JP2014060850A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a change of the timing of starting intermittent oscillation control.SOLUTION: A switching power supply 1 having an LLC resonant circuit and switch elements Q1, Q2 detects an error between a voltage value of an output voltage and a target value of the output voltage determined by a supply voltage of a reference voltage source Vref, and changes a voltage of a first terminal P1 in accordance with the detection result. An input voltage detection section 20 detects an input voltage or a voltage depending on the input voltage, and a control circuit 10 sets a maximum oscillation frequency of the switching power supply 1 in accordance with the voltage detected by the input voltage detection section 20. The control circuit 10 further controls an on-off frequency of the switch elements Q1, Q2 on the basis of the maximum oscillation frequency thus set and the voltage of the first terminal P1.

Description

  The present invention relates to a switching power supply.

  Conventionally, a switching power supply having a resonant circuit has been proposed (see, for example, Non-Patent Document 1).

[Configuration of Switching Power Supply 100]
FIG. 9 is a circuit diagram of a switching power supply 100 according to a conventional example. The switching power supply 100 includes a transformer T, a primary circuit connected to the primary winding W1 of the transformer T, and a secondary circuit connected to the secondary windings W2 and W3 of the transformer T.

  First, the primary side circuit will be described. The primary side circuit includes switch elements Q1 and Q2 configured by N-channel MOSFETs, a control circuit 110, a capacitor C1, an inductor L, and a phototransistor PC2.

  The switch elements Q1 and Q2 form a half bridge circuit, and the input terminal IN is connected to the drain of the switch element Q1. An input terminal GND connected to a reference potential source is connected to the source of the switch element Q2. One end of the primary winding W1 is connected to the source of the switch element Q1 and the drain of the switch element Q2 via the capacitor C1 and the inductor L. Capacitor C1, inductor L, and primary winding W1 form an LLC resonant circuit. An input terminal GND is connected to the other end of the primary winding W1.

  A control circuit 110 is connected to the gate of the switch element Q1 and the gate of the switch element Q2. The control circuit 110 is connected to the input terminal GND and to the emitter of the phototransistor PC2 at the first terminal P1. A voltage source V1 is connected to the collector of the phototransistor PC2.

  Next, the secondary circuit will be described. The secondary circuit includes diodes D1 and D2, capacitors C2 and C3, resistors R1 to R4, a reference voltage source Vref, an error amplifier AMP, and a photodiode PC1.

  One end of the secondary winding W2 is connected to the anode of the diode D1, and the other end of the secondary winding W3 is connected to the anode of the diode D2. The output terminal OUT1 is connected to the cathode of the diode D1 and the cathode of the diode D2. The output terminal OUT2 is connected to the other end of the secondary winding W2 and one end of the secondary winding W3. The output terminal OUT1 and the output terminal OUT2 are connected through a capacitor C2 and are connected through resistors R3 and R4.

  The output terminal OUT1 is connected to one end of the resistor R3, one end of the resistor R4 is connected to the other end of the resistor R3, and the output terminal OUT2 is connected to the other end of the resistor R4. An inverting input terminal of the error amplifier AMP is connected to the other end of the resistor R3 and one end of the resistor R4, and an output terminal of the error amplifier AMP is connected via the capacitor C3 and the resistor R2. The positive terminal of the reference voltage source Vref is connected to the non-inverting input terminal of the error amplifier AMP, and the output terminal OUT2 is connected to the negative electrode of the reference voltage source Vref.

  The output terminal of the error amplifier AMP is connected to the cathode of the photodiode PC1, and the anode of the photodiode PC1 is connected to the output terminal OUT1 via the resistor R1. The photodiode PC1 is provided in a pair with the phototransistor PC2, and the photodiode PC1 and the phototransistor PC2 constitute a photocoupler.

[Operation of Switching Power Supply 100]
In the switching power supply 100 having the above configuration, the control circuit 110 controls the on / off frequency of the switching elements Q1 and Q2 according to the voltage of the first terminal P1, and the input inputted from the input terminals IN and GND. The voltage is converted into a predetermined voltage and output from the output terminals OUT1 and OUT2 as output voltages.

