JPS6151827B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electronic equipment, such as television receivers, in which the output of a high frequency oscillator is transformed and rectified via a transformer, and is widely used as an operating power source for various parts within the receiver. The purpose of this is to prevent the power supply from rising too much due to the circuit abnormality.

When the above-mentioned power supply voltage rises due to a circuit abnormality, for example in a television receiver, the picture tube anode voltage rises and X-rays are emitted or a high-pressure discharge occurs.
This also causes various problems such as damage to other elements, and conventionally, to obtain this anode voltage, a method of step-up rectifying the output pulse of an oscillator of several KHz to several tens of KHz is sometimes used. .

Also, this oscillator does not have to be a dedicated one; for example, a horizontal deflection oscillator of a picture tube may be used.
It is also common practice to boost and rectify the output flyback pulse to obtain the anode voltage.

Therefore, in order to prevent the problems caused by abnormally high voltage as described above, a pulse proportional to the output pulse is obtained using a transformer or a capacitor voltage divider, and then rectified. Some devices have been designed to stop the oscillation by applying a DC voltage higher than a predetermined value.

The one shown in FIG. 1 is an example, where 1 is a horizontal deflection oscillation circuit, 2 is a horizontal deflection output circuit,
3 is a flyback transformer, 4 is a high-voltage rectifier diode, 5 is a picture tube, 6 is its anode, and 7
1 is a sensing voltage rectifying diode, 8 is a smoothing capacitor, 9 is a Zener diode, 10 is a transistor, and 11 is a dropper resistor for the DC power supply supplied to the horizontal deflection oscillation circuit 1.

The horizontal deflection period waveform generated by the horizontal deflection oscillator circuit 1 is guided to the picture tube deflection coil (not shown) through the output stage of the horizontal deflection output circuit 2 to perform a predetermined deflection operation, and at the same time, during the flyback period. , a pulse P ₀ is generated, which is boosted through the primary winding 3 a and secondary winding 3 b of the flyback transformer 3 to become a pulse P ₁ , which is rectified by the high voltage rectifying diode 4 and applied to the anode 6 . Therefore, in the event of a circuit failure, such as an increase in the DC voltage +E _B supplied to the horizontal deflection output circuit 2, the pulse _P1 will increase, and therefore the DC high voltage applied to the anode 6 will also increase, Various inconveniences as described above will occur.

Therefore, the tertiary winding 3 of the flyback transformer 3
Since the pulse P ₂ obtained at c is proportional to the pulse P ₁ (that is, pulse P ₂ and pulse P ₃ have the same frequency), it is rectified by the detection voltage rectifier diode 7 and then connected to the smoothing capacitor. Smooth with 8,
When a DC voltage E ₀ is obtained and this DC voltage E ₀ exceeds the Zener voltage and becomes conductive to the transistor 10, the DC voltage +E _B is applied to the horizontal deflection oscillation circuit 1 through the dropper resistor 11. However, since a DC bypass is created through the transistor 10, no DC power is applied to the horizontal deflection oscillation circuit 1, and the oscillation of the horizontal deflection oscillation circuit 1 is stopped. Therefore, a high DC voltage is generated to the anode 6. I won't.

The problem here is that it is fine when the transistor 10 is completely conductive like this, but for example, +E _B
When the voltage gradually increases, the transistor 10 may not be completely conductive, so-called half-on, and in such a case, the DC voltage at point A only decreases, causing the horizontal deflection oscillator circuit 1 to The oscillation does not stop, and an abnormally high voltage may continue to appear at the anode 6 of the picture tube 5. Also, the horizontal deflection oscillation circuit 1 may cause abnormal oscillation, and the output transistor of the horizontal deflection output circuit 2 may become overloaded. There were problems such as aging and damage. If a thyristor or a circuit similar to a thyristor that conducts by a trigger and continues to conduct even if the trigger is removed is used instead of the transistor 10, there will be no problem since there will be no half-on state like this. The transistor 10 is more expensive than the circuit shown in FIG. 1 which uses only one transistor, and once it becomes conductive, it continues to be conductive even if there is no input, and does not recover, so it is difficult to prevent discharges in the picture tube 5, etc. Even when the pulses P ₁ and P ₂ rise momentarily, the operation of the horizontal deflection oscillator circuit 1 is stopped, and the device cannot resume normal operation unless the power is turned off and then turned on again. It was hot. Therefore, for the purpose of preventing this abnormally high voltage, it is desirable to have a protection circuit in which the transistor 10 does not remain in a half-on state, and returns to normal operation immediately after the abnormal state ends.

FIG. 2 shows an embodiment according to the present invention, in which reference numerals 1, 2, 3, 4, 5, 6, 10
are the same as the symbols shown in FIG. 1, and have the same function. Explanation will be omitted. 12
13 is a diode for rectifying the voltage from the average level of the negative pulse P ₃ of the tertiary winding 3c of the flyback transformer 3 to the pulse base (base side) to obtain a positive DC voltage E ₂ ; With the smoothing capacitor, this DC voltage E ₂ is often used as a power source for other circuits in the equipment, while 14 rectifies the voltage (pulse side) from the average level of P ₃ to the pulse peak. Diode to obtain negative voltage E ₃ , 1
5 is a smoothing capacitor, 16 and 17 are voltage dividing resistors,
This value means that the base voltage E ₀ of the transistor 10 is
Under normal conditions, it is set to be negative and turn off the transistor 10. 18 is a Zener diode.

Here, the important thing is that B of the horizontal deflection oscillator 1
The point is selected such that when the transistor 10 is in the half-on state, its oscillation frequency becomes high, and when the transistor 10 is in the on state, the oscillation stops completely. . This is illustrated in the example of FIG. Here, numeral 1 is a horizontal deflection oscillator circuit (hereinafter referred to as an oscillator) having the same purpose as that shown in FIGS. 1 and 2.
Also, 10 is a transistor that has the same function as the one shown in FIG. 2, and 20 is a transistor,
21 is an oscillation transformer, 22 and 23 are capacitors and resistors that determine the oscillation time constant, and 24 and 25 are bias resistors. Assuming that the transistor 10 is initially off, when a DC voltage + _Ecc is applied to the point A of this circuit, a blocking oscillation occurs according to the well-known principle, and a pulse P is taken out from the point C, and then passed to the point B. As the transistor 10 gradually becomes conductive, this oscillation frequency increases, and when the transistor 10 becomes completely conductive, the transistor 20 becomes constantly conductive and oscillation stops. Therefore, the aforementioned objective is achieved. Of course, the circuit of the oscillator 1 which stops while increasing the oscillation frequency by conducting the transistor 10 is not limited to the one shown in FIG. 3, but may take various other forms.

Here, in the circuit shown in Figure 2, DC power supply + E _B
If for some reason increases, the high voltage applied to the anode 6 increases as described above, but on the other hand, the DC voltage E ₂ also increases in proportion to the DC voltage + _EB . When this DC voltage E ₂ rises to exceed the Zener voltage of the Zener diode 18, a base bias current begins to flow through the transistor 10, and at the same time, a collector current of the transistor 10 begins to flow and becomes conductive. Then, as described above, the oscillation frequency of the oscillator 1 increases. When this oscillation frequency increases, the pulse P ₀ generated at one end of the primary winding 3a is determined by P ₀ = (πT - T _P /T _P +1) E _B (1), so only the oscillation period T is shortened. Thus, since the pulse width T _P remains unchanged, the pulse peak value P ₀ becomes smaller. Furthermore, the primary winding 3
If the winding ratio between a and the tertiary winding 3c is n, then the pulse P ₃ obtained at the tertiary winding 3c is: P ₃ = nP ₀ = n・πT−T _P /T _P E _B +n・E _B ...(2), and the first term in equation (2) is the value from the average level to the pulse peak, as shown in Figure 5, and therefore the DC value obtained by rectifying this. Voltage
The absolute value of E ₃ is approximately this value. Also, the second term in equation (2) is the voltage between the average level and the pulse base, and therefore the DC voltage obtained by rectifying this
The absolute value of E ₂ is approximately n·E _B.

