JPH06311740A - Switching power supply equipment - Google Patents

Abstract

PURPOSE:To generate a secondary output voltage with a given blunt characteristic in waveform at a rise time regardless of the time at which the output voltage rises. CONSTITUTION:A control system includes a light emitting element 24 of a photocoupler that is supplied with electricity at rise time of a secondary-side output voltage while a capacitor 23 is charged for a given time after the secondary output voltage reaches a given level that is set previously. In a switching circuit the operation is controlled through a photodetector of the photocoupler so that the secondary output voltage is reduced. By using this control system, in which a rise in secondary output voltage is reduced, a soft starting circuit 21 is constituted for providing a blunt characteristic in waveform at the rise time.

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 device having a soft start circuit.

[0002]

2. Description of the Related Art FIG. 6 is a block circuit diagram of a conventional switching power supply device. In the figure, 1 is a transformer,
It has P, D, S1, and S2 windings. Reference numeral 2 is an input terminal of the P winding, to which a DC voltage (hereinafter referred to as “input voltage”) V _{2 obtained} by rectifying a commercial AC voltage is applied. Reference numeral 3 is a field effect transistor (hereinafter referred to as “MOS • FET”), and the P winding is connected to the source. 4 is a grounding resistor connected to the drain of the MOS / FET 3; 5 is a drive circuit for switching the MOS / FET 2; 6 is a drive circuit 5
The control unit 7 controls the switching operation of the control unit 6, and the control unit 6 controls the control unit 5 via the resistor 8 to start the control voltage (hereinafter, “V ₇
Is a diode for rectifying the voltage induced in the D winding, and 10 is a capacitor for smoothing the rectified voltage. The charging voltage of the control unit 6 is a driving voltage (hereinafter, referred to as “V ₁₀ ")) Is applied. Reference numeral 11 is a light receiving element that constitutes a photocoupler, and 12 is a resistor that limits the current i ₁₁ flowing into the controller 6 through the light receiving element 11.

Next, 13 is a rectifying diode connected to the S1 winding via a relay 14, 15 is a capacitor for smoothing the rectified voltage, and 16 is a smoothed first DC voltage (hereinafter, "V"). ₁₆ "), 17 is a rectifying diode connected to the S2 winding, 18 is a smoothing capacitor, and 19 is a second DC voltage (hereinafter," V ₁₉ ").
A second output terminal for outputting V), 20 is an error amplifier for suppressing V ₁₆ from exceeding a set value, 21 is a soft start circuit for blunting the rising waveform of V ₁₆ , and 22 and 23 are soft start circuits. 21 is a series body of a resistor and a capacitor that determine the time constant of 21, and 24 is a light emitting element that constitutes a photocoupler. V ₁₉ supplies a drive current i ₂₁ to the soft start circuit 21 via the light emitting element 24 and also a resistor. The drive current i ₂₀ is also supplied to the error amplifier 20 via the device 25.

First, the operating conditions of this conventional example will be described.
The rising characteristic of V ₁₆ is the characteristic a in FIG. 7 when it rises freely, and it reaches the set value V at time t ₁ and reaches the set value V at time t _3. As described above, the soft start circuit 21 dulls it.

Further, it is assumed that the relay 14 is closed, V ₂ is applied to the input terminal 2 at time t ₀ , and at the same time, it starts to rise.

Next, the rising operation of the drive voltage V ₁₀ of the controller 6 will be described. First, when V ₇ is applied to the input terminal 7, charging of the capacitor 10 is started, and the terminal voltage of the capacitor 10 (hereinafter referred to as “V ₁₀ ”) goes from the 0 point to the a point in FIG. 8A. When the voltage rises and exceeds the minimum operating voltage of the control unit 6 (hereinafter referred to as "V ₁₀ '"), the control unit 6 becomes operable. After this, at time t ₀ , the input terminal 2
When V ₂ is applied to the drive circuit 5, the drive circuit 5 is controlled by the control unit 6 to turn on the MOS • FET 3, a current starts to flow in the P winding, and at the same time a drive current starts to flow in the control unit 6,
V ₁₀ descends from point a to point b. On the other hand, when the voltage induced voltage is rectified by a diode 9 of the winding D from time t ₀ (FIG. 8 (b)) is higher than the terminal voltage V ₁₀ of the capacitor 10 at time t ₄ when applied to the capacitor 10 C Then, charging of the capacitor 10 is started, so that V ₁₀ rises again. As a result, V ₁₀ has a waveform as shown in FIG.

In this case, the value V _C of V _{10 at} the point _C is
The capacity and the like of the capacitor 10 are set so as not to become lower than the minimum operating voltage V ₁₀ ′ of the control unit 6.

