Charging device for flash lamp capacitor

Abstract

To provide a charging device for a flash lamp capacitor capable of coping with capacitance and a charging voltage of any main discharge capacitor, rapidly performing charging, and greatly reducing power consumption.SOLUTION: A charging device 100 for a flash lamp capacitor housed in a metal outer casing 300 includes: a switching element 106; a signal gate 166; a main discharge capacitor 157; a charging circuit that charges the main discharge capacitor 157 by on / off control of the switching element 106; an off-period setting circuit 103 of the switching element 106; a compensation capacitor 171; a first comparator 152 that discharges the compensation capacitor 171 when a charging voltage signal of the main discharge capacitor 157 matches a predetermined value; a second comparator 167 that outputs a signal when a voltage signal based on a current passing through the switching element 106 matches a voltage value based on a charging voltage of the compensation capacitor 171; an order setting circuit 165; and a time limit circuit 141.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a charging device for a capacitor for a flash lamp. [Background technology]

[0002] In recent years, flash lamps, which use xenon gas as the inert gas, have been used as light sources for spectroscopic analysis because they can emit a strong emission spectrum across a wide range from ultraviolet to infrared. Applications include water quality testing equipment, automobile exhaust gas monitors, and nitrogen oxide monitors. Because light emission is achieved through an arc discharge caused by the discharge of a charging capacitor, these lamps have higher light output, less heat generation, and a longer lifespan than light sources such as deuterium lamps. Their energy-saving and maintenance-free nature make them popular as light sources.

[0003] However, when a flash lamp emits light, the main discharge capacitor is completely discharged with each arc discharge, so the main discharge capacitor must be recharged from approximately 0 V to a predetermined voltage before the next light can be emitted. In actual spectroscopic analysis, a flash lamp may be emitted multiple times, the photoelectromotive force obtained from the light-receiving element each time light is emitted is integrated, and the accumulated photoelectromotive force is analyzed by analog-to-digital conversion or other methods. This method requires a reduction in the charging time of the main discharge capacitor in order to increase the number of light emissions per unit time in order to shorten the analysis time, and various improvements have been attempted.

[0004] As an example of this improvement, an integrated control element specialized for shortening the charging time for rapid charging of capacitors has been applied to products. However, this type of integrated control element is not used for general-purpose switching power supply control, so it is produced in small quantities and is expensive, making it economically unsuitable for incorporation into rapid charging devices for flash lamp capacitors, and so has not yet provided a fundamental solution.

[0005] Patent Document 1 discloses a discharge lamp lighting device that can prevent damage to elements in the circuit. More specifically, since a capacitor is nearly empty after flash discharge, a large current flows when the capacitor starts to store charge after flash discharge, which can cause various malfunctions in the quick charger. The document describes a control circuit that suppresses the on / off duty ratio of a switching element during a suppression period until the capacitor's charging voltage reaches a predetermined reference voltage value that is lower than the target voltage value, thereby increasing the current flowing through the switching element so that it does not exceed the reference current value.

[0006] Patent Document 2 discloses a power supply circuit for a xenon flash lamp that can perform stable charging even when repeatedly flashing at high speeds. More specifically, in a power supply circuit for a xenon flash lamp, increasing the charging rate makes it difficult to stop charging the main discharge capacitor at a target voltage. If the capacitor is charged beyond the target voltage, a voltage is applied between the anode and cathode of the lamp, causing arcing even without a trigger from the trigger power supply. Therefore, the patent document discloses a power supply circuit that includes a charging means for charging the capacitor and a charge control circuit for controlling the charging means. The charge control circuit charges the capacitor at a predetermined charging rate until the capacitor voltage reaches a predetermined voltage, and then charges the main discharge capacitor at a rate slower than the predetermined charging rate until the capacitor voltage reaches the target voltage from the predetermined voltage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5915946 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-37095 Summary of the Invention

[0008] Patent Documents 1 and 2 disclose charging technologies that overcome the various drawbacks that arise from rapid charging of the main discharge capacitor, but because the energy of a single arc discharge varies depending on how the user uses it, the capacity of the main discharge capacitor varies depending on the model, and even for the same model, the charging voltage of the main discharge capacitor varies from low to high. What is needed is a charging circuit for a flash lamp that can accommodate these different main discharge capacitor capacities and charging voltages, can charge quickly, and can significantly reduce power consumption.

[0009] In view of the above problems, the present invention aims to provide a charging device for a flash lamp capacitor that can accommodate any capacitance and charging voltage of the main discharge capacitor, can charge quickly, and can significantly reduce power consumption. [Means for solving the problem]

