JP4699245B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that is suitably implemented as a so-called AC-DC converter, DC-DC converter, or the like and that outputs a DC stable voltage.

  FIG. 13 shows a switching power supply device 100 of a conventional ringing choke converter (RCC method).

  As shown in the figure, the switching power supply 100 includes a fuse F1, an across-the-line capacitor C1 (hereinafter referred to as a line capacitor C1) for removing noise from an input AC voltage, a common mode choke coil L1 (hereinafter referred to as a line filter). L1), a line capacitor C1, a bridge diode BD1 that rectifies and smoothes the AC voltage from which noise has been removed by the line filter L1 and converts it to a DC voltage, a smoothing capacitor C4, a primary winding N1, and a secondary winding. A transformer T1 having a line N2 and a control winding N3, and a main switching element connected in series downstream to the primary winding N1 of the transformer T1 and converting the DC voltage into a high-frequency AC voltage by turning on and off the DC voltage Q1, a secondary side rectifying / smoothing circuit 8 connected to the secondary winding N2 of the transformer T1, and a secondary side rectifying / smoothing circuit 8 As the force voltage is constant, and a main control circuit 6 that controls the on and off of the main switching element Q1.

  The resistors R2, R3, and R5 are starting resistors of the main switching element Q1, and the main switching element Q1 uses an n-channel MOSFET here, but may be other switching elements. Hereinafter, the main switching element Q1 is referred to as MOSFET Q1. Further, the polarity relationship of each winding of the transformer T1 is indicated by black circles attached to each winding of the transformer T1 in the drawing. The primary winding N1 has a black circle on the current downstream side terminal, the secondary winding N2 has a black circle on the current upstream side terminal, and the control winding N3 has a direct current of the diode bridge DB1. A black circle is attached to the terminal connected to the side return. Specifically, when power is turned on, an induced electromotive force is generated in each winding from the black circle to the direction where the black circle is not described. When the MOSFET Q1 is turned off, an induced electromotive force is generated in each winding in the reverse direction, that is, from the direction where the black circle is not described toward the black circle.

  Hereinafter, the terminal of the primary winding N1 that is not marked with a black circle is referred to as “one end of the primary winding N1,” and the terminal of the primary winding N1 that is marked with a black circle is referred to as “primary winding N1. The other end of the secondary winding N2 is marked with the black circle terminal “secondary winding N2 one end” and the secondary winding N2 with the black circle not marked “secondary” The other end of the winding N2 ”, the terminal without the black circle of the control winding N3 is“ one end of the control winding N3 ”, and the terminal with the black circle of the control winding N3 is“ control winding ” This is referred to as the other end of the line N3.

  The main control circuit 6 includes a resistor R1, a bias resistor R4, capacitors C3 and C5, a photocoupler PC1 (phototransistor), and a control transistor Q2 (NPN type). The bias resistor R4 and the capacitor C5 are connected in series between one end of the control winding N3 of the transformer T1 and the gate of the MOSFET Q1, and the photocoupler PC1 (the collector of the phototransistor) is connected to the connection point between the capacitor C5 and the gate of the MOSFET Q1. And the photocoupler PC1 (the emitter of the phototransistor) is connected to the base of the control transistor Q2.

  Further, one end of the resistor R1 is connected to a connection point between one end of the control winding N3 of the transformer T1 and the bias resistor R4, and the other end of the resistor R1 is connected to the control winding N3 of the transformer T1 via the capacitor C3. Is connected to the other end. Further, the base of the control transistor Q2 is connected to the connection point between the other end of the resistor R1 and one end of the capacitor C3, and the collector of the control transistor Q2 is connected to the connection point between the gate of the MOSFET Q1 and one end of the starting resistor R5. The emitter of the control transistor Q2 is connected to a connection point between the other end of the control winding N3 of the transformer T1 and the other end of the starting resistor R5.

  The secondary side rectifying and smoothing circuit 8 includes a diode D1 connected in series to one end of the secondary winding N2 of the transformer T1, a smoothing capacitor C2 connected in parallel to the secondary winding N2 of the transformer T1, and a voltage detection circuit. 7.

  Next, the operation of the switching power supply apparatus 100 will be described.

