JPH0339932Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a variable voltage limiting circuit that changes the variable voltage range obtained by a variable resistor, and in particular, the invention relates to a variable voltage limiting circuit that changes the variable voltage range obtained by a variable resistor. A circuit that narrows the variable voltage range obtained by a resistor by simply operating a single button compared to manual operation, and allows the viewer to view an image in an almost standard state by operating this button [see below] “OBC
(One Button Color) circuit].

(b) Prior art Figure 1 shows a conventional OBC circuit, in which a constant DC voltage (for example, +12V) is applied from the power supply terminal +B.
2 circuits 2 provided in OBC switch unit 1
It is supplied to the intermediate terminals 3b and 5b of the first switch section 3 and the third switch section 5 of the slide switch 2 as contacts. One end of a fixed resistor _R1 is connected to the terminal 3a of the first switch section 3, one end of a fixed resistor _R2 is connected to the terminal 3c, and each of the fixed resistors _R1 ,
The other ends of _R2 are connected together, and also connected to one end of a brightness adjustment variable resistor _VR1 provided in the control volume unit 7. On the other hand, the other end of the variable resistor VR ₁ is connected to the intermediate terminal 4b of the second switch section 4 of the slide switch 2, and a fixed resistor _R3 is connected between the terminal 4a of the second switch section 4 and the ground point. A fixed resistor _R4 is connected between the terminal 4c and the ground point. Furthermore, fixed resistances R ₅ , R ₆ ,
R ₇ , R ₈ and a variable resistor VR ₂ for hue adjustment are appropriately connected to each terminal 5a, 5b, 5c, 6a, 6b, 6c. Regarding the values of the resistances for the first and second switch sections 3 and 4, R ₁ = 21.3 (KΩ), R ₂ = 3.3.
(KΩ), R ₃ = 3.4 (KΩ), R ₄ = 1.2 (KΩ), and the resistance value between the grounding point of power terminal +B when slide switch 2 is connected to terminals 3a and 4a is the slide The resistance value between the power supply terminal +B and the ground point is set to be larger than that when the switch 2 is connected to the terminals 3c and 4c, and each fixed resistor _R5 connected to the third and fourth switch parts 5 and 6 , R ₆ , R ₇ ,
The value of _R8 is set similarly.

Now, when the OBC circuit is off, that is, when the slide switch 2 is set to the terminals 3c and 4c, the fixed resistor R ₂ and the fixed resistor R ₄ are set as described above, so the sliding of the variable resistor VR ₁ is The range of variable voltage obtained by the slider 8 is wide, so that the viewer can adjust the brightness according to his/her preference by adjusting the slider 8. Also, variable resistor VR ₂
The same goes for , and by adjusting this, you can adjust the hue according to your preference.

Then, when the OBC circuit is turned on, that is, the slide switch 2 is set to the terminals _3a and _4a side, the slider 8 of the variable resistor VR ₁ is The range of variable voltage obtained by . This also applies to the variable voltage range obtained by the slider 9 of the variable resistor VR ₂ . Therefore,
By keeping the OBC circuit on, viewers can view images with approximately standard brightness and hue settings.

By the way, control volume unit 7
and OBC switch unit 1 are connected using lead wires.
Since it is performed by l ₁ , l ₂ , l ₃ , and l ₄ , it is different from the conventional
The OBC circuit requires two lead wires for each variable resistor. For this reason, if variable resistors for contrast adjustment and saturation adjustment are provided in addition to variable resistors for brightness adjustment and hue adjustment, a total of 8 lead wires are required, which makes the connection work troublesome and the lead wires It also has the disadvantage that the shaping work is complicated.

Furthermore, when four variable resistors are used, the slide switch also requires a slide switch with four circuits and two contacts, which has the drawback of increasing the price of the slide switch.

(c) Purpose of the invention The present invention has been devised in view of the above-mentioned drawbacks, and aims to reduce the number of lead wires required for connection between the control volume unit and the OBC switch unit as much as possible, thereby simplifying the work of connecting the lead wires. It is an object of the present invention to provide a variable voltage limiting circuit that is simplified and devised so that the OBC on/off switch can be an inexpensive one-circuit, one-contact switch.

