CA1105985A - Flash capacitor charging circuit - Google Patents
Flash capacitor charging circuitInfo
- Publication number
- CA1105985A CA1105985A CA283,711A CA283711A CA1105985A CA 1105985 A CA1105985 A CA 1105985A CA 283711 A CA283711 A CA 283711A CA 1105985 A CA1105985 A CA 1105985A
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- CA
- Canada
- Prior art keywords
- voltage
- charging
- capacitor
- flash
- firing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- 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
- H05B41/32—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp for single flash operation
Landscapes
- Fixing For Electrophotography (AREA)
- Control Of Electrical Variables (AREA)
- Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A capacitive energy-storing unit is discharged through a flash discharge lamp, to cause the latter to edit radiation to fix fusable toner on copying material in an electrophotographic copying machine. The charging circuit for the capacitive energy-storing unit is connectable to a source of periodic voltage, and it includes a charging impedance and an electronic charging switch. The charging switch is periodically rendered conductive, but the firing angle of the charging switch is automatically varied relative to the periodic voltage in dependence upon the voltage developed across the capaci-tive energy-storing unit.
A capacitive energy-storing unit is discharged through a flash discharge lamp, to cause the latter to edit radiation to fix fusable toner on copying material in an electrophotographic copying machine. The charging circuit for the capacitive energy-storing unit is connectable to a source of periodic voltage, and it includes a charging impedance and an electronic charging switch. The charging switch is periodically rendered conductive, but the firing angle of the charging switch is automatically varied relative to the periodic voltage in dependence upon the voltage developed across the capaci-tive energy-storing unit.
Description
'11~5~5 1 The invention relates to flash arrangements, especial-ly those used to fix a fusible toner on copying material in an electrophotographic copying machine. Such flash arrangements comprise a flash discharge lamp, a flash capacitor operative for accumulating energy which is to be discharged through the lamp, and a charging circuit for the flash capacitor which includes a charging resistor and an electronic charging switch used to interrupt the charging current.
It is known to provide a charging resistor of low resistance in the charging current path for the energy-storing flash capacitor, in order to assure that charging of the flash capacitor occurs quickly. Often, a charging switch is incorporated in the charging current path, to interrupt the charging current, so that charging current will not be furnished to the capacitor during a time interval commencing shortly before a flash discharge operation and ending shortly after the completion of the flash discharge opera-tion, in order to prevent the prolongation of the flash discharge operation which would result if the capacitor were supplied with charging current during the discharge operation itself.
This type of known arrangement~is not suitable when very quick charging of a capacitor of high energy-storing capacity is required. At the start of the charging of the uncharged capacitor, the low impedance afforded by the low-resistance charging resistor, results in an exceedingly high initial draw of charging current from the voltage source. If the voltage source is, for example, simply the electrical system of an office in which a copying machine pro-vided with such a flash arrangement is being used, the initial draw of charging current from the electrical system of the office will make itself felt in all electrical devices powered by the electrical system. The loading of the electrical system during the initial flow
It is known to provide a charging resistor of low resistance in the charging current path for the energy-storing flash capacitor, in order to assure that charging of the flash capacitor occurs quickly. Often, a charging switch is incorporated in the charging current path, to interrupt the charging current, so that charging current will not be furnished to the capacitor during a time interval commencing shortly before a flash discharge operation and ending shortly after the completion of the flash discharge opera-tion, in order to prevent the prolongation of the flash discharge operation which would result if the capacitor were supplied with charging current during the discharge operation itself.
This type of known arrangement~is not suitable when very quick charging of a capacitor of high energy-storing capacity is required. At the start of the charging of the uncharged capacitor, the low impedance afforded by the low-resistance charging resistor, results in an exceedingly high initial draw of charging current from the voltage source. If the voltage source is, for example, simply the electrical system of an office in which a copying machine pro-vided with such a flash arrangement is being used, the initial draw of charging current from the electrical system of the office will make itself felt in all electrical devices powered by the electrical system. The loading of the electrical system during the initial flow
-2- ~
1~5~5 1 of charging current is further increased due to the very con-siderable heat-dissipation energy loss resulting from the flow of the initial spike of charging current through the low-resistance charging resistor.
It is a general object of the invention to provide a flash arrangement of the type in question, but of such a design that flash capacitors of high energy-storing capacity can be quickly charged without abruptly loading the electrical system employed by drawing therefrom high-magnitude spikes of charging current.
According to one concept of the invention, the above object is achieved by powering the flash arrangement from a source of periodic voltage, periodically rendering the electronic charging switch conductive, and varying the firing angle of the charging switch relative to the periodic voltage in automatic dependence upon the instantaneous voltage of the flash capacitor.
