Patent Publication Number: US-9426869-B2

Title: Multi-output electronic ballast

Description:
FIELD OF THE INVENTION 
     The invention is related to an electronic ballast, and more particularly to a multi-output electronic ballast which can selectively stop outputting the output voltage. 
     BACKGROUND OF THE INVENTION 
     Illumination is the basic need for the human kind. In recent years, with the surge of the global economy and the commercial activity, the electricity utility for illumination has been boosted. Therefore, the overall demands of illumination are considerable. The low-pressure gas discharge lamp is by far the most widely used lamp. The gas discharge lamp is also known as a fluorescent lamp or a daylight lamp. Therefore, if the energy consumption of the low-pressure gas discharge lamp can be reduced efficiently, a considerable amount of electricity can be saved. With the evolvement of time and the promotion of living quality, the conventional drivers for driving illumination device have been outdated. Therefore, the electronic ballast which is featured by low electromagnetic interference, high efficiency, high power density, zero flickering, light weight, high-quality illumination, and high energy-saving performance, have become the mainstream of illumination device. 
     The electronic ballast used for illuminant purpose has a complex circuit structure. The conventional single-output electronic ballast includes an AC/DC converter and an inverter. In operation, the AC/DC converter converts an AC input voltage into a high DC voltage, which in turn is converted by the inverter into a high-frequency AC output voltage for driving the gas discharge lamp. The AC/DC converter may possess a power factor correction function for boosting the power factor of the electronic ballast. The inverter is able to provide illumination with high efficiency, zero flickering, and high quality through the regulation of operating frequency. 
     Nowadays, a vast amount of fluorescent lamps are widely used for indoor illumination in a spacious place such as a warehouse. When fluorescent lamps are used in daylight situations, outdoor situations with sufficient lighting, or indoor situations without operators, part of the fluorescent lamps may be turned off to avoid the waste of energy and save energy consumption. 
     To meet the goal of selectively turning off part of the fluorescent lamps, a multi-output electronic ballast has been proposed for driving two lamp assemblies. The conventional multi-output electronic ballast includes a first AC/DC converter, a second AC/DC converter, a first inverter, and a second inverter. The first AC/DC converter has a first input terminal and a first output terminal. The first output terminal of the first AC/DC converter is connected to the first inverter, and the power circuit consisted of the first AC/DC converter and the first inverter is used to drive the first lamp assembly. Likewise, the second AC/DC converter has a second input terminal and a second output terminal. The second output terminal of the second AC/DC converter is connected to the second inverter, and the power circuit consisted of the second AC/DC converter and the second inverter is used to drive the second lamp assembly. 
     In order to allow the user to control whether the second lamp assembly is illuminating or not, a first external switch is connected in series with the first input terminal of the first AC/DC converter and a second external switch is connected in series with the second input terminal of the second AC/DC converter. In this manner, the input voltage can be manipulated to be selectively applied to the first AC/DC converter and the second AC/DC converter by the switching operation of the first external switch and the switching operation of the second external switch. As a result, the external switches can be used to selectively turn off the fluorescent lamps. 
     As each power circuit for driving the lamp assembly is independent from each other, the multi-output electronic ballast must possess a plurality of AC/DC converters. Furthermore, the AC/DC converter includes a plurality of expensive electronic components. Hence, the conventional multi-output electronic ballast is bulky and expensive. 
     It is therefore needed to develop a multi-output electronic ballast with small size and low cost. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a multi-output electronic ballast with a low manufacturing cost and small size for allowing the user to selectively turn off a plurality of lamp assemblies. 
     To this end, a broad aspect of the invention is achieved by providing a multi-output electronic ballast for driving a plurality of lamp assemblies. The inventive multi-output electronic ballast includes an AC/DC converter connected to a second external switch and a DC bus for converting an AC input voltage into a high DC voltage through the second external switch; a first inverter connected to the DC bus for selectively converting the high DC voltage into a first AC voltage and outputting the first AC voltage to a first lamp assembly; a second inverter connected to the DC bus for selectively converting the high DC voltage into a second AC voltage and outputting the second AC voltage to a second lamp assembly; an auxiliary voltage generator for generating an auxiliary voltage; and a control circuit connected to a first external switch, the auxiliary voltage generator, and a first inverter controller of the first inverter for selectively receiving the auxiliary voltage according to the switching operation of the first external switch and outputting a control signal to the first inverter controller accordingly; wherein when the control signal is transmitted to the first inverter controller, the first inverter controller is activated to drive the first inverter to convert the high DC voltage into the first AC voltage and outputting the first AC voltage to the first lamp assembly. 
