JPS63169883A - Brightness control circuit - Google Patents

Abstract

PURPOSE:To always obtain a constant brightness characteristic by connecting a rectifier circuit and a control transistor (TR) between a brightness adjustment means and a terminal of a horizontal output transformer to cancel completely the dispersion of the range in the brightness change attended with the dispersion in the cut-off characteristic of a cathode-ray tube. CONSTITUTION:Output pulses P1, P2 generated from secondary windings 6, 7 of a horizontal output transformer 5 are rectified by rectifier circuits 8, 9, and smoothed by smoothing capacitors 23, 24. A 2nd variable resistor 14 provided for external brightness adjustment is reduced to a minimum value, then a voltage V20 at the minimum brightness setting is varied by 1st variable resistor 13 and the collector-emitter voltage VCE of a 2nd control TR 16 is controlled and selected in an optimum value. With the 2nd variable resistor 13 selected at a maximum, the variable resistor 12 is varied to control the collector-emitter voltage VCE of a 1st control TR 15 is controlled to select the voltage V10 in an optimum value. Thus, the minimum to maximum brightness is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a brightness control circuit in television receivers and CRT display devices.

(b) Conventional technology The first variable resistor (1) for brightness adjustment provided inside the device and the second variable resistor (2) for brightness adjustment provided outside each device, (3) The first grid (G
l) A configuration for adjusting the DC voltage is used.

As the conventional example, Fig. 3 shows a serial system, and one example is the DArA DISPLAY CRT-40 published by Sanyo Electric.
/CRT-41 SCHEMAIl, CDIAGRAM
FIG. 4 shows the same circuit in a parallel system, in which a video output signal of negative polarity is applied to the cathode (K) of the cathode ray tube (3) through the terminal (4), and the cathode (K) of the cathode ray tube (3) is
3) is driven. In the figure, the DC potential (VK) of the cathode (K) is held constant.

In this case, when controlling the first grid voltage of the cathode ray tube (3), the brightness adjustment is performed by setting the second variable resistor (2) to the maximum position and then adjusting the first variable resistor (1) to the maximum brightness. Set. As a result, if the voltage v1 in Figure 3 is set, for example, the cathode ray tube (3) used in each device
Due to the variation in the cutoff voltage of the first
The adjustment position of the variable resistor (1) varies.

(C) Problems to be Solved by the Invention According to the conventional brightness control circuit, as mentioned above, due to variations in the cutoff voltage of the cathode ray tubes used in each device,
When the adjustment position of the first variable resistor (1) varies, the impedance between 0 and 0 in FIGS. 3 and 4 changes, and therefore the second variable resistor (2) is tightened. This had the disadvantage that images would disappear quickly and some images would not disappear.

(d) Means for solving the problem The present invention provides a horizontal circular quadrangle, first and second terminals connected to the horizontal circular quadrangle and deriving mutually different voltages, and a It comprises first and second rectifier circuits and first, second, and second control transistors connected between the terminal and the brightness adjustment means, respectively, and the output terminal of the brightness adjustment means is connected to a predetermined position of the cathode ray tube of the CR1 display device. It is connected to an electrode, and the maximum brightness and minimum brightness can be arbitrarily set by the brightness adjusting means.

(E) Function In the brightness control circuit of the present invention, the first and second rectifier circuits and the first and second rectifier circuits are connected between the first and second terminals of the horizontal circular quadrangle and the brightness adjustment means, respectively. After the voltages at the first and second terminals are set by the control transistor, the brightness adjustment means can adjust the brightness, thereby eliminating irregularities in the brightness change range due to variations in the power and off characteristics of the cathode ray tube. It is completely resolved and constant brightness characteristics are always obtained.

(F) Embodiment The present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the brightness control circuit of the present invention, and No. 21V is a block diagram showing the basic configuration of the circuit.

Next, in the drawings, elements that are the same as those in FIGS. 3 and 4 are given the same reference numerals, and (5) is a horizontal circular quadrangle having secondary windings (6) and (7); (
9) are the first and second rectifying and smoothing circuits, respectively; (10)
(11) are the first and second DC/DC conversion circuits, (
12) (13) are the first variable resistors for brightness adjustment provided inside the device, and (14) are the second variable resistors for brightness adjustment provided outside for the user to adjust the brightness. , (I
s) (16) are respectively predetermined voltages v1 and ■.

first and second control transistors, (17)
(18) is a six-wire resistor for applying a bias voltage to the base of each transistor, (19) (20),
(21), (22), (23), and (24) respectively indicate a series resistor, a rectifying diode, and a smoothing capacitor that constitute the rectifying circuit.

