JP2016059182A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply unit of pseudo resonance type, capable of achieving optimum conversion efficiency under all input and output conditions.SOLUTION: The switching power supply unit (11) includes: a bottom detection circuit (1) for detecting the bottom of a resonance voltage; a bottom skipping number determination circuit (2) for determining a bottom skipping number for skipping the bottom defining the timing at which a switching element (Q) turns on so that an input current value is minimum.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a quasi-resonant switching power supply, and more particularly to a switching power supply that performs bottom skip control.

  In recent years, a switching power supply apparatus has become a mainstream of a quasi-resonant RCC (Ringing Choke Converter) system having characteristics of high efficiency and low noise. In the quasi-resonant switching power supply device, the switching frequency increases as the load becomes lighter. For this reason, since the switching loss of a switching element increases at the time of light load, conversion efficiency deteriorates.

  A so-called bottom skip technique is known as a technique for improving conversion efficiency against such deterioration of conversion efficiency. In the bottom skip, the increase in the switching frequency can be suppressed by turning on the next cycle at the bottom of the resonance that occurs after the switching element is turned off using the resonance waveform of the drain voltage of the switching element.

  For example, Patent Document 1 discloses a switching power supply device to which such bottom skip control is applied. This switching power supply device detects the load state with high accuracy on the primary side and performs bottom skip control.

International Publication No. WO2011 / 122314 (Released on October 6, 2011)

  However, the switching power supply described in Patent Document 1 performs a switching operation by dividing the load state into several levels and using a number of bottom skips set in advance corresponding to each level. Since conversion efficiency depends on the inductance value that determines the switching frequency, which is one of the element selection and transformer specifications, the switching power supply device can set the number of bottom skips at which optimum conversion efficiency is obtained. There is a problem that it is not always.

  In general, it is a loss of a switching element, a transformer (coil), a diode or the like that affects the conversion efficiency. When the number of bottom skips is increased, the switching frequency decreases, but there is a trade-off relationship that the peak value of the switching current and the effective current value are increased. That is, the loss includes a loss depending on the switching frequency and a loss depending on the effective current value. Therefore, there is a bottom skip number that can optimize the conversion efficiency in a state where these losses are balanced. Further, the loss depending on the switching frequency and the loss depending on the effective current value are affected by an inductance value that determines the switching frequency, which is one of the specifications of element selection and transformer (coil). Therefore, unless these specifications are determined, the optimum number of bottom skips cannot be determined.

  However, as the load becomes lighter, there is a qualitative tendency that the conversion efficiency is improved by increasing the number of bottom skips and lowering the switching frequency. Therefore, the switching power supply described in Patent Document 1 also improves the conversion efficiency. Can do. However, the switching power supply device described in Patent Document 1 does not consider the loss depending on the effective current value in order to determine the number of bottom skips, so it cannot be said that the conversion efficiency is sufficiently improved.

  In view of such circumstances, an object of the present invention is to provide a quasi-resonant switching power supply device that operates with the number of bottom skips that can obtain optimum conversion efficiency under all input / output conditions.

  In order to solve the above problems, a switching power supply according to an aspect of the present invention includes an inductor, a switching element connected to the inductor, a capacitor connected in parallel to the switching element, the inductor, A bottom detection circuit for detecting a bottom of a resonance voltage generated based on resonance with a capacitor, and a bottom skip number determination circuit for determining a bottom skip number for skipping the bottom for defining a timing at which the switching element is turned on, The bottom skip number determination circuit determines the bottom skip number that minimizes the input current value by changing the bottom skip number so that the input current value of the switching power supply device is reduced. .

  According to one aspect of the present invention, it is possible to provide a quasi-resonant switching power supply device that operates with the number of bottom skips that can obtain optimum conversion efficiency under any input / output conditions.

It is a circuit diagram which shows the structure of the switching power supply device which concerns on Embodiment 1 of this invention. 2 is a timing chart showing a basic operation of the switching power supply device of FIG. 1. FIG. 2 is a block diagram illustrating a bottom skip number determination circuit in the switching power supply device of FIG. 1. 3 is a flowchart showing a procedure for changing the number of bottom skips by the bottom skip number determination circuit of FIG. 2. It is a wave form diagram which shows the bottom skip operation | movement of the switching power supply device of FIG. FIG. 3 is a diagram illustrating a relationship between a bottom skip number adjustment process and a transition of an input current value by a bottom skip number determination circuit in FIG. 2. It is a circuit diagram which shows the structure of the switching power supply apparatus which concerns on Embodiment 2 of this invention. It is a graph which shows the instantaneous value of the input current in the switching power supply device of FIG. It is a block diagram which shows the structure of the input electric current value detection circuit in the switching power supply device of FIG. It is a circuit diagram which shows the structure of the switching power supply device which concerns on Embodiment 3 of this invention. It is a flowchart which shows the change procedure of the bottom skip number by the bottom skip number determination circuit in the switching power supply device of FIG. It is a circuit diagram which shows the structure of the switching power supply which concerns on Embodiment 4 of this invention.