     Now the foregoing and other features and advantages of the present invention will be best understood through the following descriptions with reference to the accompanying drawings, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit block diagram showing the circuit structure of the multi-output electronic ballast according to an exemplary embodiment of the invention; 
         FIG. 2  is a detailed circuit diagram showing the detailed circuitry of the control circuit of the multi-output electronic ballast according to an exemplary embodiment of the invention; and 
         FIG. 3  is a detailed circuit diagram showing the detailed circuitry of the multi-output electronic ballast according to an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment embodying the features and advantages of the present invention will be expounded in following paragraphs of descriptions. It is to be realized that the present invention is allowed to have various modification in different respects, all of which are without departing from the scope of the present invention, and the description herein and the drawings are intended to be taken as illustrative in nature, and are not intended to be taken as a confinement to limit the invention. 
       FIG. 1  is a circuit block diagram showing a multi-output electronic ballast according to an exemplary embodiment of the invention. In  FIG. 1 , the multi-output electronics ballast  2  and a plurality of lamps  3  are mounted in the lamp fixture  1 . The multi-output electronics ballast  2  is used to output a plurality of output voltages for driving the lamps  3  respectively. In this embodiment, the multi-output electronic ballast  2  is used to convert the AC input voltage Vin provided by the power supply  4  into a high-frequency first AC output voltage Vo  1  and a second AC output voltage Vo 2 . Each lamp assembly  31  or  32  includes at least one lamp. The multi-output electronics ballast  2  includes an AC/DC converter  21 , a first inverter  22 , a second inverter  23 , an auxiliary voltage generator  24 , and a control circuit  25 . The input end of the AC/DC converter  21  is connected to the power supply  4 , and the output end of the AC/DC converter  21  is connected to a DC bus  20 . The AC/DC converter  21  is used to convert the AC input voltage Vin into a DC voltage Vdc with a voltage level of 450V, for example. 
     The input side of the first inverter  22  is connected to the DC bus  20  and the output side of the first inverter  22  is connected to the first lamp assembly  31 . The first inverter  22  is used to selectively convert the DC voltage Vdc into a high-frequency first AC voltage Vol. The input side of the second inverter  23  is connected to the DC bus  20  and the output side of the second inverter  23  is connected to a second amp assembly  32 . The second inverter  23  is used to convert the DC voltage Vdc into a high-frequency second AC voltage Vo 2 . The auxiliary voltage generator  24  is used to generate an auxiliary voltage Vcc with a voltage level of 15V, for example. The control circuit  25  is connected to the DC bus  20 , the auxiliary voltage generator  24 , and a first inverter controller  221  of the first inverter  22 , and is connected to the power supply  4  through a first switch S 1  which is located outside the ballast  2 . The control circuit  25  is used to apply the auxiliary voltage Vcc and the DC voltage Vdc to the first inverter controller  221  to control whether the first inverter  22  is operating or not. Therefore, the first lamp assembly  31  may be selectively turned off. In this embodiment, the ballast  2  may further include a bus capacitor Cb which is connected to the DC bus  20  for filtering the DC voltage Vdc. 
     Referring to  FIG. 1 , in order to allow the user to control whether the lamp assemblies  31  and  32  are illuminating or not, the detecting terminal  25 a of the control circuit  25  is connected in series with the first switch S 1 . Also,the input side of the AC/DC converter  21  is connected in series with a second switch S 2 . The ON/OFF state of the second switch S 2  is used to determine whether the first inverter  22  and the second inverter  23  is operating. When the second switch S 2  is turning on, the AC input voltage Vin is applied to the input side of the AC/DC converter  21  through the second switch S 2 . The AC/DC converter  21  converts the AC input voltage Vin into a DC voltage Vdc. The second inverter  23  converts the DC voltage Vdc into a second AC voltage Vo 2  and drives the second lamp assembly  32  to illuminate accordingly. 
