KR950009557Y1 - Automatic back-light control circuit of a camcorder - Google Patents

Abstract

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Description

Camcorder's Automatic Back-Light Control Circuit

1 is a conventional circuit diagram.

2 is a circuit diagram of the present invention.

3 is a waveform diagram of an incident light control signal.

* Explanation of symbols for main parts of the drawings

10: buffer 20: smoothing circuit

30: incident light detection unit 40: level determination unit

50: photoelectric coupling part Q1, Q2: transistor

OP1: Comparator LED1: Light Emitting Device

Cds: Light receiving element ZD1, ZD2: Zener diode

R1-R5: resistors C1, C3: capacitors

D1: diode

The present invention relates to a circuit of a function of automatically adjusting the backlight of a camcorder, and more particularly, to an automatic backlight control circuit of a camcorder for automatically correcting a video signal that is likely to become dark during a backlight shooting of a camcorder.

Such a conventional circuit includes a switch SW for switching between a normal state and a backlight state, and a diode for smoothing the luminance signal YL input through the buffer 10 as shown in FIG. A smoothing circuit 20 consisting of D1) and a condenser C1, an incident light IRIS detector 30 for detecting the magnitude (brightness) of incident light from the smoothing circuit 20, the output of the switch SW and the incident light It is comprised by the comparator OP1 which compares the output of the detection part 30. FIG.

Referring to the conventional circuit operation configured as described above, after the luminance signal YL is smoothed through the buffer 10 and the smoothing circuit 20, the incident light is detected by the incident light detector 30, and the non-inverting (+) input of the comparator OP1 is performed. Is applied to the terminal.

In addition, when a signal of a predetermined level is applied through the backlight control signal terminal B / L, a and c are connected to the contacts of the switch SW so that a signal of 0 (V) is applied to the inverting (-) input terminal of the comparator OP1. Is applied and a signal of 0 (V) is applied to the backlight control signal terminal B / L, b and c are connected to the contacts of the switch SW so that V1 is applied to the inverting (-) input terminal of the comparator OP1. Since the signal is applied, the IRIS control is performed by the signal appearing at the output terminal of the comparator OP1.

However, according to the conventional configuration, since the switch (SW) must be switched to the backlight mode at the time of backlighting, a human's eyes normally detect the normal state and the backlight state when shooting with a camcorder while viewing the black and white viewfiner. There was a drawback that the backlight mode could not be properly used as it could not be properly confirmed.

In view of the above, the present invention allows the user to automatically select and adjust the backlight mode by using the incident light control signal of the camera, so that the user can take a picture without a switch operation even during backlighting. The same reference numerals refer to the same in detail according to the accompanying drawings as follows.

2 is a circuit diagram for automatic backlight adjustment according to the present invention. The configuration of the buffer 10, the smoothing circuit 20, the incident light detector 30, and the comparator OP1 is the same as in the related art. Zener diodes (ZD1) (ZD2), transistors (Q1) (Q2), which input an aperture control signal according to the camera and incident light to input terminals, and switch on / off a predetermined DC voltage according to the magnitude of this input level. The level determining unit 40 composed of the resistor R3 and the condenser C3, and the light emitting element LED1, the light receiving element Cds, and the resistor whose resistance values of the light receiving unit change according to the switching of the level determining unit 40. The photoelectric conversion part 50 which consists of R1) (R4) (R5) is comprised.

In the figure, reference numeral R2 denotes a resistor, C2 denotes a capacitor, and VCC denotes a power supply terminal.

Referring to the effect of the present invention configured as described above are as follows.

The incident light control signal of the level as shown in part (a) of FIG. 3 is applied from the camera to the input terminal IN of the level determining unit 40 so that the zener diodes ZD1 and ZD2 have a higher voltage than the zener set voltage. When the bias current is applied to the base of the transistor Q1 and the transistor Q1 is brought into a conductive state, a low state signal is applied to the base of the transistor Q2, so that the transistor Q2 is turned off.

Accordingly, the light emitting device Cds maintains a constant resistance value as the light emitting device LED1 of the photoelectric conversion unit 50 connected to the emitter of the transistor Q2 does not emit light, thereby inverting the comparator OP1. To the negative input terminal, the resistor R5 from the control signal voltage input terminal V1 and the divided voltage by the light receiving element Cds are applied as the signal voltage.

On the other hand, when the backlight is photographed in a dark state, the level of the incident light control signal applied to the input terminal IN is lowered as shown in part (c) of FIG. 3 to be lower than the zener set voltages of the zener diodes ZD1 and ZD2. As a result, a low state signal is applied to the base of the transistor Q1 to block the transistor Q1, and a high state signal through the resistor R3 is applied to the base of the transistor Q2.

In this way, when the transistor Q2 is turned on, the light emitting element LED1 connected to the emitter emits light to apply light to the light receiving element Cds, so that the comparison of the comparison OP1 through the resistor R5 and the resistor R1 is performed. The low state signal is applied to the inverting (-) input terminal.

On the other hand, the level of the incident light control signal applied to the input terminal IN is a section between (a) and (c) of FIG. 3, i.e., a section represented by (b) is an incident light control section that approximates the light emitting element LED1. The photo coupler made of the light receiving element Cds operates to linearly vary the resistance, thereby controlling the output voltage.

In FIG. 2, the capacitor C3 bypasses a signal of an AC component included in the incident light control signal applied to the input terminal IN to ensure stable operation.

The present invention, which is operated as described above, can automatically adjust the selection of the backlight or the dense mode by the switching of the switch by the camera IRIS control output signal, thereby making it inconvenient for the user to operate the switch even during backlighting. It provides the effect that you can shoot without.

Claims (1)

A smoothing circuit section for smoothing the input luminance signal, an incident light detecting section for detecting the level size of incident light by detecting the level of the luminance signal smoothed by the smoothing circuit section, and a level plate for detecting / determining the level of the input camera IRIS control output. And a photoelectric conversion unit for outputting a stable voltage value according to the output of the level determination unit, and a comparison unit for comparing IRIS control with the output of the photoelectric conversion unit and the output of the incident light detection unit. Backlight Control Circuit.