ES2374420T3 - EXCITATION CIRCUIT FOR A DISCHARGE TUBE AND EXCITATION METHOD OF A DISCHARGE TUBE. - Google Patents

Abstract

The drive circuit comprises a primary circuit and a secondary circuit, both arranged to deliver power to the discharge tube. The primary circuit comprises a first power supply and a first controller for controlling the delivery of power from the first power supply to the discharge tube.The secondary circuit comprises a power storage arrangement, and at least one second controller for controlling the discharge of the power storage arrangement. The second controller is arranged to selectively discharge the power storage arrangement at intervals determined by the first controller, such that the selective discharge maintains the voltage across the discharge tube above a threshold voltage necessary to maintain a discharge arc.

Description

Excitation circuit for a discharge tube and excitation method of a discharge tube

The present invention relates to an excitation circuit and particularly, but not exclusively, to an excitation circuit for a discharge tube and to an excitation method of a discharge tube (also known as a discharge lamp).

Typically, the discharge tubes comprise an arrangement of electrodes in a gas, housed within a temperature-resistant insulating glass or ceramic sheath. The discharge tubes work by ionizing the gas with a voltage applied across the electrodes, to create a conduction path within the gas located between the electrodes. The dielectric rupture of the gas produces a plasma discharge with the result that, when a current passes through the plasma, an intense optical pulse is generated when the free electrons inside the plasma combine with the atoms of ionized gas.

Discharge tubes are usually energized using a circuit, such as that illustrated in Figure 1 of the accompanying drawings. In such a circuit, a capacitor 11 is charged by a direct current source 10 (dc). The DC supply 10 and the capacitor 11 are electrically connected to a discharge tube 12, by means of a first series of windings arranged on the core of a transformer (not shown). However, the discharge tube 12 does not produce any output in this initial state, since there is no conductive path through the gas 13 between the electrodes 14.

The conductive path is created by ionizing the gas inside the tube 12, and this is carried out using an activator circuit 15. The activator circuit 15 induces a high voltage supply in the first series of windings (not shown), which causes the gas 13 to rupture inside the discharge tube 12. Usually, the activator circuit is controlled by a controller 16 and comprises a second smaller series of windings, in the same core of the transformer as the first series of windings, to create a tension lift. This high voltage produced through the tube creates a conduction path between the electrodes of the tube, thereby allowing the capacitor 11 to discharge and thus produce an intense arc.

It is also known to energize the discharge tube using alternating current sources (ac).

US 6 193 711 B1, for example, discloses a charge / discharge circuit for a flash lamp that is used to pump an Er: YAG laser system. In this document, a capacitor bank is charged from an AC mains supply through a transistor switch, which is controlled through a controller. The controller is further arranged to discharge the capacitor bank through the flash lamp, in order to provide the required pumping of the active medium. However, in these systems it is first necessary to rectify the signal, for example with a diode bridge.

In Figure 2 of the accompanying drawings, the well-known waveform 17 of a rectified full-wave sinusoidal voltage is shown. The figure also provides an indication of the time interval (illustrated as the interval t1-t2) over which the voltage is sufficient to maintain a discharge arc. Thus, when the voltage of the rectified sine waveform reaches a threshold voltage (Vth), for example, 70 V at time t1, an optical emission (ie an arc) will occur that will continue until the voltage of the rectified waveform falls, for example, to 50 volts at time t2.

U.S. Patent UU. 6 965 203 discloses a method and circuits for repetitively lighting a flash lamp that is energized with a periodic voltage signal. However, a problem with the excitation of the discharge tubes that use a rectified power supply is that the optical emission is limited to a flash frequency twice the frequency of the power grid (ie 100 Hz for a power supply of 50 Hz, and 120 Hz for a power supply of 60 Hz), and the optical emission from the discharge pipe will continue only as long as the voltage of the power network exceeds the threshold voltage. Once the mains voltage drops below the threshold voltage, the optical emission from the discharge tube will end.

A known solution for this problem is to incorporate a capacitor bank next to the diode bridge, to maintain the voltage above the threshold voltage. It is found that said capacitor bank softens the supply of voltage to the discharge tube. However, said arrangement is prone to fluctuations in the voltage supply 18, as shown in Figure 3 of the attached drawings, and this is manifested as a fluctuation of the optical emission of the discharge arc.

In addition, certain applications require the application of a pulse of stationary radiation from a discharge tube, for a period of time less than the service cycle of the rectified mains supply.

