JPS6314838B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric circuit for accumulating electric charge in a flash discharge device that stores electric charge in a capacitor and discharges it through a flash discharge tube. The discharge device Increase the efficiency of
This is an attempt to improve reliability.

In a flash discharge device, a switching power supply circuit is used as a circuit for charging a capacitor in order to reduce the size and weight. When this switching power supply circuit is used as an AC power source, generally the AC is rectified by a rectifier circuit, and then smoothed using a large-capacity smoothing capacitor to convert it into DC. The DC voltage is then converted to high-frequency AC using a DC-AC converter and boosted. Furthermore, this high frequency alternating current is rectified by passing through a charging current limiting coil.
Charge the charge storage capacitor. In such a flash discharge device, the charging energy, the set charging completion voltage, the time required to reach the capacitance charging voltage of the capacitor (hereinafter referred to as charging time),
When the conditions for the oscillation frequency of the DC-AC converter are set, the impedance of the chiyoke coil is determined, and the load conditions of the DC-AC converter cannot be set freely. Therefore, it is not possible to appropriately control the instantaneous current flowing to the switching element and the input current flowing from the AC power supply in each switching cycle, and it is difficult to reduce the loss in the switching element and the rush current at the start of recharging after a flash. I can't wait. If the loss is large, the efficiency of the discharge device will be poor. Furthermore, if the inrush current is large, it is necessary to estimate the power supply capacity to be large.
Furthermore, since the voltage of the booster circuit section is applied to the flash discharge tube through the choke coil, a high voltage is directly applied to the flash discharge tube during recharging after flash discharge, and the flash discharge tube is likely to cause self-sustaining discharge. This self-sustaining discharge is more likely to occur if the inrush current is large during recharging after a flash discharge. This self-sustaining discharge is a phenomenon that must not occur in a flash discharge device, and the fact that it easily occurs means that the reliability of the device is low.

As described above, the present invention improves the efficiency of the discharge device by appropriately controlling the output voltage and charging current of the charging circuit, reducing the loss that occurs during charging, and preventing self-sustaining discharge of the flash discharge tube. The aim is to increase reliability and improve reliability.

A conventional example of a flash discharge device is shown in FIG. The operation of the conventional example will be explained below.

The output of the AC power supply 1 is rectified by a rectifier circuit 2, and further smoothed by a smoothing capacitor 3 to become DC.
The above is the DC power supply section. When direct current is applied to the DC-AC converter 4, it is converted into high-frequency alternating current and boosted by a switching operation, rectified by a rectifier circuit 5, passed through a choke coil 6, and stored in a capacitor 7.

During charging to accumulate charges, the voltage of the flash discharge capacitor 7 is detected by the voltage detection circuit 8. When the voltage of the capacitor 7 reaches the set charge completion voltage, the output voltage of the voltage detection circuit 8 becomes higher than the output voltage of the charge completion reference voltage circuit 9. At this time, the voltage comparator 10 operates and turns off the output signal. When the output signal of voltage comparator 10 turns off, DC
- AC converter 4 stops switching operation. When the switching operation is stopped, the capacitor 7 is not charged, so the voltage of the capacitor 7 becomes the set charging completion voltage.

Next, when a trigger pulse generation command signal is applied to the trigger pulse generation circuit 11, a trigger pulse is output to the trigger electrode 13 of the flash discharge tube 12. When a trigger pulse is applied, the charge stored in the capacitor 7 is discharged through the flash tube 12.

Due to the discharge, the voltage of the flash discharge capacitor 7 decreases, and the output voltage of the voltage detection circuit 8 becomes lower than the output voltage of the charge completion reference voltage circuit 9, so that the output signal of the voltage comparator 10 turns ON. Therefore,
The DC-AC converter 4 starts a switching operation. By repeating the above operations,
Flash discharge can be performed intermittently.

In the above conventional example, since the charging current is limited by the charging current coil 6, the charging energy, the set charging completion voltage, the capacitance of the capacitor 7, the charging time, and the oscillation frequency of the DC-AC converter 4 are set. The inductance of is fixed, and the load conditions seen from the DC-AC converter 4 cannot be freely set.

