WO2013170432A1

WO2013170432A1 - Resonant ignition for hid lamps

Info

Publication number: WO2013170432A1
Application number: PCT/CN2012/075487
Authority: WO
Inventors: Junguo CUI; Zhijun Luo
Original assignee: General Electric Company
Priority date: 2012-05-15
Filing date: 2012-05-15
Publication date: 2013-11-21
Also published as: WO2013170505A1

Abstract

A method for igniting a HID lamp using a resonant full bridge or half bridge inverter where a discovery voltage is applied to the inverter and a first frequency is selected from a list of frequencies. The inverter is operated at the selected frequency and the lamp voltage is measured. If the lamp voltage is not greater than a threshold, a next frequency is selected and the inverter is operated at the next selected frequency and the lamp voltage is measured. If the measured lamp voltage is above the threshold, an operating voltage is applied to the inverter and the inverter is operated at the selected frequency to ignite the lamp.

Description

RESONANT INGITION FOR HID LAMPS

BACKGROUND Field

[0001] The aspects of the present disclosure relate generally to ballast circuits for high intensity discharge (HID) lamps, and in particular to resonant ignition circuits and methods for igniting HID lamps.

Description of Related Art

[0002] A high intensity discharge (HID) lamp is a class of light-producing electric devices that generally produce light by creating a plasma discharge with an electric arc. HID lamps are preferred for their ability to generate high levels of light from a small amount of energy and are often used in industrial and infrastructure applications where large areas need to be lighted at relatively low costs. As improved control techniques are developed, HID lamps are gaining popularity in other applications, such as automobile headlamps, because of the HID lamp's ability to generate a large amount of light from a small package. Several types of HID lamps are commonly used and are typically named for the gas or vapor contained in the arc tube. Common HID lamp types include mercury vapor, metal halide, ceramic metal halide, high pressure sodium vapor, and xenon short-arc lamps.

[0003] HID lamps create an electric arc between two electrodes, typically made from tungsten, that are placed inside a translucent or transparent arc tube made of high temperature materials such as fused quartz or fused alumina. The arc tube is typically filled with a mixture of gas and metal salts where the gas comprises a Penning mixture used to initiate the arc. Once the arc has started, it heats and evaporates the metal salts to form plasma which greatly enhances the production of light and reduces the lamps power consumption.

[0004] When a HID lamp is started it passes through three phases. These phases include breakdown, non-thermionic glow discharge, and thermionic arc. In the breakdown phase, a high voltage is used to ionize the gas and initiate an electric arc between the electrodes. After the arc is initiated (starting of the arc is referred to herein as ignition) the voltage must be maintained high enough to continue the glow discharge while the electrodes are heated to a temperature that will support thermionic emission. Once thermionic emission is reached the lamp will continue to heat during a run-up period until a steady state is achieved.

[0005] To achieve ignition, in the pre-breakdown period, the electrodes of the lamp must be brought to a high voltage for a short period of time. Typical HID lamps require a minimum of about 3 to 5 kilovolts (KV) for a period of about several hundred microseconds. These requirements can be provided by resonant circuits. However, the resonant frequency of these circuits can vary significantly due to tolerances of the components and variations in installations. Thus, the resonant circuits are often designed to withstand voltages far in excess of the minimum required breakdown voltage in order to ensure reliable ignition resulting in undesirable cost increases.

[0006] HID lamp drivers generally use three stages: (1) a power factor correction (PFC) stage; (2) a current mode controlled dc-dc converter; and (3) an inverter. An external ignition circuit is typically added to provide the high voltage necessary for ignition. Coupling a resonant circuit to the load of the inverter allows elimination of the external ignition circuit resulting in an attendant reduction in cost. To achieve the required ignition voltages using a resonant circuit, the resonant circuit needs to be excited with a signal that is at or close to the circuit's inherent resonant frequency. It is often difficult to accurately predetermine the circuit's resonant frequency, thus various ignition strategies have been attempted. These approaches include driving the third stage at a full ignition voltage while continuously sweeping the frequency through the expected resonant frequency range until ignition is detected. When sweeping the frequency with a full ignition voltage, it is important to sweep from a higher frequency down toward the resonant frequency because frequencies below the resonant frequency can result in excessive current levels. However, these previously tried approaches have various drawbacks including added stress to the lamps and increased driver costs.

