WO2012090112A1 - Circuit arrangement - Google Patents
Circuit arrangement Download PDFInfo
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- WO2012090112A1 WO2012090112A1 PCT/IB2011/055762 IB2011055762W WO2012090112A1 WO 2012090112 A1 WO2012090112 A1 WO 2012090112A1 IB 2011055762 W IB2011055762 W IB 2011055762W WO 2012090112 A1 WO2012090112 A1 WO 2012090112A1
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- WIPO (PCT)
- Prior art keywords
- current
- switching element
- terminal
- voltage
- half period
- Prior art date
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Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/288—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without preheating electrodes, e.g. for high-intensity discharge lamps, high-pressure mercury or sodium lamps or low-pressure sodium lamps
- H05B41/2881—Load circuits; Control thereof
- H05B41/2882—Load circuits; Control thereof the control resulting from an action on the static converter
- H05B41/2883—Load circuits; Control thereof the control resulting from an action on the static converter the controlled element being a DC/AC converter in the final stage, e.g. by harmonic mode starting
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/288—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without preheating electrodes, e.g. for high-intensity discharge lamps, high-pressure mercury or sodium lamps or low-pressure sodium lamps
- H05B41/2885—Static converters especially adapted therefor; Control thereof
- H05B41/2887—Static converters especially adapted therefor; Control thereof characterised by a controllable bridge in the final stage
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/288—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without preheating electrodes, e.g. for high-intensity discharge lamps, high-pressure mercury or sodium lamps or low-pressure sodium lamps
- H05B41/292—Arrangements for protecting lamps or circuits against abnormal operating conditions
- H05B41/2921—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions
- H05B41/2925—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions against abnormal lamp operating conditions
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
Definitions
- the invention relates to a circuit arrangement for operating a lamp equipped with an inverter comprising:
- a first series arrangement comprising a first switching element and a second switching element and connecting the input terminals
- a second series arrangement comprising a first capacitor and a second capacitor and connecting the input terminals
- a load circuit comprising a series arrangement of an inductive element and lamp connection terminals and connecting a first terminal of the first series arrangement between the first switching element and the second switching element with a second terminal of the second series arrangement between the first capacitor and the second capacitor,
- control circuit coupled to a first control electrode of the first switching element and a second control electrode of the second switching element, for controlling the conductive state of the first switching element and the second switching element so that a periodical current with frequency f flows through the load circuit.
- Such a circuit arrangement for supplying a lamp is often referred to as a half bridge and is generally known.
- the polarity of the periodical current that flows through the load circuit is changed twice during each period. Since the lamp is comprised in the load circuit, the polarity of the lamp current also changes twice during each period. At each polarity change, also referred to as commutation, the lamp has to be reignited. To prevent an interruption in the light output that is noticeable, this reignition has to be fast.
- the voltage present at the second terminal equals l/2Vin.
- the voltage across the load circuit that is available for reignition after each commutation also equals 1 ⁇ 2Vin.
- either the circuit arrangement or the lamp or both are asymmetrical to some extent.
- the lamp has a lower resistance for current in one polarity direction than for current in the other polarity direction, this will cause the voltage at the second terminal to be higher or lower than 1/2 Vin.
- the voltage that is available for reignition is lower than 1/2 Vin for one half of the half periods and higher than l/2Vin for the other half.
- reignition becomes problematic or even impossible resulting in flickering or even extinguishing of the lamp. This problem becomes more severe in particular when the lamp is dimmed.
- the electrode that must function as the cathode for the next half period of the current has a comparatively low temperature in case the lamp is dimmed and is not at thermionic emission temperature. As a consequence the voltage required to realize ignition is higher than for a lamp operated at full power.
- the invention aims to provide a circuit arrangement for operating a lamp wherein problems with reignition after commutation of the current are avoided to a large extent also in dimmed condition.
- a circuit arrangement as mentioned in the opening paragraph is therefore according to the invention characterized in that the control circuit is equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical current so that the average value of the voltage at the second terminal is maintained at l/2Vin.
- US6919696B2 discloses a circuit arrangement comprising a half bridge, wherein the voltage at the second terminal is controlled by adapting the duty cycle of the current, or in other words the duration of the first half period and the second half period is adjusted leaving the duration of a period unchanged.
- the time lapse within each period during which the current has a first polarity and the time lapse within each period during which the current has a second polarity are adjusted so that the voltage at the second terminal is maintained at l/2Vin.
- the shape of the current includes a current pulse meant to increase the electrode temperature directly before commutation (thereby improving the reignition behavior)
- adjusting of the duty cycle of the current may result in the commutation taking place before the current pulse is generated so that the favorable effect of the pulse is completely lost.
- the many measurements of voltages and currents that the control circuit needs to do to ensure proper operation of the circuit arrangement are often synchronized with the commutation.
- the duty cycle is variable the correct timing for doing these measurements becomes more complex.
- the light source formed by the circuit arrangement together with the lamp
- the duty cycle of the lamp current is often modulated for this communication purpose.
- adjusting the duty cycle to maintain the voltage at the second terminal at l/2Vin can interfere with the modulation so that communication by the light source becomes impossible.
- a circuit arrangement wherein a first diode is coupled between the first terminal and the first input terminal and wherein a second diode is coupled between the first terminal and the second input terminal, and wherein the control circuit comprises circuitry for alternately with frequency f controlling the inverter in a first operating state during each first half period and in a second operating state during each second half period and for in the first operating state rendering the second switching element non-conductive and rendering the first switching element alternately conductive and nonconductive at a frequency higher than f, and in the second operating state rendering the first switching element non-conductive and rendering the second switching element alternately conductive and nonconductive at a frequency higher than f.