Embodiment 1
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS.

<Configuration of Switching Power Supply Device 11>
FIG. 1 is a circuit diagram showing a configuration of a switching power supply device 11 according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the switching power supply device 11 is a quasi-resonant insulated DC-DC converter (pseudo-resonant flyback converter). The switching power supply device 11 includes a smoothing capacitor Ci, a transformer T, a diode D, a switching element Q, a resonance capacitor Cr, voltage dividing resistors Ro1 and Ro2, and a smoothing capacitor Co. The switching power supply device 11 includes a bottom detection circuit 1, a bottom skip number determination circuit 2, an input current value detection circuit 3, a feedback circuit 4, a comparator 5, a flip-flop 6, and a drive circuit 7. ing.

  A smoothing capacitor Ci is connected between a power supply line (a positive side of the input line) to which a DC input voltage Vi is input and a GND (ground) line (a negative side of the input line). As a result, the input voltage Vi is obtained as the voltage across the smoothing capacitor Ci.

  The transformer T (inductor) has a primary winding P1, a secondary winding S1, and an auxiliary winding P2. A series circuit including a primary winding P1 of the transformer T, a switching element Q, and a current detection resistor Rs is connected in parallel to the smoothing capacitor Ci. The switching element Q is composed of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or the like. A resonance capacitor Cr is connected between the drain and source of the switching element Q. The parasitic capacitance between the terminals of the switching element Q also functions as a resonance capacitor.

  A series circuit including a diode D and a smoothing capacitor Co is connected to the secondary winding S1 of the transformer T, and a rectifying and smoothing circuit is configured by this series circuit. As a result, the voltage across the smoothing capacitor Co is obtained as the DC output voltage Vo. In addition, a series circuit (voltage dividing circuit) including voltage dividing resistors Ro1 and Ro2 is connected in parallel to the smoothing capacitor Co. The divided voltage of the output voltage Vo at the connection point of the voltage dividing resistors Ro1 and Ro2 is input to the feedback circuit 4.

  The feedback circuit 4 calculates a difference between the divided voltage and a reference voltage (not shown), and outputs a feedback signal corresponding to the difference.

  The feedback signal is input to the inverting input terminal of the comparator 5. The voltage across the resistor Rs is applied to the non-inverting input terminal of the comparator 5. The comparator 5 outputs a comparison signal, which is a comparison result between the feedback signal and the voltage across the resistor Rs, to the reset terminal of the flip-flop 6.

  One end of the auxiliary winding P2 of the transformer is connected to the bottom detection circuit 1, and the other end of the auxiliary winding P2 of the transformer is connected to GND.

  The bottom detection circuit 1 is a circuit that detects the bottom (minimum value) of the output voltage (resonance voltage) of the auxiliary winding P2. The bottom detection circuit 1 outputs the bottom detection result to the bottom skip number determination circuit 2 as a pulsed bottom detection signal.

  The input current value detection circuit 3 is provided before the smoothing capacitor Ci in the GND line, and is a circuit that detects an input current value. The input current value detection circuit 3 outputs the detected input current value to the bottom skip number determination circuit 2.

  The position where the input current value detection circuit 3 is installed is not limited to the above position, and may be a power supply line. The primary winding P1, the switching element Q, and the resistor Rs of the transformer T may be used. It may be at any position in the series circuit consisting of

  The bottom skip number determination circuit 2 determines the bottom skip number based on the bottom detection signal from the bottom detection circuit 1 and the detected input current value of the input current value detection circuit 3. The bottom skip number determination circuit 2 inputs a bottom skip control signal to the set terminal of the flip-flop 6 at the bottom timing next to the bottom skipped by the determined predetermined bottom skip number.

  The flip-flop 6 is set by a set signal (bottom skip control signal) input to the set terminal and is reset by a comparison signal from the comparator 5 to generate a drive control signal to be output to the drive circuit 7.

  The drive circuit 7 generates a drive output signal to be applied to the gate of the switching element Q based on the drive control signal from the flip-flop 6. The switching element Q performs a switching operation when a drive output signal is applied to the gate.

<Basic Operation of Switching Power Supply Device 11>
The basic operation of the switching power supply device 11 configured as described above will be described with reference to FIG.

  FIG. 2 is a timing chart showing the basic operation of the switching power supply device 11.

