JPH0115253Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a protection circuit for remote control television receivers, and in particular aims to prevent damage and deterioration of cathode ray tubes caused by excessive beam current using an inexpensive circuit. be.

In particular, when using a high-brightness cathode ray tube in a sealed state such as in a video projector, or when using an ordinary television receiver without sufficient heat dissipation means, even if it is instantaneous, excessive heat may be generated. When the beam flows, local heating of the phosphor surface may cause cracks, or the phosphor may partially burn off, leading to deterioration or damage to the cathode ray tube.

As a countermeasure against such accidents, a so-called hold-down circuit has been proposed, which detects an increase in the rectified output of the tertiary winding output of the flyback transformer or an excessive beam current, and stops the operation of the horizontal oscillation circuit. In the case of a receiver used under the above-mentioned conditions, there is an undeniable drawback that the response is poor, the reliability is poor, and so-called vertical line burning phenomenon easily occurs, and the circuit thereof is extremely complicated.

The present invention aims to improve the various drawbacks of the conventional example.

The details of the present invention will be described below with reference to a circuit example of a remote control video projector, which is a particularly preferred embodiment.

This circuit diagram is shown as a block diagram except for the main parts, and is roughly divided into a main body block 10 and a remote control block 40 . In the main body block 10 , 11 is a high-intensity cathode ray tube (usually three are provided corresponding to the three primary colors);
2 is a video processing circuit that serves as a light source for the projection optical system and supplies a video signal of a corresponding color to the cathode of each cathode ray tube sealed together with the projection lens; 13 is a deflection circuit for each cathode ray tube; and 14 is a high voltage common to the anode of each cathode ray tube. 15 is the main power supply for the projector main body, 20 is a detection circuit for detecting excessive beam and/or overvoltage, and 30 is a protection device operated by the output of this detection circuit. Shows the circuit.

Among these components, a known configuration can be followed except for the detection circuit 20 and the protection circuit 30 , so a detailed description thereof will be omitted. The detection circuit 20
includes an excessive beam detection circuit 210 and an excessive voltage detection circuit 220, but only the former is sufficient to achieve the main purpose of the present invention.

The excessive beam detection circuit 210 is connected to the main power supply 15.
two series resistors 211, 21 directly connected to the output (+B ₂ ) terminal of
2, a Zener diode 213 that becomes conductive only when the voltage generated at the connection midpoint A of both resistors exceeds a predetermined voltage that indicates an excessive beam, and a switching transistor that becomes conductive by receiving a base current due to the conduction of this diode. 214 and a CR integrator circuit 215 connected to the collector of this transistor, and when the Zener diode 213 detects an excessive beam voltage after a certain period of time, that is, the time when the cathode ray tube is not damaged by the excessive beam, switching is performed. The output of an integrating circuit 215 connected to the collector of transistor 214 produces a constant DC output sufficient to drive the next stage switching transistor. Note that the connection between the point A and the video processing circuit 12 indicates that a so-called ABL circuit (automatic brightness control circuit) is formed.

The overvoltage detection circuit 220 is the same as the deflection circuit 1.
3. Or, if another circuit is provided to independently supply a switching voltage to the flyback transformer, the resistor voltage divider circuit 221 connected between the power supply terminal (+B ₁ ) to that circuit and ground, and this circuit. When the output of the voltage dividing point B exceeds a predetermined value, the Zener diode 222 that detects the overvoltage and the integration circuit 215 are connected in common. generates enough DC output to turn on the switching transistor of

Separately, in order to prevent the detection circuit from inadvertently malfunctioning due to large changes in the beam current or voltage when the brightness level of the video signal or synchronization signal changes widely due to switching of video sources, etc. A capacitor 216 with a relatively large capacity is connected between the collector of the switching transistor 214 and the ground. Resistor 217 is this capacitor 21
This is for discharging the charged charge of No. 6.

In the remote control block 40 , auxiliary power supplies 41 and 42 independent of the main power supply are used for a decoder whose input is the output of a remote control signal receiving means such as an infrared receiver or an ultrasonic microphone.
IC, (for example, ICM manufactured by Mitsubishi Electric Corporation)
58485P), 47 indicates a switching transistor which receives the power switch on/off output of this IC as an input and controls a remote control switch 44 such as a relay or SCR.

The auxiliary power supply 41 rectifies and smoothes the AC voltage supplied from the main switch 50 of the video projector, supplies operating voltage to the IC and remote control switch 44, and also connects the IC to the power outage control terminal 45.
When the main switch 50 is off or there is a power outage, a low level output is applied as an input.

The above IC includes a so-called power outage countermeasure circuit that generates an on/off control output at a power control terminal 46 in response to an input to a power outage control terminal 45 (the power input terminal is shared).

This power outage countermeasure circuit changes the output of the power control terminal 46 of the IC to a low level when the output of the auxiliary power supply 41 becomes zero due to a power outage or the like and the input voltage of the power input terminal 45 functioning as a power outage control terminal becomes 0. Then, the remote control switch 44 (relay in the embodiment) is turned off via the switching transistor 47, and after the power outage is restored, the auxiliary power supply 4 is turned off.
1 is restored, the output of the power control terminal 46 remains at zero until the remote control on signal is detected by the decoder or the main switch 50 is turned on again. .

The protection circuit 30 utilizes the function of such a power failure countermeasure circuit.

That is, the collector of the switching transistor 31 constituting this protection circuit 30 is connected to the power input terminal 45 which also functions as the power outage control terminal of the IC.
The emitter is connected to ground, and the integration circuit 215
When an excessive beam current or excessive voltage is detected, the output of the switching transistor 31 is controlled to conduct as a base input, and the switching transistor 31 is turned on.
By forcibly reducing the voltage of 5 to zero, the function of the above-mentioned power outage countermeasure circuit is utilized, and by turning off the remote control switch 44, all power supply to the video projector body is completely cut off.
Prevents damage and deterioration of cathode ray tubes.

As described above, according to the present invention, a reliable cathode ray tube protection circuit can be realized at low cost by using an existing power failure countermeasure circuit.

In the above description, an embodiment has been described for a video projector, but it goes without saying that the present invention may also be applied to a television receiver equipped with a remote control circuit equipped with a power outage countermeasure circuit.

[Brief explanation of the drawing]

The drawing is a circuit diagram of an implementation of the present invention. 10 ...Main block, 15...Main power supply, 13
... Deflection circuit, 14 ... High voltage circuit, 20 ... Detection circuit, 30 ... Protection circuit, 40 ... Remote control block.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A television receiver equipped with a power outage countermeasure circuit that detects a power outage and turns off a remote control switch, comprising means for detecting beam current exceeding a predetermined value, and the output of this means. A protection circuit for a remote control television receiver configured to operate the power outage countermeasure circuit and turn off the remote control switch. (2) Protection of a remote control television receiver according to claim 1, wherein the terminal whose input is controlled by the output of the detection means is shared with the input terminal of the power outage countermeasure circuit. circuit. (3) A protection circuit for a remote control television receiver according to claims 1 and 2, wherein the television receiver is a video projector equipped with a high-brightness cathode ray tube.