Advantageously, during the course of the charging of the flash capacitor, the firing angle of the electronic charging switch is progressively decreased, each decrease being dependent upon the increasing voltage across the capacitor being charged. As a result of the progressive decrease of the firing angle, the ampli-tude of the portion of the periodic voltage transmitted through the charging switch to the capacitor to be charged, becomes progressively greater. Inasmuch as the voltage across the capacitor itself is mean-while becoming progressively greater, the effective value of the charging voltage remains substantially constant. As a result, the amplitudes of the successive charging-current pulses are at least approximately the same, so that the loading of the electrical system powering the flash arrangement will be maintained quite uniform and at an acceptable level during the entirety of the charging operation.
The firing angle of the charging switch is preferably ~5~8S
1 varied using a comparator and a feedback voltage from the capacitor being charged. One input of the comparator receives the feedback voltage. The other comparator input receives a ramp voltage which is synchronized with the periodic voltage from the electrical system (e.g., the A.C. voltage of an office electrical system). When the comparator detects coincidence between its two input signals, it furnishes an output signal which causes the charging switch to become conductive.
According to another concept of the invention, the charging impedance used to limit the charging current drawn by the flash capacitor is provided in the form of a reactive impedance, preferably a choke comprised of a low-resistance coil wound with an air gap around an~iron core. ThiS expedient serves, on the one hand, to avoid the heat-dissipation energy loss resulting from the use of a resistive charging impedance and serves, on the other hand, to further reduce the loading on the electrical system.
The novel features which are considered as character-istic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following de-scription of specific embodiments when read in connection with the accompanying drawing.
FIG. 1 is a schematic block circuit diagram of an exemplary embodiment of the invention; and FIG. 2 is a wave and pulse diagram illustrating the operation of the circuit of FIG. 1.
In FIG. 1, numeral 12 denotes a flash discharge lamp used to fix fusable toner on copying material in an electrophoto-graphic copying machine. The negative (lower) terminal of a flash 1 capacitor 8 and the positive (upper) terminal of a flash capacitor 9 are connected by a conductor 30. The positive terminal of capa-citor 8 is connected by conductors 5, 13 to the upper main electrode of flash discharge tube 12; the lower terminal of capacitor 9 is connected by conductors 7, 14 to the lower main electrode of discharge tube 12. Two diodes 10, 11 are connected in respective branches 4, 6, and the latter are connected in common to a line 1 which includes a charging switch in the form of a triac 3, a charging impedance 2 in the form of a non-resistive choke comprised of a coil wound with an air gap around an iron core, and the line 1 is connected to the upper terminal of the voltage source. The lower terminal of the A.C. v~ltage source is connected, via a line 31, to the junction between capacitors 8 and 9.
The trigger electrode 19 of flash discharge lamp 12 receives a trigger voltage pulse via line 18 from a trigger circuit .. ;?
17. The latter is activated by a control signal on line 16, which latter is connected to the unstable-state output of a monostable r circuit 15, in turn triggered via a trigger line 27.
Charging triac 3 is rendered conductive by a firing-angle control circuit 20 (e.g., SGS-ATES, IC component type L 120).
Firing-angle control circuit 20 includes a comparator 21, an AND-gate 24 and a trigger-pulse generator 25. A sawtooth voltage gene-rator 22 applies to the upper input of comparator 21 a sawtooth voltage synchronized with the A.C. voltage from the A.C. source. A
feedback stage 32 applies to the lower input of comparator 21 a voltage dependent upon the instantaneous voltage across flash capa-citor 9. The input of feedback stage 32 is connected via a line 23 to the line 30 joining capacitors 8 and 9.
The output of comparator 21 is connected to the upper input of AND-gate 24, the lower input of which is connected to the 5~S
1 stable-state outPUt of monostable circuit 15. The output of AND-gate 24 is connected to the input of trigger pulse generator 25.
The output of the latter is connected via a line 26 to the firing electrode of triac 3.
The operation of the illustrated circuit is as follows:
The charging of the flash capacitors 8, 9 is effected by the periodic voltage from the voltage source, through the inter-mediary of rectifier diodes 10, 11, on a voltage-doubler basis. The air-gap iron-core choke 2 connected in the charging circuit serves as a non-resistive (reactive) current-limiting impedance, and therefore produces no heat-dissipation energy loss such as would be involved if a resistive current-limiting impedance were employed.
The flow of charging current is regulated via the triac 3, the latter being controlled by means of the firing-angle control circuit 20 in dependence upon the increasing voltage across the flash capacitors.
During positive half-cycles of the A.C. voltage, charging current flows through choke 2, triac 3 and diode 10 into the upper electrode of capacitor 8, and out of the lower electrode of capacitor 8 through line 31 to the lower terminal of the A.C.
voltage source. During negative half-cycles of the A.C. voltage, charging current flows out of the lower terminal of the A.C. voltage source, through line 31, into the upper electrode of capacitor 9, out of the lower electrode of capacitor 9, through diode 11, and through triac 3 and choke 2 to the upper terminal of the A.C. voltage source. Thus, the two capacitors 8, 9 are charged during alternate half-cycles.