  The voltage of the first terminal P1 changes according to the output voltage. Specifically, the error amplifier AMP detects an error voltage that is an error between the voltage value of the output voltage and the target value of the output voltage determined by the power supply voltage of the reference voltage source Vref, and the amount of light corresponding to the detection result is detected. From the photodiode PC1 to the phototransistor PC2. The phototransistor PC2 allows a current corresponding to the amount of light received from the photodiode PC1 to flow from the voltage source V1 toward the first terminal P1. According to this, the voltage of the first terminal P1 changes according to the error voltage.

  By the way, in the switching power supply as described above, there has been proposed a technique for intermittently oscillating the switch element at light load or no load. When the switch element is intermittently oscillated, the switching operation is temporarily suspended. For this reason, since the switching frequency per unit time can be reduced and the switching loss per unit time can be reduced, the power conversion efficiency at the time of light load or no load can be improved.

  For example, a case where intermittent oscillation control is started in the switching power supply 100 according to the conventional example shown in FIG. 9 will be described below.

  When the load becomes lighter, the oscillation frequency fsw of the switching power supply 100 increases due to the parasitic capacitance of the diode D1 and the parasitic capacitance of the diode D2. Even if the oscillation frequency fsw rises to the maximum oscillation frequency fmax that is the upper limit of the predetermined oscillation frequency fsw, the oscillation frequency fsw cannot be increased if the load is further reduced. Therefore, as shown in FIG. Vo rises. When the output voltage Vo rises, as shown in FIG. 13, the voltage VP1 of the first terminal P1 also rises according to the error voltage and becomes equal to or higher than the threshold voltage Vbst preset in the control circuit 110. When the voltage VP1 of the first terminal P1 becomes equal to or higher than the threshold voltage Vbst, the control circuit 110 starts intermittent oscillation control and temporarily stops the oscillation of the switch elements Q1 and Q2. FIG. 11 is a diagram illustrating a change in the output voltage Vo at a light load, in which the vertical axis represents the output voltage Vo and the horizontal axis represents time. FIG. 12 is a diagram illustrating the relationship between the output voltage Vo and the oscillation frequency fsw. In FIG. 12, the vertical axis indicates the output voltage Vo, and the horizontal axis indicates the oscillation frequency fsw of the switching power supply 100. FIG. 13 is a diagram illustrating a change in voltage of the first terminal P1 of the switching power supply 100 at a light load. The vertical axis indicates the voltage VP1 of the first terminal P1, and the horizontal axis indicates time.

  In FIG. 12, the oscillation frequency fsw when the output voltage Vo is V1 is f1, and the oscillation frequency fsw when the output voltage Vo is V2 is f2. Then, the load current from when the oscillation frequency fsw becomes the maximum oscillation frequency fmax until the voltage VP1 of the first terminal P1 corresponding to the output voltage Vo becomes equal to or higher than the threshold voltage Vbst is the output voltage Vo is V1. It is the same whether it is V2 or V2. For this reason, the load current from when the oscillation frequency fsw reaches the maximum oscillation frequency fmax to when the intermittent oscillation control is started is equal regardless of whether the output voltage Vo is V1 or V2.

  However, the load current from when the load starts to light down until the oscillation frequency fsw reaches the maximum oscillation frequency fmax is as shown by Δ1 and Δ2, depending on whether the output voltage Vo is V1 or V2. Different.

  For this reason, as described above, the timing of starting the intermittent oscillation control differs depending on the voltage value of the output voltage Vo.

  Similarly, there is a correlation between the oscillation frequency of the switching power supply and the output voltage Vo. Similarly, there is a correlation between the oscillation frequency of the switching power supply and the input voltage. Therefore, the timing for starting the intermittent oscillation control varies depending on the voltage value of the input voltage.

  Therefore, in order to solve such a problem, in the switching power supply 100A as shown in FIG. 10, a technique for intermittently oscillating the switch element at the time of light load or no load has been proposed (for example, see Patent Document 1). . The switching power supply 100 </ b> A detects an output voltage, and a signal is output to the intermittent oscillation signal generator 120 via the insulation circuit 130. When the load driven by the output voltage of the switching power supply 100A is in a light load state or no load state, an intermittent oscillation signal is output from the intermittent oscillation signal generator 120 to the control circuit 110A, and intermittent oscillation control is started.

