EP2181568B1 - Drive circuit for a discharge tube and a method of driving a discharge tube - Google Patents
Drive circuit for a discharge tube and a method of driving a discharge tube Download PDFInfo
- Publication number
- EP2181568B1 EP2181568B1 EP08737204A EP08737204A EP2181568B1 EP 2181568 B1 EP2181568 B1 EP 2181568B1 EP 08737204 A EP08737204 A EP 08737204A EP 08737204 A EP08737204 A EP 08737204A EP 2181568 B1 EP2181568 B1 EP 2181568B1
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- European Patent Office
- Prior art keywords
- discharge
- discharge tube
- drive circuit
- controller
- power supply
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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
- H05B41/30—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp
Definitions
- the present invention relates to a drive circuit and particularly, but not exclusively, to a drive circuit for a discharge tube and a method of driving a discharge tube (also known as a discharge lamp).
- Discharge tubes typically comprise an arrangement of electrodes In a gas, housed within an insulating, temperature resistant glass or ceramic envelope. Discharge tubes operate by Ionising the gas with an applied voltage across the electrodes, to create a conduction path within the gas between the electrodes. The electrical breakdown of the gas produces a plasma discharge with the result that upon passing a current through the plasma, an intense optical pulse is generated as the tree electrons within the plasma combine with the Ionised gas atoms.
- Discharge tubes are typically powered using a circuit such as that illustrated In Figure 1 of the accompanying drawings.
- a capacitor 11 is charged by a direct current (dc) source 10.
- the dc supply 10 and capacitor 11 are electrically connected to a discharge tube 12 by a first series of windings arranged upon the core of a transformer (not shown).
- the discharge tube 12 does not produce any output in this initial state, since there is no conductive path through the gas 13 between electrodes 14.
- the conductive path is created by Ionising the gas within the tube 12, and this is performed using a trigger circuit 15.
- the trigger circuit 15 induces a high voltage supply on the first series of windings (not shown) causing the gas 13 within the discharge tube 12 to break down.
- the trigger circuit is typically controlled by a controller 16 and comprises a second series of fewer windings on the same transformer core as the first series of windings, to create a step up In voltage. This high voltage produced across the tube creates a conduction path between the tube electrodes, thereby allowing the capacitor 11 to discharge and thus produce an Intense arc.
- US6193711B1 discloses a charge/discharge circuit for a flashlamp which is used to pump a Er.YAG laser system.
- a capacitor bank is charged from an ac mains supply via a transistor switch, which is controlled via a controller.
- the controller is further arranged to discharge the capacitor bank across the flashlamp to provide the required pumping of the gain medium.
- it is first necessary to rectify the so signal, for example with a diode bridge.
- the well-known waveform 17 of a full wave rectified sinusoidal voltage is shown in Figure 2 of the accompanying drawings.
- the figure further provides an indication of the time interval (illustrated as the interval t 1 -t 2 ) over which the voltage is sufficient to maintain a discharge arc.
- V th a threshold voltage of, for example, 70V at time t 1
- an optical output that is, an arc
- US Patent 6,965,203 discloses a method and circuitry for repetitively firing a flash lamp that is powered with a periodic voltage signal.
- a problem with powering discharge tubes using a rectified mains supply is that the optical output is limited to a flash rate of twice the mains frequency (that is 100 Hz for a 50 Hz mains supply and 120 Hz for a 60 Hz mains supply) and the optical output from the discharge tube will only continue while the mains voltage exceeds the threshold voltage. Once the mains voltage drops below the threshold voltage, the optical output from the discharge tube will terminate.
- a known solution to this problem is to incorporate a capacitor bank after the diode bridge in order to hold the voltage above the threshold voltage.
- Such a capacitor bank is found to smooth the voltage supply to the discharge tube.
- Such an arrangement is prone to fluctuations in the voltage supply 18 as shown in Figure 3 of the accompanying drawings and this manifests as a fluctuation in the optical output of the discharge arc.