[0010] In order to solve the above problem, the invention of claim 1 provides a flash lamp capacitor, comprising: a switching element; a signal gate for driving the switching element; a charging circuit for charging the flash lamp capacitor by controlling the on / off of the switching element; an off-period setting circuit for the switching element; a compensation capacitor that is charged with a constant current; a first comparator that discharges the compensation capacitor when a charging voltage signal of the flash lamp capacitor matches a predetermined charging voltage target value; and a second comparator that outputs a signal when a voltage signal based on the current passing through the switching element matches a voltage value based on the charging voltage of the compensation capacitor. a sequence setting circuit, and a time limit circuit that starts its operation in response to an input of a start signal, wherein the sequence setting circuit outputs an ON signal to the signal gate and stops the operation of the OFF period setting circuit in response to a signal output from the OFF period setting circuit, and outputs an OFF signal to the signal gate and starts the operation of the OFF period setting circuit in response to a signal output from the second comparator, and the time limit circuit outputs a trigger signal that starts a preliminary discharge prior to arc discharge of the flash lamp, and closes the signal gate, and opens the signal gate when the time limit circuit finishes its operation after a predetermined time has elapsed. According to the invention as set forth in claim 1, it is possible to provide an inexpensive quick charging device for a flash lamp capacitor that can accommodate any capacity and charging voltage of the main discharge capacitor. The invention described in claim 2 is the charging device for a flash lamp capacitor described in claim 1, characterized in that the charging circuit is provided with a first filter means, the charging voltage signal of the flash lamp capacitor is input to the first comparator via the first filter means, and a second filter means is provided in the circuit that discharges the compensation capacitor using the first comparator. According to the invention described in claim 2, it is possible to provide a rapid charging device for a flash lamp capacitor that can charge quickly and without overshooting the target charging voltage regardless of the capacity and charging voltage of the main discharge capacitor. The invention described in claim 3 is a charging device for a capacitor for a flash lamp, comprising a switching element, a signal gate that drives the switching element, a capacitor for a flash lamp, a charging circuit that charges the capacitor for the flash lamp by controlling the on / off of the switching element, an operating power supply circuit that supplies operating voltage to the charging circuit, and a metal enclosure that surrounds the charging circuit, characterized in that a capacitor for absorbing high-frequency noise is provided between a terminal leading to the outside of the charging circuit and the metal enclosure, and a pulse noise reduction filter circuit that attenuates internal noise is provided between the sleep terminal of the operating power supply circuit and the terminal leading to the outside. According to the invention described in claim 3, it is possible to provide a rapid charging device for a flash lamp capacitor that can eliminate failure of the sleep function due to internal noise and significantly reduce power consumption when the charging circuit that charges the flash lamp capacitor is in standby mode. [Effects of the Invention]

[0011] The flash lamp capacitor charging device of the present invention can accommodate any capacitance and charging voltage of the main discharge capacitor, and can charge quickly, greatly reducing power consumption. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a partially cutaway perspective view of a flash lamp according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan cross-sectional view of a sparker of the flash lamp of FIG. 1. [Figure 3] FIG. 2 is a side cross-sectional view of a sparker of the flash lamp of FIG. 1. [Figure 4] 1 is a partial block circuit diagram of a charging device for a flash lamp capacitor according to an embodiment of the present invention; [Figure 5] 1 is a partial block circuit diagram of a prior art rapid charging device for a flash lamp capacitor; [Figure 6]3 is a waveform diagram showing the relationship between various signals and current and voltage in a rapid charging mode of a charging device for a flash lamp capacitor according to one embodiment of the present invention. FIG. [Figure 7] 1 is a waveform diagram showing the relationship between various signals and current and voltage in a relaxed charging mode of a charging device for a flash lamp capacitor according to one embodiment of the present invention. [Figure 8(A)] 4A and 4B are waveform diagrams of the voltage of the main discharge capacitor and related waveform diagrams; [Figure 8(B)] 1A and 1B are voltage waveform diagrams of a conventional main discharge capacitor and related waveform diagrams. [Figure 9] FIG. 2 is a partial block circuit diagram showing details of a buck-boost converter according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention (hereinafter referred to as examples) will be described with reference to the drawings. In the following drawings, common parts are given the same reference numerals, and duplicated explanations of parts with the same reference numerals will be omitted.

[0014] [Configuration of flash lamp 1] The configuration of a suitable flash lamp 1 using a flash lamp capacitor charging device 100 (hereinafter referred to as charging device 100) of this embodiment will be described with reference to Figure 1. As shown in Figure 1, flash lamp 1 is composed of a lamp housing 2 sealed and filled with inert gas, a cathode 20 and an anode 30 that generate an arc discharge, a trigger electrode 40 that performs a preliminary discharge prior to the arc discharge, and multiple sparkers (a first sparker 60 and a second sparker 70) that promote ionization for starting the arc discharge. The first sparker 60 and the second sparker 70 are spaced apart so that when they discharge, the sparks spark without mixing or interfering with each other. The inert gas to be filled is, for example, xenon gas.

[0015] The cathode 20 and anode 30 have opposing end faces with roughly conical shapes at their tips, each with a small spherical surface, to ensure a stable arc discharge path. Lead rods 21 and 31 are press-fitted into the other ends of the cathode 20 and anode 30, respectively, and the electrodes are further secured to leads 22 and 32 by spot welding or the like.

[0016] The lead 32 electrically connected to the anode 30 is embedded so as to penetrate the metallic, disk-shaped stem 3 via a glass, hemispherical insulator 33 that ensures a long creepage distance.

[0017] The lamp housing 2 is composed of a stem 3, a metal cap 4, and a transmission glass 5. One end of the cap 4 is fitted onto the outer periphery of the metal stem 3, and the fitting is welded and sealed. Meanwhile, the transmission glass 5 is welded to the inside of the flange at the other end of the cap 4, allowing arc discharge light from the cathode 20 and anode 30 to pass through.

[0018] A metal exhaust pipe 6 is welded to the center of the stem 3, and an inert gas such as xenon gas is injected through the exhaust pipe 6, and then the exhaust pipe 6 is sealed to hermetically seal the lamp housing 2.

[0019] 1, the tip of the trigger electrode 40 is positioned slightly closer to the cathode 20 on the approximate line connecting the small spherical portions of the opposing end faces of the cathode 20 and the anode 30. A lead 42 is fixed to the trigger electrode 40 by spot welding or the like, and, like the anode 30, is embedded so as to penetrate the stem 3 via a glassy insulator 43 and extend to the outside of the lamp housing 2. In this embodiment, the leads 22, 32, 42, 62, 72, the stem 3, the cap 4, and the exhaust pipe 6 are made of metal, such as Kovar metal.

