JPH09149641A - Switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an overvoltage at the time of mode switching by a method wherein, while the output voltage stabilization control based upon a first voltage is discontinued, a second voltage is temporarily elevated and the discontinuation of the output voltage stabilization control is temporarily delayed. SOLUTION: When a control voltage applied to a monitor control terminal 32 is changed from 0V to 5 V, an output voltage of 140V is outputted from an intermediate voltage output terminal 11 a time Ta later. During the time Ta, the control of a switching controller 16 in accordance with the intermediate voltage is not performed. On the other hand, if a monitor control voltage is changed from 0V to 5V while the output voltage of a low voltage output terminal 21 is 14.5V, a low voltage output voltage detecting transistor 26 is turned off and the control of the switching controller 16 is not performed. Then, if the output voltage of a low voltage output terminal 21 is elevated to 15.5 V for the time Ta only, the potential of the base 27 of the low voltage output voltage detecting transistor 26 is high enough to turn on the transistor 26 and hence the control of the switching controller 16 is performed for the time Ta only. As a result, an overvoltage can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light load mode in which only a VTR (video tape recorder) is operated and a VTR.
The present invention relates to a switching power supply circuit for an electronic device, such as a TV with a VTR having a TV mode for operating both a TV and a television (television receiver), which requires stable supply of a first power supply voltage and a second power supply voltage. It is a thing.

[0002]

2. Description of the Related Art Regarding a conventional switching power supply circuit,
A case of a TV with a VTR having a light load mode in which only the VTR operates and a TV mode in which both the VTR and the TV operate will be described. FIG. 3 is a circuit diagram of a conventional switching power supply circuit, in which the DC input voltage terminals 1 and 2 are connected to the primary winding 5 of the switching transformer 4 via the switching output circuit 3 and the secondary transformer for medium voltage of the switching transformer 4 is connected. One terminal 7 of the winding 6 is connected to the intermediate pressure output terminal 11 via the rectifying diode 8 and the contact 10 of the relay 9, and the intermediate pressure output voltage detection circuit 12 connected to the intermediate pressure output terminal 11 outputs the intermediate voltage. The voltage detection terminal 13 is a medium voltage output voltage detection diode 1
4, it is connected to the switching control circuit 16 via the photo coupler 15, and the switching control circuit 16 is connected to the switching output circuit 3. 17 is a medium voltage output terminal 11
Is a smoothing capacitor connected between the ground and the ground. On the other hand, one terminal 19 of the low voltage secondary winding 18 of the switching transformer 4 is connected to a low voltage output terminal 21 via a rectifying diode 20, and the low voltage output terminal 21 is a voltage dividing resistor 23 of a low voltage output voltage detection circuit 22. Connected to ground via 24, the connection point 25 of the voltage dividing resistors 23, 24 is connected to the base 27 of the low voltage output voltage detection transistor 26, and the collector 28 of the low voltage output voltage detection transistor 26 has a low voltage output voltage detection diode 29, It is connected to the switching control circuit 16 via the photocoupler 15, and the emitter 30 of the low voltage output voltage detecting transistor 26 is connected to the ground via the low voltage output voltage setting zener diode 31. The monitor control terminal 32 has a collector 3 on the base 27 of the low voltage output voltage detecting transistor 26 of the low voltage output voltage detecting circuit 22.
3 is connected to the base 35 of the mode switching transistor 34
To the connection point 38 of the delay circuit resistor 36 and the bias resistor 37 via the delay circuit resistor 36 and the bias resistor 37.
A delay circuit capacitor 39 and a delay circuit diode 40 are connected between the ground and the monitor control terminal 32, and a delay circuit resistor 41 is connected between the base 35 of the mode switching transistor 34 and the ground. 42 is a smoothing capacitor connected between the low voltage output terminal 21 and the ground. The monitor control terminal 32 is a relay drive resistor 4
Base 4 of the relay drive transistor 44 through 3
5, the collector 46 of the relay drive transistor 44 is connected to the low voltage output terminal 21 via the relay drive coil 47 of the relay 9, and the emitter 48 is connected to the ground.

