JPS6053941B2 - Bias light drive method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light amount control system for a bias light provided in a television camera apparatus using a photoconductive image pickup tube to reduce afterimage phenomenon.

In general, this type of television camera device has the drawback that an afterimage phenomenon occurs, which deteriorates the quality of the captured image, especially when capturing an image of a subject with low illumination. This afterimage phenomenon is caused by photoconductive image pickup tubes and can be broadly classified into photoconductive afterimages and capacitive afterimages, but in any case, these afterimages occur when uniform light is applied to the photocathode of the image pickup tube. It is known that this can be reduced by irradiating light, and the light source for this purpose is called a bias light.

As a method of uniformly irradiating the photocathode with the light of this bias light, a method has been proposed in which the light from an incandescent bulb is guided using a light guide such as a mirror or optical fiber, but the amount of light that should be applied to the photocathode is The optimum value varies depending on the type of photoconductive image pickup tube and the purpose of use, and if the amount of light is too large, the contrast ratio that can be captured will be narrowed, and shading may occur due to non-uniformity of the amount of light.

Additionally, if the amount of light changes over time, it may cause fluctuations in the black level of the imaged video signal, and especially in color TV camera equipment, changes in the black level for each primary color signal result in changes in the black balance. Hail may cause deterioration in image quality. Therefore, when driving a bias light, two conditions are required: 1. The light intensity can be set within a wide range depending on the purpose of use, and 2. The set light intensity is always maintained constant. Therefore, conventionally, a circuit as shown in FIG. 1 has been used as a bias write drive circuit.

This circuit determines the amount of light from the lamp L as a bias light by its applied voltage E.

It can be changed by changing the
Voltage E. is set by the voltage regulator 11, which is set by the differential amplifier 12 between the voltage from the voltage regulator 11 and the standard voltage source 1.
This is done by controlling the amplifier 14 according to the difference between the voltages of 3 and 3 and kept constant. Now, in such a circuit, the power consumed by the lamp L and the drive circuit is approximately equal to the input voltage Ei and the current 1 flowing through the lamp L.

The product is Ei-10. However, the power consumed by lamp L is E. - Since this is the case, electric power other than this (E
i above o)・IO will be consumed within the drive circuit,
Considering that the lamp L is an incandescent bulb and requires a relatively large current, the power consumption within this drive circuit results in a large power loss. Particularly, when a television camera device is driven by a battery power source or the like, such power loss shortens the duration of operation of the device. SUMMARY OF THE INVENTION An object of the present invention is to provide a bias light drive system that can reduce power loss in a bias light drive circuit and set the amount of light at a stable value over a wide range.

In the present invention, synchronization is performed with a periodic signal normally generated in a television camera device (this includes a synchronization signal, horizontal and vertical drive signals generated from this synchronization signal, and various periodic signals for creating a synchronization signal). A rectangular wave signal with a predetermined period and width can be set arbitrarily is created, and this rectangular wave signal turns on and off a switching element, thereby controlling the switching of the power supply to the lamp and supplying a pulsed signal to the lamp. By making the width of this pulsed signal variable, the amount of light from the lamp can be freely set, and power consumption in parts other than the lamp can be reduced.

Examples of the present invention will be described below.

FIG. 2 is a circuit diagram of an embodiment of the present invention, which includes a simple multivibrator 21 and its output pulse. It consists of a switching transistor 22 whose switching is controlled by .

Since the bias light lamp L is connected between the collector of the transistor 22 and the power source E, it is connected to the power source E when the transistor 22 is in a conductive state. In addition, the monostable multivibrator 21 includes a capacitor 23 and a variable resistor 24.
is connected, and the output pulse width is set by this variable resistor 24. For an explanation of the operation of this circuit, please also refer to Figure 3, which shows the input and output signal waveforms of the monostable multivibrator 21.
and explain.

First, the monostable multivibrator 21 is triggered by a vertical synchronizing signal as shown in FIG.
3 and the variable resistor 24, the pulse width is determined by the time constant of the variable resistor 24.

This output pulse causes the transistor 22 to perform a switching operation, and the power source E is connected to the lamp L for the output pulse width time t1 of the monostable multivibrator 21, that is, the ON time of the transistor 22. Therefore, the lamp L
repeats blinking periodically, but since this cycle is small, it is essentially in a lit state, and its brightness is determined by the transistor 21.
It is determined by the product of the on time of E and the voltage of power supply E.
Since the on-time of the transistor 21 can be set more freely than the adjustment of the output pulse width time t of the monostable multivibrator 21 using the variable resistor 24, the amount of light can be set arbitrarily over a wide range. Furthermore, since the vertical synchronization signal produced by the television camera device has very small period fluctuation, the period and width of the output pulse of the monostable multivibrator produced in synchronization with this signal are also almost constant. Due to this,
The light amount of the lamp L is stably maintained at the set value, and therefore the black level of the captured video signal does not vary. In addition, the power loss of this drive circuit is caused by a periodic period due to the product of the slight power consumption in the monostable multivibrator 21, which is unrelated to the current 1 flowing through the lamp L, and the saturation voltage when the transistor 22 is in the on state, and the current 1. Even if the current flowing through the lamp L is quite large, the power loss is very small.

