Electronic ballasts

Abstract

Methods and apparatus are described that can provide improved power factor correction and total harmonic distortion, efficiency and/or direct feedback of load current variations to a power source inverter. In one example, a power supply, for example, a ballast, can have an input circuit, an output circuit and an inverter circuit coupled between the input circuit and the output circuit. A current feedback circuit is coupled between the output circuit and the inverter circuit and configured to feed current back to the inverter circuit through a transformer stage separate from the inverter as a function of a current level in the output circuit.

What is claimed is: 
     
         1 . A ballast circuit comprising:
 an input circuit characterized by having a power factor;   an output circuit having circuit portions for delivering current to a load;   a parallel resonant inverter circuit coupled between the input circuit and the output circuit;   a power feedback circuit coupled between the input circuit and the inverter circuit and configured to be able to adjust the power factor of the ballast circuit; and   a high-frequency-current blocking component in the power feedback circuit.   
     
     
         2 . The ballast circuit of  claim 1  wherein the control circuit includes a diode bridge. 
     
     
         3 . The ballast circuit of  claim 2  wherein the diode bridge is configured to form a high frequency rectifying bridge. 
     
     
         4 . The ballast circuit of  claim 1  wherein the high-frequency-current blocking component includes a transformer stage. 
     
     
         5 . The ballast circuit of  claim 4  wherein the transformer stage includes an inductor and a capacitor. 
     
     
         6 . The ballast circuit of  claim 4  wherein the transformer stage includes a current transformer. 
     
     
         7 . The ballast circuit of  claim 4  wherein the control circuit includes a high frequency bridge and a capacitor across the power feedback circuit, wherein the capacitor is sized such that at line voltage zero crossing, a current approximately equal to the entire lamp current is bypassed through the capacitor. 
     
     
         8 . The ballast circuit of  claim 1  further including an output transformer in the output circuit and an inductor in series with a secondary of the output transformer. 
     
     
         9 . The ballast circuit of  claim 8  wherein the inductor, the secondary of the output transformer and a lamp are in series. 
     
     
         10 . The ballast circuit of  claim 1  wherein the control circuit operates at a substantially constant current. 
     
     
         11 . A ballast circuit comprising:
 an input circuit;   an output circuit;   an inverter circuit coupled between the input circuit and the output circuit;   a control circuit coupled between the input circuit and inverter circuit comprising:   a current level feedback loop feeding back the substantially constant lamp current from the output circuit to the input circuit, and wherein the current level delivered to the input circuit is adjusted with a transformer different from that used in the output circuit.   
     
     
         12 . The ballast circuit of  claim 11  wherein the transformer is a resonant transformer. 
     
     
         13 . The ballast circuit of  claim 12  wherein the resonant inductor circuit includes a capacitor in parallel with the inductor. 
     
     
         14 . The ballast circuit of  claim 11  wherein the transformer is a current transformer. 
     
     
         15 . The ballast circuit of  claim 14  wherein the control circuit contains a high frequency rectifying bridge. 
     
     
         16 . A ballast circuit comprising:
 an input circuit;   an output circuit;   an parallel resonant inverter circuit coupled between the input circuit and the output circuit; and   a current feedback circuit coupled between the output circuit and the input circuit and configured to feed current back to the input circuit through a transformer stage separate from the inverter as a function of a current level in the output circuit and wherein the current feedback circuit includes a capacitor across the feedback circuit.   
     
     
         17 . The ballast circuit of  claim 16  wherein the current feedback circuit is coupled in series with a secondary of a transformer in the output circuit. 
     
     
         18 . The ballast circuit of  claim 16  wherein the transformer stage includes a resonant transformer circuit. 
     
     
         19 . The ballast circuit of  claim 16  wherein the transformer stage includes a current transformer. 
     
     
         20 . The ballast circuit of  claim 16  wherein the current feedback circuit includes a high frequency rectifying circuit. 
     
     
         21 . A power driving circuit comprising:
 an input circuit;   an output circuit for being coupled to a load so that the power driving circuit can drive the load;   an inverter circuit coupled between the input circuit and the output circuit; and   a transformer element coupled to the output circuit and also coupled to the inverter circuit, wherein the transformer element is configured to apply to the inverter circuit a signal proportional to a current in the output circuit.   
     
     
         22 . The circuit of  claim 21  wherein the inverter circuit includes a high frequency bridge. 
     
     
         23 . The circuit of  claim 21  wherein the output circuit includes a secondary of a transformer and wherein the transformer element is coupled in series with the secondary of the transformer. 
     
     
         24 . The circuit of  claim 21  wherein the transformer element includes a resonant inductor. 
     
     
         25 . The circuit of  claim 24  further including a capacitor coupled in parallel with the transformer element. 
     
     
         26 . The circuit of  claim 21  wherein the transformer element includes a current transformer. 
     