- This way of operating a half bridge circuit is often referred to as "commutating forward". Commutating forward allows a very efficient operation of the circuit arrangement.
- the present invention is fully compatible with commutating forward operation.
- first and second diode may be implemented as discrete devices but may also be implemented as the internal body diodes of the switching elements.
- the control loop in a circuit arrangement according to the invention preferably decreases the current through the load circuit during the first half period of the current and increases the current during the second half period of the current when the voltage at the second terminal is higher than 1/2 Vin and the control loop preferably increases the current through the load circuit during the first half period of the square wave current and decreases the current during the second half period of the current when the voltage at the second terminal is lower than 1/2 Vin.
- Such a control loop was found to be comparatively simple and very effective. It has also been found that the control loop did not interfere with any of the other functions of the control circuit such as communication and performance of
- control loop it is also preferred to design the control loop so that the band width of the control loop is smaller than f. This design avoids unstable operation that could be caused by the control loop trying to compensate the ripple on the voltage at the second terminal that is caused by the commutation.
- FIG. 1 shows a schematic representation of a first embodiment of a circuit arrangement according to the invention
- Fig. 2 shows a schematic representation of a second embodiment of a circuit arrangement according to the invention
- Fig. 3 shows a schematic diagram illustrating a control loop comprised in the circuit arrangements shown in Fig. 1 and Fig. 2 for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical current so that the voltage at the second terminal is maintained at l/2Vin.
- reference numeral 1 indicates a circuit arrangement according to the invention.
- Kl and K2 are input terminals for connection to a supply voltage source supplying a DC voltage Vin.
- reference numeral I indicates the supply voltage source, which comprises a mains voltage source AC that is connected to a filter 2, said filter 2 being connected to a preconditioner 3 that is schematically represented as an up-converter comprising an inductor Lboost, a diode D and a switching element T.
- a supply voltage source such as schematically represented in Fig. 1 is well known in the art and will therefore not be discussed in detail.
- Output terminals (not shown) of supply voltage source I are connected to the input terminals Kl and K2.
- Reference number II indicates the inverter formed by a half bridge.
- Input terminals Kl and K2 are connected by a first series arrangement of switching elements Tl and T2.
- Switching element Tl forms a first switching element and is shunted by diode Dl
- switching element T2 forms a second switching element and is shunted by diode D2.
- Input terminals Kl and K2 are also connected by means of a second series arrangement of capacitor CI and capacitor C2.
- Capacitor CI forms a first capacitor and capacitor C2 forms a second capacitor.
- a first terminal N between first switching element T 1 and second switching element T2 is connected to a second terminal M between capacitors CI and C2 by means of a load circuit that comprises an inductor L arranged in series with respectively a first lamp connection terminal LK1, a lamp LA and a second lamp connection terminal LK2.
- the lamp LA in this embodiment is a high pressure discharge lamp and is shunted by a capacitor C R that is also part of the load circuit.
- CC is a control circuit for controlling the conductive state of switching element Tl and switching element T2 so that a periodical current with frequency f flows through the load circuit.
- a first and second output terminal of control circuit CC are respectively connected to a control electrode of the first switching element Tl and a control electrode of the second switching element T2.
- the control circuit CC is also equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical square wave current so that the voltage at the second terminal M is maintained at l/2Vin.
- an input terminal of the control circuit CC is connected to second terminal M.
- the supply voltage source I generates a DC voltage Vin out of an AC voltage supplied by the mains.
- This voltage Vin is present across the series arrangement of switching elements Tl and T2 and also across the series arrangement of capacitors CI and C2.
- the operation mode of the half bridge circuit that is formed by switching elements Tl and T2, capacitors CI and C2, the control circuit CC and the load circuit is "commutating forward".
- the control circuit alternately with frequency f controls the inverter in a first operating state during the first half period of the current and in a second operating state during a second half period of the current.
- the control circuit CC renders the second switching element non-conductive and renders the first switching element alternately conductive and nonconductive at a frequency f 1 higher than f.
- f is often chosen in the order of 100
- this first operating state control circuit CC renders the first switching element Tl conductive when the current through the load circuit equals first reference value. The current then increases until it reaches a second reference value. When this second predetermined reference value is reached, the first switching element is rendered non-conductive. As a consequence the current decreases until it equals the first reference value so that the first switching element T 1 is rendered conductive again and the cycle is repeated. In this way a current is generated that is a DC-current with a constant amplitude with an AC-current with a very small amplitude superimposed on it. This very small amplitude corresponds to the fact that the two reference values are chosen very close to each other. For all practical purposes this current can be considered as a DC current with a constant amplitude and a first polarity.
- the control circuit renders the first switching element T2 non-conductive and renders the second switching element alternately conductive and nonconductive at a frequency higher than f.
- a current is generated of a second polarity that is opposite to the first polarity of the current generated during the first operating state.
- the amplitude of the current is maintained between two reference values chosen close to each other so that again the resulting current can for all practical purposes be considered as a DC current with a constant amplitude.
- the current resulting from alternately operating in the first and in the second operating state has a square wave shape.
- the control loop comprised in the control circuit CC adjusts the value of the two reference values at the beginning of each half period of the current in dependency of the voltage present at second terminal M averaged over a current period.
- the reference values are decreased since the current flows through the load circuit to the second terminal M so that during this half period the voltage at M is caused to increase by the current.
