KR100214103B1 - Shutdown system in a television receiver - Google Patents

Abstract

On a television receiver. Voltages applied to loudspeakers 40 and 42 at audio amplifiers 48 and 50 are low pass filtered and coupled to threshold detector 52. Normal audio is attenuated to prevent the detector from tripping. Normal DC is passed through the filter to trip the detector. The detector 50 output is coupled to the X-ray protection circuits 26, 60, 62 of the receiver which turn off the receiver.

Description

Stop system of television receiver

1 is a block diagram of a conventional television receiver in which the present invention can be used.

2 is a block diagram of an apparatus according to the invention.

3 is a low pass filter of a second device according to another embodiment of the present invention. Schematic diagram of a fault detector and a shut-down actuator.

* Explanation of symbols for main parts of the drawings

18: detector 22: video processor

26. Audio Processor 32. 34: Channel Processor

[background]

The present invention relates to a protection circuit of a load. In particular it relates to a protection circuit for a load DC coupled to the output of a push-pull class AB or class B amplifier powered from a split voltage.

Conventional amplifiers useful in audio systems that do not use an output transformer are arranged in a push-pull amplifier structure with a pair of transistors at the output connected in series across a single voltage power supply in a totem pole configuration. in this case. The output signal is fed to a loudspeaker coupled between the junction of the output transistor pair and ground through a relatively large coupling capacitor. Coupling capacitors are for consumer products. Usually it is an electrolytic capacitor. This output coupling capacitor prevents the DC voltage at the output transistor junction, which is about half of the power supply voltage on ground, from being applied to the loudspeaker. But. Low frequency audio signals, such as bass signals, are nearly attenuated by coupling capacitors. It is not played by the loudspeaker. Also. Such a capacitor is a so-called non-polarization electrolytic capacitor which prevents high frequency signals from being attenuated by the inductive reactance caused by the internal coil windings of the capacitor plate. These nonpolarized electrolytic capacitors are larger than standard polarized electrolytic capacitors for comparable values of voltage rating and capacitance. It is also expensive.

An alternative approach to eliminating the aforementioned deficiencies for output coupled capacitors is to use a split voltage power supply having the same plus and minus supply voltages for ground. In this case, the output transistors are also connected in series with each other across the entire power supply. However, this structure allows the bias of the output transistor to be adjusted to maintain the junction of the transistor at the DC ground potential. Likewise. Both sides of the loudspeaker are at the same DC potential of ground. Since the loudspeaker does not accept any DC voltage, it can be connected directly between the junction of the transistor and ground which do not require an output coupling capacitor. therefore. Coupling capacitors can be removed. Very low bass frequency audio signals can be coupled to loudspeakers with little attenuation. The latter feature is very important in high power audio systems with larger loudspeakers with improved reproduction of bass frequency signals.

One risk of connecting the loudspeaker directly to the output amplifier transistor junction is that if the amplifier fails, a DC voltage can be applied to the output terminals and the loudspeaker. In a typical single voltage power supply system. If the output coupling capacitor itself is not broken, the output coupling capacitor. It will block this faulty DC voltage from the loudspeaker. In any case, this output DC voltage can damage the loudspeaker.

Some prior art amplifiers provide fuses in series or between and in series with the loudspeaker to protect against excessive current in the loudspeaker due to the DC voltage or between the output transistor and the power supply. However, because the fuse also carries the signal current, it is difficult to size the fuse properly. The fuse may blow even if it is not in a fault condition. Also. Fast-acting fuses will often not operate at a sufficient speed to protect the output transistors from damage.

Another method is to use a DC detector circuit that detects a failure before the damage occurs that connects the DC voltage to the loudspeaker causing the amplifier to stop. One such detector is disclosed in US Patent No. 4.010.402 to Miyata. Such a circuit is provided with a lowpass filter to drive a threshold detector that operates a relay or silicon controlled rectifier (SCR) that either disconnects or shunts the loudspeaker.