- a drive circuit for a discharge tube comprising a primary circuit and a secondary circuit both arranged to deliver power to the discharge tube, the primary circuit comprising a power supply and a first controller for controlling the delivery of power from the first power supply to the discharge tube, the secondary circuit comprising power storage means and at least one second controller for controlling the discharge of the power storage means, the second controller being arranged to selectively discharge the power storage means at times when the rectified power supply is below a threeshold, as determined by the first controller, such that the selective discharge maintains the voll-tage across the discharge tube above a threshold voltage necessary to maintain a discharge arc.
- the drive circuit according to the Invention Is enabled to supply a substantially constant power supply to the discharge tube.
- the primary circuit preferably includes a diode bridge for rectifying ac mains supply.
- a diode bridge for rectifying ac mains supply.
- Such a diode bridge preferably provides full wave rectification of the ac mains.
- the primary circuit includes a trigger mechanism for inducing a high voltage spike across the discharge tube to ionise the gas within the discharge tube.
- the first controller preferably comprises a timing circuit to time the triggering of the trigger mechanism with the rectified ac mains supply.
- a timing circuit preferably enables the trigger mechanism to be triggered only in those intervals when the rectified ac mains voltage is above a threshold voltage.
- the threshold voltage is the minimum voltage necessary to sustain a discharge arc.
- the rectified mains supply is continuously monitored by the first controller.
- the secondary circuit preferably comprises a power supply such as a direct current (dc) supply for charging the power storage means.
- a power supply such as a direct current (dc) supply for charging the power storage means.
- the power storage means comprises at least one capacitor, such as a capacitor bank.
- the at least one second controller preferably causes such a capacitor bank to discharge in order to compensate for the drop in voltage from the rectified ac mains supply and to maintain the voltage across the discharge tube above the threshold voltage, between duty cycles of the rectified mains voltage,
- the discharge arc is terminated by a switch, such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).
- MOSFET Metal Oxide Semiconductor Field Effect Transistor
- the first controller and the at least one second controller are arranged in electronic communication to enable synchronous discharge of the capacitor (such as the capacitor bank) with the rectified voltage.
- the first embodiment of the present invention provides for the discharge of a substantially uniform pulse of radiation from the discharge tube for durations greater than the given duty cycle of the rectified mains voltage.
- the power storage means preferably further comprises an inductor.
- the at least one second controller preferably comprises a semiconductor switch, such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), which in the "OFF" state prevents the current from the power supply in the primary circuit and the charge from the capacitor bank from passing through the discharge tube.
- MOSFET Metal Oxide Semiconductor Field Effect Transistor
- the inductor preferably discharges across the discharge tube to maintain a discharge while the MOSFET is "OFF”. While the MOSFET is "OFF”, this further enables the capacitor bank to preferably recharge from the power supply in the primary circuit, such that it can subsequently discharge across the tube when the MOSFET is switched back "ON".
- the switched state of the MOSFET is controlled by the first controller.
- the source terminal of the MOSFET is connected to substantially zero voltage, or ground.
- the second embodiment of the present invention provides for the discharge of a substantially uniform pulse of radiation from the discharge tube for durations less than a given cycle period of the power supply signal in the primary circuit.
- a drive circuit 100 comprising a primary circuit 101 and a secondary circuit 102a, for powering a discharge tube 103.
- the primary circuit 101 powers the discharge tube 103 and the secondary circuit 102a compensates for the variation in the rectified ac power supply in the primary circuit 101 to provide a substantially constant voltage between duty cycles of the rectified power supply.
- the primary circuit 101 comprises a diode bridge 106, which rectifies the incoming ac mains power supply 104 from an isolation transformer 105, to provide a full wave rectified voltage signal.
- the output of the diode bridge 106 is electrically connected to the discharge tube 103 via a single diode 107 which ensures unidirectional flow of current toward the discharge tube 103 from the power supply 104.
- the rectified voltage is insufficient to initiate a discharge within the tube 103, since there is no conduction path between the electrodes 108 of the discharge tube 103.
- the primary circuit 101 includes a controller 109 for controlling a trigger circuit 110.
- the controller 109 receives an input signal from the output of the diode bridge 106 and monitors the variation in waveform via digital signal processing means (not shown).
- the controller 109 includes an output for outputting a voltage as input to the trigger circuit 110.
- the trigger circuit 110 typically includes a step-up transformer (not shown) which produces a high voltage spike across the tube electrodes 108.