[0007] Accordingly, it would be desirable to provide methods and apparatus for driving a

HID lamp that solve at least some of the problems identified above.

SUMMARY OF THE INVENTION

[0008] As described herein, the exemplary embodiments overcome one or more of the above or other disadvantages known in the art.

[0009] One aspect of the present disclosure relates to a method for igniting a lamp, where a microcontroller controls a voltage produced by a DC power regulator and operates a resonant inverter at a lamp ignition frequency and lamp ignition voltage to ignite the lamp. In one embodiment, the method includes the microcontroller controlling the DC power regulator to apply a discovery voltage to the resonant inverter, the discovery voltage being less than a lamp operating voltage and configured to produce a lamp voltage that is below the lamp ignition voltage, the lamp operating voltage being configured to produce a lamp voltage that is above the lamp ignition voltage. A first inverter operating frequency is selected as an operating frequency of the resonant inverter. The resonant inverter is operated at the discovery voltage and selected operating frequency to generate a lamp voltage. A magnitude of the generated lamp voltage is measured and compared to a predetermined discovery threshold voltage. If the measured magnitude of the generated lamp voltage is not greater than the discovery threshold voltage, a next inverter operating frequency is selected as the operating frequency of the resonant inverter and the operate, measure and compare steps are repeated. If the measured magnitude of the lamp voltage is greater than the discovery threshold voltage, the selected operating frequency is set as the lamp ignition frequency of the resonant inverter. The DC power regulator is set to apply the operating voltage of the lamp to the resonant inverter, and the inverter is operated at the operating voltage of the lamp and set lamp ignition frequency to ignite the lamp.

[0010] Another aspect of the present disclosure relates to an apparatus for igniting a lamp.

A DC to DC regulator configured to receive a first DC power and produce a regulated DC power. In one embodiment, the apparatus includes an inverter that receives the regulated DC power and produces an AC inverter power. A resonant circuit receives the AC inverter power and produces a lamp voltage. A microcontroller is coupled to the DC to DC regulator and to the inverter and is configured to control a voltage of the regulated DC power and a frequency of the AC inverter power. The microcontroller is configured to control the regulated DC power at a discovery voltage, the discovery voltage being less than an operating voltage of the lamp and configured to produce a lamp voltage that is below an ignition voltage of the lamp. The operating voltage of the lamp is configured to produce a lamp voltage that is above the ignition voltage of the lamp. The microcontroller selects a first inverter frequency as the frequency of the AC inverter power and operates the inverter at the discovery voltage and selected inverter frequency. A magnitude of the lamp voltage produced by operation of the inverter at the discovery voltage and selected inverter frequency is measured and compared to a predetermined discovery threshold voltage. If the measured magnitude of the lamp voltage is not greater than the discovery threshold voltage a next inverter frequency is selected as the frequency of the AC inverter power and the operate, measure and compare steps are repeated. If the measured magnitude of the lamp voltage is greater than the discovery threshold voltage, a lamp ignition frequency is set to the selected inverter frequency, the regulated DC power is controlled at the operating voltage of the lamp, and the inverter is operated at the lamp ignition frequency and operating voltage to ignite the lamp.

[0011] These and other aspects and advantages of the exemplary embodiments will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the drawings:

[0013] Figure 1 illustrates an exemplary HID lamp drive circuit incorporating aspects of the present disclosure. [0014] Figure 2 illustrates an exemplary embodiment of an H-Bridge resonant inverter incorporating aspects of the present disclosure.