That is, the load seen from the DC-AC converter 4 is a series circuit of the chiyoke coil 6 and the capacitor 7, and the composite load impedance is determined by the combination of each impedance. In order to store a predetermined charging energy in the capacitor 7, the capacitance of the capacitor 7 and the set charge completion voltage are determined, and the DC-AC converter 4 is operated at a predetermined oscillation frequency to complete charging within a predetermined charging time. If you try to
The impedance of is uniquely determined.

This will be explained using the simplified circuit shown in FIG. Here, DC power supply 14 and switch 1
5 is considered to be equivalent to DC-AC converter 4. In this case, assuming that the DC-AC inverter outputs a square wave alternating current, and considering one half cycle, when switch 15 is closed, it is the start of the half cycle, and when it is opened, it is the start of the half cycle. It can be said that it is the end. The current flowing at this time is i, the inductance of the chiyoke coil 6 is L ₁ , the capacitance of the capacitor 7 is C ₁ ,
If the voltage of the DC power supply is E ₁ , the following formula holds.

L ₁ di/dt+1/C ₁ ∫idt=E _1Here , if the charge of capacitor 7 is q ₁ and solve the above equation, q ₁ = C ₁ E ₁ (1−cosω _p t ……1 becomes.

Figure 3 shows the temporal changes in q ₁ and i ₁ .

In the conventional example shown in FIG. 1, there is a rectifier circuit, so the accumulated charge will not decrease unless it is flash discharged. Therefore, the DC-AC converter 4 continues to operate as described above until a predetermined amount of charge is accumulated in the capacitor 7. It can be thought of as something that happens intermittently. From this, it can be seen that the time until a predetermined charge is accumulated and the flowing current are uniquely determined by L ₁ and C ₁ .

As shown above, in the conventional example, when the charging energy, set charging completion voltage, capacitance of the capacitor 7, charging time, and oscillation frequency of the DC-AC converter 4 are set, the impedance of the chiyoke coil 6 is determined. AC converter 4
It is not possible to freely set the load conditions from the perspective of the user. Therefore, DC−
The instantaneous current waveform output from the AC converter 4 and the current waveform flowing through the switching element cannot be controlled. Generally, most of the loss in switching power supplies occurs when the switching element is turned on.
-This is said to be due to switching loss when turning off. This switching loss is the product of the voltage applied to the switching element and the current flowing through it. Therefore, in order to reduce switching loss and increase circuit efficiency, it is necessary to control the instantaneous current that flows in each switching cycle and to prevent excessive current from flowing when the switching element turns ON and OFF. It is. In the conventional example, since it is not possible to control the instantaneous current waveform, improvement in efficiency cannot be expected by optimizing the instantaneous current waveform.

Furthermore, since the change in the input current from the AC power supply from the start of charging to the completion of charging is uniquely determined and cannot be controlled, it is possible to reduce the inrush current at the start of recharging after a flash, or to reduce the input current. You cannot expect a reduction in the maximum value. Therefore, it is not possible to expect to improve the reliability of the discharge device by preventing self-sustaining discharge of the flash discharge tube, or to improve the performance of the discharge device by reducing the required input current capacity.

As described above, in a flash discharge device using a charging circuit in which the voltage is boosted only by the DC-AC converter and the charging current is limited only by the choke coil, the current flowing through the switching element cannot be appropriately controlled. The disadvantage was that the switching loss increased. Furthermore, when recharging after a flash discharge, not only is it impossible to suppress the inrush current to the charging capacitor, but also a high charging voltage is applied directly to the flash discharge tube, which prevents the self-sustaining discharge of the flash discharge tube. The disadvantage is that it is easy to occur.

An embodiment of the present invention is shown in FIG. 4, and its configuration and operation will be explained below.

The output of the AC power supply 1 is rectified by a rectifier circuit 2, and further smoothed by a smoothing capacitor 3 to become DC.
When direct current is applied to the DC-AC converter 4, it is converted to high-frequency alternating current and boosted by the switching operation, passes through the choke coil 6, is boosted and rectified by the N-doubler rectifier circuit 16, and charges the capacitor 7. accumulate.