- the high potential difference created across the electrodes 108 by the trigger circuit 110 causes the gas 111 within the tube 103 to ionise, thereby reducing the impedance of the tube 103.
- the controller 109 monitors the rectified voltage via connection 112 and outputs a signal to the trigger circuit 110 at a time determined by digital signal processing means (not shown) to cause the trigger circuit 110 to produce the voltage spike.
- digital signal processing means not shown
- the circuit 100 further comprises a secondary drive circuit 102a which includes a second (dc) power supply 113 arranged in series with the rectified voltage supply, and which used to charge a capacitor bank 114.
- a secondary drive circuit 102a which includes a second (dc) power supply 113 arranged in series with the rectified voltage supply, and which used to charge a capacitor bank 114.
- the secondary circuit further includes a second controller 115 arranged in electronic communication with the first controller 109 to control selective discharge of the capacitor bank 114.
- the first controller 109 causes the trigger circuit 110 to produce a high voltage across the electrodes 108, causing the gas 111 within the tube 103 to ionise, when the rectified voltage across the tube electrodes 108 from a given duty cycle reaches the minimum value necessary to maintain a discharge arc.
- the second controller 115 causes the capacitor bank 114 to progressively discharge, so as to compensate for the fall in voltage on the rectified voltage input. This maintains a constant voltage across the tube electrodes 108 and therefore a uniform discharge arc.
- the discharge of the capacitor bank 114 is quite small. However, as the rectified voltage is reduced further from the threshold voltage, the rate of discharge of the capacitor bank 114 increases, so as to offset the fall in rectified voltage. As the rectified voltage begins to rise again on the next duty cycle, the capacitor bank 114 begins to progressively recharge from the second power supply 113, so that it is ready to discharge again in accordance with the fall in rectified voltage.
- the second controller 115 monitors the first controller 109 in order to ,time the selective charge and discharge of the capacitor bank 114. In this manner, the cyclic charge and discharge of the capacitor bank 114 can be used to maintain the discharge arc for a desired time period.
- a semiconductor switch 116 such as a metal oxide semiconductor field effect transistor (MOSFET), arranged in electrical connection with the cathode of the discharge tube 103, is switched to the "OFF" state by the first controller 109 to inhibit the flow of current between the electrodes 108 of the discharge tube 103.
- MOSFET metal oxide semiconductor field effect transistor
- the primary circuit 101 can be seen to comprise those components of the primary circuit according to the first embodiment.
- the secondary circuit 102b however, comprises a first secondary controller 117 and a second secondary controller 118.
- the first secondary controller 117 is arranged in electrical communication with the first controller 109 arranged in the primary circuit 101 and is arranged to discharge a capacitor bank 119 arranged in the secondary circuit 102b at a time which corresponds to a period following the application of a pulse to the trigger circuit 110.
- the first controller 109 arranged in the primary circuit 101 monitors the variation of the rectified mains voltage and outputs a pulse to the trigger circuit 110 when the voltage level of the rectified mains voltage passes above a threshold value for producing a discharge arc, which may be 60-70V.
- the trigger pulse causes a high voltage spike to be applied across the electrodes 108 of the discharge tube 103 which ionises the gas 111 within the tube 103 and thus creates a conduction path between the electrodes 108 such that the charge stored on the capacitor bank 119 can discharge across the tube 103 to produce a pulse of radiation.
- the current which exits the tube 103 passes through an inductor coil 120 arranged in the secondary circuit 102b and subsequently though the second secondary controller 118, which may comprise a semiconductor switch, such as a MOSFET, also arranged in the secondary circuit 102b, before passing to ground.
- the gate terminal of the MOSFET 118 is connected to the first controller 109 arranged in the primary circuit 101, such that the first controller 109 arranged in the primary circuit 101 can control the "ON/OFF" state of the switch 118 and thus control the current passing from the capacitor bank 119 and the primary circuit 101 through the tube 103.
- the MOSFET 118 is switched to the "OFF" state. This causes the magnetic field in the inductor 120 to collapse creating a high voltage spike which is applied across the electrodes 108 of the tube 103 so as to maintain a voltage above the threshold. This collapse of magnetic field causes a current to flow within the secondary circuit 102b through diode 121 and between the electrodes 108 of the tube 103 to maintain a discharge arc.