[0015] Figure 3 illustrates a series resonant circuit incorporating aspects of the present disclosure.

[0016] Figure 4 illustrates a flowchart for an exemplary frequency discovery and ignition process incorporating aspects of the present disclosure.

[0017] Figure 5 shows a graph illustrating exemplary regulated DC power and lamp voltages incorporating aspects of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0018] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations.

[0019] Figure 1 illustrates one embodiment of an exemplary HID lamp drive circuit 100 incorporating aspects of the present disclosure. The drive circuit 100 is of the three stage type comprising a first stage 102, a second stage 108 and a third stage 114. The third stage 114 drives a load 120, also referred to herein as a lamp 120. The first stage 102, which includes electromagnetic interference (EMI) filtering and power factor control (PFC), provides input power conditioning and filtering, and produces a direct current (DC) bus voltage 106. Line voltage or power 104 is received by the first stage 102. The line voltage 104 can be any suitable source of AC power such as for example the 120 volt root-mean-square (Vrms) 60 Hertz (Hz) grid voltage available in North America, 230Vrms 50Hz power available in Europe, 220Vrms 50Hz power available in China. In one embodiment, the first stage 102 can include a rectifier to convert the AC line voltage 104 to a DC power, an EMI filter to reduce electromagnetic interference below levels required by local regulations, and power factor correction to improve overall efficiency of the lamp drive 100. The first stage 102 provides a DC bus voltage 106 for use by the second stage 108 as well as the VDD power supply 116 and the VCC power supply 112.

[0020] The second stage 108, also referred to as the regulator or buck stage, regulates the bus voltage 106 to produce regulated DC power 110. The second stage 108 receives the DC bus voltage 106 and produces a voltage and current regulated DC power 110. The second stage 108 is used to regulate the DC power 110 and along with the frequency of the third stage 114 is used to control the voltage delivered to the lamp 120. In the embodiment shown in Figure 1, the second stage 108 comprises a switching power regulator formed with a buck topology. Alternatively, any topology or type of power regulator that can produce a DC power with generally constant power and/or regulated current may be advantageously used. The DC power 110 is provided to the third stage 114 that converts the DC power 110 to an AC voltage. As will be discussed in more detail below, the AC voltage is applied to a resonant circuit which produces the lamp power 118.

[0021] The third stage 114, also referred to as the inverter stage, chops the regulated DC power 110 to provide an alternating current (AC) lamp power 118 to drive the lamp 120.

[0022] In one embodiment, the inverter 114 may be of an H-Bridge or full bridge type, a half bridge type, or other inverter topology capable of converting a DC voltage to an AC voltage. For purposes of the disclosure herein, the terms full bridge and H-bridge are used interchangeably .

[0023] In one embodiment, the exemplary lamp drive 100 of Figure 1 includes a VDD power supply 116 that receives power produced by the first stage 102 and produces a voltage, V_DD, to operate a microcontroller 122. A VCC power supply 1 12 is included to receive power from the first stage 102 and produce a voltage VCC used by low level control circuitry in the regulator stage 108 and the inverter stage 114. The microcontroller unit (MCU) 122 includes a memory configured to store computer code and data, and a processor capable of operating on data and executing computer code in order to carry out logic and processes necessary to operate the lamp driver 100. In one embodiment, the microcontroller unit 122 is configured to execute program instructions in the form of computer readable code or machine-readable instructions that are executable by a processing device. The MCU 122 uses a control signal 124 to control the voltage of the DC power 110 produced by the regulator 108 and uses a control signal 126 to control the frequency of the inverter 114.