Often, various safety mechanisms are provided on television receivers. Detecting insecure conditions takes several steps. When a microprocessor is used. The microprocessor can be programmed to shut down the primary power supply and to turn on the receiver again after a certain time. If a fault is still detected after a certain number of attempts. The microprocessor then keeps the receiver off. Optionally, the safety circuit can turn off the receiver. Keep the receiver off when detecting faults. The latter form of the circuit is used in the TX-81 chassis of the French poop. Especially. Its chassis has a horizontal deflection circuit. Especially when the failure of the capacitor of the deflection part, if the failure is tolerated, can cause damage. An X-ray protection circuit is provided that is operative to stop the horizontal output transistor. The stopping of this horizontal deflection circuit stops the secondary power supply which is powered from the flyback transformer. From the TX-81 chassis. The secondary power supply supplies power to the minimum vertical deflection and audio section. Circuitry for such a TX-81 chassis is disclosed in RCA Patent Document No. 85,758, filed under British Provisional Application No. 8.927.103.3.

[Overview of invention]

In short, the present invention relates to a stop system responsive to fault detection in an audio power amplifier of a television system. A stop system with a protection circuit used to protect damage from other faults. In a preferred embodiment. The voltage applied from the audio amplifier to the loudspeaker is coupled to the low pass filtered DC detector and coupled to the threshold detector. Normal audio is attenuated to prevent interference with the detector. Normal DC is passed through the filter. Interfere with the detector. The detector output is coupled to the X-ray protection circuit of the receiver which stops the receiver off when an audio fault is detected.

after. For a more detailed description of the invention will be described with reference to the accompanying drawings.

1 shows a conventional television receiver device.

antenna. Cable system. Satellite communication receiver. A television RF signal provided to a source such as a VCR or the like is received at the input terminal 12 and the received signal is tunably selected and heterodyne using a local oscillator (not shown) and a mixer that generates an IF signal at the output 16. do. The IF signal is coupled to an IF processor and detector 18 which generates a baseband video signal coupled to video processor 22 via output 20 and an audio signal coupled to audio processor 26 via output 24. do. Video processor 22 is luminance. Including saturation and synchronization processing circuitry. Generate a color video signal that is coupled to the CRT 30 via an output 28. The horizontal (H) and vertical synchronization signals generated by the video processor (22) are deflected and high voltage portions (23) that generate horizontal (H) and vertical (V) deflection signals and alternate supply voltages of the CRT (30). ) Is combined. The audio processor (26) is for amplification and processing by each audio channel processor (32, 34) including each power amplifier (48.50) as shown in FIG. Left at (29,31). The audio component included in the detected audio signal is detected, amplified and matrixed in the portion 18 providing the right channel audio signal. Signals from processors 32 and 34 are coupled to respective loudspeakers 40 and 42 via outputs 36 and 38. Power supply 44 provides various power supply voltages, indicated at 46, to receive power from a suitable power source, such as an AC power source or a battery (not shown), and to power the various set components described above. . The controller 62 based on the microprocessor controls various parts of the television receiver, such as the tuner 14 and the power supply 44.

The deflection and high voltage section 23 built into the video section 29 is a possible unsafe condition occurring in the receiver. That is, they are typically found on television sets to protect against excessive kinescope beam current or excessive kinescope alternating voltage, which can cause X-ray generation beyond the permitted safe range when electrons in the scanning beam hit the shadow mask and faceplate. It includes an X-ray protection circuit. The normal procedure of operation upon detection of this condition is to stop (shunt down) the horizontal deflection circuit providing power to the flyback circuit from which the alternating voltage is derived. As an alternative. As shown in FIG. The power supply can be stopped by stopping the entire receiver including the horizontal deflection circuit. Using a microprocessor. Selective measures are taken by stopping only certain selection circuits or primary or secondary power supply units. Suitable X-ray protection circuitry is disclosed in US Pat. No. 4.641,064 for Testin's television power supply stop circuit.