- the capacitor 119 is recharged by the voltage from the rectified mains voltage within the same duty cycle and once charged, the MOSFET 120 is then switched back "ON", so as to discharge the capacitor 119 across the tube 103.
- a modulated pulsed signal to the gate terminal of the MOSFET 120 once the voltage of the rectified mains signal initially passes above a threshold value, it is possible to maintain a discharge arc for a desired period of time.
- the drive circuit of the present invention enables a discharge tube, powered from a mains supply, to produce a discharge arc of a desired period of time.
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Abstract
Description
- The present invention relates to a drive circuit and particularly, but not exclusively, to a drive circuit for a discharge tube and a method of driving a discharge tube (also known as a discharge lamp).
- Discharge tubes typically comprise an arrangement of electrodes In a gas, housed within an insulating, temperature resistant glass or ceramic envelope. Discharge tubes operate by Ionising the gas with an applied voltage across the electrodes, to create a conduction path within the gas between the electrodes. The electrical breakdown of the gas produces a plasma discharge with the result that upon passing a current through the plasma, an intense optical pulse is generated as the tree electrons within the plasma combine with the Ionised gas atoms.
- Discharge tubes are typically powered using a circuit such as that illustrated In
Figure 1 of the accompanying drawings. In such a circuit, acapacitor 11 is charged by a direct current (dc)source 10. Thedc supply 10 andcapacitor 11 are electrically connected to adischarge tube 12 by a first series of windings arranged upon the core of a transformer (not shown). However, thedischarge tube 12 does not produce any output in this initial state, since there is no conductive path through thegas 13 betweenelectrodes 14. - The conductive path is created by Ionising the gas within the
tube 12, and this is performed using atrigger circuit 15. Thetrigger circuit 15 induces a high voltage supply on the first series of windings (not shown) causing thegas 13 within thedischarge tube 12 to break down. The trigger circuit is typically controlled by acontroller 16 and comprises a second series of fewer windings on the same transformer core as the first series of windings, to create a step up In voltage. This high voltage produced across the tube creates a conduction path between the tube electrodes, thereby allowing thecapacitor 11 to discharge and thus produce an Intense arc. - It is also known to power discharge tubes using alternating current (ac) sources.
-
US6193711B1 , for example, discloses a charge/discharge circuit for a flashlamp which is used to pump a Er.YAG laser system. In this document, a capacitor bank is charged from an ac mains supply via a transistor switch, which is controlled via a controller. The controller is further arranged to discharge the capacitor bank across the flashlamp to provide the required pumping of the gain medium. However, in such systems it is first necessary to rectify the so signal, for example with a diode bridge. - The well-known
waveform 17 of a full wave rectified sinusoidal voltage is shown inFigure 2 of the accompanying drawings. The figure further provides an indication of the time interval (illustrated as the interval t1-t2) over which the voltage is sufficient to maintain a discharge arc. In this manner, when the voltage of the rectified sinusoidal waveform reaches a threshold (Vth) voltage of, for example, 70V at time t1, an optical output (that is, an arc) will be produced that will continue until the rectified waveform voltage drops to, for example 50 volts at time t2. -
US Patent 6,965,203 discloses a method and circuitry for repetitively firing a flash lamp that is powered with a periodic voltage signal. A problem with powering discharge tubes using a rectified mains supply, however, is that the optical output is limited to a flash rate of twice the mains frequency (that is 100 Hz for a 50 Hz mains supply and 120 Hz for a 60 Hz mains supply) and the optical output from the discharge tube will only continue while the mains voltage exceeds the threshold voltage. Once the mains voltage drops below the threshold voltage, the optical output from the discharge tube will terminate. - A known solution to this problem is to incorporate a capacitor bank after the diode bridge in order to hold the voltage above the threshold voltage. Such a capacitor bank is found to smooth the voltage supply to the discharge tube. However, such an arrangement is prone to fluctuations in the
voltage supply 18 as shown inFigure 3 of the accompanying drawings and this manifests as a fluctuation in the optical output of the discharge arc. - Moreover, certain applications require the application of a steady pulse of radiation from a discharge tube for a time period less that the duty cycle of a rectified mains supply.