[0024] Referring now to Figure 2 an exemplary embodiment of an H-Bridge resonant inverter 200 incorporating aspects of the present disclosure is illustrated. The H-Bridge inverter 200 is appropriate for use in the inverter stage 114 of the lamp drive 100 as illustrated in Figure 1. Generally, an inverter is a circuit topology used to convert DC power into AC power and can be of an H-bridge topology, a half bridge topology, or other topology suitable for converting a DC voltage into an AC voltage. The exemplary inverter illustrated in Figure 2 is of a type known as an H-bridge or full-bridge inverter and includes four switching devices S 1 , S2, S3, S4, one of which is configured in each leg 226, 228 of the "H" as illustrated in Figure 2. The load 120 is disposed in the center branch 222, i.e. the branch between nodes 216 and 218. The positive side of supply voltage 104 is coupled to the upper node 204 of the two legs 226, 228. Switch S I is disposed between node 204 and 216, while switch S3 is disposed between node 204 and node 218, these branches of the resonant inverter 200 also being referred to as the "upper legs." Switch S2 is disposed between node 216 and node 207, while switch S4 is disposed between node 218 and node 207, node 207 being the negative or return side of the supply voltage 104. The branches of the resonant inverter 200 including the switches S2 and S4 are generally referred to as the "lower legs." Switch control signals, denoted by CI , C2, C3, C4 are used to operate the four switching devices, S I , S2, S3, S4 respectively. By alternately closing pairs of switches, SI , S4 or S2, S3, an AC inverter voltage, V,„_v, is applied to the load 120, i.e. the inverter voltage, V,„_v, is applied across circuit nodes 216 and 218. As used herein, a switching device is "on" or "closed" when it is in a state that is conducting current and is "off, or "open" when it is not conducting current. In the exemplary resonant inverter 200 illustrated in Figure 2, the switching devices S1 -S4 are metal oxide semiconductor field effect transistors (MOSFETs). Alternatively, any switching device such as bipolar junction transistors (BJTs), field effect transistors (FETs), or other semiconductor, or mechanical switching device capable of efficiently switching the voltage and current at the desired frequencies and voltages may be advantageously employed. The load 120 of the resonant inverter 200 is coupled between circuit nodes 216 and 218, generally indicated as center branch 222, such that the V,„_v is applied to the load 120. In the embodiment shown in Figure 2, the center branch 222 generally comprises a series resonant circuit and includes an inductor 206 coupled in series with a capacitor 208 at node 212 and the lamp 120 is coupled in parallel with the capacitor 208. Thus the voltage across the capacitor 208 supplies power to the lamp 120 and will be referred to as the lamp voltage Wi_amp- [0025] By operating the switches in pairs, SI and S4 being one pair, and S2 and S3 being another pair, the inverter 200 can be used to apply both a positive or a negative voltage to the load which is coupled between circuit nodes 216 and 218. In one embodiment, to avoid damaging shoot through current switches SI and S2 are generally not turned on at substantially the same time. Similarly switches S3 and S4 are generally turned on at substantially the same time. Alternately, turning on the first pair, SI and S4, then the second pair, S2 and S3 of switches creates an AC inverter voltage, and by controlling the rate at which the switch pairs are alternately operated allows controlling the frequency of the inverter voltage, V,„_v. Thus, an AC inverter voltage at a desired frequency can be applied to the load 120 by configuring the MCU 122 of Figure 1 to appropriately drive the control signals CI, C2, C3, C4.

[0026] Those skilled in the art will recognize that in certain embodiments it is advantageous to use a half-bridge inverter arrangement in place of the H-Bridge arrangement illustrated in Figure 2 without straying from the spirit or scope of the present disclosure. A half- bridge inverter uses two switching devices to alternately apply the input voltage or zero volts to the load.

