JPH11146302A - Secondary output voltage correction circuit for switching power supply output - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent noise from being caused in a video output signal of a BS tuner by preventing lowering of a specified corrected voltage to supply a voltage of the BS tuner from a secondary side output voltage of a switching power supply by impressing the specified voltage when a mode is switched to a full-load mode to receive a ground wave, etc. SOLUTION: In a moment when a relay 4 is conducted and a high voltage deflection output voltage 140 V (e) is started, the large amount of an inrush current flows to a smoothing capacitor 8 and when a voltage correction circuit 37 is not put on, 7 V (c) to supply the voltage of 5 V of the BS tuner is momentarily lowered (to <=5 V). A starting part of a power supply control signal (b) from a microprocessor 21 is differentiated, impressed on a base of a transistor 16 and conducted by the voltage correction circuit 37. Thus, the corrected voltage is impressed on the 7 V (c) from 14 V (d) through a resistor 30 and momentary lowering of the voltage is corrected by the 7 V (c). Then, the voltage of 5 V to be supplied to the BS tuner is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-converter switching power supply for a television receiver, which is used to prevent a momentary drop in the secondary output voltage of the switching power supply when switching from a light load mode to a full load mode. It relates to a correction circuit.

[0002]

2. Description of the Related Art In recent years, a large-size television receiver generally has a built-in BS. The TV power supply and the BS power supply are integrated from the viewpoint of miniaturization and space saving of the power supply circuit, and the full load mode to receive the terrestrial wave and the light load mode to operate only the circuit to receive the BS broadcast are controlled stably by the switching circuit. A switching power supply of a one-converter type is generally used.

Hereinafter, an example of a conventional switching power supply circuit will be described with reference to the drawings. FIG. 3 shows a circuit diagram of a conventional switching power supply circuit.

In FIG. 3, reference numeral 1 is a switching transformer, 2 is a switching power supply output MOSFET, 3 is a photocoupler, 4 is a relay for turning on and off a high-voltage deflection power supply voltage, 5 to 7 are rectifier diodes, 8 to 11 are smoothing capacitors, Reference numeral 18 denotes a shunt regulator for detecting fluctuations in the high-voltage deflection power supply voltage, 19 to 20 denote constant voltage regulators, 21
Is a microprocessor that outputs a signal for switching the on / off and control of the relay 4; 36 is a relay driving resistor; 38 is a high-voltage deflection power supply voltage adjusting resistor;
5 is a resistor, 11 is a control switching timing adjustment capacitor, 14 is a relay drive transistor, 13 is a control switching transistor, 17 is a power supply voltage stabilizing Zener diode at light load operation, 22 is a high voltage deflection output circuit,
23 is a BS tuner circuit.

The switching operation of the switching power supply circuit configured as described above between the full load mode (receiving terrestrial waves) and the light load mode in which only the BS circuit is operated will be described.

In the light load mode in which only the BS circuit operates, the power supply control signal b from the microprocessor 21 is low, the relay drive transistor 14 is cut off, and the relay 4 for turning on and off the high-voltage deflection power supply voltage.
Becomes nonconductive, and the high-voltage deflection power supply voltage e becomes 0V.

[0007] The feedback voltage to the shunt regulator 18 also becomes 0V. At this time, the feedback current flowing through the photocoupler 3 is controlled by the control switching transistor 13
Flows through the Zener diode 17 due to conduction.

[0008] Secondary voltage d (14 V) of the switching power supply
And c (7V) are stabilized by the feedback current flowing through the Zener diode 17.

Here, when the power button is pressed by the remote control device, the power control signal b from the microprocessor 21 becomes High, the relay drive transistor 14 becomes conductive and the relay 4 becomes conductive.

At this time, the transistor 13 is turned off and the feedback current flowing through the photocoupler 3 flows through the shunt regulator 18.

At the moment when the relay 4 is turned on, a large rush current flows through the smoothing capacitor 8. Therefore 5 of BS tuner
7V (c) supplying the V voltage drops momentarily as shown in FIG. 3 (2) (to 5V or less), and the output voltage 5V of the constant voltage regulator drops momentarily as shown in FIG. 3 (3). .

The BS tuner 5V drops momentarily to 4.7V
Below this, the microprocessor in the BS tuner is reset, and a large noise is momentarily generated in the video output signal.

[0013]

However, in such a conventional configuration, when the mode is switched from the light load mode in which only the BS circuit is operated to the full load mode in which a terrestrial wave or the like is received, 5 V of the BS tuner drops, However, there is a problem that large noise is instantaneously generated in the video output signal and the quality of the BS video signal is impaired.

In view of the above problems, the present invention provides a 5V BS tuner which is generated when switching from a light load mode in which only the BS circuit is operated to a full load mode for receiving terrestrial waves or the like.
It is an object of the present invention to provide a switching power supply voltage correction circuit that suppresses a drop of 7 V (c) that supplies a voltage, stabilizes a 5 V voltage of a BS tuner, and prevents noise generated in a video output signal of the BS tuner.

[0015]

In order to achieve the above object, the present invention provides a method for switching from a light load mode in which only a BS circuit is operated to a full load mode for receiving terrestrial waves or the like.
The correction voltage is applied to 7 V (c) supplying the 5 V voltage of the BS tuner from the secondary output 14 V (d) of the switching power supply to prevent the 7 V voltage from decreasing.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a one-converter switching power supply, which differentiates a rising portion of a switching signal from a light load mode for receiving satellite broadcasting (hereinafter, BS) to a full load mode for receiving terrestrial waves. A switching power supply for a television receiver characterized in that a switching pulse is made, a voltage correction transistor is turned on by the switching pulse, and a BS power supply voltage is supplied from another power supply voltage to prevent an instantaneous decrease in the power supply voltage. A secondary-side output voltage correction circuit that effectively suppresses a drop of 7 V (c) that supplies a 5 V voltage of the BS tuner,
This has the effect of preventing noise generated in the video output signal of the tuner.