Attention is directed to FIG. 2.
The three half-cycles shown in line (a) are the (negative) half-cycles of the A.C. voltage, used to charge capacitor ~ s 1 9. For the sake of simplicity, the voltage half-cycles used to charge capacitor 8 are not depicted.
Line (b) of FIG. 2 depicts the ramp voltage V22 generated at the output of unit 22. As can be seen, the zero-value point of the ramp voltage V22 is synchronized with the zero-through-pass of the A.C. voltage from the source. The ramp-voltage cycles shown in broken lines are not involved in the charging of capacitor 9, but instead in the charging of capacitor 8, and are shown merely for the sake of orientation.
The ramp voltage V22 is applied to the upper input of comparator 21, the lower input receives the output voltage V32 from feedback unit 32. When, during the course of a half-cycle, the value of the ramp voltage V22 reaches the value of the feedback voltage ~;~
V32, the comparator 21 produces an output signal. This signal is transmitted through the AND-gate 24 (which is in gated condition), r and applied to the trigger pulse generator 25. The latter furnishes, via line 26, a trigger pulse which renders triac 3 conductive.
During the first half-cycle depicted in FIG. 2, the ramp voltage V22 reaches the value of the feedback voltage V32 at moment A. At this moment, the value of the feedback voltage V32 is V32 ~ as indicated in line (b) of FIG. 2. Thus, at moment A, the triac 3 becomes conductive. As can be seen, during this first half-cycle, with the voltage across capacitor 9 initially near zero, the moment A at which triac 3 is fired occurs rather late in the half-cycle; i.e., the firing angle (the angular portion of the half-cycle prior to the firing moment A) is relatively large. Accordingly, triac 3 is rendered conductive at a point in the half-cycle when the magnitude of the voltage half-cycle is relatively low. As a result, the almost completely uncharged capacitor 9 is now charged by a relatively low charging voltage. When the voltage across capacitor 9, s~æs 1 during this first charging half-cycle, approaches the charging voltage itself, the voltage across triac 3 and the current there-through become too low to maintain conduction: accordingly, triac 3 becomes non-conductive, at the moment denoted by A' in FIG. 2.
At the start of the second voltage half-cycle for capacitor 9, the voltage across the capacitor is now somewhat higher.
Accordingly, for reasons explained below,the feedback voltage V32 is now somewhat lower. As a result, the ramp voltage V22 becomes equal to the feedback voltage V32 somewhat earlier in the second half-cycle than in the first half-cycle, and in particular at moment B; at this moment the value of the feedback voltage V32 is V32 Accordingly, the firing angle of triac 3 has now been decreased;
i.e., triac 3 is fired sooner within this half-cycle. When triac 3 is fired at moment B, the magnitude of the charging voltage is some-what higher than at moment A in the first half-cycle. However, the actual voltage across capacitor 9 is also somewhat higher, because capacitor 9 was charged during the first half-cycle. Accordingly, the effective charging voltage (approximately equal to the differ-ence between the magnitude of the charging voltage at moment B and the voltage across capacitor 9) is substantially the same for the second half-cycle as for the first half-cycle. Accordingly, the charging current drawn during the second half-cycle is substantially the same as that drawn during the first half cycle. When the voltage across capacitor 9, during this second charging half-cycle, becomes approximately equal to the charging voltage itself, the triac 3 again becomes conductive, at the moment denoted by B' in FIG. 2.
For the third charging half-cycle for capacitor 9 shown in FIG. 2, the sequence of events is substantially the same as before.
However, because the voltage across capacitor 9 is now higher, due to the charging during the second half-cycle, the triac 3 is fired 1~59~5 (at moment C) still earlier in the half-cycle; i.e., the firing angle of the triac has been made still smaller. Accordingly, the magnitude of the charging voltage pulse applied to capacitor 9 is higher, but because the capacitor voltage itself is higher, the effective magnitude of the charging pulse is substantially the same as before.
The feedback voltage V32 is depicted in line (d) of FIGURE 2.
As can be seen, prior to the first charging of capacitor 9, the value of voltage V32 is relatively high, i.e., so high that the ramp voltage V22 does not reach this value until relatively late in the half-cycle (at moment A). Then, during the first charging of capacitor 9 (from time A to time A'), the feedback voltage V32 decreased by an amount proportional to the increase r in the voltage across capacitor 9. Accordingly, during the second half-cycle, the ramp voltage V22 reaches the now lower value of the feedback voltage V32 earlier in the half-cycle (at moment B). Then, during this second charging of capacitor 9 (from time B to time B'), the feedback voltage V32 decreases by an amount proportional to the increase in the voltage across capacitor 9. The same applies to the third charging half-cycle.
The relationship between the feedback voltage V32 and the actual voltage across capacitor 9 can be seen with respect to the wave diagrams in lines (c) and (d) of FIGURE 2.
