Output Voltage Regulation System

Abstract

A time constant circuit comprising a variable resistor and a capacitor has a differencial amplifier connected thereto. Between the time constant circuit and the differential amplifier, an unidirectional feedback path is connected to provide the regulated output voltage.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention relates to an improvement over the systems and circuits disclosed and claimed in U. S. Pat. application Ser. No. 78,391 entitled "An Exposure Value Controlling Apparatus," filed Oct. 6, 1970, by KANEHIRO SORIMACHI, Electrical Engineer, at 14-19, Tsutsujigaoka, Midori-ku, Yokohama-shi, Kanagawa-ken, Japan, TADASHI ITO, Electrical Engineer, at 789-12, Shimoda-machi, Kohoku-ku, Yokohama-shi, Kanagawa-ken, Japan, and MITSUTOSHI OGISO, Mechanical Engineer, at 673, Ichinotsubo, Kawasaki-shi, Kanagawa-ken, Japan and U. S. Pat. application Ser. No. 90,580, entitled "An Electronic Shutter for Cameras," filed Nov. 18, 1970, by MITSUTOSHI OGISO, Mechanical Engineer, at 673, Ichinotsubo, Kawasaki-shi, Kanagawa-ken, Japan, and MITSUO ISHIKAWA, Mechanical Engineer, at 650-8, Kami Sakunobe, Kawasaki-shi, Kanagawa-ken, Japan.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an output voltage regulation system.

The conventional output voltage regulation systems and circuits disclosed in the above applications are found unsatisfactory because the change in resistance of a resistor in a charging circuit affects somewhat the output voltage. More specifically the Zener point of the Zener diode changes as the resistance of the photoconductive element changes so that the voltage charged across the capacitor changes accordingly. As a consequence the conventional voltage regulation systems and circuits are not suitable for use with the timers such as the automatic shutter speed control devices which must function with a higher degree of accuracy.

It is therefore the primary object of the present invention to provide an improved output voltage regulation system especially adapted for use with an automatic exposure control system for cameras.

SUMMARY OF THE INVENTION

Briefly stated, an output voltage regulation system of the present invention is characterized in that a voltage divided by a bleeder resistor is applied to one input terminal of a difference amplifier as one input voltage; a unidirectinal feedback path is provided between a point at which the other input voltage to be applied to the other input terminal of the difference amplifier is derived and a point (the output terminal of the difference amplifier) at which the output voltage of the difference amplifier is derived so that the other input voltage may derive the stabilized output voltage; and the other input voltage is derived through the charging or discharging of a time constant circuit comprising a variable resistor and a capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an automatic exposure control device incorporating a prior art output voltage regulation system;

FIG. 2 is a view illustrating various waveforms of the output voltages derived in the circuit shown in FIG. 1;

FIG. 3 is a view illustrating various waveforms of the output voltages produced by the output voltage regulation system in accordance with the present invention;

FIGS. 4, 5, 6 and 7 are circuit diagrams of several preferred embodiments of the present invention; and

FIGS. 8 and 9 are circuit diagrams of automatic exposure control devices incorporating the output voltage regulation systems in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Prior Art, FIGS. 1 and 2)

In order to distinctly and specifically point out the new and improved features of the present invention, the prior art exposure control device for cameras incorporating a constant-voltage charging circuit will be described in brief prior to the description of the preferred embodiments of the present invention.

Referring to FIG. 1, A denotes a control circuit including a shutter and an aperture disphragm or blade assembly; E, a power source; SM, a main switch; Rc and R.sub.D, resistors; C, a capacitor; Dz, a Zener diode; and S.sub.1 and S.sub.2, switches. When the start switch S.sub.1 is closed for example in response to the depression of a shutter release button (not shown), the capacitor is charged with a time constant depending upon the capacitor C and the resistor Rc because the movable contact of the switch S.sub.2 closes the fixed contact a, and when the capacitor C is charged to a potential that is determined by the Zener diode Dz and the resistor Rc, the potential at the junction D is maintained at this potential and remains unchanged thereafter. It is seen that an appropriate aperture stop may be determined during this charging process and after the appropriate aperture stop has been determined, the switch S.sub.2 is switched to the fixed contact b, thereby opening the shutter. Then the capacitor C is discharged with a time constant depending upon the capacitor C and the resistor R.sub.D. In this case it is seen that an appropriate shutter speed may be determined in the control circuit A in response to this discharge.

Referring to FIG. 2, the potential V.sub.C at the junction D when the capacitor C is charged is plotted against time T, where T = 0 when the start switch S.sub.1 is closed, with the resistor R.sub.C as a parameter. E.sub.C is the voltage of the power source E; R.sub.C1 <R.sub.C2 <R.sub.C3 ; and V.sub.D1 >V.sub.D2 >V.sub.D3. It is seen that the potential at D changes as the resistor R.sub.C changes so that the prior art circuit is not expected to function with a higher degree of accuracy in regulating or stabilizing the output voltage.

The Invention, FIGS. 3-9

As shown in FIG. 3, it is desired that the potential V.sub.D at the junction D will not change even though the resistor R.sub.C changes, and this will be accomplished by the present invention in a reliable and stable manner with a higher degree of accuracy, as will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawing.

