JPH075510Y2 - Picture tube brightness variable circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a color image reproducing circuit using a picture tube,
The present invention relates to a luminance variable circuit of a video signal amplifier circuit supplied to the cathode of a picture tube.

(Prior Art) FIG. 2 is a circuit diagram showing an example of a video signal amplifier circuit including a conventional brightness variable circuit.

The video signal supplied from the video signal input terminal 1 and the bright pulse output from the bright pulse generation circuit 6 are supplied to the adder 2, the direct current component is cut by the capacitor C, and the base terminal of the NPN transistor TR ₁ is cut. Output to. The emitter terminal of NPN transistor TR ₁ is grounded through resistor R ₁ , and the collector terminal is NPN transistor T 1.
It is connected to the emitter terminal of R ₂ and constitutes a cascode amplifier 3.

The base terminal of the NPN transistor TR ₂ is connected to the DC power supply V _D , and the collector terminal is connected via the resistor R ₂ to the DC power supply V _CC.
Is connected to a cathode 12 of a picture tube (hereinafter referred to as CRT) 11 and a direct current regeneration circuit 5 for feedback. The direct current regeneration circuit 5 is connected to a base terminal of an NPN transistor TR ₁ .

In the bright pulse generation circuit 6, the resistors R ₄ and R ₃ are connected in series, the variable resistor VR ₁ is connected in parallel with these resistors, and the DC voltage V ₀ is supplied to each resistor. . Then, the resistance R ₄ respectively between the variable resistor VR ₁ of the resistor R ₃ terminals 7a, 7b is is provided with the switch 7 is switched by the clamp pulse supplied from the clamp circuit 4. The switch 7 is connected to the adder 2 and supplies a bright pulse.

When the clamp pulse supplied from the clamp circuit 4 to the switch 7 is at L level, the switch 7 is connected to the 7a side, and the voltage V _{A obtained} by dividing the DC voltage V ₀ by the resistor R ₃ and the resistor R ₄ is bright. When the clamp pulse is at the H level, the switch 7 is connected to 7b, and the voltage V _B divided by the variable resistor VR ₁ is supplied from the bright pulse generating circuit 6 to the adder 2 by the pulse generating circuit 6. Is supplied to.

The adder 2 adds the video signal supplied from the video signal input terminal 1 and the bright pulse supplied from the bright pulse generation circuit 6 and supplies the result to the cascode amplifier 3, which is inverted and amplified by the cascode amplifier 3 and then CRT11. The cathode 1
Supplied to 2.

Further, the DC regenerating circuit 5 feeds back from the output terminal of the cascode amplifier 3 to the input terminal in order to keep the DC level of the signal supplied to the cathode 12 of the CRT 11 constant. The direct current regeneration circuit 5 supplies the cascode amplifier 3 to the cathode 12 in synchronization with the clamp pulse of the clamp circuit 4.

FIG. 3 shows the waveforms at the portions indicated by a to d in the circuit shown in FIG.

a is a waveform representing the video signal and the sync signal of the pedestal portion supplied from the video signal input terminal 1 to the adder 2,
Reference numeral b is a waveform representing a bright pulse supplied from the bright pulse generation circuit 6 to the adder 2. c is a waveform that a and b are added by the adder 2 and is supplied to the cascode amplifier 3, and d is a waveform of a signal that is supplied to the cathode 12.

Since the DC regeneration circuit 5 is clamped in synchronization with the bright pulse shown in FIG. 3b, when the brightness of the screen of the CRT 11 is adjusted from the outside, the variable resistor VR ₁ is changed to change the voltage V
_B is changed to change the level of the bright pulse output from the bright pulse generation circuit 6. When the level of the bright pulse supplied to the adder circuit 2 is changed, the cathode
The DC potential supplied to 12 can be changed to change the brightness of the screen of the CRT 11.

(Problems to be solved by the invention) When the pedestal part potential in the waveform d of FIG. 3 is V _PL , this potential V _PL is the bias potential of the transistors TR ₁ and TR ₂ of the cascode amplifier of FIG. , The operation of the cascode amplifier 3 is determined to be optimum.

The current in the no-signal state (hereinafter referred to as the idling current) is the resistance between the power supply V _CC and the pedestal part potential V _PL.
It is a value divided by R ₂ and has a great influence on the output frequency characteristic of the cascode amplifier 3 and the like.

Therefore, by changing the brightness of bright pulse, CRT11
When the luminance of is changed, the pedestal part potential V _PL changes, the idling current changes, and the output frequency characteristic of the cascode amplifier 3 changes or deteriorates.

Also, when brightening the screen, the magnitude of the bright pulse is changed so that the idling current increases,
The current flowing through the cascode amplifier 3 also increases, the power supply V _CC used for the cascode amplifier 3 must have a large current capacity, and the heat sink used for the cascode amplifier 3 is large enough to handle a large idling current. There were problems such as having to use the ones.

(Means for Solving the Problem) As a means for solving the above problems, the present invention provides an additional pulse generating circuit for generating a pulse in synchronization with a clamp pulse and a pulse supplied from the additional pulse generating circuit. An adder for adding to the signal, a cascode amplifier for inverting and amplifying the signal supplied by the adder to the cathode of the picture tube, a DC power supply for supplying a current source to the cascode amplifier, and an output of the cascode amplifier In a picture tube brightness variable circuit including a DC regenerating circuit connected to, an inverting amplifier for inverting and amplifying the pulse supplied from the additional pulse generating circuit and supplying the inverting amplifier to the adder, and an output of the DC power supply. , And a series regulator for adjusting the voltage of this DC power supply and supplying it to the cascode amplifier.