The input of feedback unit 32 is connected, via feedback line 23, to the lower terminal of capacitor 9. It is assumed, for simplicity, that the junction between capacitors 8, 9, connected via line 31 to the lower terminal of the A.C. voltage source, is grounded. Accordingly, the voltage V23 on feedback line 23 is negative with respect to ground, as shown in line (c) of FIGURE 2, and is equal to the actual voltage across the capacitor 9.
5~ 5 1 This negative voltage V32 is applied to the input of feedback unit 32. The latter includes a voltage divider and an im-pedance converter. The impedance converter serves to prevent capa-citor 9 from freely discharging into feedback unit 32. The voltage divider within feedback unit 32 serves to produce a negative voltage equal to a small fraction of the negative voltage V23, and pro-portional thereto. This is, in general, necessary, because the voltage across capacitor 9 will be much larger than should be applied to the comparator 21. Finally, feedback unit 32 adds to this pro-portional negative voltage a positive base voltage. The magnitude of the positive base voltage is such that, no matter how larger the negative voltage V23 becomes, the output voltage V32 will always be positive.
The variation in the feedback voltage V32 is depicted in line (d) of FIG. 2. Prior to moment A, the voltage across capacitor 9 is zero or near zero. Accordingly, the component of feedback voltage V32 proportional to the negative capacitor voltage is substantially zero, and the feedback voltage V32 therefore consists almost entirely of the pOSitLVe base-voltage component thereof.
As the capacitor 9 is charged between times A and A' within the first charging half-cycle, its negative voltage increases in magnitude. Accordingly, the negative component of voltage V32 increases, and voltage V32 becomes somewhat lower. For clarity, the increase in the magnitude of the capacitor voltage, line (c), and the decrease in the magnitude of the feedback voltage V32, line (d), are shown to be approximately equal. However, as indicated above, the amount by which voltage V32 decreases is equal to a small pro-portional fraction of the amount by which the magnitude of the negative capacitor voltage increases.
As capacitor 9 is charged further between times B and '5~
1 B' within the second charging half-cycle, its negative voltage increases further in magnitude. Accordingly, the feedback voltage V32 decreases by a proportional amount.
The same applies to the third charging half-cycle for capacitor 9.
For simplicity, in the illustrated circuit, the feed-back voltage V32 is dependent only upon the voltage across capacitor 9, even though it is also used to similarly control the firing of triac 3 for the charging of capacitor 8, during the charging half-cycles which alternate with those illustrated in line (a) of FIG.
2. This is an acceptable simplification~ because the desired prog-ressive decrease of the triac firing angle, and the corresponding progressive increase of the amplitude of the transmitted charging voltage, will occur.
The AND-gate 24 connected between the comparator 21 and the trigger pulse generator 25 assures that the triac 3 can only be rendered conductive when the monostable circuit 15 is in its stable state. This will be the case during the charging of the flash capacitors 8r 9. To trigger the discharge of flash discharge lamp 12, a trigger signal is applied to the monostable circuit 15, via trigger line 27. This trigger signal will be applied in syn-chronism with the operation of the eIectrophotographic copying ma-chine provided with the flash arrangement. When monostable circuit 15 is triggered, AND-gate 24 becomes disabled, thereby preventing further charging of capacitors 8, 9. At the same time, a trigger signal is furnished at the lower (unstable-state) output of circuit 15, and applied via line 16 to firing unit 17. The latter, in turn, furnishes via line 18 a firing voltage pulse to the firing electrode 19 of the discharge lamp 12. After a time interval long enough to allow for co~pletion of the flash operation, the monostable circuit ~ 5~3S
15 reverts to its stable state, thereby again enabling AND-gate 24, and charging of capacitors 8, 9 is performed again.
It will be understood that each of the elements de-scribed above, or two or more together, may also find a useful application in other types of circuit configurations differing from the types described above.
While the invention has been illustrated and described as embodied in a flash arrangement including two flash capacitors connected in voltage-doubler configuration, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
... , . ~
1~5~5 1 of charging current is further increased due to the very con-siderable heat-dissipation energy loss resulting from the flow of the initial spike of charging current through the low-resistance charging resistor.
It is a general object of the invention to provide a flash arrangement of the type in question, but of such a design that flash capacitors of high energy-storing capacity can be quickly charged without abruptly loading the electrical system employed by drawing therefrom high-magnitude spikes of charging current.
According to one concept of the invention, the above object is achieved by powering the flash arrangement from a source of periodic voltage, periodically rendering the electronic charging switch conductive, and varying the firing angle of the charging switch relative to the periodic voltage in automatic dependence upon the instantaneous voltage of the flash capacitor.
Advantageously, during the course of the charging of the flash capacitor, the firing angle of the electronic charging switch is progressively decreased, each decrease being dependent upon the increasing voltage across the capacitor being charged. As a result of the progressive decrease of the firing angle, the ampli-tude of the portion of the periodic voltage transmitted through the charging switch to the capacitor to be charged, becomes progressively greater. Inasmuch as the voltage across the capacitor itself is mean-while becoming progressively greater, the effective value of the charging voltage remains substantially constant. As a result, the amplitudes of the successive charging-current pulses are at least approximately the same, so that the loading of the electrical system powering the flash arrangement will be maintained quite uniform and at an acceptable level during the entirety of the charging operation.