We have devised an excitation circuit for a discharge tube and an excitation method of a discharge tube, which alleviate these problems.

In accordance with the present invention, considered from a first aspect, an excitation circuit for a discharge tube is disclosed, the excitation circuit comprising a primary circuit and a secondary circuit, both arranged to deliver energy to the discharge tube,

the primary circuit comprising a power supply and a first controller to control the delivery of energy from the first power supply to the discharge tube,

the secondary circuit comprising energy storage means and at least a second controller for controlling the discharge of the energy storage means,

the second controller being arranged to selectively discharge the energy storage medium in the periods in which the rectified power supply is below the threshold, which is determined by the first controller, so that the selective discharge maintains the voltage at through the discharge tube above a threshold voltage necessary to maintain a discharge arc.

With these means, the excitation circuit according to the invention is allowed to provide a substantially constant power supply to the discharge tube.

The primary circuit preferably includes a diode bridge to rectify the supply of the AC power grid. Said diode bridge preferably provides a full wave rectification of the AC power grid.

Preferably, the primary circuit includes an activating mechanism to induce a high voltage peak through the discharge tube, in order to ionize the gas inside the discharge tube.

The first controller preferably comprises a synchronization circuit to synchronize the activation of the activating mechanism with the supply of the rectified ac power grid. Said synchronization circuit preferably allows the activation mechanism to be activated only at those intervals in which the voltage of the rectified ac mains is above a threshold voltage.

Preferably, the threshold voltage is the minimum voltage necessary to maintain a discharge arc.

Preferably, the rectified power supply is continuously monitored by the first controller.

According to the first embodiment of the present invention, the secondary circuit preferably comprises a power supply, such as a direct current supply (dc), for charging the energy storage medium.

Preferably, the energy storage means comprises at least one capacitor, such as a capacitor bank.

Said, at least, a second controller preferably causes said capacitor bank to discharge to compensate for the voltage drop from the supply of the rectified ac mains, and to maintain the voltage through the discharge tube above the threshold voltage, between the service cycles of the rectified grid voltage.

Preferably, the discharge arc is terminated by a switch, such as a metal oxide semiconductor field effect transistor (MOSFET, Metal Oxide Semiconductor Field Effect Transistor).

Preferably, the first controller and said, at least, a second controller are arranged in electronic communication to allow synchronous discharge of the capacitor (such as the capacitor bank) with the rectified voltage.

Preferably, the first embodiment of the present invention provides the discharge, from the discharge tube, of a substantially uniform radiation pulse, for times longer than the given duty cycle of the rectified grid voltage.

According to a second embodiment of the present invention, the energy storage means further comprises, preferably, an inductor.

Said, at least, a second controller preferably comprises a semiconductor switch, such as a metal oxide semiconductor field effect transistor (MOSFET), which in the state "OFF (disconnected)". 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, preferably, the inductor is discharged through the discharge tube, to maintain a discharge while the MOSFET is "OFF (disconnected)". While the MOSFET is "OFF (disconnected)", this also allows the capacitor bank to recharge, preferably, from the power supply in the primary circuit, so that it can be subsequently discharged through the tube when the MOSFET returns to be "ON (connected)".

Preferably, the switched state of the MOSFET is controlled by the first controller. Preferably, the source terminal of the MOSFET is substantially connected to zero voltage, or to 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 times less than a given cycle period of the power supply signal in the primary circuit.

In accordance with the present invention, considered from a second aspect, an excitation method of a discharge tube is disclosed, the method comprising

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providing an excitation circuit according to the invention;

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energize the discharge tube using the primary circuit;

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selectively energize the discharge tube using the secondary circuit, at the 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 excitation circuit for a discharge tube, as described above;

Figure 2 is a graphical representation of the voltage waveform of the supply of the rectified ac power grid, using said conventional circuit, as described above;

Figure 3 is a graphical representation of the voltage waveform of a rectified ac power supply, after flattening by a capacitor bank, as described above;

Figure 4 is a circuit diagram of an example excitation circuit, in accordance with a first embodiment of the present invention; Y

Figure 5 is a circuit diagram of an example excitation circuit, in accordance with a second embodiment of the present invention.

In accordance with a first embodiment of the present invention, shown in Figure 4, an excitation circuit 100 comprising a primary circuit 101 and a secondary circuit 102a is disclosed to energize a discharge tube 103. The circuit Primary 101 energizes 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 the service cycles of the rectified power supply.