JP 2008-109766 A

NCP1397A, [online], [Search August 6, 2012], Internet <URL: http://www.onsemi.com/pub_link/Collateral/NCP1397JP.rev4.pdf>

  However, the switching power supply 100A shown in FIG. 10 needs to be provided with an insulation circuit 130, and the insulation circuit 130 has a complicated configuration. As a result, there is a problem that the circuit configuration of the entire switching power supply 100A is complicated. It becomes.

  In view of the above-described problems, an object of the present invention is to suppress a change in timing for starting intermittent oscillation control.

The present invention proposes the following items in order to solve the above-described problems.
(1) The present invention relates to a resonance circuit (e.g., equivalent to an LLC resonance circuit formed by the capacitor C1, the inductor L, and the primary winding W1 in FIG. 1) and a switch element (for example, the switch element Q1, FIG. 1 is a switching power supply (corresponding to, for example, the switching power supply 1 in FIG. 1), and detects a voltage according to the input voltage, the input voltage, the output voltage, or the voltage according to the output voltage (For example, equivalent to the input voltage detection unit 20 in FIG. 1) and control means (for example, equivalent to the control circuit 10 in FIG. 1) for controlling the on / off frequency of the switch element, the control means Detects a voltage at the time of starting the intermittent oscillation control by the voltage detection means, and according to this voltage, a correction means for setting a frequency at the time of starting the intermittent oscillation control (for example, 1) and a first terminal (e.g., corresponding to the first terminal P1 in FIG. 1), the frequency at which the intermittent oscillation control is started, and the first The switching power supply is characterized in that the on / off frequency of the switch element is controlled based on the voltage at the terminal of the switch.

  According to this invention, the voltage detection means and the control means are provided in the switching power supply having the resonance circuit and the switch element. The voltage detection means detects the input voltage, the voltage according to the input voltage, the output voltage, or the voltage according to the output voltage. Further, the control means is provided with a correction means and a first terminal, and the correction means detects the voltage at the time when the intermittent oscillation control is started by the voltage detection means, and the time when the intermittent oscillation control is started according to this voltage. It was decided to set the frequency. Then, the control means controls the on / off frequency of the switch element based on the frequency at the time of starting the intermittent oscillation control set by the correction means and the voltage of the first terminal.

  According to this, the correction means sets the frequency at the time of starting the intermittent oscillation control according to the output voltage or the voltage corresponding to the output voltage. Therefore, even if the voltage value of the output voltage is different, the frequency at the time of starting the intermittent oscillation control is set according to the output voltage, and the oscillation frequency of the switching power supply starts the intermittent oscillation control after the load starts to lighten. The load current up to the frequency at the start time can be made equal. Therefore, it is possible to suppress a change in timing for starting the intermittent oscillation control.

  (2) In the switching power supply of (1), the present invention provides a switching power supply characterized in that a maximum oscillation frequency that is an upper limit of an oscillation frequency of the switching power supply is a frequency at the time of starting the intermittent oscillation control. is suggesting.

  According to the present invention, even if the voltage value of the output voltage is different in the switching power source of (1), the maximum oscillation frequency is set according to the output voltage and the oscillation of the switching power source starts after the load begins to lighten. The load current until the frequency reaches the maximum oscillation frequency can be made equal. Therefore, it is possible to suppress a change in timing for starting the intermittent oscillation control.

  (3) In the switching power supply of (1) or (2), the control unit includes a second terminal (e.g., corresponding to the second terminal P2 in FIG. 4), and the correction unit includes: According to the voltage detected by the voltage detection means, the resistance value of the resistor connected to the second terminal (for example, equivalent to the variable resistor R0 in FIG. 4) or the current value flowing through the resistor is controlled, A switching power supply is proposed in which a value of a frequency at the time of starting intermittent oscillation control corresponding to a resistance value or a current value is obtained, and a frequency at the time of starting the intermittent oscillation control is set to the obtained value. ing.

  According to the present invention, in the switching power supply of (1) or (2), the control means is provided with the second terminal, and the correction means is connected to the second terminal according to the voltage detected by the voltage detection means. Controls the resistance value of the resistor or the current flowing through this resistor, obtains the frequency value at the time of starting intermittent oscillation control according to the resistance value or current value, and starts the intermittent oscillation control at the obtained value It was decided to set the frequency. Therefore, the resistance value or current value is controlled by the correcting means, and as a result, the frequency at the time when the intermittent oscillation control is started can be set according to the output voltage or the voltage corresponding to the output voltage. Therefore, the same effects as those described above can be achieved.

