JP3048998U - television - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In some cases, the remaining voltage of a picture tube cannot be completely discharged when power is turned off. SOLUTION: Drive transistors Tr1, Tr
2, Tr3 amplifies and outputs a negative primary color drive signal using the divided output of the resistors R1 to R7 of the power supply Vcc2 as an emitter bias and supplies the amplified signal to the cathode side of the CRT 20, and uses the switching transistor Str when the power is off. When the connection end of the resistor R1 and the resistors R2, R4, and R6 is grounded to lower the emitter bias and discharge the remaining voltage of the CRT 20, the diodes D1, D2, D3
To bypass the resistors R2, R4, and R6.
Television capable of sufficiently discharging the remaining voltage of the television set.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a television that prevents high voltage from remaining on the anode side of a picture tube when the power is turned off.

[0002]

[Prior art]

 Conventionally, as this type of television, a television disclosed in Japanese Patent Application Laid-Open No. Hei 2-323777 shown in FIG. 3 is known. In FIG. 1, a chroma circuit 1 performs signal processing on a signal transmitted from a tuner (not shown) through intermediate frequency amplification and video detection to generate three color difference signals RY, GY, and BY. Are input to the bases of the driving transistors t1, t2, and t3. One ends of resistors r1, r2, and r3 are connected to the emitters of these driving transistors t1, t2, and t3, respectively, and the other ends of the resistors r1, r2, and r3 are connected and output from the Y amplifier 2. Luminance signal is input.

The driving transistors t 1, t 2, and t 3 receive the luminance signal voltages divided by the resistors r 1, r 2, and r 3 on the emitter side, respectively, generate RGB primary color drive signals, and output the signals from the collector side. The cathode side of the CRT 3 is connected to a high voltage circuit 4 including a flyback transformer (not shown) connected to the anode side of the CRT 3 to supply power.

It is conventionally known that a high voltage remains on the anode side of a CRT when the power is turned off, and a switching circuit 5 is provided to discharge such a high voltage. The switching circuit 5 includes a diode d1 having an anode connected between the resistors r1, r2, and r3 and the Y amplifier 2, a switching transistor st having a collector connected to the cathode side of the diode d1, and having a grounded emitter. Consists of

A control signal from the microcomputer 6 is input to the base of the switching transistor st, and the control signal is inverted from a low level to a high level when the power is turned off. Then, the collector-emitter of the switching transistor st conducts, the emitter potentials of the driving transistors t1, t2, and t3 decrease, and the driving transistors t1, t2, and t3 no longer output the primary color drive signal. Although not described above, the drive signal of the same primary color has a negative polarity, and the fact that the drive signal of the same primary color is not output means that the drive transistors t1, t2, and t3 are forcibly operated in the white direction. Therefore, the electron beam is emitted from the cathode side of the CRT 3 to the anode side (the screen shines for a moment), and the high voltage remaining on the anode side of the CRT 3 is discharged.

[0006]

[Problems to be solved by the invention]

 The above-mentioned conventional television has the following problems. Even if the power supply is turned off, the voltage may remain in the resistors r1, r2, and r3 connected to the emitters of the driving transistors t1, t2, and t3, so that the remaining voltage on the anode side of the CRT 3 is sufficiently discharged. There was something I could not do. In particular, this phenomenon appears remarkably when a black image is displayed when the power is turned off. That is, in the case of a negative primary color drive signal, as shown in FIG. 4, the collector potential (primary color drive signal voltage) of the driving transistors t1, t2, and t3 is lower in the white image than in the black image. Therefore, when the power is turned off, the drive transistors t1, t2, and t3 operate on the white side. However, when a black image is originally displayed, the collector potential is reduced when the emitter potential of the drive transistors t1, t2, and t3 remains. It is difficult to lower the potential. For this reason, when the black image is displayed when the power is turned off, the collector potentials of the driving transistors t1, t2, and t3 may be higher than when the white image is displayed. The high voltage on the anode side of the CRT 3 is not discharged and tends to remain.

The present invention has been made in view of the above problems, and has as its object to provide a television capable of reliably discharging a high voltage remaining on the anode side of a picture tube when power is turned off.

[0008]

[Means for Solving the Problems]

 In order to achieve the above object, the invention according to claim 1 is a reverse bias circuit for applying a reverse bias to an emitter of a drive transistor for amplifying and outputting a negative drive signal and supplying the amplified drive signal to a cathode side of a picture tube. A switching transistor that is connected to the emitter of the driving transistor via the same reverse bias circuit and that performs switching operation when the power is off to ground the connection end to the same reverse bias circuit; In some cases, a bypass circuit that bypasses the reverse bias circuit and connects the drive transistor and the connection terminal is provided.

