JPS60134570A - Multi-tube type television receiver - Google Patents

Abstract

PURPOSE:To allow a picture tube to exhibit the lighting capability to the utmost while the safety of each CRT is secured by detecting each beam current from a cathode current of each CRT and providing an automatic luminance limit circuit based on the mean value and peak value of each detecting current. CONSTITUTION:When a video signal SV is fed to a terminal 4, the signal SV is fed to a signal processing circuit 5, from which red/green/blue signals are outputted. Then each chrominance signal is fed to a CRT1R or the like and a beam current IbR or the like is detected. When one of the currents IbR or the like reaches a limit beam current, any of transistors (TRs) 27R, 27G, 27B of a peak value ABL circuit 200 is turned on, a prescribed voltage VPABL is generated at a connecting point of each collector and this voltage is fed to a peak value ABL control terminal. Moreover, the current IbR flowing to the TR24 is integrated by a capacitor 25, from which an average current IbRA is obtained and the current is fed to an emitter of a TR36 via a resistor 35R from a terminal 34. This processing is similar to the green and blue CRT beam.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention detects a beam current by detecting the cathode current of a cathode ray tube, and the brightness level is limited based on this detected current. This invention relates to a type television receiver.

BACKGROUND TECHNOLOGY AND PROBLEMS Conventionally, ABL circuits (automatic brightness limiting circuits) have been proposed to: ■ protect cathode ray tubes due to heat generation, ■ prevent X-ray emission due to excessive beam current, and ■ prevent overload of high voltage generation circuits. ing. That is, the beam current of the cathode ray tube is limited by detecting the beam current and feeding back this detection signal negatively to the brightness adjustment circuit. This more advanced ABL circuit is similarly provided, for example, in a three-tube projector having cathode ray tubes for red, green, and blue.

By the way, ABL control includes an average value ABL that is performed based on the average value of the beam current and a peak value ABL that is performed based on the peak value of the beam current.

For example, in the above-mentioned three-tube glossier, the average value ABL is conventionally determined by the detection circuit (2) as shown in FIG.
Cathode ray tube (IR) for red, green and blue.

Detect the total high voltage current flowing through (1G) and (1B),
This was intended to provide a lot of control. In FIG. 1, numeral 1 is a high voltage, and (3R), (3G) and (3B) are drive circuits, respectively.

However, in this case, it is difficult to maximize the luminous ability of the cathode ray tube. For example, each cathode ray tube (IR)
Let us consider a case where a beam current of 1 mA L on average cannot be passed through (IG) and (1B), respectively. In this case, if the brightness level, that is, the beam current, is limited by a detection current of 1 mA, the current flowing to each cathode ray tube (IR), (IG), and (IB) for white, red, green, and blue screens. Since the average beam current is limited to the level shown in FIG. 2A, problems such as damage to the cathode ray tube do not occur. however,
In case of white screen, each cathode ray tube (IR), (IG)
The average beam current flowing through the cathode ray tubes (IR), (1B) and (1B) is significantly less than 1 mA, and the light emitting capabilities of the cathode ray tubes (IR), (IG) and (1B) are not fully utilized. On the other hand, if the brightness level, that is, the beam current, is limited by a detection current of 2.2 mA, for example, for white, red, green, and blue screens, the respective cathode ray tubes (IR), (IG), and ( Since the average beam current flowing through 1B) is limited to the level shown in Figure 2B, the brightness in the case of a white screen is 2.2 times higher, making it possible to fully utilize the multi-light capability.
Cathode ray tube (IR), (IG
) and (IB) have an average beam current of 2.2 mA.
i, causing problems such as damage to the multi-cathode ray tube. In this way, cathode ray tubes (IR), (IG) and (
1B) cannot maximize its luminous ability while ensuring safety.

In addition, in the three-tube projector described above, the peak value ABL is determined by each cathode ray tube (IR) as shown in FIG.
, detecting the peak values of the red, green and blue primary color signals R, G and B supplied to the cathodes of (IG) and (1B);
This was intended to provide a lot of control.

However, in this case, if the ABL setting value is constant,
When characteristics such as mutual conductance, cutoff, gamma, etc. of cathode ray tubes (IR), (IG), and (1B) vary, the beam current to be limited varies, causing a disadvantage that accurate control cannot be performed.