     One end of the first switch S 1  is either connected to a first terminal  4   a  of the power supply  4  (the live wire) or connected to a second terminal  4   b  of the power supply  4  (the earth wire). The other end of the first switch S 1  is connected to the detecting terminal  25   a  of the control circuit  25 . In this embodiment, the first-switch S 1  is connected to the second terminal  4   b  of the power supply  4 . When the first switch S 1  is turned on, the energy of the AC input voltage Vin is transmitted to the detecting terminal  25   a  of the control circuit  25 , thereby allowing the control circuit  25  to output a control signal Vc to the first inverter controller  221  in response to the ON state of the first switch S 1 . The energy required by the control signal Vc is either provided by the auxiliary voltage Vcc and provided by the DC voltage Vdc. Under this condition, the first inverter controller  221  of the first inverter  22  drives the first inverter  22  to operate in response to the control signal Vc, thereby converting the DC voltage Vdc into the first AC voltage Vol and driving the first lamp assembly  31  to illuminate accordingly. Moreover, when lamp assemblies are employs in outdoor situations, indoor situations with sufficient lighting, or indoor situations without operators, the user may turn off the first switch Si to prevent the energy of the AC input voltage Vin from being transmitted to the detecting terminal  25   a  of the control circuit  25  through the first switch S 1 . The control circuit  25  will stop outputting the control signal Vc to the first inverter controller  221  in response to the OFF state of the first switch Sl, thereby ceasing the operation of the first inverter  22 . 
     Referring to  FIG. 2  and  FIG. 1 , in which  FIG. 2  is a detailed circuit diagram showing the detailed circuitry of the control circuit of the multi-output electronic ballast according to an exemplary embodiment of the invention. As shown in  FIG. 2 , the control circuit  25  includes a detector  251 , a first switch element Q 1 , and a first resistor R 1 . The detector  251  is connected to the control terminal Q 1   a  of the first switch element Q 1  and the first switch S 1  for driving the first switch element Q 1  to turn on or off according to the ON/OFF state of the first switch S 1 . The first switch element Q 1  is connected to the auxiliary voltage generator  24  and connected to the first inverter controller  221  through the first resistor R 1 . In this embodiment, the detector  251  includes a voltage dividing and rectifying circuit  2511 , a first capacitor C 1 , a first zener diode ZD 1 , a first voltage divider  2512 , a second switch element Q 2 , and a second resistor R 2 . The voltage dividing and rectifying circuit  2511  is connected to the first switch S 1 . The cathode of the first zener diode ZD 1  is connected to the voltage dividing and rectifying circuit  2511  and one end of the first capacitor Cl. The anode of the first zener diode ZD 1  is connected to the first voltage divider  2512 . The first voltage divider  2512  is connected between the first zener diode ZD 1  and the control terminal Q 2   a  of the second switch element Q 2 . The current input terminal Q 2   b  of the second switch element Q 2  is connected to the control terminal Q 1   a  of the first switch element Q 1  through the second resistor R 2 . 
     In this embodiment, the voltage dividing and rectifying circuit  2511  includes a third resistor R 3 , a fourth resistor R 4 , and a first diode Dl. The third resistor R 3 , the first switch S 1 , and the first diode D 1  are connected in series with each other for dividing and rectifying the AC input voltage Vin which is transmitted through the first switch S 1 . Therefore, a first DC voltage Vdc 1  is generated on the first capacitor C 1 . The zener diode ZD 1  is used to determine if the level of the first DC voltage Vdcl is larger than a threshold level of  10 V to turn on the zener diode ZD 1 . The zener diode D 1  does not turn on until the first capacitor C 1  is charged to promote the first DC voltage Vdc 1  to be larger than the threshold level. 
     The first voltage divider  2512  includes a fifth resistor R 5  and a sixth resistor R 6 . The fifth resistor R 5  is connected between the first zener diode ZD 1  and the control terminal Q 2   a  of the second switch element Q 2 . The sixth resistor R 6  is connected to the fifth resistor R 5  and the control terminal Q 2   a  of the second switch element Q 2 . When the first zener diode ZD 1  is turned on, the first voltage divider  2512  divides the first DC voltage Vdcl through the fifth resistor R 5  and the sixth resistor R 6  to generate a second DC voltage Vdc 2 . The second DC voltage Vdc 2  drives the second switch element Q 2  to turn on to allow the detector  251  to output a switching signal Vs 1  with a low level. In this embodiment, the switching signal Vs 1  is relatively lower than the DC voltage Vdc and the auxiliary voltage Vcc, and thus the first switch element Q 1  is turned on. In this embodiment, the control circuit  25  further includes a current-limiting seventh resistor R 7  which is connected to the current-inputting terminal Q 1   b  of the first switch element Q 1  and the DC bus  20 . When the first switch element Q 1  is turned on, the DC voltage Vdc and the auxiliary voltage Vcc are transmitted to the first inverter controller  221  through the first switch element Q 1 , thereby generating a control signal Vc and outputting the control signal Vc to the first inverter controller  221  to allow the first lamp assembly  31  to illuminate. 