In the invention according to claim 1 configured as described above, when the power is turned on, a reverse bias is applied to the emitter of the drive transistor from the reverse bias circuit, and the drive signal of the negative polarity is amplified. It is output and supplied to the cathode side of the picture tube. Here, when the power supply is turned off, the switching transistor performs a switching operation to ground the connection terminal to the reverse bias circuit. Therefore, the emitter of the driving transistor is grounded through the reverse bias circuit. At this time, the bypass circuit bypasses the reverse bias circuit and connects the driving transistor and the connection terminal. As a result, the reverse bias applied to the emitter of the driving transistor decreases rapidly. Then, no drive signal is output from the drive transistor, and since the drive signal has a negative polarity, an electron beam is emitted from the cathode side of the picture tube to the anode side, and the remaining voltage on the anode side is discharged. Is done.

The reverse bias is a voltage applied in a narrow sense by adjusting a base current to an appropriate value in order to set a desired operating point on an operating characteristic of a transistor. Means the voltage applied in the direction in which no current flows. However, here, the reverse bias is broadly regarded as a voltage for setting the operating point. Therefore, applying a reverse bias to the emitter means setting the operating point of the drive transistor by raising the emitter potential and amplifying and outputting the drive signal.

A general primary-color drive television has drive transistors corresponding to each of the RGB colors. When a reverse bias is applied to each drive transistor, a constant power supply voltage is appropriately divided. In many cases, pressure is supplied. Therefore, as a preferable example in such a case, the invention according to claim 2 is directed to the television according to claim 1, wherein the reverse bias circuit includes a predetermined power supply and a power supply connected in series to the power supply. First, second, and third resistors connected to each other, and a divided output by the first, second, and third resistors is applied as the reverse bias, and the switching transistor includes first and second resistors. The bypass circuit includes a diode connected in parallel with the second resistor with the first resistor side being a cathode and the third resistor side being an anode. There is a configuration.

In the invention according to claim 2 configured as described above, the reverse bias circuit includes first, second, and third resistors connected in series to a predetermined power supply, A voltage divided output by the first, second and third resistors is applied as a reverse bias to the emitter of the driving transistor to amplify and output the drive signal. When the power is turned off here, the switching transistor performs a switching operation as described above. Since the switching transistor is connected between the first and second resistors, the emitter of the driving transistor is grounded via the second resistor. However, since the diode is connected in parallel to the second resistor as described above, and the voltage drop is very small and can be ignored, the driving transistor can be regarded as being directly grounded. Then, the reverse bias of the driving transistor rapidly decreases.

On the other hand, as an example of a specific configuration of the switching transistor, the invention according to claim 3 is the television according to claim 1, wherein the switching transistor has a collector connected to the bypass. An npn-type transistor connected to the circuit side and having the emitter grounded. When the power is turned off, a high-level signal is applied to the base and the collector-emitter connection is made conductive.

[0014] In the invention according to claim 3 configured as described above, the switching transistor is formed of an npn-type transistor whose emitter is grounded, and the signal input to the base of the transistor is turned off when the power is turned off. High level. Then, since the collector-emitter conducts, the driving transistor is bypassed by the bypass circuit and is directly grounded, and the reverse bias is rapidly reduced.

[0015]

[Effect of the invention]

 As described above, the present invention bypasses the reverse bias circuit when the power is turned off, and grounds the emitter of the driving transistor.Therefore, no voltage remains on the emitter side, and the remaining voltage of the picture tube is surely reduced. Can be provided.

Further, according to the present invention, the reverse bias applied to the emitter of the driving transistor can be easily reduced without largely changing the circuit configuration.

Further, according to the present invention, a switching transistor can be easily configured.

[0018]

[Embodiment of the invention]

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a main part of a television according to an embodiment of the present invention. In the figure, a chroma IC 10 is configured by integrating various color signal circuits into one chip, and performs R, G, B conversion of a carrier color signal transmitted from a tuner (not shown) through intermediate frequency amplification and video detection through color signal processing. Outputs primary color drive signal. Here, the output primary color drive signals are input to the bases of the driving transistors Tr1, Tr2, Tr3, respectively.

The driving transistors Tr 1, Tr 2, and Tr 3 are each formed of an npn-type transistor, and amplify the negative-polarity RGB primary color drive signal inputted by increasing the potential on the emitter side and output the amplified signal from the collector side. The amplified primary color drive signal is supplied to the cathode side of the CRT 20. The CRT 20 is connected to a high-voltage circuit 30 having a flyback transformer (not shown) on the anode side and receives power supply, and is driven by a primary color drive signal input to the cathode side.