- the reference values are increased since the current through the load circuit flows away from second terminal M so that during this half period the voltage at M is caused to decrease by the current.
- the reference values are increased since the current flows through the load circuit to second terminal M so that during this half period the voltage at M is caused to increase by the current.
- the reference values are decreased since the current through the load circuit flows away from second terminal M so that during this half period the voltage at M is caused to decrease by the current.
- the control loop maintains the difference between the reference values at a constant value, only one of the reference values needs to be adjusted since the value of the other will automatically be adapted.
- the voltage across the load circuit In the first operating state when switching element T 1 is conductive, the voltage across the load circuit equals the voltage at input terminal Kl minus the voltage at second terminal M. In the second operating state when switching element T2 is conductive, the voltage across the load circuit equals the voltage at second terminal M minus the voltage at second input terminal K2. Since the control loop maintains the average voltage at second terminal M at l/2Vin, the voltage across the load circuit is l/2Vin both in the first as well as in the second operating state. During reignition, at the beginning of each half period of the current the voltage across the lamp is also approximately 1/2 Vin.
- Enough voltage is thus available for the lamp to reignite at the beginning of each half period even in dimmed operation, so that stable lamp operation is achieved and dimming can be realized to a lower light output than is possible in a circuit without a control loop for controlling the voltage at second terminal M.
- circuit parts and components corresponding to circuit parts and components of the circuit arrangement shown in Fig. 1 are labeled with the same reference symbols.
- Input terminals Kl and K2 are connected by a first series arrangement of switching element Tl, inductive element LI, inductive element L2 and switching element T2. Terminal N between inductive element LI and inductive element L2 forms a first terminal in this embodiment.
- a terminal between second switching element T2 and inductive element L2 is connected to input terminal Kl by means of a first diode Dl.
- a terminal between first switching element Tl and inductive element LI is connected to the second input terminal K2 by means of a second diode D2.
- Input terminals Kl and K2 are also connected by a second series arrangement of a first capacitor CI and a second capacitor C2.
- a common terminal M between the first capacitor C 1 and the second capacitor C2 forms a second terminal in this embodiment.
- a series arrangement of inductive element L, a first lamp connection terminal LK1, a high pressure discharge lamp LA and a second lamp connection terminal LK2 connects first terminal N with second terminal M.
- This series arrangement together with a capacitor Cr forms a load circuit.
- First terminal N is connected with the first input terminal Kl by means of a capacitor C3 and is also connected to the second input terminal K2 by means of a capacitor C4.
- CC is a control circuit for controlling the conductive state of switching element Tl and switching element T2 so that a periodical square wave shaped current with frequency f flows through the load circuit.
- a first and second output terminal of control circuit CC are therefore respectively connected to a control electrode of the first switching element Tl and a control electrode of the second switching element T2.
- the control circuit CC is also equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical square wave current so that the voltage at the second terminal M is maintained at l/2Vin. To this end an input terminal of the control circuit CC is connected to second terminal
- a supply voltage source such as the one shown in Fig. 1 supplies a DC voltage Vin, that is present across the first series arrangement and also across the second series arrangement of capacitors CI and C2.
- the operation mode of the circuit arrangement shown in Fig. 2 is "commutating forward".
- the control circuit alternately with frequency f controls the inverter in a first operating state during the first half period of the current and in a second operating state during a second half period of the current. In the first operating state the control circuit CC renders the second switching element T2 non- conductive and renders the first switching element T 1 alternately conductive and
- f is often chosen in the order of 100 Hz and fl in the order of 100 kHz.
- CC renders the first switching element Tl conductive when the current through the load circuit equals a first reference value that is chosen equal to zero. The current then increases until it reaches a second reference value. When this second reference value is reached, the first switching element T 1 is rendered non-conductive. As a consequence the current decreases until it equals zero again so that the first switching element Tl is rendered conductive again and the cycle is repeated. In this way a current flowing through inductive element LI is generated that is a triangularly shaped current.
- control circuit In the second operating state the control circuit renders the first switching element T2 non-conductive and renders the second switching element T2 alternately conductive and nonconductive at a frequency f 1 higher than f.
- control circuit CC renders the second switching element Tl conductive when the current through the load circuit equals the first reference value that is chosen equal to zero. The current then increases until it reaches the second reference value. When this second reference value is reached, the second switching element T2 is rendered non-conductive. As a consequence the current decreases until it equals zero again so that the second switching element T2 is rendered conductive again and the cycle is repeated. In this way a current flowing through inductive element L2 is generated that is a triangularly shaped current.
- the current through the load circuit and the lamp is a DC current with a substantially constant amplitude, since the filter is dimensioned so that only a high frequency ripple with a very small amplitude is present in the current.
- This current has opposite polarities during the first operating state (the first half period of the current) and during the second operating state (the second half period of the current).
- the current flowing through the lamp is thus a square wave shaped AC current.
- the control loop comprised in the control circuit CC adjusts the value of the second reference value at the beginning of each half period of the current in dependency of the voltage present at second terminal M averaged over a current period.
- the second predetermined value is decreased since the current flows to the second terminal M so that during this half period the voltage at M is caused to increase by the current.
- the second predetermined value is increased since the current flows away from second terminal M so that during this half period the voltage at M is caused to decrease by the current.
- Both the circuit arrangement shown in Fig. 1 as well as the circuit arrangement shown in Fig. 2 behave to a large extent as a current source since in both circuit arrangements the switching moments are triggered by a current level. This current source behavior is favorable for dimming.
