JPH036068Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field This invention relates to an automatic aperture control circuit for a television camera lens used in CCTV cameras for monitoring purposes.

Prior Art FIG. 1 shows a schematic configuration of an automatic aperture control circuit for a television camera lens to which this invention is applied.

To explain this simply, a video signal from the TV camera body including an image pickup tube (not shown) is input to the brightness detection circuit 1, a rectified and smoothed brightness detection signal VS is input to the level adjustment circuit 2, and a target aperture is input to the brightness detection circuit 1. The level is adjusted by comparing it with a reference level set according to the value, and a voltage signal for driving the aperture is input to the drive circuit 3.

In response to the signal, the drive circuit 3 applies current to the drive coil of the switching device 4 to open and close the aperture blades. At this time, the opening/closing speed of the aperture blades is detected and feedback is applied via the braking circuit 5 to prevent hunting.

In such automatic aperture control circuits for television camera lenses, especially in interchangeable lens television cameras, the voltage supplied from the camera body side to the lens side varies.

On the other hand, in the level adjustment circuit 2 in Fig. 1, a circuit that divides the power supply voltage using a resistor and a potentiometer (variable resistor) is generally used to set the reference level according to the target value of the aperture. However, in such a circuit, when the power supply voltage changes, the reference level fluctuates in response to the change, so the aperture value has the disadvantage of being different from the set value.

Therefore, a supply voltage stabilization circuit is provided that regulates the voltage to ground by the forward voltage of the diode or the Zener voltage of the Zener diode, and the output voltage is divided by a potentiometer to obtain a reference level. There have also been proposals that eliminate the effects of changes in power supply voltage.

However, even if this is done, in the case of a circuit configuration that uses an operational amplifier as a comparator, there is a problem that adjustment may become impossible depending on the level adjustment range unless a compensation circuit such as offset adjustment is provided separately. .

Purpose This invention was created with a focus on the above problems.It is not easily affected by changes in the power supply voltage, can obtain a wide level adjustment range with a level adjustment circuit using an operational amplifier, and has a low offset. An object of the present invention is to provide an automatic aperture control circuit for a television camera lens that does not require a separate adjustment circuit or the like.

Configuration Therefore, the automatic aperture control circuit for a television camera lens devised according to this invention uses the Zener voltage obtained by dividing the power supply voltage by two resistors and a Zener diode, without worrying about the voltage with respect to ground, to set the target aperture value. The voltage is divided by a potentiometer that can be adjusted according to the voltage and another resistor, and the divided voltage output of the potentiometer is used as the other input of a first operational amplifier that receives the luminance detection signal as one input, and its output terminal and The aperture of the lens is driven by the output voltage signal obtained between the output terminal of the second operational amplifier as a voltage follower that inputs the voltage obtained by dividing the power supply voltage by two resistors. It is something.

Embodiment An embodiment of this invention will be explained with reference to FIG. 2 of the accompanying drawings.

In this embodiment, a Zener diode ZD is inserted between the power supply voltage supply terminals 10 and 11 from the television camera and between the first resistor R ₁ and the second resistor R ₂ and connected in series to stabilize the voltage. A series circuit consisting of a potentiometer (variable resistor) VR and a third resistor _R3 that can be adjusted according to the target aperture value is connected in parallel to the Zener diode ZD.

Then, the divided voltage output from the potentiometer VR is applied to the other input of the first operational amplifier _OP1 as a comparator, which receives the luminance detection signal VS as one input, that is, as the reference voltage Vr.

In addition, a voltage follower that divides the power supply voltage V ₀ by a series circuit of a fourth resistor R ₄ and a fifth resistor R ₅ in parallel with the voltage stabilizing circuit described above, and receives the divided voltage output V ₅ as an input. A second operational amplifier OP ₂ is provided, and the aperture of the lens is controlled by the output voltage signal Vout obtained between the output terminals 12 and 13 of the second operational amplifier OP ₂ and the first operational amplifier OP ₁ . Drive.

Here, the resistance values of the first to fifth resistors R ₁ to _{R 5} and the potentiometer VR are respectively R ₁ , R ₂ , R ₃ , R ₄ ,
Assuming R ₅ and VR, each resistance value is set so that R ₂ ×R ₄ =R ₁ ×R ₅ and the resistance value of VR + R ₃ is larger than that of R ₁ +R ₂ .

Then, the power supply voltage is V ₀ , the voltage on the cathode side of the Zener diode is V ₁ , and the voltage on the anode side is
V ₂ , Zener voltage is VZD, output voltage is Vout, potentiometer VR of output voltage Vout when VS = 0
The adjustment range is calculated as follows.