  As shown in FIG. 2, when the current flowing through the resistor Rs increases and the voltage across the resistor Rs reaches the output signal (feedback signal) of the feedback circuit 4, the comparator 5 resets to the reset terminal of the flip-flop 6. A comparison signal is output as a signal. As a result, the output signal (drive control signal) of the flip-flop 6 falls and the drive output signal of the drive circuit 7 also falls, so that the switching element Q is turned off. Then, resonance occurs between the secondary winding S1 of the transformer T and the resonance capacitor Cr, so that the drain-source voltage Vds of the switching element Q starts to oscillate.

  In this state, when the bottom detection circuit 1 detects the bottom of the output voltage of the auxiliary winding P2 in the transformer T, the bottom detection circuit 1 outputs a detection signal to the bottom skip number determination circuit 2. Here, since it is assumed that the number of bottom skips is 0, the bottom skip number determination circuit 2 outputs a set signal (bottom skip control signal) to the set terminal of the flip-flop 6. As a result, the output signal of the flip-flop 6 rises and the drive output signal of the drive circuit 7 also rises, so that the switching element Q is turned on. By repeating such an operation, the switching element Q is driven.

<Configuration of Bottom Skip Number Determination Circuit 2>
The configuration of the bottom skip number determination circuit 2 will be described with reference to FIG.

  FIG. 3 is a block diagram showing the bottom skip number determination circuit 2.

  As shown in FIG. 3, the bottom skip number determination circuit 2 includes an input current value comparison circuit 20, an input current value storage circuit 21, a bottom skip number adjustment circuit 22, a bottom skip number setting circuit 23, and a bottom counting circuit. 24 and a bottom number comparison circuit 25.

The input current value comparison circuit 20 (input current value comparison unit) includes the input current value I (detected value) detected by the input current value detection circuit 3 and the input current value I ₀ stored in the input current value storage circuit 21. (Memory value) is compared. Further, the input current value comparison circuit 20 determines the sign of the command value ΔN (change value) of the bottom skip number based on the comparison result, and outputs the determination result to the bottom skip number adjustment circuit 22.

The input current value comparison circuit 20 stores the input current value storage circuit 21 as the input current value I ₀ detected by the input current value detection circuit 3 in the initial state of the control of the number of bottom skips. Further, the input current value comparison circuit 20 newly stores the input current value I detected later as the input current value I ₀ in the input current value storage circuit 21.

  The bottom skip number adjustment circuit 22 is a circuit that outputs a command value ΔN together with a sign determined by the input current value comparison circuit 20 based on an output signal from the input current value comparison circuit 20.

The bottom skip number setting circuit 23 is a circuit that changes and sets N ₀ + ΔN as a new bottom skip number N ₀ based on the command value ΔN and sign from the bottom skip number adjustment circuit 22.

  In the bottom skip number determination circuit 2, the bottom skip number adjustment circuit 22 and the bottom skip number setting circuit 23 constitute a bottom skip number changing unit that changes the bottom skip number.

  The bottom counting circuit 24 is a circuit that counts the bottom detection signal (number of pulses) of the bottom detection circuit 1.

The bottom number comparison circuit 25 is a circuit that compares the bottom number counted by the bottom counting circuit 24 with the bottom skip number N ₀ set by the bottom skip number setting circuit 23. When the bottom number reaches the bottom skip number N ₀ based on the comparison result, the bottom number comparison circuit 25 outputs the bottom detection signal to the set terminal of the flip-flop 6 at the next timing when the bottom detection circuit 1 outputs the bottom detection signal. A set signal is output. The rising edge of the set signal defines the timing at which the switching element Q is turned on.

<Change of bottom skip count by bottom skip count determination circuit 2>
The change of the number of bottom skips by the bottom skip number determination circuit 2 will be described with reference to FIG.

  FIG. 4 is a flowchart showing a procedure for changing the number of bottom skips by the bottom skip number determination circuit 2.

(Step S1)
First, after the switching power supply device 11 is activated, the bottom skip number setting circuit 23 sets the initial value of the bottom skip number N ₀ to N ₀ = 0.

(Step S2)
When the input current value detection circuit 3 detects the input current value I ₀ , the input current value storage circuit 21 stores the detected input current value I ₀ (first detection value).

(Step S3)
The input current value comparison circuit 20 outputs a positive sign as the sign of the command value ΔN in the initial state. The bottom skip number adjustment circuit 22 receives this sign and outputs a positive command value ΔN to the bottom skip number setting circuit 23. The bottom skip number setting circuit 23 sets and stores a new bottom skip number N _{0 in} which the bottom skip number is changed from N ₀ to the command value ΔN. The command value ΔN is not limited to a value of 1.

(Step S4)
The input current value detection circuit 3 detects the input current value I.