- An important advantage of allowing the high frequency current in LI and L2 to become zero is that the switching losses are substantially reduced since the switching element is rendered conductive while the current through is zero. These low switching losses allow the frequency of the current in LI and L2 comparatively high (as already mentioned in the order Of 100 kHz). This high frequency allows the use of inductors that have a low inductance and small dimensions. A comparatively small circuit arrangement is thus possible. However, in the circuit arrangement shown in Fig.
- the wave shape of the current in the load circuit generated by a circuit arrangement shown in Fig. 1 or Fig. 2 is not necessarily exactly a square wave shaped current.
- the current can be controlled to differ from a square wave shape.
- the current may be so controlled that it has the shape of a square wave with a short current pulse superimposed on it directly before each commutation.
- Fig. 3 illustrates that the voltage Vin between input terminals Kl and K2 and the voltage V M present at second terminal M is measured and that a signal representing
- 1/2 Vin - V M is generated and is present at the input terminal of an integrator.
- the integrator generates a signal that represents the value of l/2Vin - V M averaged over a period of the current through the load circuit.
- This signal present at the output of the integrator is sampled by a sample and hold circuit with a frequency f.
- the sampled value is multiplied with a square wave shaped signal with frequency f that is in phase with the current through the load circuit and has a unit amplitude.
- a signal is generated that has a square wave shape, has a frequency equal to f, is in phase with the current through the load circuit and has an amplitude that equals the output signal of the integrator.
- This signal is present at the output terminal of the multiplier "product” and is added to a signal Iref that corresponds to the second reference value.
- switching element Tl is switched off when the current has increased to this value in the first operating state and switching element T2 is switched off when the current has increased to this value in the second operating state.
- This second reference value is for instance generated by a power control loop that is also part of the circuit arrangement.
- the addition of the signal present at the output of the multiplier "product" to the second reference value (Iref) results in a modulation of the signal Iref in the form of an increase of the signal Iref during half a period of the current and an decrease of the signal Iref during the next half a period of the current.
- the modulated signal Iref is used to control the current by functioning as the second reference value. Since the modulation decreases the second reference value during half a period and increases the second reference value during the next half a period by the same amount, the average amplitude of the current over a period thus remains constant so that the power supplied to the lamp does not change, but the amplitude in subsequent half periods of the current differs. The result is that the average value of the voltage V M at the second terminal is maintained at a value that substantially equals 1/2 Vin.
- the first reference value can be controlled at a value that differs from the second reference value by a constant C, so that only the second reference value needs to be adjusted by the power control loop and the control loop for maintaining the average value of the voltage at second terminal M at l/2Vin.
- the first reference value then automatically adjusts to a value that is equals the second reference value minus C. In case of a circuit arrangement according to Fig. 2 the first reference value is zero.
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Abstract
A half bridge circuit is operated in the commutating forward mode. A control loop monitors the voltage of a terminal between the two half bridge capacitors and adjusts the current level in each half period so that the voltage at the terminal remains equal to half the rail voltage. A dependable reignition of the lamp at the beginning of each half period of the lamp current is obtained resulting in stable operation even when the lamp is dimmed.
Description
CIRCUIT ARRANGEMENT
FIELD OF THE INVENTION
The invention relates to a circuit arrangement for operating a lamp equipped with an inverter comprising:
a first input terminal and a second input terminal for connection to a supply voltage source supplying a DC voltage Vin,
a first series arrangement comprising a first switching element and a second switching element and connecting the input terminals,
a second series arrangement comprising a first capacitor and a second capacitor and connecting the input terminals,
a load circuit comprising a series arrangement of an inductive element and lamp connection terminals and connecting a first terminal of the first series arrangement between the first switching element and the second switching element with a second terminal of the second series arrangement between the first capacitor and the second capacitor,
a control circuit, coupled to a first control electrode of the first switching element and a second control electrode of the second switching element, for controlling the conductive state of the first switching element and the second switching element so that a periodical current with frequency f flows through the load circuit.
BACKGROUND OF THE INVENTION
Such a circuit arrangement for supplying a lamp is often referred to as a half bridge and is generally known. The polarity of the periodical current that flows through the load circuit is changed twice during each period. Since the lamp is comprised in the load circuit, the polarity of the lamp current also changes twice during each period. At each polarity change, also referred to as commutation, the lamp has to be reignited. To prevent an
interruption in the light output that is noticeable, this reignition has to be fast. In case both the lamp and the inverter are symmetrical in the sense that the impedance of the inverter for currents of each polarity is identical, the voltage present at the second terminal equals l/2Vin. As a consequence, the voltage across the load circuit that is available for reignition after each commutation also equals ½Vin.
However, in practice either the circuit arrangement or the lamp or both are asymmetrical to some extent. In case the for instance the lamp has a lower resistance for current in one polarity direction than for current in the other polarity direction, this will cause the voltage at the second terminal to be higher or lower than 1/2 Vin. As a consequence the voltage that is available for reignition is lower than 1/2 Vin for one half of the half periods and higher than l/2Vin for the other half. At the beginning of those half periods in which the voltage available is substantially less than 1/2 Vin, reignition becomes problematic or even impossible resulting in flickering or even extinguishing of the lamp. This problem becomes more severe in particular when the lamp is dimmed. The electrode that must function as the cathode for the next half period of the current has a comparatively low temperature in case the lamp is dimmed and is not at thermionic emission temperature. As a consequence the voltage required to realize ignition is higher than for a lamp operated at full power.