- We have now devised a drive circuit for a discharge tube and a method of driving a discharge tube which alleviates these problems.
- In accordance with the present invention as seen from a first aspect, there is provided a drive circuit for a discharge tube, the drive circuit comprising a primary circuit and a secondary circuit both arranged to deliver power to the discharge tube,
the primary circuit comprising a power supply and a first controller for controlling the delivery of power from the first power supply to the discharge tube,
the secondary circuit comprising power storage means and at least one second controller for controlling the discharge of the power storage means,
the second controller being arranged to selectively discharge the power storage means at times when the rectified power supply is below a threeshold, as determined by the first controller, such that the selective discharge maintains the voll-tage across the discharge tube above a threshold voltage necessary to maintain a discharge arc. - By this means, the drive circuit according to the Invention Is enabled to supply a substantially constant power supply to the discharge tube.
- The primary circuit preferably includes a diode bridge for rectifying ac mains supply. Such a diode bridge preferably provides full wave rectification of the ac mains.
- Preferably, the primary circuit includes a trigger mechanism for inducing a high voltage spike across the discharge tube to ionise the gas within the discharge tube.
- The first controller preferably comprises a timing circuit to time the triggering of the trigger mechanism with the rectified ac mains supply. Such a timing circuit preferably enables the trigger mechanism to be triggered only in those intervals when the rectified ac mains voltage is above a threshold voltage.
- Preferably the threshold voltage is the minimum voltage necessary to sustain a discharge arc.
- Preferably, the rectified mains supply is continuously monitored by the first controller.
- In accordance with the first embodiment of the present Invention the secondary circuit preferably comprises a power supply such as a direct current (dc) supply for charging the power storage means.
- Preferably, the power storage means comprises at least one capacitor, such as a capacitor bank.
- The at least one second controller preferably causes such a capacitor bank to discharge in order to compensate for the drop in voltage from the rectified ac mains supply and to maintain the voltage across the discharge tube above the threshold voltage, between duty cycles of the rectified mains voltage,
- Preferably, the discharge arc is terminated by a switch, such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).
- Preferably, the first controller and the at least one second controller are arranged in electronic communication to enable synchronous discharge of the capacitor (such as the capacitor bank) with the rectified voltage.
- Preferably, the first embodiment of the present invention provides for the discharge of a substantially uniform pulse of radiation from the discharge tube for durations greater than the given duty cycle of the rectified mains voltage.
- In accordance with the second embodiment of the present invention, the power storage means preferably further comprises an inductor.
- The at least one second controller preferably comprises a semiconductor switch, such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), which in the "OFF" state prevents the current from the power supply in the primary circuit and the charge from the capacitor bank from passing through the discharge tube. In this state, the inductor preferably discharges across the discharge tube to maintain a discharge while the MOSFET is "OFF". While the MOSFET is "OFF", this further enables the capacitor bank to preferably recharge from the power supply in the primary circuit, such that it can subsequently discharge across the tube when the MOSFET is switched back "ON".
- Preferably, the switched state of the MOSFET is controlled by the first controller. Preferably, the source terminal of the MOSFET is connected to substantially zero voltage, or ground.
- Preferably, the second embodiment of the present invention provides for the discharge of a substantially uniform pulse of radiation from the discharge tube for durations less than a given cycle period of the power supply signal in the primary circuit.
- In accordance with the present invention as seen from a second aspect, there is provided a method of driving a discharge tube, the method comprising
- providing a drive circuit according to the invention:
- powering the discharge tube using the primary circuit;
- selectively powering the discharge tube using the secondary circuit at times when the first power supply is below a threshold value.
- Preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:
-
Figure 1 is a circuit diagram of a conventional drive circuit for a discharge tube, as described above; -
Figure 2 is a graphical representation of the voltage waveform of the rectified ac mains supply using such a conventional circuit, as described above; -
Figure 3 is a graphical representation of the voltage waveform of a rectified ac mains supply, following smoothing by a capacitor bank as described above; -
Figure 4 is a circuit diagram of an exemplary drive circuit according to a first embodiment of the present invention; and, -
Figure 5 is a circuit diagram of an exemplary drive circuit according to a second embodiment of the present invention. - According to the first embodiment of the present invention as shown in
Figure 4 , there is provided adrive circuit 100 comprising aprimary circuit 101 and asecondary circuit 102a, for powering adischarge tube 103. Theprimary circuit 101 powers thedischarge tube 103 and thesecondary circuit 102a compensates for the variation in the rectified ac power supply in theprimary circuit 101 to provide a substantially constant voltage between duty cycles of the rectified power supply. - The
primary circuit 101 comprises adiode bridge 106, which rectifies the incoming acmains power supply 104 from anisolation transformer 105, to provide a full wave rectified voltage signal. The output of thediode bridge 106 is electrically connected to thedischarge tube 103 via asingle diode 107 which ensures unidirectional flow of current toward thedischarge tube 103 from thepower supply 104. However, the rectified voltage is insufficient to initiate a discharge within thetube 103, since there is no conduction path between theelectrodes 108 of thedischarge tube 103. - The
primary circuit 101 includes acontroller 109 for controlling atrigger circuit 110. Thecontroller 109 receives an input signal from the output of thediode bridge 106 and monitors the variation in waveform via digital signal processing means (not shown). Thecontroller 109 includes an output for outputting a voltage as input to thetrigger circuit 110. Thetrigger circuit 110 typically includes a step-up transformer (not shown) which produces a high voltage spike across thetube electrodes 108. - The high potential difference created across the
electrodes 108 by thetrigger circuit 110, causes thegas 111 within thetube 103 to ionise, thereby reducing the impedance of thetube 103. However, in order to ensure that thetrigger circuit 110 applies the high voltage spike at the correct time, that is, when the rectified voltage is sufficient to create a discharge arc, thecontroller 109 monitors the rectified voltage viaconnection 112 and outputs a signal to thetrigger circuit 110 at a time determined by digital signal processing means (not shown) to cause thetrigger circuit 110 to produce the voltage spike. However, with such a system, there is no control over the duration or frequency of the discharge arc. - Accordingly, the
circuit 100 according to the present invention further comprises asecondary drive circuit 102a which includes a second (dc)power supply 113 arranged in series with the rectified voltage supply, and which used to charge acapacitor bank 114. - The secondary circuit further includes a
second controller 115 arranged in electronic communication with thefirst controller 109 to control selective discharge of thecapacitor bank 114. - In use, the
first controller 109 causes thetrigger circuit 110 to produce a high voltage across theelectrodes 108, causing thegas 111 within thetube 103 to ionise, when the rectified voltage across thetube electrodes 108 from a given duty cycle reaches the minimum value necessary to maintain a discharge arc. - As the rectified voltage subsequently falls below the threshold voltage within the same duty cycle, the
second controller 115 causes thecapacitor bank 114 to progressively discharge, so as to compensate for the fall in voltage on the rectified voltage input. This maintains a constant voltage across thetube electrodes 108 and therefore a uniform discharge arc. - Initially, the discharge of the
capacitor bank 114 is quite small. However, as the rectified voltage is reduced further from the threshold voltage, the rate of discharge of thecapacitor bank 114 increases, so as to offset the fall in rectified voltage. As the rectified voltage begins to rise again on the next duty cycle, thecapacitor bank 114 begins to progressively recharge from thesecond power supply 113, so that it is ready to discharge again in accordance with the fall in rectified voltage. - The
second controller 115 monitors thefirst controller 109 in order to ,time the selective charge and discharge of thecapacitor bank 114. In this manner, the cyclic charge and discharge of thecapacitor bank 114 can be used to maintain the discharge arc for a desired time period. - When it is desired to terminate the arc, a
semiconductor switch 116, such as a metal oxide semiconductor field effect transistor (MOSFET), arranged in electrical connection with the cathode of thedischarge tube 103, is switched to the "OFF" state by thefirst controller 109 to inhibit the flow of current between theelectrodes 108 of thedischarge tube 103. - In accordance with a second embodiment of the present invention as shown in