[0020] As shown in the cross-sectional views of Figures 2 and 3, the first sparker 60 has a structure in which a sparker pin 61 made of tungsten or the like is surrounded by a cylindrical insulator 64 made of alumina or the like with sufficient tracking resistance, and the periphery of this is surrounded by a nickel plate 65 which serves as the cathode. The nickel plate 65 is fixed by welding to the stem 3. One end of the sparker pin 61 is led out to the outside of the lamp housing 2 via a lead 62 which is embedded so as to penetrate the stem 3 via a glassy insulator 63. As shown in Figure 2, the end faces of the sparker pin 61, insulator 64 and nickel plate 65 are arranged at the other end of the sparker pin 61 in a manner that is substantially flush with each other, and a creeping or space discharge occurs between the sparker pin 61 and the nickel plate 65. The second sparker 70 also Similar to the first sparker 60 , it is composed of a glass insulator 73 , a cylindrical insulator 74 made of alumina or the like, a nickel plate 75 , a lead 72 and a sparker pin 71 .

[0021] In the flash lamp 1 configured as described above, the flash lamp capacitor (hereinafter referred to as the main discharge capacitor, 157 in FIG. 4) connected in parallel between the cathode 20 and anode 30 that generate the arc discharge is charged to approximately 300 V to 1000 V with the cathode 20 at a negative potential and the anode 30 at a positive potential, and then a steep spike voltage of approximately minus 4000 V is applied between the cathode 20 and the sparker pin 61 of the first sparker 60, the sparker pin 71 of the second sparker 70, the trigger electrode 40, and the anode 30, with the cathode 20 as the reference potential.

[0022] When the steep spike voltage drops to about minus 4000V and reaches a spike voltage value of about minus 500V to minus 2500V after a few hundred nanoseconds, preliminary discharges start at different spike voltage values between the cathode 20 and the trigger electrode 40, between the nickel plate 65 electrically connected to the cathode 20 and the sparker pin 61, and between the nickel plate 75 and the sparker pin 71, and ionization for starting the arc discharge progresses. After that, about 1 microsecond later, the space filled with inert gas between the cathode 20 and the anode 30 breaks, causing an arc discharge and light emission.

[0023] [Partial block circuit diagram of charging device 100] Next, a partial block circuit diagram of charging device 100 of the present invention will be described with reference to Fig. 4. In Fig. 4, positive and negative DC voltages are applied from power supply terminals A and B, respectively. Charging device 100, including flash lamp 1, is housed in a metal enclosure 300.

[0024] In this embodiment, the DC input voltage ranges from the 3.3V system used in USB power supplies to the 24V system used in factory automation control, but the present invention is not limited to this voltage range. Smoothing capacitor 104 is connected in parallel to power supply terminals A and B. Connected in series across smoothing capacitor 104 are the primary winding input of flyback transformer 105, the drain and source terminals of MOSFET 106, which serves as a switching element, and current detection resistor 107, which detects the current passing through MOSFET 106, in this order. The connection point between smoothing capacitor 104 and resistor 107 serves as the GND (ground) of charging device 100, and a gate drive signal gate 166 is connected to the gate terminal of MOSFET 106.

[0025] Here, an example using a step-up / step-down converter will be described as operating power supply circuit 109. Step-up / step-down converter 109 is a step-up / step-down converter that uses power supply terminals A and B as its power source, and enables charging device 100 to operate over a wide range of input DC voltages from 3.3V to 24V. To do this, it always supplies a stable operating voltage of 12V from Vcc 12V regardless of the power supply voltage, and serves as the power source for operating signal gate 166 and gate driver 147 of IGBT 139. Three-terminal regulator 110 receives the output from step-up / step-down converter 109 as its input, and in this case supplies a stable 5V from Vcc 5V to each control element.

[0026] A bias resistor 111 is connected between the power supply input terminal I of the buck-boost converter 109 and the output on / off control terminal EN, allowing it to operate even when the I terminal is at a low voltage. The elements enclosed by the dashed line, a noise absorbing capacitor 117, a noise voltage attenuation resistor 112, a noise absorbing varistor 113, and the like, either alone or in combination, form a pulse noise reduction filter circuit 114 that protects the EN terminal from damage caused by external noise.

[0027] When the sleep terminal C and GND terminal D of resistor 112 are short-circuited, the EN terminal voltage of buck-boost converter 109 drops, causing buck-boost converter 109 to enter a disabled state and stop operating. At this time, the voltage of Vcc12V at output terminal O of buck-boost converter 109 becomes approximately 0V, so charging device 100 is maintained in a low-power sleep state. On the other hand, when the sleep terminal C and GND terminal D of resistor 112 are opened, buck-boost converter 109 starts operating, and charging device 100 charges main discharge capacitor 157.

[0028] In the above explanation, an example was described in which operating power supply circuit 109 uses a step-up / step-down converter to accommodate a wide range of input DC voltages from 3.3 V to 24 V, but operating power supply circuit 109 is not limited to this step-up / step-down converter, and for example, a step-up converter can be used if the input DC voltage is about 12 V or less, and a step-down converter or series regulator can be used if the input DC voltage is about 12 V or more. It is clear that the object of this application can be achieved by controlling the sleep function with any converter or regulator as long as it can always supply a stable operating voltage of 12 V from Vcc 12 V regardless of the input DC voltage.

[0029] The secondary winding output of the flyback transformer 105 is configured to charge the main discharge capacitor 157 via a reverse-blocking diode 115. A reverse-charge prevention diode 119 is also provided in parallel with the main discharge capacitor 157, in the opposite direction to the charging polarity. This diode prevents the main discharge capacitor 157 from being reverse-charged by the oscillating current generated during rapid discharge of the main discharge capacitor 157. Both ends of the main discharge capacitor 157 are connected to the anode 30 and cathode 20 of the flash lamp 1 via a discharge stabilization diode 120, forming an arc discharge circuit. The capacitance of the main discharge capacitor 157 can be varied, from a small capacitance of approximately 0.02 microF to a large capacitance of approximately 0.33 microF, and the charging voltage can also be adjusted accordingly. This allows the single discharge energy of the flash lamp 1 to be selected to meet various customer requirements. This means that any capacitance and charging voltage of the main discharge capacitor 157 can be accommodated. The flyback transformer 105, diode 115, and main discharge capacitor 157 form a charging circuit.