SUMMARY OF THE INVENTION
The invention aims to provide a circuit arrangement for operating a lamp wherein problems with reignition after commutation of the current are avoided to a large extent also in dimmed condition.
A circuit arrangement as mentioned in the opening paragraph is therefore according to the invention characterized in that the control circuit is equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical current so that the average value of the voltage at the second terminal is maintained at l/2Vin.
Because the control loop maintains the voltage at the second terminal at
1/2 Vin, the voltage that is available for reignition after a commutation is always equal to
1/2 Vin. It has been found that a circuit arrangement according to the invention operates the lamp in a stable way, even when the lamp is dimmed.
It be mentioned that US6919696B2 discloses a circuit arrangement comprising a half bridge, wherein the voltage at the second terminal is controlled by adapting the duty cycle of the current, or in other words the duration of the first half period and the second half period is adjusted leaving the duration of a period unchanged. The time lapse within each period during which the current has a first polarity and the time lapse within each period during which the current has a second polarity are adjusted so that the voltage at the second terminal is maintained at l/2Vin. Although the reignition problem is effectively solved in the circuitry disclosed in US6919696B2, adjusting the duty cycle of the current is associated with severe disadvantages. For instance in case the shape of the current includes a current pulse meant to increase the electrode temperature directly before commutation (thereby improving the reignition behavior), adjusting of the duty cycle of the current may result in the commutation taking place before the current pulse is generated so that the favorable effect of the pulse is completely lost. Furthermore in practice the many measurements of voltages and currents that the control circuit needs to do to ensure proper operation of the circuit arrangement are often synchronized with the commutation. In case the duty cycle is variable the correct timing for doing these measurements becomes more complex. Moreover, in case the light source (formed by the circuit arrangement together with the lamp) is also used for communication for commissioning or other purposes, the duty cycle of the lamp current is often modulated for this communication purpose. In this case adjusting the duty cycle to maintain the voltage at the second terminal at l/2Vin can interfere with the modulation so that communication by the light source becomes impossible. These important disadvantages of the prior art are avoided in a circuit arrangement according to the invention.
Good results have been found for a circuit arrangement according to the invention wherein a first diode is coupled between the first terminal and the first input terminal and wherein a second diode is coupled between the first terminal and the second input terminal, and wherein the control circuit comprises circuitry for alternately with frequency f controlling the inverter in a first operating state during each first half period and in a second operating state during each second half period and for in the first operating state
rendering the second switching element non-conductive and rendering the first switching element alternately conductive and nonconductive at a frequency higher than f, and in the second operating state rendering the first switching element non-conductive and rendering the second switching element alternately conductive and nonconductive at a frequency higher than f. This way of operating a half bridge circuit is often referred to as "commutating forward". Commutating forward allows a very efficient operation of the circuit arrangement. The present invention is fully compatible with commutating forward operation.
It be remarked that the first and second diode may be implemented as discrete devices but may also be implemented as the internal body diodes of the switching elements.
The control loop in a circuit arrangement according to the invention preferably decreases the current through the load circuit during the first half period of the current and increases the current during the second half period of the current when the voltage at the second terminal is higher than 1/2 Vin and the control loop preferably increases the current through the load circuit during the first half period of the square wave current and decreases the current during the second half period of the current when the voltage at the second terminal is lower than 1/2 Vin. Such a control loop was found to be comparatively simple and very effective. It has also been found that the control loop did not interfere with any of the other functions of the control circuit such as communication and performance of
measurements.
It is also preferred to design the control loop so that the band width of the control loop is smaller than f. This design avoids unstable operation that could be caused by the control loop trying to compensate the ripple on the voltage at the second terminal that is caused by the commutation.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of a circuit arrangement according to the invention will be further explained making use of a drawing.
In the drawing Fig. 1 shows a schematic representation of a first embodiment of a circuit arrangement according to the invention;
Fig. 2 shows a schematic representation of a second embodiment of a circuit arrangement according to the invention, and
Fig. 3 shows a schematic diagram illustrating a control loop comprised in the circuit arrangements shown in Fig. 1 and Fig. 2 for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical current so that the voltage at the second terminal is maintained at l/2Vin.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In Fig. 1 reference numeral 1 indicates a circuit arrangement according to the invention. Kl and K2 are input terminals for connection to a supply voltage source supplying a DC voltage Vin. In Fig. 1 reference numeral I indicates the supply voltage source, which comprises a mains voltage source AC that is connected to a filter 2, said filter 2 being connected to a preconditioner 3 that is schematically represented as an up-converter comprising an inductor Lboost, a diode D and a switching element T. A supply voltage source such as schematically represented in Fig. 1 is well known in the art and will therefore not be discussed in detail. Output terminals (not shown) of supply voltage source I are connected to the input terminals Kl and K2.
Reference number II indicates the inverter formed by a half bridge. Input terminals Kl and K2 are connected by a first series arrangement of switching elements Tl and T2. Switching element Tl forms a first switching element and is shunted by diode Dl and switching element T2 forms a second switching element and is shunted by diode D2. Input terminals Kl and K2 are also connected by means of a second series arrangement of capacitor CI and capacitor C2. Capacitor CI forms a first capacitor and capacitor C2 forms a second capacitor. A first terminal N between first switching element T 1 and second switching element T2 is connected to a second terminal M between capacitors CI and C2 by means of a load circuit that comprises an inductor L arranged in series with respectively a first lamp connection terminal LK1, a lamp LA and a second lamp connection terminal LK2. The lamp LA in this embodiment is a high pressure discharge lamp and is shunted by a capacitor CRthat is also part of the load circuit.