Next, the operation of the soft start circuit 21 will be described. 7 is V ₇ to terminal 7 before the time t ₀ is applied, with in V ₂ to the terminal 2 time t ₀ is applied beginning rise V ₁₆ and V _19, the error amplifier through a light-emitting element 24 at the same time 20 and the soft start circuit 21 are applied with a drive voltage, the current i is supplied to the error amplifier 20 while V ₁₆ does not reach the set voltage V _{12.
Since 20} does not flow, only the charging current i ₂₁ of the capacitor 23 flows, and when V ₁₉ becomes a constant potential at time t ₂ , i ₂₁ gradually increases.
Decreases and becomes zero at time t ₃ . As a result, V ₁₆
Shows a waveform in which the rising characteristic is blunted like the characteristic b in FIG.

Next, the operation of the error amplifier 20 will be described. The error amplifier 20 controls the operation of the control unit 6 via the photocoupler so as to return it to V when V ₁₆ exceeds the set value V. That is, if V ₁₆ becomes higher than the preset voltage V, a driving current flows through the light emitting element 24 and the resistor 25 to the error amplifier 20, and the light emitting signal of the light emitting element 24 is received by the light receiving element 11. A signal current corresponding to the amount of received light is input to the control unit 6. When the control unit 6 receives this signal current, it determines that V ₁₆ has exceeded V, and suppresses the operation of the MOS • FET 3 via the drive circuit 5 so that the voltage fluctuation of the P winding becomes small. As a result, the induced voltage in the S1 winding also drops, so V ₁₆
Decreases as it approaches V.

On the contrary, when V ₁₆ becomes lower than V, the error amplifier 20 does not operate, so that no current flows through the light emitting element 24. Therefore, since the light receiving element 11 is in the off state, no signal current is input to the control unit 6. In this case, the control unit 6 determines that V ₁₆ is lower than V, and controls the MOS · F via the drive circuit 5 so that the voltage fluctuation of the P winding becomes large.
ET3 is driven, and as a result, V ₁₆ rises toward V.

[0011]

However, as shown in FIG. 9, in the power supply device, the relay 14 is turned on at a time point t ₅ when V ₁₆ is delayed from the start time point t ₀ of V _19. In this case, since the soft start circuit 21 has started the blunting action before the rise of V ₁₉ , the sufficient suppression effect cannot be obtained, and in the power supply device with a fast rise rate of V ₁₆ , as shown in FIG. a waveform overshoot Gimi to reach V at time t ₆ after a short time from t _5, occurs problem on the breakdown voltage characteristic high peak voltage is generated in the case of generating a high voltage using a step-up transformer There were problems such as.

The present invention has been made for the purpose of solving the above problems, and even in a power supply device in which the rising time of the first output voltage is later than the rising time of the driving power supply of the soft start circuit. An object of the present invention is to obtain a switching power supply device including a soft start circuit that can slow the rise of the first output voltage.

[0013]

A switching power supply device according to the present invention is obtained by rectifying a switching circuit for controlling an energization amount on a primary side of a transformer and a voltage induced on a secondary side of the transformer. The photocoupler light-emitting element whose energization is controlled according to the output voltage and the photocoupler light-receiving element which is arranged facing the light-emitting element to control the switching circuit are provided, and the output voltage on the secondary side of the transformer is When the set value is exceeded, the light emitting element of the photocoupler is energized and the switching circuit is controlled via the light receiving element to reduce the energization amount on the primary side to reduce the output voltage on the secondary side and to output it. When the voltage drops below the set value, in the switching power supply device that controls the switching circuit to increase the energization amount on the primary side to increase the output voltage on the secondary side, Those having a soft start circuit during a so as to energize the light-emitting element of the photo coupler before it is charged capacitor with from the time of reaching the voltage determined because a predetermined time constant.

[0014]

The soft start circuit according to the present invention acts to dull the output waveform from the time when the output voltage reaches the predetermined value.

[0015]

EXAMPLES Example 1. 1 is a circuit diagram of Embodiment 1 of the invention, and the same reference numerals as those in FIG. 6 denote the same parts,
The parts other than the configuration of the soft start circuit 21 are the same, and operate in the same manner. In FIG. 1, 25, 2
Reference numeral 6 denotes a voltage dividing resistor connected in series between the output terminal 16 and the ground, which divides V ₁₆ at a predetermined ratio to a predetermined value before V ₁₆ reaches V (hereinafter referred to as “V ₀ ”). ) Is reached, the base is connected to the connection point of the resistors 25 and 26, the collector is connected to the light emitting element 24, and the emitter is connected to the capacitor 23 via the resistor 22.
The resistance value is set so that 7 is turned on. Two
Reference numeral 8 denotes a diode, an anode of which is connected to a connection point of the resistor 22 and the capacitor 23, and a cathode of which is connected to the base of the transistor 27.
It discharges through and protects the transistor 27.

Next, the operation of the part different from the conventional example when V ₁₆ and V ₁₉ rise simultaneously will be described with reference to FIG.
Even if V ₇ is applied from terminal 7 and V ₁₉ rises, V 7
_Since the transistor 27 in the soft start circuit 21 is not turned on before reaching ₀ , the soft start circuit 21 does not operate.

