JP2002330368A - Flyback transformer fault detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flyback transformer fault detection circuit that can detect not only a significant fault in a load of a high voltage deflection circuit but also a slight fault inside of a flyback transformer. SOLUTION: The flyback transformer fault detection circuit is provided with a power supply current detection circuit section 3, a beam current detection circuit section 4, and a fault current detection circuit section 14. The power supply current detection circuit section 3 detects a power supply current supplied to the flyback transformer 2. The beam current detection circuit section 4 detects a beam current supplied to a cathode ray tube via the flyback transformer 2. The fault current detection circuit section 14 subtracts the current detected by the beam current detection circuit section 4 from the current detected by the power supply current detection circuit section 3 to detect a fault in the power supply current supplied to the flyback transformer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flyback transformer abnormality detection circuit for detecting an abnormality of a flyback transformer attached to a high-voltage deflection circuit in a television receiver or the like.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional example of this type of flyback transformer abnormality detection circuit. This circuit converts the power supplied from the high-voltage deflection power supply 1 to the flyback transformer 2, that is, the power supply current (high-voltage deflection power supply current), to the abnormality detection circuit unit 3.
, And the processing circuit unit 5 that operates in response to the detection result is configured to ensure safe operation. In addition,
The high-voltage deflection power supply current is a component corresponding to a deflection current flowing through a horizontal deflection coil (not shown), a cathode ray tube (not shown).
And a component corresponding to a current necessary for performing other operations of the flyback transformer 2.

FIG. 6 is an explanatory diagram showing the operation of the circuit of FIG. 5, in which FIG. 6 (a) shows a change in beam current due to the amount of image drive to a CRT according to the screen brightness adjustment. (B) shows a change in the high-voltage deflection power supply current depending on the amount of video drive to the cathode ray tube. FIG.
The current change waveform in (b) is also the waveform of the potential at point a in the circuit of FIG.

[0006] As shown in FIG. 6 (a), as the image drive amount to the CRT increases, the beam current of the CRT increases to a predetermined beam current limit level.
Therefore, in the normal operation, as shown in FIG.
As the amount of video drive to the CRT increases,
As the beam current increases, the high-voltage deflection power supply current also increases.

Here, in the conventional circuit of FIG. 5, since the abnormality of the circuit is detected from the change of the high-voltage deflection power supply current, as shown in FIG. 6B, the maximum current value A ( A current value B larger than the beam current limit level) must be set as a safe operation detection level, and when the high voltage deflection power supply current exceeds the safe operation detection level B, it must be determined that the circuit is abnormal.

[0006]

However, in such a configuration, in a state where the image is dark and the beam current is small, the high-voltage deflection power supply current does not exceed the safe operation detection level B unless a considerably large abnormal power is generated. Therefore, even if a large load abnormal state of the high-voltage deflection circuit can be detected, it is difficult to detect even a minor abnormal state inside the flyback transformer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a flyback transformer abnormality detection circuit capable of detecting not only a large load abnormality of a high-voltage deflection circuit but also a minor abnormality state inside a flyback transformer.

[0008]

A flyback transformer abnormality detecting circuit according to the present invention is provided with power supply current detecting means for detecting a power supply current supplied to a flyback transformer, and supplied to a cathode ray tube via the flyback transformer. Beam current detecting means for detecting a beam current to be detected, and detecting an abnormality of the power supply current supplied to the flyback transformer based on both the detection result by the power supply current detecting means and the detection result by the beam current detecting means. And an abnormal current detecting means.

In the flyback transformer abnormality detection circuit, the abnormal current detection means is supplied to a flyback transformer based on a result obtained by subtracting a detection result by the beam current detection means from a detection result by the power supply current detection means. It may detect abnormalities in the power supply current.

[0010] In the flyback transformer abnormality detection circuit, power supply shutoff means for shutting off power when the abnormal current detection means detects an abnormality in the power supply current may be provided.

Further, the flyback transformer abnormality detecting circuit may include a beam current limiting means for limiting an upper limit of a beam current in the cathode ray tube to a predetermined level based on a detection result by the beam current detecting means.

In the flyback transformer abnormality detecting circuit, a power supply shutoff means for shutting off a power supply when the beam current increases to a predetermined value or more based on a detection result by the beam current detection means may be provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing the embodiments.

Embodiment 1 FIG. 1 shows a high-voltage deflection circuit including a flyback transformer abnormality detection circuit according to Embodiment 1 of the present invention. The same or equivalent parts as those of the conventional circuit shown in FIG. 5 are denoted by the same reference numerals.
This high-voltage deflection circuit is a circuit mounted on a television receiver, and includes a high-voltage deflection power supply 1 and a flyback transformer 2.
As in the conventional circuit shown in FIG. 5, a power supply current detection circuit section 3 for detecting the power supplied from the high voltage deflection power supply 1 to the flyback transformer 2, that is, the high voltage deflection power supply current, is interposed therebetween. The circuit section 3 includes a diode D1, resistors R1, R2, R3, and a transistor Tr.

A beam current detection circuit for detecting a beam current supplied to the cathode ray tube via the flyback transformer 2 is provided between the power supply current detection circuit unit 3 and one end of the secondary winding 2b of the flyback transformer 2. The circuit section 4 is interposed. The other end of the secondary winding 2b of the flyback transformer 2 is connected to the anode of the cathode ray tube. The beam current detection circuit section 4 includes a resistor R. Further, an abnormal current detection circuit section 14 is provided over both circuit sections 3 and 4. The abnormal current detection circuit section 14 includes resistors R, R
3, R4, and the capacitor C1. The abnormal current detection circuit unit 14 is configured to detect the power supply current detection circuit unit 3 based on both the detection result obtained by the power supply current detection circuit unit 3 and the detection result obtained by the beam current detection circuit unit 4. Based on the result obtained by subtracting the detection result by the beam current detection circuit unit 4 from the result, an abnormality in the power supplied to the flyback transformer 2, that is, the power supply current is detected.

Further, at the next stage of the abnormal current detecting circuit 14, a power shutoff circuit 5 for shutting off the high voltage deflection power supply 1 when the abnormal current detecting circuit 14 detects an abnormality of the power supply current.
Is provided. The circuit unit 5 includes a microcomputer 6 used for overall control of the television receiver.
And a resistor R5 constituting an input section of the detection signal.

The primary winding 2a of the flyback transformer 2 is connected to a horizontal output transistor 10 for flowing a deflection current according to a horizontal synchronization signal to a horizontal deflection coil (not shown). A steady load 7 is connected to another secondary winding 2c of the flyback transformer 2. This steady load 7
Is composed of a diode D2, a capacitor C2, and a load Z.

FIG. 2 is an explanatory diagram of a flyback transformer abnormality detecting operation in the high voltage deflection circuit. The operation of the circuit of FIG. 1 will be described below with reference to this explanatory diagram.

When the high-voltage deflection power supply current supplied from the high-voltage deflection power supply 1 to the flyback transformer 2 increases, the base potential of the transistor Tr in the power supply current detection circuit 3 decreases, and the current flowing through the transistor Tr increases. , The voltage drop at the resistor R3, that is, the potential at the point a increases. The potential at the point a is a detection result of the power supply current from the high-voltage deflection power supply 1.

On the other hand, during normal operation, if the amount of image drive to the CRT increases and the beam current increases, a
Since the current flowing from the point to the cathode ray tube via the resistor R of the beam current detection circuit unit 4 also increases, the voltage drop at the resistor R also increases. This voltage drop is a detection result of the beam current. The potential at the point b is obtained by subtracting the voltage drop at the resistor R from the potential at the point a. Note that the resistor R4 and the capacitor C
The noise at point b is removed with a time constant of 1.

Since the potential at the point a and the voltage drop at the resistor R both increase when the image drive amount to the cathode ray tube increases and the beam current increases, by appropriately setting the values of the circuit elements, , The potential at point b is substantially constant regardless of the increase in beam current. Since the current corresponding to the beam current is shunted to the resistor R side, the voltage drop at the resistor R3, that is, the potential at the point a decreases according to the shunt. In order to keep the potential at the point b constant irrespective of the increase or decrease of the beam current, the value of the circuit element in the entire circuit may be appropriately set in consideration of this fact.
In general, the value of the resistor R is set to be much larger than the value of the resistor R3. However, depending on the setting of the values of the circuit elements as a whole, in the extreme case, the potential at the point b is kept constant even without the resistor R. It is also possible to maintain. The entity of the beam current detection circuit unit 4 in that case is the shunt signal line itself, and the shunted beam current itself is the detection result in the circuit unit 4.