[0030] A high-voltage pulse voltage of approximately minus 4000 V is output from the secondary winding of trigger transformer 121, and DC blocking capacitors 122, 123, 124, and 125 have one end connected to the secondary winding of trigger transformer 121 and the other end connected to the anode 30, trigger electrode 40, first sparker 60, and second sparker 70 of flash lamp 1, respectively, as shown in the figure, and high-resistance discharge resistors 126, 127, 128, and 129 are connected in parallel to each of capacitors 122, 123, 124, and 125.

[0031] In this embodiment, the flash lamp 1 has been described as having two sparkers, the first and second sparkers 60 and 70, but even if there is only one sparker, this does not affect the performance of the charging device 100, and the present invention is not limited to this embodiment.

[0032] A charging circuit for a pulse-generating capacitor 135 is formed from the intermediate winding of the secondary winding of the flyback transformer 105 to the primary side of the trigger transformer 121 via a reverse-blocking diode 133. A regulator circuit for keeping the charging voltage of the capacitor 135 constant between approximately 100 V and approximately 200 V is provided in the middle of the charging circuit, and is formed by a MOSFET 134, a resistor 137, and a Zener diode 138. An IGBT 139 discharges the charge stored in the capacitor 135 to the primary side of the trigger transformer 121. Diodes 136 and 140 are diodes for bypassing reverse current, and a driver 147 is a driver for driving the gate of the IGBT 139.

[0033] The anode side of the light-emitting diode inside photocoupler 142 is connected to start-up signal input terminal G via current-limiting resistor 143, and the cathode side of the light-emitting diode is connected to trigger input return terminal H. Meanwhile, a pull-up resistor 144 is connected to the collector of the phototransistor inside photocoupler 142. When a voltage signal that serves as a start-up signal is input from terminals G and H to charging device 100, the collector end on the phototransistor side of photocoupler 142 inverts from logic Hi to logic Lo during the pulse input period, and one-shots 145 and 146 begin time-limited operation, causing flash lamp 1 to emit light.

[0034] One-shots 145 and 146 form timing circuit 141, and one-shot 145 outputs a time-delay pulse of approximately 500 microseconds at its Q output terminal, which is logic high. Therefore, the logic low input terminal of signal gate 166 goes to logic high during this period, and the switching operation of MOSFET 106 is temporarily halted for the duration of the 500 microsecond pulse output.

[0035] In parallel with this operation, one-shot 146 outputs a time-delayed pulse, here logic High, of about 20 microseconds to gate driver 147. The logic Low input terminal of gate driver 147 goes Low for this period, turning on IGBT 139, and the charge stored in capacitor 135 excites the primary winding of pulse transformer 121. A steep pulse voltage of about minus 4000 V is applied from the secondary winding via capacitors 122 to 125, with cathode 20 as the reference potential, to cathode 20, sparker pin 61 of first sparker 60, sparker pin 71 of second sparker 70, trigger electrode 40, and anode 30. An arc discharge occurs between anode 30 and cathode 20 by a mechanism described below, causing flash lamp 1 to emit light.

[0036] First comparator 152, whose output terminal is of an open collector type, outputs a signal to a downstream circuit for maintaining the charging voltage of main discharge capacitor 157 at a predetermined constant voltage in the range of approximately 300 V to 1000 V in this embodiment. A divided voltage obtained by dividing the charging voltage of main discharge capacitor 157 using series-connected voltage-dividing resistors 148 and 149 is applied to the negative feedback terminal of first comparator 152. On the other hand, the charging voltage of main discharge capacitor 157 can be changed depending on the voltage value applied to the positive feedback terminal of first comparator 152.

[0037] A changeover switch 156 selects either the voltage signals from the external voltage control terminals E and F or the voltage signal set by the semi-fixed resistor 153, and supplies this to the positive feedback terminal of the comparator 152. Resistors 118 and 130 are both resistors for limiting the voltage setting range, connected to the high and low potential sides of the semi-fixed resistor 153. The positive feedback terminal of the first comparator 152 is connected to the common terminal of the changeover switch 156 via a resistor 158 for noise attenuation.

[0038] A short logic High pulse is output from output terminal 168 of oscillator 160 in off-period setting circuit 103 of switching element (MOSFET) 106 to set terminal S of sequence setting circuit 165, and logic High is output from output terminal #Q of sequence setting circuit 165 at the rising edge of output terminal 168 changing from logic Low to logic High.

[0039] At input terminal 169 of oscillator 160, timing resistors 161 and 162 and a timing capacitor 163 connected in series to each other and determining the output period of oscillator 160 are provided between Vcc5V and GND, and the junction of resistor 162 and capacitor 163 is connected to input terminal 169. In addition, MOSFET 177 is connected in parallel between the junction of resistors 161 and 162 and GND, and its gate terminal is connected to the output terminal of sequence control circuit 165. The configuration of these functional components forms off-period setting circuit 103.

[0040] Constant current generator 170, powered by Vcc 5V, constantly charges compensation capacitor 171 at approximately 1 mA. Compensation capacitor 171 is provided with voltage-dividing resistors 174 and 176 connected in series via reverse-blocking diode 173 in parallel. Resistor 176 is connected in parallel with Zener diode 175, which functions as a voltage limiter, and a voltage value based on the charging voltage of compensation capacitor 171 is supplied to the negative feedback terminal of second comparator 167. In this way, by providing Zener diode 175, which functions as a voltage limiter, a clipped voltage is generated, and when the charging voltage of compensation capacitor 171 exceeds a certain voltage, the maximum value of the current flowing through MOSFET 106 also becomes constant, ensuring stable current control.

[0041] The output terminal of the second comparator 167 is connected to the reset terminal R of the sequence setting circuit 165, and the reset terminal R of the sequence setting circuit 165 operates at the rising edge of the output terminal of the second comparator 167 changing from logic Lo to Hi, and this edge operation causes logic Lo to be output from the #Q output terminal of the sequence setting circuit 165.