The firing angle of the charging switch is preferably ~5~8S
1 varied using a comparator and a feedback voltage from the capacitor being charged. One input of the comparator receives the feedback voltage. The other comparator input receives a ramp voltage which is synchronized with the periodic voltage from the electrical system (e.g., the A.C. voltage of an office electrical system). When the comparator detects coincidence between its two input signals, it furnishes an output signal which causes the charging switch to become conductive.
According to another concept of the invention, the charging impedance used to limit the charging current drawn by the flash capacitor is provided in the form of a reactive impedance, preferably a choke comprised of a low-resistance coil wound with an air gap around an~iron core. ThiS expedient serves, on the one hand, to avoid the heat-dissipation energy loss resulting from the use of a resistive charging impedance and serves, on the other hand, to further reduce the loading on the electrical system.
The novel features which are considered as character-istic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following de-scription of specific embodiments when read in connection with the accompanying drawing.
FIG. 1 is a schematic block circuit diagram of an exemplary embodiment of the invention; and FIG. 2 is a wave and pulse diagram illustrating the operation of the circuit of FIG. 1.
In FIG. 1, numeral 12 denotes a flash discharge lamp used to fix fusable toner on copying material in an electrophoto-graphic copying machine. The negative (lower) terminal of a flash 1 capacitor 8 and the positive (upper) terminal of a flash capacitor 9 are connected by a conductor 30. The positive terminal of capa-citor 8 is connected by conductors 5, 13 to the upper main electrode of flash discharge tube 12; the lower terminal of capacitor 9 is connected by conductors 7, 14 to the lower main electrode of discharge tube 12. Two diodes 10, 11 are connected in respective branches 4, 6, and the latter are connected in common to a line 1 which includes a charging switch in the form of a triac 3, a charging impedance 2 in the form of a non-resistive choke comprised of a coil wound with an air gap around an iron core, and the line 1 is connected to the upper terminal of the voltage source. The lower terminal of the A.C. v~ltage source is connected, via a line 31, to the junction between capacitors 8 and 9.
The trigger electrode 19 of flash discharge lamp 12 receives a trigger voltage pulse via line 18 from a trigger circuit .. ;?
17. The latter is activated by a control signal on line 16, which latter is connected to the unstable-state output of a monostable r circuit 15, in turn triggered via a trigger line 27.
Charging triac 3 is rendered conductive by a firing-angle control circuit 20 (e.g., SGS-ATES, IC component type L 120).
Firing-angle control circuit 20 includes a comparator 21, an AND-gate 24 and a trigger-pulse generator 25. A sawtooth voltage gene-rator 22 applies to the upper input of comparator 21 a sawtooth voltage synchronized with the A.C. voltage from the A.C. source. A
feedback stage 32 applies to the lower input of comparator 21 a voltage dependent upon the instantaneous voltage across flash capa-citor 9. The input of feedback stage 32 is connected via a line 23 to the line 30 joining capacitors 8 and 9.
The output of comparator 21 is connected to the upper input of AND-gate 24, the lower input of which is connected to the 5~S
1 stable-state outPUt of monostable circuit 15. The output of AND-gate 24 is connected to the input of trigger pulse generator 25.
The output of the latter is connected via a line 26 to the firing electrode of triac 3.
The operation of the illustrated circuit is as follows:
The charging of the flash capacitors 8, 9 is effected by the periodic voltage from the voltage source, through the inter-mediary of rectifier diodes 10, 11, on a voltage-doubler basis. The air-gap iron-core choke 2 connected in the charging circuit serves as a non-resistive (reactive) current-limiting impedance, and therefore produces no heat-dissipation energy loss such as would be involved if a resistive current-limiting impedance were employed.
The flow of charging current is regulated via the triac 3, the latter being controlled by means of the firing-angle control circuit 20 in dependence upon the increasing voltage across the flash capacitors.
During positive half-cycles of the A.C. voltage, charging current flows through choke 2, triac 3 and diode 10 into the upper electrode of capacitor 8, and out of the lower electrode of capacitor 8 through line 31 to the lower terminal of the A.C.
voltage source. During negative half-cycles of the A.C. voltage, charging current flows out of the lower terminal of the A.C. voltage source, through line 31, into the upper electrode of capacitor 9, out of the lower electrode of capacitor 9, through diode 11, and through triac 3 and choke 2 to the upper terminal of the A.C. voltage source. Thus, the two capacitors 8, 9 are charged during alternate half-cycles.
Attention is directed to FIG. 2.
