JP2696816B2 - TV receiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a television receiver, and more particularly to a radiation protection circuit. 2. Description of the Related Art Generally, a television receiver, particularly a television receiver for the United States and Canada, is always provided with a radiation protection circuit. Hereinafter, a conventional example will be described. FIG. 2 shows a power supply stabilization circuit, a horizontal oscillation circuit, a horizontal AFC circuit, a horizontal drive circuit, a horizontal output circuit, and a radiation protection circuit of the television receiver. An outline of the configuration and operation of FIG. 2 will be described. The commercial AC power is passed through the power supply rectifying / smoothing circuit 1 and converted to DC, output to its output terminal, and supplied to the anode of the silicon controlled rectifier Q1 via the winding L1 of the flyback transformer T1. The gate of the silicon controlled rectifier Q1 is connected to the trigger pulse generation circuit 2. The trigger pulse generation circuit 2 is supplied with a detection output signal of a voltage detection circuit 3 connected to the cathode of the silicon controlled rectifier Q1 and a horizontal pulse from the flyback transformer T1. Parts of silicon controlled rectifier Q1 (anode and gate)
FIG. 3 shows the voltage waveform of FIG. That is, the silicon controlled rectifier element Q1 enters a conductive state by a pulse from the trigger pulse generation circuit 2, and is turned off by a flyback negative pulse generated by the winding L1. When the potential of the cathode of the silicon controlled rectifier Q1 decreases, the trigger pulse supplied from the trigger pulse generation circuit 2 to the gate of the silicon controlled rectifier Q1 by the detection output of the voltage detection circuit 3 that detects the cathode voltage, The generation timing is earlier, the conduction period of the silicon control rectifier Q1 is longer,
The charge supplied to the capacitor C1 and the like is increased to compensate for the decrease in the cathode potential of the silicon control rectifier Q1. Conversely, when the cathode potential of the silicon controlled rectifier Q1 rises, the trigger pulse generation timing is delayed,
Shorten the conduction period of Q1. Note that the start circuit when the power is turned on is not directly related to the present invention, and is therefore omitted. On the other hand, a circuit 4 in which the sync separation, horizontal oscillation, and AFC circuit are integrated is connected to a horizontal output transistor Q2 via a horizontal drive circuit 5. The collector of the horizontal output transistor Q2 is connected to a power supply via a deflection yoke (not shown), the primary winding L2 of the flyback transformer T1, and the series resonance circuits L3 and C2. The operation of the series resonance circuits L3 and C2 will be described later. The cathode of the cathode ray tube (not shown) is connected to the high-voltage winding L4 of the flyback transformer T1, and the CR of the high-voltage winding L4 is
The terminal opposite to the terminal connected to T is connected to a grounding or B power supply with a smoothing capacitor C4 and a suitable impedance, and sometimes to a circuit for controlling the brightness of the CRT. That is, the potential at the intersection of the capacitor C4 and the impedance element Z decreases in proportion to the increase in the anode current of the CRT. This point is connected to the adding circuit 6. The winding L5 generates a voltage substantially proportional to the CRT anode voltage by the rectifier diode D1 and the smoothing capacitor C3, and this voltage is supplied to the adding circuit 6. This addition circuit 6 is for protecting the radiation, and the above-mentioned winding L5
And the output of the winding L5, or the output of the intersection of the capacitor C4 and the impedance element Z and the appropriate calculated value of the output of the intersection of the capacitor C4 and the impedance element Z exceed a certain value. Then, the output of the adding circuit 6 becomes "H" (high level), turning on the transistor Q3. That is, when some abnormality occurs and the anode voltage of the cathode ray tube rises or the anode current increases and exceeds a certain value, the output of the adding circuit 6 becomes "H" and the transistor Q3 is turned on. During other normal operations, the output of the adder circuit 6 is "L".
(Low level), transistor Q3 is off. On the other hand, the free oscillation frequency of the horizontal oscillation circuit in the circuit 4 is determined by the time constant of the variable resistor R1, the resistor R2, and the capacitor C5.
