Lamp ignition system and lamp ignition method

This application claims priority to China Application Serial Number 201210245890.3, filed Jul. 16, 2012, which is herein incorporated by reference in its entirety.

1. Technical Field

The present disclosure relates to electronic technology, and more particularly, to a lamp ignition system and a lamp ignition method.

2. Description of Related Art

FIG. 1 is a circuit block diagram of a conventional gas-discharge lamp system 100 . As shown in FIG. 1 , a converter 110 converts an input voltage Vin into an operating voltage for a DC HID (High Intensity Discharge) lamp, and a high voltage generator 120 generates a high DC voltage for igniting this lamp, in which the driving circuit 121 drives the transformer T 1 for outputting high-voltage pulses to a diode D 9 and a capacitor C 9 , so as to supply a DC voltage (1.5 kV) across the lamp 130 . The high-voltage diode D 2 can prevent the DC voltage from damaging other components of the converter 110 . Generally, a forward voltage drop of the high-voltage diode D 2 is relatively high. Before the lamp 130 is ignited, no current flows through the high-voltage diode D 2 , and therefore no loss occurs. After the lamp 130 is ignited, a lamp current flows through the high-voltage diode D 2 to produce large steady-state loss, and therefore the efficiency of the ballast is reduced, where waveforms of a lamp voltage and the lamp current are shown in FIG. 2 .

In view of the foregoing, there still exist some inconveniences and defects in conventional designs for lamp ignition that await further improvement. However, those skilled in the art sought vainly for a solution. In order to solve or circumvent above problems and disadvantages, there is an urgent need in the related field to improve system efficiency.

The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the present invention or delineate the scope of the present invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

In one or more various aspects, the present disclosure is directed to a lamp ignition system and a lamp ignition method, so as to improve system efficiency.

According to one embodiment of the present invention, a lamp ignition system includes a converter, a transformer and a driving circuit. The converter converts an input voltage into an operating voltage suitable for a gas discharge lamp. The transformer has a primary winding and a secondary winding, where the secondary winding is connected to the gas discharge lamp in series. The driving circuit is electrically connected to the primary winding for driving the transformer in a lamp ignition stage, so that the secondary winding of the transformer can output a high-frequency voltage to ignite the gas discharge lamp.

According to another embodiment of the present invention, a lamp ignition method includes steps of (a) converting an input voltage into an operating voltage suitable for a gas discharge lamp, where the gas discharge lamp is connected to a secondary winding of a transformer in series; (b) driving the transformer in a lamp ignition stage, so that a secondary winding of the transformer can output a high-frequency voltage to ignite the gas discharge lamp.

Technical advantages are generally achieved, by embodiments of the present invention. In present invention, the winding of the transformer is connected to the gas discharge lamp (e.g., the direct-current lamp) in series, so that the high-voltage diode D 2 in conventional art can be removed from the system, and therefore the loss that results form the high-voltage diode D 2 can be circumvented.

Many of the attendant features will be more readily appreciated, as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings.

The present description will be better understood from the following detailed description read in light of the accompanying drawing, wherein:

FIG. 1 is a circuit block diagram of a conventional gas-discharge lamp system;

FIG. 2 is a waveform diagram of a lamp voltage and a lamp current of the gas-discharge lamp system of FIG. 1 ;

FIG. 3 is a circuit block diagram of a lamp ignition system according to one embodiment of the present disclosure;

FIG. 4 is a circuit block diagram of the lamp ignition system according to another embodiment of the present disclosure;

FIG. 5 is a circuit block diagram of the lamp ignition system according to yet another embodiment of the present disclosure;

FIG. 6 is a waveform diagram of the lamp ignition system of FIG. 5 in a symmetric driving manner;

FIG. 7 is a waveform diagram of the lamp ignition system of FIG. 5 in an asymmetric driving manner;

FIG. 8 is a circuit block diagram of the lamp ignition system according to still yet another embodiment of the present disclosure;

FIG. 9 is a waveform diagram of an output signal of a driver of FIG. 8 ; and

FIG. 10 is a waveform diagram of the lamp voltage of the lamp ignition system of FIG. 8 .

