JP2870353B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply suitable for a TV receiver or a monitor provided with a remote control (hereinafter referred to as "remote control") receiving circuit.

[0002]

2. Description of the Related Art It is known that a power supply for a main circuit of a television receiver (TV) having a remote control and a power supply for a remote control reception circuit are constituted by a common switching regulator. FIG. 4 shows a switching power supply of this type.
Transistor 6 as a switching element between one terminal 2 and the other terminal (ground terminal) 3 of DC power supply 1 comprising a rectifying and smoothing circuit connected to an AC power supply terminal via primary winding 5 of transformer 4 Is connected. The transistor 6 is of an npn type, and has a collector connected to the primary winding 5 and an emitter connected to the ground terminal 3.
The transformer 4 includes a secondary winding 7, a tertiary winding 8 in addition to the primary winding 5.
And a quaternary winding 9. The secondary winding 7 has a tap 10 substantially in the middle, and is divided into a first winding 7a and a second winding 7b. Note that the first and second windings 7a and 7b can be independently provided instead of providing the tap 10. 2
The secondary winding 7 functions as a first output winding (main load winding) and a first output terminal 14 via a first rectifying and smoothing circuit 13 including a rectifying diode 11 and a smoothing capacitor 12.
It is connected to the. T is connected between the first output terminal 14 and the ground terminal 15 via an internal power switch 16 of the TV.
A first load consisting of a V main power supply circuit, namely a main load 17, is connected.

The tertiary winding 8 functions as a drive winding for driving the transistor 6 in a positive feedback manner. One end is connected to the base of the transistor 6 via a resistor 18 and the other end is connected to the emitter.

A quaternary winding 9 having a smaller number of turns than the secondary winding 7
Functions as a second output winding, that is, an auxiliary output winding for remote control, and is connected to a remote control receiving circuit 22 as a second load via a second rectifying and smoothing circuit 21 including a rectifying diode 19 and a smoothing capacitor 20. Have been.

The tap 10 is for supplying power to the remote control receiving circuit 22 during standby (standby).
Here, a third rectifying / smoothing circuit 25 including a diode 23 and a capacitor 24 is connected. The output line 26 of the third rectifier circuit 25 is connected to the remote control receiving circuit 22 via a pnp first transistor 27. In order to operate the first transistor 27 only during standby, an npn-type second transistor 28 is connected between the base and the ground.
8 are connected to the switching signal supply terminal 29.
The switching signal goes low during main operation and goes high during standby. Therefore, during the main operation, the transistor 28 is turned off, the transistor 27 is also turned off, and the third rectifying / smoothing circuit 25 is disconnected from the remote control receiving circuit 22. Even if the transistor 27 is turned off during the main operation, the remote control receiving circuit 22 is operated by the second rectifying / smoothing circuit 21.

A voltage control circuit AVC for controlling on / off of the main transistor 6 so as to perform constant voltage control includes a control transistor 30, a phototransistor 31, a diode 3
2, a capacitor 33, a tertiary winding 8 and a resistor 18 are provided. In order to control the ON period of the main transistor 6, the pnp control transistor 30 is
Is connected between the base and the emitter of This control transistor 30 forms a bypass circuit for the base current of the main transistor. The phototransistor 31 is connected to the base of the control transistor 30 as a control element for controlling the conduction state of the control transistor 30. The diode 32 and the capacitor 33 constitute a rectifying and smoothing circuit for applying a bias voltage to the phototransistor 31. The cathode of the diode 32 is connected to the tertiary winding 8, and the anode is connected to the lower end of the tertiary winding 8 via the capacitor 33. Therefore, the capacitor 33 is charged with a substantially constant voltage obtained in the tertiary winding 8 during the off period of the transistor 6.

In order to control the phototransistor 31 according to the change of the main output voltage, an error signal forming circuit comprising output voltage detecting resistors 34 and 35, a zener diode 36 for a reference voltage source, an error amplifying transistor 37 and a resistor 40. E
An AMP is provided, to which a light emitting diode 38 and a current limiting resistor 39 are connected. The detection resistors 34 and 35 are connected between the output terminal 14 and the ground terminal 15, and this voltage division point is connected to the base of the error amplification transistor 37. The Zener diode 36 is connected between the output terminals 14 and 15 via the resistor 40, and applies the reference voltage obtained here to the emitter of the transistor 37. In this embodiment, when the output voltage increases, the error amplifying transistor 3
7 has a lower collector potential. The anode of the light emitting diode 38 optically coupled to the phototransistor 31 is connected to the output terminal of the second rectifying / smoothing circuit 21 via the resistor 39, and the cathode is connected to the collector of the error amplifying transistor 37.