[0042] In this case, the operation of off period setting circuit 103 is similar to that of a so-called one-shot, and the operation of sequence setting circuit 165 is similar to that of a so-called flip-flop. When a predetermined time has elapsed since the start of operation, off period setting circuit 103 outputs a short logic high pulse signal from output terminal 168 of its internal oscillator 160 to set terminal S of sequence setting circuit 165. Then, sequence setting circuit 165 outputs a logic high on signal from output terminal #Q to signal gate 166 and outputs an on signal to MOSFET 177 to stop the operation of off period setting circuit 103 and turn on MOSFET 106.

[0043] Next, when the rising voltage from resistor 107 matches the output voltage of compensation capacitor 171, second comparator 167 outputs a signal that rises from logic Lo to logic Hi from its output terminal to reset terminal R of sequence setting circuit 165. As a result, an off signal of logic Lo is output from the #Q output terminal of sequence setting circuit 165 to signal gate 166, which outputs an off signal to MOSFET 177 to start operation of off period setting circuit 103 and turn off MOSFET 106.

[0044] A detection voltage of a resistor 107 that detects the current flowing through the primary winding of the flyback transformer 105, i.e., the MOSFET 106, is applied to the positive feedback terminal of the second comparator 167. The output terminal of the first comparator 152 is connected to the output terminal of a constant current generator 170 of a compensation capacitor 171 via a discharge resistor 172.

[0045] With the above-described configuration, the main discharge capacitor 157 is charged by constant current charging, which keeps the maximum value of the current flowing through the primary winding of the flyback transformer 105 constant through the operation of the second comparator 167, and the charging voltage of the main discharge capacitor 157 is controlled by voltage feedback control, which discharges the charging voltage of the compensation capacitor 171 using the constant current generator 170 through the operation of the first comparator 152.

[0046] Next, a partial block circuit diagram of a prior art flash lamp lighting device will be described with reference to FIG. 5. In FIG. 5, components with the same functions as those in FIG. 4 are assigned the same numbers. FIG. 5 differs from FIG. 4 in that the input terminal of gate 159, which has an open-collector output, is connected to the time-delay pulse output terminal #Q of one-shot 145, which has a logic low, and the output terminal of gate 159 is connected to the connection terminal between first comparator 152 and resistor 172; signal gate 166 is not provided; and the #Q output terminal of sequence setting circuit 165 is connected to gate driver 108 for MOSFET 106. The rest of the circuit configuration is the same as the circuit in FIG. 4.

[0047] [Operation of the charging device 100] The operation of the charging device 100 will be explained using Figures 6, 7, 8(A), and 8(B). Figure 6 is a relational waveform diagram showing the operating state of the charging device 100 in rapid charge mode, and Figure 7 is a relational waveform diagram of the charging device 100 in relaxed charge mode. Figure 8(A) is a voltage waveform diagram of the main discharge capacitor 157 and its relational waveform diagram. Figure 8(B) is a voltage waveform diagram of the conventional main discharge capacitor 157 and its relational waveform diagram. In each waveform diagram, the vertical axis represents the voltage value or current value, and the horizontal axis represents the time. Since the operation of the charging device 100 of the present invention overlaps in many parts with the operation of the conventional technology (the circuit of Figure 5), the operation of the conventional technology will be explained first.

[0048] The voltage at input terminal 169 of oscillator 160 repeats as shown by the voltage waveform (250H in FIG. 6), and timing capacitor 163 is charged from Vcc 5V by timing resistors 161 and 162. Meanwhile, when MOSFET 177 is turned on, timing capacitor 163 is discharged by timing resistor 162.

[0049] A short logic High pulse is output from output terminal 168 of oscillator 160 to set terminal S of sequence setting circuit 165 at the peak of the waveform input at input terminal 169, as shown in the voltage waveform (251H in FIG. 6) due to the action of the Schmitt trigger or voltage comparator inside oscillator 160. A logic High is output from the #Q output terminal of sequence setting circuit 165 at the rising edge of the change from logic Low to logic High at output terminal 168, as shown in the voltage waveform (252H in FIG. 6). As a result, the gate of MOSFET 106 is set to 12V by MOSFET 106 gate drive driver 108, turning MOSFET 106 on. A current whose value rises linearly over time flows through the primary winding of flyback transformer 105, as shown in 253H in FIG. 6, and MOSFET 177 is also turned on, causing timing capacitor 163 to begin discharging via timing resistor 162.

[0050] In the state indicated by 254H, when the voltage at the positive feedback terminal of the second comparator 167 is at the Zener voltage of the Zener diode 175, the main discharge capacitor 157 is in a mode in which it is rapidly charged, and constant-current charging is performed in which the maximum value of the current flowing through the primary winding of the flyback transformer 105 is determined by the Zener voltage of the Zener diode 175.

[0051] When the voltage drop across current detection resistor 107 reaches the Zener voltage of Zener diode 175, the output of second comparator 167 inverts from logic Low to Hi, a reset signal is output to the R terminal of sequence setting circuit 165, its #Q terminal inverts to logic Low, the input logic of gate drive driver 108 also becomes Low, MOSFET 106 turns off, and the current to the primary winding of flyback transformer 105 is cut off. As a result, current now flows from the secondary winding of the flyback transformer via diode 115 to main discharge capacitor 157, and main discharge capacitor 157 is charged once. In parallel with this operation, MOSFET 177 also turns off, and timing capacitor 163 is again charged from Vcc 5V by timing resistors 161 and 162.

[0052] As this charging progresses, when a short logic high pulse is output again from output terminal 168 of oscillator 160 to set terminal S of sequence setting circuit 165 at the peak of the waveform input at input terminal 169, the same operation as above is repeated.