[0027] As shown in Figure 2, the load 120 of the inverter 200 comprises the series resonant circuit 222 that produces the lamp voltage, Wi_amp, across the capacitor 208. An analogous series resonant circuit is illustrated in Figure 3 where the inductor L is analogous to the resonant inductor 206, the capacitor C is analogous to the resonant capacitor 208, the driving voltage e is analogous to the inverter voltage V,„_v, the output voltage V₀ is analogous to the lamp voltage Vi_amp, and R represents the parasitic resistance of the circuit 300 which is analogous to the parasitic resistances of the load 120 between circuit nodes 216 and 218. The impedance of the series resonant circuit 300 is given by the equation: (1) where z is the complex impedance of the circuit 300, ^i:-^s is the angular frequency of the applied voltage e, and j is the square root of -1. Using the impedance z given by equation (1), the output voltage V₀ is given by the equation:

and the magnitude of the output voltage is given by the equation:

A resonant effect occurs when the reactance of the inductor L and capacitor C are equal in absolute value. The frequency at which this occurs is known as the resonant frequency, and is given by the equation:

where L is the inductance in henries, c is the capacitance in farads and is an angular frequency in radians per second. A quality factor, or Q, of a resonant circuit is generally defined by the equation:

* R (5) When the angular frequency of the signal applied to the resonant circuit is close to the resonant frequency, ¾ , the output voltage is given by the equation: i¾i = pH (6) where z can be expressed in terms of the quality factor, Q, and the resonant, -^'-ν , and applied, , frequencies as:

(V)

Equation (6) shows that higher Q provides a higher output voltage magnitude, The above analysis shows that the magnitude of the output voltage, is related to magnitude and frequency of the applied voltage, M , in a predictable fashion. Further, when the frequency of the applied voltage is fixed, the magnitude of is linearly related to the magnitude of the applied voltage, .

[0028] Ignition of the lamp 120 of Figure 2 occurs when an arc is formed between the lamp terminals, generally shown as 214 and 224 in Figure 2. To achieve ignition a high voltage is applied across the electrodes 214, 224 of the lamp 120. The high voltage ionizes gas contained within the lamp 120 thereby allowing an arc to form between the lamp electrodes 214, 224. The ignition voltage required to initiate an arc is often as much as approximately 3 to 5 Kilovolts (KV). In typical multi-stage lamp drivers, such as the exemplary lamp driver 100 described above, the voltage 110 applied to the inverter stage 114 can be significantly lower than the required ignition voltage, often in the range of less than a few hundred volts. To achieve the required ignition voltage, an AC inverter voltage is applied to the resonant circuit 200 with a frequency at or close to the resonant frequency M of the circuit. As shown above, a resonant circuit 222 with sufficiently high Q will provide a gain at its resonant frequency that will achieve an adequately high lamp voltage, Wi_amp, to achieve ignition of the lamp 120. An examination of equation (6) shows that increasing the quality factor Q of a resonant circuit proportionately increases the gain of the circuit 222 at its resonant frequency. Further, equation (6) shows that the gain of the resonant circuit 222 is also very sensitive to the applied frequency such that varying the applied frequency, either to a higher frequency or lower frequency, causes the gain of the resonant circuit 222 to fall significantly from its peak gain which is achieved at the resonant frequency.

[0029] Manufacturing tolerances of circuit components, such as the inductor 206 and the capacitor 208 of the resonant circuit 222 shown in Figure 2 can result in variation of the resonant frequency. These variations can often be large enough to prevent ignition of the lamp 120 when the applied ignition frequency is set to a nominal design frequency. The nominal design frequency is the resonant frequency calculated using the nominal or design values of inductance and capacitance and ignoring any manufacturing tolerances. Thus, manufacturing lamp drives that can achieve reliable ignition can be difficult and add cost. In addition to manufacturing tolerances of the components, other factors can cause variations of the actual resonant frequency, such as for example, installing the lamp remotely from the driver circuit. Thus achieving reliable ignition can be problematic and often leads to complex control circuits and/or shorter lamp life.