     
         27 . The circuit of  claim 26  further including a capacitor in parallel with either winding of the current transformer. 
     
     
         28 . The circuit of  claim 26  wherein the current transformer is configured to have a number of windings in a primary circuit wherein the number of windings in the primary circuit is proportional to a desired input power. 
     
     
         29 . The circuit of  claim 28  wherein the windings in the primary circuit are N1 and the windings in the secondary circuit are N2 and the ratio of N1 over N2 is within 20% of the ratio N 1 /N 2 =P/(V in *I l ). 
     
     
         30 . The circuit of  claim 26  wherein the current transformer is configured to have a number of windings in a primary circuit wherein the number of windings in the primary circuit is proportional to the inverse of the current in the primary circuit. 
     
     
         31 . The circuit of  claim 30  wherein the number of windings in the primary circuit is N1 and wherein N1 is within 20% of the ratio N 1 =N2*P/(V in *I l ). 
     
     
         32 . The circuit of  claim 26  wherein the current transformer is configured to have a number of windings in a primary circuit wherein the number of windings in the primary circuit is proportional to the inverse of a peak voltage at the input circuit. 
     
     
         33 . The circuit of  claim 32  wherein the number of windings in the primary circuit is N1 and wherein N1 is within 20% of the ratio N 1 =N2*P/(V in *I l ). 
     
     
         34 . The circuit of  claim 26  wherein the current transformer is configured to have a number of windings in a primary circuit wherein the number of windings in the primary circuit is proportional to a desired input power and inversely proportional to a current in the primary circuit and a peak voltage at the input circuit. 
     
     
         35 . The circuit of  claim 34  wherein the number of windings in the primary circuit is N1 and wherein N1 is within 20% of the ratio N1=N2*P/(V in *I l ). 
     
     
         36 . The circuit of  claim 34  further including a capacitor coupled in parallel with the primary circuit of the current transformer 
     
     
         37 . A driver circuit for driving a load, the driver circuit comprising:
 an input circuit from a line input;   an output circuit for being coupled to a load, the output circuit including a transformer for inducing a load current through the load;   a parallel resonant inverter circuit between the input circuit and the output circuit; and   a feedback inductance separate from the transformer coupled to the output circuit so that load current passes through the inductance, the feedback inductance also being coupled to the parallel resonant inverter circuit.   
     
     
         38 . The driver circuit of  claim 37  wherein a parallel resonant inverter circuit includes a high frequency rectifier. 
     
     
         39 . The driver circuit of  claim 38  wherein the high frequency rectifier is a high frequency rectifier bridge having an input and wherein the feedback inductance is coupled in series with the input to the high frequency rectifier bridge. 
     
     
         40 . The driver circuit of  claim 39  further including a capacitor coupled to an output of the high frequency rectifier bridge. 
     
     
         41 . The driver circuit of  claim 37  further including a capacitor coupled in parallel across the feedback inductance. 
     
     
         42 . The driver circuit of  claim 37  wherein the feedback inductance includes a resonant inductance. 
     
     
         43 . The driver circuit of  claim 37  wherein the feedback inductance includes a current transformer. 
     
     
         44 . The driver circuit of  claim 37  wherein the feedback inductance includes a transformer having a turns ratio proportional to a selected input power. 
     
     
         45 . The circuit of  claim 44  wherein the transformer has input windings N1 and output windings N2 and wherein N1 is within 20% of the ratio N 1 =N2*P/(V in *I l ). 
     
     
         46 . A method of adjusting current in a load circuit, the method comprising:
 producing in a driving circuit a high frequency alternating current;   driving the load with an output current proportional to the high frequency alternating current;   transforming part of the output current and applying the transformed output current to the driving circuit.   
     
     
         47 . The method of  claim 46  wherein transforming part of the output current includes passing the output current through a parallel circuit of an inductor and a capacitor. 
     
     
         48 . The method of  claim 46  wherein transforming part of the output current includes passing the output current through a resonant inductor. 
     
     
         49 . The method of  claim 46  wherein transforming part of the output current includes passing the output current through primary windings of a transformer. 
     
     
         50 . The method of  claim 46  wherein applying the transformed output current to the driving circuit includes applying the transformed output current to a rectifier circuit. 
     
     
         51 . The method of  claim 46  wherein the transformed output current applied to the driving circuit increases and decreases with increases and decreases in the output current. 
     
     
         52 . The method of  claim 46  wherein transforming part of the output current and applying the transformed output current to the driving circuit includes applying the output current to the driving circuit as a function of only the output current. 
     
     
         53 . A method of driving a load with a load current, the method comprising:
 receiving an input from a line circuit;   converting the input to a high frequency alternating current;   applying the high frequency alternating current to an output for producing load current in a load circuit;   producing through a transformer in the output a feedback current different in magnitude than the load current; and   applying the feedback current to an inverter.   
     
