JP2519356Y2 - Overvoltage and overload protection circuit for TV receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an improvement of a protection circuit for a power supply device equipped in a television receiver.

(Prior Art) In a television receiver, a flyback transformer (31), a horizontal output circuit (38) and a hold-down circuit (35) are provided as shown in FIG. 1 in order to supply a high voltage to the cathode of a cathode ray tube. ) Is equipped with a horizontal deflection circuit (3), and an AC rectifier circuit (22) and a power supply circuit (2) including a voltage stabilizing circuit (23) are connected to the circuit (3).
The horizontal output circuit (38) includes a horizontal oscillation circuit (32), a horizontal drive circuit (33), a horizontal output transistor (34), a resonance capacitor (30) and a horizontal deflection coil (36), and a flyback generated by resonance. The pulse is boosted by the flyback transformer (31), and the high-voltage pulse obtained by this is rectified and supplied to the cathode of the cathode ray tube.

For example, if the supply voltage B connected to the primary winding of the flyback transformer (31) rises and exceeds the rated value due to a malfunction of the voltage stabilizing circuit (23), the hold-down circuit (35) Operates to stop the horizontal output circuit (38). As a result, the load of the power supply circuit (2) becomes lighter, the supply voltage B further rises, and there is a risk that electronic components of the secondary side circuit will be destroyed. Further, if the horizontal deflection circuit (3) is short-circuited for some reason or the load impedance is drastically reduced, the current will be concentrated in the lower portion of the load impedance, which may cause heat generation or printed circuit board burnout. become.

Therefore, conventionally, as shown in FIG. 4, an auxiliary winding (25) is arranged in a converter transformer (24) in a power supply circuit (2), and an overvoltage protection circuit utilizing the drooping characteristic of a switching control type power supply circuit. (71) and overload protection circuit (72)
Is equipped with a power supply protection circuit (7), and when an overvoltage or an overload occurs, this is detected by the auxiliary winding (25) and the operation of the power supply circuit (2) is stopped.

(Problems to be solved) However, in the conventional circuit, the overvoltage protection circuit (71) and the overload protection circuit (7) composed of a relatively large number of electronic components are used.
Since 2) and 2) are provided separately, the whole circuit becomes complicated, and there is a problem that the device becomes large and the cost increases.

(Means for Solving Problems) An object of the present invention is to provide a protection circuit which has higher output voltage detection accuracy than the conventional one and has a simple structure.

The overvoltage and overload protection circuit according to the present invention has a protection function against an overvoltage of a hold-down circuit (35) which is usually equipped to regulate the amount of X-rays generated from a cathode ray tube.
The control function of the electronic tuning unit (1) including a microcomputer is used for the protection operation to simplify the circuit configuration.

That is, the protection circuit of the present invention provides the horizontal deflection circuit (3) with a horizontal output circuit (38) when the peak value of the flyback pulse obtained from the flyback transformer (31) exceeds a predetermined value.
Equipped with a hold-down circuit (35) that stops the operation of the, to detect the occurrence of overvoltage.

In addition, an output detector that generates an output detection voltage LB according to the input voltage to the flyback transformer (31) is provided in the flyback transformer (31), so that the output detection based on the operation of the hold-down circuit is performed. When the voltage LB drops,
A decrease in output detection voltage LB due to the occurrence of overload is detected.

The output detection voltage LB is supplied to the flyback transformer (31).
To the key signal input terminal of the electronic tuning unit (1) via the control circuit (4) that creates a protection key signal when the amount of decrease in the output detection voltage LB due to the decrease in input voltage to the Connecting.

The electronic tuning unit (1) is provided with a signal processing unit that creates a power stop signal based on the protection key signal, and the power stop signal is sent to the power circuit (2) and the power circuit (2). Stop the operation of.

(Operation) During normal operation The electronic tuning unit (1) determines whether or not a key signal generated by various key operations such as volume adjustment and reception channel switching is input, and also whether or not a protection key signal is input. Repeat a series of processing.

During normal operation, the protection key signal is not input, so the power supply circuit (2) does not stop operating.

When overvoltage occurs When the supply voltage B output from the power supply circuit (2) exceeds the rated value, the peak value of the flyback pulse obtained from the flyback transformer (31) exceeds a predetermined value, which causes the holddown circuit (35). ) Operates to stop the switching operation of the horizontal output circuit (38).

As a result, the level of the output detection voltage LB obtained from the output detector drops and falls below a predetermined value, and the protection key control circuit (4) creates a protection key signal.