[0030] The aspects of the disclosed embodiments address the ignition problem by identifying an appropriate ignition frequency immediately before each ignition attempt. Referring to Figure 4, a flowchart illustrating a discovery process flow 400 incorporating aspects of the disclosed embodiments is illustrated. In one embodiment, the discovery process flow 400 shown in Figure 4 can be used for discovering an appropriate ignition frequency for the lamp drive 100 shown in Figure 1 and may be implemented by the controller 122 of the exemplary lamp drive 100. Initially, the regulated DC power 110 used to supply the inverter 114 is regulated 402 at a low level input voltage that will not cause ignition of the lamp 120. This low level voltage is referred to herein as a discovery voltage, and can be determined by considering the maximum gain of the resonant circuit 222 of Figure 2 and the minimum ignition voltage of the lamp 120. The discovery voltage is selected such that applying the maximum gain of the resonant circuit 222 to the discovery voltage yields a voltage that is below the lowest ignition voltage of the lamp 120.

[0031] A frequency is selected 404 from a predetermined list of frequencies. In one embodiment, the first frequency in the list is selected to be above a resonant frequency of the resonant circuit 222. Each subsequent frequency in the list of frequencies is incrementally less than the previous frequency. Next, the lamp voltage, Vout, is determined 406. The lamp voltage Vout is determined or checked by operating the inverter 114 at the selected frequency in step 404 and measuring the resulting lamp voltage. The resulting lamp voltage is then compared to a predetermined discovery threshold voltage to determine 408 if the lamp voltage has reached the predetermined threshold. The predetermined discovery threshold voltage can be determined from the minimum voltage necessary for reliable ignition of the lamp 120, the gain relationship of the resonant circuit 222 described above and illustrated in Equation (6), and the difference between the discovery voltage and an operating voltage of the regulated DC power 110. If it is determined 408 that Vout is not greater 410 than the discovery threshold voltage, the next frequency is selected 404 and Vout is again checked 406. In one embodiment, each frequency in the list is less than the previous frequency and is closer to the resonant frequency of the resonant circuit 222 so it will produce an incrementally greater Vout. Once it is determined 408 that Vout exceeds 412 the discovery threshold voltage, the operating frequency of the inverter is set or fixed 414 as the currently selected frequency, referred to as the ignition frequency. The voltage of the regulated DC power is then increased 416 to its ignition level to provide a high level input to the lamp 120. The inverter 200 can then be operated to apply a short burst of AC power to the resonant circuit 222 at the ignition frequency, which was set at 414, to cause ignition 418 of the lamp 120. Alternatively, the procedure 400 can be begun using a frequency that is below the resonant frequency, then each subsequent frequency will be incrementally higher than the previous frequency, thereby approaching the ignition frequency from below the resonant frequency. In the exemplary embodiment shown in Figure 4, a next frequency is selected 404 from a predetermined list of frequencies. Alternatively, in certain embodiments it is advantageous to compute the next frequency by applying an algorithm to the currently selected frequency. An example of such an algorithm would be to compute the next frequency to use by subtracting (or by adding when approaching the resonant frequency from below) a frequency increment from the present frequency to find the next frequency.

[0032] Operation of the discovery and ignition process 400 is illustrated in the graph 500 shown in Figure 5. Graph 500 shows voltage on the horizontal axis and time on the vertical axis. The voltage of the regulated DC power, which is provided to the inverter 222 of Figure 2 as its input power, is shown by the generally upper curve indicated with numeral 502, and Vout, which is also the lamp voltage, is shown by the generally lower curve 504. Note that a different vertical scale is used for the two curves 502, 504. The operating voltage 506 of the regulated DC power is around 300 volts and the ignition voltage peak 508 exceeds 3 kilovolts. With respect to the process flow 400 of Figure 4, the regulated DC power is set 402 to a discovery voltage at time 510 while the inverter 200 remains off. Next a first frequency is selected 404. The inverter 200 is then operated to apply an AC signal at the selected frequency 512 to the resonant circuit 222 and the resulting lamp voltage, Vout, is determined or measured 406. Vout is compared 408 to the discovery threshold, and the frequency selection step 404 and check Vout step 406 are repeated. In the example of Figure 5, this is repeated a total of eleven times as indicated by 514, until Vout exceeds the discovery threshold 516. It should be noted that the number of times the frequency selection 404 and check Vout 406 steps are repeated may vary each time the lamp 120 is started. The ignition frequency is then set 412 to the discovered frequency. The voltage of the regulated DC power 110 is then set to an ignition level 518, which is generally greater than the discovery voltage. The inverter 114 of Figure 1 is then operated to apply a short burst of AC voltage to the resonant circuit 222 to produce a sufficient voltage 508 to ignite the lamp 120.

