JPS6042545Y2 - Abnormal high pressure detection circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an abnormal high voltage detection circuit used in television receivers and the like.

In the cathode ray tube of a television receiver, X-rays are emitted when an abnormally high voltage is applied to the anode of the cathode ray tube, so the amount of radiation must be kept within safety standards.

For this reason, conventionally, there is a system in which the high voltage output of the flyback transformer is detected and when this output exceeds a certain level, the oscillation operation of the horizontal oscillation circuit is stopped to suppress the abnormal high voltage.

In addition, it is thought that a device that detects the relationship between high voltage and beam current, that is, detects the power applied to the cathode ray tube, and prevents X-ray radiation, is designed to prevent X-ray radiation by detecting the relationship between high voltage and beam current. Since the detection circuit to suppress the ABL circuit (automatic brightness limit circuit) and the beam current detection for the abnormal high voltage prevention circuit are integrated, the characteristics of the detection circuit differ depending on when the ABL circuit is on and off. The problem is that the operating point of the abnormal high voltage prevention circuit is different.

This idea was made in view of the above circumstances, and AB
It is an object of the present invention to provide an accurate abnormal high voltage detection circuit that has stable beam current detection characteristics without being affected by the on/off operation of the L circuit.

Embodiments of this invention will be described in detail below with reference to FIGS. 1 to 3.

That is, in FIG. 1, 11 is a video circuit to which a video signal is applied to its input terminal, and a brightness adjustment circuit 12 is provided.

Further, an ABL circuit 16 is connected to the video circuit 11, so that the DC reference voltage can be automatically controlled.

A resistor 1 is connected to the ABL circuit 14 from the power supply terminal 15.
A predetermined voltage is applied via 6.

A beam current detection circuit 17 is connected to the ABL circuit 14.

This beam current detection circuit 17 detects the beam current of the picture tube 13 to which the output of the video circuit 11 is applied, and generates a control signal when the beam current exceeds a specified value. It is connected to circuit 18.

This X-ray prevention circuit 18 includes the beam current detection circuit 17.
The abnormal high pressure applied to the picture tube 13 can be suppressed by, for example, stopping the oscillation operation of a horizontal oscillation circuit (not shown) using a control signal from the picture tube 13 .

Further, the beam current detection circuit 17 is connected to a secondary winding (for high voltage generation) of a flyback transformer 19, and forms part of a beam current path.

Therefore, the output terminal of the secondary winding of the flyback transformer 19 is connected to the anode of the picture tube 13 via a rectifier.

Note that the above circuit configuration may be used in common with the high voltage detection circuit 20.

That is, the flyback transformer 19 is provided with a tertiary winding N, 3 for picking up abnormal high voltage, the output of this winding is obtained as a control signal from the high voltage detection circuit 20, and the
A means for controlling the line prevention circuit 18 may be added.

One embodiment of this invention is made as described above, and the beam current path includes the power supply terminal 15, the resistor 16, the ABL circuit 14
, beam current detection circuit 17, flyback transformer 19
The secondary winding of the image tube 13 is formed by a thread path called the picture tube 13.

By the way, the ABL circuit 14 and the beam current detection circuit 1
The specific structure of 7 is shown in FIG.

That is, the connection terminal 21 of the video circuit 11 is connected to the resistor 22.
, a first diode 23, and a second diode 24 connected in series.

At the connection point of the first and second diodes 23 and 24,
The power supply terminal 15 is connected via a resistor 16.

Further, the connection points of the diodes 23 and 24 are grounded via a capacitor 25 for bypassing the alternating current, and are also connected via a resistor 26 to a flyback transformer connection terminal 27.

A series circuit of a plurality of diodes D1 to Dn and a resistor 28 connected in series to the series circuit are connected in parallel between both terminals of the resistor 26.

Further, the flyback transformer connection terminal 27 is connected to the resistor 2.
It is connected to the flyback transformer via 9 and grounded via a series circuit of resistors 30 and 31.

The connection point of this resistor 30°31 is the X-ray prevention circuit 18.
The terminal 32 is connected to the terminal 32 to the terminal 32.

Next, the operation of the above devised circuit will be explained.

First, the voltage at point A shown in FIG. 2 has the characteristics shown in FIG. 3 a.

That is, when the ABL circuit is in the off state (the diode 24 as a constant voltage element is conductive), the potential set by the diode 24 (approximately 0.6 V in the illustrated example) is maintained.