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram of a switching power supply secondary-side output voltage correction circuit according to the present invention, and FIG. 2 is a voltage waveform diagram of each part in FIG.

In FIG. 1, reference numeral 1 is a switching transformer, 2 is a switching power supply output MOSFET, 3 is a photocoupler, 4 is a relay for turning on and off a high-voltage deflection power supply voltage, 5 to 7 are rectifier diodes, 8 to 10 smoothing capacitors, 18 Is a shunt regulator for detecting fluctuations in the high-voltage deflection power supply voltage, 19 to 20 are constant voltage regulators, 21
Is a microprocessor for outputting a signal for switching on and off the relay 4 and switching control, 36 is a relay driving resistor, 38 is a high-voltage deflection power supply voltage adjusting resistor, 25 to 2
9 and 35 are resistors, 12 is a timing adjustment capacitor for control switching, 14 is a relay drive transistor, 13
Is a control switching transistor, 17 is a power supply voltage stabilizing zener diode at light load operation, 22 is a high voltage deflection output circuit, 23 is a BS tuner circuit, 37 is a voltage correction circuit,
Reference numerals 15 and 16 denote voltage correction transistors, 11 denotes a power supply control signal rising portion differential capacitor, 31 to 34 denote resistors, and 30 denotes a voltage correction resistor.

The operation of the switching power supply secondary-side output voltage correction circuit configured as described above will be described.

In the light load mode in which only the BS circuit operates, the power supply control signal b from the microprocessor 21 is low, the relay drive transistor 14 is cut off, and the relay 4 for turning on and off the high-voltage deflection power supply voltage.
Becomes nonconductive, and the high-voltage deflection power supply voltage e becomes 0V.

The feedback voltage to the shunt regulator 18 also becomes 0V. At this time, the feedback current flowing through the photocoupler 3 flows through the Zener diode 17 when the control switching transistor 13 is turned on. Switching power supply secondary side voltage d (14V) and c
(7V) is stabilized by the feedback current flowing through the Zener diode 17.

Here, when the power button is pressed by the remote control device, the power control signal b from the microprocessor 21 becomes High, the relay drive transistor 14 is turned on, the relay 4 is turned on, and the high-voltage / deflection output voltage 140 V (e). Stand up.

At this time, the transistor 13 is turned off, and the hood-back current flowing through the photocoupler 3 flows through the shunt regulator 18. At the moment when the relay 4 is turned on and the high voltage / deflection output voltage 140V (e) rises,
If the voltage correction circuit 37 is not provided because a large inrush current flows through the smoothing capacitor 8, the BS tuner 5
7V (c) supplying the V voltage drops momentarily as shown in FIG. 2 (2) (to 5V or less), and the output voltage 5V of the constant voltage regulator drops momentarily as shown in FIG. 2 (3).

Next, the operation of the voltage correction circuit 37 will be described. The rising portion of the power control signal b from the microprocessor 21 FIG.
FIG. 2 (6) which is differentiated by the
Apply to base No. 6.

During this period T, the transistor 16 conducts,
The voltage shown in FIG. 2 (7) is applied to the base of the voltage correction transistor 15, and the voltage correction transistor 15 becomes conductive.

When the voltage correction transistor 15 conducts, 1
A correction voltage is applied from 4V (d) to 7V (c) via the resistor 30, and the 7V (c) can correct a momentary drop in the voltage as shown in FIG. This effectively suppresses the drop of 7V (c) supplying the 5V voltage of the BS tuner, which occurs when switching from the light load mode in which only the BS circuit is operated to the full load mode for receiving terrestrial waves or the like, and effectively suppresses the BS tuner. 2 (3) to be supplied to the BS and the noise generated in the video output signal of the BS tuner can be prevented.

[0027]

As described above, the switching power supply secondary-side output voltage correction circuit of the present invention provides a BS tuner which is generated when switching from the light load mode in which only the BS circuit is operated to the full load mode in which terrestrial waves or the like are received. It is possible to effectively suppress the drop of 7V (c) supplying the 5V voltage, stabilize the 5V voltage supplied to the BS tuner, and prevent noise generated in the BS video output signal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a secondary-side output voltage correction circuit of a switching power supply according to an embodiment of the present invention.

FIG. 2 is a voltage waveform diagram of each part in FIG.

FIG. 3 is a circuit diagram of a conventional switching power supply circuit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 switching transformer 2 switching power supply output MOSFET 3 photocoupler 4 relay for turning on / off high-voltage deflection power supply voltage 5, 6, 7 current diode 8, 9, 10 smoothing capacitor 12 control switching timing adjustment capacitor 13 control switching transistor 14 relay drive transistor 17 Power supply voltage stabilizing Zener diode 18 Shunt regulator 19,20 Constant voltage regulator (AVR) 21 Microprocessor 22 High voltage deflection output circuit 23 BS tuner 25-29 Resistance 30 Voltage correction resistance 31,32 Resistance 33 Differential resistance 34,35 Resistance 36 Relay Drive resistance 37 Voltage correction circuit

Claims (1)

[Claims] 1. A switching pulse is generated by differentiating a rising portion of a switching signal from a light load mode for receiving a satellite broadcast (hereinafter, BS) to a full load mode for receiving a terrestrial wave in a one-converter switching power supply. And a secondary-side output voltage correction for a switching power supply for a television receiver, wherein a voltage correction transistor is turned on by the switching pulse, and a BS power supply voltage is supplied from another power supply voltage to prevent an instantaneous decrease in the power supply voltage. circuit.