The three half-cycles shown in line (a) are the (negative) half-cycles of the A.C. voltage, used to charge capacitor ~ s 1 9. For the sake of simplicity, the voltage half-cycles used to charge capacitor 8 are not depicted.
Line (b) of FIG. 2 depicts the ramp voltage V22 generated at the output of unit 22. As can be seen, the zero-value point of the ramp voltage V22 is synchronized with the zero-through-pass of the A.C. voltage from the source. The ramp-voltage cycles shown in broken lines are not involved in the charging of capacitor 9, but instead in the charging of capacitor 8, and are shown merely for the sake of orientation.
The ramp voltage V22 is applied to the upper input of comparator 21, the lower input receives the output voltage V32 from feedback unit 32. When, during the course of a half-cycle, the value of the ramp voltage V22 reaches the value of the feedback voltage ~;~
V32, the comparator 21 produces an output signal. This signal is transmitted through the AND-gate 24 (which is in gated condition), r and applied to the trigger pulse generator 25. The latter furnishes, via line 26, a trigger pulse which renders triac 3 conductive.
During the first half-cycle depicted in FIG. 2, the ramp voltage V22 reaches the value of the feedback voltage V32 at moment A. At this moment, the value of the feedback voltage V32 is V32 ~ as indicated in line (b) of FIG. 2. Thus, at moment A, the triac 3 becomes conductive. As can be seen, during this first half-cycle, with the voltage across capacitor 9 initially near zero, the moment A at which triac 3 is fired occurs rather late in the half-cycle; i.e., the firing angle (the angular portion of the half-cycle prior to the firing moment A) is relatively large. Accordingly, triac 3 is rendered conductive at a point in the half-cycle when the magnitude of the voltage half-cycle is relatively low. As a result, the almost completely uncharged capacitor 9 is now charged by a relatively low charging voltage. When the voltage across capacitor 9, s~æs 1 during this first charging half-cycle, approaches the charging voltage itself, the voltage across triac 3 and the current there-through become too low to maintain conduction: accordingly, triac 3 becomes non-conductive, at the moment denoted by A' in FIG. 2.
At the start of the second voltage half-cycle for capacitor 9, the voltage across the capacitor is now somewhat higher.
Accordingly, for reasons explained below,the feedback voltage V32 is now somewhat lower. As a result, the ramp voltage V22 becomes equal to the feedback voltage V32 somewhat earlier in the second half-cycle than in the first half-cycle, and in particular at moment B; at this moment the value of the feedback voltage V32 is V32 Accordingly, the firing angle of triac 3 has now been decreased;
i.e., triac 3 is fired sooner within this half-cycle. When triac 3 is fired at moment B, the magnitude of the charging voltage is some-what higher than at moment A in the first half-cycle. However, the actual voltage across capacitor 9 is also somewhat higher, because capacitor 9 was charged during the first half-cycle. Accordingly, the effective charging voltage (approximately equal to the differ-ence between the magnitude of the charging voltage at moment B and the voltage across capacitor 9) is substantially the same for the second half-cycle as for the first half-cycle. Accordingly, the charging current drawn during the second half-cycle is substantially the same as that drawn during the first half cycle. When the voltage across capacitor 9, during this second charging half-cycle, becomes approximately equal to the charging voltage itself, the triac 3 again becomes conductive, at the moment denoted by B' in FIG. 2.
For the third charging half-cycle for capacitor 9 shown in FIG. 2, the sequence of events is substantially the same as before.
However, because the voltage across capacitor 9 is now higher, due to the charging during the second half-cycle, the triac 3 is fired 1~59~5 (at moment C) still earlier in the half-cycle; i.e., the firing angle of the triac has been made still smaller. Accordingly, the magnitude of the charging voltage pulse applied to capacitor 9 is higher, but because the capacitor voltage itself is higher, the effective magnitude of the charging pulse is substantially the same as before.
The feedback voltage V32 is depicted in line (d) of FIGURE 2.
As can be seen, prior to the first charging of capacitor 9, the value of voltage V32 is relatively high, i.e., so high that the ramp voltage V22 does not reach this value until relatively late in the half-cycle (at moment A). Then, during the first charging of capacitor 9 (from time A to time A'), the feedback voltage V32 decreased by an amount proportional to the increase r in the voltage across capacitor 9. Accordingly, during the second half-cycle, the ramp voltage V22 reaches the now lower value of the feedback voltage V32 earlier in the half-cycle (at moment B). Then, during this second charging of capacitor 9 (from time B to time B'), the feedback voltage V32 decreases by an amount proportional to the increase in the voltage across capacitor 9. The same applies to the third charging half-cycle.
The relationship between the feedback voltage V32 and the actual voltage across capacitor 9 can be seen with respect to the wave diagrams in lines (c) and (d) of FIGURE 2.