  When the switching power supply device 100 is turned on, the input AC voltage is denoised through the noise filter F1, the line capacitor C1, and the line filter L1, and then passed through the bridge diode BD1 and the smoothing capacitor C4. Rectified and smoothed and converted to a DC voltage. When the DC voltage of the smoothing capacitor C4 rises, the main power supply voltage rises. When the divided voltage value at the starting resistors R2, R3, and R5 becomes equal to or higher than the operating voltage of the MOSFET Q1, the MOSFET Q1 is turned on, and the transformer T1 Excitation energy is accumulated in the primary winding N1.

  At the same time, a voltage V1 in the same direction as the primary winding N1 of the transformer T1 is induced in the control winding N3 of the transformer T1, and the induced current is given to the gate of the MOSFET Q1 via the bias resistor R4 and the capacitor C5. As a result, the MOSFET Q1 is kept on.

  Next, the induced current induced in the control winding N3 of the transformer T1 is charged in the capacitor C3 via the phototransistor of the photocoupler PC1, and when the charged voltage becomes equal to or higher than the operating voltage of the control transistor Q2, the control is performed. Transistor Q2 is turned on. As a result, the gate potential of the MOSFET Q1 is lowered and the MOSFET Q1 is turned off. At this time, since the voltage V3 opposite to the voltage V1 induced when the MOSFET Q1 is turned on is induced in the control winding N3 of the transformer T1, the charge of the capacitor C3 is extracted through the resistor R1, Preparation for the next ON operation of MOSFET Q1 is performed.

  When the MOSFET Q1 is turned off, the excitation energy stored in the primary winding N1 of the transformer T1 is supplied to the secondary winding N2 of the transformer T1, and the voltage detection circuit 7 is connected via the diode D1 and the smoothing capacitor C2. The output voltage is detected. The output voltage is transmitted from a photocoupler PC1 (light emitting element) (not shown) to the photocoupler PC1 (phototransistor) of the main control circuit 6, and the on / off of the MOSFET Q1 is controlled.

  Thereafter, when the excitation energy is released, resonance occurs between the parasitic capacitance generated in the primary winding N1 of the transformer T1 and the inductor of the primary winding N1 of the transformer T1, and a ringing voltage is generated. The ringing voltage is also transmitted to the control winding N3 of the transformer T1, and is supplied to the gate of the MOSFET Q1 through the bias resistor R4 and the capacitor C5, so that the MOSFET Q1 is turned on again. By repeating the above operation, MOSFET Q1 is turned on / off.

  The switching frequency f of the switching power supply device 100 as described above is expressed by the following equation (1). If each of the following values is constant, the switching frequency f is constant.

f = (Vi−Vds) ² / 8LpVoIo (1)
Vi: input voltage of transformer T1 Vds: drain-source voltage of MOSFET Q1 Lp: inductance of primary winding N1 of transformer T1 Vo: output voltage Io: output current
JP-A-6-189545 (published July 8, 1994)

  By the way, in the above conventional configuration, when the output current Io increases, the switching frequency f decreases, and as a result, problems such as noise performance and efficiency decrease occur. This is because the switching frequency f is determined by the respective parameters.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to realize a switching power supply apparatus that can be arbitrarily controlled to increase the switching frequency f regardless of changes in the output load. That is.

In order to solve the above-described problems, a switching power supply according to the present invention is connected to a transformer including a primary winding, a secondary winding, and a control winding, and to the primary winding of the transformer. In an RCC type switching power supply device having a main switching element that converts it to a high-frequency AC voltage by turning it on and off, a voltage that appears at the high potential side terminal of the main switching element when the main switching element is off is A potential raising means for raising the potential at a predetermined location with a time constant is provided, and before the main switching element in the off state is turned on by ringing, the predetermined location is determined according to the time constant by the potential raising means. Off-period setting means for controlling the off-period of the main switching element by turning on at the timing when the potential is reached The off period setting means includes time constant changing means for changing the time constant according to the magnitude of the output load of the switching power supply device, and according to the magnitude of the output load of the switching power supply apparatus. The time constant changing means for changing the time constant includes a diode that rectifies and smoothes a voltage that varies in accordance with the magnitude of the output load of the switching power supply, which appears in the control winding of the transformer when the main switching element is turned off, and A capacitor, a Zener diode that turns on / off according to the level of the diode and the voltage rectified and smoothed by the capacitor, and a circuit that turns on when the Zener diode is turned on to determine the time constant are added. By changing the circuit configuration that determines the time constant, the photo camera changes the time constant. It is characterized in that it comprises and La.

