JPH0112418Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a control voltage switching circuit used in various electrical equipment such as television receivers, and in particular to a control voltage switching circuit that switches the variable range of the control voltage into two stages, large and small. Regarding this kind of circuit.

(b) Prior art For example, in a television receiver, viewers can adjust the screen brightness, contrast, color saturation, etc. according to their preferences.
The hue and the like can be manually adjusted, and each adjustment is performed by changing each DC control voltage applied to the video and chroma signal processing circuits using a variable resistor or the like. However, each adjustment range is set to be quite large to accommodate the preferences of various viewers, so it is very difficult for inexperienced people to make adjustments. Therefore, for such people, it is desirable to make sure that the image quality does not deviate too much from the proper state even when each variable resistor for adjustment is operated.

From this point of view, recent television receivers are equipped with a control voltage switching circuit for switching the variable range of each control voltage mentioned above into two stages, large and small. A conventional example of this circuit is configured as shown in Figure 1. ing. That is,
The circuit in the figure has brightness, contrast, color saturation,
4-circuit 3-contact adjustment range switching switch for 4 variable resistors VRa to VRd for each hue adjustment
A SW is provided, and each contact of this switch and each of the variable resistors mentioned above are connected through multiple resistors, and the state shown in the figure is set to a large variable range of each control voltage taken out to the output terminals Ta to Td. This is a case where the variable range is small when the switch SW is switched in the opposite direction as shown.

By the way, in the case of such a conventional circuit, 4 circuits 3
Since a switch with interlocking contacts is required, this alone increases the cost considerably, and if a so-called push type switch is used as the switch SW for the convenience of the viewer, the cost will increase further for the following reasons. Moreover, there was a drawback that workability during assembly of the receiver was poor. In other words, since multi-circuit push-type switches do not have terminal pins for each contact protruding in a direction parallel to the switch's operating stroke, this switch SW was installed as shown in Figure 2. Printed board PB
must be placed perpendicular to the receiver's control panel CP. However, printed board PB
When installed in this way, conversely, the variable resistors for each adjustment (VR in Figure 2), whether rotary or sliding, can be directly installed on the printed board PB. Since it cannot be installed, it must be installed on the operation panel CP side as shown in the same figure.
Moreover, each variable resistor must be connected to the circuit on the printed board using a plurality of lead wires LW.

(c) Purpose of the invention The present invention has been made with the above points in mind, and aims to provide a control voltage switching circuit that has the same functions as conventional circuits, is inexpensive, and has good workability during assembly. It is something to do.

(d) Structure of the invention The control voltage switching circuit of the invention changes the DC voltage applied to each of the plurality of variable resistors for each adjustment to 1.
By switching using a circuit switch, multiple switching diodes, and one switching transistor, it is possible to switch the variable range of each control voltage taken out from each of the variable resistors into two levels, large and small. be.

(E) Embodiment FIG. 3 shows the circuit configuration of an embodiment of the control voltage switching circuit according to the present invention, where VRa to VRd represent the aforementioned brightness, contrast, color saturation, and
Variable resistors for adjusting hue, Ta to Td are output terminals for taking out control voltage, R1a to R1d are first resistors, R2a to R2d are second resistors, R3a
~R3d is each third resistor, D1a~D1d are the first
, D2a to D2d are second diodes, SW is a push-type adjustment range changeover switch with 1 circuit and 2 contacts, TR is a switching transistor, and R0 is its base current limiting resistor.

In this embodiment, when the switch SW is currently closed as shown in the figure, the switching transistor TR is turned on with a DC voltage (+B) applied to its base, and therefore, All of the second diodes D2a to D2d are also turned on.
Further, a series circuit including third resistors R3a to R3d and first diodes D1a to D1d is connected in parallel to each of the first resistors R1a to R1d. Therefore, each variable resistor
A relatively large voltage will be applied across VRa to VRd, and therefore output terminals Ta to Td
The control potential obtained for each of them varies greatly depending on the adjustment of each variable resistor. That is, this state is a state in which the variable range of each control voltage is set to a large value.

Next, when the switch SW is opened, the switching transistor TR is turned off, and all of the second diodes D2a to D2d are also turned off.
Moreover, the above-mentioned series circuit consisting of each of the third resistors R3a to R3d and the first diodes D1a to D1d is also separated from each of the first resistors R1a to R1d. Therefore, in this state, the voltage applied across each of the variable resistors VRa to VRd is smaller than in the above case. Therefore, the output terminal Ta
This means that the variable range of each control voltage of ~Td is set to a small value.

Note that the first diodes D1a to D1d and the second diodes D2a to D2d have a separating function to prevent each of the control voltages from influencing each other.

FIG. 4 shows a state in which a push type switch SW is used for the switch SW shown in FIG. 3, and a printed board to which this switch is attached is placed inside the receiver. That is, as shown in the figure, in the push type switch SW with 1 circuit and 2 contacts, each terminal pin P1, P2 is provided in the operating stroke (in the direction of the arrow in the figure), so this switch SW and the variable resistor VR ( Third
(corresponding to each of VRa to VRd in the figure) can be directly mounted on the same side of the printed board PB, and this printed board PB can be used as the receiver's operation panel.
This means that it can be placed parallel to the CP.

(f) Effects of the invention As described above, according to the control voltage switching circuit of the invention, a changeover switch requires only one circuit and two contacts, so it can be realized at low cost, and the operating stroke of this switch is very low. Since a push-type switch with terminal pins in both directions can be used, this switch and each variable resistor for adjustment can be mounted directly on the same printed board, improving workability when assembling it into equipment. This will lead to further cost reductions.

[Brief explanation of the drawing]

Figure 1 shows a conventional control voltage switching circuit;
The figure is a simplified side sectional view showing the arrangement of a printed board incorporating this circuit. FIG. 3 shows an embodiment of the control voltage switching circuit of the present invention, and FIG. 4 is a simplified side sectional view showing the layout of the printed circuit board in this case. SW……Adjustment range switching switch, VRa to VRd
...Variable resistor, R1a to R1d...First resistor, R
2a to R2d... second resistor, R3a to R3d...
Third resistor, D1a to D1d...first diode,
D2a to D2d...second diode, TR...switching transistor.

Claims (1)

[Scope of utility model registration request] A plurality of circuits in which a first resistor, a variable resistor, and a second resistor are connected in series in this order are connected in parallel so that the first resistor is on the DC power supply line side and the second resistor is on the reference potential point side. The middle points of the connections between the first resistor and the variable resistor of each set are commonly connected to one terminal of a switch for switching the adjustment range via the first diode, and the other terminal of this switch is connected to the DC In addition to connecting to the power supply line, the midpoints of the connections between the variable resistors and the second resistors of each set are commonly connected to the input electrodes of the switching transistors via second diodes, and the output electrodes are connected to the reference potential point. A control voltage switching circuit, wherein a control electrode of the connected transistor is connected to the one terminal of the switch, and each control voltage is taken out from the sliding terminal of each set of variable resistors.