[0053] 7, where the voltage at the positive feedback terminal of second comparator 167 is lower than the Zener voltage of Zener diode 175, the state is indicated by 254L. Main discharge capacitor 157 is in a relaxed charge mode after nearly reaching the target charge voltage, and constant current charging is performed, with the maximum value of the current flowing through the primary winding of flyback transformer 105 being lower than the Zener voltage of Zener diode 175. When the voltage drop across current detection resistor 107 reaches the level of 254L, MOSFET 106 turns off in the same manner as described above, preventing current from flowing to the primary winding of flyback transformer 105. MOSFET 177 also turns off, and timing capacitor 163 is recharged from Vcc 5V by timing resistors 161 and 162.

[0054] When a start signal is input to photocoupler 142, current flows to the light-emitting diode side of photocoupler 142, the phototransistor turns on, one-shot 146 of timing circuit 141 starts timing operation, and in this case a pulse of about 20 microseconds serving as a trigger signal for starting preliminary discharge prior to arc discharge in flash lamp 1 is output to the input terminal of driver 147. At this time, the logic Lo input terminal of driver 147 is also Lo, so a signal for driving the gate of IGBT 139 is output from driver 147, and when IGBT 139 turns on, the charge stored in pulse-generating capacitor 135 is discharged to the primary side of trigger transformer 121. As described above, a high-voltage, steep spike voltage of approximately minus 4000 V, with the cathode 20 as the reference potential, is output from the secondary winding of the trigger transformer 121 between the cathode 20 and the sparker pin 61 of the first sparker 60, the sparker pin 71 of the second sparker 70, the trigger electrode 40, and the anode 30, causing the flash lamp 1 to arc.

[0055] In this way, the flash lamp lights up instantly, and the charging voltage of the main discharge capacitor 157 drops rapidly, as shown by 257b in Fig. 8(B). In parallel with this, the one-shot 145 also starts its time-limit operation, outputting a 500 microsecond time-limit pulse. This corresponds to the period T0b in Fig. 8(B), and a logic low signal is sent from the #Q terminal of the one-shot 145 to the open collector driver 159.

[0056] Because this output terminal becomes Low, the charge in compensation capacitor 171 is discharged via resistor 172 during this time, and since the voltage becomes nearly 0 V, MOSFET 106 turns off and charging of main discharge capacitor 157 stops for 500 microseconds. This state is shown schematically by the voltage waveform (255b in FIG. 8(B)) of the negative feedback terminal of second comparator 167. Note that 255 in the figure indicates the 0 V potential of compensation capacitor 171.

[0057] During this 500-microsecond period T0b, the inert gas inside flash lamp 1 returns from the ionized state it was in at the time of light emission to its original inactive state. 500 microseconds after flash lamp 1 starts arc discharge, which is the deionization time, one-shot 145 ends its time-delay operation and returns to its original stable state. After the stable state (258b), open-collector driver 159 turns off its output, charging compensation capacitor 175 from constant current generator 170. The charging voltage gradually increases, and main discharge capacitor 157 is charged. At this time, main discharge capacitor 157 initially goes through a relaxed charging state shown at 254L in FIG. 7, and then transitions to a rapid charging mode shown at 254H in FIG. 6. Therefore, the charging state of main discharge capacitor 157 follows the charging curve shown at 256b in FIG. 8(B), and the initial charging time (T1b) is required.

[0058] When charging of the main discharge capacitor 157 to the predetermined voltage is completed and thereafter, the mode switches to relaxed charge mode, and the voltage at the negative feedback terminal of the first comparator 152 repeatedly matches and mismatches with the voltage at the positive feedback terminal. As a result, the discharge of the compensation capacitor 171 from the first comparator 152 via the resistor 172 and the charge from the constant current generator 170 are balanced, resulting in the state shown by 254L in Figure 7.

[0059] Next, the operation of the charging device 100 of the present invention will be explained based on Fig. 4. Note that explanations of parts that overlap with the operation of the prior art (Fig. 5) will be omitted. When the one-shots 145 and 146 start their time-limited operation, one-shot 146 outputs a 20 microsecond pulse that serves as a trigger signal, the flash lamp is instantly lit, and the charging voltage of main discharge capacitor 157 drops rapidly as shown by 257a in Fig. 8(A).

[0060] A logic high 500 microsecond time-limited pulse is output from the Q output of one-shot 145 to signal gate 166, which closes the gate and causes its output terminal to go low. This corresponds to period T0a in Figure 8(A), during which MOSFET 106 is turned off and charging of main discharge capacitor 157 is stopped for 500 microseconds.

[0061] During this 500 microsecond period T0a, the negative feedback terminal of first comparator 152 is approximately 0 V, so the output of first comparator 152 is turned off, and compensation capacitor 171 is not discharged by resistor 172, so the input terminal of second comparator 167 quickly returns to the voltage of Zener diode 175. This state is shown schematically by the voltage waveform (255a in FIG. 8A) of the negative feedback terminal of second comparator 167.

[0062] When one-shot 145 finishes its time-limit operation and returns to its original stable state, the negative logic input terminal of signal gate 166 goes to logic low, opening the gate. Constant-current charging is then performed, with the current flowing through the primary winding of flyback transformer 105 at a predetermined constant current value from the time charging of main discharge capacitor 157 begins (258a in FIG. 8A). Thereafter, the charging state of main discharge capacitor 157 follows the charging curve 256a shown in FIG. 8A, requiring time (T1a) at the beginning of charging. This charging time (T1a) is shorter than the charging time (T1b) of the prior art.

[0063] 6, in the state indicated by 254H in which main discharge capacitor 157 is in the rapid charging mode, MOSFET 106 is on for T3, which is determined by the voltage of smoothing capacitor 104, the inductance of the primary winding of flyback transformer 105, and the current of the primary winding of flyback transformer 105, which is set to a constant rising value. Meanwhile, MOSFET 106 is off for T4, which is determined by the time until timing capacitor 163 is recharged from Vcc 5V by timing resistors 161 and 162, and this charging progresses until a short logic high pulse is again output from output terminal 168 of oscillator 160.