In order to solve the above-described problems, a switching power supply according to the present invention is connected to a transformer including a primary winding, a secondary winding, and a control winding, and to the primary winding of the transformer. In an RCC type switching power supply device having a main switching element that converts it to a high-frequency AC voltage by turning it on and off, a voltage that appears at the high potential side terminal of the main switching element when the main switching element is off is A potential raising means for raising the potential at a predetermined location with a time constant is provided, and before the main switching element in the off state is turned on by ringing, the predetermined location is determined according to the time constant by the potential raising means. Off-period setting means for controlling the off-period of the main switching element by turning on at the timing when the potential is reached The potential raising means includes off period modulation means for modulating the off period by periodically varying the period until the predetermined location reaches the predetermined potential by the time constant, and the off period modulation The means includes a resistor that divides the voltage of the input line, and supplies the electric potential increasing means with a part of the electric charge that the electric potential increasing means processes as a part of the charge that the electric potential increasing means processes. The OFF period is modulated.

Switching power supply device according to the reference of the present invention, in order to solve the above problems, a primary winding, a transformer with a secondary winding, and control winding is connected to the primary winding of the transformer, DC In an RCC type switching power supply device including a main switching element that converts a voltage to a high-frequency AC voltage by turning the voltage on and off, a voltage that appears at a high potential side terminal of the main switching element when the main switching element is turned off is used. And a potential raising means for raising the potential at a predetermined place with a certain time constant, and before turning on the main switching element in the off state by ringing, the potential raising means causes the predetermined place according to the time constant. OFF period setting means for controlling the OFF period of the main switching element by turning ON at the timing when becomes a predetermined potential It is characterized in that it comprises.

  The main switching element of the conventional RCC switching power supply device changes from the on state to the off state, and then turns on by ringing when it is turned on again.

  Therefore, the off period setting means of the switching power supply according to the present invention turns on the main switching element in the off state before turning on by ringing as in the prior art by the potential raising means. Thereby, the off period of the main switching element can be controlled, that is, shorter than the off period determined by the ringing. As a result, the switching frequency of the switching power supply device can be increased.

  Further, by setting the time constant to a desired value, the off period of the main switching element can be arbitrarily shortened. As a result, the switching frequency of the switching power supply device can be arbitrarily increased. Thereby, the switching power supply according to the present invention has an effect that it can be arbitrarily controlled so as to increase the switching frequency regardless of a change in output load.

  Incidentally, in order to solve the problems of the present invention, conventionally, an auxiliary winding (additional winding) is provided in the transformer (see Patent Document 1). However, in this case, since the number of pins used in the transformer is increased, the degree of freedom in the pin arrangement of the transformer is reduced. However, in the switching power supply device according to the present invention, the above-described off period setting means solves the problems of the present invention, so that it is not necessary to add an extra winding as described above, and accordingly, the pin arrangement of the transformer is free. There is also an effect that the degree is not lowered.

Switching power supply according to the reference of the present invention, the primary winding, the transformer comprising a secondary winding, and control winding is connected to the primary winding of the transformer by turning on and off the DC voltage In an RCC type switching power supply device having a main switching element for converting to a high-frequency AC voltage, the voltage appearing in the control winding of the transformer when the main switching element is turned on is used to raise the potential at the first predetermined location. In addition, the second predetermined portion is set to a potential lower than the predetermined potential, and the potential at the second predetermined portion is increased with a certain time constant by using the potential at the first predetermined portion when the main switching element is turned off. Before turning on the main switching element in the off state by the ringing by the potential raising means according to the time constant. The second predetermined portion is by turning on at the timing at which a said predetermined potential is characterized by comprising an off-period setting means for controlling the off period of the main switching element.

  As described above, the off period setting means of the switching power supply device described first solves the problem of the present invention by using the voltage that appears at the high potential side terminal of the main switching element when the main switching element is off. Yes. However, the means for solving the problems of the present invention is not limited to the above configuration. The off period setting means of the switching power supply apparatus solves the problem of the present invention by using a voltage appearing in the control winding of the transformer when the main switching element is turned on.

