)=5:1)      
         [0073]      FIG. 18 . Minimum dimming output voltage waveform simulation and rms value measurement for circuit in  FIGS. 12,13 ,  14  and  15 . (implementation 1 of power supply  200 ) (In one implementation, lamp resistance=1.8 ohm at minimum dimming; switching frequency=90 kHz, C 3 =259 nf, L 1 =27 uh,turns ratio (primary:secondary)=5:1)  
         [0074]      FIG. 19 . Implementation 2 of power supply  200  for lamp: Half-bridge primary series resonant converter for converter  206  in  FIG. 7 . 2.(1) without feedback 
    (a) Power source comes from AC sinusoidal power line     (b) Power source comes from DC constant voltage      
         [0077]      FIG. 20 . Implementation 2 of power supply  200  for lamp: Half-bridge primary series resonant converter for converter  206  in  FIG. 8 . 2.(2) with feedback (feedback signal comes from auxiliary winding coupled with lamp voltage) 
    (a) Voltage source comes from AC sinusoidal power line;     (b) Voltage source comes from DC constant voltage      
         [0080]      FIG. 21 . Implementation 2 of power supply  200  for lamp: Half-bridge primary series resonant converter for converter  206  in  FIG. 8      2.(3) with feedback (feedback signal comes from current sense resistor)     (a) Power source VDC comes from AC sinusoidal power line     (b) Power source VDC comes from DC constant voltage      
         [0084]      FIG. 22 . Implementation 2 of power supply  200  for lamp: Half-bridge primary series resonant converter for converter  206  in  FIG. 8      2.(4) with feedback (feedback signal comes from auxiliary winding coupled with lamp voltage and current sense resistor)     (a) Voltage source comes from AC sinusoidal power line     (b) Voltage source comes from DC constant voltage      
         [0088]      FIG. 23 . Implementation 2 of power supply  200  for lamp: Half-bridge primary series resonant converter for converter  206  in  FIG. 9      2.(5) with feedback (feedback signal comes directly from lamp)     (a) Voltage source comes from AC sinusoidal power line     (b) Voltage source comes from DC constant voltage      
         [0092]      FIG. 24 . Lamp voltage rms value vs switching frequency calculation for power supply based on resonant converter of FIGS.  19 , 20 , 21 , 22  and  23 . (implementation 2 of power supply  200 )  
         [0093]      FIG. 25 . Normal operation output voltage waveform simulation and rms value measurement for circuit in FIGS.  19 , 20 , 21 , 22  and  23 . (in one implementation, lamp resistance=7.2 ohm at normal operation; switching frequency=60 kHz, C 3 =8.3 nf, L 1 =847 uh, turns ratio (primary:secondary)=5:1)  
         [0094]      FIG. 26 . Minimum dimming output voltage waveform simulation and rms value measurement for circuit in FIGS.  19 , 20 , 21 , 22  and  23 . (in one implementation, lamp resistance=1.8 ohm at minimum dimming operation; switching frequency=90 kHz, C 3 =8.3 nf, L 1 =847 uh, turns ratio (primary:secondary)=5:1) 
     
    
     DETAILED DESCRIPTION  
       [0095]      FIG. 7  is block diagrams of a power supply  200  for a connected output device. (e.g., lamp  211 ) without feedback;  FIG. 8,9  are block diagram of a power supply  200  for a connected output device with feedback.  
         [0096]     In one implementation (for example: power source is AC sinusoidal voltage from line), power supply  200  includes an RF 1   201 , an input filter  202 , a rectifier  203 , a resonant converter  206 , a controller  209 , dimmer  204 , active startup circuit  208  and Lamp  211 , feedback circuit  205 , sample circuit  207  shown in FIGS.  7 ( a ), 8 ( a ) and  9 ( a ), power source  210  or  220 .  
         [0097]     In the other implementation, (for example: power source is DC substantially constant voltage ) RF 1   201 , an input filter  202 , a rectifier  203  can be removed shown in FIGS.  7 ( b ), 8 ( b ) and  9 ( b ).  
         [0098]     The power supply can have more blocks or fewer blocks than  FIGS. 7, 8  and  9 . (For example,  206 , 208 , 209  can be one integrated block or  208  can be removed in some implementation. Main switch of converter  206  or active startup circuit  208  can be integrated in the controller  209 ). The sequence and position of some blocks can be changed. (For example, position of  202  and  203  can be exchanged). Each block can use all kinds of different circuits with function as the following.  