Next, the operation of the above conventional switching power supply circuit will be described. The DC input voltage of the DC input voltage terminals 1 and 2 is switched by the switching output circuit 3 and is added to the primary winding 5 of the switching transformer 4, and the secondary winding 6 for medium voltage and the secondary winding 18 for low voltage are respectively used for TV. Take out the medium voltage output voltage for VTR and the low voltage output voltage for VTR,
Rectifying diodes 8 and 20 and smoothing capacitors 17 and 42
Each of them is rectified and smoothed, and an output is directly obtained at the low voltage output terminal 21 via the relay contact 10 at the intermediate voltage output terminal 11. Next, the error of the medium voltage output voltage or the low voltage output voltage is detected by the medium voltage output voltage detection circuit 12 or the low voltage output voltage detection circuit 22, and the error signal is transmitted to the switching control circuit 16 via the photocoupler 15, and this error is detected. The output voltage of the switching output circuit 3 is controlled so that the signal becomes minimum.

In such a state, when the monitor control voltage Em applied to the monitor control terminal 32 changes from 0V to 5V as shown in the voltage waveform diagram of FIG.
The monitor control voltage Em of 5V is applied to the base 45 of the relay drive transistor 44 via the relay drive resistor 43, and the relay drive transistor 4
4, the relay drive current flows through the relay drive coil 47, the relay contact 10 is closed, and the voltage of one terminal 7 of the intermediate voltage secondary winding 6 of the switching transformer 4 at the intermediate voltage output terminal 11, for example, The 140V TV medium voltage output voltage set by the voltage output voltage detection circuit 12 appears.
As shown in FIG. 4B, there is a time delay of Tα from the application of the 5V monitor control voltage Em to the monitor control terminal 32 until the relay contact 10 is closed. There will be a time when there is no output of
During that time, the switching output circuit 3 is not controlled based on the error signal of the medium voltage output voltage. However, at that time, the monitor control voltage E of 5 V applied to the monitor control terminal 32 is applied.
As shown in (c) of FIG. 4, m is added to the base 35 of the mode switching transistor 34 with a delay of Tβ by a delay circuit including a delay circuit resistor 36, a delay circuit capacitor 39, etc. 34 becomes conductive, the low-voltage output voltage detection transistor 26 is turned off, and the control of the switching output circuit 3 based on the error signal of the low-voltage output voltage is not performed because Tβ is applied after the monitor control voltage Em of 5V is applied. After time, T
By selecting α <Tβ, the state where the control of the switching output circuit 3 is completely lost is eliminated. At this time, the low-voltage output voltage appearing at the low-voltage output terminal 21 becomes a voltage set by the winding ratio of the intermediate-voltage secondary winding 6 and the low-voltage secondary winding 18 of the switching transformer 4 and the voltage set at the load, for example, 14.5V.

Conversely, when the monitor control voltage Em changes from 5V to 0V, the relay drive transistor 44 is turned on.
Turns off, the relay drive current flowing through the relay drive coil 47 disappears, and the monitor control voltage Em is 0V.
The relay contact 10 opens after Tα time after switching to
The intermediate voltage output voltage of the intermediate voltage output terminal 11 becomes 0, the output from the intermediate voltage output voltage detection circuit 12 disappears, and the switching output circuit 3 is not controlled based on the error signal of the intermediate voltage output voltage. On the other hand, the state in which the output of the low-voltage output voltage detection circuit 22 that controls the switching output circuit 3 was 0 before the monitor control voltage Em was switched to 0V immediately changed even when the monitor control voltage Em was switched to 0V. Then, the control signal does not appear in the low voltage output voltage detection circuit 22, but the control signal appears by the delay circuit including the delay circuit resistor 36, the delay circuit capacitor 39, etc. after the monitor control voltage Em is switched to 0V. After Tβ time, Tα
Since <Tβ, there is no output from the low-voltage output voltage detection circuit 22 for a while after the output from the medium-voltage output voltage detection circuit 12 disappears, and the control signal is sent to the low-voltage output voltage detection circuit 22 after a certain period of time. Is what appears. At this time,
The mode switching transistor 34 becomes non-conductive, the low voltage output voltage detection transistor 26 becomes conductive, and the low voltage output terminal 21
The low-voltage output voltage appearing at is determined by the division ratio of the voltage dividing resistors 23 and 24 for setting the low-voltage output voltage, the base voltage of the low-voltage output voltage setting zener diode 31 and the low-voltage output voltage detecting transistor 26, and is, for example, 14.5V.

