Control Circuit For Photoflash Discharge Lamps

Abstract

Photoflash discharge lamps are controlled by a circuit which employs a glow tube operable in connection with the terminal voltage of a condenser, which stores energy from a source of voltage. The voltage source is interruptable by an intermittent current due to the flashing of the glow tube. A monitor circuit is provided which is driven by the discharge current of the glow tube to negatively control the terminal voltage of the glow tube and control the ratio of the voltage at the beginning of discharge to the voltage at the termination of discharge. As a result, the terminal voltage of the condenser is maintained substantially constant.

Description

The present invention relates to a circuit for controlling photoflash discharge lamps using a glow tube operable in connection with the terminal voltage of a main condenser.

There has been proposed a device which operates a monitor circuit by making use of the discharge characteristic of a glow tube for the purpose of stability of quantity of light in a circuit for photoflash discharge lamps, reduction of recharging time, reduction of useless consumption of a battery, etc. However, in the known device, the system thereof has made use of the discharge characteristic of a glow tube itself containing many unstable elements, so that fluctuation of the glow tube itself has resulted in fluctuation of a product thereof and accordingly it has been very unstable for practical use. Besides, in accordance with the range from the voltage at the beginning of discharge to the voltage at the termination of discharge of the glow tube, the range and the time of monitor operating voltage are decided, so that it has been impossible to adjust so as to meet fully the above-mentioned items which are the aims for a monitor circuit.

The principal object of the present invention is to overcome said defects of the conventional devices and provides an electric circuit capable of adjusting monitor operation at will between the beginning of lighting a glow tube and the termination thereof.

According to the present invention, it is possible to adjust monitor operation to a great extent within the range from the voltage at the beginning of discharge of the glow tube to the voltage at the termination of discharge thereof, so that even though a glow tube, the operating voltage of which is not uniform, is put to use, it is possible to regulate the upper limit of terminal voltage of a main condenser and also the lower limit thereof.

Furthermore, in accordance with the present invention, the input to the controlling circuit is an intermittent current so that the controlling circuit is very simple in constitution and the operation thereof is reliable and stable in comparison with the conventional method in which the circuit is controlled by the difference of current flowing through the glow tube between the voltage at the beginning of discharge and at the termination of discharge of the glow tube.

The present invention will be described more clearly referring to an illustrative embodiment shown in the accompanied drawing, in which:

FIG. 1 is a circuit diagram of an embodiment of the present invention; and

FIG. 2 shows the performance characteristics of the present invention.

In FIG. 1, reference numeral 1 designates an electric power source battery, 2 is a switch for the power source, 3 is a DC-DC converter, 4 is a main condenser, 5, 6, and 7 voltage dividing resistors respectively for dividing the terminal voltage of the main condenser, and 6' and 7' are movable contact pieces respectively for said voltage dividing resistors 6 and 7. Further, 8 indicates a glow tube, 9 is a transistor, 10 is a base resistor for transistor 9, 11 is an emitter resistor, 12 a switching means (monitor circuit) for interrupting the operation of said converter 3 by means of output current from said transistor 9, 13 is a trigger circuit, 14 is a photoflash discharge lamp, and 15 is a synchro-switch.

These circuit elements are connected as shown in FIG. 1.

In general, a glow tube, when its terminal voltage is increased, begins suddenly to discharge at a certain voltage. Under this condition, even though the terminal voltage is decreased a little, discharge continues, and does not terminate until the voltage is decreased down to a certain value. These voltages at the beginning and at the termination of discharge vary considerably depending on an individual glow tube and it is very difficult to make all such glow tubes uniform in operation.

Referring to FIG. 1, when switch 2 for the power source is closed, the converter 3 operates the terminal voltage of the main condenser 4 is increased. Thereupon, when movable contact piece 6' is adjusted so that the discharge voltage of the glow tube 8 is increased to a given voltage, discharge current flows to the base circuit of transistor 9 and the emitter current controls switch means 12 to interrupt operation of converter 3. At the same time, since the collector of transistor 9 is connected to one point 7' of voltage dividing resistor 7, transistor 9 connects movable contact piece 7' to terminal (-). Therefore, the voltage between movable contact piece 6' and said terminal (-), namely, the terminal voltage of glow tube 8 drops. However, in this case, movable contact piece 7' should be adjusted within the extent that glow tube 8 continues to discharge.

When operation of converter 3 is interrupted, the terminal voltage of main condenser 4 drops gradually due to self-discharge of main condenser 4 and the parallel resistance in the circuit, and at the same time, the terminal voltage of glow tube 8 also drops to the termination voltage so that discharge of the glow tube is interrupted. When the discharge of the glow tube 8 is interrupted, transistor 9 turns off, so that operation of the switch means 12 is interrupted and the converter 3 is operated for charging current to the main condenser 4, and accordingly the voltage of the main condenser 4 increases and operation of converter 3 is again interrupted by means of glow tube 8, transistor 9, switching means 12, etc., and thus operation is repeated over and over again.

In FIG. 2, this repetition operation is shown as a graph of voltage and current against time, and the broken lines show the terminal voltage of the glow tube in the case when there is no connecting action in accordance with the invention. That is, A indicates change of the terminal voltage of main condenser 4 relative to time, B shows change of the terminal voltage of glow tube 8 relative to time, and C shows current change through glow tube 8. Supposing when A gets to the given voltage E.sub.1 at point a.sub.1, B discharges at E.sub.4 and the increase of voltage A is interrupted. At the same time B drops down to E.sub.5 due to the bridge connecting action given by operation of transistor 9, but discharge continues. Therefore, voltage A (the terminal voltage of main condenser 4) drops gradually, so that B also drops, and when getting to voltage E.sub.6 at point b.sub.1, which shows the termination of discharge, said connection action given by operation of transistor 9 is released to increase up to E.sub.7 ; however, E.sub.7 is lower than voltage E.sub.4 at the beginning of discharge so that the globe tube 8 does not discharge. Therefore, the voltage A begins again to increase and interrupts increasing at point a.sub.2 as described above, and thus the same operations are repeated over and over again.

In this manner, within the range from E.sub.4 to E.sub.6 of B, it is possible to adjust monitor operation to a great extent, so that even though a glow tube, the operating voltage of which is not uniform, is put to use it is possible to regulate the upper limit of terminal voltage of main condenser 4 by means of movable contact piece 6' and also the lower limit of terminal voltage by means of movable contact piece 7', and the terminal voltage of the main condenser is maintained substantially constant.

Claims

What we claim is:

1. Electronic photoflash apparatus comprising a DC voltage source, a condenser connected to the voltage source, the condenser being adapted to have a photoflash discharge lamp connected thereto, and a monitor circuit for controlling the terminal voltage of the condenser including a potentiometer connected in parallel with the main condenser, a glow tube actuated in accordance with the terminal voltage of the condenser through the potentiometer, means for dropping the voltage of the glow tube to near its discharge termination voltage when the glow tube begins its discharge, and switching means actuated by the glow tube for periodically terminating the supply of energy from the voltage source to the condenser while the glow tube is discharging.

2. Electronic photoflash apparatus according to claim 1, wherein the means for dropping the voltage of the glow tube includes a transistor the base of which is connected to the glow tube, the collector to the potentiometer, and the emitter to the switching device.

3. Electronic photoflash apparatus according to claim 2, wherein the potentiometer has two adjustable contacts connected to the glow tube and to the collector of the transistor, respectively.

4. Electronic photoflash apparatus according to claim 2, further comprising a DC-DC converter for raising the voltage of the voltage source; and wherein the switching means acts to periodically terminate the oscillation of the DC-DC converter while the glow tube is discharging.