JPH01265791A - Drive circuit for cathode ray tube - Google Patents

Abstract

PURPOSE:To eliminate need for the adjustment of the cathode bias by connecting a constant current circuit to a cathode electrode of the cathode ray tube, supplying a bias voltage with a video signal superimposed thereupon to a 1st grid electrode and supplying a fixed prescribed voltage to a 2nd grid electrode. CONSTITUTION:The cathode ray tube 1 is provided with a cathode electrode K, the 1st grid electrode G1 and the 2nd grid electrode G2. Then the constant current circuit 20 is connected to the cathode electrode K and the bias voltage with a video signal superimposed thereupon is supplied to the 1st grid electrode G1, and a fixed prescribed voltage is supplied to the 2nd grid electrode G2. In case of deciding the 2nd grid voltage Ec2 and a beam current 1K, i.e., the current of the constant current circuit 20, the cathode voltage EK is decided and since the cathode voltage EK is varied over a wide range, the 2nd grid voltage Ec2 is fixed. The constant voltage circuit 20 is provided to the cathode electrode K to decide the cathode voltage EK and to fix the 2nd grid voltage Ec2, the no adjustment of the DC operating point of the cathode ray tube 1 is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to a cathode ray tube drive circuit suitable for use, for example, in setting the DC operating point of a cathode ray tube for a black and white television.

[Summary of the invention]

This invention provides a cathode ray tube having at least a cathode electrode, a first crit electrode, and a second grid electrode, in which a constant current circuit is connected to the cathode electrode, and a bias voltage of a video signal is applied to the first grid electrode. By supplying a fixed predetermined voltage to the second grid electrode, 111 (
This eliminates the need for adjustment and selection of the cathode ray section, thereby reducing the number of parts and improving design efficiency.

[Conventional technology]

Conventionally, for example, to drive cathode ray sensors (CHT) for black and white TV and video! ! Something like the one shown in Figure 83 is proposed.

CR'I'' (11 has a cathode salt 44, a first grid electrode Gt, a second grid electrode G2, a third grid electrode G3 and an anode-1 electrode to which high voltage is applied, and a cathode electrode K For the flyback transformer (i=' B
T) A bias voltage is supplied through the variable resistor (4), which is a semi-rigid Jl resistor, and resistors (5) and (6). (4
) is changed by 1 to adjust the bias voltage and determine the DC operating point (brightness).

In addition, the anode side of the tie auto (7) is connected to a predetermined winding (not shown) of the I-IJ Tf21, and the cup-1 side is grounded via the resistors (8) to (11).
iJ transformer resistor (12), resistor (13>, (11
).・In other words, connect the resistor (8+,
(91, (10) series circuit and IM variable resistor 12)
, (13) are connected in parallel. Then, taps '1'1 and 1'2, which are bridged with solder, are installed between the resistors (8) and (9) and between (9) and (10), respectively. The output side of '1'7 is the second
Clino 1 - 1 connected to electrode G), tap ゛]゛1 and '1
The voltage of the second grid 1 is changed by switching the voltage 2. In addition, the iiJ variable resistor (J2) is
Each time the third grid voltage is changed by changing J, focus A-cus Ild adjustment is performed.

Further, (4) is an I-run source constituting the video amplifier, its -1- terminal is connected to the input terminal (15), its emitter is grounded, and its collector is connected to the resistor (
It is connected to the positive power supply terminal +VCC via the capacitor (17) and the U resistor (18), and is connected to the first crit terminal 88C,+ via the capacitor (17) and the resistor (18).
? ) and the resistor (ill) are connected to the first grid electrode G.
It is grounded via a high-resistance resistor (19) called IMΩ so as not to impair the input impedance of 1.

In the case of simple black-and-white television broadcasting where there is not much need for internal direct current, the first grid electrode G1 is driven by a directly heated cathode as described above, and the first grid electrode G1 is driven by a directly heated cathode as described above. is used with a fixed bias.

In such a case, the beam current of CRi'' (11 is the first
Voltage 1 on the cathode electrode relative to the potential on the grid electrode G1:! :K(V) and voltage EC2 of second grid electrode G2
(V) (However, other parameters such as high pressure are assumed to be constant).

14: When the potential of the upper first Gliso I/electrode G1 is set to the ground potential, the cathode voltage EK and the second Gliso! voltage E at which the current of CR'l''+11 is cut off are 14.
The relationship of c2 is shown in FIG. 4, and the characteristics vary over a fairly wide range due to manufacturing variations in the minimum distance between poles.

For example, if G is a straight line a, then 1iK is 150 (v), Hc2=2
At 00 (v), the force yl-off, and some straight lines are already broken, so E becomes -50 (v), IΣC2' = 600
In (v), the cuff 1-off occurs.

In reality, in order to make both sides emit light, a beam current of several tens (to μ) is passed through the CRT (11), but this can be done by increasing the second grid voltage EC2 or by lowering the cathode voltage +=g by one. It is necessary to determine the DC operating points Q and Q' shown on the lines c and d, respectively.The curve C9d is also a parameter for the current 1'.

When the second grid voltage EC2 is kept constant, the beam current IK
The voltage drop amount ΔI of the cathode voltage EK required for the current flow J: x (v) is expressed as the drive voltage Ed (v) (corresponding to Figure 11'Q, P'Q'), and the cathode voltage IE
When K is fixed and a signal is applied to the first grid electrode, the image amplitude level (V'p-p) and beam current amount are 9
．． By the way, in the case of the conventional circuit with the configuration shown in Fig. 3, the operating point of C R T (L) is In order to determine this, since the characteristics of C R T fil vary as mentioned above (4), the sink distribution is determined in advance on the +!M manufacturing line of C R i'' (1) according to the characteristics as shown in Figure 4. I'm going to have a good time (!!L, )C
Tap i” on the board according to R 'I' flll
+, 'l';! and the rJI transformer (4) as a fixed resistor were switched each time.This is mainly due to the following three reasons.

■) The voltage range of the second grid voltage IEC2 is approximately 2oO ~
60 (L V is large, and if the Ka-I and voltage EK are fixed uniformly, a special 'd1J compensation product is required for the normally used semi-fixed resistor, and a general product is at most about 2 oo ■), and in terms of cost. The shape is also unsatisfactory.

2) In the mass production level, the value of the output voltage of FI"r for the second crit voltage EC2 is approximately 5% uneven, and the length of the high voltage semi-fixed resistor is several MΩ (high abrasive resistance), so for general products it is 1.
There is a 20% variation, and a design with sufficient margin is required for the FjJ variation range for adjustment.

3) Second Griso 1: If only voltage EC2 is fixed,
A bulb (C) that requires a cathode voltage Ex of 150v? 'F
) exists, and in order to adjust the cathode voltage E, 1-
'13 It is necessary to add a separate winding to T to obtain a voltage source,
1-"B T's "Toss"i' Sozu also requires electric power in terms of performance, and a portable type that uses dry batteries etc. is not satisfactory.

As shown above, in the case of conventional equipment, there are problems with parts,
Two, there was the power issue, and the third was the design issue.

Also, the operating point of CR'V (11 is the first Grino (・Den 8!
The potential series of G1 is determined by the potential of the second grid electrode G2 and the potential of the cathode electrode. - electrode 1 (and first grid electrode G1
As the distance between the capacitors (17 and 17 ) is also required.

This invention was made in consideration of this point, and was made using a CRT (1
1 (7,) Ra7 division, F B 'rf21 (D
The object of the present invention is to provide a cathode ray tube drive circuit that does not require a power source for each of the electrodes and the cathode electrode, and can drive the first grid electrode G1 by direct current connection.

[Means for Solving the Problems j] A cathode ray tube drive circuit according to the present invention includes a cathode ray tube (1) having at least a first clear 1 electrode G1 and a second grid electrode G2 on the cathode electrode, A constant current circuit (20) is connected to supply a bias voltage on which a video signal is superimposed to the first grid electrode G1, and a bias voltage on which a video signal is superimposed is supplied to the first grid electrode G1.
It is configured to supply a fixed predetermined electric ratio to the crit electrode G2.

[Operation] A constant current is applied to the electrode K of the cathode ray tube (1).
0) and apply a fixed predetermined voltage to the second grid electrode C2. From the characteristics shown in Fig. 4, the second crisscross voltage EC2
If we determine the current of the constant current circuit (2o) and the beam current lK, then the cathode current 1-. K is determined automatically.

Since this cathode voltage Ex can be varied over a wide range, the second grid voltage EC2 can be fixed. In this way, the constant voltage circuit (20) is provided for the cathode electrode K to determine the cathode voltage Ex. Since the second grid voltage EC2 is also fixed, it is possible to eliminate the need to adjust the DC operating point of the cathode ray tube (1).

[Embodiment] Hereinafter, an embodiment of the present invention will be described in detail based on FIGS. 1 and 2.

FIG. 1 shows the circuit configuration of this embodiment, which corresponds to FIG. 3 (the IP portion is given the same reference numeral, and detailed explanation thereof will be omitted).