(Step S5)
Input current value comparing circuit 20 compares the input current value I ₀ is stored the previous detection value is a current value detected input current value I (second detected value).

(Step S6)
Input current value comparing circuit 20, the result of the comparison in step S5, if the input current value I is equal to or less than the input current value I _0, it does not reverse the sign of the command value .DELTA.N. That is, the input current value comparison circuit 20 determines that there is a possibility that the input current value I may further decrease by changing the bottom skip number N ₀ with the polarity of the current command value ΔN.

(Step S7)
When the input current value comparison circuit 20 determines that the input current value I is greater than the input current value I _{0 as} a result of the comparison in step S5, the input current value comparison circuit 20 inverts the sign of the command value ΔN. That is, the input current value comparison circuit 20 determines that changing the bottom skip number N ₀ with the polarity of the current command value ΔN is the opposite direction to decreasing the input current value I.

(Step S8)
The input current value comparison circuit 20 stores the input current value I detected this time in the input current value storage circuit 21 as a new input current value I ₀ .

Thereafter, the process returns to step S2. The bottom skip number N ₀ is changed based on such a procedure. Thus, the switching element Q, it is possible to input current I to the switching operation a plurality of number of bottom skips N ₀ unfixed containing bottom skip number N ₀ as a minimum. Specifically, as can be seen from the above procedure, starting from a change in the number of bottom skips N ₀ in the initial state, the magnitude determination between the input current value I and the input current value I _0, and the bottom skip based on this magnitude judgment By repeating the change of the number N _0, the bottom skip number N ₀ at which the input current value I is always the minimum is tracked, and therefore the bottom skip number N ₀ is not fixed.

<Bottom Skip Operation of Switching Power Supply Device 11>
The bottom skip operation of the switching power supply device 11 will be described with reference to FIG.

  FIG. 5 is a waveform diagram showing the bottom skip operation of the switching power supply device 11. In FIG. 5, it is assumed that | ΔN | = 1.

As shown in FIG. 5, the switching power supply device 11 starts operation with the number of bottom skips N ₀ = 0 in the period T0. In the subsequent period T1, when the input current value detection circuit 3 detects the input current value I ₀ and the input current value comparison circuit 20 stores the input current value I ₀ in the input current value storage circuit 21, the number of bottom skips The setting circuit 23 changes the bottom skip number N ₀ to 1. In this period T1, the drive circuit 7 outputs the drive output signal that rises at the second rise of the output signal from the bottom detection circuit 1, thereby turning on the switching element Q.

In the subsequent period T2, the input current value comparing circuit 20, as a result of comparing the input current value I ₀ stored and the input current value I detected, determines the input current value I is the input current value I ₀ is less than. In this case, since the sign of the command value .DELTA.N is not inverted, the bottom skip number setting circuit 23 changes the number of bottom skips N ₀ to 2 by adding the command value ΔN (= 1) to the bottom skip number N _0. In this period T2, the drive circuit 7 turns on the switching element Q at the third rise of the output signal from the bottom detection circuit 1.

In the subsequent period T3, the input current value comparing circuit 20, and compares the input current I and the input current value I ₀ result, determines the input current value I is the input current value I ₀ is less than. Again, the sign of the command value .DELTA.N is not inverted, the bottom skip number setting circuit 23, similarly to the period T2, the number of bottom skips N ₀ by adding the command value ΔN (= 1) to the number of bottom skips N ₀ Change to 3. In this period T3, the drive circuit 7 turns on the switching element Q at the fourth rise of the output signal from the bottom detection circuit 1.

In the subsequent period T4, the input current value comparing circuit 20, and compares the input current I and the input current value I ₀ result, determines the input current value I is greater than the input current value I _0. In this case, since the sign of the command value .DELTA.N is inverted, the bottom skip number setting circuit 23 changes the number of bottom skips N ₀ to 2 by subtracting the command value ΔN (= 1) from the bottom skip number N _0. In this period T4, the drive circuit 7 turns on the switching element Q at the third rise of the output signal from the bottom detection circuit 1.

In the subsequent period T5, the input current value comparing circuit 20, and compares the input current I and the input current value I ₀ result, determines the input current value I is the input current value I ₀ is less than. In this case, no inverted sign of the command value .DELTA.N, bottom skip number setting circuit 23, similarly to the period T4, the bottom skip number N ₀ by subtracting the command value ΔN (= 1) from the bottom skip number N ₀ 1 Change to In this period T5, the drive circuit 7 turns on the switching element Q at the second rising edge of the output signal of the bottom detection circuit 1.

<Effects of the switching power supply device 11>
The adjustment process of the number of bottom skips and the transition of the input current value will be described with reference to FIG. FIG. 6 shows the process of increasing the bottom skip number N ₀ from 0 to 3 and returning it to 1, and the transition of the input current value I associated therewith.

