JP2000078603A - Power supply circuit for television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit where no damage is caused to its rectifier circuit even on the occurrence of a momentary power failure. SOLUTION: The power supply circuit is provided with a main relay 13 that is controlled by a microcomputer 12 at application of a power switch 2 to connect a power supply 1 to a rectifier circuit 8 via a rush current preventing resistor 7, a changeover relay 3 that supplies a degaussing current to a degaussing circuit 4 for a prescribed time at application of the main relay 13 and bypasses the rush current preventing resistor 7 to connect the power supply 1 to the rectifier circuit 8 after the lapse of a prescribed time, and a momentary power failure detector 14 that detects a momentary power failure of the power supply 1, turns off the main relay 13 under the control of the microcomputer 12 and connects the main relay 13 again later.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply circuit for a television receiver.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a conventional power supply circuit. In the figure, 1 is an AC power supply, 2 is a power switch, 3 is a switching relay, 4 is a degaussing circuit, which is composed of a series body of a thermistor 5 having a positive characteristic and a degaussing coil 6. 7 is an inrush current prevention resistor which is an inrush current prevention element, 8 is a rectifier circuit, which is a bridge rectifier diode 9 and a smoothing capacitor 1.
0. Reference numeral 11 denotes a load such as an electric circuit of a television receiver, and reference numeral 12 denotes a microcomputer (hereinafter, referred to as a “microcomputer”) constituting a control circuit.

Next, the operation of the conventional example will be described with reference to the timing chart of FIG. When the power switch 2 is off,
The common terminal C of the switching relay 3 is connected to the normally closed contact A. When the power switch 2 is turned on at time t0, an attenuated alternating current flows through the degaussing circuit 4 to degauss a color cathode ray tube (not shown). At the same time, the AC power supply 1 is applied to the rectifier circuit 8 via the inrush current prevention resistor 7, and the load 1
Power supply to 1 is started. The microcomputer 12 switches the switching relay 3 at time t1 several seconds after the power switch 2 is turned on.
Is switched to the normally open contact B, whereby the power supply to the degaussing circuit 4 is cut off and the degaussing operation ends, and the inrush current prevention resistor 7 is short-circuited to shift to the steady operation state.

[0004]

Since the conventional power supply circuit is constructed as described above, if an instantaneous power failure occurs between times t2 and t3 as shown in FIG. Is short-circuited by the switching relay 3, there is a problem that an inrush current flows through the rectifier circuit 8 at the time of recovery from the power failure and the bridge rectifier diode in the rectifier circuit 9 is destroyed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. Even if there is an instantaneous power failure during a steady operation, an inrush current flows through the rectifier circuit 8 to destroy the rectifier diode. The aim is to get no power supply circuit.

[0006]

A power supply circuit of a television receiver according to the present invention is controlled by a control circuit when a power supply switch is turned on, and is connected to a rectifier circuit through an inrush current prevention element to connect a power supply to a rectifier circuit. Controlled by the control circuit, supplies a degaussing current to the degaussing circuit for a predetermined time when the main relay is turned on, and after the predetermined time,
A switching relay for connecting the power supply by bypassing the inrush current prevention element to the rectifier circuit, an instantaneous power failure for detecting an instantaneous power failure of the power supply, turning off the main relay via the control circuit, and then re-energizing the main relay It has a detector.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described with reference to the drawings showing the embodiments. Embodiment 1 FIG. FIG. 1 is a block diagram showing a power supply circuit of a television receiver according to Embodiment 1 of the present invention. In the figure, 1 is an AC power supply, 2 is a power switch having an input terminal connected to one end of the AC power supply 1, 13 is a main relay having an input terminal connected to an output terminal of the power switch 2, and 3 is an output terminal of the main relay. A switching relay having a normally closed contact A and a normally open contact B connected to a common terminal C, and a demagnetizing circuit 4 connected between the normally closed contact A and the other end of the AC power supply 1, and having a positive characteristic thermistor. 5 and a degaussing coil 6 in series. 7 is an inrush current prevention resistor which is an inrush current prevention element connected between the common terminal C of the switching relay 3 and the normally open contact B, and 8 is connected between the normally open contact B and the other end of the AC power supply 1. The rectifier circuit includes a bridge rectifier diode 9 and a smoothing capacitor 10, and the output of the rectifier circuit 8 is supplied to a load 11 such as a television circuit. Reference numeral 14 denotes an instantaneous power failure detector that detects an instantaneous power failure of the AC power supply 1, and reference numeral 12 denotes a microcomputer that constitutes means for controlling the operation of the entire circuit.