CC is a control circuit for controlling the conductive state of switching element Tl and switching element T2 so that a periodical current with frequency f flows through the load circuit. In practice it is often desirable to control the switching elements in such a way that a periodical square wave shaped AC current is generated, it is emphasized though that a circuit arrangement according to the invention can generate many other periodical current shapes. In the following it will be assumed that the current has a square wave shape. A first and second output terminal of control circuit CC are respectively connected to a control electrode of the first switching element Tl and a control electrode of the second switching element T2. The control circuit CC is also equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical square wave current so that the voltage at the second terminal M is maintained at l/2Vin. To this end an input terminal of the control circuit CC is connected to second terminal M.
The operation of the circuit arrangement shown in Fig. 1 is as follows.
During operation the supply voltage source I generates a DC voltage Vin out of an AC voltage supplied by the mains. This voltage Vin is present across the series arrangement of switching elements Tl and T2 and also across the series arrangement of capacitors CI and C2. The operation mode of the half bridge circuit that is formed by switching elements Tl and T2, capacitors CI and C2, the control circuit CC and the load circuit is "commutating forward". The control circuit alternately with frequency f controls the inverter in a first operating state during the first half period of the current and in a second operating state during a second half period of the current. In the first operating state the control circuit CC renders the second switching element non-conductive and renders the first switching element alternately conductive and nonconductive at a frequency f 1 higher than f. In practice for a circuit arrangement as shown in Fig. 1 f is often chosen in the order of 100
Hz and fl in the order of 10 kHz. During this first operating state control circuit CC renders the first switching element Tl conductive when the current through the load circuit equals first reference value. The current then increases until it reaches a second reference value. When this second predetermined reference value is reached, the first switching element is rendered non-conductive. As a consequence the current decreases until it equals the first
reference value so that the first switching element T 1 is rendered conductive again and the cycle is repeated. In this way a current is generated that is a DC-current with a constant amplitude with an AC-current with a very small amplitude superimposed on it. This very small amplitude corresponds to the fact that the two reference values are chosen very close to each other. For all practical purposes this current can be considered as a DC current with a constant amplitude and a first polarity.
In the second operating state the control circuit renders the first switching element T2 non-conductive and renders the second switching element alternately conductive and nonconductive at a frequency higher than f. In this second operating state a current is generated of a second polarity that is opposite to the first polarity of the current generated during the first operating state. Also in the second operating state the amplitude of the current is maintained between two reference values chosen close to each other so that again the resulting current can for all practical purposes be considered as a DC current with a constant amplitude.
The current resulting from alternately operating in the first and in the second operating state has a square wave shape.
The control loop comprised in the control circuit CC adjusts the value of the two reference values at the beginning of each half period of the current in dependency of the voltage present at second terminal M averaged over a current period. At the beginning of a half period during which the half bridge is operated in the first operating state and the average voltage at M is higher than 1/2 Vin, the reference values are decreased since the current flows through the load circuit to the second terminal M so that during this half period the voltage at M is caused to increase by the current. At the beginning of a half period during which the half bridge is operated in the second operating state and the average voltage at M is higher than l/2Vin, the reference values are increased since the current through the load circuit flows away from second terminal M so that during this half period the voltage at M is caused to decrease by the current.
At the beginning of a half period during which the half bridge is operated in the first operating state and the average voltage at M is lower than 1/2 Vin, the reference values are increased since the current flows through the load circuit to second terminal M so that
during this half period the voltage at M is caused to increase by the current. At the beginning of a half period during which the half bridge is operated in the second operating state and the average voltage at M is lower than l/2Vin, the reference values are decreased since the current through the load circuit flows away from second terminal M so that during this half period the voltage at M is caused to decrease by the current. In case the control loop maintains the difference between the reference values at a constant value, only one of the reference values needs to be adjusted since the value of the other will automatically be adapted.
In the first operating state when switching element T 1 is conductive, the voltage across the load circuit equals the voltage at input terminal Kl minus the voltage at second terminal M. In the second operating state when switching element T2 is conductive, the voltage across the load circuit equals the voltage at second terminal M minus the voltage at second input terminal K2. Since the control loop maintains the average voltage at second terminal M at l/2Vin, the voltage across the load circuit is l/2Vin both in the first as well as in the second operating state. During reignition, at the beginning of each half period of the current the voltage across the lamp is also approximately 1/2 Vin. Enough voltage is thus available for the lamp to reignite at the beginning of each half period even in dimmed operation, so that stable lamp operation is achieved and dimming can be realized to a lower light output than is possible in a circuit without a control loop for controlling the voltage at second terminal M.
In Fig. 2 circuit parts and components corresponding to circuit parts and components of the circuit arrangement shown in Fig. 1 are labeled with the same reference symbols.