  (4) According to the present invention, in the switching power supply of (1) or (2), the correction means determines the relationship between the voltage detected by the voltage detection means and the frequency at the time of starting the intermittent oscillation control. Information (e.g., corresponding to a table to be described later) is stored in advance, and using the information, a value of a frequency at the time of starting intermittent oscillation control according to the voltage detected by the voltage detection unit is obtained, A switching power supply is proposed in which the frequency at the time of starting the intermittent oscillation control is set to the obtained value.

  According to the present invention, in the switching power supply of (1) or (2), the correcting means previously stores information indicating the relationship between the voltage detected by the voltage detecting means and the frequency at the time of starting the intermittent oscillation control. It was supposed to be held. Then, the correction means obtains the value of the frequency at the time of starting the intermittent oscillation control according to the voltage detected by the voltage detection means using the above-mentioned information, and the time of starting the intermittent oscillation control to the obtained value. It was decided to set the frequency. For this reason, the frequency at the time of starting intermittent oscillation control can be set according to the output voltage or the voltage corresponding to the output voltage. Therefore, the same effects as those described above can be achieved.

  (5) The present invention provides the switching power supply according to any one of (1) to (4), wherein the control means is provided on a primary side of the switching power supply, and outputs the output voltage or a voltage corresponding to the output voltage. There is proposed a switching power supply comprising transmission means (for example, equivalent to the photodiode PC1 and the phototransistor PC2 in FIG. 1) for transmitting a signal from the secondary side to the primary side of the switching power supply.

  According to this invention, in the switching power supply of any one of (1) to (4), the control means is provided on the primary side of the switching power supply, and the output voltage or the voltage corresponding to the output voltage is supplied from the secondary side of the switching power supply. Transmission means for transmitting a signal to the primary side was provided. For this reason, even when the control means is on the primary side of the switching power supply, the output voltage or a voltage corresponding to the output voltage can be transmitted to the control means, and the same effects as described above can be obtained. it can.

  (6) In the switching power supply according to any one of (1) to (4), the control unit is provided on the secondary side of the switching power supply, and controls the on / off frequency of the switch element. A switching power supply, wherein a control signal is transmitted to the switch element via a transmission means (for example, equivalent to the insulating circuit 41 in FIG. 7) for transmitting a signal from the secondary side to the primary side of the switching power supply. Has proposed.

  According to this invention, in the switching power supply of any one of (1) to (4), the control means is provided on the secondary side of the switching power supply, and the control means controls the on / off frequency of the switch element by this control means. The signal is transmitted to the switch element via a transmission means for transmitting a signal from the secondary side to the primary side of the switching power supply. For this reason, even when the control means is on the secondary side of the switching power supply, the on / off frequency of the switch element can be controlled by the control means, and the same effects as described above can be obtained. .

  (7) In the switching power supply according to any one of (1) to (6), the present invention includes a power factor correction circuit (e.g., equivalent to the power factor correction circuit 30 in FIG. 6) at the input portion of the switching power supply. We propose a switching power supply characterized by

  According to the present invention, in any one of the switching power supplies of (1) to (6), the power factor correction circuit is provided at the input portion of the switching power supply. For this reason, during the period when electric power is supplied to the power factor correction circuit, the power factor correction circuit can suppress the deterioration of the power supply characteristics of the switching power supply.

  According to the present invention, it is possible to suppress a change in timing for starting intermittent oscillation control.