Here, for example, in the drive transistor Tr1, the power supply Vcc1 is connected to the collector side via a resistor, and the emitter side is connected to the resistors R1, R2, and R3 connected in series to the power supply Vcc2. A partial pressure output is applied. Further, a diode D1 having the resistor R1 side as the cathode side and the resistor R3 side as the anode side is connected in parallel to the resistor R2. In the figure, the electrolytic capacitor C1 is a decoupling capacitor, and the resistor R8 and the capacitor C2 improve the frequency characteristics, but these are not described in detail.

On the other hand, the driving transistors Tr2 and Tr3 also have the same configuration as the driving transistor Tr1, and as shown in the drawing, the output of the driving transistor Tr2 is divided by resistors R1, R4 and R5. And a diode D2 is connected in parallel to the resistor R4. On the other hand, a voltage divided output by the resistors R1, R6 and R7 is added to the emitter of the driving transistor Tr3, and a diode D3 is connected to the resistor R6. Are connected in parallel.

That is, an emitter bias obtained by dividing the voltage of the power supply Vcc2 by the resistors R1 to R7 is applied to the emitters of the driving transistors Tr1, Tr2 and Tr3. Tr 3 amplifies the input primary color drive signal without distortion and outputs it from the collector. Therefore, the power supply Vcc2 and the resistors R1 to R7 connected to the power supply Vcc2 as described above constitute a reverse bias circuit.

The collector of an npn-type switching transistor Str having a grounded emitter is connected between the resistor R1 and the resistors R2, R4, and R6, and the base thereof is connected to a microcomputer 40 connected via a resistor R8. Power control signal is input. The microcomputer 40 includes a remote control signal receiving section (not shown), receives an infrared remote control signal from the remote controller 50, and controls various hardware operations based on the infrared remote control signal. For example, when the power supply is turned off by the remote controller 50, the microcomputer 40 detects and turns off the operation of various circuits such as a horizontal oscillation circuit (not shown), and the power control signal is inverted from a low level to a high level. Invert. These two operations have a certain timing. Note that this inversion time may be short, and may be supplied from a capacitor or the like.

When the oscillation of the horizontal oscillation circuit is turned off, the flyback transformer in the high voltage circuit 30 is subsequently turned off, and the supply voltage from the flyback transformer is turned off. For this reason, even when the voltage is supplied to the anode side of the CRT 20, a period during which the electron beam is not emitted from the cathode side to the anode side occurs slightly. High voltage may remain on the anode side.

As described above, the power control signal output from the microcomputer 40 is inverted to a high level when the power is turned off, so that the collector and the emitter of the switching transistor STr conduct. Then, the emitters of the driving transistors Tr1, Tr2, Tr3 are grounded via the resistors R2, R4, R6, respectively.

However, since the resistors R2, R4 and R6 are bypassed by the diodes D1, D2 and D3, respectively, the emitters of the driving transistors Tr1, Tr2 and Tr3 are directly grounded. Therefore, no voltage remains in the resistors R2, R4, and R6, and the emitter bias of the driving transistors Tr1, Tr2, and Tr3 decreases rapidly. Since the base potential is almost constant, the collector potential decreases rapidly. I do. In this sense, the diodes D1, D2, and D3 connected as described above constitute a bypass circuit.

Since the primary color drive signal here has a negative polarity, a decrease in the collector potential of the driving transistors Tr1, Tr2, Tr3 means that the transistor operates to the white side, and the CRT 20 is driven. An electron beam is emitted from the cathode side to the anode side. Then, the screen of the CRT 20 shines for a moment, and as a result, a high voltage on the anode side is discharged.

FIG. 2 is a timing chart showing the relationship among the collector potential of the driving transistor Tr 1, the potential on the anode side of the CRT 20, and the power control signal as an example of the driving transistor. In the drawing, the dashed line indicates a white image, and the solid line indicates a black image. As is clear from the figure, when the primary color signal is negative, when the white image is compared with the black image, it is easily understood that the latter has a higher collector potential. Then, when the power supply is instructed from the remote controller 50, the power control signal is inverted from the low level to the high level, and the collector potential of the driving transistor Tr1 rapidly decreases as described above.

As described above, the emitter of the driving transistor Tr1 is grounded without intervening a resistor or the like for inducing a residual voltage. Therefore, a white image is displayed when the power is turned off, or a black image is displayed. It converges to almost the same voltage value regardless of whether it was displayed. Accordingly, the voltage on the anode side of the CRT 20 is sufficiently discharged regardless of the white image and the black image.