Next, when the beam current increases and the relationship becomes BRIIH<VD, the ABL circuit becomes on-state (the diode 24 as a constant voltage element is non-conductive).

In addition, B is the voltage applied to the power supply terminal 15, and R□ is the resistance 16.
The value of IH is the beam current flowing through this point A.

When the ABL circuit is turned on, the potential at point A drops in proportion to the beam current with a slope of 10B-RIIH.

Next, considering the potential at point B shown in Figure 2, the potential at this point is VD when the ABL circuit is off, as shown in Figure 3.
The curve of R21)1 becomes ○.

However ■.

;Terminal voltage R2 of diode 24;Value of resistor 26 When the ABL circuit is turned on next, the diode 24 is in the off state, and the diodes (D□ to Dn) are turned on.

Then, the potential at point B shown in the figure changes as shown by curve 3 in FIG.

In other words, it is connected linearly to the curve ◯.

The above means that whether the ABL circuit is on or off, the rate of change in partial pressure (detection sensitivity) of resistor 30.31 is
means no change.

The ability to maintain constant sensitivity in this way is a result of providing the diodes D1 to Dn.

The reason for this is explained below. First, assuming that there is no flow path for the diodes D□ to Dn, when the ABL circuit operates, the potential at point B becomes B-RlIH-R2I.

However, R2 is the value of resistor 26. Therefore, the slope of ll-1 is -(R1+R2), so the slope of the curve is large,
It looks like the curve ○ or the curve @ in Figure 3.

For the circuit that detects the voltage at point B and obtains the control signal for X-ray prevention, this means that the sensitivity has changed between when the ABL circuit is on and when the ABL circuit is off, so it is necessary to obtain accurate detection. is not desirable.

However, according to this idea, by providing a diode (Di to Dn) that acts as a constant voltage element, the inclination angle when moving from the curve ○ to the next curve can be adjusted by adding a constant voltage to this diode. It is possible.

Further, in the sense of fine adjustment of the tilt angle, it is advantageous to use a variable resistor as the resistor 28, since the detection sensitivity of changes in beam current can be adjusted, and the X-ray protection can be readjusted in accordance with legal standards.

However, in order not to damage the ABL characteristics, (R3 + R4)
> R2 is the condition.

(R2: value of resistor 30, R1: value of resistor 31) Furthermore, at the time of design, as a condition that the detection voltage has a certain relationship with the beam current (value of resistor 28 R3 = 0) VD "2 'H'' B n Vo R11H, so it is preferable to design as R1-R2 (1+n) VD = B.

Note that when the number of diodes increases, a Zener diode may be connected in series with one diode.

If the detection sensitivity is stable as described above, the horizontal oscillation stop or horizontal output stage stop signal can be stably derived from the output terminal 32.

As explained above, this invention maintains the beam current detection sensitivity constant without being affected by the on/off operation of the ABL circuit, and accurately suppresses abnormal high voltage operation. It is possible to provide an abnormal high voltage prevention circuit with stable detection sensitivity.

[Brief explanation of the drawing]

Figure 1 is a block configuration diagram showing an embodiment of this invention, Figure 2 is a circuit diagram showing the main parts of this invention, Figure 3a is a voltage characteristic diagram at point A of the circuit in Figure 2, This figure is a voltage characteristic diagram shown to explain the voltage characteristic at point B of the circuit of FIG. 2. 11... Video circuit, 12... Brightness adjustment circuit, 13... Picture tube, 14... A
BL circuit, 16...Resistor, 17...Beam current detection circuit, 18...X-ray prevention circuit, 1
9...Flyback transformer, 24...
・Diode, D□~Dn・・・Diode, 2
6...Resistance, 30, 31...Resistance.

Claims (2)

[Scope of utility model registration request] (1) A first resistor whose one end is connected to the power supply terminal and whose other end is connected to one end of the first constant voltage element;
a second resistor interposed between one end of the connection point with the first constant voltage element whose other end is connected to a reference potential and the winding of the flyback transformer; 2
An abnormality characterized in that at least one first constant voltage element connected between both ends of the resistor and a voltage detection means for detecting the voltage of the second resistor satisfy a certain relational expression. High voltage detection circuit. (2) The voltage of the power supply terminal is 81, the resistance value of the first resistor is R2, the resistance value of the first resistor is R2, the first,
When the constant voltage value of one second constant voltage element is VD, and the numbers of the first and second constant voltage elements are 1 and n, respectively, R□=R2, B= (1+n)Vo An abnormal high voltage detection circuit according to claim 1, which satisfies the following.