JPH0513093Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a reset circuit when an abnormal discharge occurs in a cathode ray tube of a television receiver. In particular, it relates to the reset circuit of a microcomputer built into a television receiver.

[Prior Art] A conventional circuit of this type is shown in FIG. In the figure, 1 is a microcomputer (hereinafter referred to as microcomputer), 2 is a power supply circuit that supplies power to each part of the television receiver, and 3 is a reset circuit. Here, the power applied from the power input terminal is stabilized while generating a predetermined voltage in the power supply circuit 2, and is also supplied to the microcomputer 1.
Here, the microcomputer 1 performs internal control such as volume control, input switching, channel selection, and image quality control within the television receiver. In addition, a reset circuit connected to the power supply circuit 2 monitors the power supply voltage, and releases the reset of the microcomputer 1 if the power supply voltage is within a predetermined voltage when the power is turned on and off.
If the voltage is other than the predetermined voltage, a reset operation is performed.

[Problems with the prior art] Since the conventional reset circuit is configured as described above, it prevents the microcomputer from operating abnormally due to abnormal operation of the power supply voltage when turning on or turning off the power. However, no countermeasures had been taken to prevent the abnormal operation of the microcomputer due to discharge inside the cathode ray tube, which is common in television receivers equipped with cathode ray tubes.

Further, if attention is paid to the countermeasure against discharge in a cathode ray tube, an example shown in FIG. 4 was found. The figure shows a circuit around the microcomputer 1 shown in FIG. 3, where R1-3 is a discharge protection resistor, C is a discharge protection capacitor, and Vcc is a power supply line. In other words, regardless of the reset circuit, insert resistors R1-3 in series with the signal line in each input/output port of the microcontroller, or insert a capacitor C between the power line and ground to prevent abnormal voltage during discharge. It was used to prevent microcontroller malfunctions. Furthermore, when this circuit is mounted on a printed circuit board, measures to prevent discharge have been taken through trial and error in the routing and arrangement of power supplies, ground lines, etc. Therefore, these countermeasures against electric discharge have drawbacks such as an increase in the number of parts, and the countermeasures themselves require know-how and are complicated.

[Purpose of the invention] The present invention was developed to eliminate the above-mentioned drawbacks of the conventional devices. The purpose of this is to prevent abnormal operation of the microcomputer during discharge in the cathode ray tube.

[Example] Hereinafter, an example of this invention will be described based on the drawings. In FIG. 1, parts equivalent to those in FIG. 3 are designated by the same reference numerals, and 5 is a reset circuit that generates a reset signal not only by a trigger from the power supply circuit but also by a trigger from a high voltage detection circuit, which will be described later.
The output of this reset circuit is connected to the reset input terminal of the microcomputer. 6 is a differential circuit, 7 is a high voltage detection circuit, and 8 is a high voltage generation circuit that supplies high voltage to the anode of the cathode ray tube 9.

Next, the operation of this invention will be explained. A high voltage of +kV is normally applied to the anode of the cathode ray tube by the high voltage generating circuit 8. The high voltage detection circuit 7 divides and steps down the high voltage anode voltage, differentiates it by the differentiating circuit 6, and resets it by the reset circuit 5.
Add to. Under normal conditions, a constant bias voltage is applied to the reset circuit because no sudden changes occur in the anode voltage. However, when a discharge occurs within the cathode ray tube between the cathode, anode, focus, etc., the anode voltage drops rapidly. The high voltage detection circuit 7 detects this change and the next stage differentiation circuit 6
to be transmitted. The differentiating circuit 6 differentiates the sudden change, converts it into a signal with a predetermined pulse width corresponding to this change, and applies it to the reset circuit 5. Therefore, the microcomputer 1 is reset by a reset signal from the reset circuit 5, and is refreshed within the range controlled by the microcomputer 1. Therefore, even if an unpredictable discharge occurs and there is no discharge protection element around the microcomputer, the microcomputer can be reset without malfunctioning and safety can be guaranteed.

Further, a more specific embodiment according to FIG. 1 is shown in FIG. Components equivalent to those in FIG. 1 are designated by the same reference numerals. Here, the anode voltage is divided by a high resistance R4 of several hundreds of Mohms and a variable resistance R5 and applied to the base of the PNP transistor Q1. The collector of transistor Q1 is connected to the base of NPN transistor Q2, and the emitter of transistor Q2 is connected to ground. The emitter of transistor Q1 and the collector of transistor Q2 are both connected to power supply Vcc through a load resistor R8. Therefore, the output of this high voltage detection circuit 8 is a high voltage during normal times, and changes to a low voltage during discharge.
This change in output is caused by the time constant R6 of the differentiating circuit 6,
C1 results in a low pulse for a predetermined time. When this pulse is applied to a reset circuit 5 including a transistor Q4 and a capacitor C2, a reset signal corresponding to the pulse width is generated, so that the microcomputer 1 is maintained in a reset state during discharging. So microcontroller 1
The related control system will be reset.

Therefore, the abnormally large current and changing voltage generated by the discharge inside the cathode ray tube will cause the microcomputer to malfunction and go into a runaway state, so if a reset operation is performed during or immediately after the discharge, the microcomputer and its system will malfunction. can be prevented.

[Effects of the invention] As described above, according to this invention, the high voltage detection circuit, differentiator circuit, reset circuit, etc. are configured to operate so that the reset operation occurs simultaneously with the discharge in the cathode ray tube. This eliminates the need for protective elements for each port, making it possible to drastically reduce the number of parts. Furthermore, the know-how technique that requires trial-and-error examination of printed circuit board patterns, which was conventionally necessary, is no longer required, and the labor and cost required for countermeasures against electric discharge can be significantly reduced, which is extremely useful.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a schematic circuit diagram that is a more specific version of FIG. 1, FIG. 3 is a conventional reset circuit diagram, and FIG. 4 is a conventional circuit diagram for countermeasures against discharge. 1... Microcomputer, 2... Power supply circuit, 3... Reset circuit, 6... Differential circuit, 7...
...High voltage detection circuit.

Claims (1)

[Scope of utility model registration request] In a discharge countermeasure circuit for a television receiver equipped with a cathode ray tube and controlled by a microcomputer, a high voltage detection circuit detects a change in the anode voltage of the cathode ray tube by a voltage dividing resistor connected between the anode and ground; a differentiating circuit connected to the output of the high voltage detection circuit and generating a pulse of a predetermined time; and a reset circuit connected to the output of the differentiating circuit, supplied with the pulse, and applying a reset pulse to the reset terminal of the microcomputer. A discharge countermeasure circuit for a television receiver, characterized by comprising: