JPS6323714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high voltage limiting circuit for preventing the voltage supplied to a cathode ray tube from becoming abnormally high in a television receiver.

In color television receivers, the CRT
Because high voltage of 20KV~30KV is applied,
X-rays are emitted from a cathode ray tube. The amount of X-rays is specified by the safety standards of each country, and in the United States, for example, it must be 0.5 mR/h or less. The amount of X-rays increases as the voltage applied to the cathode ray tube increases. Therefore, if the voltage becomes abnormally high due to a circuit failure or the like, an X-ray generation prevention circuit (herein referred to as a high voltage limiting circuit) is required that automatically stops the circuit operation.

FIG. 1 shows a circuit diagram of a conventional high voltage limiting circuit.

In Figure 1, 1 is the high voltage winding of the flyback transformer, 2 is the primary winding, and 3 is the high voltage limiting circuit winding. It is wound so as to be tightly coupled to the masterpiece winding wire 1. 4 is a rectifier diode, 5 is a smoothing capacitor, 6 is a voltage divider, and 7 is a Zener diode. When a voltage above a certain level is applied across these ends, the Zener diode 7 becomes conductive, and a voltage appears across the detection resistor 8. , horizontal oscillation output circuit 9
operation stops. 10 is a resonant circuit for the purpose of attenuating the harmonics of the flyback transformer and improving the regulation of the voltage (hereinafter referred to as high voltage) applied to the cathode ray tube; 11 is a cathode ray tube; and 12 is a diode.

The broken line a in Figure 2 is the X emitted from the cathode ray tube.
The solid line b shows the relationship between the high voltage and the anode current flowing through the cathode ray tube 11 when the amount of line is 0.5 mR/h (hereinafter referred to as the cathode ray tube limit curve). Shows the relationship between currents. Therefore, the high voltage limiting circuit does not need to operate when the television receiver is operating between dashed line a and solid line b, but needs to operate when it exceeds dashed line a.
However, in the conventional high voltage limiting circuit, the ratio between the output voltage and the voltage of the winding 3 for the high voltage limiting circuit is kept constant, and the Zener diode 7 is used to always operate at a constant voltage. operates at a constant high pressure irrespective of the second
It operates when the solid line c shown in the figure is crossed.

Therefore, when the anode current is small, the difference between the operating voltage of the high voltage limiting circuit and the output voltage of the flyback transformer, that is, the high voltage, becomes small, and there is a risk of malfunction due to an error in the resistance value of the voltage divider 6, etc. Furthermore, when the anode current is large, the difference between the cathode ray tube limit curve c and the output voltage b of the flyback transformer becomes small, and due to errors in the voltage divider 6, etc., a high voltage exceeding the cathode ray tube limit curve is applied to the cathode ray tube 11, causing Even if the amount exceeds the standard value, the high voltage limiting circuit may not operate.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art and provide a high voltage limiting circuit that does not cause malfunctions.

In order to achieve the above object, the present invention changes the high voltage limiting circuit operating point as the anode current changes.

Hereinafter, an embodiment of the high voltage limiting circuit according to the present invention will be shown with reference to FIG.

As shown in FIG. 3, in the present invention, one side of the output voltage smoothing capacitor 5 of the high voltage limiting circuit winding 3 is not connected to ground, and the harmonic damping resonant circuit 10
connected to the output side of the The amplitude of the resonant voltage generated across the resonant circuit 10 increases as the cathode ray tube anode current increases. Therefore, the detected voltage supplied to the voltage divider 6 varies depending on the resonant voltage generated in the resonant circuit 10, and takes the waveforms shown in FIGS. 4a and 4b.

In FIGS. 4a and 4b, the horizontal axis represents time, and FIG. 4a shows the case where the anode current is small, and FIG. 4b shows the case where the anode current is large. The high voltage limiting circuit operates at the maximum value P of this voltage, so the higher the anode current, the lower the output voltage of the diode 4.The high voltage limiting circuit operates at a voltage _V2 proportional to the high voltage, and when the anode current is small, Operates at a voltage V ₁ proportional to the high voltage. The solid line c shown in FIG. 5 indicates the operating point in the high voltage limiting circuit according to the present invention, and there is a margin of voltage difference of ΔV ₁ when the anode current is small, and ΔV ₂ when the anode current is large. . Therefore, even if an error occurs in the resistance value of the voltage divider 6, malfunctions are unlikely to occur.

As explained above, according to the present invention, as the current value of the anode current flowing through the cathode ray tube increases, the operating point at which the high voltage limiting circuit operates is set to a lower voltage, and as the current value of the anode current decreases, the operating point is set to a lower voltage. Since the voltage can be set to a high voltage at the voltage divider, the high voltage limiting circuit will not malfunction even if there is an error in the resistance value of the voltage divider.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional high voltage limiting circuit, Fig. 2 is a characteristic diagram showing the operating point of the conventional high voltage limiting circuit, Fig. 3 is a circuit diagram of a high voltage limiting circuit according to the present invention, and Fig. 4 is a circuit diagram of a conventional high voltage limiting circuit.
Figures a and b are waveform diagrams showing the input voltage supplied to the voltage divider in the present invention, and Fig. 5 is a characteristic diagram showing the operating point of the high voltage limiting circuit of the present invention. 1... High voltage winding, 2... High voltage winding, 3... Winding for high voltage limiting circuit, 4... Rectifier diode, 5...
Smoothing capacitor, 6...voltage divider, 10...resonant circuit.

Claims (1)

[Claims] 1 A primary winding connected to a horizontal oscillation output circuit,
A flywheel with a high voltage winding electromagnetically coupled to the primary winding, a resonant coil connected in series to the primary winding, and a high voltage limiting circuit winding electromagnetically coupled to the high voltage winding. A diode that is connected to the high-voltage limiting circuit winding of the back transformer and rectifies the voltage generated in the high-voltage limiting circuit winding, a smoothing capacitor that smoothes the voltage rectified by the diode, and a smoothing capacitor that smooths the voltage that is rectified by the diode. The horizontal oscillation output circuit is equipped with a voltage divider that divides the voltage divided by the voltage divider, and a Zener diode that conducts when the voltage divided by the voltage divider exceeds a predetermined voltage. In the high-voltage limiting circuit that stops the operation of the flyback transformer to prevent abnormally high voltage from continuing to occur in the high-voltage winding of the flyback transformer, the other end of the smoothing capacitor connected to the diode is connected to the primary winding of the flyback transformer. A high voltage limiting circuit characterized in that it is connected to the connection point of the line and the resonant circuit.