Purpose of the Invention In view of the above, the present invention provides an average value ABL e that can maximize the light emitting ability of each cathode ray tube while ensuring the safety of each cathode ray tube in a multi-tube television receiver.
In addition, it is possible to multiply the peak value ABL by an accurate peak value ABL.

Summary of the Invention In order to achieve the above object, the present invention detects the cathode current of each cathode ray tube to detect the beam current of each cathode ray tube.
ABL is applied based on both the average value and the peak value of each detected current.

Therefore, since the detection beam current of each cathode ray tube is looked at and multiplied by the average value ABL'i, it is possible to maximize the light emitting ability of each cathode ray tube while ensuring its safety. Furthermore, since the beam current detected by detecting the cathode current of each cathode ray tube is multiplied by the peak value ABL Th, an accurate peak value ABL can be multiplied without variations due to the characteristics of the cathode ray tubes.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. This example is an example in which the present invention is applied to a three-tube projector.

In the figure, (4) is a terminal to which the color video signal Sv is supplied, and the video signal Sv from now on is supplied to the signal processing circuit (5), and the output side is the red, green, and blue primary color signals R. , G and B are obtained. and signals R, G and B
are supplied to red, green and blue cathode ray tubes (IR), (IG) and (1B) via drive circuits, respectively.

In addition, the respective cathode ray tubes (IR), (IG) and (1
The respective beam currents are detected on the cathode side of B).

In addition, since the cathode ray tube (1(,), (IB) part is constructed in the same way as the cathode ray tube (1R) part (100),
It is omitted in FIG. 4.

The red primary color signal R is supplied via a terminal (6) to an npn transistor (7) and a pnp transistor (8) that constitute a drive circuit. A signal obtained at the connection point of each emitter is supplied to the cathode of the cathode ray tube (1R), thereby driving the cathode ray tube (1R).

In addition, the collector of the transistor (7) is a diode (9
) through the anode and cathode of positive DC voltage element B1 (
For example, +250 V) is supplied to the power supply terminal (1[)
connected to. In addition, the power supply terminal Q (e is connected to the collector of the npn transistor (2) via the emitter and collector of the pnp transistor α.Also, the pace of the transistor α is connected to the anode of the diode (9). In this case, the transistor αη and the diode (9) constitute a current mirror circuit, and the same current flows through the transistor 0■ and the diode (9).

In addition, the collector of the transistor (8) is the collector-emitter of the npn transistor (to), and the resistor 1llL4
t- to ground. Furthermore, the emitter of the transistor (2) is grounded via a resistor. Further, the pace of transistor (2) is connected to its collector to form a diode connection. Also, transistor (2) and a
The paces of the mangoes are connected to each other. In this case, transistors (2) and (2) constitute a current mirror circuit, and equal currents flow through the transistors.

In addition, the collector of the transistor (8) is connected to the capacitor CI
It is grounded through a mountain pass.

Further, the collector of the transistor (8) is connected to the npn type transistors a and α. The collector of the transistor α is connected to its pace, making it a diode connection. In this case, the transistors Ct'I) and (c) constitute a current mirror circuit, and the same current flows through the transistors a'I) and (14).

Further, the collector of the transistor α is connected via a resistor (G) to a power terminal member to which a positive DC voltage element B2 (for example, +12V) is supplied. In addition, the emitter of the transistor QI is connected to the pnp transistor ■ via the resistor Q■.
grounded through the emitter-collector of Also, the emitter of the transistor α is connected to the pnp via the resistor.
Connected to the emitter of a type transistor (c). The collector of this transistor (c) is connected to the pace to form a diode connection. Also, the pace of this transistor (c) is grounded via a capacitor (c). In this case, the transistors (A) and (C) constitute a current mirror circuit, and equal currents flow through the transistors (A) and (C).

In the configuration in item i, there is a parasitic capacitance (c) at the cathode of the cathode ray tube (1R);
Charging the child with electrical current. flows from the diode (9).

Here, since a current mirror circuit is constituted by the transistor aρ and the diode (9), the transistor α
A current Ic flows through ρ, and this current ■. is a transistor (
Flows into (b). Further, since a current mirror circuit is formed by the transistors (6) and (2), the current Ie is allowed to flow through the transistors (6) and (2). On the other hand, a current (IbR + Ic), which is the sum of the beam current Ib8 and the current Ic from the parasitic capacitance (c), flows into the transistor (8). And this current (IbR+Ic)
Of these, a current I0 flows through the transistor a field. Therefore, only the beam current IbR flows into the transistor CI.