Is a variable resistor for adjusting it. A flyback pulse is supplied from the winding L6 of the flyback transformer T1 to the synchronous separation, horizontal oscillation, and AFC circuit 4 via the resistor R3 and the capacitor C6. A video signal is supplied from another terminal, and the phase of the flyback pulse is compared with the phase of the sync signal separated by the sync separation circuit in the circuit 4. The comparison output is supplied to a horizontal oscillation circuit, and the horizontal oscillation is output. Synchronized with the signal. However, as described above, when the output of the adding circuit 6 becomes “H” and the transistor Q3 is turned on, the capacitors C5,
The free horizontal oscillation frequency determined by the resistors R1 and R2 becomes higher than the holding range of the horizontal AFC because both ends of the resistor R2 are short-circuited. To an abnormal screen and inform the viewer that an abnormality has occurred. The resistor R6 between the intersection of the resistors R1 and R2 and the collector of the transistor Q3 may be inserted to prevent the horizontal oscillation frequency when the transistor Q3 is turned on from becoming too high. The series resonant circuits C2 and L3 in the collector of the horizontal output transistor Q2 in parallel with the winding L2 are used to shape the waveform of the negative horizontal flyback pulse that appears at the silicon-controlled rectifier Q1 terminal of the winding L1. belongs to. Problems to be Solved by the Invention Normally, the frequency holding range of this horizontal AFC circuit is a normal NTS
In the C system, about ± 1 to 1.5k around 15.7kHz
There is about Hz. Therefore, in order to prevent the horizontal oscillation frequency from being synchronized by turning on the transistor Q3, the horizontal free oscillation frequency must be about 17.2 kHz or more when the transistor Q3 is turned on. This must be guaranteed including the adjustment position of the variable resistor R1 and the variations of the resistor R2, the circuit 4, the capacitor C5 (R6 when the resistor R6 is inserted), etc. The horizontal free oscillation frequency needs to be set to about 19 to 20 kHz, and the maximum is considered to be about 22 to 23 kHz when the above-mentioned variation is included. When the anode current of the CRT increases, the voltage waveform of the anode of the silicon controlled rectifier element Q1 becomes thinner as shown by the fourth broken line due to a change in the magnetic impedance of the flyback transistor T1 and the like. come. When this happens, a silicon controlled rectifier Q1 turns off, the anode of the silicon controlled rectifier Q1 is because it takes time from when the potential than the cathode is sufficiently low, turned off at the time of tau _1. Therefore, the anode potential of tau ₁ silicon controlled rectifier Q1 when SCR Soshii Q1 is turned off, the come increased with CRT anode current increases, the silicon controlled rectifier Q1 finally this flyback pulse It does not turn off when applied to the anode. At this time, the silicon controlled rectifier Q1 conducts and is released, so that the cathode potential of the silicon controlled rectifier Q1 abnormally rises, overloading the circuit connected to the cathode, and eventually destroying the circuit. At this time, if the resonance circuit of the inductance L3 and the capacitor C2 is added, even if the anode current of the CRT increases, the narrowing of the pulse waveform as shown by the chain line in FIG. 4 decreases. Therefore, the disadvantages described above can be eliminated. Also, the resonance circuit L
3, The effect is closer as the resonance frequency of C2 is closer to 15.7 kHz, usually the inductance L3 and the capacitor so that they are higher than the horizontal frequency when the transistor Q3 is turned on, and as low as possible in that range. Determine the value of C2. This is because if the horizontal oscillation frequency becomes the resonance frequency of the resonance circuits L3 and C2, the resonance current of L3 and C2 flows through the horizontal output transistor Q2, and the horizontal output transistor Q2 is instantaneously destroyed. Therefore, the resonance frequency of C2 and L3 is
Must be equal to or higher than the horizontal oscillation frequency when the switch is turned on. However, as the resonance frequency increases, the effect of the pulse shaping of the flyback of the anode of Q1 of the silicon controlled rectifier described above decreases. Therefore, conventionally, in order to solve the above problem, when the capacitor C5, the resistor R2, the circuit 4, the capacitor C2, the inductance L3, and the resistors R1 and R6 are inserted, the variation of the resistor R6 and other components is strictly reduced. Regulation and sacrifices the maximum high-voltage output of the flyback transformer T1. That is, the performance of the cathode ray tube may not be sufficiently exhibited, which significantly lowers the commercial value. The present invention is to solve such a conventional problem,
By adding a simple circuit, it is possible to provide a means capable of lowering the horizontal oscillation frequency when the radiation protection circuit is operated as compared with the conventional case. Means for Solving the Problems The present invention is characterized in that when the radiation protection circuit is activated, the horizontal AFC circuit loop of the television receiver is opened or the gain of the AFC loop is reduced. . Function In the television receiver of the present invention, a certain abnormality occurs, the radiation protection circuit of the receiver operates, the horizontal oscillation frequency of the receiver is forcibly increased, an out-of-synchronization state is created, and the viewer is notified of the abnormality. When closing, the loop of horizontal oscillation AFC circuit,