(d) Structure of the invention The variable voltage limiting circuit of the invention includes a series circuit in which a fixed resistor and a variable resistor are connected between a power supply terminal and a ground point, a switch means, and a switch means that controls the power supply by opening and closing the switch means. and a semiconductor switch element to which a switching voltage is applied from a terminal and a conductive path is connected to both ends of the fixed resistor, and the semiconductor switch element is made conductive or non-conductive by the switching voltage, thereby obtaining the effect of the variable resistor. The variable voltage range is changed.

The variable voltage limiting circuit is used, for example, as an OBC circuit in a television receiver, and the voltage obtained by the variable resistor is used for brightness adjustment, contrast adjustment, etc.

(E) Embodiment An embodiment of the present invention will be described with reference to FIGS. 2 to 4.

Figure 2 shows the variable voltage limiting circuit of the present invention, in which the first and second terminals are connected between the power supply terminal +B and the ground point.
A series circuit 10 is provided in which fixed resistors R ₁₁ , R ₁₂ , variable resistor VR _{11 ,} and third and fourth fixed resistors R ₁₃ , R ₁₄ are connected in this order. 11 is a switch, and one end 11a of the switch 1 is connected to the first resistor.
The other end 11b is connected to the power supply terminal +B side of _R11 , and the other end 11b is connected to the anode of a switching diode _D1 , which is connected in parallel to the switch 11 _and the first resistor _R11 . Connected to the base of transistor TR ₁ . Further, the collector of the switching transistor _TR1 is connected to the connection point between the third resistor _R13 and the fourth resistor _R14 , and the emitter is grounded.

Now, if the switch 11 is in the open state, no bias is supplied to the switching diode _D1 and the switching transistor _TR1 , so the diode _D1 and the transistor _TR1 are both non-conductive, and therefore the power supply terminal +B Since the first to fourth resistors R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ are connected in series between the variable resistor VR 11 and the ground point, the variable voltage range that can be obtained by adjusting with the slider 12 of the variable resistor VR ₁₁ becomes small.

Next, when the switching means 11 is closed, the power supply voltage +B is applied as a switching voltage to the switching diode D ₁ so as to apply a forward bias, so that the diode D ₁ becomes conductive and the first resistor R ₁₁
There is a substantially short state between both ends of . At the same time, the base of switching transistor _TR1
Since a forward bias is applied between the emitter and the power source terminal voltage, the transistor TR ₁ also becomes conductive, and therefore, the terminals of the fourth resistor R ₁₄ are substantially shorted. Therefore, only the second fixed resistor R ₁₂ , the variable resistor VR ₁₁ and the third fixed resistor R ₁₃ are inserted between the power supply terminal +B and the ground point, so that the slider 12 of the variable resistor VR ₁₁ has a The variable voltage range becomes larger. The first to fourth fixed resistors R ₁₁ ,
The values of R ₁₂ , R ₁₃ , and R ₁₄ are, for example, R ₁₁ = 18KΩ, R ₁₂ =
3.3KΩ, R ₁₃ = 1.2KΩ, R ₁₄ = 2.2KΩ.

FIG. 3 shows a configuration diagram when the variable voltage limiting circuit of the present invention is implemented in an OBC circuit of a television receiver, and the same parts as in FIG. 2 are given the same figure numbers. In the figure, reference numeral 13 is an OBC switch unit equipped with a switch 11 having one circuit and one contact, and the switch unit 13 and the control volume unit 14 are connected by two lead wires.
They are connected by l ₅ and l ₆ , and there are two variable voltage limiting circuits as shown in Figure 2, but each variable voltage limiting circuit is connected in common by two lead wires l ₅ and l ₆ . Because it can supply the power supply voltage +B, use the lead wire.
The connection work of _l5 and _l6 is easy, and the wiring is also simple.

Next, the operation of this circuit will be explained.

When the OBC circuit is on, that is, the switch 11 is open, the switching diodes D ₁ and D ₂
is non-conducting and the switching transistor
Since TR ₁ and TR ₂ are also non-conducting, the series circuit 10 of fixed resistors R ₁₁ to _{R 14} and the series circuit 15 of fixed resistors R ₂₁ to _{R 24} are inserted as they are between the power supply terminal +B and the ground point, so the variable resistor VR ₁₁ , each slider 12 of VR ₂₂ ,
The variable voltage range obtained with 16 becomes smaller.