If the power supply current of the high-voltage deflection power supply 1 is abnormal due to the abnormality in the normal operation described above,
Since the potential at the point b rises, an abnormality in the high-voltage power supply current is detected from the fluctuation in the potential at the point b. The detection result is input to the power cutoff circuit unit 5, and an abnormality is determined by comparison with a reference value preset in the microcomputer 6. In the event of an abnormality, the microcomputer 6 protects the circuit by shutting off a protection relay (not shown) provided in the high-voltage deflection power supply 1 or a power supply unit (not shown) upstream thereof.

In this case, the abnormality detection level (safe operation detection level) of the potential at the point b can be lowered to the level C lower than the beam current limit level A. Therefore, the beam current limit level A as in the conventional circuit of FIG. Compared to detecting an abnormal current at the level B (FIG. 6B), even a lighter short-circuit phenomenon in the flyback transformer 2 can be easily detected, and a more reliable protection operation can be performed. This makes it possible to prevent overheating of the flyback transformer and smoke failure. In addition, since not only a failure inside the flyback transformer 2 but also an overcurrent of an external load can be detected with high accuracy, a product with higher safety can be obtained.

Embodiment 2 FIG. FIG. 3 shows a high-voltage deflection circuit including a flyback transformer abnormality detection circuit according to Embodiment 2 of the present invention. In this circuit, the first embodiment is used.
In this circuit, a beam current limiting circuit 8 for limiting the upper limit of the beam current is interposed between the abnormal current detecting circuit 14 and the secondary winding 2b of the flyback transformer 2. The circuit section 8 includes resistors r, R6, R7, a diode D3, a capacitor C3, and a video signal processing circuit 9. The resistance r is equal to the connection point between the resistances R and R4 in the abnormal current detection
It is interposed between the secondary winding 2b.

Utilizing that the voltage drop at the resistor r fluctuates due to the fluctuation of the beam current, the beam current limiting circuit 8 limits the upper limit of the beam current in the CRT to a predetermined level. That is, the potential at the point b is constant irrespective of the fluctuation of the beam current as described above, and therefore the potential at the point c fluctuates according to the fluctuation of the beam current. The noise at point c is removed by the time constant of the resistor R6 and the capacitor C3, and an excessive voltage is prevented from reaching the video signal processing circuit 9 by the diode D3. If the beam current in the cathode ray tube exceeds a predetermined level and increases, the potential at the point c also drops below a predetermined value. The gain control of the AGC or the like is performed in the circuit 9 so that the beam current of the CRT is limited so as not to increase any more. As a result, the maximum beam current during normal use is set, and it is possible to prevent a beam current exceeding a certain value from flowing through the cathode ray tube. Other configurations are the same as those in the first embodiment.

Embodiment 3 FIG. 4 shows a high-voltage deflection circuit provided with a flyback transformer abnormality detection circuit according to Embodiment 3 of the present invention. In this circuit, an extraordinary beam current detection circuit 11 which operates when an extraordinary beam current exceeding the operation range of the beam current limiting circuit 8 flows is added to the circuit of the second embodiment (FIG. 3) in FIG. ing. The abnormal beam current detection circuit unit 11 includes a flyback transformer-side end of the resistor r in the beam current limiting circuit unit 8;
The zener diode ZD is interposed between the abnormal current detection circuit unit 14 and the point b. Other configurations are the same as those in the second embodiment.

In this case, the abnormal beam current detection circuit 11
Is substantially equal to the voltage drop across the resistor r. When an abnormal beam current flows and this voltage exceeds a predetermined value, the Zener diode ZD turns on and the potential at the point b drops to a value lower than the normal level. That is, an abnormal beam current can be detected by setting a potential lower than the normal level of the potential at the point b as the abnormal beam current detection level.

The detection of the abnormal beam current is performed by the power supply cutoff circuit 5. That is, the detection voltage input terminal of the microcomputer 6 constituting the power cutoff circuit 5 is provided with a function of a window comparator for detecting both the high voltage and the low voltage, and the detection level higher than the normal level of the potential at the point b is provided. The discrimination operation of the input signal is performed using both C and a predetermined voltage level (abnormal beam current detection level) lower than the normal state of the potential at the point b as thresholds. That is, the power supply cutoff circuit unit 5 performs not only when the potential at the point b exceeds the detection level C due to the abnormality of the high-voltage deflection power supply current, but also when an abnormal beam current flows so that the potential at the point b is lower than the normal level. Shut off the power when it drops. Thus, the protection operation can be reliably performed even when an abnormal beam current occurs in the cathode ray tube, and the safety of the product is further improved.