As shown in FIG. 6, when the number of bottom skips N ₀ is 1, as a result of comparing the input current value I (detected value) with the input current value I ₀ (stored value), the input current value I becomes the input current value. Since it is smaller than I ₀ , the bottom skip number N ₀ is changed to 2 by adding 1. Thus, the bottom skip number N ₀ always varies in the order of 1 → 2 → 3 → 2 → 1 → 2..., Including 2 where the input current value I is minimum.

The operation of changing such bottom skip number N _0, with the change of the input and output conditions, even the number of bottom skips N ₀ the input current value I is minimized fluctuates, the bottom skip to follow the fluctuations It becomes possible to find the number N ₀ . Therefore, it is possible to provide a quasi-resonant switching power supply device that operates with a bottom skip number N ₀ that provides optimum conversion efficiency.

That is, in the switching power supply device 11, by determining the bottom skip number N ₀ that minimizes the input current value I as needed, not only the loss depending on the switching frequency but also the loss depending on the current effective value is taken into account. The number of bottom skips N ₀ can be determined. Thereby, the switching power supply device 11 can further improve the conversion efficiency as compared with the switching power supply device described in Patent Document 1.

[Embodiment 2]
The second embodiment of the present invention will be described below with reference to FIGS.

  For convenience of explanation, in this embodiment, constituent elements having functions equivalent to those of the constituent elements in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

<Configuration of Switching Power Supply Device 12>
FIG. 7 is a circuit diagram showing a configuration of the switching power supply device 12 according to the second embodiment of the present invention. FIG. 8 is a graph showing the instantaneous value of the input current in the switching power supply device 12.

  As shown in FIG. 7, the switching power supply device 12 is a quasi-resonant insulated AC-DC converter. Similar to the switching power supply device 11 in the first embodiment, the switching power supply device 12 includes a smoothing capacitor Ci, a transformer T, a diode D, a switching element Q, a resonance capacitor Cr, voltage dividing resistors Ro1 and Ro2, A smoothing capacitor Co, a bottom detection circuit 1, a bottom skip number determination circuit 2, an input current value detection circuit 3, a feedback circuit 4, a comparator 5, a flip-flop 6, and a drive circuit 7 are provided. Unlike the switching power supply device 11, the switching power supply device 12 includes a bridge diode 8 and a polarity detection circuit 9.

  One output terminal of the bridge diode 8 is connected to one end (positive side) of the smoothing capacitor Ci, and the other output terminal of the bridge diode 8 is connected to one input terminal of the input current value detection circuit 3.

  The polarity detection circuit 9 is a circuit that detects the polarity of the AC input voltage. The polarity detection circuit 9 is connected to the L line and the N line constituting the AC line, and determines the polarity of the AC input voltage by determining which of the L line potential and the N line potential is higher. Is detected. For example, the polarity detection circuit 9 outputs a High signal when the potential of the L line is higher, and outputs a Low signal when the potential of the N line is higher. These signals are given to the input current value detection circuit 3.

  In the switching power supply device 12, a capacitor input type rectifier circuit including a bridge diode 8 and a smoothing capacitor Ci is configured. In the switching power supply device 12 including the capacitor input type rectifier circuit, as shown in FIG. 8, it can be seen that the instantaneous value of the input current has a large instantaneous fluctuation.

<Configuration of Input Current Value Detection Circuit 3>
FIG. 9 is a block diagram showing the configuration of the input current value detection circuit 3.

  The input current value detection circuit 3 includes an input current instantaneous value detection circuit 31 and an input current average value calculation circuit 32.

  The input current instantaneous value detection circuit 31 is connected between the bridge diode 8 and the smoothing capacitor Ci, and is a circuit that detects an instantaneous value of the input current from the capacitor input rectifier circuit.

  Based on the instantaneous value of the input current detected by the input current instantaneous value detection circuit 31 and the output signal of the polarity detection circuit 9, the input current average value calculation circuit 32 starts from the timing when the output signal of the polarity detection circuit 9 is inverted. It is a circuit which calculates the average value of the input current until the inversion timing of. The input current average value calculation circuit 32 may calculate the effective value of the input current instead of the average value of the input current.

  With this configuration, the input current value detection circuit 3 can calculate the average value of the input current in a half cycle of the AC power supply cycle. As a result, it is possible to detect the input current at both 60 kHz and 50 kHz AC power supply frequencies.

<Effects of the switching power supply device 12>
In the switching power supply device 12, the input current value detection circuit 3 calculates the average value (or effective value) of the input current every 1/2 cycle of the AC power supply as described above. As a result, when the time variation of the input current is large, for example, even when a capacitor input type rectifier circuit is configured, it is possible to more accurately calculate the input current value correlated with the variation of the input power. . In this case, the update cycle of the bottom skip number N ₀ is a half cycle of the AC power supply.

