JPS6026278B2 - Flash lamp light emission control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the amount of light emitted from a flash lamp.

Conventionally, as shown in Fig. 1, a flash lamp 24 is connected to an AC power supply 21 via a step-up leakage transformer 22, a rectifier 23, and a capacitor C, and the terminal voltage of the capacitor C is divided by voltage dividing resistors R and R'. It is detected and compared with the reference voltage by the comparator 26. When the capacitor C is charged and its terminal voltage matches the reference voltage, the output of the comparator 26 turns off the switching element 27 provided on the primary side of the leakage transformer 22. The charging of the capacitor C is stopped, thereby controlling the amount of light emitted by the flash lamp 24, which emits light in response to a trigger signal.

However, in such a conventional method, since the light emission amount control circuit 30 operates by detecting the voltage of the high voltage section for the flash lamp 24, the detection resistor R' etc. must be made of a high withstand voltage, and the control circuit The ground for the power source for 30 gates must be shared with the ground for the power source for 24 flash lamps. Moreover, since the control circuit 30 is connected to the high voltage part for the flash lamp 24, if the ground of the control circuit 30 is floating or the detection resistor R' is disconnected, high voltage will be applied to the control circuit 3. Therefore, not only is there a danger, but there is also a risk that the control circuit 30 may break down or other circuits that share a power source with the control circuit 30 may be damaged. Furthermore, if the ground of the control circuit 30 is shared with the ground of a circuit in which a large current flows in pulses, such as a flash lamp, there are various drawbacks such as being susceptible to noise interference. It is an object of the present invention to eliminate the drawbacks of the above-mentioned conventional methods and to provide a method for controlling the amount of light emitted from a flash lamp, which controls the amount of light emitted from the flash lamp without directly detecting the voltage of the high voltage section for the flash lamp. It is.

The present invention will be described with reference to embodiments shown in the drawings.

As shown in FIG. 2, the secondary winding of the boosting leakage transformer 2 to which the AC power supply 1 is input is connected to the N. , N2, and a flash lamp 4 is connected to N through a rectifier 3 and a capacitor C.

The resistor R is used to discharge the charge in the capacitor C when there is a power outage while charging the flash lamp 4 or when the flash lamp 4 is defective, and the trigger circuit 5
uses a part of the charge in the capacitor C as trigger energy and causes the flash lamp 4 to emit light in response to an external trigger signal, and the secondary winding N2 of the leakage transformer 2 has a A capacitor C2 is connected through a rectifier 3', and a resistor R2 and a comparator 6 are connected to this capacitor C2.
A feedback control system is constructed in which the output of the comparator 6 controls the switching element 7 provided on the primary side of the leakage transformer 2 so that the charging voltage of the leakage transformer 2 is maintained at a predetermined level. The power supply 8 is for the control circuit including the comparator 6,
The light emission detector 9 detects light emission from the flash lamp 4 and generates a signal, and the transistor TR receives the detection signal from the light emission detector 9 and discharges the charge in the capacitor C2. Here, capacitors C,,C2
The characteristics of are related to each other and selected as follows.

That is, the terminal voltages of the secondary windings N, , N2 wound around the common iron core of the leakage transformer 2 are respectively EN,
, EN2, then E...:EN2=N,:N2
... Since the relationship of {11 holds true, the charging voltage Vc, of the capacitor C, as a function of time t, Vc,=
f(t) ・・・・・・■ If the charging voltage Vc2 of capacitor C2 is V=Af(t) (however, A
= Science)...Select the characteristics of C2 so that A3.

If this is done, the charging voltages Vc, Vc2 of the capacitors C and C2 will show charging progresses that are similar to each other as shown in FIG. Moreover, if we compare the windings N, and N2, the load on N is much larger, so if we change the windings to N,》N2 accordingly, the internal impedance of N2 will be extremely small, and therefore, the internal impedance of N2 will be extremely small. Terminal EN is determined by the charging current of capacitor C, so '1
) formula determines the terminal voltage EN2 of N2, and since capacitor C2 can be considered to be charged by a constant voltage source with an instantaneous value of EN2, capacitor C2
capacity can be selected from a wide range. The above circuit works as follows.

When the AC power supply 1 is applied to the primary side of the leakage transformer 2, the capacitors C, C2 are curved Vc, C2 in FIG. 3, respectively.
, Vc2, and when the charging voltage of the capacitor C2 reaches a predetermined level, the comparator 6 generates an output, and the switching element is configured to maintain this charging level of the capacitor C2. Control 7. And '2} between capacitors C and C2
, VCI derived from formula {3} = V large 2 = mother VC2
... Since the relationship {4) exists, if the charging voltage Vc2 of the capacitor C2 is maintained at a predetermined level, the capacitor C.
The charging voltage Vc, is also maintained at a predetermined level, so that when the flash lamp 4 receives the trigger signal a, it emits light at a predetermined amount by discharging the capacitor C, and at this time, the capacitor C2 is activated by the light emission detector 9. Discharge simultaneously depending on the signal. Of course, by adjusting the comparator 6, the amount of light emitted by the flash lamp 4 can be set arbitrarily. Subsequently, the capacitors C, C2 are charged again and reach their respective predetermined levels as shown in FIG. 4 does not emit light, not only the capacitor C is not discharged, but also the capacitor C2 is not discharged because the light emission detector 9 does not operate. Therefore, as shown by the solid line in FIG. Maintain the regular condition maintained at the level.