The primary circuit 101 comprises a diode bridge 106, which rectifies the power supply 104 of the incoming electrical network, 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 through a single diode 107 that ensures the unidirectional flow of current to the discharge tube 103 from the power supply 104. However, the rectified voltage is insufficient to initiate a discharge inside 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 to control an activator circuit 110. The controller 109 receives an input signal from the output of the diode bridge 106, and monitors the variation of the waveform, by means of the signal processing means digital (not shown). Controller 209 includes an output for

delivering a voltage as input to the activator circuit 110. The activator circuit 110 usually includes a booster transformer (not shown) that produces a high voltage peak through the electrodes 108 of the tube.

The high potential difference created through the electrodes 108 by the activator circuit 110 causes the gas 111 inside the tube 103 to ionize, thereby reducing the impedance of the tube 103. However, to ensure that the activator circuit 110 applies the high voltage peak at the right time, that is, when the rectified voltage is sufficient to create a discharge arc, the controller 109 monitors the rectified voltage through connection 112, and delivers a signal to the trigger circuit 110 at a time determined by the digital signal processing means (not shown), in order to cause the trigger circuit 110 to produce the voltage peak. 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 a secondary excitation circuit 102a that includes a second power supply (dc) 113 arranged in series with the rectified voltage supply, and which is used to charge a capacitor bank 114

The secondary circuit also includes a second controller 115 arranged in electronic communication with the first controller 209 to control the selective discharge of the capacitor bank 114.

In use, the first controller 109 causes the activator circuit 110 to produce a high voltage through the electrodes 108, causing the gas 111 inside the tube 103 to ionize, when the rectified voltage through the electrodes 108 of the tube , from a given service cycle, it reaches the minimum value necessary to maintain a discharge arc.

When the rectified voltage subsequently falls below the threshold voltage within the same service cycle, the second controller 115 causes the capacitor bank 114 to discharge progressively, to compensate for the voltage drop at the rectified voltage input. This maintains a constant voltage across the electrodes 108 of the tube and, therefore, a uniform discharge arc.

Initially, the discharge of the capacitor bank 114 is very small. However, when the rectified voltage is reduced more than the threshold voltage, the discharge rate of the capacitor bank 114 is increased, to compensate for the drop in the rectified voltage. When the rectified voltage begins to rise again in the next duty cycle, the capacitor bank 114 begins to recharge progressively from the second power supply 113, so that it is ready to discharge again based on the voltage drop rectified

The second controller 115 monitors the first controller 209 to synchronize the selective charge and discharge of the capacitor bank 114. In this way, the cyclic charge and discharge of the capacitor bank 114 can be used to maintain the discharge arc for a desired period of time.

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 the discharge tube 103, is switched to the "OFF" state (disconnected ) " by the first controller 109, to inhibit the flow of current between the electrodes 108 of the discharge tube 103.

According to a second embodiment of the present invention, which is shown in Figure 5, it can be seen that the primary circuit 101 comprises the components of the primary circuit according to the first embodiment. However, the secondary circuit 102b 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 the battery 119 of capacitors arranged in the secondary circuit 102b, at a time corresponding to a period following the application of a pulse to the activator circuit 110.

The first controller 109 arranged in the primary circuit 101 monitors the variation of the voltage of the rectified electrical network, and delivers a pulse to the activator circuit 110 when the voltage level of the voltage of the rectified electrical network exceeds a threshold value to produce a discharge arc, which can be from 60 to 70 V. The activating pulse causes a high voltage peak to be applied through the electrodes 108 of the discharge tube 103, which ionizes the gas 111 inside the tube 103 and, of that way, it creates a conduction path between the electrodes 108, such that the charge stored in the capacitor bank 119 can be discharged through the tube 103 to produce a radiation pulse.

The current leaving the tube 103 passes through an inductor coil 120 disposed in the secondary circuit 102b and, subsequently, through the second secondary controller 118, which may comprise a semiconductor switch, such as a MOSFET, also arranged in the circuit secondary 102b, before going to ground. The door terminal of the MOSFET 118 is connected to the first controller 209 disposed in the primary circuit 101, so that the first controller 109 disposed in the primary circuit 101 can control the status "ON (connected) / OFF (disconnected)". of the switch 118 and, therefore, control the current passing from the capacitor bank 119 and the primary circuit 101, through the tube 103.