The collector of the second transistor 28 for lowering the output voltage of the first output terminal 14 during standby is connected to the base of the first transistor 27 via a resistor 41 and to a photo transistor via a diode 42. The transistor 38 is connected to the cathode, and the emitter is connected to the ground. Further, a bias circuit of resistors 43 and 44 is connected to the base of the second transistor 28.

A remote control power supply terminal, that is, a second output terminal 45
The remote control receiving circuit 22 connected to is for performing various operations of the TV receiver, and also controls on / off of the switch 16 of the load 17. While the remote control receiving circuit 22 controls the switch 16 to be turned off, a high level remote control standby signal is obtained at the terminal 29.

[0010]

[Operation] When a power switch (not shown) included in the DC power supply 1 is turned on, a base current flows to the transistor 6 via the starting resistor 46, and the transistor 6 is turned on. As a result, a voltage is applied to the primary winding 5, a feedback voltage is obtained to the tertiary winding 8, and a sufficient base current is supplied so that the transistor 6 performs a saturation operation. Since the primary winding 5 has an inductance, the collector current of the transistor 6 flows so as to increase with time. Then, the transistor 6
This turns off when saturation of the can no longer be maintained.
The diodes 11, 19, and 23 of the first, second, and third rectifying / smoothing circuits 13, 21, and 25 are turned on during the off period of the transistor 6, and release the energy stored in the transformer 4 to the load side during the on period. I do. When this release ends,
The transistor 6 is turned on again.

When the switch 16 is on, the switching signal terminal 29 is at a low level, and the transistors 27 and 28
Is in the off state. Therefore, the control based on the light emitting diode 38 is the same as the general constant voltage control, and the light emitting diode 38 emits light with the intensity corresponding to the output voltage, and the phototransistor 31 and the control transistor 30 correspond to the light of the light emitting diode 38. The conductive state. For example, when the output voltage becomes higher than the reference value, the resistance of the phototransistor 31 decreases, the current of the control transistor 30 increases, the base current of the main transistor 6 decreases, the ON time width decreases, and the output Voltage drops. When the load 17 is driven, the transistor 27 is off, so the third rectifying / smoothing circuit 25 is irrelevant to the remote control receiving circuit 22, and the remote control receiving circuit (second load) 22 is connected to the fourth winding 9. A constant voltage (5 V) is supplied from the second rectifying and smoothing circuit 21 that has been performed.

When the remote control receiving circuit 22 controls the switch 16 to turn off and generates a high level output at the switching signal terminal 29, the transistors 28 and 27 are turned on. When the transistor 28 is turned on, the cathode of the light emitting diode 38 is connected to the ground via the diode 42 and the transistor 28, and emits light substantially independently of the error amplifying transistor 37. That is, the light emitting diode 38 is substantially in a saturated light emitting state, and the feedback control is interrupted. As a result, the phototransistor 31 is also substantially in a saturated operation state. At this time, the collector-base voltage of the control transistor 30 and the collector-emitter voltage of the phototransistor 31 become substantially constant.
The voltage of No. 3 also becomes substantially constant. When the phototransistor 31 enters the saturation operation state, the current of the control transistor 30 also becomes sufficiently large, and the base current of the main transistor 6 becomes extremely small. As a result, the time (on period) from the start of turning on the main transistor 6 to saturation is shortened, and the voltage of the first output terminal 14 is reduced to about １ ／ of the normal state. At the time of a light load in which the load 17 is disconnected, the feedback control of the output voltage is interrupted, and
Since the fixed bias is controlled by the voltage of 3, a stable operation state can be obtained. Note that the first output terminal 1 is in standby mode.
When the voltage of 4 is reduced, the power loss is reduced.

This switching power supply has a feature that the voltage of the output terminal 14 can be automatically reduced when the main load 17 such as a horizontal deflection circuit is driven.

[0014]

By the way, it is desirable to set the voltage of the remote control power supply terminal 45 to an optimum value (for example, 5 V) even during standby. During standby, the voltage at the second output terminal 45 is set to the tertiary winding 8 and the secondary winding 7.
Can be adjusted by the number of turns of the second winding 7b, but fine adjustment by this is difficult.