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to attain a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

As used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes reference to the plural unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the terms “comprise or comprising”, “include or including”, “have or having”, “contain or containing” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. As used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

As used herein, “around”, “about” or “approximately” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about” or “approximately” can be inferred if not expressly stated.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In one aspect, the present disclosure is directed a lamp ignition system for improving system efficiency. Referring to FIG. 3 , illustrated is a circuit block diagram of a lamp ignition system 200 according to one embodiment of the present disclosure. This system may be easily inserted into ballast and may be applicable or readily adaptable to all technologies.

The lamp ignition system 200 includes a converter 210 , a high voltage generator 220 and a gas discharge lamp 230 . The high voltage generator 220 includes a transformer T 1 and a driving circuit 221 . The transformer T 1 has a primary winding T 1 - 1 and a secondary winding T 1 - 2 , where the primary winding T 1 - 1 is electrically connected to the driving circuit 221 , and the secondary winding T 1 - 2 is connected to the gas discharge lamp 230 in series. In the following description, the gas discharge lamp is a direct-current (DC) lamp for example. The converter 210 may be a DC-DC converter or an AC-DC converter. The DC-DC converter, such as Buck, Flyback, Forward, Speic, Cuk, etc., converts input DC voltage Vin into the operating voltage for the DC lamp 230 . The AC-DC converter converts input AC voltage Vin into the operating voltage for the DC lamp 230 . In should be noted that the winding of the transformer T 1 in the high voltage generator 220 is connected to the DC lamp 230 in series, so that the high-voltage diode D 2 in conventional art can be removed from the system, and therefore the loss that results form the high-voltage diode D 2 can be circumvented. Thus, the system efficiency is increased dramatically

In FIG. 4 , the converter 210 is a buck converter circuit. The buck converter circuit includes a capacitor C 1 , an inductor L 1 , a resistor Rcs, a freewheeling diode D 1 and a control switch Q 1 .

One terminal of the capacitor C 1 is electrically connected to the secondary winding T 1 - 2 of the transformer T 1 , and another terminal of the capacitor C 1 is electrically connected to the DC lamp 230 . The inductor L 1 is electrically connected to the secondary winding T 1 - 2 of the transformer T 1 . The resistor Rcs is electrically connected to the DC lamp 230 . The anode of the freewheeling diode D 1 is electrically connected to the resistor Rcs, and the cathode of the freewheeling diode D 1 is electrically connected to the inductor L 1 . One end of the control switch Q 1 is electrically connected to the cathode of the freewheeling diode D 1 , and another end of the control switch Q 1 is electrically connected to the input voltage Vin. In FIG. 4 , the control switch Q 1 is a metal oxide semiconductor field effect transistor (MOSFET), and a controller can control an on/off state of the MOSFET.

When lamp ignition system 200 operates, the converter 210 converts the input voltage Vin into the operating voltage for the DC lamp 230 , and the driving circuit 221 drives the transformer T 1 in a lamp ignition stage, so that the secondary winding T 1 - 2 of the transformer T 1 can output a high-frequency voltage. Referring to a loop composed of the capacitor C 1 , the secondary winding T 1 - 2 of the transformer T 1 and the DC lamp 230 , a voltage drop across the capacitor C 1 is very low, and most of high-frequency voltage is applied to the DC lamp 230 , so that the DC lamp 230 can be ignited.

After the DC lamp 230 has been ignited, the driving circuit 221 stops working, and a lamp current flow through the secondary winding T 1 - 2 . Referring to the design formula of magnetic device: L*I=N*B*Ae, if the transformer T 1 operates in an unsaturated state after the DC lamp 230 has been ignited, the number of turns N is more, and therefore loss of the wiring will increase and the efficiency decreases accordingly. In this embodiment, the transformer T 1 operates in an unsaturated state during the lamp ignition stage, and a designer can choose the number of turns of the wiring depending on the requirements for outputting high voltage; in steady operation, the transformer T 1 operates in a saturated state. Thus, the number of turns of the secondary winding T 1 - 2 is relatively less. Moreover, the current flowing through the secondary winding T 1 - 2 is a DC current. Even if the transformer T 1 operates in the saturated state, the loss of the transformer T 1 still remains very low. In such design, the number of turns of the secondary winding T 1 - 2 is less, and therefore after the DC lamp 230 is ignited, the loss of the secondary winding T 1 - 2 is reduced. For example, when a HID lamp (240 W) is ignited, the system efficiency is improved at least 1.4%, as compared with the conventional art.