During charging to accumulate charges, the voltage of the flash discharge capacitor 7 is detected by the voltage detection circuit 8. When the voltage of the capacitor 7 reaches the set charge completion voltage, the output voltage of the voltage detection circuit 8 becomes higher than the output voltage of the charge completion reference voltage circuit 9. At this time, the voltage comparator 10 operates and turns off the output signal. When the output signal of voltage comparator 10 turns off, DC
- AC converter 4 stops switching operation. When the switching operation stops, the capacitor 7 is not charged, so the voltage of the capacitor 7 becomes the set charging completion voltage.

Next, when a trigger pulse generation command signal is applied to the trigger pulse generation circuit 11, a trigger pulse is output to the trigger electrode 13 of the flash discharge tube 12. When a trigger pulse is applied, the charge stored in the capacitor 7 is discharged through the flash tube 12.

Due to the discharge, the voltage of the flash discharge capacitor 7 decreases, and the output voltage of the voltage detection circuit 8 becomes lower than the output voltage of the charge completion reference voltage circuit 9, so that the output signal of the voltage comparator 10 turns ON. Therefore,
The DC-AC converter 4 starts switching operation. By repeating the above operations,
Flash discharge can be performed intermittently.

Furthermore, an embodiment of the DC-AC converter is shown in FIG. The operation of the DC-AC converter will be explained below. The output pulses of the pulse oscillator circuit 25 cause the two outputs of the flip-flop circuit 26 to alternately go high. When the output signal from the voltage comparator 10 is at a high level, the outputs from the pulse oscillation circuit 25 and the flip-flop circuit 26 cause the gate circuits 27 and 28 to alternately issue pulses. The drive transistors 29 and 30 are activated alternately for a period according to the pulse width by the output pulses of the gate circuits 27 and 28.
turns on, drive transformer 31, resistor 32,
A drive pulse is output through 33. The main transistors 34 and 35 are alternately turned on by the drive pulse. Main transistors 34, 35
is turned ON alternately, the DC input from the smoothing capacitor 3 is 1/2 of the oscillation frequency of the pulse oscillation circuit 25.
is switched at the frequency of This is DC-AC
This is the oscillation frequency of the converter. Due to the switching, the current from the smoothing capacitor 3 flows through the primary winding of the main transformer 36 in opposite directions for each switch. Therefore, a rectangular wave AC voltage corresponding to the step-up ratio of the main transformer 36 is generated in the secondary winding.

In this DC-AC converter, if the output voltage of the voltage comparator 10 is at a low level, no pulses are output from the gate circuits 27 and 28. Therefore, drive transistors 29, 30 and main transistors 34, 35 do not operate and do not perform a switching operation. Therefore, no voltage is generated on the output side of the DC-AC converter 4. As mentioned above, the output of the voltage comparator 10 allows the DC-AC
The switching operation of converter 4 is controlled.

In the embodiment of the present invention, the charging current is limited by the choke coil 6 and the capacitors 17, 18, 19, 20 used in the N-voltage rectifier circuit. Therefore, charging energy, set charging completion voltage, capacitance of capacitor 7, charging time, DC -
Even if the oscillation frequency of the AC converter 4 is set, the inductance of the choke coil 6 and the capacitor 1
The combinations of capacitances 7, 18, 19, and 20 and the load conditions viewed from the DC-AC converter 4 can be freely set. However, capacitor 1
The capacitance of 7, 18, 19, 20 is capacitor 7
It can be a small value compared to the capacitance of . In other words, the load seen from the DC-AC converter 4 is the chiyoke coil 6 and the capacitors 17, 18, 19, 20.
and a capacitor 7, and the composite load impedance is determined by the combination of each impedance. Therefore, in order to store a predetermined charging energy in the capacitor 7, even if the capacitance of the capacitor 7 and the set charging completion voltage are determined, the DC-AC converter 4 is operated at a predetermined oscillation frequency and the predetermined charge energy is stored in the capacitor 7. The inductance of the choke coil 6 and the capacitance of the capacitors 17, 18, 19, and 20, which are necessary to complete charging within the charging time, are not uniquely determined and can be freely set in combination.