[0006]

However, in the above-mentioned conventional switching power supply circuit, the monitor control voltage Em is switched from 5V to 0V to open the relay contact 10 and the intermediate voltage output voltage detection circuit 12 becomes non-active. After that, the voltage stabilization control in the low voltage output voltage detection circuit 22 becomes active when the delay circuit resistor 36 and the delay circuit capacitor 3 are activated.
Since it is delayed that the mode switching transistor 34 becomes non-conductive in the delay circuit including the delay circuit 9 and the like, the delay circuit diode 4
0, even if the improvement circuit of the delay circuit resistance 41 is attached, the interruption of the voltage stability control cannot be completely eliminated, and, for example, an overvoltage at the low voltage output voltage as shown in FIG. 4D is generated. Had a problem.

The present invention aims to solve the above conventional problems.

[0008]

In order to solve the above-mentioned problems, the present invention outputs a first voltage and a second voltage,
In a switching power supply circuit including a voltage control circuit that stably controls the output voltage based on the voltage obtained by detecting the output voltage, the first voltage does not appear due to a delay in the operation of the relay during mode switching, and the first voltage While the control of the output voltage stabilization based on the voltage of is interrupted, the second voltage is temporarily made higher than the voltage in the normal state, and the control of the output voltage stabilization based on the second voltage is temporarily interrupted. This delays the situation in which the output voltage stabilization control is completely lost.

As a result, it is possible to obtain a switching power supply circuit in which the occurrence of overvoltage during mode switching is stably suppressed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention outputs a first voltage and a second voltage, and stabilizes the output voltage based on the voltage obtained by detecting the output voltage. The first voltage does not appear due to the delay of the operation of the relay at the time of mode switching, and the control of the output voltage stabilization based on the first voltage is interrupted while the second voltage in the normal state is provided. It is a switching power supply circuit that eliminates the situation where the output voltage stabilization control is completely lost by temporarily raising the voltage higher than the voltage and temporarily stopping the interruption of the output voltage stabilization control based on the second voltage. At the time of switching, the voltage stabilization control based on the second voltage is continuously performed until the voltage stabilization control based on the first voltage is performed.

According to a second aspect of the present invention, a voltage control circuit for stably controlling the output voltage based on the voltage obtained by detecting the output voltage of the first voltage and the second voltage, Switching means for switching between a mode for cutting off the output of the first voltage and outputting only the second voltage and a mode for outputting both the first voltage and the second voltage; and the first and second voltage outputs. The first and second detection means for detecting the above, and the control means for generating a control signal for simultaneously controlling the switching control of the switching means and the operation / non-operation control of the second detection means. When the voltage of and the second voltage are output at the same time,
The voltage applied to the voltage control circuit is detected by the first detection means, and when only the second voltage is output, the voltage applied to the voltage control circuit is detected by the second detection means and the switching is performed. A switching power supply circuit to which a voltage for holding the second detection means in an operating state is temporarily added until the first voltage is output by the switching control of the means, and the first voltage is controlled by the switching control. Since the second detecting means is in the operating state until the output of, the voltage based on the second voltage is applied during the switching operation of the switching means even before the voltage control based on the first voltage is performed. Control is performed.

According to a third aspect of the present invention, the first voltage is a medium voltage in the TV mode in which both the VTR and the TV are operated, and the second voltage is in the light load mode in which only the VTR is operated. The switching power supply circuit according to claim 2, wherein the voltage is a low voltage, and voltage control based on the low voltage in the light load mode is performed even before the medium voltage in the TV mode appears during the switching operation to the TV mode by the switching means. Be seen.

Embodiments of a switching power supply circuit according to the present invention will be described below with reference to the drawings.

(Embodiment) FIG. 1 is a circuit diagram according to an embodiment of the present invention, in which parts having the same structure, operation, and operation as those of the conventional example shown in FIG. Is omitted.

In FIG. 1, a resistor 49 is inserted and connected between the collector 33 of the mode switching transistor 34 and the base 27 of the low voltage output voltage detecting transistor 26, and the delay circuit resistor 36, the delay circuit capacitor 39 and the delay circuit diode in FIG. 40 except that the delay circuit resistor 41 is removed from FIG.
3 is a circuit diagram of the same configuration as FIG.