At this time, the horizontal oscillation frequency in the out-of-synchronization state is not made much higher than the broadcasting frequency by opening the horizontal comparison pulse from the flyback transformer by means such as cutting off the horizontal comparison pulse or by lowering the gain of the AFC loop. Overload on a horizontal output transistor, a power supply circuit, or the like can be prevented. Embodiment An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the same components as those in FIG. In order to solve the problems of the conventional example in FIG. 1, it is sufficient if there is a method of avoiding a state in which the silicon controlled rectifier element Q1 remains conductive when the effect of the resonance circuits C2 and L3 is increased. This can be achieved by lowering the horizontal free oscillation frequency when the transistor Q3 is turned on. For this purpose, the holding range of the horizontal AFC when the transistor Q3 is turned on is extremely reduced, or if the horizontal AFC circuit is opened, the CRT will become an abnormal screen by only slightly shifting the horizontal free oscillation frequency. I can do it. The resistors R4 and R5 and the transistor Q4 are circuits added according to the present invention.The transistor Q4 has a collector connected to a connection point between the capacitor C6 and the resistor R3, an emitter grounded, and a base connected to the resistors R4 and R5. ing. One end of the resistor R4 is connected to the output terminal of the adding circuit 6. In the above configuration, when the transistor Q3 is turned on, the transistor Q4 is also turned on, and the comparison flyback pulse supplied from the winding L6 of the flyback transformer T1 to the horizontal AFC circuit becomes conductive with the resistor R3. Therefore, it is attenuated and does not enter the circuit 4. Therefore, at this time, the horizontal AFC circuit is open, AFC operation is not performed, AFC has almost no frequency holding range,
An out-of-synchronization state can be created by shifting the horizontal free oscillation frequency a little by about 100 to 200 Hz. To reduce the horizontal free oscillation frequency as described above when the transistor Q3 is turned on, an appropriate resistor R6 may be inserted into the collector of the transistor Q3. In this way, even when the so-called radiation protection circuit operates and shifts the horizontal frequency, this frequency only needs to be one dimension of the regular 15.7 kHz, and it is easy to set it to 17 kHz or less, so that the resonance frequency of the resonance circuits C2 and L3 Can be set lower than the conventional one, which is very effective in eliminating the disadvantageous phenomenon that the silicon control rectifier element Q1 remains conductive when the anode current of the CRT increases. Such an effect is effective even when the power supply voltage increases. That is, when there is no thinning of the anode waveform silicon controlled rectifier Q1, since the anode potential of the silicon controlled rectifier Q1 at the time of tau ₁ of FIG. 3 becomes lower than when there is no resonance circuit L3, C2, silicon It is also highly effective for malfunctions in which the control rectifier Q1 remains conductive. Further, when this configuration is used, the range in which the variations of the circuits 4, C5, R1, C2, L3, etc. are allowed is increased, and the design is easy and the cost is reduced. In this example, the supply path of the comparison pulse was cut to make the horizontal AFC loop open, but the video signal input to the sync separation circuit may be cut off, or the output of the sync separation circuit may be cut off. Is also good. Instead of opening the horizontal AFC loop, the loop gain of the AFC circuit may be sufficiently reduced. Effects of the Invention As described above, according to the present invention, extremely inexpensive, it is possible to eliminate the failure of the television receiver, ease of design,
Also, variations in capacitors C2 and C5, which are expensive parts, integrated circuits, and the like can be widely accepted, and the effect is extremely large. In addition, when the radiation protection circuit is activated, creating an abnormal state at a horizontal frequency that is not significantly different from that during normal operation can create an abnormality under a load condition that is not significantly different from normal, and in this regard, the horizontal output circuit and power supply circuit etc. Reliability is also improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a television receiver according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional television receiver, and FIGS. FIG. 4 is a main part voltage waveform diagram for explaining the operation of FIG. 2. T1: Flyback transformer, 4: Synchronous separation / horizontal oscillation / AFC circuit, 6: Addition circuit, Q2: Horizontal output transistor, Q3, Q4: Transistor, R1: Variable resistor, R
2 to R6: resistor, C1 to C6: capacitor.

Claims (1)

(57) [Claims] First detection means for outputting a detection signal corresponding to the anode current of the cathode ray tube; second detection means for outputting a detection signal corresponding to the anode voltage; and detection outputs from the first and second detection means. Calculating means for outputting a synthesized signal obtained by calculating and synthesizing; detecting an abnormality when a detection output from the first detecting means, a detection output from the second detecting means, or a value of the synthesized signal output becomes a predetermined value or more; Abnormality detection means for outputting a signal, a horizontal oscillation circuit having a switchable oscillation time constant circuit, flyback pulse supply means for supplying a flyback pulse, which is compared in phase with a synchronization signal of a video signal, to an AFC circuit, Supply control means for controlling the flyback pulse supply means with an abnormality detection signal, and switching the time constant of the oscillation time constant circuit with the abnormality detection signal output from the abnormality detection means By making the horizontal oscillation frequency of the horizontal oscillation circuit different from the horizontal synchronization signal of the broadcast signal, and by controlling the flyback pulse supply means by the supply control means to attenuate the flyback pulse, the loop of the AFC circuit is reduced. A television receiver, which is open or reduces the gain of this loop.