  Specifically, the potential at the first predetermined location is raised by the voltage appearing in the control winding of the transformer when the main switching element is turned on. However, since the main switching element is turned on by raising the potential at the second predetermined position to a predetermined potential, the potential at the second predetermined position is previously lower than the predetermined potential when the main switching element is turned on. Keep potential.

  Next, when the main switching element is turned off, the potential at the first predetermined location is used, and the potential at the second predetermined location is raised to the predetermined potential with a certain time constant. Similar to the off period setting means of the switching power supply device, the main switching element in the off state is turned on before being turned on by ringing. As a result, an effect similar to that of the off period setting means of the switching power supply device described first can be obtained.

  The voltage appearing in the control winding of the transformer when the main switching element is turned off has the opposite polarity to the voltage appearing in the control winding of the transformer when the main switching element is turned on. Therefore, if this is utilized, an operation different from when the main switching element is turned on, the potential at the second predetermined place is raised using the potential at the first predetermined place when the main switching element is turned off. Can be performed.

The off-period setting means of the switching power supply according to the reference of the present invention includes, in addition to the above configuration, time constant changing means for changing the time constant according to the output load of the switching power supply. Preferably it is.

  The off-period setting means of the switching power supply device described first is configured to determine the off-period of the main switching element by the conventional ringing by setting the time constant to a predetermined value as described above. Therefore, it can be arbitrarily shortened.

  Therefore, when the output load is large, the time constant changing means makes the off period of the main switching element shorter than the off period determined by the off period setting means of the switching power supply device described first. By changing the time constant, the switching frequency of the switching power supply device can be further increased. On the other hand, when the output load is small, the time constant is not changed, that is, when the output load is large by setting the off period determined by the off period setting means of the switching power supply device described first. In comparison, the switching frequency can be lowered.

  In this way, by providing the time constant changing means in the off period setting means of the switching power supply device described first, it is arbitrarily controlled to increase the switching frequency according to the size of the output load. As a result, there is an effect that high efficiency can be obtained regardless of the change in the output load.

In addition to the above-described configuration, the potential raising unit of the switching power supply according to the reference of the present invention can change the off period by periodically varying the period until the predetermined part reaches the predetermined potential by the time constant. It is preferable to provide an off period modulation means for modulating.

  According to the above configuration, the potential increasing unit includes the off period modulation unit that modulates the off period by periodically changing a period until the predetermined portion reaches the predetermined potential by the time constant. . Since the off period of the main switching element can be modulated by the off period modulation means, the switching frequency of the switching power supply device can be modulated accordingly. Thereby, it is possible to prevent the energy of noise depending on the harmonics of the switching frequency from being concentrated on a specific frequency, and as a result, the filter configuration of the switching power supply device can be minimized. There is an effect.

  By the way, the rated input voltage of the power supply apparatus corresponding to the whole world needs to respond | correspond to the wide range of AC100V-AC240V. However, in the conventional RCC switching power supply, in the case of the wide range input as described above, the switching frequency fluctuates over a wide range, and as a result, noise performance is particularly deteriorated.

  Therefore, in addition to the above configuration, the off period setting unit of the switching power supply according to the present invention includes a time constant changing unit that changes the time constant according to the magnitude of the input voltage of the switching power supply. Preferably it is.

  The off-period setting means of the switching power supply device described first is configured to determine the off-period of the main switching element by the conventional ringing by setting the time constant to a predetermined value as described above. Therefore, it can be arbitrarily shortened.

  Therefore, by the time constant changing means, when the input voltage is small, the time constant is not changed, that is, by setting the off period determined by the off period setting means of the switching power supply device described first, The switching frequency can be increased. On the other hand, when the input voltage is large, the time constant is changed so that the off period of the main switching element is longer than the off period determined by the off period setting means of the switching power supply device described first. Thus, the switching frequency can be lowered.

  In this way, by providing the time constant changing means in the off period setting means of the switching power supply device described first, the switching frequency can be arbitrarily controlled according to the magnitude of the input voltage, As a result, it is possible to prevent the switching frequency from fluctuating even in the case of the wide range input as described above, and it is possible to obtain a power supply device corresponding to the wide range input.