[0064] Therefore, the time constant defined by the capacitance of timing capacitor 163 and timing resistors 161 and 162 is set so that time T4 is approximately equal to the time it takes for a flyback current to flow through the secondary winding of flyback transformer 105 and charge main discharge capacitor 157. If the sum of T3 and T4 is 20 microseconds, the operating cycle is 50 kHz, and main discharge capacitor 157 has a capacitance of 0.02 microF, then it will take only about 65 charging cycles to reach a charging voltage of 600 V when the power supply voltage is 5 V. Therefore, if it takes a long time for the charging voltage of main discharge capacitor 157 to settle to the target charging voltage, it will be the same as if the apparent charging time were longer, so reducing the above-mentioned overshoot and charging voltage ripple is an important issue.

[0065] Resistor 150 and capacitor 151 connected in series are connected in parallel to voltage dividing resistor 148. These are provided to prevent the charging voltage of main discharging capacitor 157 from exceeding the target charging voltage and overshooting by temporarily increasing the voltage across voltage dividing resistor 149 while main discharging capacitor 157 is being charged.

[0066] On the other hand, resistor 154 and capacitor 155 are provided to integrate the output voltage of voltage dividing resistor 149 and apply the result to the negative feedback terminal of first comparator 152, thereby enabling the charging voltage to reach the target charging voltage as quickly as possible at the end of charging main discharge capacitor 157, thereby shortening the charging time. Resistor 150 and capacitor 151, and resistor 154 and capacitor 155 constitute a first filter means.

[0067] Furthermore, resistor 131 and capacitor 132 connected in series to each other form an integrating circuit provided between the output terminal of first comparator 152 and GND, and constitute second filter means. The second filter means can reduce pulsation in the charging current of main discharge capacitor 157, and is therefore effective in reducing ripple in the charging voltage, and in cooperation with the first filter means, achieves high-quality rapid charging of main discharge capacitor 157.

[0068] [Sleep function] Next, in order to explain the sleep function according to the present invention, Fig. 9 shows details of the step-up / step-down converter 109 of the flash lamp capacitor charging device 100 and the pulse noise reduction filter circuit 114. Parts with the same functions as those in Fig. 4 are assigned the same numbers, and duplicated explanations will be omitted.

[0069] 9, the buck-boost converter 109 is shown enclosed by a dashed line, and the boost converter element is indicated by 186, and is configured as a SEPIC converter using, for example, a buck-boost converter element LM5001 manufactured by Texas Instruments, Inc. Note that the terminal numbers of the boost converter element 186 are assigned the same numbers as those of the SO-8 package product.

[0070] Capacitor 199 is a buffer capacitor provided between the power supply input terminal (2) and the GND terminal (4). Inductor 187 is connected between the power supply input terminal (2) and the switching pin (1). Capacitor 188 and inductor 189 are connected in series between the switching pin (1) and the GND terminal (4). Furthermore, a Schottky diode 190 and a capacitor 191 are connected in parallel to inductor 189, and both ends of capacitor 191 form the output terminal of the step-up / step-down converter 109.

[0071] In order to maintain the voltage of capacitor 191 at a constant 12 V in this example, a feedback voltage is fed back to feedback input (6) from the junction of voltage-dividing resistors 192 and 193 connected in parallel to capacitor 191, and an impedance network consisting of resistor 194, capacitor 195, and capacitor 196, which form a loop compensation circuit, is connected between COMP pin (7) and feedback input (6). Furthermore, an operation stabilization capacitor 197 is connected to regulator terminal (3), and a resistor 198 is connected to frequency setting terminal (5).

[0072] 4, terminals A to F are provided as terminals leading out to the outside, and power supply terminals A and B, sleep terminal C and GND terminal D, start signal input terminal G and start signal input return terminal H, external voltage control terminals E and F are connected to metal enclosure 300 by respective high frequency noise absorbing capacitors 178, 179, 180, 181, 182, 183, 184, and 185. Each terminal leading out to the outside is connected to a shielded cable or the like, which is taken out to the outside of metal enclosure 300 and used to connect to a device that controls charging device 100. The shielded wire of the shielded cable is usually connected to enclosure 300.

[0073] When the flash lamp 1 is turned on, a high-voltage pulse output from the trigger transformer 121 causes high-frequency noise to radiate through the metallic enclosure 300 or the shielded cable connected to the terminals. To prevent this, high-frequency noise absorbing capacitors 178-185 are usually provided. A high-voltage trigger pulse is required to turn on the flash lamp 1, but because it is difficult to ensure sufficient creepage and clearance between the electronic components configured to make the charging device 100 compact, or between the electronic components and the metallic enclosure 300, discharges can occur between these components, and high-voltage noise voltages are superimposed between the sleep terminal C and the GND terminal D via the high-frequency noise absorbing capacitors 178-185.

[0074] In this embodiment, high-frequency noise absorbing capacitors 178 to 185 are connected to all of terminals A to H that are led out to the outside, but for example, because terminals G and H are connected to photocoupler 142 and are not connected to the GND (ground) of capacitor charging device 100, providing high-frequency noise absorbing capacitors here may not be effective in preventing high-frequency noise radiation, and so high-frequency noise absorbing capacitors may be provided only to some of the terminals rather than all of the terminals that are led out to the outside. Also, even if high-frequency noise absorbing capacitors are provided to some of the terminals, a high-voltage noise voltage will be superimposed between sleep terminal C and GND terminal D via the high-frequency noise absorbing capacitors.

[0075] Furthermore, if the shielded cable is long, noise may be superimposed on the shielded cable, and similarly pass through high-frequency noise absorbing capacitors 178-185, causing a noise voltage to appear between sleep terminal C and GND terminal D. Since there is no connection between sleep terminal C and GND terminal D when lamp lighting device 300 is operating, excessive voltage may be applied to the EN terminal of step-up / step-down converter 109, destroying step-up / step-down converter 109.