For a further understanding of the above driving circuit, refer to FIG. 5 , the half bridge circuit 310 and a resonant circuit 320 constitute the high voltage generator 220 , in which an inductance L 2 , a capacitor C 2 and the transformer T 1 constitute the resonant circuit 320 . The resonant circuit 320 is electrically connected to the half bridge circuit 310 . The inductance L 2 and the capacitor C 2 are connected to two ends of the primary winding T 1 - 1 of the transformer T 1 , respectively. The inductance L 2 may be an added inductor, a leakage inductance of the transformer T 1 , or the combination thereof.

The half bridge circuit 310 includes a first switch Q 2 , a second switch Q 3 and a driver 311 . The first switch Q 2 and the second switch Q 3 are connected in series, where the first switch Q 2 is connected to a voltage source Vbus, and the second switch Q 3 is grounded. The driver 311 is electrically connected to respective control terminals of the first and second switches Q 2 and Q 3 . In FIG. 5 , the first switch Q 2 and the second switch Q 3 are two metal oxide semiconductor field effect transistors(MOSFET), and each MOSFET may have a body diode.

The voltage source Vbus can be the input voltage Vin, the voltage across the capacitor C 1 or an external voltage source.

In use, the driver 311 can control the first and second switches Q 2 and Q 3 to operate alternately. The working frequency of the first and second switches Q 2 and Q 3 is 10-500 kHz, so that resonant circuit 320 can resonate, and therefore the secondary winding T 1 - 2 of the transformer T 1 can output the high-frequency voltage as an ignition voltage.

FIG. 6 and FIG. 7 are respective waveform diagrams of the high voltage generator of FIG. 5 . As shown in FIG. 6 , the first and second switches Q 2 and Q 3 are controlled in a symmetric driving manner. In the symmetric driving manner, the driver 311 outputs a first pulse 610 to the first switch Q 2 and a second pulse 620 to the second switch Q 3 alternately, wherein a width of the first pulse 610 is equal to a width of the second pulse 620 , and a corresponding voltage applied to the DC lamp is a symmetric high-frequency ignition voltage. Alternatively, as shown in FIG. 7 , the first and second switches Q 2 and Q 3 are controlled in an asymmetric driving manner. In the asymmetric driving manner, the driver 311 outputs a first pulse 710 to the first switch Q 2 and a second pulse 720 to the second switch Q 3 alternately, wherein a width of the first pulse 610 is different from a width of the second pulse 620 , and a corresponding voltage applied to the DC lamp is an asymmetric high-frequency ignition voltage.

Alternatively, as shown in FIG. 8 , the driving circuit includes an inductance L 2 , a switch device Q 5 and a driver 510 . The inductance L 2 is electrically connected to the primary winding T 1 - 1 of the transformer T 1 and a voltage source Vbus, where the transformer T 1 has parasitic capacitance. The driver 510 controls an on/off state of the switch device Q 5 . In FIG. 8 , the switch device Q 5 is a metal oxide semiconductor field effect transistor.

In use, the driver 510 outputs a high-frequency driving signal to turn on the switch device Q 5 , and then the inductance L 2 and the transformer T 1 including the parasitic capacitance constitute a resonant circuit 520 , and the secondary winding T 1 - 2 can output the ignition voltage. The working frequency of the switch device Q 5 is 10-500 kHz, and the duty ratio of the switch device Q 5 is 0.2%-10%, as shown in FIG. 9 . For the performance of the driver, the working frequency of the switch device Q 5 is 200 kHz, and the duty ratio is 3%, so as to select a low-cost driver chip and further reduce the volume of the transformer T 1 . Moreover, the inductance L 2 may be an added inductor, a parasitic inductance of the transformer T 1 , or the combination thereof, and a waveform diagram of the lamp voltage is shown in FIG. 10 .