  The off period setting means of the switching power supply according to the present invention is supplied from a resistor that divides a voltage appearing at a high-potential side terminal of the main switching element when the main switching element is turned off, and a voltage dividing point by the resistor. By accumulating charge with the time constant, a capacitor that raises the potential of its own high potential side terminal, which is the predetermined location, and the main switching element are turned on when the predetermined location reaches the predetermined potential. It is preferable that the potential raising means is constituted by a circuit including the resistor and the capacitor.

  The off-period setting means is configured as described above, and uses the voltage appearing on the high-potential side terminal of the main switching element when the main switching element is off to ring the main switching element in the off state. Turn it on before turning it on. Thereby, the off period of the main switching element can be controlled, that is, shorter than the off period determined by the ringing. As a result, the switching frequency of the switching power supply device can be increased.

  Further, the time constant can be set to a desired value by changing the configuration of the circuit. As a result, the off period of the main switching element can be arbitrarily shortened, and accordingly, the switching frequency of the switching power supply device can be arbitrarily increased. Thereby, the switching power supply according to the present invention has an effect that it can be arbitrarily controlled so as to increase the switching frequency regardless of a change in output load. Further, since there is no need to add an extra winding, there is an effect that the degree of freedom of the pin arrangement of the transformer is not lowered.

The off period setting means of the switching power supply according to the present invention includes a diode for rectifying a voltage appearing in the control winding of the transformer when the main switching element is turned on, and an electric charge by the voltage rectified by the diode By doing so, the first capacitor that increases the potential of its own high potential side terminal, which is the first predetermined location, and the voltage rectified by the diode are turned on and supplied to the second location. By discharging the electric charge, the electric charge due to the voltage of the first capacitor is accumulated with the time constant when the main switching element is turned off and the transistor that makes the second predetermined portion lower than the predetermined electric potential. The second capacitor for raising the potential of its own high potential side terminal, which is the second predetermined location, to the predetermined potential. With the door, the potential rise means is preferably composed of a circuit including the aforementioned diode and the first capacitor and the transistor and the second capacitor.

  The off period setting means is configured as described above, and uses the voltage appearing in the control winding of the transformer when the main switching element is turned on to turn on the main switching element in the off state by ringing. Turn it on before. Thereby, the off period of the main switching element can be controlled, that is, shorter than the off period determined by the ringing. As a result, the switching frequency of the switching power supply device can be increased.

  Further, the time constant can be set to a desired value by changing the configuration of the circuit. As a result, the off period of the main switching element can be arbitrarily shortened, and accordingly, the switching frequency of the switching power supply device can be arbitrarily increased. Thereby, the switching power supply according to the present invention has an effect that it can be arbitrarily controlled so as to increase the switching frequency regardless of a change in output load. Further, since there is no need to add an extra winding, there is an effect that the degree of freedom of the pin arrangement of the transformer is not lowered.

The time constant changing unit of the switching power supply according to the reference of the present invention is configured to change a voltage that appears in the control winding of the transformer when the main switching element is turned off and varies according to the output load of the switching power supply. A diode and capacitor for rectifying and smoothing, a Zener diode that turns on and off according to the level of the voltage rectified and smoothed by the diode and the capacitor, and a circuit that turns on when the Zener diode is turned on and determines the time constant are newly added. It is preferable to provide a photocoupler that changes the circuit configuration for determining the time constant and changes the time constant by adding a simple element.

  The time constant changing means is configured as described above, so that when the output load is large, the off period of the main switching element is determined by the off period setting means of the switching power supply device described first. It can be made shorter than the off period, and the switching frequency of the switching power supply device can be further increased. On the other hand, when the output load is small, the off-period determined by the off-period setting means of the switching power supply device described at the beginning can be set, and the switching frequency is made lower than when the output load is large. be able to.

  Thus, the time constant changing means can be arbitrarily controlled to increase the switching frequency according to the size of the output load by being configured as described above. There is an effect that high efficiency can be obtained regardless of the change in the output load.

The off-period modulation means of the switching power supply according to the reference of the present invention includes a resistor that divides the voltage of the input line, and the potential raising means processes the charge supplied from the resistor, the amount of which changes periodically. It is preferable to modulate the off period by supplying the electric potential increasing means as a part of the electric charge.

  The off-period modulation means can be configured as described above to modulate the off-period of the main switching element, and accordingly, the switching frequency of the switching power supply device can be modulated. Thereby, it is possible to prevent the energy of noise depending on the harmonics of the switching frequency from being concentrated on a specific frequency, and as a result, the filter configuration of the switching power supply device can be minimized. There is an effect.