5 After the discharge of the capacitor bank 119, which can take place for a period of time significantly less than the service cycle of the rectified mains voltage, the MOSFET 118 is switched to "OFF (disconnected)" ;. This causes the magnetic field in the inductor 120 to collapse, creating a high voltage peak that is applied through the electrodes 108 of the tube 103, in order to maintain the voltage above the threshold. This collapse of the magnetic field causes a current to flow inside the circuit

10 secondary 102b through diodes 121, and between electrodes 108 of tube 103, to maintain a discharge arc. During this period, the capacitor 119 is recharged by the voltage from the rectified mains voltage, within the same service cycle and, once charged, the MOSFET 120 is switched back to "ON (connected)". , to discharge the capacitor 119 through the tube 103. Thus, by applying a modulated pulsed signal to the MOSFET gate terminal 120, once the voltage of the mains signal

15 rectified initially exceeds a threshold value, it is possible to maintain a discharge arc for a desired period of time.

Furthermore, and in common with the first embodiment, it is possible to produce and maintain a discharge arc during selected periods within a given service cycle of the supply of the rectified power grid, such as with the second embodiment, or during periods comprising several network supply service cycles

20 electrical rectified, as with the first embodiment, with the application of only a single activating pulse.

Therefore, it is clear from the foregoing that the excitation circuit of the present invention allows a discharge tube, energized from a supply of the power grid, to produce a discharge arc of a desired period of time.

Claims (15)

1. An excitation circuit (100) for a gas discharge tube (103), the excitation 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 rectified power supply and a first controller (108) to control the delivery of energy from the power supply to the discharge tube, and the secondary circuit comprising means (114) for storing energy and, at least, a second controller (115) for controlling the delivery of energy from the energy storing means to the discharge tube, characterized in that, the second controller is arranged to selectively discharge the energy storage medium, only at times when the rectified power supply is below a threshold value, as determined by the first controller, so that the selective discharge maintains the tension through the discharge tube above a minimum voltage necessary to maintain a discharge arc in the discharge tube.

2.

 An excitation circuit according to claim 1, wherein the power supply comprises a supply of the AC mains (104), and the primary circuit comprises a diode bridge (106) to rectify the supply of the mains of ac.

3.

 An excitation circuit according to claim 1 or 2, wherein the first controller is arranged to continuously monitor the energy variation of the power supply.

Four.

 An excitation circuit according to any preceding claim, wherein the primary circuit includes an activating mechanism to induce a high voltage peak through the discharge tube, in order to ionize the gas

(111) inside the discharge tube. 5. An excitation circuit according to claim 4, wherein the first controller comprises a circuit (110) of synchronization arranged to activate the activating mechanism only at times when the rectified power supply is above a threshold voltage.

6.

An excitation circuit according to claim 5, wherein the energy storage means comprises at least one capacitor, and the second controller is arranged to cause said at least one capacitor to discharge to compensate for a voltage drop from the rectified power supply, and to maintain the voltage through the discharge tube above the minimum voltage.

7.

 An excitation circuit according to claim 6, wherein the first controller and the second controller are arranged in electronic communication to allow the synchronous discharge of said at least one capacitor with the rectified power supply.

8.

 An excitation circuit according to claim 6 or 7, which provides the discharge of a substantially uniform radiation pulse from the discharge tube, for intervals greater than a given duty cycle of the rectified power supply.

9.

 An excitation circuit according to any of the preceding claims, further comprising a switch (116), such as a metal oxide semiconductor field effect transistor (MOSFET), for terminating the discharge arc.

10.

 An excitation circuit according to any one of claims 1 to 5, wherein the energy storage means comprises an inductor.

eleven.

 An excitation circuit according to claim 10, wherein the energy storage means further comprises a capacitor.

12.

 An excitation 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 the switching of the semiconductor switch.

13.

An excitation circuit according to claim 12, wherein the semiconductor switch has a source terminal substantially connected to zero voltage, or to ground.

14.

 An excitation circuit according to any one of claims 10 to 13, which provides the discharge, from the discharge tube, of a substantially uniform radiation pulse, for intervals less than a given duty cycle of the rectified power supply.

fifteen.

 Excitation method of a discharge tube, the method comprising: - arranging an excitation circuit according to any one of claims 1 to 14; - deliver the rectified power supply to the discharge tube; -selectively deliver energy to the discharge tube from the secondary circuit, only in the

moments when the rectified power supply is below the threshold value.