[0029]

According to a first aspect of the present invention, there is provided a flyback transformer abnormality detecting circuit for detecting power supply current supplied to a flyback transformer, and supplying the current to a cathode ray tube via the flyback transformer. Beam current detecting means for detecting a beam current to be detected, and detecting an abnormality of the power supply current supplied to the flyback transformer based on both the detection result by the power supply current detecting means and the detection result by the beam current detecting means. Since the abnormal current detecting means is provided, a lighter short-circuit phenomenon or the like in the flyback transformer can be easily detected, and a more reliable protection operation can be performed.

In a flyback transformer abnormality detecting circuit according to a second aspect of the present invention, the abnormal current detecting means is configured to subtract a result of detection by the beam current detecting means from a result of detection by the power supply current detecting means. Since the abnormality of the power supply current supplied to the flyback transformer is detected, it is possible to reliably detect the abnormality of the power supply current while eliminating the influence of the increase and decrease of the beam current.

In the flyback transformer abnormality detecting circuit according to a third aspect of the present invention, when the abnormal current detecting means detects the abnormality of the power supply current, the power supply shutoff means for shutting off the power supply is provided. The power supply can be reliably shut down in response to the occurrence of an abnormality, and the safety of the product can be improved.

A flyback transformer abnormality detecting circuit according to a fourth aspect of the present invention includes a beam current limiting means for limiting an upper limit of a beam current in the cathode ray tube to a predetermined level based on a detection result by the beam current detecting means. Therefore, it is possible to prevent the abnormal beam current from flowing through the cathode ray tube.

According to a fifth aspect of the present invention, there is provided a flyback transformer abnormality detecting circuit, comprising: a power cutoff means for shutting off a power supply when the beam current increases to a predetermined value or more based on a detection result by the beam current detection means. Because it was provided,
When an abnormal beam current occurs in the cathode ray tube, the protection operation can be reliably performed, and the safety of the product is further improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a high-voltage deflection circuit including a flyback transformer abnormality detection circuit according to a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the circuit of FIG. 1;

FIG. 3 is a circuit diagram showing a high-voltage deflection circuit including a flyback transformer abnormality detection circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a high-voltage deflection circuit including a flyback transformer abnormality detection circuit according to Embodiment 3 of the present invention.

FIG. 5 is a circuit diagram showing a high-voltage deflection circuit provided with a conventional flyback transformer abnormality detection circuit.

6 is an explanatory diagram of a change in beam current and a change in high-voltage deflection power supply current in the circuit of FIG. 5;

[Explanation of symbols]

1 high voltage deflection power supply, 2 flyback transformer, 3 power supply current detection circuit, 4 beam current detection circuit, 5 power supply cutoff circuit, 8 beam current limiting circuit, 11 abnormal beam current detection circuit, 14 abnormal current detection circuit Department.

Claims (5)

[Claims] 1. A power supply current detecting means for detecting a power supply current supplied to a flyback transformer, a beam current detecting means for detecting a beam current supplied to a cathode ray tube via the flyback transformer, and the power supply current detection Abnormal current detecting means for detecting an abnormality in the power supply current supplied to the flyback transformer based on both the detection result by the means and the detection result by the beam current detecting means. Back transformer abnormality detection circuit. 2. The power supply supplied to a flyback transformer according to claim 1, wherein said abnormal current detection means subtracts a detection result by said beam current detection means from a detection result by said power supply current detection means. Flyback transformer abnormality detection circuit that detects abnormal current. 3. The flyback transformer abnormality detection circuit according to claim 1, further comprising a power supply cutoff means for shutting off a power supply when the abnormal current detection means detects an abnormality in the power supply current. 4. The flyback transformer according to claim 1, further comprising a beam current limiting unit that limits an upper limit of a beam current in the cathode ray tube to a predetermined level based on a detection result by the beam current detecting unit. Abnormality detection circuit. 5. The fly according to claim 1, further comprising a power cutoff means for shutting off a power supply when the beam current increases to a predetermined value or more based on a detection result by the beam current detection means. Back transformer abnormality detection circuit.