[0033] The ignition frequency discovery and ignition process 400 disclosed herein may also be advantageously employed in other lamp drive topologies, such as for example, a two stage lamp drive or other lamp drive topologies. A two stage lamp drive generally includes a first stage to convert an AC line voltage to a DC voltage and typically incorporates EMI filtering and PFC into the first stage. The second stage generally includes an inverter and a resonant circuit coupled to the lamp. The discovery and ignition process 400 may be advantageously applied to any of these circuits to provide reliable ignition even when the resonant frequency necessary for ignition is unknown.

[0034] Thus, while there have been shown, described and pointed out, fundamental novel features of the invention as applied to the exemplary embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. Moreover, it is expressly intended that all combinations of those elements, which perform substantially the same function in substantially the same way to achieve the same results, are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

CLAIMS What is claimed is:

1. A method for igniting a lamp, the method comprising:

using a microcontroller to control a voltage produced by a DC power regulator and operate a resonant inverter at a lamp ignition frequency and lamp ignition voltage to ignite the lamp,

wherein the microcontroller is configured to:

control the DC power regulator to apply a discovery voltage to the resonant inverter, the discovery voltage being less than a lamp operating voltage and configured to produce a lamp voltage that is below the lamp ignition voltage, the lamp operating voltage being configured to produce a lamp voltage that is above the lamp ignition voltage;

select a first inverter operating frequency as an operating frequency of the resonant inverter;

operate the resonant inverter at the discovery voltage and selected operating frequency to generate a lamp voltage;

measure a magnitude of the generated lamp voltage;

compare the measured magnitude to a predetermined discovery threshold voltage; and

if the measured magnitude of the generated lamp voltage is not greater than the discovery threshold voltage, select a next inverter operating frequency as the operating frequency of the resonant inverter and repeat the operate, measure, and compare steps; if the measured magnitude of the lamp voltage is greater than the discovery threshold voltage:

set the selected operating frequency as the lamp ignition frequency of the resonant inverter;

set the DC power regulator to apply the operating voltage of the lamp to the resonant inverter; and operate the inverter at the operating voltage of the lamp and set lamp ignition frequency to ignite the lamp.

2. The method of claim 1 , wherein selecting the first inverter operating frequency comprises selecting an inverter operating frequency from a predetermined list of operating frequencies, and wherein selecting the next inverter operating frequency comprises selecting an inverter operating frequency from the predetermined list of operating frequencies.

3. The method of claim 2, wherein a first frequency in the predetermined list of operating frequencies is greater than a resonant frequency of the resonant inverter, and each subsequent frequency in the list of operating frequencies is lower than a previous frequency in the list of operating frequencies.

4. The method of claim 2, wherein a first frequency in the predetermined list of operating frequencies is less than a resonant frequency of the resonant inverter, and each subsequent frequency in the list of operating frequencies is greater than a previous frequency in the list of operating frequencies.

5. The method of claim 1, wherein selecting the first inverter operating frequency comprises selecting an inverter operating frequency that is greater than a resonant frequency of the resonant inverter, and wherein selecting the next inverter operating frequency comprises reducing the selected inverter operating frequency by a predetermined amount.