         [0099]     Voltage source  210  can be AC or DC. Voltage source  220  is DC. If voltage source is DC voltage, RF 1   201 , an input filter  202 , a rectifier  203  can be removed. In one implementation, voltage source  210  is 60 Hz, 120 v sinusoidal AC voltage from power line. (Or 50 Hz, 220 v sinusoidal AC voltage from power line).  
         [0100]     Input RF 1   201  provides input current protection for converter  200 . In particular, in one implementation, input fuse is designed to provide current protection for converter  206  by cutting off current flow to converter  206  in an event that current being drawn through input fuse  201  exceeds a predetermined design rating. In another implementation, RF 1   201  is a flameproof, fusible, wire wound type and functions as a fuse, inrush current limiter. In another implementation, RF 1   210  can be a NTC or PTC thermister.  
         [0101]     Input filter  202  minimizes an effect of electromagnetic interference (EMI) on power supply  200 , converter  206  and exterior power system. Input filter  202  can be LC filter π filter, common mode filter, differential mode filter or any type filter that provide a low impedance path for high-frequency noise to protect power supply  200  and exterior power system from EMI. Input filter  202  can be placed in front of rectifier  203  or behind rectifier  203 .  
         [0102]     Rectifier  203  converts the input AC source voltage from voltage source  210  (like  FIG. 10 ) into DC voltage (like  FIG. 11 ) when the blocking capacitor in converter  206  is large enough.  
         [0103]     In one implementation, rectifier  203  is a full-wave rectifier that includes four rectifiers in a bridge configuration as in  FIG. 12 . In another implementation, rectifier  203  contains 2 diodes Rectifier can be any type or bridgeless PFC.  
         [0104]     Resonant converter  206  converts the substantially DC constant voltage like  FIG. 11  received from rectifier  203  into a band envelope contain high frequency component suitable to support an output device (e.g., halogen lamp  211 ).  
         [0105]     Controller  209  is operable to regulate output voltage at predetermined value.  
         [0106]     Controller  209  can be any type and have any type of control with PFC or without PFC function. (Such as digital control, analogy control, DSP, bang-bang control, skipping switching cycles and Pulse Train control etc.)  
         [0107]     In such an implementation, controller  209  is operable to adjust the duty cycle, switching frequency or on time of main switch of converter  206  so that converter  206  outputs an AC high frequency component contained in band envelope having a predetermined rms voltage value. Controller  209  can control an output voltage level of converter  206  responsive to a predetermined value set by dimmer. In one implementation, dimmer can be a voltage divider and potentiometer. Controller  209  can have over current protection (current sense), over voltage protection, over temperature protection etc functions.  
         [0108]     Normal operating; predetermined value set to rating voltage of lamp; dimming operating, predetermined value set to lower voltage than rating voltage of lamp.  
         [0109]     Controller  209  can have feedback function or no feedback function. Feedback control voltage comes from feedback circuit  205 , as discussed in greater detail below.  
         [0110]     Sample  207  sense the signal proportional to output AC rms lamp voltage. It can come from lamp or other component in converter  206 .  
         [0111]     Dimmer  204  is operable to provide a dimming control voltage to controller  209  for dimming (or reducing) output voltage (e.g., halogen lamp  211 ). In one implementation, dimming voltage is realized by changing switching frequency (increase or decrease); In one implementation, dimming lamp is realized by changing potentiometer value and voltage divider ratio to change voltage reference for controller  209  in feedback.  
         [0112]     In one implementation (non-isolated feedback),  204  can be realized by a resistor voltage divider (or zener diode and resistor voltage divider) and voltage cross one resistor goes to feedback pin of controller  209 ;  
         [0113]     In one implementation (isolated feedback)  205  can be realized by a resistor voltage divider (or zener diode and resistor voltage divider) and voltage across one resistor or voltage across secondary winding is coupled to Feedback pin of controller  209  by auxiliary winding, opto-coupler or digital isolator etc  
         [0114]     Feedback circuit  205  can have all kinds of different feedback way.  
         [0115]     The feedback signal can come from transformer winding coupled with lamp output voltage for output voltage regulation as  FIGS. 13 and 20 , current sense resistor whose voltage is proportional to lamp rms current for output current regulation as  FIGS. 14 and 21 , or from both auxiliary winding and current sense resistor for output power feedback as  FIG. 22 . Or the feedback signal can come directly from lamp as  FIGS. 15 and 23 .  
         [0116]     In real application, block can be more or less than  FIGS. 7, 8  and  9 . Some blocks may be different from  FIGS. 7, 8  and  9 .  