The input of feedback unit 32 is connected, via feedback line 23, to the lower terminal of capacitor 9. It is assumed, for simplicity, that the junction between capacitors 8, 9, connected via line 31 to the lower terminal of the A.C. voltage source, is grounded. Accordingly, the voltage V23 on feedback line 23 is negative with respect to ground, as shown in line (c) of FIGURE 2, and is equal to the actual voltage across the capacitor 9.
5~ 5 1 This negative voltage V32 is applied to the input of feedback unit 32. The latter includes a voltage divider and an im-pedance converter. The impedance converter serves to prevent capa-citor 9 from freely discharging into feedback unit 32. The voltage divider within feedback unit 32 serves to produce a negative voltage equal to a small fraction of the negative voltage V23, and pro-portional thereto. This is, in general, necessary, because the voltage across capacitor 9 will be much larger than should be applied to the comparator 21. Finally, feedback unit 32 adds to this pro-portional negative voltage a positive base voltage. The magnitude of the positive base voltage is such that, no matter how larger the negative voltage V23 becomes, the output voltage V32 will always be positive.
The variation in the feedback voltage V32 is depicted in line (d) of FIG. 2. Prior to moment A, the voltage across capacitor 9 is zero or near zero. Accordingly, the component of feedback voltage V32 proportional to the negative capacitor voltage is substantially zero, and the feedback voltage V32 therefore consists almost entirely of the pOSitLVe base-voltage component thereof.
As the capacitor 9 is charged between times A and A' within the first charging half-cycle, its negative voltage increases in magnitude. Accordingly, the negative component of voltage V32 increases, and voltage V32 becomes somewhat lower. For clarity, the increase in the magnitude of the capacitor voltage, line (c), and the decrease in the magnitude of the feedback voltage V32, line (d), are shown to be approximately equal. However, as indicated above, the amount by which voltage V32 decreases is equal to a small pro-portional fraction of the amount by which the magnitude of the negative capacitor voltage increases.
As capacitor 9 is charged further between times B and '5~
1 B' within the second charging half-cycle, its negative voltage increases further in magnitude. Accordingly, the feedback voltage V32 decreases by a proportional amount.
The same applies to the third charging half-cycle for capacitor 9.
For simplicity, in the illustrated circuit, the feed-back voltage V32 is dependent only upon the voltage across capacitor 9, even though it is also used to similarly control the firing of triac 3 for the charging of capacitor 8, during the charging half-cycles which alternate with those illustrated in line (a) of FIG.
2. This is an acceptable simplification~ because the desired prog-ressive decrease of the triac firing angle, and the corresponding progressive increase of the amplitude of the transmitted charging voltage, will occur.
The AND-gate 24 connected between the comparator 21 and the trigger pulse generator 25 assures that the triac 3 can only be rendered conductive when the monostable circuit 15 is in its stable state. This will be the case during the charging of the flash capacitors 8r 9. To trigger the discharge of flash discharge lamp 12, a trigger signal is applied to the monostable circuit 15, via trigger line 27. This trigger signal will be applied in syn-chronism with the operation of the eIectrophotographic copying ma-chine provided with the flash arrangement. When monostable circuit 15 is triggered, AND-gate 24 becomes disabled, thereby preventing further charging of capacitors 8, 9. At the same time, a trigger signal is furnished at the lower (unstable-state) output of circuit 15, and applied via line 16 to firing unit 17. The latter, in turn, furnishes via line 18 a firing voltage pulse to the firing electrode 19 of the discharge lamp 12. After a time interval long enough to allow for co~pletion of the flash operation, the monostable circuit ~ 5~3S
15 reverts to its stable state, thereby again enabling AND-gate 24, and charging of capacitors 8, 9 is performed again.
It will be understood that each of the elements de-scribed above, or two or more together, may also find a useful application in other types of circuit configurations differing from the types described above.
While the invention has been illustrated and described as embodied in a flash arrangement including two flash capacitors connected in voltage-doubler configuration, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
... , . ~
Claims (4)
1. In a flash arrangement, particularly for fixing fusible toner on copying material in an electrophotographic copying machine, in combination, flash discharge lamp means; energy-storing capacitor means connected to the flash discharge lamp means for discharging energy through the latter; and means for charging the capacitor means, including means defining a charging-current path for the capacitor means connectable to a source of periodic voltage and including a charging impedance and an electronic charging switch;
and means operative for periodically rendering the electronic charg-ing switch conductive, including firing-angle control means operative for automatically varying the firing angle of the electronic charging switch relative to the periodic voltage in dependence upon the volt-age across the capacitor means, the firing-angle control means comprising means for generating a feedback signal whose value is indicative of the voltage across the capacitor means, means for generating a ramp signal synchronized with the periodic voltage, and comparator means receiving the feedback signal and the ramp signal and operative for rendering the electronic charging switch conductive when a predetermined relationship between the values of the two signals is reached.
and means operative for periodically rendering the electronic charg-ing switch conductive, including firing-angle control means operative for automatically varying the firing angle of the electronic charging switch relative to the periodic voltage in dependence upon the volt-age across the capacitor means, the firing-angle control means comprising means for generating a feedback signal whose value is indicative of the voltage across the capacitor means, means for generating a ramp signal synchronized with the periodic voltage, and comparator means receiving the feedback signal and the ramp signal and operative for rendering the electronic charging switch conductive when a predetermined relationship between the values of the two signals is reached.