The protection key signal is sent to the electronic tuning unit (1), whereby the signal processing unit of the electronic tuning unit (1) creates a power supply stop signal and stops the operation of the power supply circuit (2).

When overload occurs When the output current of the flyback transformer (31) increases or the input current to the flyback transformer increases due to an abnormality in the horizontal deflection circuit (3), the supply voltage B of the power supply circuit (2) droops. The output detection voltage LB falls below the rated value due to the characteristics.

As a result, the protection key control circuit (4) creates a protection key signal.

The protection key signal is sent to the electronic tuning unit (1), which causes the electronic tuning unit (1) to generate a power supply stop signal and stop the operation of the power supply circuit (2).

(Effect of the Invention) In the present invention, by providing a signal processing unit in the electronic tuning unit (1), a program to be set in the microcomputer constituting the electronic tuning unit (1) is partially modified to provide a protection key. This can be done very easily by inserting a procedure for creating a power stop signal from a signal.

Therefore, the protection circuit according to the present invention has a simpler circuit configuration than the conventional circuit.

(Embodiment) FIG. 1 shows an embodiment of a protection circuit according to the present invention.

The electronic tuning unit (1) is a tuning 4-bit microcomputer including a CPU, RAM, ROM, counter, input / output port (for example, M504 manufactured by Mitsubishi Electric Corporation).
39-520SP), the key matrix (5) is connected to the input / output port, and the control signal for the tuner (8) is created from the key signal based on the key operation according to the program written in the ROM. The procedure is repeatedly executed at a cycle of approximately 8 msec.

In the key matrix (5), a plurality of operation keys (50) such as a channel switching key and a volume adjusting key are set, and a pair of input / output signal lines (51) (not used to configure the operation keys The emitter and collector of a transistor (42) provided in a protection key control circuit (4) described later are connected to 52).

The AC rectifier circuit (22) in the power circuit (2) has a power relay (2
Equipped with 1).

Further, the flyback transformer (31) is provided with a holddown winding (61) for detecting the flyback pulse FP, and holds the supply voltage B of the power supply circuit (2) and the flyback pulse FP. Connect to (35).

The hold-down circuit (35) is a circuit having a simple structure including, for example, a hold circuit (37) including an SCR element as shown in FIG. 3, and the supply voltage B or the flyback pulse FP has a predetermined value. When it exceeds, the operation of the horizontal oscillation circuit (32) is stopped, and the amount of X-rays generated from the cathode ray tube is maintained below a specified value.

On the secondary side of the flyback transformer (31), the LB detection winding (6) that generates the power supply for the signal circuit and serves as an output detector is installed, and the output signal of the LB detection winding (6) is rectified. Then, it is converted into an output detection voltage LB and sent to a protection key control circuit (4) described later. As a result, the output detection voltage LB has a level proportional to the supply voltage B with the ratio of the number of turns of the primary winding of the flyback transformer (31) and the number of turns of the LB detection winding (6) as a proportional constant. It becomes a DC signal.

The protection key control circuit (4) includes first and second transistors (41) and (42) that are turned on when the output detection voltage LB falls below a predetermined value, and the second transistor (42) is turned on. As a result, a protection key signal is generated and input to the electronic tuning unit (1).

The program shown in FIG. 2 is written in the ROM of the microcomputer constituting the electronic tuning unit (1).

When the television receiver is powered on, the microcomputer first determines whether or not each key of the key matrix has been operated (9), and if there is a key operation, creates a control signal according to the key operation. , Control the tuner (91).

When there is no key operation and after the control signal is sent, it is judged whether or not the protection key signal is input from the protection key control circuit (4) (92). If there is no input, the hexadecimal counter is used. Procedure for resetting the checked counter and judging the presence / absence of the key operation (9)
Return to In addition, the check counter will count up 1
If it is repeated for a second, it will overflow.

When the protection key signal is input, the check counter is counted up (94), and then it is determined whether the check counter overflows (95). If the overflow does not occur, the protection key signal generation time is less than 1 second, and there is a possibility that the protection key control circuit (4) may malfunction due to some reason. Return to 9).

If the check counter overflows, that is, if the protection key signal is input for 1 second, it is judged that an overvoltage or overload has truly occurred, and a power stop signal is generated (96) and the power relay is turned on. To operate. As a result, the power supply circuit (2) is turned off.

When the above program is set in the microcomputer of the electronic tuning unit (1), it is possible to partially modify the program already set for the tuner operation, so that it is not necessary to rewrite the entire program. Absent.