Figure 5 , theprimary circuit 101 can be seen to comprise those components of the primary circuit according to the first embodiment. Thesecondary circuit 102b however, comprises a firstsecondary controller 117 and a secondsecondary controller 118. The firstsecondary controller 117 is arranged in electrical communication with thefirst controller 109 arranged in theprimary circuit 101 and is arranged to discharge acapacitor bank 119 arranged in thesecondary circuit 102b at a time which corresponds to a period following the application of a pulse to thetrigger circuit 110. - The
first controller 109 arranged in theprimary circuit 101 monitors the variation of the rectified mains voltage and outputs a pulse to thetrigger circuit 110 when the voltage level of the rectified mains voltage passes above a threshold value for producing a discharge arc, which may be 60-70V. The trigger pulse causes a high voltage spike to be applied across theelectrodes 108 of thedischarge tube 103 which ionises thegas 111 within thetube 103 and thus creates a conduction path between theelectrodes 108 such that the charge stored on thecapacitor bank 119 can discharge across thetube 103 to produce a pulse of radiation. - The current which exits the
tube 103 passes through aninductor coil 120 arranged in thesecondary circuit 102b and subsequently though the secondsecondary controller 118, which may comprise a semiconductor switch, such as a MOSFET, also arranged in thesecondary circuit 102b, before passing to ground. The gate terminal of theMOSFET 118 is connected to thefirst controller 109 arranged in theprimary circuit 101, such that thefirst controller 109 arranged in theprimary circuit 101 can control the "ON/OFF" state of theswitch 118 and thus control the current passing from thecapacitor bank 119 and theprimary circuit 101 through thetube 103. - Following the discharge of the
capacitor bank 119, which may take place over a time period significantly less that the duty cycle of the rectified mains voltage, theMOSFET 118 is switched to the "OFF" state. This causes the magnetic field in theinductor 120 to collapse creating a high voltage spike which is applied across theelectrodes 108 of thetube 103 so as to maintain a voltage above the threshold. This collapse of magnetic field causes a current to flow within thesecondary circuit 102b throughdiode 121 and between theelectrodes 108 of thetube 103 to maintain a discharge arc. During this period, thecapacitor 119 is recharged by the voltage from the rectified mains voltage within the same duty cycle and once charged, theMOSFET 120 is then switched back "ON", so as to discharge thecapacitor 119 across thetube 103. In this manner, by applying a modulated pulsed signal to the gate terminal of theMOSFET 120 once the voltage of the rectified mains signal initially passes above a threshold value, it is possible to maintain a discharge arc for a desired period of time. - Moreover, and in common with the first embodiment, it is possible to produce and maintain a discharge arc over selected periods within a given duty cycle of the rectified mains supply as with the second embodiment or over periods comprising several duty cycles of the rectified mains supply, as with the first embodiment, with the application of only a single trigger pulse.
- From the foregoing therefore, it is evident that the drive circuit of the present invention enables a discharge tube, powered from a mains supply, to produce a discharge arc of a desired period of time.
Claims (15)
- A drive circuit (100) for a gas discharge tube (103), the drive circuit comprising a primary circuit (101) and a secondary circuit (102a) both arranged to deliver power to the discharge tube,
the primary circuit comprising a rectitied power supply and a first controller (108) for controlling delivery of power from the power supply to the discharge tube, and
the secondary circuit comprising power storage means (114) and at least one second controller (115) for controlling delivery of power from the power storage means to the discharge tube, characterised In that,
the second controller is arranged to selectively discharge the power storage means only at times when the rectified power supply is below a threshold value, as determined by the first controller, such that the selective discharge maintains the voltage across the discharge tube above a minimum voltage necessary to maintain a discharge arc in the discharge tube. - A drive circuit according to claim 1, wherein the power supply comprises ac mains supply (104) and the primary circuit comprises a diode bridge (106) for rectifying the ac mains supply.
- A drive circuit according to claim 1 or 2, wherein the first controller is arranged to continuously monitor variation in power from the power supply,
- A drive circuit according to any preceding claim, wherein the primary circuit Includes a trigger mechanism for inducing a high voltage spike across the discharge tube so as to ionise gas (111) within the discharge tube.
- A drive circuit according to claim 4, wherein the first controller comprises a timing circuit (110) arranged to trigger the trigger mechanism only at those times when the rectified power supply is above a threshold voltage.