Here, since a current mirror circuit is configured with the transistors II and II, the current bR flows into the transistor (11, and from this current R flows into the transistor). Also, here, into the transistor) and ( Since a current mirror circuit is configured in (c), R flows through the transistor (c) rather than the current.

In this way, when the transistor α is flowing, more R flows than the current, so the collector of this transistor α→ has vR=+B2
-IbRXR, , (R1, is the voltage of the resistor (11 (7) resistance value) is obtained. This voltage v8 is passed through the terminal (27R) to the pnp that constitutes the peak value ABL circuit (200).
A type transistor (28R) is supplied to the base. Cathode ray tube for green and blue (1G) obtained in the same manner
and (1B) from the beam current. and voltage corresponding to IbB.

and VB are supplied to the leads of pnp transistors (28G) and (28B) via terminals (27G) and (27B), respectively. These transistors (28R),
The collectors of (28G) and (28B) are connected to each other, and the connection point is grounded through a resistor (29) t-. In addition, these transistors (28R), (28
The emitters of G) and (28B) are each connected to the emitter of a pnp transistor (G), and their connection point is connected to the power supply terminal - via a resistor 0◇. Further, the collector of this transistor (G) is grounded. In addition, the power terminal - is grounded through the series circuit of resistors 0 and (a), and the voltage V obtained at the connection point of resistor 0 →
□ is supplied to the transistor pace as a bias voltage.

In this case, the voltage vlLlcF is set to 10B2-R4,X limit beam current.

In such a configuration, from the beam current IbR.

When any one of the transistors (27R), (27G), and (27B) is turned on, a predetermined voltage vPABL is generated at one connection point of each collector. And this voltage vP
The ABL is supplied to the peak amplification ABL control terminal (5P) of the signal processing circuit (5) and multiplied by the peak (,1ABL). In other words, the brightness level is limited and the beam current ■bRz I
l) G and B are limited so that they do not exceed the critical beam current.

In addition, as mentioned above, the current IbR flowing through the transistor (H't) is integrated by the capacitor (A) and made to be RA from the average current.
is supplied to the emitter of the pnp transistor (to) through the. Although not shown, the beam currents of the green and blue cathode ray tubes obtained in the same manner are used. and from the average current of B (A and IbBA are supplied to the emitter of transistor 0Q through terminals (34G) and (34B) and resistors (35G) and (35B), respectively. In this case, Resistors (35R), (35G) and (35B)
For example, the resistance values are the same. In addition, the transistor (C) is a transistor for setting IA, and is 0″t)
is a power supply terminal to which a positive DC voltage 1B3 (for example, +12V) is supplied. The voltage obtained at the emitter of this transistor (2) is applied via resistors (35R), (35G) and (35B) to the npn transistors (38R), (38G) which constitute the average value ABL circuit (300).
) and (38B) as a near bias voltage, and is also applied as a near bias voltage to the base of the npn transistor 0Q via the resistor 01.

Also, transistors (38R), (38G) and (
The emitters of 38B) are connected together, and the connection point is grounded via resistors Oη and Α). Further, the respective collectors are connected to each other, and the connection point is a diode 1.

It is connected to the power supply terminal - via the zero field anode and cathode. Also, the emitter of the transistor is connected to a resistor (41
> and O→, and its collector is connected to the power supply terminal). Further, the anode of the diode θ is connected to a pnp transistor. The collector of this transistor is grounded through a resistor, and its emitter is connected to a power supply terminal. Also,
The collector of this transistor is connected to the base of the npn transistor (2). The emitter of this transistor (c) is grounded via a resistor 19, and its collector is connected to a power supply terminal (e) via a resistor. Further, the transistor 〇PACE is connected to a power supply terminal - to which a positive DC voltage 1B4 (for example, +135V) is supplied via a resistor -. In this case, the resistance value of resistor - R49
is, when any one of RA, IboA, and aA becomes the set current, the voltage drop factor maxxR4, due to the current ■max, which will be described later, flowing through this resistor θ field is 10B.
4-ImaXxR49=10B2 vllll+ ・(+)
It is set to a value that satisfies all conditions and turns on the transistor. ■□ is the voltage between the transistor's pace and emitter.

In addition, normally the power supply terminal is connected to the resistor 61 and the diode.
Current flows to the power supply terminal - through the transistor (/4
41 is placed in the off state.