 The protection circuit operates as follows.

If there is no abnormality in the circuit, the electronic tuning unit (1)
The judgment procedure (9) (92) and the check counter reset (93) shown in FIG. 2 are repeatedly executed, and when a key is operated, the tuner is operated to adjust the volume and switch the receiving channel.

When the overvoltage occurs, if the supply voltage B output from the power supply circuit (2) exceeds the rated value, the peak value of the flyback pulse FP obtained from the holddown winding (61) of the flyback transformer (31). Exceeds a predetermined value, the holddown circuit (35) operates, and the horizontal output circuit (38) stops operating. As a result, LB detection winding (6)
The output detection voltage LB obtained from the above decreases and falls below a predetermined value.

When an overload occurs, the supply voltage B of the power supply circuit (2) decreases as the output current of the flyback transformer (31) increases, and the output detection voltage LB falls below the rated value.

Therefore, in any of the above-mentioned abnormal states, the first and second transistors (41) (42) of the control circuit (4) are
When turned on, a protection key signal is sent to the electronic tuning unit (1).

As a result, the electronic tuning unit (1) creates a power supply stop signal and the power supply circuit (2) stops, so that the secondary side circuit of the flyback transformer (31) and the horizontal deflection circuit (3) are
Overcurrent or overvoltage that exceeds the allowable range does not occur, and therefore the electronic components constituting the circuit are protected from destruction.

After an abnormality occurs and the power supply circuit (2) is stopped, the circuit can be returned to the operating state by turning on the power again. In this case, if a program is set in the microcomputer of the electronic tuning unit (1) to prohibit the ON operation of the power switch for a few seconds after the power supply circuit (2) is temporarily stopped due to an error, the error will still occur. When the state continues, the power supply circuit (2) can be prevented from restarting for a certain period of time.

In the conventional circuit shown in FIG. 4, a timer circuit and a sequence control circuit are required in order to prevent malfunction and to hold the protection operation for a certain period of time, but in the protection circuit according to the present invention, Since these circuits are configured as software, the hardware circuit is greatly simplified.

In the protection circuit according to the present invention, the output detector is provided in the flyback transformer (31), and the output detection voltage LB is accurately proportional to the input voltage of the flyback transformer (31). The accuracy is higher than before.

Further, in both cases of occurrence of overvoltage and occurrence of overload, these states are detected as a decrease in the output detection voltage LB. Therefore, a series of signal processing circuits that create a power supply stop signal from the output detection voltage Unlike the conventional circuit, it is not necessary to form a separate circuit for each abnormal state, but a circuit common to each abnormal state can be formed.

Of course, the holddown circuit (35) has an extremely simple structure and is often equipped for X-ray protection. In this case, therefore, the holddown circuit may also be used for overvoltage protection. I can.

The configuration of each part of the present invention is not limited to the above embodiment, and it is needless to say that various modifications can be made within the technical scope described in the scope of claims for utility model registration.

[Brief description of drawings]

FIG. 1 is a block diagram of an overvoltage overload protection circuit according to the present invention, FIG. 2 is a flow chart showing the operation of an electronic tuning unit, and FIG. 3 is an electric circuit diagram showing a holddown circuit.
FIG. 4 is a block diagram showing a conventional power supply circuit. (1) ... Electronic tuning unit, (2) ... power supply circuit, (3)
… Horizontal deflection circuit, (31)… Flyback transformer,
(4) ... Protection key control circuit, (5) ... Key matrix

Claims (1)

(57) [Scope of utility model registration request] 1. A power supply circuit (2) comprising an electronic tuning unit (1) for generating a tuner control signal based on a key operation and a power supply stop signal for the power supply circuit (2).
A horizontal deflection circuit (3) including a flyback transformer (31) and a horizontal output circuit (38) is interposed between the anode and the anode to convert the supply voltage B from the power supply circuit (2) into a high voltage. In the television receiver for sending to the anode, a horizontal output stop circuit (35) that detects that the supply voltage B output from the power supply circuit (2) exceeds a rated value and stops the horizontal output circuit (38) ), And a control circuit that detects an overvoltage and an overload when the amount of decrease in the input voltage to the flyback transformer (31) exceeds a predetermined value and supplies a control signal to the electronic tuning unit (1), A signal processing unit for generating a power supply stop signal and sending it to the power supply circuit (2) when the control signal provided in the electronic tuning unit (1) is detected and the control signal is supplied for a predetermined time. Is provided with Overvoltage and overload protection circuit for television receivers.