In such a state, when the monitor control voltage Em applied to the monitor control terminal 32 changes from 0V to 5V, as shown in the voltage waveform diagram of FIG.
As shown in FIG. 2B, the medium voltage output terminal 11 has 140
The V medium voltage output voltage for TV appears after time Tα. 5
The control of the switching control circuit 16 based on the medium-voltage output voltage for TV is not performed for the time Tα after V is applied. On the other hand, as shown in FIG. 2C, the low voltage output terminal 2
Monitor control voltage E while low voltage output voltage of 1 is 14.5V
When m changes from 0V to 5V, the low voltage output voltage detection transistor 26 becomes non-conductive, and the switching control circuit 16 is not controlled based on the low voltage output voltage. Therefore, in the present embodiment, 14.5 of the low voltage output terminal 21 is used.
By setting the low voltage output voltage of V to 15.5V for the time of Tα, even if the monitor control voltage Em changes from 0V to 5V, the potential of the base 27 of the low voltage output voltage detection transistor 26 is low voltage output voltage detection transistor. 26 becomes high enough to conduct 26, and the switching control circuit 16 based on the low voltage output voltage is controlled for the time of Tα. After the time of Tα, the switching control circuit based on the intermediate voltage output voltage is controlled. Until the control of 16 is performed, the control of the switching control circuit 16 is not interrupted.

[0017]

As described above, the present invention outputs the first voltage and the second voltage and stably controls the output voltage based on the voltage obtained by detecting the output voltage. In a switching power supply circuit equipped with
The first voltage does not appear due to the operation delay of the relay, and while the control of the output voltage stabilization based on the first voltage is interrupted, the second voltage
A situation in which the output voltage stabilization control is completely lost by temporarily increasing the voltage of the output voltage above the voltage in the normal state and temporarily delaying the interruption of the output voltage stabilization control based on the second voltage. This makes it possible to stably suppress the occurrence of overvoltage during mode switching.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a switching power supply circuit of the present invention.

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

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

4 is a voltage waveform diagram in each part of the circuit diagram of FIG.

[Explanation of symbols]

 1, 2 DC input voltage terminal 3 Switching output circuit 4 Switching transformer 8 Rectifying diode 9 Relay 10 Contact 11 Medium pressure output terminal 12 Medium pressure output voltage detection circuit 13 Medium pressure output voltage detection terminal 14 Medium pressure output voltage detection diode 15 Photo coupler 16 switching control circuit 21 low voltage output terminal 22 low voltage output voltage detection circuit 23, 24 voltage dividing resistor 26 low voltage output voltage detection transistor 29 low voltage output voltage detection diode 32 monitor control terminal 34 mode switching transistor 36, 41 delay circuit resistance 37 bias resistance 39 Delay circuit capacitor 40 Delay circuit diode 44 Relay drive transistor 47 Relay drive coil 49 Resistance

Claims (3)

[Claims] 1. A voltage control circuit for outputting a first voltage and a second voltage, and stably controlling the output voltage based on a voltage obtained by detecting the output voltage, and operating a relay at the time of mode switching. While the first voltage does not appear due to the delay and the control of the output voltage stabilization based on the first voltage is interrupted, the second voltage is temporarily made higher than the voltage in the normal state,
The switching power supply circuit eliminates the situation where the output voltage stabilization control is completely lost by temporarily delaying the interruption of the output voltage stabilization control based on the voltage. 2. A voltage control circuit for stably controlling an output voltage based on a voltage obtained by detecting an output voltage of a first voltage and a second voltage, and shutting off the output of the first voltage. Switching means for switching between a mode for outputting only the second voltage and a mode for outputting both the first voltage and the second voltage, and first and second detection for detecting the first and second voltage outputs. Means and a control means for generating a control signal for simultaneously controlling the switching control of the switching means and the operation / non-operation control of the second detection means, and the first voltage and the second voltage are simultaneously output. The voltage applied to the voltage control circuit is detected by the first detection means when the voltage control circuit is being output, and the voltage applied to the voltage control circuit is output from the second detection means when only the second voltage is output. The first voltage is detected by the switching control of the switching means. A switching power supply circuit in which a voltage for holding the second detecting means in an operating state is temporarily added until output. 3. The method according to claim 2, wherein the first voltage is a medium voltage in the TV mode in which both the VTR and the TV are operated, and the second voltage is a low voltage in the light load mode in which only the VTR is operated. Switching power supply circuit.