- A drive circuit according to claim 5, wherein the power storage means comprises at least one capacitor, and the second controller is arranged to cause the at least one capacitor to discharge in order to compensate for a drop in voltage from the rectified power supply and to maintain the voltage across the discharge tube above the minimum voltage.
- A drive circuit according to claim 6, wherein the first controller and the second controller are arranged in electronic communication to enable synchronous discharge of the at least one capacitor with the rectified power supply.
- A drive circuit according to claim 6 or 7, which provides for the discharge of a substantially uniform pulse of radiation from the discharge tube for durations greater than a given duty cycle of the rectified power supply.
- A drive circuit according to any preceding claim, further comprising a switch (116), such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) for terminating the discharge arc.
- A drive circuit according to any of claims 1 to 5, wherein the power storage means comprises an inductor.
- A drive circuit according to claim 10, wherein the power storage means further comprises a capacitor.
- A drive circuit according to claim 10 or 11, wherein the second controller comprises at least one semiconductor switch, such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), and the first controller is arranged to control switching of the semiconductor switch.
- A drive circuit according to claim 12, wherein the semiconductor switch has a source terminal connected to substantially zero voltage, or ground.
- A drive circuit according to any of claims 10 to 13, which provides for the discharge of a substantially uniform pulse of radiation from the discharge tube for durations less than a given duty cycle of the rectified power supply.
- A method of driving a discharge tube, the method comprising;- providing a drive circuit according to any of claims 1 to 14;- delivering the rectified power supply to the discharge tube;- selectively delivering power to the discharge tube from the secondary circuit only at times when the rectified power supply is below the threshold value.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DKPA200700578 | 2007-04-20 | ||
DKPA200700582 | 2007-04-20 | ||
GB0717322A GB2448560A (en) | 2007-04-20 | 2007-09-06 | Drive circuit for discharge tube |
PCT/GB2008/050279 WO2008129325A1 (en) | 2007-04-20 | 2008-04-21 | Drive circuit for a discharge tube and a method of driving a discharge tube |
Publications (2)
Publication Number | Publication Date |
---|---|
EP2181568A1 EP2181568A1 (en) | 2010-05-05 |
EP2181568B1 true EP2181568B1 (en) | 2011-11-02 |
Family
ID=39671491
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP08737204A Not-in-force EP2181568B1 (en) | 2007-04-20 | 2008-04-21 | Drive circuit for a discharge tube and a method of driving a discharge tube |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP2181568B1 (en) |
AT (1) | ATE532388T1 (en) |
DK (1) | DK2181568T3 (en) |
ES (1) | ES2374420T3 (en) |
HK (1) | HK1143486A1 (en) |
WO (1) | WO2008129325A1 (en) |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4486691A (en) * | 1980-07-02 | 1984-12-04 | Beggs William C | Sequential capacitive discharge circuit for flash lamps |
US6193711B1 (en) | 1997-12-12 | 2001-02-27 | Coherent, Inc. | Rapid pulsed Er:YAG laser |
US6888319B2 (en) * | 2001-03-01 | 2005-05-03 | Palomar Medical Technologies, Inc. | Flashlamp drive circuit |
-
2008
- 2008-04-21 EP EP08737204A patent/EP2181568B1/en not_active Not-in-force
- 2008-04-21 ES ES08737204T patent/ES2374420T3/en active Active
- 2008-04-21 WO PCT/GB2008/050279 patent/WO2008129325A1/en active Application Filing
- 2008-04-21 AT AT08737204T patent/ATE532388T1/en active
- 2008-04-21 DK DK08737204.1T patent/DK2181568T3/en active
-
2010
- 2010-10-22 HK HK10110011.2A patent/HK1143486A1/en not_active IP Right Cessation
Also Published As
Publication number | Publication date |
---|---|
EP2181568A1 (en) | 2010-05-05 |
ATE532388T1 (en) | 2011-11-15 |
ES2374420T3 (en) | 2012-02-16 |
DK2181568T3 (en) | 2012-02-13 |
WO2008129325A1 (en) | 2008-10-30 |
HK1143486A1 (en) | 2010-12-31 |
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