         [0117]     A number of implementations are described as the following.  
         [0000]     1.Implementation 1 of Power Supply  200  for Lamp Based on Half-Bridge Secondary Series Resonant Converter  
         [0118]     In one implementation, we set fs=60 kHz during rating voltage operation (12 v) and fs=90 kHz during minimum dimming (2 v). For example, 20 W 12V Halogen Lamp, resistance=7.2 ohm at 12 volt; resistance=1.8 ohm at 2 volt. We use the area (inductance area) where switching frequency is greater than resonant frequency. We calculated and got C 3 =259 nF, L 1 =27 uH. Transformer turns ratio primary to secondary 5:1. C 3  can select nearest standard value 270 nF. Inductor can be custom made with core and winding.  
         [0119]     Of course if you select different frequency range or different operation area or even the same for normal operation or dimming, the value of C 3  and L 1  can be different.  
         [0120]     This value is applied to  FIGS. 12,13 ,  14  and  15 .  
         [0121]     Normal operation waveform simulation result is shown in  FIG. 17  at fs=60 kHz, lamp resistance=7.2 ohm; Minimum dimming waveform simulation result is shown in  FIG. 18  at fs=90 kHz, Lamp resistance=1.8 ohm. (Simulation software PSIM6.0)  
         [0000]     1. (1) Without Feedback  
         [0122]      FIG. 12  shows one implementation for the block diagram of  FIG. 7 . In real application, components can be more or less than  FIG. 12 .  
         [0123]     In one implementation V 1  is AC power line voltage, (120 v AC sinusoidal).  
         [0124]     V 1  functions as voltage source  210  in  FIG. 7 .  
         [0125]     In another implementation, V 1  is a constant DC voltage.  
         [0126]     R 3  is a fuse that functions as block  201  in block diagram  FIG. 7 .  
         [0127]     L 2 , C 4  function as filter  202  in  FIG. 7 .  
         [0128]     D 1 , D 2 , D 3  and D 4  function as rectifier  203  in  FIG. 7 .  
         [0129]     C 5  behaves as a filter similar to  202  in  FIG. 7 .  
         [0130]     Q 1 , Q 2 , C 1 , C 2 , T 1 , L 1 , R 1  and C 3  compose of a half bridge resonant converter that function as resonant converter  206  in  FIG. 7 . Q 1  and Q 2  are bipolar transistor or Mosfet. In one implementation, it is complementary turn on/off that is when Q 1  turns on, Q 2  turns off; when Q 2  turns on, Q 1  turns off; Meanwhile duty cycle is selected as close or equal to 50%. (In other implementation, duty cycle can select from 0% to 100% or transistor Q 1  and Q 2  do not complementarily turn on/off.) C 1  and C 2  are block and clamp capacitor with large value. C 1  and C 2  clamp the peak of AC voltage and block DC component. Thus the voltage across transformer primary almost equals to half of peak AC sinusoidal voltage in steady state.  
         [0131]     In secondary of transformer T 1 , inductor L 1 , lamp resistance R 1  and capacitor C 3  compose of a series resonant converter.  
         [0132]     R 2  is current sense resistor to sense over current and shutdown the converter. In other implementation, R 2  can be 0 ohm or short.  
         [0133]     Calculation of lamp voltage VP 1  is in  FIG. 16 .  
         [0134]     The lamp output voltage waveform simulation at normal operating is shown in  FIG. 17 . Lamp resistance=7.2 ohm during rating voltage (for example 12 v). We can see the output voltage is high frequency sinusoidal waveform in a band envelope.  
         [0135]     The lamp output voltage waveform at minimum dimming is shown in  FIG. 18 . It is high frequency triangular waveform in a band envelope. Both  FIG. 17  and  FIG. 18  have no low frequency component or we can see low frequency component is trivial compared to  FIG. 2 . So eyes will not adjust with low frequency flicker. It helps to prevent eyes from myopia.  
         [0136]     Dimming is realized by adjusting dimmer to change switching frequency. In one implementation, changes from 60 kHz for normal rating voltage to 90 kHz minimum dimming. Dimmer can be a potentiometer. Change potentiometer resistance value to change switching frequency of controller  209 . Then the output voltage on lamp is decreased as shown in  FIG. 16 . The lamp voltage is a band including high frequency sinusoidal or triangular waveform. During dimming, the amplitude of the band envelope becomes smaller and smaller as dimming voltage goes down. My invention doesn&#39;t turn on/off input line voltage and has no inrush current compare with  FIG. 5  and  FIG. 6 .  