     
         54 . The method of  claim 53  further including producing from the output a feedback current that increases or decreases with increases or decreases in the load current. 
     
     
         55 . The method of  claim 53  further including converting the input to a high frequency alternating current through a parallel resonant inverter. 
     
     
         56 . A method of producing a driver circuit for driving a load, the method comprising:
 identifying a desired input power as a function of an anticipated load;   identifying a load current to be applied to the anticipated load;   configuring a parallel resonant inverter circuit with an output for producing the load current to be applied to the anticipated load;   configuring a current feedback circuit in series with the anticipated load wherein the current feedback circuit includes a transformer element.   
     
     
         57 . The method of  claim 56  wherein configuring the current feedback circuit includes configuring the current feedback circuit to include a current transformer. 
     
     
         58 . The method of  claim 56  wherein configuring the current feedback circuit includes configuring the current feedback circuit to include a resonant transformer. 
     
     
         59 . The method of  claim 57  further including selecting the transformer to have a plurality of turns. 
     
     
         60 . The method of  claim 57  further including selecting the transformer to have a primary and a secondary having respective turns defining a turns ratio, and wherein the turns ratio is proportional to the input power. 
     
     
         61 . The method of  claim 60  wherein selecting the current transformer includes selecting the current transformer to have a primary and a secondary having respective turns N1 and N2 defining a turns ratio, and wherein the turns ratio is within 20% of N 1 /N 2 =P/(V in *I l ). 
     
     
         62 . The method of  claim 57  further including selecting the transformer to have a primary and a secondary having respective turns defining a turns ratio, and wherein the turns ratio is proportional to the inverse of the load current. 
     
     
         63 . The method of  claim 62  wherein selecting the current transformer includes selecting the current transformer to have a primary and a secondary having respective turns N1 and N2 defining a turns ratio, and wherein the turns ratio is within 20% of N 1 /N 2 =P/(V in *I l ). 
     
     
         64 . The method of  claim 57  further including selecting the transformer to have a primary and a secondary having respective turns defining a turns ratio, and wherein the turns ratio is proportional to the inverse of a peak voltage in the input circuit. 
     
     
         65 . The method of  claim 64  wherein selecting the current transformer includes selecting the current transformer to have a primary and a secondary having respective turns N1 and N2 defining a turns ratio, and wherein the turns ratio is within 20% of N 1 /N 2 =P/(V in *I l ). 
     
     
         66 . The method of  claim 57  further including placing a capacitance across the transformer. 
     
     
         67 . The method of  claim 66  further including placing the capacitance across a secondary winding of the transformer. 
     
     
         68 . A method of driving a load with a load current, the method comprising:
 receiving an input from a line circuit;   converting the input to a high frequency alternating current;   applying the high frequency alternating current to an output for producing load current in a load circuit;   producing through an inductance connected to the output a feedback current different in magnitude than the load current; and   applying the feedback current to an inverter.   
     
     
         69 . The method of  claim 68  further including producing from the output a feedback current that increases with increases in the load current. 
     
     
         70 . The method of  claim 68  further including converting the input to a high frequency alternating current through a parallel resonant inverter. 
     
     
         71 . A method of driving a load with a load current, the method comprising:
 receiving an input from a line circuit;   converting the input to a high frequency alternating current in an inverter;   applying the high frequency alternating current to an output for producing load current in a load circuit;   applying a positive current feedback from the load to the inverter.   
     
     
         72 . The method of  claim 71  further including changing the feedback. 
     
     
         73 . The method of  claim 71  further including changing the feedback with a bypass element. 
     
     
         74 . A power driving circuit comprising:
 an input circuit;   an output circuit for being coupled to a load so that the power driving circuit can drive the load;   an inverter circuit coupled between the input circuit and the output circuit;   a transformer element coupled to the output circuit and also coupled to the inverter circuit, wherein the transformer element is configured to apply to the inverter circuit a signal proportional to a current in the output circuit; and   a feedback changing circuit.   
     
     
         75 . The circuit of  claim 74  wherein the transformer element includes a resonant transformer element. 
     
     
         76 . The circuit of  claim 74  wherein a transformer element includes a current transformer. 
     
     
         77 . The circuit of  claim 74  wherein the feedback changing circuit is sensitive to current in the feedback circuit. 
     
     
         78 . The circuit of  claim 74  wherein the feedback changing circuit is sensitive to voltage in the feedback circuit. 
     
     
         79 . The circuit of  claim 74  wherein the feedback changing circuit includes a circuit for shunting part of the current in the feedback circuit. 
     
     
         80 . The circuit of  claim 79  wherein the circuit for shunting includes a gate having a threshold. 
     
     
         81 . The circuit of  claim 79  wherein the circuit for shunting includes a bypass device. 
     
     
         82 . The circuit of  claim 81  wherein the bypass device includes a SIDAC.