Next, when V ₁₆ reaches V ₀ at time t ₇ ,
The transistor 27 is turned on, the charging current i ₂₁ starts to flow from V ₁₉ to the capacitor 23 via the light emitting element 24, the transistor 27, and the resistor 22, and V ₁₆ is the drive voltage V ₁₀ of the control unit 6 and the minimum operating voltage. action blunts from time t ₁ exceeds the V ₁ to be V _C of the soft start circuit 21 is started, is continued while weakening the action blunts gradually until time t ₃ when the subsequent i ₂₁ becomes zero. As a result, the rising waveform of the V ₁₆ are as shown in V ₁₆ in FIG.

In FIG. 3, the time t ₅ at which V ₁₆ starts to rise is
7 is a waveform diagram of the first embodiment when rising from time t ₅ later than the rising start time t ₀ of V ₁₉ .

Also in this case, the time t ₈ at which i ₂₁ starts to flow
Is from the time when V ₁₆ reaches V ₀ , the output waveform of V ₁₆ similar to that in the case of FIG. 2 is obtained.

When the relay 14 is turned off after V ₁₆ rises to V, the transistor 27 is turned off and a reverse voltage V _EB0 is applied between the emitter and the base, but a voltage higher than the voltage drop of the diode 28 is applied. Since this does not occur, the transistor 27 is not destroyed.

Further, since the charge charged in the capacitor 23 is discharged through the diode 28 and the resistor 26, even if the relay 14 is turned on again, the soft start circuit 21 operates and the rising waveform of the first output voltage. To blunt.

Example 2. 4 is a circuit diagram showing a second embodiment of the present invention, in which the same reference numerals as those in FIG. 1 denote the same or corresponding parts, 29 is a microcomputer constituting the soft start circuit 21, and 30 is a first output terminal. 1
6 is a protective resistor for supplying power to the microcomputer 29. The microcomputer 29 is a resistor 3
The soft start operation is performed by detecting the first output voltage via 0 and controlling the amount of current flowing through the light emitting element 24.

FIG. 5 is a waveform diagram of the first output voltage of the second embodiment, and the control operation of the microcomputer 29 of the second embodiment will be described below with reference to FIG. Microcomputer 29
The first output voltage value is V _A = V ₁ , V _B , V _C ...
Each value of V _n = V, the current value to be supplied to the light emitting element 24 are pre-programmed when it reaches, the energization amount is the closer from V _A to V _n, are sequentially decreased, V _n = V
It is set to zero when it becomes. Therefore, from the time t _A when V ₁₆ reaches V _A , a current starts to flow in the light emitting element 24, the rise of V ₁₆ starts to slow down, and time t _B
In a little less how blunts switched to slightly less current reaches the voltage V _B, below, Yuki with less how blunts by reducing the sequential current value upon reaching the set voltage, the time t _n When the set value V = V _n is reached, the current value is set to zero. As a result, the rising waveform of V ₁₆ becomes an appropriate rising waveform as shown in FIG.

[0024]

According to the present invention, since the operation of the soft start circuit is started when the output voltage, which tends to make the rising waveform dull, reaches a predetermined value, the soft start circuit starts operating at the rising start time of the output voltage. Without a certain blunting effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is an output waveform diagram of a first operation example of the first embodiment.

FIG. 3 is an output waveform diagram of a second operation example of the first embodiment.

FIG. 4 is a circuit diagram of a second embodiment of the present invention.

FIG. 5 is an output waveform diagram of the second embodiment.

FIG. 6 is a circuit diagram of a conventional switching power supply device.

FIG. 7 is an output waveform diagram of a first operation example of a conventional example.

FIG. 8 is a rising waveform diagram of a control unit drive voltage in a conventional example.

FIG. 9 is an output waveform diagram of a second operation example of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 transformer 3 MOS / FET 5 drive circuit 6 control section 9 diode 10 capacitor 11 photocoupler light receiving element 13 diode 14 relay 15 capacitor 17 diode 18 capacitor 20 error amplifier 21 soft start circuit 22 resistor 23 capacitor 24 photocoupler light emitting element 25 resistor 26 resistor 27 transistor 28 diode 29 microcomputer P primary winding S1 secondary winding S2 secondary winding D secondary winding

Claims (1)

[Claims] 1. A switching circuit for controlling an energization amount on a primary side of a transformer, and a photocoupler for energization controlled corresponding to an output voltage obtained by rectifying a voltage induced on a secondary side of the transformer. A light emitting element, the light receiving element of the photocoupler arranged to face the light emitting element to control the switching circuit, and the light emitting element of the photocoupler when the output voltage on the secondary side of the transformer exceeds a set value. Is energized to control the switching circuit via the light receiving element to reduce the energization amount on the primary side to reduce the output voltage on the secondary side, and the output voltage falls below the set value. In this case, in the switching power supply device in which the switching circuit is controlled to increase the energization amount on the primary side to increase the output voltage on the secondary side, the output voltage reaches a predetermined voltage. A switching power supply device comprising a soft start circuit configured to energize a light emitting element of the photocoupler from a point of time until the capacitor is charged with a predetermined time constant.