The above will be explained by replacing it with the simplified circuit model shown in FIG. Here, it is assumed that the DC power supply 14 and the switch 15 are equivalent to the DC-AC converter 4. In this case, assuming that the DC-AC converter outputs a square wave alternating current, and considering one of the half cycles, when the switch 15 closes, it is the start of the half cycle, and when the switch 15 opens, the half cycle begins. It can be said that it is the end. Further, the chiyoke coil 37 is the same as the chiyoke coil 6 shown in FIG. 4, and the capacitor 38 is the capacitor 17, 18, 1 shown in FIG.
This is a capacitor having a combined capacitance of capacitors 9 and 20 and capacitor 7. In the circuit shown in Fig. 6, if the current flowing when the switch 15 is closed is i ₂ , the inductance of the choke coil 37 is L ₂ , the capacitance of the capacitor 38 is C ₂ , and the voltage of the DC power supply is E ₂ , the following equation holds. .

L ₂ di ₂ /dt+1/C ₂ ∫i ₂ dt=E _2Here , when the charge of the capacitor 22 is set as q ₂ and the above equation is solved, q ₂ =C ₂ E ₂ (1−cos w ₀ t)... 4 becomes. Figure 7a shows the temporal changes in q ₂ and i ₂ .

Since the embodiment shown in FIG. 4 includes the N-times voltage rectifier circuit 16, the accumulated charges will not decrease unless flash discharge occurs. In addition, the operation of the N double voltage rectifier circuit 16 is such that the capacitor 17 is charged in a cycle when the output terminal b of the DC-AC converter 4 is positive, and the voltage of the capacitor 17 and the DC-AC converter 4 are charged in a cycle when the output terminal b is negative. The operation is such that the capacitor 18 is charged with the voltage obtained by adding the output voltages of 2 and 3, and the capacitor 18 is sequentially charged to finally obtain a high output voltage. Therefore, the operation of charging the small capacity capacitors 17, 18, 19, and 20 is repeated every cycle. Especially capacitor 1
Since capacitor 7 is connected in series with all other capacitors, it greatly contributes to the size of the composite impedance and also greatly affects the size of the charging current.

During the above charging, in order to reduce the switching loss of the DC-AC converter 4, the switching element must be turned on or off every switching cycle.
It is necessary to reduce the current that flows when turning off. For this purpose, switching may be performed at a location where the current value of the current _i2 in FIG. 7a is small.
Voltage applied to the switching element when switching the switching element at a point where i ₂ = o
v _CE is shown in Figure 7b. If the current i ₂ is the output current of the DC-AC converter 4, the current flowing through the switching element will be proportional to i ₂ . Therefore, the switching loss is K×i ₂ ×v _CE . By the way, since switching is performed when i ₂ =0, K×i ₂ ×v _CE becomes 0. In reality, since there is a delay in the operation of the switching element, the loss will not be zero, but it can be set to the minimum. As the sequential charging progresses, charge will remain in each capacitor, so the switching element will turn on at the timing shown in FIG. 7c, and the current will begin to flow from the middle of the current waveform in FIG. 7a. Due to the presence of diodes 21, 22, 23, 24, no negative current flows, and the current flowing during the switching cycle gradually decreases.

As described above, the relationship between the switching timing, the instantaneous current flowing in each switching cycle, and the change in the current flowing from the start of charging to the completion of charging has been explained. As described above, in the present invention, the combination of the inductance of the chiyoke coil 6 and the capacitance of the capacitors 17, 18, 19, and 20 can be freely set, so that Equation 5
As shown in the figure, the change in instantaneous current for each switching cycle can be freely set. Therefore, changes in the current flowing from the start of charging to the completion of charging can also be freely set.