The time constant changing means for changing the time constant according to the magnitude of the input voltage of the switching power supply of the switching power supply according to the present invention divides the voltage of the smoothing capacitor that smoothes the rectified voltage of the input voltage. A resistor, a Zener diode connected in series to the resistor, and turned on / off according to the voltage level of the smoothing capacitor, and turned on by a voltage supplied from a voltage dividing point of the resistor by turning on the Zener diode; It is preferable to include a transistor that changes the circuit configuration for determining the time constant by adding a new element to the circuit for determining the time constant to change the time constant.

  The time constant changing means is configured as described above, so that when the input voltage is small, the time constant changing means can be an off period determined by the off period setting means of the switching power supply device described first. The switching frequency can be increased. On the other hand, when the input voltage is large, the off-period of the main switching element can be made longer than the off-period determined by the off-period setting means of the switching power supply device described first, and the switching frequency can be lowered. can do.

  As described above, the time constant changing means is configured as described above, so that the switching frequency can be arbitrarily controlled according to the magnitude of the input voltage. Even in the case of wide range input, it is possible to prevent the switching frequency from fluctuating, and it is possible to obtain a power supply device that supports wide range input.

As described above, the switching power supply according to the present invention is connected to the transformer including the primary winding, the secondary winding, and the control winding, and the primary winding of the transformer, and turns on / off the DC voltage. In the RCC type switching power supply device having a main switching element for converting to a high-frequency AC voltage by using the voltage that appears at the high potential side terminal of the main switching element when the main switching element is turned off, with a certain time constant A potential raising means for raising the potential at a predetermined location is provided, and before the main switching element in the off state is turned on by ringing, the predetermined location becomes a predetermined potential according to the time constant by the potential raising means. The off-period setting means for controlling the off-period of the main switching element by being turned on at a predetermined timing, The period setting means includes time constant changing means for changing the time constant according to the magnitude of the output load of the switching power supply device, and the time constant according to the magnitude of the output load of the switching power supply device. A time constant changing means for changing the diode, a capacitor for rectifying and smoothing a voltage that appears in the control winding of the transformer when the main switching element is turned off and fluctuates according to the magnitude of the output load of the switching power supply device, A zener diode that is turned on / off according to the level of the voltage rectified and smoothed by the diode and the capacitor, and a new element is added to the circuit that determines the time constant by turning on the zener diode. And a photocoupler for changing the time constant and changing the time constant. There.

As described above, the switching power supply according to the present invention is connected to the transformer including the primary winding, the secondary winding, and the control winding, and the primary winding of the transformer, and turns on / off the DC voltage. In the RCC type switching power supply device having a main switching element for converting to a high-frequency AC voltage by using the voltage that appears at the high potential side terminal of the main switching element when the main switching element is turned off, with a certain time constant A potential raising means for raising the potential at a predetermined location is provided, and before the main switching element in the off state is turned on by ringing, the predetermined location becomes a predetermined potential according to the time constant by the potential raising means. The off-period setting means for controlling the off-period of the main switching element by being turned on at a predetermined timing, The level raising means includes an off period modulation means for modulating the off period by periodically changing a period until the predetermined location reaches the predetermined potential by the time constant, and the off period modulation means includes: A resistor for dividing the voltage of the input line is provided, and the off-off current is supplied to the potential raising means as a part of the charge to be processed by the potential raising means by periodically supplying the charge supplied from the resistor to the potential raising means. Modulate the duration.

  Since the switching power supply according to the present invention includes the off period setting means for controlling the off period of the main switching element by the potential increasing means for turning on the main switching element in the off state before turning it on by ringing. There is an effect that it is possible to arbitrarily control the switching power supply device so as to increase the switching frequency regardless of the change in the output load.

[Embodiment 1]
An embodiment as a reference mode of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a circuit configuration of a switching power supply device 11 according to the present embodiment. The switching power supply device 11 includes an off period setting circuit 1 (off period setting means) that controls the off period of the MOSFET Q1 (main switching element) included in the switching power supply device 100 in addition to the switching power supply device 100 described in the above prior art. It is added. Therefore, here, the off-period setting circuit 1 will be described. Moreover, in the figure shown below, the member which attached | subjected the code | symbol same as the switching power supply device 100 shown in FIG. 13 shall have the same function unless it demonstrates especially.