  Since the operation of the bottom skip number determination circuit 2 is the same as that of the first embodiment, the description thereof is omitted here.

[Embodiment 3]
Embodiment 3 of the present invention will be described below with reference to FIGS. 10 and 11.

  For convenience of explanation, in this embodiment, constituent elements having functions equivalent to those of the constituent elements in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

<Configuration of Switching Power Supply Device 13>
FIG. 10 is a circuit diagram showing a configuration of the switching power supply device 13 according to Embodiment 3 of the present invention.

  As shown in FIG. 10, the switching power supply device 13 is a quasi-resonant insulated DC-DC converter. As with the switching power supply device 11 in the first embodiment, the switching power supply device 13 includes a smoothing capacitor Ci, a transformer T, a diode D, a switching element Q, a resonance capacitor Cr, voltage dividing resistors Ro1 and Ro2, A smoothing capacitor Co, a bottom detection circuit 1, an input current value detection circuit 3, a feedback circuit 4, a comparator 5, a flip-flop 6, and a drive circuit 7 are provided. Unlike the switching power supply device 11, the switching power supply device 13 includes an input voltage detection circuit 10, and includes a bottom skip number determination circuit 2 </ b> A instead of the bottom skip number determination circuit 2.

  The input voltage detection circuit 10 is connected between the power supply line and the GND line, and is a circuit that detects the input voltage Vi (DC input voltage).

  The bottom skip number determination circuit 2A has a function equivalent to that of the bottom skip number determination circuit 2 in the switching power supply device 11, but further has a comparison function between the input voltage Vi and the control start voltage Vi_start. Specifically, when the input voltage Vi is equal to or lower than the preset control start voltage Vi_start, the bottom skip number determination circuit 2A does not perform the bottom skip number change operation described in the first embodiment, and the input voltage Vi. Is higher than a preset control start voltage Vi_start (threshold voltage), the bottom skip number changing operation is performed.

<Change of bottom skip count by bottom skip count determination circuit 2>
The change of the number of bottom skips by the bottom skip number determination circuit 2 will be described with reference to FIG.

  FIG. 11 is a flowchart showing a procedure for changing the number of bottom skips by the bottom skip number determination circuit 2. In steps S14 to S20 in the flowchart of FIG. 11, processes equivalent to the processes of steps S2 to S8 corresponding to the flowchart of FIG. 2 are performed.

(Step S11)
First, after the switching power supply device 13 is activated, the bottom skip number setting circuit 23 sets the initial value of the bottom skip number N ₀ to N ₀ = 0.

(Step S12)
The input voltage detection circuit 10 detects the input voltage Vi. The detected input voltage Vi is supplied to the bottom skip number determination circuit 2A.

(Step S13)
When the bottom skip number determination circuit 2A compares the input voltage Vi with the control start voltage Vi_start and determines that the input voltage Vi is equal to or lower than the control start voltage Vi_start, the process returns to step S2. In this state, since the bottom skip number N ₀ is set to 0 as described above, the switching power supply device 13 has the bottom skip number N ₀ of 0 as described with reference to FIG. 2 in the first embodiment. It works when it is.

  When the bottom skip number determination circuit 2A determines that the input voltage Vi is higher than the control start voltage Vi_start as the voltage across the smoothing capacitor Ci increases, the process proceeds to step S14. Thereby, the process equivalent to the process after step S2 shown by the flowchart of FIG. 4 in Embodiment 1 is performed.

<Effects of the switching power supply device 13>
When the switching power supply 13 is turned on, the input current surely increases. Therefore, it is not necessary to determine the bottom skip number N ₀ by comparing the input current value I with the input current value I _0. N ₀ is determined to be 0. In the switching power supply device 13 of the present embodiment, the bottom skip number determination circuit 2A does not perform the bottom skip number change operation when the input voltage Vi is equal to or lower than the preset control start voltage Vi_start. Thereby, it is possible to reduce the power consumption resulting from the operation for determining the number of bottom skips N ₀ immediately after the power is turned on.

  Note that the configuration of the present embodiment can also be applied to the switching power supply device 12 of the second embodiment described above.

<Additional notes>
As mentioned above, although Embodiment 1-3 was demonstrated, this invention is not limited to Embodiment 1-3 mentioned above, A various change is possible in the range shown to the claim. The switching power supply according to the present invention is a quasi-resonant switching power supply that turns on the switching element at the timing when the resonance voltage reaches the bottom by utilizing the resonance phenomenon of the inductor and the resonance capacitor. Therefore, the present invention is not limited to the quasi-resonant flyback converter shown in the first embodiment, and can be applied to a critical mode boost converter, a critical mode boost type power factor improving circuit, and the like. In the present embodiment, an example in which the present invention is applied to a critical mode boost converter will be described in the following fourth embodiment.