Now, the power supply of the TV circuit has been described.
A similar problem exists in another circuit device having a main load and a sub load.

It is an object of the present invention to provide a switching power supply device that can easily adjust a low output voltage when a high output voltage and a low output voltage are obtained by the same switching circuit. .

[0017]

In order to achieve the above object, the present invention will be described with reference to the reference numerals in the drawings showing the embodiments. The present invention is connected to a DC power supply 1 via a primary winding 5 of a transformer 4. Switching element 6, a secondary winding 7 composed of first and second windings 7 a and 7 b connected in series with each other and electromagnetically coupled to the primary winding 5, and a secondary winding 7
A first rectifying / smoothing circuit 13 connected to the auxiliary output winding 9; an auxiliary output winding 9 having fewer windings than the secondary winding 7 and electromagnetically coupled to the primary winding 5; A second rectifying / smoothing circuit 21 connected to the line 9 and a third rectifying / smoothing circuit 25 connected to the second winding 7b of the secondary winding 7
And a first output terminal 14 for outputting a voltage of the first rectifying / smoothing circuit 13 and a ground, and a difference between a detected value of the voltage of the first output terminal 14 and a reference voltage. And an error signal forming circuit EAMP configured to increase the error output voltage when the voltage of the first output terminal 14 decreases, and the voltage of the second rectifying and smoothing circuit 21. Output terminal 45 for outputting
And a light emitting diode 38 connected between the output terminal of the error signal forming circuit EAMP and an emitter connected to the third rectifying / smoothing circuit 25 and a collector connected to the second output terminal 45. 1 transistor 27 and the collector of the first transistor 27
A second transistor 28 having an emitter connected to the ground, a diode 42 connected between a cathode of the light emitting diode 38 and a collector of the second transistor 28, The second transistor 28 is turned off when a first output voltage is obtained at the output terminal 14, and the second transistor 28 is turned off when a second output voltage lower than the first output voltage is obtained at the first output terminal 14. A switching control means for controlling the second transistor to be turned on, and a light receiving element 31 optically coupled to the light emitting diode 38 for controlling the switching element 6, and the light receiving amount of the light receiving element 31 increases. And a control circuit AVC set so as to shorten the on-time of the switching element 6 when the switching power supply is turned on. A resistor 47 is connected between the flow smoothing circuit 25 and the base of the second transistor 28, and a switching element 48 is connected between the base of the second transistor and ground as the switching control means. The present invention relates to a switching power supply device characterized in that: In addition, as shown in claim 2, the resistance 47
It is desirable to connect a Zener diode 46 in series with the.

[0018]

According to the present invention, the resistor 47 connected between the third rectifying / smoothing circuit 25 and the base of the second transistor 28 functions as a base current supply circuit for the second transistor 28. When lowering the voltage of the first output terminal 14 from the first output voltage to the second output voltage, the second
Transistor 28 is turned on, and this base current flows through the resistor 47. If the voltage of the DC power supply 1 increases, the output voltage of the third rectifying / smoothing circuit 25 also increases, and the base current of the second transistor 28 increases.
As a result, the current flowing through the circuit composed of the light emitting diode 38, the diode 42 and the second transistor 28 using the second output terminal 45 as a power supply increases, and the light emitting diode 3
8, the amount of light emission increases, and an operation of lowering the output voltage occurs. As a result, a substantially constant voltage can be obtained at the third rectifying / smoothing circuit 25 and the second output terminal 45. In the present invention, since the voltage of the second output terminal 45 can be adjusted by adjusting the value of the resistor 47, fine adjustment of the voltage of the second output terminal 45 can be easily achieved. Further, when the Zener diode 46 is connected as described in claim 2, the stability of the voltage during standby is improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a switching power supply device for a TV according to an embodiment of the present invention will be described with reference to FIGS. However, in FIG. 1, portions common to FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. The switching power supply device of FIG. 1 is obtained by adding a zener diode 46, a resistor 47, and a third transistor 48 to the switching power supply device of FIG. The Zener diode 46 is connected between the third rectifying / smoothing circuit 25 and the base of the second transistor 28 via a resistor 47. The third transistor 48 is connected between the base of the second transistor 28 and the ground. The base of the third transistor 48 is connected to the switching signal terminal 29a. The switching signal terminal 29a in FIG. 1 receives a high-level signal during operation and a low-level signal during standby , contrary to the switching signal terminal 29 in FIG. Further, in the circuit of FIG. 1, the base bias resistors 43 and 44 of the second transistor 28 provided in the circuit of FIG. 4 are unnecessary.