From this, as mentioned above, when the oscillation frequency becomes higher (the oscillation period T becomes shorter), the absolute value of the DC voltage E ₃ decreases, but the DC voltage E ₂ is independent of the oscillation period T. Therefore, as a result, the base voltage E ₀ of the transistor 10 becomes more positive, accelerating the transistor 10 more and more, and finally the transistor 10 becomes completely conductive, stopping the oscillation of the oscillator 1, and the anode 6 of the picture tube 5. High pressure is no longer applied to. In other words, due to this acceleration effect, the first
As in the conventional example shown in the figure, when the DC voltage +E _B gradually rises, the transistor 10 becomes completely non-conducting, a so-called half-on state, and the DC voltage at point A only decreases, leveling off. The oscillation of the deflection oscillation circuit 1 remains unstable and does not stop, and therefore there is no possibility that an abnormally high voltage will continue to be applied to the anode 6 of the picture tube 5.

Furthermore, when the oscillation stops, the pulse P ₃ also disappears, so the DC voltage E ₂ also attenuates with a time constant determined by the smoothing capacitor 13 and the load of the DC voltage E ₃ .
Eventually, the transistor 10 is turned off, so the oscillator 1 starts oscillating again. Therefore, although the entire circuit repeats activation and deactivation, the voltage at the anode 6 of the picture tube 5 decreases by the amount of time that the circuit is inactive. In reality, since the capacitance of the smoothing capacitor 13 is sufficiently large, the ratio of operating to non-operating times can be more than 1:10, and the anode 6
voltage can be reduced to less than one-tenth.

If the configuration is configured to perform repeated operations in this way, the transistor 10 may be damaged once due to an abnormal surge, etc.
Even if the circuit becomes conductive, it is possible to design the circuit so that it returns to its original normal operation when the power supply returns to normal.
Note that if the DC voltage E ₂ is not taken from both ends of the smoothing capacitor 13, but is obtained directly from the DC voltage +E _B or by dividing it with a potentiometer, the DC voltage +E _B increases and the transistor 1 is immediately
0 can be made conductive so that it will not return unless the main power is turned off and then turned on again.

Further, the negative pulse _P3 does not necessarily have to be obtained from the winding of the flyback transformer 3 as shown in FIG. 2; this will be explained with reference to FIG. 4, for example.

In FIG. 4, numerals 31 to 36 indicate examples of elements included in the horizontal deflection output circuit 2 shown in FIG. 2, that is, 31 is an output transistor, 32 is a damper diode,
33 and 34 are capacitors for retrace resonance, 35 is a horizontal deflection coil, and 36 is a capacitor for direct current blocking or S-shaped correction of the horizontal deflection coil 35.
Here, the pulse P ₄ is connected to the retrace resonance capacitor 33,
It is obtained from 34 connection points, and is in the form of a capacitor-divided pulse _P0 . In a typical design, P ₀ is
Since it is designed to be 800 to 900 volts and _P4 is designed to be about -40 to 50 volts, the capacitance ratio of the retrace resonance capacitors 33 and 34 is about 1:20. Here, the pulse width of the pulse P ₀ is mainly determined by the combined capacitance value of the retrace resonance capacitors 33 and 34 and the horizontal deflection coil 3.
5 and the combined inductance of the primary winding 3a of the flyback transformer 3, and the narrower this width, the higher the height of the pulse _P0 .
Therefore, if the combined capacitance value of the retrace resonance capacitors 33 and 34 decreases due to defective capacitors or aging, the pulse P ₀ increases, and as a result, as described above, the anode high voltage applied to the picture tube increases. There is a risk of generating X-rays. However, as mentioned above, the retrace resonance capacitor 33
The capacitance value of 34 and 34 is sufficiently large, so
The combined capacitance value of both is determined mostly by the value of the retrace resonance capacitor 33. Therefore, the above-mentioned danger becomes a problem when the capacitance of the retrace line resonance capacitor 33 is reduced, but there is no problem with the other retrace line resonance capacitor 34.

However, in this case, the retrace resonance capacitor 33
When the capacitance decreases, the height of the pulse P ₀ decreases, but on the other hand, the value of the DC voltage +E ₂ remains unchanged, so the base potential of the transistor 10 moves in the positive direction, making the transistor 10 conductive. Work at. Therefore, in the case of such a configuration, generation of X-rays can be prevented not only when the DC voltage +E _B increases but also when the capacitance of the retrace resonance capacitor 33 decreases.