The voltage source Vbus can be the input voltage Vin, the voltage across the capacitor C 1 or an external voltage source. Those skilled in the art may choose a suitable voltage source depending on the desired application.

In one embodiment, the driving circuit further includes an absorbing circuit 530 . The absorbing circuit 530 is electrically connected to the switch device Q 5 and the resonant circuit 520 . The absorbing circuit 530 includes a diode D, a capacitor C and a resistor R.

In one embodiment, the driving circuit further includes a current limit circuit 540 . The current limit circuit 540 is electrically connected to the switch device Q 5 . The current limit circuit 540 includes a bipolar junction transistor (BJT) and resistors R 1 and R 2 .

In use, the absorbing circuit 530 limits voltage applied to the switch device Q 5 when the switch device Q 5 is cut off. The current limit circuit 540 limits current flowing through the switch device Q 5 , so as to prevent the switch device Q 5 from being damaged.

From the above, the present disclosure is directed to a lamp ignition method. This lamp ignition method includes steps of (a) converting an input voltage Vin into an operating voltage suitable for a gas discharge lamp, such as a DC lamp 230 , where the DC lamp 230 is connected to a secondary winding T 1 - 2 of a transformer T 1 in series; (b) driving the transformer T 1 in a lamp ignition stage, so that the secondary winding T 1 - 2 of the transformer T 1 can output a high-frequency voltage to ignite the DC lamp 230 .

During the lamp ignition stage, the transformer T 1 operates in an unsaturated state.

The lamp ignition method further includes a step of stopping driving the transformer T 1 after the DC lamp 230 has been ignited, so that the transformer T 1 operates in a saturated state.

In the lamp ignition method, as shown in FIG. 5 , an inductance L 2 , a capacitor C 2 and the transformer T 1 constitute a resonant circuit 320 , a half bridge circuit 310 includes a first switch Q 2 and a second switch Q 3 connected in series, and the step (b) includes: controlling the first and second switches Q 2 and Q 3 to operate alternately, so that the secondary winding T 1 - 2 of the transformer T 1 outputs the high-frequency voltage as an ignition voltage.

In one embodiment, the step of controlling the first and second switches Q 2 and Q 3 includes: outputting a first pulse 610 to the first switch Q 2 and a second pulse 620 to the second switch Q 3 alternately, wherein a width of the first pulse is equal to a width of the second pulse, and the lamp voltage of the DC lamp 230 is shown in FIG. 6 .

In another embodiment, the step of controlling the first and second switches Q 2 and Q 3 includes: outputting a first pulse 710 to the first switch Q 2 and a second pulse 720 to the second switch Q 3 alternately, wherein a width of the first pulse is different from a width of the second pulse, and the lamp voltage of the DC lamp 230 is shown in FIG. 7 .

In the lamp ignition method, as shown in FIG. 8 , an inductance L 2 and the transformer T 1 having parasitic capacitance constitute a resonant circuit 520 , a switch device Q 5 is electrically connected to the resonant circuit 520 , and the step (b) includes: controlling an on/off state of the switch device Q 5 , so that the secondary winding T 1 - 2 of the transformer T 1 outputs the high-frequency voltage as the ignition voltage.

In one embodiment, the lamp ignition method further includes a step of providing an absorbing circuit 530 , which is electrically connected to the switch device Q 5 and the resonant circuit 520 , and limiting voltage applied to the switch device Q 5 by use of the absorbing circuit 530 when the switch device Q 5 is cut off.

Alternatively or additionally, the lamp ignition method further includes a step of providing a current limit circuit 540 , which is electrically connected to the switch device Q 5 , and limiting current flowing through the switch device Q 5 by use of the current limit circuit 540 , so as to prevent the switch device Q 5 from being damaged.

In above-mentioned lamp ignition method, the steps are not recited in the sequence in which the steps are performed. That is, unless the sequence of the steps is expressly indicated, the sequence of the steps is interchangeable, and all or part of the steps may be simultaneously, partially simultaneously, or sequentially performed. It should be noted that those implements to perform the steps in the lamp ignition method are disclosed in above embodiments and, thus, are not repeated herein.

The reader's attention is directed to all papers and documents which are filed concurrently with his specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. §112, 6th paragraph. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. §112, 6th paragraph.