6. The method of claim 1 , wherein selecting the first inverter operating frequency comprises selecting an inverter operating frequency that is lower than a resonant frequency of the resonant inverter, and wherein selecting the next inverter operating frequency comprises increasing the selected inverter operating frequency by a predetermined amount.

7. The method of claim 1, wherein the lamp ignition voltage is applied to the lamp for a predetermined period of time.

8. The method of claim 1, wherein the lamp comprises a high intensity discharge lamp.

9. The method of claim 1, wherein using a microcontroller to control a voltage produced by a regulated DC power regulator further comprises:

using an AC to DC converter to receive an AC line power and produce a DC power; and,

providing the DC power to the DC power regulator,

wherein the AC to DC converter comprises power factor correction.

10. An apparatus for igniting a lamp, the apparatus comprising: a DC to DC regulator configured to receive a first DC power and produce a regulated DC power;

an inverter, the inverter configured to receive the regulated DC power and produce an AC inverter power;

a resonant circuit coupled to the AC inverter power, the resonant circuit configured to receive the AC inverter power and produce a lamp voltage; and

a microcontroller coupled to the DC to DC regulator and to the inverter, the

microcontroller being configured to control a voltage of the regulated DC power and a frequency of the AC inverter power,

wherein the microcontroller is further configured to:

control the regulated DC power at a discovery voltage, the discovery voltage being less than an operating voltage of the lamp and configured to produce a lamp voltage that is below an ignition voltage of the lamp, the operating voltage of the lamp being configured to produce a lamp voltage that is above the ignition voltage of the lamp;

select a first inverter frequency as the frequency of the AC inverter power;

operate the inverter at the selected inverter frequency;

measure a magnitude of the lamp voltage produced by operation of the inverter at the discovery voltage and selected inverter frequency;

if the measured magnitude of the lamp voltage is not greater than the discovery threshold voltage, select a next inverter frequency as the frequency of the AC inverter power and repeat the operate, measure, and compare steps; or if the measured magnitude of the lamp voltage is greater than the discovery threshold voltage:

set a lamp ignition frequency to the selected inverter frequency;

control the regulated DC power at the operating voltage of the lamp; and operate the inverter at the lamp ignition frequency and operating voltage to ignite the lamp.

11. The apparatus according to claim 10, wherein the inverter comprises an H-bridge inverter.

12. The apparatus according to claim 10, wherein the inverter comprises a half bridge inverter.

13. The apparatus according to claim 10, wherein selecting the first inverter frequency comprises selecting a first frequency from a predetermined list of frequencies, and wherein selecting the next inverter frequency comprises selecting a next frequency from the predetermined list of frequencies.

14. The apparatus according to claim 13, wherein the first frequency in the predetermined list of operating frequencies is greater than a resonant frequency of the resonant inverter.

15. The apparatus according to claim 14, wherein each frequency in the predetermined list of operating frequencies is lower than a previous frequency in the predetermined list of operating frequencies.

16. The apparatus according to claim 13, wherein the first frequency in the

predetermined list of operating frequencies is less than a resonant frequency of the resonant inverter.

17. The apparatus according to claim 16, wherein each subsequent frequency in the predetermined list of operating frequencies is greater than a previous frequency in the predetermined list of operating frequencies.

18. The apparatus according to claim 10, wherein selecting the first inverter frequency comprises selecting a frequency of the AC inverter power that is greater than a resonant frequency of the resonant circuit, and selecting the next inverter frequency comprises using an algorithm to determine a next frequency of the AC inverter power that is less than a previous selected frequency.

19. The apparatus according to claim 10, wherein selecting the first inverter frequency comprises selecting a frequency of the AC inverter power that is lower than a resonant frequency of the resonant circuit, and selecting the next inverter frequency comprises using an algorithm to determine a next frequency of the AC inverter power that is greater than a previous selected frequency.

20. The apparatus according to claim 10, wherein the applying a lamp ignition voltage to the lamp comprises applying the lamp ignition voltage to the lamp for a predetermined period of time.