In this embodiment, a constant current circuit (20) is connected to the cathode electrode K. At this time, the cathode voltage EK is automatically determined by determining the second Gliso 1 voltage EC2 and the beam current 1y (equal to the current flowing through the constant current circuit (20)) from the characteristics shown in FIG. In other words, a separate power supply would normally have to be provided for CR'V (1+), but in this example, the cathode The voltage Ex is determined by the constant current circuit (20) on the axis (1) shown in FIG.
Since the current flows to the ground through the capacitors C1 and C2 for preventing T-heater ringing, the constant current circuit (20) only functions to determine the DC operating point.

Further, in this embodiment, the output side of the diode 7) is connected to the second grid electrode G2, and the second grid voltage EC2 is fixed. In this case, the cathode voltage E can be changed over a wide range and can therefore be fixed.

There is no problem even if this second grid voltage EC2 has a variation of about 10%.

Focus adjustment is done using an i5J transformer (12) connected between the diode (7) and ground via a resistor (13').
This can be done by varying the voltage of the third grid electrode G3.

Further, in this embodiment, the first grid electrode G1 is connected to a resistor (1
8) Connect directly to the collector of the transistor (4) via (rJJ deleted as necessary). In the case of Fig. 3, the cathode bias is substantially fixed by the variable resistor (/I), which is a semi-fixed resistance, so the voltage of via 2 cannot follow changes in the input video signal. Since it is impossible to suppress the change in brightness over time, a transistor ("
Although it was necessary to insert a capacitor (17) between the collector of 4) and the first grid electrode G1 and ground it with a high-resistance resistor (19), in this example, the constant current circuit (2)
0) The negative cathode bias follows the manually input video signal with automatic bias, and the change in brightness over time is substantially suppressed, so the capacitor (I7) and resistor (19)
This eliminates the need for direct current connection, making it possible to connect directly to direct current. In the case of this DC coupling, since the potential of the cap-to-lid average current (approximately 1/2 V cc) of the video amplifier and this transistor (14) is applied to the first grid electrode G+, the operating point may vary slightly depending on the signal. , there is no practical problem.

FIG. 2 shows an example of a constant current circuit (20).
It has a transistor (21) and an operational amplifier (22) as a voltage core, and the collector of the transistor (21) is connected to the power supply terminal +V C through a resistor (23).
C, its base is connected to the output side of the operational amplifier (22), its emitter is grounded through the resistor (24) and connected to the inverting input terminal of the operational amplifier (22), and the operational amplifier The non-inverting input terminal of (22) has a reference voltage of 111F! (25) is connected.

The operational amplifier (22) connects the transistor (
21). The reference voltage of the reference voltage source (25) is set to V
ref, and the value of the resistor (24) is R1, the current IE flowing through the emitter of the transistor (21) is It = V
It is represented by ref/'R1.

The resistor (23) is inserted to prevent the collector potential of the transistor (21) from rising too much and to prevent the transistor (14) from being destroyed by discharge within the tube, and of course also increases a predetermined voltage peak. The breakdown voltage of the transistor (14) is V
CEO + vcl! The resistor (24) prevents it from being destroyed even in the oven.

■1 In this way, in this example, the cathode bias is automated,
Since the second grid voltage is fixed, it is not necessary to rank the cathode ray tubes, and only need to manage the range.

Also, there is no need for a margin for the flybank transformer, so some variation is fine. Further, a power source for the cathode voltage EK is not required, and a constant current circuit is sufficient.

Furthermore, since changes in brightness over time are suppressed, the first grid electrode can be driven directly with direct current, and the number of parts can be reduced.

〔Effect of the invention〕

As described above, according to the present invention, a constant current circuit is connected to the cathode electrode of the cathode ray tube, a bias voltage on which a video signal is superimposed is supplied to the first grid electrode, and a fixed predetermined voltage is supplied to the second grid electrode. This eliminates the need for adjusting cathode bias and selecting CRTs, allowing design margins such as de-BT, reducing the overall number of parts, lowering costs, and ensuring long-term reliability. can ensure sex. In addition, since the change in u)j noise over time is suppressed, the direct current connection to the first grid electrode can be made 61 times, which also reduces the number of parts and reduces costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a circuit configuration diagram of essential parts of the invention, FIG. 3 is a circuit configuration diagram showing an example of a conventional circuit, and FIG. 4 is a cathode voltage - It is a figure which shows the 2nd grid voltage characteristic. (1) is a cathode ray tube, (2) is a flyback I rank, (7) is a diode, (14) is a transistor, (2o
) is a constant current circuit.

Claims (1)

[Claims] In a cathode ray tube having at least a cathode electrode, a first grid electrode, and a second grid electrode, a constant current circuit is connected to the cathode electrode, and a bias voltage on which a video signal is superimposed is applied to the first grid electrode. A drive circuit for a cathode ray tube, characterized in that: a fixed predetermined voltage is supplied to the second grid electrode.