[Embodiment 4]
The following describes Embodiment 4 of the present invention with reference to FIG.

  For convenience of explanation, in this embodiment, constituent elements having functions equivalent to those of the constituent elements in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

<Configuration of Switching Power Supply Device 14>
FIG. 12 is a circuit diagram showing a configuration of the switching power supply device 13 according to Embodiment 3 of the present invention.

  As shown in FIG. 12, the switching power supply device 14 is a quasi-resonant critical mode boost converter. As with the switching power supply device 11 in the first embodiment, the switching power supply device 14 includes a smoothing capacitor Ci, a diode D, a switching element Q, a resonance capacitor Cr, voltage dividing resistors Ro1 and Ro2, and a smoothing capacitor Co. , A bottom skip number determination circuit 2, an input current value detection circuit 3, a feedback circuit 4, a comparator 5, a flip-flop 6, and a drive circuit 7. Unlike the switching power supply device 11, the switching power supply device 13 includes a choke coil L (inductor), and includes a bottom detection circuit 1 </ b> A instead of the bottom detection circuit 1.

  Unlike the switching power supply device 11, the switching power supply device 13 does not include a transformer T, and therefore the drain of the switching element Q is connected to the anode of the diode D.

  The choke coil L (coil) has a main winding MAIN and a sub winding SUB. One end of the main winding MAIN is connected to one end (positive side) of the smoothing capacitor Ci, and the other end of the main winding MAIN is connected to the anode of the diode D. One end of the sub winding SUB is connected to the GND line, and the other end of the sub winding SUB is connected to the bottom detection circuit 1. That is, the series circuit connected in parallel to the smoothing capacitor Ci is a series circuit including the main winding MAIN of the choke coil L, the switching element Q, and the resistor Rs, and an input signal (bottom detection signal) to the bottom detection circuit 1A. Appears on the auxiliary shoreline SUB.

  The bottom detection circuit 1A is configured in the same manner as the bottom detection circuit 1 in the switching power supply device 11 except that a bottom detection signal is given from the choke coil L.

<Operation of Switching Power Supply Device 14>
Unlike the switching power supply device 11 of the first embodiment, the switching power supply device 14 includes a choke coil L instead of including the transformer T. For this reason, when the switching element Q is turned off, resonance occurs between the auxiliary winding SUB of the choke coil L and the resonance capacitor Cr, so that the drain-source voltage Vds of the switching element Q starts to oscillate. Therefore, unlike the bottom detection circuit 1 in the switching power supply device 11, the bottom detection circuit 1A detects the bottom state of the output voltage (resonance voltage) of the sub winding SUB and determines the number of bottom skips using the detection result as the bottom detection signal. Output to circuit 2.

<Effects of the switching power supply device 14>
Also in the switching power supply 14 is a critical mode boost converter quasi resonant type, the bottom skip number determination circuit 2, the number of bottom skips N ₀ following the variation of the number of bottom skips N ₀ the input current value I is minimized Can be found. Therefore, it is possible to provide a quasi-resonance type critical mode boost converter that operates at the bottom skip number N ₀ where optimum conversion efficiency can be obtained.

  Note that the switching power supply device 14 can also be applied to the switching power supply device 12 of the second embodiment.

[Summary]
A switching power supply according to the first aspect of the present invention includes an inductor (transformer T, choke coil L), a switching element Q connected to the inductor, and a capacitor (resonance capacitor Cr) connected in parallel to the switching element Q. ), A bottom detection circuit 1 for detecting a bottom of a resonance voltage generated based on resonance between the inductor and the capacitor, and a bottom skip number for skipping the bottom that defines a timing at which the switching element Q is turned on. A bottom skip number determination circuit 2, and the bottom skip number determination circuit 2 changes the bottom skip number so that the input current value of the switching power supply device becomes small, whereby the input current value is minimized. Determine the number of bottom skips.

  According to said structure, bottom skip is changed so that the input electric current value which has the same tendency qualitatively as the input electric power value of a switching power supply device may become the minimum. As a result, the switching power supply device can operate with the number of bottom skips that can provide optimum conversion efficiency under any input / output conditions.

The switching power supply apparatus according to aspect 2 of the present invention further includes an input current value detection circuit 3 that detects the input current value in the aspect 1, and the bottom skip number determination circuit 2 includes the detected input current value. The first detection value (input current value I ₀ ) is compared with the second detection value (input current value I) that is the input current value detected next to the first detection value. And when the second detection value is less than or equal to the first detection value, the bottom skip number is changed in the same direction as the previous change direction, When the second detection value is greater than the first detection value, a bottom skip number changing unit (bottom skip number adjusting circuit 2) that changes the bottom skip number in a direction opposite to the direction in which the bottom skip number has been changed last time. And bottom skip number setting circuit 23) and may have.