1 is a circuit diagram of a switching power supply according to a first embodiment of the present invention. It is a figure which shows the relationship between the output voltage of the said switching power supply, and an oscillation frequency. It is a circuit diagram of the switching power supply concerning a 2nd embodiment of the present invention. It is a circuit diagram of the switching power supply which concerns on 3rd Embodiment of this invention. It is a circuit diagram of the switching power supply which concerns on 4th Embodiment of this invention. It is a circuit diagram of the switching power supply concerning a 5th embodiment of the present invention. It is a circuit diagram of the switching power supply which concerns on 6th Embodiment of this invention. It is a circuit diagram of the switching power supply which concerns on 7th Embodiment of this invention. It is a circuit diagram of the switching power supply concerning a prior art example. FIG. 10 is a circuit diagram of a switching power supply according to a conventional example different from FIG. 9. It is a figure which shows the change of the output voltage of the said switching power supply at the time of light load. It is a figure which shows the relationship between the output voltage of the said switching power supply, and an oscillation frequency. It is a figure which shows the change of the voltage of the 1st terminal of the said switching power supply at the time of light load. It is a figure which shows the change of the voltage of the 1st terminal of the said switching power supply at the time of the light load concerning the Example different from FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the constituent elements in the following embodiments can be appropriately replaced with existing constituent elements, and various variations including combinations with other existing constituent elements are possible. Accordingly, the description of the following embodiments does not limit the contents of the invention described in the claims.

<First Embodiment>
[Configuration of Switching Power Supply 1]
FIG. 1 is a circuit diagram of a switching power supply 1 according to the first embodiment of the present invention. The switching power supply 1 is different from the switching power supply 100 according to the conventional example shown in FIG. 9 in that the input power detection unit 20 is provided and the control circuit 10 is provided instead of the control circuit 110. In the switching power supply 1, the same components as those of the switching power supply 100 are denoted by the same reference numerals, and the description thereof is omitted.

  The control circuit 10 includes a first terminal P1, a second terminal P2, and a correction unit 11. The input terminal GND is connected to the second terminal P2 via the variable resistor R0. The input voltage detector 20 is connected to the variable resistor R0 so that the resistance value can be set according to the voltage detected by the input voltage detector 20.

[Operation of switching power supply 1]
In the switching power supply 1, the input voltage detection unit 20 detects an input voltage or a voltage corresponding to the input voltage, and sends a signal corresponding to the detection result to the variable resistor R0.

  Here, the voltage corresponding to the input voltage is a voltage that changes following the change of the input voltage. For example, the input voltage is divided using a resistor, or input using an amplifier circuit. It is an amplified version of the voltage.

  In addition, the control circuit 10 sets the resistance value of the variable resistor R0 according to the voltage detected by the input voltage detection unit 20 by the correction unit 11, and sets the oscillation frequency of the switching power supply 1 according to the set resistance value. Set the maximum oscillation frequency that is the upper limit. Specifically, the correction unit 11 refers to the voltage detected by the input voltage detection unit 20 and the maximum oscillation frequency, and the value of the maximum oscillation frequency according to the voltage detected by the input voltage detection unit 20 And set the maximum oscillation frequency to the obtained value.

  The difference between the oscillation frequency and the maximum oscillation frequency is made equal for each voltage detected by the input voltage detection unit 20. For example, as shown in FIG. 2, the difference between the oscillation frequency f1 when the output voltage Vo is V1 and the maximum oscillation frequency fmax1 at this time is Δ0. Then, the difference between the oscillation frequency f2 when the output voltage Vo is V2 and the maximum oscillation frequency fmax2 at this time is also Δ0.

  The control circuit 10 controls the on / off frequency of the switch elements Q1 and Q2 based on the maximum oscillation frequency set by the correction unit 11 and the voltage of the first terminal P1.

  According to the above switching power supply 1, the following effects can be produced.

  The switching power supply 1 sets the maximum oscillation frequency according to the voltage corresponding to the input voltage. For this reason, even if the input voltages are different, the load currents from when the load starts to light until the oscillation frequency fsw of the switching power supply 1 reaches the maximum oscillation frequency can be made equal. Therefore, it can suppress that the timing which starts intermittent oscillation control changes.

Second Embodiment
[Configuration of Switching Power Supply 1A]
FIG. 3 is a circuit diagram of a switching power supply 1A according to the second embodiment of the present invention. The switching power supply 1A is different from the switching power supply 1 according to the first embodiment of the present invention shown in FIG. 1 in that a control circuit 10A is provided instead of the control circuit 10, and the input voltage detection unit 20 is replaced with a variable resistor R0. Is different from that connected to the control circuit 10A. In the switching power supply 1A, the same components as those of the switching power supply 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The control circuit 10A includes a first terminal P1 and a correction unit 11A.

[Operation of Switching Power Supply 1A]
In the switching power supply 1, the input voltage detection unit 20 detects an input voltage or a voltage corresponding to the input voltage, and sends a signal corresponding to the detection result to the control circuit 10.