     When the first switch S 1  is turned on to drive the first switch element Q 1  to turn on, the energy of the control signal Vc may be supplied by the auxiliary voltage Vcc. In this manner, the first inverter  22  may output the first AC voltage Vo 1 . The auxiliary voltage generator  24  may generate the auxiliary voltage Vcc by using the energy of the second AC voltage Vo 2  or the DC voltage Vdc. When the circuit start operating and the level of the auxiliary voltage Vcc is insufficient, the first inverter controller  221  may not be provided with enough energy to operate. In alternative embodiments, when the first inverter  22  is stabilized, the energy of the control signal Vc may be supplied by the DC voltage Vdc and the auxiliary voltage Vcc. In other words, when the level of the auxiliary voltage Vcc is insufficient, the energy of the DC voltage Vdc is transmitted to the first inverter controller  221  through the first switch element Q 1 . This is, the energy of the control signal Vc is supplied by the DC voltage Vdc. Next, after the level of the auxiliary voltage Vcc is promoted to a sufficient value, the energy of the auxiliary voltage Vcc is transmitted to the first inverter controller  221  through the first switch element Q 1 . That is, the energy of the control signal Vc is supplied by the auxiliary voltage Vcc. In this embodiment, the control circuit  25  further includes a second zener diode ZD 2  and a second capacitor C 2 , in which the second zener diode ZD 2  is connected to the current input terminal Q 1   b  of the first switch element Q 1  for preventing the level of the control signal Vc from being excessive. The second capacitor C 2  is connected to the current input terminal Ql b  of the first switch element Q 1  for filtering and retaining the energy required by the control signal Vc. When the first switch S 1  is turned on to start the operation of the circuit and the level of the auxiliary voltage Vcc is insufficient, the energy of the control signal Vc may be supplied by the DC voltage Vdc and the second capacitor C 2 . In this manner, the declining rate of the level of the control signal Vc can be reduced. Next, when the level of the auxiliary voltage Vcc is sufficient, the energy of the control signal Vc is supplied by the auxiliary voltage Vcc. In this embodiment, the control circuit  25  further includes an eighth resistor R 8  which is connected between the control terminal Ql a  and the current input terminal Q 1   b  of the first switch element Q 1  for preventing the faulty operation of the first switch element Q 1  as a result of noises and interferences. 
     Referring to  FIG. 3  and  FIG. 1 , in which  FIG. 3  is a detailed circuit diagram showing the detailed circuitry of the multi-output electronic ballast according to an exemplary embodiment of the invention. As shown in  FIG. 3 , the AC/DC converter  21  includes an electromagnetic interference filter  211 , a rectifier  212 , and a power factor correction circuit  213 . The electromagnetic interference filter  211  is connected to the second switch S 2  and the AC side of the rectifier  212 . The DC side of the rectifier  212  is connected to the input side of the power factor correction circuit  213 . The output side of the power factor correction circuit  213  is connected to the DC bus  20 . 
     In this embodiment, the power factor correction circuit  213  includes a power factor correction controller  2131 , a first inductor L 1 , a second diode D 2 , a ninth resistor R 9 , and a third switch element Q 3 . One end of the first inductor L 1  is connected to the DC side of the rectifier  212  and the other end of the first inductor L 1  is connected to the anode of the second diode D 2 . The cathode of the second diode D 2  is connected to the DC bus  20 . The third switch element Q 3  is connected to the ninth resistor R 9 , the first inductor L 1 , and the second diode D 2 . The power factor correction controller  2131  is connected to the control terminal Q 3   a  of the third switch element Q 3 , and is configured to control the switching operation of the third switch element Q 3  in order to allow the current waveform of the AC input current Iin to be analogous to the sinusoidal waveform of the AC input voltage Vin. In this manner, the power factor of the AC input current Tin is promoted. The electromagnetic interference filter  211  is used to block the high-frequency noises of the multi-output electronic ballast  2  and the noises resulted from the AC input voltage Vin, thereby preventing the occurrences of the crossover effect. 