As shown in FIG. 1, in response to detection of a condition causing X-ray generation. The X-ray protection circuit of the deflection and high voltage portion 23 generates each signal indicated by XRP in FIG. The XRP signal is coupled to a microprocessor controller 62 programmed to couple an off command to the power supply 44 in a preferred embodiment.

therefore. The water phase is turned off and the generation of potentially harmful X-rays is prevented.

In the television receiver shown in FIG. The additional use of the X-ray protection device is made to protect the left and right loudspeakers 40 and 42 from the form of DC failure associated with the failure of the power amplifiers 48 and 50 in the left and right audio signal channel processors 32 and 34. . Especially. The DC detector and output (L DC fault and R DC fault) signals in the processors 32,34 are ORs represented by an OR gate 63 at any input of the microprocessor controller 62 as an X-ray protection signal (XRP). Coupled by a function circuit. therefore. If a DC fault is detected in the power amplifier of both audio signal channel processors 32,34. The power supply 44 will be off so that one loudspeaker 40, 42 will be protected. Aspects of the receiver shown in FIG. 1 will be described in more detail with respect to FIGS. 2 and 3.

FIG. 2 is a detailed block diagram of the television receiver section shown in FIG. 1 particularly relevant to the present invention. A configuration for one of the audio signal processors 32,34 is shown and described. Similar devices are used in other processors. Power supply 44 supplies positive and negative power supply voltages to left and right stereo power amplifiers 48 and 50 with respect to ground via lines 46b and 46a.

The power supply 44 described in connection with the audio power amplifier is a display power supply. For example, it consists of a primary power supply or a secondary power supply derived from a primary power supply or flyback transformer. The power amplifiers 48 and 50 have loudspeakers 40 and 42 which are DC coupled between the junction of the output transistors and ground and complementary output transistors connected in series across the positive and negative power supply voltages. This is shown in FIG. This will be described later in more detail. The signal coupled to the loudspeakers 40 and 42 is also coupled to a failure detector 52 consisting of a low pass filter 54 and a threshold detector 56.

The normal audio signal coupled to the loudspeakers 40 and 42 is attenuated in the low pass filter 54 such that the detector is not disturbed (triggered) by the normal audio signal. But if the normal DC voltage is above or below a certain threshold. The normal DC signal through the filter and detector 56 will be activated. When the output signal from detector 56 is coupled to the base electrode of transistor 58, the output signal of detector 56 is coupled to transistor 58 so that the collector electrode is low.

Transistor 60 is the output of the X-ray protection circuit 25 of the deflection and high voltage portion 23. 60 is conducted in response to a parameter indicative of the generation of transient X-rays. The appropriate signal input of the microprocessor 62 goes low with the collector electrode of the transistor 60 going low. As mentioned above. In a typical embodiment. The microprocessor 62 is programmed to stop the power supply 44. As shown in FIG. The collector electrode of transistor 58 determines that the low signal from transistor 58 is an X-ray protection fault. Microprocessor 62 generates excessive X-rays. That is, coupled to the input signal line of the microprocessor 62 to operate to take programmed measures that are protected against power supply 44 off. therefore. Power supply voltages + Vb and -Vb are removed from power amplifiers 48 and 50.

In FIG. 3 a schematic of the fault detector 52 is shown. The complementary audio power output transistors 64 (NPN) and 66 (PNP) of the power amplifiers 48 and 50 are provided with a positive voltage (+ Vb) power supply terminal 46b and a negative voltage (-Vb) power supply. It has an emitter and a collector electrode coupled to the device terminal 46a. The power amplifiers 48 and 50 can be combined with integrated circuits such as the UPC1188H available from NEC Corporation of Japan. Optionally. Discrete devices can be used. When discrete output transistors are used, it is not common for thermally stable components, such as resistors, to be inserted into the emitter circuit of the discrete device.