  The control circuit 10A sets the maximum oscillation frequency according to the voltage detected by the input voltage detection unit 20 by the correction unit 11A.

  Specifically, the correction unit 11A stores in advance a table indicating the relationship between the voltage detected by the input voltage detection unit 20 and the maximum oscillation frequency. Then, referring to this table, the maximum oscillation frequency corresponding to the voltage detected by the input voltage detector 20 is obtained, and the maximum oscillation frequency is set to the obtained value.

  Note that the information defined in the two types of tables stored in the correction unit 11A has the same difference between the oscillation frequency and the maximum oscillation frequency for each voltage detected by the input voltage detection unit 20. It is supposed to be. For example, as shown in FIG. 2, the difference between the oscillation frequency f1 when the output voltage Vo is V1 and the maximum oscillation frequency fmax1 at this time is Δ0. Then, the above information is determined in the above table so that the difference between the oscillation frequency f2 when the output voltage Vo is V2 and the maximum oscillation frequency fmax2 at this time is also Δ0.

  Further, the control circuit 10A controls the on / off frequencies of the switch elements Q1 and Q2 based on the maximum oscillation frequency set by the correction unit 11A and the voltage of the first terminal P1.

  According to the above switching power supply 1 </ b> A, the same effects as those described above that can be achieved by the switching power supply 1 can be achieved.

<Third Embodiment>
[Configuration of Switching Power Supply 1B]
FIG. 4 is a circuit diagram of a switching power supply 1B according to the third embodiment of the present invention. The switching power supply 1B is different from the switching power supply 1 according to the first embodiment of the present invention shown in FIG. 1 in the connection of the phototransistor PC2. Therefore, when the load becomes light and the oscillation frequency fsw cannot be increased, the voltage VP1 of the first terminal P1 decreases according to the error voltage as shown in FIG. 14, and is equal to or lower than a threshold voltage Vbst preset in the control circuit. become. When the voltage VP1 of the first terminal P1 becomes equal to or lower than the threshold voltage Vbst, the control circuit 110 starts intermittent oscillation control and temporarily stops the oscillation of the switch elements Q1 and Q2. In the switching power supply 1B, the same components as those of the switching power supply 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The first terminal P1 is connected to the collector of the phototransistor PC2, and the input terminal GND is connected to the emitter of the phototransistor PC2.

  According to the above switching power supply 1B, the same effect as the above-mentioned effect which the switching power supply 1 can show | play can be show | played.

<Fourth embodiment>
[Configuration of Switching Power Supply 1C]
FIG. 5 is a circuit diagram of a switching power supply 1C according to the fourth embodiment of the present invention. The switching power supply 1C is different from the switching power supply 1A according to the second embodiment of the present invention shown in FIG. 3 in the connection of the phototransistor PC2. In the switching power supply 1C, the same components as those of the switching power supply 1A are denoted by the same reference numerals, and the description thereof is omitted.

  The first terminal P1 is connected to the collector of the phototransistor PC2, and the input terminal GND is connected to the emitter of the phototransistor PC2.

  According to the above switching power supply 1C, the same effects as those described above that can be achieved by the switching power supply 1A can be achieved.

<Fifth Embodiment>
[Configuration of Switching Power Supply 1D]
FIG. 6 is a circuit diagram of a switching power supply 1D according to the fifth embodiment of the present invention. The switching power supply 1D is different from the switching power supply 1A according to the second embodiment of the present invention shown in FIG. 3 in that a power factor correction circuit 30 is provided in the input section. In the switching power supply 1D, the same components as those of the switching power supply 1A are denoted by the same reference numerals and description thereof is omitted.

[Operation of switching power supply 1D]
The power factor correction circuit 30 forms a boost converter and operates when the input voltage of the switching power supply 1D is higher than a predetermined threshold. For this reason, when the input voltage is higher than the threshold value, the power factor correction circuit 30 boosts the input voltage and narrows the input voltage range. On the other hand, when the input voltage is equal to or lower than the threshold (for example, during a power failure), the power factor correction circuit 30 does not operate.

  According to the above switching power supply 1D, in addition to the above-described effects that the switching power supply 1A can exhibit, the following effects can be achieved.