     In this embodiment, the first inverter  22  includes a first inverter controller  221 , a first switch circuit  222 , a second voltage divider  223 , and a first resonant circuit  224 . The first inverter controller  221  is connected to the control circuit  25  and the first switch circuit  222  for controlling the operation of the first switch circuit  222 . The second voltage divider  223  is connected to the DC bus  20  for generating a fractional voltage (Vdc/ 2 ). The first resonant circuit  224  includes a first resonant inductance Lrl and a first resonant capacitance Cr  1  which are connected in series to form a series resonant circuit for generating a resonant response. When the first switch S 1  and the second switch S 2  are turned on at the same time, the AC/DC converter  21  converts the AC input voltage Vin into a DC voltage Vdc. The control circuit  25  outputs a control signal Vc with a low level to the first inverter controller  221 . In the meantime, the first inverter controller  221  controls the operation of the first switch circuit  222  to allow the energy of the DC voltage Vdc to be selectively outputted to the first resonant circuit  224  through the first switch circuit  222 . 
     In this embodiment, the first switch circuit  222  includes a fourth switch element Q 4  and a fifth switch element Q 5 . The fourth switch element Q 4  and the fifth switch element Q 5  are connected in series with each other. The second voltage divider  223  a third capacitor C 3  and a fourth capacitor C 4 . The third capacitor C 3  and the fourth capacitor C 4  are connected in series with each other. The first inverter  22  is able to convert the DC voltage Vdc into a high-frequency first AC voltage Vol by alternately turning on and off the fourth switch element Q 4  and the fifth switch element Q 5  and the resonant response of the first resonant circuit  224 . In this embodiment, the first inverter  22  further includes a first pre-heating winding  225 . The first pre-heating winding  225  is, namely, a first pre-heater. The first pre-heater  225  shares the same magnetic core with the first resonant inductance Lrl of the first resonant circuit  224 , and is used to pre-heat the first lamp assembly  31 . 
     Besides, the second inverter  23  includes a second inverter controller  231 , a second switch circuit  232 , a third voltage divider  233 , a second resonant circuit  234 , and a second pre-heating winding  235 . The second pre-heating winding  235  is, namely, a second pre-heater. The connection topology and operating principle of the internal components of the second inverter  23  are similar to the connection topology and operating principle of the internal components of the first inverter  22 , and it is not intended to dwell upon the connection topology and operating principle of the internal components of the second inverter  23  herein. However, the power source of the second inverter controller  231  comes from the auxiliary voltage Vcc generated by the auxiliary voltage generator  24 . Therefore, the second inverter  23  may start operating as the second switch S 2  is turned on. 
     In this embodiment, the first and second inverters  22  and  23  further include a first protection circuit  226  and a second protection circuit  236 . The protection circuits  226  and  236  are used to protect the multi-output electronic ballast  2  when the first lamp assembly  31  or the second lamp assembly  32  is malfunctioned. Next, the first lamp assembly  31  will be taken as an example to illustrate the function of the protection circuit. The first protection circuit  226  includes a third diode D 3  and a fourth diode D 4  that are connected to the second voltage divider  223 . When the first lamp assembly  31  is malfunctioned, the discharging of the first lamp assembly  31  is not symmetrical during the positive and negative cycles of the first AC input voltage Vol. For example, the first lamp assembly  31  only discharges in the positive cycles. In the case that the first protection circuit  226  is not connected, either the voltage value of the third capacitor C 3  or the voltage of the fourth capacitor C 4  will be excessive. For example, either the voltage value of the third capacitor C 3  or the voltage of the fourth capacitor C 4  will be high than the DC voltage Vdc. When the voltage of the fourth capacitor C 4  is higher than the DC voltage Vdc, the third diode D 3  is turned on to prevent the fourth capacitor C 4  from being charged and prevent the voltage of the fourth capacitor C 4  from damaging the fourth capacitor C 4  Likewise, the internal configuration and operation principle of the second protection circuit  236  are similar to those of the first protection circuit  226 , and it is not intended to dwell upon the internal configuration and operation principle of the second protection circuit  236 . 
     In conclusion, the invention provides a multi-output electronic ballast which includes an AC/DC converter and is used to control the operation of the internal inverters by a control circuit. Unlike the conventional multi-output electronic ballast which includes a plurality of AC/DC converters, the inventive multi-output electronic ballast can save the manufacturing cost of the electronic ballast. More advantageously, the control circuit of the electronic ballast is simple and small. Overall, when the user turns off the first switch, the control circuit may cease the operation of the first inverter by stopping the supply of the energy required to operate the first inverter controller, thereby turning off the first lamp assembly. 
     While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention need not be restricted to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the invention which is defined by the appended claims.