In FIGS. 4 through 7 illustrating several preferred embodiments of the present invention, same parts are designated by same reference characters. That is, E designates a power source; S.sub.M, a main switch; R.sub.C, resistor; C, a capacitor; D.sub.Z, a constant-voltage element such as a Zener diode; R.sub.11, R.sub.12, a fixed and variable resistors; R.sub.1, R.sub.2 and R.sub.3, resistors; T.sub.1 and T.sub.2, transistors constituting a difference amplifier; D.sub.O, a diode for providing a unidirectional feedback path; and P.sub.1 and P.sub.2, potentiometers. In the instant embodiments, the resistor R.sub.C2 represents a photoconductive element as shown in FIG. 5 and the resistor PTr represents a phototransistor as shown in FIG. 6. The resistor in FIG. 7 represents a combination of a photodiode PD and a transistor To so that the charging time constant may be dependent on the impedance of the transistor as shown in FIG. 7.

Next the typical mode of operation will be described particularly with reference to the third embodiment shown in FIG. 6 and the modes of operation of the other embodiments will be apparent from this description. The equivalent impedance between the collector and emitter of the phototransistor PTr changes in response to the intensity of light incident thereupon so that the charging time of the capacitor C changes accordingly. A voltage divided by the resistor R.sub.11 and the Zener diode D.sub.Z in turn is divided by the potentiometer P and applied to the base of the transistor T.sub.2, and the potential V.sub.C at the point D when the capacitor C is charged is applied to the base of the transistor T.sub.1 to control it. Since the transistors T.sub.1 and T.sub.2 constitute a difference amplifier, the transistor T.sub.1 remains turned off until the potential V.sub.C at the point D reaches a predetermined charged voltage V.sub.D, whereeas the transistor T.sub.2 remains turned on. When the potential V.sub.C reaches V.sub.D, the transsistor T.sub.1 is turned on, while the transistor T.sub.2 remains on. In this case, the diode D.sub.O serves to supply current so that the capacitor C will not be charged with the current passing through the resistor R.sub.1. Various arrangements are shown in other embodiments so as to vary the base potential of the transistor T.sub.2, but not detailed description will be made as they are apparent to those skilled in the art.

Next the automatic exposure control devices for cameras incorporating the output voltage regulation system in accordance with the present invention will be described with reference to FIGS. 8 and 9. In the embodiment show in FIG. 8, the charging resistor R.sub.C is provided independently of the discharging resistor R.sub.D, whereas in the embodiment shown in FIG. 9, one photoconductive element R.sub.CD is used as a common charging and discharging resistor. In this case, the diode D.sub.O may be eliminated by an arrangement in which a switch S.sub.2, closes either contacts a' or b' in response to the actuation of the switch S.sub.2. An aperture stop is designated by F and the potentiometer is set to an appropriate value depending upon the sensitivity or speed of a film used.

Reference characters T.sub.3 and T.sub.4 designate transistors constituting a Schmitt circuit; T.sub.5, a power transistor; R.sub.4 -- R.sub.6, resistors; R.sub.7, an adjustment resistor; and M.sub.1 and M.sub.2, magnets. The magnet M.sub.1 serves to set an aperture to a predetermined stop while the magnet M.sub.2 serves to open and close the shutter.

Next the mode of operation of the automatic exposure control device shown in FIG. 9 will be described, from which the mode of operation of the device shown in FIG. 8 will be apparent to those skilled in the art. Upon depression of a shutter button (not shown), the main switch S.sub.M is closed and next the switch S.sub.2 closes the contact a while the switch S.sub.1 is also closed, so that an aperture setting device (not shown) starts to rotate at a predetermined rotational speed and is stopped when the potential at the point D reaches a predetermined potential level after a predetermined time to energize the magnet M.sub.1, whereby an appropriate aperture stop may be set. When the potential at the point D reaches a level which is determined by the resistor R.sub.I, the Zener diode D.sub.Z and the potentiometer P, the shutter is opened while the switch S.sub.2 is switched from the fixed contact a to the fixed contact b, whereby the measurement of a shutter speed or a time interval after the shutter is opened is started. The capacitor C is discharged through the photoconductive element R.sub.CD, and when the potential at the point D reaches a predetermined level, the Schmitt circuit triggers again to energize the magnet M.sub.2 to close the shutter. Thus the automatic exposure control device is reset as shown in FIG. 9 as in the case of the circuits shown in FIGS. 3 and 8.

Claims

We claim:

1. An output voltage regulation system adapted to apply a voltage divided by a bleeder resistor to one input terminal of a difference amplifier as one input voltage, a unidirectional feedback path being provided between a first point at which the other input voltage of said difference amplifier is derived and a second point at which the output voltage of said difference amplifier is derived, said feedback path being adapted to cause a flow of current from said first point to said second point only when the voltage across said other input is higher than the output voltage of said difference amplifier so that said other input voltage may derive the stabilized output voltage, and the said other input voltage being derived through the charging or discharging of a time constant circuit comprising a variable resistor and a capacitor.

2. An output voltage regulation system as specified in claim 1 in which the variable resistance means comprises a combination of a photodiode (FIG. 7 PD) and a transistor (FIG. 7 T).

3. An output voltage regulation system as specified in claim 1 wherein said variable resistor in said time constant circuit is a photoconductive element.

4. An output voltage regulation system as specified in claim 1 wherein said one input voltage is controllable whereby the output voltage may become controllable.

5. An output voltage regulation system as specified in claim 1 wherein said one input voltage is stabilized by means of a constant-voltage element.