FIG. 4 is a circuit diagram showing another embodiment of the present invention, in which a counter 41 that counts the number of pulses of a vertical synchronizing signal, a counter 42 that counts a pulse meter of a horizontal synchronizing signal, and the output of the counter 41 are set as inputs. It consists of a flip-flop 43 whose reset input is the output of the counter 42, and a switching transistor 44 whose switching is controlled by the output of this flip-flop 43.A lamp is connected between the collector of the transistor 44 and the power supply E as in FIG. L is connected.

The circuit operation when the counter 41 and the counter 42 are used as a 112 counter and a 1/N counter, respectively, will be explained with reference to FIG. 5 showing input/output signal waveforms of each part.

First, the counter 41 counts the pulses of the vertical synchronizing signal as shown in FIG. Output. The flip-flop 43 is set by this output pulse, but the counter 42 is reset every frame by the output pulse of the counter 41.
Simultaneously with the setting of , pulses of the horizontal synchronizing signal as shown in FIG. 5C are counted, and when the Nth pulse is reached, a pulse is output as shown in FIG. Therefore, from the flip-flop 43, as shown in FIG.
A double pulse is obtained, and the transistor 44 performs a switching operation using this pulse, so that the power source E is connected to the lamp L in a pulsed manner only when the transistor 44 is in an on state. In this embodiment, the on time of the transistor 44 is determined by the count value N of the counter 42, and this count value N
can be set freely, so the light intensity can be set arbitrarily over a wide range, and since it is synchronized with the horizontal synchronization signal, there is no fluctuation in pulse width, making it possible to supply a very stable light intensity.

Further, as in the example shown in FIG. 2, the power loss is the sum of the slight power consumption in the counters 41, 42 and the flip-flop 43 and the periodic power consumption in the transistor 44, and is very small. FIG. 6 is a diagram showing a third embodiment of the present invention, which includes a monostable multivibrator 61 and a switching transistor 62 as shown in FIG. In this example, by adding a differential amplifier 65 for voltage correction, a function is provided to correct light intensity fluctuations due to voltage fluctuations of the power source E, etc.

66 is a reference voltage source.

To explain the operation of this circuit, first, a horizontal synchronizing signal is applied to the monostable multivibrator 61, and the transistor 62 is caused to perform a switching operation by output pulses having a predetermined period and a predetermined width, which is similar to the embodiment shown in FIG. In this embodiment, an integrating circuit 63 is further connected between the collector of the transistor 62 and the lamp L, and a DC voltage is obtained by integrating the pulsed voltage. At step 65, the voltage is compared with the voltage of a reference voltage source 66.

By adding the output of this differential amplifier 65 to the monostable multivibrator 61 and controlling its output pulse width, a negative feedback function is provided. The voltage is automatically corrected so that the voltage supplied to the lamp L does not fluctuate and the amount of light does not fluctuate due to voltage fluctuations due to temperature fluctuations or the like. The light intensity is set using the adjustment resistor 64.
The automatic voltage correction function described above makes it possible to obtain a very stable amount of light, and as with the previous embodiments, power loss is minimal.

Although the present invention has been explained using three embodiments, the circuit for switching the transistor in order to supply a pulsed signal to the lamp L may include a monostable multivibrator, a counter, a flip-flop, and various other modifications. This is obvious, and although we have explained the case where a vertical synchronization signal and a horizontal synchronization signal are used as input signals, there are also other signals that are synchronized with the synchronization signal, such as horizontal and vertical drive signals generated within the television camera device. It is also clear that it can be used as long as it is a specific signal.

As described above, according to the present invention, by utilizing periodic signals generated within the television camera device, the bias light drive circuit can minimize power loss and supply a very stable amount of light. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram schematically showing an example of a conventional bias write drive circuit, FIG. 2 is a circuit diagram schematically showing an embodiment of a bias write drive circuit according to the present invention, and FIG.
The figure is a diagram showing the input/output signal waveforms of each part in Figure 2, Figure 4 is a circuit diagram showing another embodiment of the present invention, and Figure 5 is a diagram showing seven input/output signal waveforms of each part. , FIG. 6 is a circuit diagram showing a third embodiment of the present invention. The main reference numbers in the drawings are as follows. 11... Resistor for pulse width adjustment, 12...
Differential amplifier, 14...Amplifier, L...Lamp,
21, 61... Monostable muffle pipe plater, 2
2, 44, 62... switching transistor, 4
1, 42...Counter, 43...Flip-flop, 63...Integrator circuit, 65...Differential amplifier.

Claims (1)

[Claims] 1. In a television camera device equipped with a bias light and using a photoconductive image pickup tube, a switching element for turning on and off a drive current to the bias light, and a horizontal or vertical synchronization signal generated in the television camera device. means for generating a pulsed signal that turns on and off the switching element in synchronization with the rise of a periodic signal such as, and the pulse width of the pulsed signal is varied to arbitrarily control the amount of light from the bias light. Bias light drive system characterized by being able to be set.