         [0000]     Advantage:  
         [0000]    
       
          1. Lamp voltage in my invention doesn&#39;t include low frequency component. So eyes don&#39;t feel tiredness caused by low frequency component light flicker. Thus my invention helps to prevent people from myopia or prevent from myopia deepening.  
          2. My invention doesn&#39;t need external dimmer. My invention only needs changing frequency to realize dimming without feedback. So control is very simple and cost goes down.  
          3. My invention prolongs lamp&#39;s life for it doesn&#39;t turn on/off bus line voltage for dimming compared with traditional dimming waveform shown in  FIGS. 5 and 6 . 
 
 1. (2) With Feedback (Feedback Signal Comes from Secondary of Transformer Coupled with Lamp) 
 
       
     
         [0140]      FIG. 13  shows one implementation for the block diagram of  FIG. 8 . In real application, components can be more or less than  FIG. 13 .  
         [0141]     Other components functions are the same as  FIG. 12 . The only difference is feedback transformer T 2  and resistance R 4 . We can use opto-coupler, digital isolator to replace transformer T 2 . The lamp output voltage is coupled to secondary of T 2 . It passes voltage divider and goes to feedback pin of controller  209 .  
         [0142]     Controller  209  reads rms voltage of Feedback signal on feedback pin and compare with reference voltage set by dimmer.  
         [0143]     In one implementation, if the feedback voltage is greater than reference voltage, switching frequency will be changed to decrease output voltage until output voltage equals to setting voltage set by dimmer. If the feedback voltage is less than reference voltage, switching frequency will be changed to increase output voltage until output voltage equal to setting voltage set by dimmer. In other implementation, the duty cycle and switching frequency can both be adjusted until output voltage equals to setting voltage  
         [0144]     Advantage: Accurate voltage feedback and dimming  
         [0000]     Disadvantage: One extra transformer T 2  increases the cost  
         [0000]     1. (3) Current Sense Feedback (Feedback Signal comes from Current Sense)  
         [0145]     In  FIG. 14 , other components function the same as  FIG. 12 . Feedback can be realized by signal from current sense resistor R 2 . Reading rms voltage on R 2  that is proportional to output current rms voltage and compare with reference voltage set by dimmer to set output current at predetermined level.  
         [0146]     Advantage: Feedback with low cost and remove extra transformer T 2 .  
         [0147]     Disadvantage: Need complex DSP algorithm or analog circuit to read rms voltage of R 2  and accuracy is not as good as lamp voltage feedback.  
         [0000]     1.(4) Feedback comes Directly from Lamp  
         [0148]      FIG. 15  is similar to 1(2), the only difference is no coupled transformer. Lamp voltage is sent to feed back pin through voltage divider or rectifier. Controller reads the rms voltage or current to compare with reference set by dimmer. And voltage is regulated to predetermined rms voltage set by dimmer.  
         [0149]     Advantage: Cost is minimum. Disadvantage: Primary and secondary has no isolation or limited isolation.  
         [0150]     Feedback can also be realized by other methods.  
         [0151]     As above, implementation 1(1), 1(2), 1(3), 1(4); all use secondary series resonant converter. The output voltage waveform at normal operation is shown in  FIG. 17 ; the output voltage waveform at minimum dimming is shown in  FIG. 18 . In one implementation, C 3 =259 nF, L 1 =27 uH, Transformer turns ratio primary to secondary=5:1. The calculation of rms voltage vs. fs is shown in  FIG. 16 . When select different frequency range or different operation area (inductance area fs&gt;f 0  or capacitance area fs&lt;f 0 ) or even same frequency range and area for normal and dimming operation, C 3  and L 1  value and transformer turns ratio can be different from above value.  
         [0000]     2.Implementation 2 of Power Supply  200  for Lamp Based on Primary Half Bridge Series-Resonant Isolated Converter  
         [0152]     We set fs=60 kHz during rating voltage operation (12 v) and fs=90 kHz during minimum dimming (2 v). For example, 20 W 12V Halogen Lamp, resistance=7.2 ohm at 12 volt; resistance=1.8 ohm at 2 volt. We use the area (inductance area) where switching frequency is greater than resonant frequency. We calculated and got C 3 =8.3 nF, L 1 =847 uH, Transformer turns ratio primary to secondary 5:1. These values are applied to FIGS.  19 , 20 , 21 , 22  and  23 . C 3  can select nearest value; L 1  can be custom made inductor with core and winding. When select different frequency range, C 3  and L 1  value and transformer ratio can be different from above value.  