  The off period setting circuit 1 controls the off period of the MOSFET Q1 using the drain voltage generated at the drain (high potential side terminal) of the MOSFET Q1 when the MOSFET Q1 is off. As described in the above prior art, MOSFET Q1 is an example of a main switching element, and may be another switching element.

  First, the configuration of the off period setting circuit 1 will be described.

  The off period setting circuit 1 includes diodes D2, D3, and D4, capacitors C6 to C9, transistors Q3 (PNP type) and Q4 (NPN type), and resistors R6 to R13. The diode D2, the capacitors C6 and C7, the resistors R6 to R9, and the resistor R12 constitute potential increasing means.

  One end of the resistor R6 is connected to a connection point between the drain of the MOSFET Q1 and the other end of the primary winding N1 of the transformer T1, and the other end of the resistor R6 is connected in series with one end of the resistor R8 via the resistor R7. Has been. One end of a capacitor C6 is connected to the voltage dividing point of the resistors R6 and R7 and the resistor R8, and further, the anode side of the diode D2 is connected.

  One end of the resistor R9 is connected to the cathode side of the diode D2, the base of the transistor Q4 is connected to the other end of the resistor R9, and the resistor R12 and one end of the capacitor C7 are further connected to the base of the transistor Q4. Has been. Further, the source of MOSFET Q1, the emitter of Q4, the other end of R12, the other end of C7, the other end of C6, and the other end of resistor R8 are connected to the DC side return of bridge diode BD1.

  Further, the base of the transistor Q3 is connected to the collector of the transistor Q4 via the resistor R11, and one end of the control winding N3 of the transformer T1 is connected to the emitter of the transistor Q3 via the diode D4. The other end of the control winding N3 of the transformer T1 is connected via the capacitor C8.

  Furthermore, the gate of MOSFET Q1 is connected to the collector of transistor Q3 via capacitor C9 and diode D3. The emitter and base of the transistor Q3 are connected by a resistor R10, and a resistor R13 is connected in parallel with the capacitor C9.

  Next, the operation of the off period setting circuit 1 will be described.

  First, when the switching power supply 11 is turned on, the input AC voltage is noise-removed by the line capacitor C1 and the line filter L1 through the fuse F1, and then passed through the bridge diode BD1 and the smoothing capacitor C4. Is rectified and smoothed and converted to a DC voltage. When the DC voltage of the smoothing capacitor C4 rises, the main power supply voltage rises. When the divided voltage value at the starting resistors R2, R3, and R5 becomes equal to or higher than the operating voltage of the MOSFET Q1, the MOSFET Q1 is turned on, and the transformer T1 Excitation energy is accumulated in the primary winding N1.

  At the same time, a voltage V1 in the same direction as the primary winding N1 of the transformer T1 is induced in the control winding N3 of the transformer T1, and the induced current is given to the gate of the MOSFET Q1 via the bias resistor R4 and the capacitor C5. As a result, the MOSFET Q1 is kept on. The induced current flows through the capacitor D8 of the off period setting circuit 1 via the diode D4, and charges are accumulated.

  Further, the induced current is charged into the capacitor C3 via the phototransistor of the photocoupler PC1, and when the charged voltage becomes equal to or higher than the operating voltage of the control transistor Q2, the control transistor Q2 is turned on. As a result, the gate potential of the MOSFET Q1 is lowered and the MOSFET Q1 is turned off.

  At this time, a high drain voltage equivalent to the DC voltage of the smoothing capacitor C4 is generated at the drain of the MOSFET Q1, and the control winding N3 of the transformer T1 has a reverse direction to the voltage V1 induced when the MOSFET Q1 is turned on. Voltage V3 is induced. When the voltage V3 is induced, a current flows through the resistor R1, the charge of the capacitor C3 is extracted, and preparation for the next ON operation of the MOSFET Q1 is performed.

  When the MOSFET Q1 is turned off, the excitation energy stored in the primary winding N1 of the transformer T1 is supplied to the secondary winding N2 of the transformer T1, and thereafter, the operation is performed as shown in the prior art. At the same time, the operation of the off period setting circuit 1 is also performed.