Vout=(V ₁ −V ₀ ×R ₅ /R ₄ +R ₅ ) ~ (V ₂ +VZD×R ₃ /VR
+R ₃ −V ₀ ×R ₅ /R ₄ +R ₅ ) = [VZD+(V ₀ −VZDQ ×R ₂ /R ₁ +R ₂ −V ₀ ×R ₅ /R ₄ +R ₅ )] ~ [(V ₀ −VZD)
×R ₂ /R ₁ +R ₂ +VZD×R ₃ /VR+R ₃ −V ₀ ×R ₅ R ₄ +R ₅ ] Here, if R ₁ = nR ₂ , R ₄ = nR ₅ , then Vout ₌ −VZD)×R ₂ /(n+1)R ₂ −V ₀ ×
R ₅ / (n+1) R ₅ ] ~ [(V ₀ −VZD) ×R ₂ / (n+1) R ₂ +VZD×R ₃ /VR+R ₃ −V ₀ ×R ₅ /
(n+1)R ₅ ] = (n×VZD/n+1) ~ (VZD×R ₃ /VR
+R ₃ -VZD/n+1), and the variable range of the output voltage Vout is the power supply voltage.
It remains constant regardless of changes in V ₀ .

For example, n=1 (R ₁ = R ₂ , R ₄ = R ₅ ), VR=
If 2×R ₃ , Vout = (VZD/2) to (-VZD/6), which varies from 1/2 to -1/6 of the Zener voltage, and it is possible to take the offset adjustment from -VZD/6. can.

Note that the positive and negative polarities here have V ₀ /2 as the reference point (0 level).

FIG _. 3 shows an example of application of this invention, which is a partially modified version of the embodiment shown in FIG. A diode D is connected in the forward direction between the connection point between the potentiometer VR and the third resistor _R3 and the output terminal 13 of the second operational amplifier _OP2 .

In this example, in addition to the conditions regarding the resistance values of each resistor and potentiometer in the embodiment of FIG. 2, a potentiometer VR having a larger resistance value than the second resistor _R3 is used.

Then, let the forward voltage of diode D be VD, and as in the previous case, the output voltage when VS = 0
The adjustment range for Vout is determined as follows.

Vout=(V ₁ −V ₀ ×R ₅ /R ₄ +R ₅ ) ~ [(V ₀ ×R ₅ /R ₄ +R ₅
−VD) −V ₀ ×R ₅ /R ₄ +R ₅ ] = [VZD + (V ₀ −VZD) × R ₂ /R ₁ +R ₂ −V ₀ ×R ₅ /R ₄ +
R ₅ ] ~ (-VD) Here, if R ₁ = nR ₂ , R ₄ = nR ₅ , Vout = [VZD + (V _{0 -} VZD) x 1/(n+1) - V ₀ /
(n+1)] ~ (-VD) = (nVZD/n+1) ~ (-VD
), and the variable range of Vout remains constant regardless of changes in the power supply voltage _V0 . Also, -VD can be used to compensate for offset adjustment.

Note that although these calculations are approximate calculations, the errors thereof are negligible in actual use.

Effects As explained above, in the automatic aperture control circuit for television camera lenses according to this invention, the level adjustment range of the aperture control signal remains constant regardless of fluctuations in the power supply voltage, so the set target aperture value is always maintained. It can be accurately controlled so as to have a wide adjustment range, and can also be used as offset adjustment for the operational amplifier, so the circuit configuration is simple and can be supplied at low cost.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an automatic aperture control circuit for a television camera to which this invention is applied, Fig. 2 is a circuit diagram showing an embodiment of this invention, and Fig. 3 is an example of application of this invention. It is a circuit. 10, 11... Power supply voltage supply terminal, 12, 13
...output terminal, _R1 ...first resistor, _R2 ...second
resistance, R ₃ ... third resistance, R ₄ ... fourth resistance,
R ₅ ...Fifth resistor, VR...Potentiometer, ZD...
Zener diode, _OP1 ...first operational amplifier, _OP2 ...second operational amplifier.

Claims (1)

[Scope of utility model registration request] Connect the first terminal between the power supply voltage supply terminals from the TV camera.
A voltage stabilizing circuit is connected in series with a Zener diode inserted between the resistor and the second resistor, and the voltage stabilizing circuit is connected in parallel to the Zener diode of the voltage stabilizing circuit and is adjustable according to the target aperture value. A series circuit of a potentiometer and a third resistor, and a comparator having one input as a luminance detection signal based on a video signal from a television camera and the other input as a divided voltage output from the potentiometer. 1 operational amplifier, a series circuit of a fourth resistor and a fifth resistor connected in parallel to the voltage stabilizing circuit, and a voltage for inputting the voltage at the connection point of the fourth resistor and the fifth resistor. A second operational amplifier as a follower, and an output voltage signal obtained between the output terminal of the second operational amplifier and the output terminal of the first operational amplifier to drive and control the aperture of the lens. and the product of the resistance values of the second and fourth resistors is equal to the product of the resistance values of the first and fifth resistors, and
A television camera lens characterized in that the resistance values of each of the resistors and the potentiometer are set so that the sum of the resistance values of the potentiometer and the third resistor is greater than the sum of the resistance values of the resistors. Automatic aperture control circuit.