  When the input voltage is higher than the threshold, the switching power supply 1D can narrow the input voltage range by the power factor correction circuit 30 and suppress the deterioration of the power supply characteristics of the switching power supply 1D.

<Sixth Embodiment>
[Configuration of Switching Power Supply 1E]
FIG. 7 is a circuit diagram of a switching power supply 1E according to the sixth embodiment of the present invention. The switching power supply 1E is different from the switching power supply 1A according to the second embodiment of the present invention shown in FIG. 3 in place of the control circuit 10A, the phototransistor PC2, the photodiode PC1, and the resistor R1. 41 and 42 are different. In the switching power supply 1E, the same components as those of the switching power supply 1 are denoted by the same reference numerals and description thereof is omitted.

  The control circuit 10B includes a first terminal P1 and a correction unit 11B, and is provided on the secondary side of the switching power supply 1E. Specifically, the control circuit 10B is directly connected to the output terminal of the error amplifier AMP at the first terminal P1. Further, the control circuit 10B is connected to the gate of the switch element Q1 and the gate of the switch element Q2 through the insulating circuit 41, and is connected to the input voltage detection unit 20 through the insulating circuit 42.

[Operation of switching power supply 1E]
The control circuit 10B receives the voltage detected by the input voltage detection unit 20 via the insulation circuit 42 by the correction unit 11B, and sets the maximum oscillation frequency according to this voltage, similarly to the control circuit 10A.

  Further, the control circuit 10B transmits a control signal corresponding to the maximum oscillation frequency set by the correction unit 11B and the voltage of the first terminal P1 to the switch elements Q1 and Q2 via the insulation circuit 41. The on / off frequency of the switch elements Q1, Q2 is controlled.

  According to the above switching power supply 1E, the same effect as the above-mentioned effect which the switching power supply 1 can show | play can be show | played.

<Seventh embodiment>
[Configuration of switching power supply 1F]
FIG. 8 is a circuit diagram of a switching power supply 1F according to the seventh embodiment of the present invention. The switching power supply 1F is different from the switching power supply 1E according to the sixth embodiment of the present invention shown in FIG. 7 in that a control circuit 10C is provided instead of the control circuit 10B, the input voltage detection unit 20, and the insulation circuit 42. Different. In the switching power supply 1F, the same components as those of the switching power supply 1E are denoted by the same reference numerals, and the description thereof is omitted.

  The control circuit 10C includes a first terminal P1 and a correction unit 11C, and is provided on the secondary side of the switching power supply 1F. Specifically, the control circuit 10C is directly connected to the output terminal of the error amplifier AMP at the first terminal P1. The control circuit 10C is connected to the output terminal OUT1, and is connected to the gate of the switch element Q1 and the gate of the switch element Q2 via the insulating circuit 41.

[Operation of switching power supply 1F]
The control circuit 10C receives the output voltage detected by the correction unit 11C and sets the maximum oscillation frequency according to the output voltage.

  Further, the control circuit 10C transmits a control signal corresponding to the maximum oscillation frequency set by the correction unit 11C and the voltage of the first terminal P1 to the switching elements Q1 and Q2 via the insulating circuit 41. The on / off frequency of the switch elements Q1, Q2 is controlled.

  According to the above switching power supply 1F, the same effects as those described above that can be achieved by the switching power supply 1E can be achieved.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made without departing from the gist of the present invention.

  For example, in each of the embodiments described above, the maximum oscillation frequency that is the upper limit of the oscillation frequency of the switching power supply is set by the correction units 11 and 11A. This is set by regarding the maximum oscillation frequency as the frequency at the time of starting the intermittent oscillation control. The correction means according to the present invention includes everything that sets the frequency at the time of starting intermittent oscillation control.

  Further, in each of the above-described embodiments, the primary side circuit is provided with the half bridge circuit. However, the present invention is not limited to this, and for example, a full bridge circuit may be provided.

  In each of the above-described embodiments, the transformer T has a so-called center tap. However, the present invention is not limited to this.

  Further, in each of the above-described embodiments, the primary side circuit is provided with the LLC resonant circuit as the resonant circuit. However, the present invention is not limited to this.