Next, the OBC circuit is turned off, in other words, switch 1
When 1 is closed, the switching diode
D ₁ and D ₂ are conductive and switching transistors
TR ₁ and TR ₂ are also supplied with forward bias through the bias resistors R ₁₅ and R ₂₅ and become conductive, so the resistors R ₁₁ and
The terminals of R ₁₄ and resistors R ₂₁ and R ₂₄ are shorted,
The range of variable voltage obtained by each slider 12, 16 is increased. Therefore, the variable resistor VR ₁₁
The voltage obtained is used for brightness adjustment, and the variable resistor
When the voltage obtained with VR ₂₂ is used for hue adjustment,
When the OBC circuit is turned on, that is, the switch means 11 is opened, the viewer can view an image whose brightness and hue are set to approximately standard conditions. Note that although transistors may be used in place of the switching diodes D ₁ and D ₂ , using diodes as in the embodiment of the present invention can simplify the circuit configuration and is advantageous in terms of cost. Needless to say.

Figure 4, in which parts corresponding to Figure 3 are given the same figure numbers, shows the implementation of the variable voltage limiting circuit of the present invention.
Shows the overall configuration of the OBC circuit, including brightness adjustment,
Variable voltage limiting circuit 1 for hue adjustment and saturation adjustment
The configurations of terminals 7, 18, and 19 are substantially the same as the configuration and operation described in FIG. 3, although the number of fixed resistors connected between the power supply terminal +B and the ground point is different. The voltage obtained by the variable resistor VR ₁₁ is supplied to the DC clamp circuit, which adjusts the brightness by controlling the DC level of the brightness signal.
The voltage obtained at VR ₂₂ is applied to the hue adjustment circuit,
The voltage obtained by the variable resistor VR ₃₃ is also applied to the bandpass amplifier.

Furthermore, the variable voltage limiting circuit 20 for contrast adjustment does not have a configuration in which a switching diode is used to switch the fixed resistor on the hot side; This is because the contrast is adjusted to the minimum (the state where the contrast is least effective).

Note that the variable resistor 21 for image quality adjustment is not provided with a means (switching diode or transistor) for limiting the variable voltage range.
This is because the resistance value is set within a range that can be seen as an image even if the first adjustment position is at the maximum or minimum position.

(f) Effects of the invention According to the invention, the number of lead wires connecting the control volume unit and the OBC switch unit can be reduced as much as possible, so the work of connecting the lead wires can be simplified. In addition, since the switch used in the OBC circuit only needs to have one circuit and one contact, it is advantageous in terms of cost.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional variable voltage limiting circuit, Fig. 2 is a diagram showing a variable voltage limiting circuit of the present invention, and Fig. 3 is a diagram showing a variable voltage limiting circuit of the present invention.
The figure shows another embodiment of the invention, and FIG. 4 shows still another embodiment of the invention. 11...Switch, R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ ,
R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ ...Fixed resistance, VR ₁₁ , VR ₂₂
... Variable resistor, D ₁ , D ₂ ... Switching diode (semiconductor switch element), TR ₁ , TR ₂ ... Switching transistor (semiconductor switch element).

Claims (1)

[Scope of claim for utility model registration] A first fixed resistor between the power terminal +B and the ground point.
R ₁₁ , R ₂₁ and variable resistor VR ₁₁ , VR ₂₂ , VR ₃₃ and second
Series circuit 1 with fixed resistors R ₁₄ and R ₂₄ connected in this order
0, 15, and a transistor TR ₁ whose collector and emitter are connected to both ends of the second fixed resistors R ₁₄ and R ₂₄ ,
TR ₂ , the first fixed resistors R ₁₁ and R ₂₁ , and the variable resistor
Diodes D ₁ and D ₂ whose cathodes are connected to the connection points with VR ₁₁ and VR ₂₂ , and the power terminal + are connected to the bases of the transistors TR ₁ and TR ₂ and the anodes of the diodes D ₁ and D ₂ .
A switching voltage from B is applied simultaneously to the transistors TR ₁ , TR ₂ and the diodes D ₁ ,
With D ₂ on, the variable resistors VR ₁₁ , VR ₂₂ ,
A variable voltage limiting circuit comprising: switching means 11 for increasing the variable voltage range obtained from sliders 12 and 16 of VR ₃₃ ;