Input terminals Kl and K2 are connected by a first series arrangement of switching element Tl, inductive element LI, inductive element L2 and switching element T2. Terminal N between inductive element LI and inductive element L2 forms a first terminal in this embodiment. A terminal between second switching element T2 and inductive element L2 is connected to input terminal Kl by means of a first diode Dl. A terminal between first switching element Tl and inductive element LI is connected to the second input terminal K2 by means of a second diode D2. Input terminals Kl and K2 are also connected by a second series arrangement of a first capacitor CI and a second capacitor C2. A common terminal M
between the first capacitor C 1 and the second capacitor C2 forms a second terminal in this embodiment. A series arrangement of inductive element L, a first lamp connection terminal LK1, a high pressure discharge lamp LA and a second lamp connection terminal LK2 connects first terminal N with second terminal M. This series arrangement together with a capacitor Cr forms a load circuit. First terminal N is connected with the first input terminal Kl by means of a capacitor C3 and is also connected to the second input terminal K2 by means of a capacitor C4. Also in this embodiment CC is a control circuit for controlling the conductive state of switching element Tl and switching element T2 so that a periodical square wave shaped current with frequency f flows through the load circuit. A first and second output terminal of control circuit CC are therefore respectively connected to a control electrode of the first switching element Tl and a control electrode of the second switching element T2. The control circuit CC is also equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical square wave current so that the voltage at the second terminal M is maintained at l/2Vin. To this end an input terminal of the control circuit CC is connected to second terminal
M.
The operation of the circuit arrangement shown in Fig. 2 is as follows.
During operation a supply voltage source such as the one shown in Fig. 1 supplies a DC voltage Vin, that is present across the first series arrangement and also across the second series arrangement of capacitors CI and C2. The operation mode of the circuit arrangement shown in Fig. 2 is "commutating forward". The control circuit alternately with frequency f controls the inverter in a first operating state during the first half period of the current and in a second operating state during a second half period of the current. In the first operating state the control circuit CC renders the second switching element T2 non- conductive and renders the first switching element T 1 alternately conductive and
nonconductive at a frequency f 1 higher than f. In practice for a circuit arrangement as shown in Fig. 2 f is often chosen in the order of 100 Hz and fl in the order of 100 kHz. During this first operating state control circuit CC renders the first switching element Tl conductive when the current through the load circuit equals a first reference value that is chosen equal to zero. The current then increases until it reaches a second reference value. When this second
reference value is reached, the first switching element T 1 is rendered non-conductive. As a consequence the current decreases until it equals zero again so that the first switching element Tl is rendered conductive again and the cycle is repeated. In this way a current flowing through inductive element LI is generated that is a triangularly shaped current.
In the second operating state the control circuit renders the first switching element T2 non-conductive and renders the second switching element T2 alternately conductive and nonconductive at a frequency f 1 higher than f. In this second operating state control circuit CC renders the second switching element Tl conductive when the current through the load circuit equals the first reference value that is chosen equal to zero. The current then increases until it reaches the second reference value. When this second reference value is reached, the second switching element T2 is rendered non-conductive. As a consequence the current decreases until it equals zero again so that the second switching element T2 is rendered conductive again and the cycle is repeated. In this way a current flowing through inductive element L2 is generated that is a triangularly shaped current.
Due to the filtering action of capacitors C3 and C4 together with inductive element L, the current through the load circuit and the lamp is a DC current with a substantially constant amplitude, since the filter is dimensioned so that only a high frequency ripple with a very small amplitude is present in the current. This current has opposite polarities during the first operating state (the first half period of the current) and during the second operating state (the second half period of the current). The current flowing through the lamp is thus a square wave shaped AC current.
The control loop comprised in the control circuit CC adjusts the value of the second reference value at the beginning of each half period of the current in dependency of the voltage present at second terminal M averaged over a current period. At the beginning of a half period during which the half bridge is operated in the first operating state and the average voltage at second terminal M is higher than 1/2 Vin, the second predetermined value is decreased since the current flows to the second terminal M so that during this half period the voltage at M is caused to increase by the current. At the beginning of a half period during which the half bridge is operated in the second operating state and the average voltage at second terminal M is higher than 1/2 Vin, the second predetermined value is increased since
the current flows away from second terminal M so that during this half period the voltage at M is caused to decrease by the current.
Both the circuit arrangement shown in Fig. 1 as well as the circuit arrangement shown in Fig. 2 behave to a large extent as a current source since in both circuit arrangements the switching moments are triggered by a current level. This current source behavior is favorable for dimming. An important advantage of allowing the high frequency current in LI and L2 to become zero is that the switching losses are substantially reduced since the switching element is rendered conductive while the current through is zero. These low switching losses allow the frequency of the current in LI and L2 comparatively high (as already mentioned in the order Of 100 kHz). This high frequency allows the use of inductors that have a low inductance and small dimensions. A comparatively small circuit arrangement is thus possible. However, in the circuit arrangement shown in Fig. 2 inductive elements LI and L2, although their inductances are nominally the same, often have real inductances that differ substantially because of spread in component properties. The asymmetry caused by this spread is more severe in case of more current source behavior. The dimming behavior of the circuit arrangement, though improved on the one hand because of improved current source behavior would be counteracted on the other hand by asymmetry in case the control circuit were not equipped with a control loop for controlling the voltage at second terminal M.
As already indicated here-above, it is observed that the wave shape of the current in the load circuit generated by a circuit arrangement shown in Fig. 1 or Fig. 2 is not necessarily exactly a square wave shaped current. The current can be controlled to differ from a square wave shape. For instance the current may be so controlled that it has the shape of a square wave with a short current pulse superimposed on it directly before each commutation.