Next, the operation of the first embodiment will be described with reference to the timing chart of FIG. When the power switch 2 is turned on at time t0, the microcomputer 12 turns on the main relay 13 at time t4. As a result, an attenuated AC current flows through the degaussing circuit 4 to degauss a color cathode ray tube (not shown). At the same time, the AC power supply 1 is applied to the rectifier circuit 8 via the inrush current prevention resistor 7, and power to the load 11 is supplied. Be started. Next, the microcomputer 12 switches the switching relay 3 to the normally open contact B at time t1 several seconds after the power switch 2 is turned on. As a result, the power supply to the degaussing circuit 4 is cut off, and the degaussing operation is completed.
Is short-circuited and shifts to a steady operation state.

Next, during a normal operation, if an instantaneous power failure occurs in the AC power supply 1 between times t2 and t3 as shown in FIG.
The instantaneous stop detector 14 sends out an instantaneous stop detection signal. The microcomputer 12 that has received the instantaneous stop detection signal turns off the main relay 13 and then switches the switching relay 3 to the normally closed contact A.
Next, when the instantaneous power failure detector 14 detects that the instantaneous power failure has recovered at time t3, the microcomputer 12 receiving this detection signal
Turns on the main relay 13 at time t5 and switches the switching relay 3 to the normally open contact B at time t6 after a predetermined time. As a result, the degaussing current is supplied to the degaussing circuit 4 from the time t5 to the time t6, and the AC power supply 1 is applied to the rectifier circuit 8 via the inrush current prevention resistor 7 from the time t5. The prevention resistor 7 is short-circuited and shifts to a steady operation state.

According to the first embodiment, when an instantaneous power failure occurs in the AC power supply 1, the main relay 13 is turned off, the switching relay 3 is switched to the normally closed contact A, and the inrush current prevention resistor 7 is connected to the rectifier circuit 8. The insertion prevents the rush current from flowing to the rectifier circuit 8 at the time of recovery from the momentary power failure, and prevents the diode of the rectifier circuit 9 from being damaged. Further, at the time of recovery from the instantaneous power failure, the degaussing current flows through the degaussing circuit 4 and the degaussing operation is performed, so that the magnetization of the color cathode ray tube due to the instantaneous power failure can be prevented.

FIG. 3 is a block diagram showing a power supply circuit of a television receiver according to a second embodiment of the present invention. 3, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. In the second embodiment, the instantaneous stop detector 14
Has the same configuration as that of the first embodiment except that the input is taken from both ends of the AC, and the same effect as that of the first embodiment can be obtained.

[0012]

The present invention is controlled by a control circuit when a power switch is turned on, is controlled by a main relay for connecting a power supply to a rectifier circuit via an inrush current prevention element, and is controlled by a control circuit. A switching relay that supplies a degaussing current to the time degaussing circuit and connects the power supply by bypassing the rush current prevention element to the rectifier circuit after a predetermined time, and detects a momentary blackout of the power supply and turns off the main relay via the control circuit When the power switch is turned on, the control circuit turns on the main relay, and after a predetermined time, switches the switching relay to the normally open contact side. When a momentary power failure is detected, the main relay is turned off, and then the switching relay is switched to the normally closed contact side. When the momentary power failure detector detects the recovery from the momentary power failure, the main relay is turned off. Since the power supply circuit of the television receiver is configured to switch the switching relay to the normally open contact side after a predetermined time after turning on the laser, even if there is an instantaneous power failure, the rectifier circuit is not damaged, Also,
Since the degaussing operation is performed at the time of recovery from the momentary power failure, an effect is obtained that no magnetization of the cathode ray tube occurs.

[Brief description of the drawings]

FIG. 1 is a block diagram of a power supply circuit according to Embodiment 1 of the present invention.

FIG. 2 is a timing chart of the first embodiment.

FIG. 3 is a block diagram of a power supply circuit according to a second embodiment of the present invention.

FIG. 4 is a block diagram of a conventional power supply circuit.

FIG. 5 is a timing chart of a conventional example.

[Explanation of symbols]

1 AC power supply, 2 power switch, 3 switching relay, 4
Degaussing circuit, 7 inrush current prevention resistor, 8 rectifier circuit,
11 load, 12 microcomputer, 13 main relay, 14 momentary power failure detector.

Claims (1)

[Claims] 1. A main relay that is controlled by a control circuit when a power switch is turned on and connects a power supply to a rectifier circuit via an inrush current prevention element, and is controlled by the control circuit and is demagnetized for a predetermined time when the main relay is turned on. A switching relay that supplies the demagnetizing current to the circuit and connects the power supply by bypassing the rush current prevention element to the rectifier circuit after the predetermined time, detects an instantaneous power failure of the power supply, and passes through the control circuit. A power supply circuit for a television receiver, comprising: a momentary power failure detector that turns off the main relay and then turns it on again.