FIG. 2 shows the Zener diode 4 shown in FIG.
6 and the resistor 47 and the vicinity thereof are shown. As is clear from this figure, the base current of the second transistor 28 is supplied by a circuit comprising the output line 26 of the third rectifying / smoothing circuit 25, the resistor 47 and the Zener diode 46. This base current depends on the voltage of the output line 26 of the third rectifying and smoothing circuit 25. If the voltage of power supply 1 rises,
The voltage of the third rectifying / smoothing circuit 25 also increases, and the base current of the second transistor 28 increases.
8, the control operation for lowering the output voltage occurs, and the voltage Vout at the second output terminal 45 of the third rectifying / smoothing circuit 25 is stabilized at a substantially constant value. That is, line 2
6 is the input voltage Vin, and the voltage of the output terminal 45 is V
If out, a constant voltage control characteristic as shown in FIG. 3 can be obtained by the circuit of FIG.

In the circuit of FIG. 1, the base current of the second transistor 28 changes by changing one or both of the Zener voltage of the Zener diode 46 and the value of the resistor 47. Therefore, the voltage of the output terminal 45 during standby can be accurately and easily set to a desired value (5 V). Note that, in the circuit of FIG.
8 and the phototransistor 31 do not saturate.

[0022]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) Voltage control circuit AVC and error amplifier circuit EAMP
Can be replaced by various known circuits. (2) When the transistor 6 is on, the diode 11
19 and 23 can be turned on.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply device according to an embodiment.

FIG. 2 is a circuit diagram showing a part of FIG.

FIG. 3 is a diagram illustrating voltage control characteristics of the circuit of FIG. 2;

FIG. 4 is a circuit diagram showing a conventional switching power supply device.

[Explanation of symbols]

 27 First transistor 28 Second transistor 46 Zener diode 47 Resistance

Claims (2)

(57) [Claims] A switching element (6) connected to a DC power supply (1) via a primary winding (5) of a transformer (4).
And first and second windings (7a, 7a) connected in series with each other.
b) and a secondary winding (7) electromagnetically coupled to said primary winding (5); a first rectifying and smoothing circuit (13) connected to said secondary winding (7); An auxiliary output winding (9) having less windings than the secondary winding (7) and electromagnetically coupled to the primary winding (5); and connected to the auxiliary output winding (9). A second rectifying / smoothing circuit (21); a third rectifying / smoothing circuit (25) connected to the second winding (7b) of the secondary winding (7); A first output terminal (14) for outputting a voltage of the smoothing circuit (13) is connected between the first output terminal (14) and the ground, and a difference between a detected value of the voltage of the first output terminal (14) and a reference voltage. An error signal forming circuit (E) configured to output a corresponding voltage and to increase the error output voltage when the voltage of the first output terminal (14) decreases. MP)
A second output terminal (45) for outputting a voltage of the second rectifying / smoothing circuit (21); and an error signal forming circuit (E).
A light emitting diode (38) connected to the output terminal of the AMP); an emitter connected to the third rectifying / smoothing circuit (25); and a collector connected to the second output terminal (45). A first transistor (27), a second transistor (28) having a collector connected to the base of the first transistor (27) via a resistor (41) and an emitter connected to ground, A diode (42) connected between a cathode of a diode (38) and a collector of the second transistor (28); and a second output terminal for obtaining a first output voltage at the first output terminal (14). The second transistor (28) is turned off to turn on the second transistor (28) when a second output voltage lower than the first output voltage is obtained at the first output terminal (14). Control means for controlling the switching element (6) including a light receiving element (31) optically coupled to the light emitting diode (38), and a light receiving amount of the light receiving element (31). A switching power supply device comprising a control circuit (AVC) set so as to shorten the on-time of the switching element (6) when the switching element (6) increases, wherein the third rectifying / smoothing circuit (25) and the second transistor ( 28), a resistor (47) is connected to the base of the second transistor, and a switching element (48) is connected between the base of the second transistor and ground as the switching control means. Switching power supply. 2. The switching power supply according to claim 1, further comprising a Zener diode connected in series with said resistor.