  Moreover, although the input voltage detection part 20 in the above-mentioned 1st Embodiment or 3rd Embodiment shall detect the input voltage or the voltage according to the input voltage, it is not restricted to this, Output voltage or A voltage corresponding to the output voltage may be detected. Even when the output voltage or the voltage corresponding to the output voltage is detected, even if the output voltage value is different, the maximum oscillation frequency is set according to this output voltage and the load is reduced. The load current from the start until the oscillation frequency of the switching power supply reaches the maximum oscillation frequency can be made equal. Therefore, it is possible to suppress a change in timing for starting the intermittent oscillation control.

  In the first embodiment described above, the correction unit 11 sets the resistance value of the variable resistor R0 according to the voltage detected by the input voltage detection unit 20. However, the present invention is not limited to this. The value of the current flowing through the resistor R0 may be set. In this case, instead of the variable resistor R0, a resistor having a fixed resistance value and a switch provided in parallel with the resistor are provided, and a current value flowing through the resistor is set by turning on / off the switch. Also good.

  Moreover, although the input voltage detection part 20 in the above-mentioned 2nd Embodiment or 4th Embodiment shall detect the input voltage or the voltage according to an input voltage, not only this but an output voltage or A voltage corresponding to the output voltage may be detected. Even when setting the maximum oscillation frequency according to the output voltage or the detection result of the voltage according to the output voltage, the load current from when the load starts to light until the switching power supply oscillation frequency reaches the maximum oscillation frequency Can be equal. Therefore, it is possible to suppress a change in timing for starting the intermittent oscillation control.

  Moreover, although the example which provided the power factor improvement circuit 30 in the above-mentioned 5th Embodiment was demonstrated, the power factor improvement circuit 30 can be provided also in other embodiment.

1, 1A, 1B, 1C, 1D, 1E, 1F, 100, 100A; switching power supply 10, 10A, 10B, 10C, 110, 110A; control circuit 11, 11A, 11B, 11C; correction unit 20; input voltage detection unit 30; Power factor correction circuit 41, 42, 130; Insulation circuit AMP; Error amplifier PC1; Photodiode PC2; Phototransistor P1; First terminal P2; Second terminal Q1, Q2; Switch element R0; Trance

Claims (7)

A switching power supply having a resonant circuit and a switch element,
Voltage detection means for detecting an input voltage, a voltage according to the input voltage, an output voltage, or a voltage according to the output voltage;
Control means for controlling the on / off frequency of the switch element,
The control means includes
A correction means for detecting a voltage at the time of starting the intermittent oscillation control by the voltage detection means, and setting a frequency at the time of starting the intermittent oscillation control according to the voltage;
A first terminal;
A switching power supply, wherein the on / off frequency of the switch element is controlled based on a frequency at the time of starting the intermittent oscillation control and a voltage of the first terminal.   2. The switching power supply according to claim 1, wherein a maximum oscillation frequency that is an upper limit of an oscillation frequency of the switching power supply is set to a frequency at a time of starting the intermittent oscillation control. The control means includes a second terminal,
The correction unit controls the resistance value of the resistor connected to the second terminal or the current value flowing through the resistor according to the voltage detected by the voltage detection unit, and sets the resistance value or the current value to the resistance value or the current value. The switching power supply according to claim 1 or 2, wherein a frequency value at the time of starting the corresponding intermittent oscillation control is obtained, and the frequency at the time of starting the intermittent oscillation control is set to the obtained value. The correction means includes
Information indicating the relationship between the voltage detected by the voltage detection means and the frequency at the time of starting the intermittent oscillation control is held in advance.
Using the information, the value of the frequency at the time of starting the intermittent oscillation control corresponding to the voltage detected by the voltage detection means is obtained, and the frequency at the time of starting the intermittent oscillation control is set to the obtained value. The switching power supply according to claim 1 or 2. The control means is provided on the primary side of the switching power supply,
5. The switching power supply according to claim 1, further comprising a transmission unit that transmits the output voltage or a voltage corresponding to the output voltage from a secondary side to a primary side of the switching power supply.   The control means is provided on the secondary side of the switching power supply, and includes a transmission means for transmitting a control signal for controlling the on / off frequency of the switching element from the secondary side to the primary side of the switching power supply. The switching power supply according to claim 1, wherein the switching power is transmitted to the switching element. The switching power supply according to any one of claims 1 to 6,
A switching power supply comprising a power factor correction circuit at an input section of the switching power supply.

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