Fig. 3 illustrates that the voltage Vin between input terminals Kl and K2 and the voltage VM present at second terminal M is measured and that a signal representing
1/2 Vin - VM is generated and is present at the input terminal of an integrator. The integrator generates a signal that represents the value of l/2Vin - VM averaged over a period of the current through the load circuit. This signal present at the output of the integrator is sampled by a sample and hold circuit with a frequency f. The sampled value is multiplied with a square wave shaped signal with frequency f that is in phase with the current through the load circuit
and has a unit amplitude. By means of the multiplication a signal is generated that has a square wave shape, has a frequency equal to f, is in phase with the current through the load circuit and has an amplitude that equals the output signal of the integrator. This signal is present at the output terminal of the multiplier "product" and is added to a signal Iref that corresponds to the second reference value. As explained here-above switching element Tl is switched off when the current has increased to this value in the first operating state and switching element T2 is switched off when the current has increased to this value in the second operating state. This second reference value is for instance generated by a power control loop that is also part of the circuit arrangement. The addition of the signal present at the output of the multiplier "product" to the second reference value (Iref) results in a modulation of the signal Iref in the form of an increase of the signal Iref during half a period of the current and an decrease of the signal Iref during the next half a period of the current. The modulated signal Iref is used to control the current by functioning as the second reference value. Since the modulation decreases the second reference value during half a period and increases the second reference value during the next half a period by the same amount, the average amplitude of the current over a period thus remains constant so that the power supplied to the lamp does not change, but the amplitude in subsequent half periods of the current differs. The result is that the average value of the voltage VM at the second terminal is maintained at a value that substantially equals 1/2 Vin.
As already indicated here-above, in case of a circuit arrangement as shown in
Fig. 1 , the first reference value can be controlled at a value that differs from the second reference value by a constant C, so that only the second reference value needs to be adjusted by the power control loop and the control loop for maintaining the average value of the voltage at second terminal M at l/2Vin. The first reference value then automatically adjusts to a value that is equals the second reference value minus C. In case of a circuit arrangement according to Fig. 2 the first reference value is zero.
Claims
1. Circuit arrangement for operating a lamp equipped with an inverter comprising:
a first input terminal and a second input terminal for connection to a supply voltage source supplying a DC voltage Vin,
a first series arrangement comprising a first switching element and a second switching element and connecting the input terminals,
a second series arrangement comprising a first capacitor and a second capacitor and connecting the input terminals,
a load circuit comprising a series arrangement of an inductive element and lamp connection terminals and connecting a first terminal of the first series arrangement between the first switching element and the second switching element with a second terminal of the second series arrangement between the first capacitor and the second capacitor,
a control circuit, coupled to a first control electrode of the first switching element and a second control electrode of the second switching element, for controlling the conductive state of the first switching element and the second switching element so that a periodical current with frequency f flows through the load circuit,
characterized in that the control circuit is equipped with a control loop for controlling the amplitude of the current during the first half period and the second half period of each period of the periodical current so that the average value of the voltage at the second terminal is maintained at l/2Vin.
2. Circuit arrangement as claimed in claim 1, wherein a first diode is coupled between the first terminal and the first input terminal and wherein a second diode is coupled between the first terminal and the second input terminal, and wherein the control circuit comprises circuitry for alternately with frequency f controlling the inverter in a first operating state during each first half period of the lamp current and in a second operating state during each second half period of the lamp current and for
in the first operating state rendering the second switching element non- conductive and rendering the first switching element alternately conductive and
nonconductive at a frequency higher than f, and
- in the second operating state rendering the first switching element non- conductive and rendering the second switching element alternately conductive and nonconductive at a frequency higher than f.
3. Circuit arrangement as claimed in claim 1, wherein the control loop decreases the current through the load circuit during the first half period of the current and increases the current during the second half period of the current when the voltage at the second terminal is higher than l/2Vin and wherein the control loop increases the current through the load circuit during the first half period of the current and decreases the current during the second half period of the current when the voltage at the second terminal is lower than l/2Vin.
4. Circuit arrangement as claimed in claim 3, wherein the band width of the control loop is smaller than f.
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EP10197131 | 2010-12-28 | ||
EP10197131.5 | 2010-12-28 |
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US6437515B1 (en) * | 2000-01-18 | 2002-08-20 | Matsushita Electric Works, Ltd. | Discharge lamp lighting device of high startability with high pulse voltage |
WO2004023851A1 (en) * | 2002-09-06 | 2004-03-18 | Koninklijke Philips Electronics N.V. | Device and method for determining the current flowing through a gas discharge lamp |
US6919696B2 (en) | 2001-07-19 | 2005-07-19 | Koninklijke Philips Electronics N.V. | Device for operating a high-pressure discharge lamp |
US20060186828A1 (en) * | 2005-02-24 | 2006-08-24 | Paten-Treuhand-Gesellschaft Fur Elektrisch Gluhlampen Mbh | Electronic ballast for a high-pressure discharge lamp having a current-measuring device |
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2011
- 2011-12-19 WO PCT/IB2011/055762 patent/WO2012090112A1/en active Application Filing
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Publication number | Priority date | Publication date | Assignee | Title |
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US6437515B1 (en) * | 2000-01-18 | 2002-08-20 | Matsushita Electric Works, Ltd. | Discharge lamp lighting device of high startability with high pulse voltage |
US6919696B2 (en) | 2001-07-19 | 2005-07-19 | Koninklijke Philips Electronics N.V. | Device for operating a high-pressure discharge lamp |
WO2004023851A1 (en) * | 2002-09-06 | 2004-03-18 | Koninklijke Philips Electronics N.V. | Device and method for determining the current flowing through a gas discharge lamp |
US20060186828A1 (en) * | 2005-02-24 | 2006-08-24 | Paten-Treuhand-Gesellschaft Fur Elektrisch Gluhlampen Mbh | Electronic ballast for a high-pressure discharge lamp having a current-measuring device |
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