Loudspeakers 40 and 42 are coupled between the junction 68 of the emitter electrode and ground. The steady state voltage generated at junction 68 is a voltage between positive supply voltage + Vb (e.g. +12 volts) and negative supply voltage -Vb (e.g. -12 volts). Ideally. If transistors 64 and 64 are properly matched and biased. Terminal 68 has a stop voltage of 0 volts relative to ground. There is no DC current flowing through the loudspeakers 40 and 42. But. Transistors 64 and 66 are either fully biased at their base electrodes or are not fully matched in dynamic range so that nominal or relatively small DC current flows through loudspeakers 40 and 42. The fault detector 52 has two input terminals 70 and 72 for each channel. The combination of the DC voltage and the signal appearing at each input terminal 70, 72 is coupled to a low pass filter 74, 76 consisting of resistors 78, 80 and capacitors 82, 84. In a preferred embodiment. The resistors (78,80) are 220 kiloohms and the capacitors (82,84) are 4.7 microfarads. This is to ensure that the cross-over frequency is below 20 Hz. A junction 83 between the resistor 78 and the capacitor 82. Junction 85 between resistor 80 and capacitor 84 includes resistors 79, 81 and 220 selected so that 83 and 85 are about + Vb / 2 on ground or +6 volts on ground in the preferred embodiment. Kiloohms) to the power supply terminal 46b. Any vise current coupled back to the loudspeakers 40,42 from the junction 83,85 to the resistors 22,85 is greater than the 8 ohm resistivity of the loudspeakers 40,42 so as to be negligible. . Resistors 71 and 73 shunt loudspeakers 40 and 42 to ground to provide DC return to ground for input terminals 70 and 72 in the absence of loudspeakers 40 and 42. The resistance of resistors 71 and 73 is greater than the internal DC resistance of loudspeakers 40 and 42, for example a 32 ohm DC resistor for loudspeakers rated at 8 ohms, so that the operation of the circuit does not change.

The low pass filter signals from input terminals 70 and 72 are coupled to transistors 86 and 90 of one channel and transistors 86 and 90 of paired transistors 88 and 92 for the other channel. 88,92 to a base electrode of a complementary pair. The emitter electrodes of transistors 86, 88, 90 and 92 are +6 volts (junctions 83 and 85) by voltage divider resistors 96 and 98 coupled between the positive supply voltage + Vb of terminal 46b and ground. Are coupled together at a common terminal 94 at the same voltage). As such, the base electrodes of NPN transistors 86,88 and PNP transistors 90,92 are placed at +6 volts by voltage dividers 79,78 and 81,80, respectively. The emitter electrode is placed at +6 volts by the voltage divider resistors 96 and 98. If at one of the junctions 83,85 the voltage rises above Vbe (0.7 volts) of the NPN transistors 86,88, the conduction threshold of each transistor 86,88 is exceeded. The transistor becomes conductive. equally. If the voltage at one of the junctions 83,85 is lowered by Vbe (0.7 volts) of the PNP transistors 90,92, then the conduction threshold of each transistor is exceeded. The transistor becomes conductive. But. Because resistors 78,79 and resistors 80,81 form a 2: 1 voltage divider for the DC voltage at each terminal 70,72. Each transistor starts to conduct with a change of 1.4 volts in each direction.

The resistors 78 and 79 in combination with the capacitor 82 and the resistors 80 and 81 in combination with the capacitor 84 are shown at the junctions (83, 85) that are joined to each junction to conduct in the manner described above. Charge time constant is provided for the DC junction of 70,72). This is desirable to prevent the circuit from falsely indicating a failure by not responding to a transient DC transition.

The collector electrodes of the NPN transistors 86, 88 of the two channels 32, 34 are connected together by a junction 102 to a junction 100, which is coupled to a positive power supply source line 46b. equally. The two channels of PNP transistors 90 and 92 have collector electrodes connected together at junction 104 and are connected to ground via resistor 106. At junction 100, the signal is coupled to the base electrode of transistor 108 via resistor 110. The emitter electrode of transistor 108 is coupled to power supply voltage + Vb at terminal 46b and the collector electrode is coupled to junction 104 by resistor 112.