Hereinafter, settings for changes in the current flowing from the start of charging to the completion of charging will be explained. The switching timing in FIG. 7b is such that the switching is performed at the point where the current i ₂ =0 in FIG. 7a, that is, the switching element is turned on for a time t ₁ of a half cycle of the vibration period expressed by Equation 5. Therefore, the current flowing from the start of charging to the completion of charging gradually decreases. On the other hand, the time during which the switching element is turned on is set to be shorter than _t1 . The operation timing of the switching element is set to 7th.
Shown in Figures d and e. As a result, at the start of charging, the battery operates as shown in FIG. 7d, and the instantaneous current is small, but as charging progresses, the battery operates as shown in FIG. 7e, and the instantaneous current increases. As described above, by changing the ON time of the switching element, that is, the oscillation frequency, it is possible to change the tendency of the current flowing from the start of charging to the completion of charging. Although the explanation has been given here on the assumption that the oscillation frequency is changed, even if the oscillation frequency is constant, the tendency of the current flowing from the start of charging to the completion of charging can be changed. That is, assuming that the ON time _t3 of the switching element is constant, the inductance of the choke coil 6 and the capacitor 1
By changing the combination of capacitances 7, 18, 19, and 20 to change the vibration frequency in Equation 6 and changing the half cycle time _t1 of the vibration frequency, the current flowing from the start of charging to the completion of charging can be changed. can change the trend.

Furthermore, the combined load impedance seen from the DC-AC converter 4 will be explained. As mentioned above, by making the half-cycle time _t1 of the vibration period and the ON time _t2 of the switching element the same,
It was assumed that the tendency of the change in current flowing from the start of charging to the completion of charging is a tendency to gradually decrease. Furthermore, by making the ON time t ₂ of the switching element smaller than the time t ₁ of the half cycle of the vibration period, the tendency of the change in the current flowing from the start of charging to the completion of charging tends to gradually increase. From this, it can be considered that the longer the ON time _t2 of the switching element is made than the time _t1 of the half cycle of the vibration period, the more the current flowing from the start of charging to the completion of charging tends to decrease.

If the efficiency and power factor of the discharge device are constant,
When storing a certain amount of energy, if you want to suppress the inrush current at the start of recharging after a flash discharge, the tendency of the input current should be lowered at the start of recharging.
It is necessary to keep it constant or increase during charging. Therefore, the time of half a cycle of the vibration period
It is necessary to make t ₁ at least longer than the ON time of the switching element. In other words, DC-AC
The inductance of the chiyoke coil 6 and the capacitors 7, 17, 18, 1 are set so that the resonant frequency of the combined load impedance seen from the converter is smaller than the oscillation frequency of the DC-AC converter.
By combining capacitances 9 and 20, inrush current can be suppressed. This can prevent self-sustaining discharge of the lamp caused by excessive inrush current flowing into the capacitor 7 at the start of recharging.

Also, the current i ₂ and the switching element in Fig. 7a are
As you can see from the relationship with the timing of turning on,
The smaller the ON time _t2 of the switching element is compared to the half-cycle time _t1 of the vibration period, the more
The peak value of the instantaneous current is relatively closer to when the switching element is turned on, that is, after it is turned off.
Therefore, loss when the switching element is turned on can be reduced. In other words,
The chiyoke coil 6
inductance and capacitor 7, 17, 1
By combining the capacitances of 8, 19, and 20, it is possible to reduce the instantaneous current when the switching element turns on.
It is possible to reduce losses in time. With the above configuration, the switching element can be turned on.
In DC-AC converters where time lag is large, loss can be reduced and efficiency can be increased.

Furthermore, since the output voltage of the N-double voltage rectifier circuit gradually increases as capacitors 17, 18, 19, 20 and capacitor 7 are charged, an excessive voltage may be applied to the flash discharge tube during recharging after flash discharge. Since the flash discharge tube is not directly exposed to water, it is possible to prevent self-sustaining discharge of the flash discharge tube during recharging.

As described above, in the present invention, the output of the DC-AC converter 4 is
The input is input to the voltage doubler rectifier circuit 16, rectified and boosted, and then input to the capacitor 7.
By appropriately controlling the output voltage and charging current of the charging circuit, it is possible to reduce the loss that occurs during charging and prevent self-sustaining discharge of the flash discharge tube 12, thereby increasing the efficiency of the discharge device.
Reliability can be improved.