  According to the above configuration, the bottom skip number is changed so as to minimize the input current value while appropriately changing the direction of changing the bottom skip number according to the magnitude of the second detection value with respect to the first detection value. . Thereby, the switching element can perform a switching operation with an unfixed number of bottom skips including the number of bottom skips that minimizes the input current value under any input / output conditions. Therefore, the switching power supply device can be operated with the number of bottom skips that can obtain the optimum conversion efficiency.

  In the switching power supply according to Aspect 3 of the present invention, in the Aspect 2, the input current value detection circuit 3 is configured such that the input current value is averaged or effective after the polarity of the AC input voltage is inverted until the next inversion. A value may be calculated.

  According to the above configuration, when the time variation of the input current is large, for example, even when the switching power supply device includes a capacitor input type rectifier circuit, the input current value correlated with the variation of the input power is more accurately calculated. It becomes possible.

  In the switching power supply according to aspect 4 of the present invention, in the above aspects 1 to 3, the bottom skip number determination circuit 2 determines the bottom skip number to 0 when the DC input voltage of the switching power supply is equal to or lower than a predetermined threshold voltage. May be.

  According to the above configuration, since the bottom skip number is not determined in a state in which the input current immediately after the switching power supply is turned on, the power consumption resulting from the operation for determining the bottom skip number is not performed. Can be reduced.

  In the switching power supply according to aspect 5 of the present invention, in the above aspects 1 to 4, the inductor may be a coil (choke coil L) connected in series with the switching element Q.

  According to the above configuration, since the switching power supply device constitutes a boost converter, even in such a boost converter, the optimum conversion efficiency is obtained by determining the number of bottom skips so that the input current value is minimized. be able to.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

  The present invention can be used for a quasi-resonant switching power supply device using bottom skip control technology.

DESCRIPTION OF SYMBOLS 1 Bottom detection circuit 1A Bottom detection circuit 2 Bottom skip number determination circuit 2A Bottom skip number determination circuit 3 Input current value detection circuit 4 Feedback circuit 5 Comparator 6 Flip-flop 7 Drive circuit 8 Bridge diode 9 Polarity detection circuit 10 Input voltage detection circuit 11 -14 Switching power supply device 20 Input current value comparison circuit (input current value comparison unit)
21 Input Current Value Storage Circuit 22 Bottom Skip Number Adjustment Circuit (Bottom Skip Number Change Unit)
23 Bottom skip count setting circuit (bottom skip count changing section)
24 Bottom Count Circuit 25 Bottom Number Comparison Circuit 31 Input Current Instantaneous Value Detection Circuit 32 Input Current Average Value Calculation Circuit Cr Resonance Capacitor
I ₀ Input current value I Input current value L Choke coil (inductor)
Q switching element T transformer (inductor)
Vi input voltage (DC input voltage)
Vi_start Control start voltage (threshold voltage)

Claims (5)

An inductor;
A switching element connected to the inductor;
A capacitor connected in parallel with the switching element;
A bottom detection circuit for detecting a bottom of a resonance voltage generated based on resonance between the inductor and the capacitor;
A bottom skip number determining circuit for determining a bottom skip number for skipping the bottom that defines the timing at which the switching element is turned on, and
The bottom skip number determination circuit determines the bottom skip number that minimizes the input current value by changing the bottom skip number so that the input current value of the switching power supply device is reduced. Switching power supply. An input current value detection circuit for detecting the input current value;
The bottom skip number determination circuit includes:
An input current value comparison unit that compares the detected first input value that is the input current value with the second detected value that is the input current value detected next to the first detected value;
When the second detection value is less than or equal to the first detection value, the bottom skip number is changed in the same direction as the direction in which the bottom skip number has been changed last time, while the second detection value is the first detection value. 2. The switching power supply according to claim 1, further comprising: a bottom skip number changing unit that changes the bottom skip number in a direction opposite to a direction in which the bottom skip number has been changed last time. apparatus.   3. The switching power supply device according to claim 2, wherein the input current value detection circuit calculates an average value or an effective value of the input current values from when the polarity of the AC input voltage is inverted until the next inversion. .   4. The switching according to claim 1, wherein the bottom skip number determination circuit determines the bottom skip number to be 0 when a DC input voltage of a switching power supply device is equal to or lower than a predetermined threshold voltage. 5. Power supply.   5. The switching power supply device according to claim 1, wherein the inductor is a coil connected in series with the switching element. 6.

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