The same applies to the third and subsequent trigger signals c, . . . .

In this regard, in the case where the capacitor C2 is discharged not by the light emission detection signal of the flash lamp 4 but by a signal synchronized with a trigger signal, for example, even if the capacitor C2 is not discharged by the trigger signal b, the capacitor C2 When only the capacitor C is discharged and subsequently charged, the capacitor C becomes overvoltage as shown by the chain line in Fig. 3, and the trigger signal c,... causes an even further overvoltage (V'c,). Compared to this, the control method of the present invention does not cause such a problem, so the control is extremely accurate. Incidentally, as the light emission detector 9, for example, a fourth
Various types as shown in Figures 1 to 8 can be used.

That is, in FIG. 4, the phototransistor PTR detects light emission, turns on the transistor TR in FIG. 2, and discharges the capacitor C2.
If the configuration is such that the phototransistor PTR and the transistor TR are not coupled with a capacitor but are connected with direct current, the short pulse generated by the light emission of the flash lamp 4 can be generated using a monostable multipipelator. The capacitor C2 may be discharged after being converted into a pulse with a relatively long time width.Furthermore, when the exposure lamp of a copying machine is controlled as a flash lamp 4, for example, it may affect the image formation of the copying machine. Therefore, it is preferable to arrange the phototransistor PTR so that the reflected light from the presser plate of the contact glass is inputted thereto. In FIG. 5, an SCR is used in place of the transistor TR in FIGS. 2 and 4, so that even if the flash lamp 4 has a short light emission time, the capacitor C2 can be reliably discharged. In FIGS. 4 and 5, it is possible to use various light receiving elements such as a photodiode, a solar cell, a CdS cell, etc. in place of the phototransistor PTR. Fig. 6 shows that since the current when the flash lamp 4 emits light reaches several tens to hundreds of amperes, a coil L is wound around the lead wire of the discharge circuit of the flash lamp 4.
This coil L detects the current of the flash lamp 4, ignites the SCR, and discharges the capacitor C2. In FIG. 7, a Hall effect switch HS is provided near the discharge circuit of the flash lamp 4, and the Hall effect switch HS detects the magnetic field generated due to the current of the flash lamp 4, ignites the SCR, and turns on the capacitor C2. It causes discharge. Fig. 8 shows a case where an inductor L is provided in series with the flash lamp 4 in order to control the light emission time of the flash lamp 4, and the current of the flash lamp 4 is detected by making the inductor L double wound. This is to discharge the capacitor C2 similarly to the above. In FIGS. 6-8, various switching elements can be used in place of the SCR. It goes without saying that the present invention is capable of various changes and modifications of the above-mentioned embodiments, including the various examples of the light emission detector 9 as described above. As described above, the present invention divides the secondary winding of the transformer into two parts, provides a flash lamp charging circuit on one side, and provides a control charging circuit with a similar charging process to the charging circuit on the other side, The input of the transformer is controlled so that the voltage of the control charging circuit is maintained at a predetermined level, and the control charging circuit is discharged by detecting the flash lamp's light emission, so that the voltage of the high voltage section for the flash lamp is The amount of light emitted by the flash lamp can be controlled without directly detecting the
Therefore, there is no need to use high-voltage parts, and there is no risk of danger.Furthermore, even if an abnormality occurs in which the flash lamp does not emit light in response to a trigger signal, each voltage of the flash lamp charging circuit and control charging circuit is Since the amount of light emitted from the flash lamp is continuously maintained at a predetermined level, the amount of light emitted from the flash lamp can be controlled reliably at all times, and has excellent effects such as being suitable for use in various applications such as copying machines.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a subsidiary, Fig. 2 is a circuit diagram showing one embodiment of the present invention, Fig. 3 is a graph of the main part of Fig. 2, and Figs. 4 to 8 are a diagram of a luminescence detector. FIG. 2 is a circuit diagram of main parts showing an example. 1, 21... AC power supply L 2, 22...
・Leakage transformer, 3, 3', 23... Rectifier, 4, 24... Flash lamp, 6, 26... Comparator, 7, 27... Switching element, C,, C2, C・
...container. Figure 1 Groove 2 Figure 3 Figure 4 Figure 6 Figure 5 Port figure Figure 8

Claims (1)

[Claims] 1. A method for controlling the amount of light emitted by a flash lamp that is connected to a light current power source via a transformer, a rectifier circuit, and a charging circuit, and that emits light in response to a trigger signal,
The secondary winding of the transformer is divided into two parts, one of which is used for the charging circuit of the flash lamp, and the other is connected to a control charging circuit whose charging progress is similar to that of the charging circuit through a rectifier circuit. the control charging circuit is connected to the primary side of the transformer to control the input of the transformer so that the voltage of the control charging circuit is maintained at a predetermined level; A method for controlling the amount of light emitted by a flash lamp, characterized in that a member for detecting light emission is provided, and the control charging circuit is discharged when the member is detected.