2. In a flash arrangement as defined in claim 1, the comparator means comprising means operative for rendering the charg-ing switch conductive when the values of the two signals become equal.
3. In a flash arrangement as defined in claim 1, the charging impedance comprising a reactive impedance.
4. In a flash arrangement as defined in claim 3, the reactive impedance being a choke comprised of a low-resistance coil wound with an air gap around an iron core.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19762634396 DE2634396C2 (en) | 1976-07-30 | 1976-07-30 | Flash device |
| DEP2634396.4 | 1976-07-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105985A true CA1105985A (en) | 1981-07-28 |
Family
ID=5984357
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA283,711A Expired CA1105985A (en) | 1976-07-30 | 1977-07-29 | Flash capacitor charging circuit |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5834833B2 (en) |
| AT (1) | AT349306B (en) |
| BE (1) | BE856572A (en) |
| CA (1) | CA1105985A (en) |
| CH (1) | CH615552A5 (en) |
| DE (1) | DE2634396C2 (en) |
| FR (1) | FR2360226A1 (en) |
| IT (1) | IT1079391B (en) |
| NL (1) | NL7707911A (en) |
| SE (1) | SE7708666L (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54126546A (en) * | 1978-03-25 | 1979-10-01 | Ricoh Co Ltd | Fixing apparatus |
| JPS56111920A (en) * | 1980-02-07 | 1981-09-04 | Olympus Optical Co Ltd | Electric power supply device for flash discharge tube |
| DE3720701A1 (en) * | 1986-09-27 | 1988-04-07 | Lothar Himmelreich | Circuit arrangement for charging a power capacitor (capacitance) of at least one power photoflash lamp (flash lamp) |
| JPS6429885A (en) * | 1987-07-25 | 1989-01-31 | Ricoh Tokuki Kk | Toner fixing device |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3375403A (en) * | 1965-10-04 | 1968-03-26 | Berkey Photo Inc | Electrical system for discharge device |
| US3585444A (en) * | 1968-09-23 | 1971-06-15 | Don Haskins Inc | Energy supply circuit |
| DE2045321C3 (en) * | 1970-09-14 | 1979-05-23 | Rollei-Werke Franke & Heidecke, 3300 Braunschweig | Discharge flash unit with adjustable flash voltage |
| DE2123912A1 (en) * | 1971-05-14 | 1972-11-23 | Multiblitz Dr.-Ing. D.A. Mannesmann Gmbh & Co Kg, 5050 Porz | Circuit arrangement for charging a storage capacitor |
| US4001640A (en) * | 1973-01-02 | 1977-01-04 | Polaroid Corporation | Single trigger photographic strobe unit |
| US3870924A (en) * | 1973-06-19 | 1975-03-11 | Chadwick Elect Inc H | Light source with optimized flash energy input to gas tube |
| US3946271A (en) * | 1974-12-26 | 1976-03-23 | Grimes Manufacturing Company | SCR strobe lamp control for preventing capacitor recharge during after-glow |
-
1976
- 1976-07-30 DE DE19762634396 patent/DE2634396C2/en not_active Expired
-
1977
- 1977-06-22 AT AT440877A patent/AT349306B/en not_active IP Right Cessation
- 1977-07-07 BE BE1008264A patent/BE856572A/en unknown
- 1977-07-15 NL NL7707911A patent/NL7707911A/en not_active Application Discontinuation
- 1977-07-22 CH CH910377A patent/CH615552A5/en not_active IP Right Cessation
- 1977-07-25 FR FR7722748A patent/FR2360226A1/en active Granted
- 1977-07-27 JP JP8938077A patent/JPS5834833B2/en not_active Expired
- 1977-07-27 IT IT5046677A patent/IT1079391B/en active
- 1977-07-28 SE SE7708666A patent/SE7708666L/en not_active Application Discontinuation
- 1977-07-29 CA CA283,711A patent/CA1105985A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL7707911A (en) | 1977-12-30 |
| DE2634396C2 (en) | 1982-06-03 |
| IT1079391B (en) | 1985-05-08 |
| FR2360226A1 (en) | 1978-02-24 |
| ATA440877A (en) | 1978-08-15 |
| AT349306B (en) | 1979-03-26 |
| BE856572A (en) | 1978-01-09 |
| JPS5317344A (en) | 1978-02-17 |
| SE7708666L (en) | 1978-01-31 |
| FR2360226B1 (en) | 1981-11-27 |
| JPS5834833B2 (en) | 1983-07-29 |
| DE2634396A1 (en) | 1978-02-02 |
| CH615552A5 (en) | 1980-01-31 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |