The present invention relates to an electronic ballast, and more particularly to an electronic ballast with a real-time current crest factor improvement function.
As known, a gas discharge lamp has many benefits such as high brightness, long life, small volume, high lighting efficiency and good color rendering efficiency. Consequently, the gas discharge lamp is widely used in a variety of outdoor, indoor or automotive lighting devices. The gas discharge lamp is usually equipped with an electronic ballast for controlling the AC current that is outputted from the gas discharge lamp.
The conventional electronic ballast at least comprises a converter and an inverter circuit. The converter is controlled by a constant power control circuit. Consequently, the DC voltage received by the converter is converted into regulated DC voltages with different voltage levels. The constant power control circuit is also used for detecting a DC voltage and a DC current from the converter. According to the detecting result, the converter is controlled by the constant power control circuit to output a constant power. The inverter circuit is for example a full-bridge inverter circuit composed of four switch elements. Two switch elements at the upper bridge arm and two switch elements at the lower bridge arm are connected with each other in parallel. Under control of an inverter control circuit, the two switch elements at the upper bridge arm and the two switch elements at the lower bridge arm are alternately turned on or turned off. Consequently, the DC voltage and the DC current from the converter are converted into an AC voltage and an AC current, respectively.
As known, the simultaneous conduction of the two switch elements at the upper bridge arm or the simultaneous conduction of the two switch elements at the lower bridge arm may cause damage of the switch elements. For avoiding simultaneous conduction, after the on-state switch elements at the upper bridge arm and the lower bridge arm are switched to the off state for a certain time interval, the off-state switch elements at the upper bridge arm and the lower bridge arm will be switched to the on state. The certain time interval is also referred as a dead time. During the dead time, the two switch elements at the upper bridge arm and the two switch elements at the lower bridge arm are simultaneously in the off state. Moreover, an ignitor is connected between the inverter circuit and the gas discharge lamp for temporarily and largely increasing the voltage level of the AC output voltage from the inverter circuit, thereby driving illumination of the gas discharge lamp.
Since the operation of the gas discharge lamp is driven by the AC current from the electronic ballast, the quality of a current crest factor (CCF) of the AC current may directly influence the use life of the gas discharge lamp.
For solving the above drawbacks, the conventional electronic ballast may further comprise a detecting circuit for detecting whether the output current from the converter fluctuates. If the output current from the converter fluctuates, the detecting circuit issues a corresponding signal to reduce the output power of the converter in order to restrain the peak current. In other words, the conventional method of restraining the peak current is passively performed after the AC output current from the electronic ballast results in the peak current. Since the action of restraining the peak current is triggered when the peak current is generated, the peak current fails to be completely restrained and the efficacy of restraining the peak current is unsatisfactory. Moreover, since the detecting circuit needs to detect and judge current fluctuation, the computation is complicated and the circuitry configuration is costly.
Therefore, there is a need of providing an electronic ballast with a real-time current crest factor improvement function in order to eliminate the above drawbacks.
The present invention provides an electronic ballast with a real-time current crest factor improvement function. The electronic ballast has a current crest factor improvement circuit for receiving two control signals that are used to control the on/off states of corresponding switch elements of an inverter circuit. During a dead time between the enabling states of two control signals, a controlling unit may reduce the output power of the converter to a predetermined value in real time or suspend the converter. Consequently, the controlling unit of the electronic ballast can actively and immediately restrain generation of the peak current and the peak voltage. Under this circumstance, the use life and the power-saving efficacy of the gas discharge lamp will be enhanced. Moreover, the circuitry configuration of the electronic ballast of the present invention is simplified and cost-effective.
In accordance with an aspect of the present invention, there is provided an electronic ballast. The electronic ballast includes a converter, an inverter circuit, a controlling unit, and a current crest factor improvement circuit. The converter is used for providing a DC voltage. The inverter circuit is connected with the converter for converting the DC voltage into an AC output voltage, so that at least one gas discharge lamp is driven by electric energy of the AC output voltage. The inverter circuit includes plural switch elements. The controlling unit is connected with the converter and the plural switch elements of the inverter circuit. The controlling unit issues a first control signal to control the converter and issues a second control signal and a third control signal with opposite enabling/disabling states to control on/off states of corresponding switch elements. During a dead time between the enabling state of second control signal and the enabling state of the third control signal, the plural switch elements are simultaneously in the off state. The current crest factor improvement circuit is connected with the controlling unit for receiving the second control signal and the third control signal. During the dead time, the current crest factor improvement circuit is triggered to generate a restraining signal to the controlling unit. According to the restraining signal, the first control signal is correspondingly adjusted by the controlling unit, so that an output power of the converter is decreased to a predetermined value in real time or the converter is suspended.
In accordance with another aspect of the present invention, there is provided an electronic ballast. The electronic ballast includes a converter, an inverter circuit, and a controlling unit. The converter is used for providing a DC voltage. The inverter circuit is connected with the converter for converting the DC voltage into an AC output voltage, so that at least one gas discharge lamp is driven by electric energy of the AC output voltage. The inverter circuit includes plural switch elements. The controlling unit is connected with the converter and the plural switch elements of the inverter circuit. The controlling unit issues a first control signal to control the converter and issues a second control signal and a third control signal with opposite enabling/disabling states to control on/off states of corresponding switch elements. During a dead time between the enabling state of second control signal and the enabling state of the third control signal, the plural switch elements are simultaneously in the off state. During the dead time, the first control signal is correspondingly adjusted by the controlling unit, wherein according to the adjusted first control signal, an output power of the converter is decreased to a predetermined value in real time or the converter is suspended.
The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.
The input filter and rectifier circuit 10 is connected with an input terminal of the electronic ballast 1, and electrically connected with the AC input power source 9. The input filter and rectifier circuit 10 is used for isolating the high-frequency noise of the electronic ballast 1 and the external noise of the AC input voltage Vin in order to reduce the interference therebetween. Moreover, the input filter and rectifier circuit 10 is also used for rectifying the AC input voltage Vin into a full-wave rectified DC voltage Vs1. The PFC circuit 11 is connected with the input filter and rectifier circuit 10. In this embodiment, the PFC circuit 11 has a boost-type circuitry configuration. By alternately turning on and turning off a switch element (not shown) of the PFC circuit 11, the distribution and envelop curve of an input current (not shown) received by the input terminal of the electronic ballast 1 becomes similar to the waveform of the AC input voltage Vin. Consequently, the power factor is increased, and the full-wave rectified DC voltage Vs1 is converted into a high DC voltage Vs2, wherein the high DC voltage Vs2 is higher than the full-wave rectified DC voltage Vs1.
As shown in
The inverter circuit 13 is connected with the converter 12 and the controlling unit 15. The inverter circuit 13 is a full-bridge circuit composed of four switch elements such as metal-oxide-semiconductor field-effect transistors. For example, these switch elements comprise a first switch element M1, a second switch element M2, a third switch element M3 and a fourth switch element M4. The first switch element M1 and second switch element M2 at the upper bridge arm are connected with each other in series. The third switch element M3 and the fourth switch element M4 at the lower bridge arm are connected with each other in series. Moreover, the upper bridge arm and the lower bridge arm are connected with each other in parallel. The first switch element M1 and second switch element M2 at the upper bridge arm are controlled by the controlling unit 15 to be alternatively turned on or turned off. The third switch element M3 and the fourth switch element M4 at the lower bridge arm are also controlled by the controlling unit 15 to be alternatively turned on or turned off. The switching operations of the upper bridge arm and the lower bridge arm are performed synchronously. In other words, by switching the four switch elements M1˜M4, the low DC voltage Vd is converted into an AC output voltage Vout for providing an electric energy to illuminate the gas discharge lamp 8. It is noted that the configuration of the inverter circuit 13 may be varied according to the practical requirements. For example, in some other embodiments, the inverter circuit 13 is a half-bridge circuit composed of two switch elements (not shown).
The ignitor 14 is connected between the inverter circuit 13 and the gas discharge lamp 8 for temporarily increasing the voltage level of the output voltage Vout to about 3˜5 KV, thereby driving illumination of the gas discharge lamp 8.
The controlling unit 15 is connected with the converter 12 and the inverter circuit 13 for controlling operations of the converter 12 and the inverter circuit 13. In this embodiment, the controlling unit 15 comprises a constant power control circuit 150 and an inverter control circuit 151. The constant power control circuit 150 is electrically connected with the switch element of the converter 12. The constant power control circuit 150 is used for outputting a first control signal S1, which is a pulse width modulation (PWM) signal. According to the first control signal S1, the switching action of the switch element of the converter 12 is correspondingly controlled. Consequently, the high DC voltage Vs2 is converted into the low DC voltage Vd by the converter 12. Alternatively, in some other embodiments, the constant power control circuit 150 is further connected with an output terminal of the converter 12 for detecting the low DC voltage Vd and a working DC current Id from the converter 12. According to the low DC voltage Vd and a working DC current Id, the first control signal S1 is adjusted by the constant power control circuit 150. Consequently, the converter 12 is controlled to output a constant power.
As shown in
In some embodiments, the controlling unit 15 is implemented by a monolithic integrated circuit such as an IRS2573D integrated circuit. The monolithic integrated circuit may have both functions of the constant power control circuit 150 and the inverter control circuit 151. Consequently, only a single integrated circuit can implement of the functions of the constant power control circuit 150 and the inverter control circuit 151.
The current crest factor improvement circuit 16 is connected with the inverter control circuit 151 for receiving the second control signal S2 and the third control signal S3. The current crest factor improvement circuit 16 is also connected with the constant power control circuit 150. During the dead time Td between the enabling state of the second control signal S2 and the enabling state of the third control signal S3, the current crest factor improvement circuit 16 is triggered to generate a restraining signal Vr to the constant power control circuit 150. According to the restraining signal Vr, the first control signal S1 is correspondingly adjusted by the constant power control circuit 150. According to the adjusted first control signal S1, the converter 12 is controlled to decrease the output power to a predetermined value (e.g. 50% reduction of the output power) in real time or suspend the converter 12. Under this circumstance, during the polarity inversion of the AC output voltage Vout from the inverter circuit 13, the lamp current Ic flowing through the gas discharge lamp 8 is less prone to generation of the peak current and the peak voltage, and thus the current crest factor is improved.
As previously described in the prior art, the peak current and the peak voltage occur during the dead time, i.e. the polarity inversion of the output voltage from the electronic ballast when the plural switch elements are simultaneously in the off state. In accordance with the present invention, the current crest factor improvement circuit 16 is triggered to generate a restraining signal Vr to the constant power control circuit 150 during the dead time Td. Consequently, during the transient polarity inversion of the output voltage from the electronic ballast 1, the controlling unit 15 may control the converter 12 to decrease the output power to the predetermined value in real time or suspend the converter 12. In other words, since the switch elements M1˜M4 are in the off state and the output voltage from the inverter circuit 13 is not generated during the dead time, the output electric energy is reduced or not generated. After the transient polarity inversion of the output voltage from the electronic ballast 1, the converter 12 cannot output high electric energy, so that the current crest factor is improved.
Please refer to
In an embodiment, the dead-time signal catch circuit 160 comprises an AND gate circuit 160a (i.e. composed of a first diode D1 and a second diode D2), a first capacitor C1, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a first transistor B1 (e.g. a PNP bipolar junction transistor). The anode of the first diode D1 is connected with the inverter control circuit 151 through a first input terminal of the dead-time signal catch circuit 160, so that the second control signal S2 is received by the anode of the first diode D1. The anode of the second diode D2 is connected with the inverter control circuit 151 through a second input terminal of the dead-time signal catch circuit 160, so that the third control signal S3 is received by the anode of the second diode D2. The cathode of the first diode D1 and the cathode of the second diode D2 are connected with a first node A. The first capacitor C1 is connected between the first node A and a ground terminal G. A first end of the first resistor R1 is connected with an external voltage Vi. A second end of the first resistor R1 is connected with a first end of the second resistor R2. A second end of the second resistor R2 is connected with a first end of the third resistor R3 and the first node A. A second end of the third resistor R3 is connected with the ground terminal G. The first resistor R1, the second resistor R2 and the third resistor R3 are collaboratively defined as a first voltage divider. The third resistor R3 is connected with the first capacitor C1 in parallel, thereby providing a discharging path of the first capacitor C1. The base of the PNP bipolar junction transistor B1 is connected with the second end of the first resistor R1 and the first end of the second resistor R2. The emitter of the PNP bipolar junction transistor B1 is connected with the first end of the first resistor R1 and the external voltage Vi. The collector of the PNP bipolar junction transistor B1 is connected with a first end of the fourth resistor R4. A second end of the fourth resistor R4, a first end of the fifth resistor R5 and an output terminal of the dead-time signal catch circuit 160 are connected with a second node B. A second end of the fifth resistor R5 is connected with the ground terminal G.
The power restraining circuit 161 comprises a second capacitor C2, a sixth resistor R6 and a second transistor B2 (e.g. an NPN bipolar junction transistor). A first end of the second capacitor C2 is connected with the output terminal of the dead-time signal catch circuit 160, the second end of the fourth resistor R4 and the first end of the fifth resistor R5 through the input terminal of the power restraining circuit 161. A second end of the second capacitor C2 is connected with the ground terminal G. The fifth resistor R5 is connected with the second capacitor C2 in parallel, thereby providing a discharging path of the second capacitor C2. The base of the NPN bipolar junction transistor B2 is connected with a first end of the second capacitor C2, and connected with the output terminal of the dead-time signal catch circuit 160, the second end of the fourth resistor R4 and the first end of the fifth resistor R5 through the input terminal of the power restraining circuit 161. That is, the base of the NPN bipolar junction transistor B2 is connected with the second node B. The emitter of the NPN bipolar junction transistor B2 is connected with the ground terminal G. The collector of the NPN bipolar junction transistor B2 is connected with a first end of the sixth resistor R6. A second end of the sixth resistor R6 is connected with the constant power control circuit 150 of the controlling unit 15 through an output terminal of the power restraining circuit 161. By setting the resistance value of the sixth resistor R6, the magnitude of the restraining signal Vr provided to the constant power control circuit 150 is correspondingly adjusted.
Hereinafter, the operations of the current crest factor improvement circuit 16 of the electronic ballast 1 will be illustrated with reference to
On the other hand, during the dead time between the enabling state of the second control signal S2 and the enabling state of the third control signal S3, both of the second control signal S2 and the third control signal S3 have a disabling level (e.g. 0V). Meanwhile, the first diode D1 and the second diode D2 of the AND gate circuit 160a of the dead-time signal catch circuit 160 are shut off. Consequently, the voltage at the first node A is decreased. Through the first voltage divider (i.e. composed of the first resistor R1, the second resistor R2 and the third resistor R3), the voltage at the first node A is transmitted to the base of the PNP bipolar junction transistor B1. Since the different between the external voltage V, received by the emitter of the PNP bipolar junction transistor B1 and the voltage at the base of the PNP bipolar junction transistor B1 is higher than the threshold voltage of the PNP bipolar junction transistor B1, the PNP bipolar junction transistor B1 is turned on. Under this circumstance, the electric energy of the external voltage Vi is transmitted to a second voltage divider (i.e. composed of the fourth resistor R4 and the fifth resistor R5) through the on-state PNP bipolar junction transistor B1, and then transmitted to the second node B (i.e. the output terminal of the dead-time signal catch circuit 160) through the second voltage divider. Meanwhile, the output terminal of the dead-time signal catch circuit 160 issues a triggering voltage Vt (e.g. 5V) to the base of the NPN bipolar junction transistor B2. Meanwhile, the voltage difference between the base and the emitter of the NPN bipolar junction transistor B2 is higher than the threshold voltage of the NPN bipolar junction transistor B2, so that the NPN bipolar junction transistor B2 is also turned on. Under this circumstance, the output terminal of the power restraining circuit 161 is electrically connected with the ground terminal G through the sixth resistor R6 and the on-state NPN bipolar junction transistor B2. Since the output terminal of the power restraining circuit 161 is electrically connected with the ground terminal G, the output terminal of the power restraining circuit 161 issues a restraining signal Vr with a zero voltage. According to the restraining signal Vr, the first control signal S1 is correspondingly adjusted by the controlling unit 15, so that the output power of the converter 12 is decreased to a predetermined value in real time or the converter 12 is suspended.
From the above descriptions, the present invention provides an electronic ballast with a real-time current crest factor improvement function. The electronic ballast has a current crest factor improvement circuit for receiving two control signals. The two control signals are used to control the on/off states of corresponding switch elements of an inverter circuit. During a dead time between the enabling states of the two control signals, the controlling unit may reduce the output power of the converter to a predetermined value in real time or suspend the converter. Consequently, the controlling unit of the electronic ballast can actively and immediately restrain generation of the peak current and the peak voltage. Under this circumstance, the use life and the power-saving efficacy of the gas discharge lamp will be enhanced. Moreover, since the controlling unit reduces the output power of the converter to the predetermined value in real time or suspends the converter during the dead time, the electronic ballast does not need complicated circuitry configuration and complicated computation to judge whether the current from the converter fluctuates. In other words, the circuitry configuration of the electronic ballast of the present invention is simplified and cost-effective. Moreover, by the electronic ballast of the present invention, the speed of restraining the peak current is increased.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited 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.
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101142766 A | Nov 2012 | TW | national |
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Number | Date | Country | |
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20140139127 A1 | May 2014 | US |