As described in detail above, the present invention is directed to an abnormality in an electronic device having a circuit or element that utilizes a DC voltage obtained by rectifying the output signal of an AC oscillator (horizontal deflection oscillation circuit 1 of the embodiment) directly or after amplification. In a voltage prevention device, the average potential of a pulsed AC voltage (pulse P ₃ in the example) having the same frequency as the pulsed AC voltage (pulse P ₀ in the example) generated by the AC oscillator. The output terminal of the first rectified voltage (DC voltage E ₃ in the example) obtained by rectifying the voltage up to the pulse tip and the voltage obtained by rectifying the voltage up to the pulse base from the average potential of the pulsed AC voltage. The pulsed alternating current generated by the alternating current oscillator is connected between the output terminal of the second rectified voltage (the direct current voltage E ₂ in the embodiment) and having the opposite polarity to the first rectified voltage. When the third rectified voltage obtained by rectifying the voltage (DC voltage E _B in the example) increases, a Zener diode (implemented Connect the example Zener diode 18),
A control voltage obtained by combining these first and second rectified voltages is applied, and when this control voltage exceeds a predetermined value, it changes from a cut-off state to a conduction state, and when it falls below a predetermined value, it changes from a conduction state to a cut-off state. A switching element (transistor 10 in the embodiment) that changes is connected between the AC oscillator and the ground point, and as the switching element gradually changes from the cut-off state to the conduction state, the oscillation frequency of the AC oscillator changes. Since this is an abnormal voltage prevention device for electronic equipment, which is characterized by a high
This invention reliably prevents damage to the equipment or abnormal phenomena caused by the power supply rising too high due to a circuit abnormality in a rectifier used as an operating power supply inside the equipment. Furthermore, when the power supply gradually increases, the switching element for stopping the operation of the AC oscillator does not remain in the half-on state, but gradually becomes conductive, and the AC oscillator changes its oscillation frequency. Accordingly, the control voltage of the switching element also increases, making the switching element conductive and stopping the operation of the AC oscillator, thereby eliminating the possibility that the oscillation of the AC oscillator would continue in an unstable state. ,Also,
By repeating the operation of stopping and starting the operation of the AC oscillator, it is possible to design the circuit to return to normal operation immediately after the circuit abnormality ends.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, FIG. 2 is a circuit diagram of an abnormal high voltage prevention device in which the present invention is applied to a television receiver, FIG. 3 is a circuit diagram for explaining a part of the present invention, and FIG. FIG. 4 is a circuit diagram showing another example of the invention, and FIG. 5 is a waveform diagram for explaining the operation of the invention. DESCRIPTION OF SYMBOLS 1... Horizontal deflection oscillation circuit, 2... Horizontal deflection output circuit, 3... Flyback transformer, 4... High voltage rectifier diode, 5... Picture tube, 6... Anode, 10... Transistor, 12... Diode, 13... Smoothing capacitor, 14 ... Diode, 15... Smoothing capacitor, 16, 17... Voltage dividing resistor, 18... Zener diode, 20... Transistor, 21... Oscillation transformer, 22... Capacitor, 23... Resistor, 24, 25
...Bias resistor, 31...Output transistor, 32
...damper diode, 33, 34...capacitor for retrace resonance, 35...horizontal deflection coil, 36...capacitor for DC current blocking or S-curve correction.

Claims (1)

[Scope of Claims] 1. An abnormal voltage prevention device for electronic equipment having a circuit or element that utilizes a DC voltage obtained by directly or amplifying and rectifying an output signal of an AC oscillator, the device comprising: from the output terminal of the first rectified voltage obtained by rectifying the voltage from the average potential of the pulsed AC voltage having the same frequency as the pulsed AC voltage to the pulse tip and the average potential of the pulsed AC voltage. The pulse generated by the AC oscillator is connected between an output terminal of a second rectified voltage obtained by rectifying the voltage up to the pulse base and having a polarity opposite to the first rectified voltage. A Zener diode is connected in a direction in which the rectified voltage of either the first or second rectified voltage decreases when the third rectified voltage obtained by rectifying the AC voltage increases; A switching element to which a control voltage obtained by combining the two rectified voltages is applied, and which reversibly changes from a cutoff state to a conduction state when this control voltage exceeds a predetermined value, and from a conduction state to a cutoff state when it becomes less than a predetermined value. is connected between the alternating current oscillator and a ground point, and the oscillation frequency of the alternating current oscillator increases as the switching element gradually changes from a cut-off state to a conductive state. Abnormal voltage prevention device for equipment.