When the NPN transistors 86 and 88 detect a forward progress fault at each of the junctions 70 and 72, the voltage is lowered at the junction 100 (smaller constant voltage). When the PNP transistors 90 and 92 detect a negative progression failure at each of the junctions 70 and 72, the voltage is higher at the junction 104 (many constant voltages). The phase inversion PNP transistor 108 is included to change the fault indication voltage change of the PNP transistors 86 and 88 so that all fault indications for both detection portions are the same. Like this. All fault indication voltages at junctions 70 and 72 result in voltage rises at junction 104, whether positive or negative.

In FIG. The X-ray protection circuit of the television receiver is designed to go low when a fault is detected. therefore. The detector output shown in FIG. 3 should go low upon failure detection for compatibility. Because the voltage at junction 104 goes high upon failure detection. Phase inverter transistor 58 is used. An output signal indicative of a fault detected in the audio system, in which a fault indication voltage change at junction 104 is coupled to the base electrode of transistor 58 via resistor 116 and outputs series resistor 120 and shunt resistor 122. A network comprising a is coupled to the bus 118 (FIG. 2) at the collector electrode of the transistor 58 via.

As mentioned above. In a preferred embodiment. The ratio of the divider resistors 78 and 79 to the resistors 80 and 81 is 2: 1 so that half of the same or positive power supply voltage appears at the junctions 83 and 85. As such, the voltage at junction 94 provided by voltage divider resistors 96 and 98 corresponds to the voltage at junction 83 and 85. This correspondence between both voltage divider voltages can be used to adjust the amount of DC voltage required at junctions 70 and 72 to indicate sensitivity or failure. For example. The divider ratio is the ratio at which resistor 78 doubles the value of resistor 79. Any change in the fault voltage at terminal 70 is divided into 1/3. 2.1 volts DC is required across loudspeaker 40 to translate to a change of 0.7 volts at junction 83. But. DC junction voltage at junction 83 is 12 volts + Vb or 2/3 of 8.0 volts. in this case. At junction 94 the voltage is set to 8.0 volts.

As the voltages at junctions 83, 85 and 94 become equal. Positive and negative fault voltages across loudspeakers 40 and 42 are symmetric in each direction. Complete Vbe conducts faults. It should be generated in the direction of each transistor to be detected. But. If the voltage of the junction 94 is below the voltage of the junction 83. The voltage of the threshold voltage part is supplied. It is necessary that no voltage increase occur at junction 83 to detect the occurrence. sure. In this case, the threshold voltage of the PNP transistor is increased and there is a loss of symmetry. But. Critical symmetry for plus and minus fault voltages can be maintained by cascading forward poled diodes or zener diodes in series with the emitter electrodes of transistors 86,88,90,92. The threshold voltage required for detection can be changed in the same way. This change in threshold can be adjusted to change in the ratio of the potentiometers 78,79 and 80,82.

Claims (13)