The embodiments of the present invention have been described above.
However, the output of the DC power supply does not necessarily have to be completely smoothed DC. The DC power source may include an AC power source and a rectifier circuit connected to the AC power source, and may output a pulsating voltage as an output. By outputting a pulsating voltage, the input current is limited when the voltage is low, so that the limiting effect on the choke coil and the N-double voltage rectifier circuit can be reduced. Therefore, when the resonant frequency of the composite impedance of the circuit section consisting of the Chi-Yoke coil, the N-times voltage rectifier circuit, and the charge storage capacitor is made lower than the oscillation frequency of the DC-AC converter, the composite impedance becomes inductive. , there is an effect that the inductance of the chiyoke coil at this time can be reduced. Furthermore, since the input from the AC power source is not smoothed by rectifying tin alone, the power factor can be improved.
A similar effect occurs when a capacitor is inserted to an extent that smoothing is not sufficient.

Further, the DC-AC converter 4 is not necessarily limited to the separately excited push-pull circuit shown in the embodiment of FIG. It may be a self-excited type, a single-stone type, a bridge type, or other circuit type. Also, DC-AC
It is clear that a DC-AC converter using a leakage type transformer instead of a combination of a converter and a chiyoke coil can have the same effect. Furthermore, it is clear that the same effect can be achieved in that the input current can be controlled even if the voltage is boosted using only a transformer instead of a DC-AC converter.

The effects of the present invention are as follows.

1. When recharging after flash discharge, it is possible to prevent self-sustaining discharge of flash discharge tubes by suppressing the inrush current to the charging capacitor and preventing the direct application of high charging voltage to flash discharge tubes. can.

2. Switching loss can be reduced by controlling the instantaneous current flowing through the switching element. Therefore, the efficiency and reliability of the discharge device can be improved.

3. Boosting is performed by the DC-AC converter and also by the N-double voltage rectifier circuit, so the voltage applied to the parts of the DC-AC converter is reduced. Therefore, components with low breakdown voltage can be used and reliability can be improved.

4. Since high voltage charging has become possible, the gas pressure in the flash discharge tube can be increased and self-sustaining discharge can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a conventional column circuit diagram, Fig. 2 is a simplified circuit model of the same, Fig. 3 is a time change diagram of current and charge, and Fig. 4 is a diagram of the conventional column circuit.
The figure is an embodiment circuit diagram of the present invention, and Figure 5 is the same DC-AC
FIG. 6 is a simplified circuit model of the converter, and FIG. 7 is a timing chart of changes in current and charge over time and voltage applied to switching elements. 4...DC-AC converter, 6...Chiyoke coil, 16...N voltage doubler rectifier circuit, 12...flash discharge tube,
11...Trigger pulse generation circuit.

Claims (1)

[Claims] 1. A flash discharge tube, a trigger pulse generation circuit for causing the discharge tube to emit light, a charging capacitor, a DC power source, and a charging circuit for charging the capacitor with the output of the DC power source. In the flash discharge device, the charging circuit includes a DC-AC converter that converts DC output into high-frequency AC, a chiyoke coil,
It is equipped with an N-doubler voltage rectifier circuit connected to the high-frequency output end of the DC-AC converter via a CHI-YOKU coil, and a capacitor for accumulating electric charge. The current is controlled and the voltage is further boosted.
A flash discharge device characterized in that electric charges are accumulated in a capacitor, and the electric charges are discharged through a flash discharge tube by an output pulse of a trigger pulse generation circuit. 2. Claim 1, characterized in that the resonant frequency of the composite impedance of the circuit section constituted by the Chi-Yoke coil, the N-times voltage rectifier circuit, and the capacitor for accumulating electric charge is lower than the oscillation frequency of the DC-AC converter. Flash discharge device as described in Section 1. 3. The flash discharge device according to claim 1 or 2, wherein the DC power source includes an AC power source and a rectifier circuit, and outputs a pulsating voltage that is not sufficiently smoothed.