[0076] Therefore, a pulse noise reduction filter circuit 114 is provided between terminal C and on / off control terminal EN of step-up / step-down converter 109, which is configured with noise voltage attenuation resistor 112 alone, or with a noise integration capacitor alone, or with noise absorbing varistor 113 alone, or with any combination of resistor 112, noise absorbing varistor 113, or noise absorbing varistor 113, to prevent breakdown of the EN terminal of step-up / step-down converter 109.

[0077] In the charging device 100 of this embodiment, the current consumption during standby mode, in which the flash lamp 1 is not illuminated and the main discharge capacitor 157 is kept charged to a predetermined voltage of several hundred volts, is approximately 200 mA or more when the input DC voltage is 5 V. This is a significant amount of power consumption that cannot be ignored when the charging device 100 is driven by a battery, for example.

[0078] When the device controlling charging device 100 connects terminals C and D via a shielded cable and controls the sleep function to be on, the current consumption of the lamp lighting device is reduced to approximately 100 microA or less. This sleep function reduces the power consumption to 1 / 2000 of that in standby mode, thereby significantly reducing power consumption.

[0079] By disabling the sleep function by opening terminals C and D, the charging device 100 can charge the main discharge capacitor 157 to a predetermined voltage of several hundred volts in about 2000 microseconds, so the sleep function can be used until just before the flash lamp 1 is turned on.

[0080] The current control compensation section, which is an element that controls the current flowing through the primary winding of the flyback transformer, charges the charge voltage control stabilizing capacitor with a constant current control of about 1 mA, and conversely, the charge voltage control stabilizing capacitor is discharged by a comparator that monitors the charging voltage of the main discharge capacitor, and the charging of the main discharge capacitor is controlled by the charging voltage of the charge voltage control stabilizing capacitor.

[0081] In the prior art, the voltage of the charge voltage control stabilizing capacitor in the current control compensation unit was lowered to pause charging of the main discharge capacitor. As a result, when charging of the main discharge capacitor resumed, the voltage of the charge voltage control stabilizing capacitor in the current control compensation unit could not rise rapidly because of the constant current charging of about 1 mA, and an unnecessary soft start operation was performed at the beginning of charging the main discharge capacitor, preventing rapid charging.

[0082] In the present invention, the suspension of charging of the main discharge capacitor is achieved by directly turning on and off the gate terminal of the MOSFET that switches the current flowing through the primary winding of the flyback transformer, rather than relying on the voltage drop control of the charge voltage control stabilizing capacitor of the current control compensation unit. Therefore, when charging of the main discharge capacitor resumes, the voltage of the charge voltage control stabilizing capacitor of the current control compensation unit is high, and a predetermined constant current operation is performed from the beginning of charging the main discharge capacitor, allowing for rapid charging. This rapid charging and the sleep function described above significantly reduce the power consumption of the flash lamp 1. Furthermore, flash lamps can be manufactured inexpensively.

[0083] The charging device for a flash lamp capacitor in the above-described embodiment is merely an example and is not intended to limit the scope of the invention. It can be embodied in various other forms and can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0084] 1 flash lamp 20 cathode 30 Anode 40 Trigger electrode 60 First Sparker 70 Second Sparker 100 Flash lamp capacitor charging device 103 OFF period setting circuit 105 Flyback transformer 106 Switching element (MOSFET) 107 Current detection resistor 109 Buck-boost converter (operating power supply circuit) 114 Pulse noise reduction filter circuit 115 Reverse blocking diode 141 Time-limited circuit 152 First Comparator 157 Main discharge capacitor (capacitor for flash lamp) 160 Oscillator 165 Sequence setting circuit 166 Signal Gate 167 Second Comparator 170 Constant current regulator 171 Compensation Capacitor 178~185 High frequency noise absorption capacitor 300 Metal Enclosure

Claims

1. A switching element; a signal gate for driving the switching element; a flash lamp capacitor; a charging circuit that charges the flash lamp capacitor by controlling the on / off of the switching element; an off-period setting circuit for the switching element; a compensation capacitor that is charged with a constant current; a first comparator that discharges the compensation capacitor when the charging voltage signal of the flash lamp capacitor matches a predetermined charging voltage target value; a second comparator that outputs a signal when a voltage signal based on the current passing through the switching element matches a voltage value based on the charging voltage of the compensation capacitor; a sequence setting circuit; a timing circuit that starts its operation in response to an input of a start signal; the sequence setting circuit outputs an ON signal to the signal gate and stops the operation of the OFF period setting circuit in response to a signal output from the OFF period setting circuit, and outputs an OFF signal to the signal gate and starts the operation of the OFF period setting circuit in response to a signal output from the second comparator; a timing circuit that outputs a trigger signal to start a preliminary discharge prior to arc discharge of the flash lamp and closes the signal gate, and opens the signal gate when the timing circuit finishes its operation after a predetermined time has elapsed.

2. 2. The charging device for a flash lamp capacitor according to claim 1, wherein the charging circuit is provided with a first filter means, the charging voltage signal of the flash lamp capacitor is input to the first comparator via the first filter means, and a second filter means is provided in a circuit that discharges the compensation capacitor using the first comparator.

3. A switching element; a signal gate for driving the switching element; a flash lamp capacitor; a charging circuit that charges the flash lamp capacitor by controlling the on / off of the switching element; an operating power supply circuit for supplying an operating voltage to the charging circuit; a metal enclosure surrounding the charging circuit; A charging device for a capacitor for a flash lamp, characterized in that a capacitor for absorbing high-frequency noise is provided between the terminal leading to the outside of the charging circuit and the metal enclosure, and a pulse noise reduction filter circuit for attenuating internal noise is provided between the sleep terminal of the operating power supply circuit and the terminal leading to the outside.

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