(Function) The power supply voltage is changed according to the magnitude of the bright pulse,
In the pedestal portion of the video signal, even if the brightness of the CRT changes, a constant idling current flows in the cascode amplifier to prevent performance deterioration such as frequency characteristics of the cascode amplifier.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of a picture tube brightness variable circuit of the present invention.

In this embodiment, an inverting amplifier 8 is provided between the bright pulse generating circuit 6 of the circuit diagram of the conventional example shown in FIG.
And a series regulator 10 including a transistor TR ₃ and a comparison amplifier 9 is inserted between the power supply V _CC and the resistor R ₂ .

The series regulator 10 supplies the negative input of the comparison amplifier 9 with the output of the collector terminal of the transistor TR ₂ of the cascode amplifier 3 via the resistors R ₂ and R ₅ and at the same time the terminal of the switch 7 of the bright pulse generation circuit 6. 7b is resistance R ₉
Connected through. The negative input is grounded via a resistor R ₆ , and the positive input is connected to the DC power supply Vs.

The output of the comparison amplifier 9, through a resistor R ₇ to the collector terminal through when connected to the base terminal of the NPN transistor TR ₃ and the resistor R ₇ simultaneously resistor R _8, and is connected with the DC power supply V _CC . The emitter terminal of transistor TR ₃ is resistor R
It is connected via ₂ to the output of the cascode amplifier 3.

When the voltage of the emitter terminal of the NPN transistor TR ₃ is the output voltage of the series regulator 10 and V _C, will operate the cascode amplifier 3 in accordance with the change of the output voltage V _C, the output voltage V _C is , The bright pulse supplied by the contact 7b of the analog switch 7 of the bright pulse generating circuit 6 changes.

Now, the voltage when the switch 7 of the bright pulse generation circuit 6 is on the contact 7a side is V _A , and the voltage when it is on the contact 7b side is V _B
Assuming that V _B > V _A , the bright pulse is inverted twice by the inverting amplifier 8 and the cascode amplifier 3, so if the variable resistor VR ₁ is operated to increase V _B , the cascode amplifier 3 In the output waveform d, since the bright pulse potential V _BL is clamped so as to be a constant voltage, the pedestal level potential V _PL is inevitably lowered.

When V _B is increased, the current flowing through the resistor R ₆ via the resistor R ₉ is increased, and the input voltage of the comparison amplifier 9 and
Since the voltage difference of the resistor R ₆ becomes almost 0 [V], the current flowing through the resistor R ₅ decreases, and the output V _{C of the} series regulator 10 decreases.
Will be lowered.

Now, assuming that the resistance value of the variable resistor VR ₁ is small enough to be ignored with respect to the resistor R ₉ , the difference between the negative input and the positive input of the comparison amplifier is 0 [V], Holds, Becomes

Here, R ₅ R ₆ represents a parallel combined resistance of the resistors R ₅ and R ₆ .

On the other hand, considering the pedestal level potential V _PL of the signal d supplied to the cathode 12, since the potential V _{BL of the} bright pulse becomes constant by the DC regeneration circuit 5, However, K is the gain (attenuation rate) of the inverting amplifier 5.

In the pedestal part of the signal, the idling current flowing is (V
_{Since C-} V _PL ) / R ₂ , If the resistance value is selected so that, the voltage V _B becomes irrelevant.

In other words, even if the brightness of the CRT 11 represented by the magnitude of the bright pulse changes, a certain amount of idling current flows through the cascode amplifier 3, and it is possible to prevent the performance deterioration of the cascode amplifier 3 due to the idling current.

(Effect of the device) Since the picture tube brightness variable circuit of the present invention is configured as described above, even if the picture tube brightness changes, the idling current does not change and a certain amount of idling current is supplied to the cascode amplifier. Therefore, it is possible to prevent performance deterioration such as frequency characteristics of the cascode amplifier.

Moreover, since an extra current does not flow to the cascode amplifier, the heat sink of the cascode amplifier can be further downsized, and the power supply used for the cascode amplifier can have a small current capacity.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a picture tube brightness variable circuit of the present invention, FIG. 2 is a circuit diagram showing a conventional example, and FIG. 3 shows waveforms at respective portions in FIGS. 1 and 2. It is a figure. 1 ... Video signal input terminal, 2 ... Adder, 3 ... Cascode amplifier, 4 ... Clamp circuit, 5 ... DC regeneration circuit, 6 ... Bright pulse generation circuit (additional pulse generation circuit), 7 ... Switch, 8 inverting amplifier, 9 comparison amplifier, 10 series regulator, 11 CRT (picture tube), 12 cathode, C capacitor, R _{1 to} R ₈
… Resistor, TR _{1 to} TR ₃ …… NPN transistor, V _{A to} V _D , V _CC ,
V ₀ , Vs …… DC power supply, V _BL …… Bright pulse potential, V _PL
…… Signal pedestal level potential, VR ₁ …… Variable resistance.

Claims (1)

[Scope of utility model registration request] 1. An additional pulse generating circuit for generating a pulse in synchronization with a clamp pulse, an adder for adding a pulse supplied from the additional pulse generating circuit to a video signal, and a signal supplied by the adder. A cascode amplifier for inverting amplification and supply to the cathode of the picture tube, a DC power supply for supplying current to this cascode amplifier, and a DC regenerating circuit connected to the output of the cascode amplifier, and supplied from the additional pulse generation circuit. In a picture tube brightness variable circuit for varying the brightness of a picture tube by the pulse generated, the pulse supplied from the additional pulse generation circuit is inverted and amplified, and the inverted amplifier is supplied to the adder and the output of the DC power supply is connected. It is equipped with a series regulator that adjusts the voltage of this DC power supply and supplies it to the cascode amplifier. In part, kinescope brightness variable circuit, characterized in that as a constant current to the cascode amplifier is supplied.