         [0153]     The calculation is shown in  FIG. 24 . Of course if you select different frequency range or different operation area or even the same for normal operation or dimming, the value of C 3  and L 1  can be different.  
         [0154]     Normal operation waveform simulation result is shown in  FIG. 25  at fs=60 kHz, lamp resistance=7.2 ohm; Minimum dimming waveform simulation result is shown in  FIG. 26  at fs=90 kHz, Lamp resistance=1.8 ohm. (Simulation software PSIM6.0)  
         [0000]     2. (1) Without Feedback  
         [0155]      FIG. 19  shows one implementation for the block diagram of  FIG. 7 . In real application, components can be more or less than  FIG. 19 .  
         [0156]     Other components functions are the same as  FIG. 12 . The only difference is C 3 , L 1  are in primary with different values and lamp resistance is in secondary.  
         [0157]     The output voltage waveform at normal operation is shown in  FIG. 25 ; the deep dimming output voltage waveform at minimum dimming is shown in  FIG. 26 .  
         [0000]     2. (2) With Voltage Feedback  
         [0158]     As shown in  FIG. 20 , other components are the same as  FIG. 19 , Lamp voltage coupled on auxiliary winding and sensed by feedback pin of controller. Controller reads signal rms voltage that is proportional to lamp voltage and compares with reference voltage set by dimmer. If signal is greater than reference, that means output voltage is higher than predetermined value then switching frequency is changed to decrease output voltage until equal to predetermined value; If signal is less than reference, that means output voltage is lower than predetermined value then switching frequency is changed to increase output voltage until equal to predetermined value;  
         [0159]     Advantage: Accurate feedback  
         [0160]     Disadvantage: auxiliary winding add cost.  
         [0161]     The output voltage waveform at normal operation is shown in  FIG. 25 ; the deep dimming output voltage waveform at minimum dimming is shown in  FIG. 26 .  
         [0000]     2. (3) Current Sense Feedback  
         [0162]     As shown in  FIG. 21 , other components are the same as  FIG. 20 . Controller  209  reads current sense resistor signal rms voltage that is proportional to lamp voltage and compares with reference set by dimmer. If signal is greater than reference, that means output voltage is higher than predetermined value then switching frequency is changed to decrease output voltage until equals to predetermined value; If signal is less than reference, that means output voltage is lower than predetermined value then switching frequency is changed to increase output voltage until equal to predetermined value;  
         [0163]     Advantage: Accurate feedback  
         [0164]     Disadvantage: complex control algorithm, DSP or analog circuit to read rms.  
         [0165]     The output voltage waveform at normal operation is shown in  FIG. 25 ; the deep dimming output voltage waveform at minimum dimming is shown in  FIG. 26 .  
         [0000]     2. (4) With Power Feedback  
         [0166]     As shown in  FIG. 22 , other components are the same as in  FIG. 19 , Controller reads current sense resistor signal rms voltage that is proportional to lamp current and auxiliary winding coupled voltage that is proportional to output lamp voltage. The feedback voltage multiplies feedback current is feedback power. Then compares with reference set by dimmer. If signal is greater than reference, that means output power is higher than predetermined value then switching frequency is changed to decrease output power until equal to predetermined value; If signal is less than reference, that means output power is lower than predetermined value then switching frequency is changed to increase output power until equal to predetermined value;  
         [0167]     Advantage: Accurate feedback  
         [0168]     Disadvantage: complex control algorithm.  
         [0000]     2. (5) With Feedback Directly from Lamp  
         [0169]     As shown in  FIG. 23 , other components are the same as in  FIG. 19 . The only difference is no coupled transformer. Lamp voltage is sent to feed back pin through voltage divider or rectifier. Controller reads the rms voltage or current to compare with reference set by dimmer. If signal is greater than reference, that means output voltage is higher than predetermined value then switching frequency is changed to decrease output voltage until equal to predetermined value; If signal is less than reference, that means output voltage is lower than predetermined value then switching frequency is changed to increase output voltage until equal to predetermined value; And voltage is regulated to predetermined rms voltage set by dimmer.  
         [0170]     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. In real application, blocks can be more or less than  FIG. 7, 8  or  9 . In real application, components can be more or less than  FIG. 12 , 13 , 14 , 15 , 19 , 20 , 21 , 22  or  23 . Moreover, the converter topologies discussed above can be used within power supplies to supply power to devices other than lamps.