Video units 22, 23, and 30 for processing video signals. Audio sections 26, 32, 34 for processing audio signals; Means (26,32,34,48,50) for amplifying an audio signal to drive a loudspeaker embedded in said audio portion. First detecting means (25) for detecting a malfunction in said video portion; To the video sections 22, 23, 30 and the audio sections 26, 32, 34, comprising means 60, 62, 63 for stopping (shunting down) at least a portion of the video section in response to the failure detection of the video section. A television system having at least one power supply device 44 for supplying an operating voltage 46, comprising: second detection means 52 for detecting a failure of the amplifying means, and failure detection by the second detection means. Means (58) for operating means (62,63) for responding (down) in response. The method of claim 1. The video section comprises means (23) for generating a high voltage in the picture tube. The first detection means (25) is coupled to the high voltage generating means. The method of claim 2. And said first detecting means (25) comprises means for detecting a condition corresponding to excessive X-ray generation. The method of claim 2. Stop means turn off one power supply 44 at the time of video fault detection. Then turn on the power unit for a period of time to test if the fault still exists. And a controller (62) for stopping the attempt to turn on again if there is still a failure. The method of claim 2. The second detection means (52) comprises a low pass filter (54) and a threshold detector (56). The method of claim 2. Said second detecting means comprises a DC detector (54) coupled to the loudspeaker. The method of claim 1. The audio portion includes a plurality of channels. Said amplification means (26,32,34,48,50) comprise a plurality of amplifier means for one channel. The second detection means 52 comprise a plurality of detector means for one channel. Each multiple detector has an input coupled to each channel and output. Stop system of a television receiver, characterized in that it has an output coupled to the actuating means. Video units 22, 23, and 30 for processing video signals. Audio sections 26, 32, and 34 for processing audio signals; Means (26,32,34,48,50) for amplifying an audio signal to drive a loudspeaker embedded in said audio portion. First means (25) for detecting a failure of the video portion; Means (60, 62, 63) for stopping at least a portion of the video portion in response to a failure detection of the video portion. This stop means comprises X-ray protection means 25, 60 connected to a microprocessor 62 coupled to at least one power supply 44 of the receiver. The microprocessor 62 turns on the receiver for a predetermined time to determine whether the failure still exists upon detection of a video system failure. If there is still a fault, the television system is provided with at least one power supply 44 for supplying an operating voltage to the video and audio sections comprising the stop means 60, 62, 63 to stop attempting to turn on the receiver. In. Second detecting means (52) for detecting a failure of the amplifying means (26, 32, 34, 48, 50). Means (58) for operating stop means (62,63) in response to a failure detection of said second detection means (52). A separate input connected to each audio channel for detecting a failure of each audio channel. A detection system for detecting a failure of one of a plurality of audio channels comprising a plurality of sensing devices (52) having an output (118) in which an output signal indicative of a failure is generated. Power supply means (44) for supplying operating power to each said audio channel; In means 62.63 for stopping the power supply means in response to an output signal 118 indicating a failure detected by one of the plurality of sensing devices, the output signal is coupled in parallel with the stopping means. And said stop means. Video units 22, 23, and 30 for processing video signals. Audio sections 26, 32, and 34 for processing audio signals; 10. A television system comprising at least one power supply (44) for supplying an operating voltage to said video and audio sections. Means (26,32,34,48,50) comprising a low pass filter (54) and threshold voltage detection means (56) for amplifying an audio signal to drive a loudspeaker embedded in the audio portion. First detection means (25,60) for detecting a failure of said video portion; Means (62,63) coupled to at least one of said power supplies for stopping at least a portion of the video portion in response to a failure detection of the video portion. Second detecting means (54,56) for detecting a failure of the amplifying means; And means (58) for operating the stop means (62) in response to the detection of said second detection means (54, 56). The method of claim 10. And said second detecting means (54,56) comprises means for adjusting a threshold at which a fault is detected. The method of claim 10. And adjustment means for adjusting the threshold at which a failure is detected is coupled to the low pass filter (54). Video units 22, 23, and 30 for processing video signals. Audio sections 26, 32, and 34 for processing audio signals; Means (26,32,34,48,50) for amplifying an audio signal to drive a loudspeaker embedded in said audio portion. First means (25) for detecting a failure of the video portion; Operation in the video and audio section, comprising means (62, 63) coupled to at least one of the power supplies (44) for stopping at least a portion of the video sections (22, 23, 30) in response to a failure detection of the video section. A television system having at least one power supply 44 for supplying a voltage. Detect failure of the amplification means. A low pass filter (54) consisting of series resistors (78, 80) and shunt capacitors (82, 84). Bias means 81,79. In a second detection means (52) comprising threshold voltage means consisting of a series resistor (79,80) and a semiconductor device (88) having a conduction threshold. The series resistors (78, 80). The shunt capacitors (82,84) and the biasing means (81,79) determine the time of a predetermined period period. The series resistors (78, 80). And said bias means (81,79) provide said means for adjusting the sensitivity to a threshold of the failure to be detected. And means for operating said stop means in response to a failure detection by said second detection means.