In such a configuration, resistors (35R), (3
5G) and (35B), respectively bRAxR35
From R2. A×R55G and “bBa xR55B(R
55B+ R55o and 35B are husband resistors (35R
), (35G) and (35B). )
is generated, and currents IbRA and ■b are generated in transistors (38R), (38G), and (38B), respectively. A and I
The current I,,I corresponding to bBA. and twists are about to flow. For example, when the husband's resistance value is as shown in the figure,
Electrician 8゜■. and , respectively, are the currents IbRA y b
It becomes equal to GA and IbBA. Now, the transistor (3
8R).

Emitter voltage of transistor 00 2 (V) '! When referenced to r, the emitter of the transistor (38R) has 1.5 [kn) X Ia (mA) +2 (V:
] is generated, and on the other hand, this transistor (38R
) is 2[v]+V,, (V) + 1.
A voltage of 5 (kΩ) x IbRA[mA] is generated, and t
, 5 (kn:] ] Electric I, (mA) +2 (V)
+V,, [V]== 2 (V) +VBE(V)
+ 1.5 (kn:] ] Electric I bRA (mA)
Tonashi, from ``a = i+A... (2).

In this way, the transistors (38R), (38G) and (38B) have currents I, I, I, which correspond to GA and BA more than RA z , respectively. and lB try to flow, but transistors (38R), (38G
) and (38B), RA from the current.

■b. Only the transistor corresponding to the largest one among A and BA is turned on. Therefore, the current IR2I,
And the largest manufacturing ma of IB! only flows.

This current ImaX is supplied through the power supply terminal - side resistor ◇I.

Then, when either RA, ■b (!□ or IbBA is the set current from the current, the current "ma" is the above (1)
) satisfies the equation, so the transistor (good) is turned on at this time. Therefore, the transistor) is not on,
A predetermined voltage vAABL is generated at its emitter. This voltage AABL is then supplied to the average value ABL control terminal (5A) of the signal processing circuit (5) and multiplied by the average value ABL. That is, the brightness level is limited and the beam current "b"
From nv, the average IbR of a and bn is limited so that baA and Ibi+A do not exceed set values.

Thus, according to the present example, each cathode ray tube (IR).

By detecting the cathode currents of (1G) and (IB), the respective beam currents IbR1IbG and lbB are detected, and the average value ABL is multiplied based on the average IbRA, IbQA, ■bBA, so it is completely safe. It is possible to maximize the light emitting capacity of each cathode ray tube while ensuring the same. For example, if the brightness level, that is, the total average beam current is limited by a detection current of 1 mA, the current flowing through each cathode ray tube will be limited to the level shown in Figure 5 for white, red, green, and blue screens. Ru.

Therefore, the emission brightness is 2.2 times higher than that of the example shown in FIG. 1 when a white image is produced, for example, without causing noise such as damage to the cathode ray tube.

Also, by detecting the cathode current, the beam current
Since t + "bat xbBk is detected and the peak value ABL'i is multiplied based on this, the accurate peak value ABL't is multiplied without variation due to the characteristics of the cathode ray tube (IR), (IG), (IB). be able to.

Note that the element values in the above-mentioned embodiment (shown in FIG. 4) are merely examples, and the present invention is not limited thereto.

Further, although the above-mentioned embodiment is an example of a three-tube type glossier, the present invention can be similarly applied to other multi-tube type television receivers.

Effects of the Invention As is clear from the embodiments described above, according to the present invention, the average value ABL is calculated by looking at the detection beam current of each cathode ray tube.
This makes it possible to ensure the safety of each cathode ray tube while maximizing its luminous ability. In addition, since the beam current detected by detecting the cathode current of each cathode ray tube is multiplied by the peak value ABL i, the peak value ABL' is accurate without variations due to the characteristics of the cathode ray tube.
It can be multiplied by i.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining the conventional average value ABL, respectively, FIG. 3 is a diagram for explaining the conventional peak value ABL, and FIG. 4 is a diagram showing an embodiment of the connection of the present invention. FIG. 5 is a diagram for illustration purposes only. (IR) (IG) and (1B) are cathode ray tubes, (5
) is a signal processing circuit, (200) is a peak value ABL circuit,
(300) is the average value ABI, circuit. Figure 1 Figure 2 Figure 13 Figure 5

Claims (1)

[Claims] A multi-tube television receiver characterized in that the beam current is detected by detecting the cathode current of a cathode ray tube, and the brightness level is controlled based on both the peak value and average value of this detected current. .