Next, to explain the operation of the present invention, after rectifying the output pulses P and P generated from the secondary windings (6) and (7) of the horizontal circular quadrangle (5) by the rectifier circuit (8) <9),
When smoothed by smoothing capacitors (23) and (24),
DC voltages are obtained, as shown in Figure 1, respectively v, , V!
appears and is applied to the collector of the first control transistor (15) and the collector of the second control transistor (16), and a resistor (17) and a variable resistor (12) are connected to each base.
1 through the resistor (18) and variable resistor (13). -C
Vb.

Vbz is added as a bias voltage.

In the above configuration, the variable resistors (12)' (13) are both for bias variable use and are of a semi-fixed type. Resistance (25
) is the spark stopper resistance for the cathode ray tube (3).

Now connect the second variable resistor (1) installed for external brightness adjustment.
4) is the electric current JhV* at the minimum brightness setting when stopped down to the minimum.
a is varied by the first variable resistor (13), and the collector-emitter voltage (VCI) of the second control transistor (16) is controlled to select an optimum value.

Next, when the second variable resistor (13) is at its maximum, that is, at the 1L
and at the top end in FIG. 2, the first variable resistor (12) is changed and the first control transistor (15)
The collector-emitter voltage (Vcm) of is controlled, and the value of voltage v1° is selected to be the optimum value.

In other words, vte*vb+−Vbe ””(1)
V* o −Vbz + Vbe”
''' (2) 0 table is off, vb□ is voltage V++Vt
The resistance division ratio (R1 + 1"l 1 )/r, !, where Vb t is the voltage v, .The resistance division ratio r, 1bar r, ,
+R@), and Vbx −(V+ + V*)(R+ + r, +)/
rt* ・−・−(3)Vbt−Virx+/
(rz*+Rz) -----.-(4) In the above equations (1) and (2), Vbe indicates the rising voltage between the base and emitter of each transistor.

Therefore, by equation (1>(2) and (3)(4), Vto-
(vx+Vz>(Rt+r++>/r+t Vbe”
...”(5) Vto-V*rt+/(r**+R*>+
From Vbe ”” (6) ■□. and Vts are determined. The first and second control transistors (15)
(16) serves as a DC/DC converter, and its base bias is connected to the first variable resistor (12) (13).
If set in , each of the above-mentioned resistance values r, □, r□2. r□
, r, by the resistance ratio including the voltage V,. and vffi,
is set to a predetermined value, and as described above, the brightness of the cathode ray tube (3) can be externally set to a desired value by the second variable resistor (14).

(G) Effects of the Invention According to the brightness control circuit of the present invention, variations in the cutoff voltage (voltage between the cathode and the grid when the raster disappears) of cathode ray tubes commonly used in equipment (usually 5
(around 0V), making it extremely difficult to control brightness.
By adjusting the external variable resistor, it is possible to change the brightness from the minimum to the maximum, and when you turn down the external brightness volume, which was previously raised, the image disappears quickly or sometimes it does not disappear. Defects can be removed.

[Brief explanation of the drawing]

The first (50) is a circuit diagram showing an embodiment of the brightness control circuit of the present invention, FIG. 2 is a block diagram of the same circuit, and FIGS. 3130 and 4 are conventional brightness control circuits. (3)...・Cathode ray tube, (5)...Horizontal quadrant, (6)(7)...Secondary winding, (8)(9)・
... Rectifier circuit, (12) ri13) ... First variable resistor, (14) ... Second variable resistor! Total, (15
)...first control transistor, (16)...second
control transistor.

Claims (1)

[Claims] 1. A horizontal output transformer, first and second terminals that are connected to the horizontal output transformer and derive mutually different voltages, and each connected between the first and second terminals and the brightness adjustment means. The output end of the brightness adjustment means is connected to a predetermined electrode of a cathode ray tube of a CRT display device, and the brightness adjustment means controls the maximum brightness and the minimum brightness. A brightness control circuit characterized in that brightness can be set arbitrarily.