Next, the operation at the time of power off of the present embodiment configured as described above will be described. When the power is turned on, the chroma IC 10 generates R, G, B primary color signals from the carrier color signal transmitted through the tuner (not shown) through the intermediate frequency amplification and the video detection through the color signal processing. Input to the base of Tr2 and Tr3. Each of the driving transistors Tr1, Tr2, Tr3 is supplied with a divided output obtained by appropriately dividing the voltage of the power supply Vcc2 by resistors R1 to R7 to an emitter, and a primary color signal is input to a base to convert the primary color signal. Amplify and output from collector. The CRT 20 receives power supply from the high voltage circuit 30 on the anode side, and is driven by inputting the amplified primary color drive signal output from the drive transistors Tr1, Tr2, Tr3 to the cathode side.

Here, when the power supply is instructed via the remote controller 50, the microcomputer 40 detects the power off and turns off the oscillation of the horizontal oscillation circuit (not shown), and stops the power supply of the high voltage circuit 30. Then, a period during which the electron beam is not emitted from the cathode side to the anode side while power is supplied to the anode side of the CRT 20 occurs slightly, so that a high voltage remains on the anode side of the CRT 20.

When turning off the power, the microcomputer 40 turns off the horizontal oscillation circuit and the like as described above, and inverts the power control signal input to the base of the switching transistor STr from low level to high level. . These two operations have a certain timing. Then, since the collector-emitter of the switching transistor STr conducts, the emitters of the driving transistors Tr1, Tr2, Tr3 are grounded via the resistors R2, R4, R6, respectively. , D3, the emitter bias decreases rapidly.

Here, since the base potentials of the driving transistors Tr1, Tr2, Tr3 are almost constant, the collector potential drops rapidly (the primary color drive signal is not output). That is, since the primary color drive signal is negative, the drive transistors Tr1, Tr2 and Tr3 operate to the white side, and an electron beam is emitted from the cathode side of the CRT 20 to the anode side, so that the screen shines for a moment. The high voltage remaining on the anode side is discharged.

As described above, the driving transistors Tr 1, Tr 2, and Tr 3 amplify and output the negative primary color drive signal by using the divided voltage output from the resistors R 1 to R 7 of the power supply Vcc 2 as the emitter bias and output the amplified signal to the cathode side of the CRT 20. When the power supply is turned off, the connection end of the resistor R1 and the resistors R2, R4, and R6 is grounded by using the switching transistor Str, and the emitter bias is reduced to discharge the residual voltage of the CRT 20. Since the resistors R2, R4 and R6 are bypassed by D2 and D3, it is possible to provide a television capable of reliably lowering the emitter bias and sufficiently discharging the remaining voltage of the CRT 20.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a television according to an embodiment of the present invention.

FIG. 2 is a timing chart showing changes in various voltage values and a power control signal when the television is turned off.

FIG. 3 is a block diagram showing a main part of a television according to a conventional example.

FIG. 4 is a timing chart showing changes in various voltage values when the television is turned off.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Chroma IC 20 ... CRT 30 ... High voltage circuit 40 ... Microcomputer 50 ... Remote control Tr1, Tr2, Tr3 ... Drive transistor R1-R7 ... Resistance D1, D2, D3 ... Diode Str ... Switching transistor

Claims (3)

[Utility model registration claims] A reverse bias circuit for applying a reverse bias to an emitter of a drive transistor for amplifying and outputting a drive signal of a negative polarity and supplying the amplified drive signal to a cathode side of a picture tube; A switching transistor that is connected with the reverse bias circuit interposed and performs a switching operation when the power is off to ground a connection end to the reverse bias circuit, and a bypass transistor that bypasses the reverse bias circuit when the power is off. A television comprising a drive transistor and a bypass circuit for connecting the connection terminal. 2. The television according to claim 1, wherein the reverse bias circuit includes a predetermined power supply and first, second, and third resistors connected in series to the power supply. The divided voltage by the first, second and third resistors is applied as the reverse bias, the switching transistor is connected between the first and second resistors, and the bypass circuit is connected to the first and second resistors. And a diode connected in parallel to the second resistor using the resistor side as a cathode and the third resistor side as an anode. 3. The television according to claim 1, wherein the switching transistor is an npn-type transistor having a collector connected to the bypass circuit and an emitter grounded. A television, characterized in that a high level signal is sometimes applied to the base to conduct between the collector and the emitter.