  The off period setting circuit 1 first probes the drain voltage by the resistor R6, and divides the drain voltage by the ratio of the sum of the resistance values of the resistors R6 and R7 and the resistance value of the resistor R8. The electric charges that have passed through the resistors R6 and R7 are accumulated in the capacitor C6. The current of the capacitor C6 flows through the diode D2 and the resistor R9 to the capacitor C7 and the resistor R12, and is applied to the base (predetermined location) of the transistor Q4. When the base potential of the transistor Q4 becomes equal to or higher than the operating voltage (predetermined potential) of the transistor Q4, the transistor Q4 is turned on. When the transistor Q4 is turned on, the base potential of the transistor Q3 is lowered and the transistor Q3 is turned on. Note that the base potential of the transistor Q4 rises due to the time constants determined by the resistance values of the resistors R6 to R9 and R12, the capacities of the capacitors C6 and C7, and the current rating of the diode D2.

  When the transistor Q3 is turned on, a current from the capacitor C8 is applied to the starting resistors R2, R3, and R5 via the transistor Q3, the capacitor C9, and the diode D3, and the voltage is applied to the gate of the MOSFET Q1, exceeding the operating voltage of the MOSFET Q1. Then, the MOSFET Q1 is turned on. That is, the off period of MOSFET Q1 ends. The electric charge accumulated in the capacitor C9 is released by the resistor R13.

  The off period of the MOSFET Q1 ends when the discharge of the excitation energy accumulated in the primary winding N1 of the transformer T1 to the secondary side ends and the parasitic capacitance generated in the primary winding N1 of the transformer T1. And the ringing voltage generated between the inductor of the primary winding N1 of the transformer T1 is transmitted to the control winding N3 of the transformer T1 and is applied to the gate of the MOSFET Q1 via the bias resistor R4 and the capacitor C5. .

  That is, the off period setting circuit 1 turns off the MOSFET Q1 by turning on the MOSFET Q1 using the drain voltage generated at the drain of the MOSFET Q1 when the MOSFET Q1 is turned off before the MOSFET Q1 is turned on with the ringing voltage as in the prior art. The period can be shortened.

  Further, the off-period setting circuit 1 changes the time constant by changing the resistance values of the resistors R6 to R9 and R12, the capacitances of the capacitors C6 and C7, and the current rating of the diode D2, thereby changing the MOSFET Q1. The off period can be arbitrarily shortened. As a result, it is possible to arbitrarily control the switching frequency f2 to be high regardless of the change in the output load VR1.

  Note that after the MOSFET Q1 is turned on, the drain voltage becomes almost zero. Therefore, the electric charges accumulated in the capacitors C6 and C7 are discharged through the resistors R12 and R8. Thus, the off period setting circuit 1 is in an initial state during the on period of the MOSFET Q1, and is prepared for the next operation.

  The operation of the off period setting circuit 1 has been described above. Next, the effect produced by the off period setting circuit 1 will be described in detail with reference to FIGS.

  FIG. 2 shows the drain voltage and drain current A1 of MOSFET Q1 provided in the conventional switching power supply apparatus 100. FIG. 3 shows the drain voltage and drain current A2 of the MOSFET Q1 included in the switching power supply device 11.

  From the figure, it can be seen that the off-period of the MOSFET Q1 of the switching power supply 11 is shorter than the off-period of the MOSFET Q1 of the switching power supply 100. That is, the off period setting circuit 1 can arbitrarily shorten the off period of the MOSFET Q1.

  Moreover, it turns out that the drain current A1 of the switching power supply apparatus 100 is a triangular wave, and the current peak value is large from the figure. As a result, the switching power supply apparatus 100 has been forced to generate heat from its components. However, it can be seen that the drain current A2 of the switching power supply device 11 is a trapezoidal wave and the current peak value is small. FIG. 4 shows the peak value of the drain current A2 of the switching power supply device 11 in detail.

  FIG. 4 shows the output current dependence of the peak value of the drain current A2 of the switching power supply 11. The thick line in the figure indicates the peak value of the drain current A1 of the switching power supply apparatus 100 shown in FIG. 2, and the alternate long and short dash line in the figure indicates the peak value of the drain current A2 of the switching power supply apparatus 11. Yes.

  From the figure, it can be seen that the peak value of the drain current A2 of the switching power supply device 11 is smaller than the peak value of the drain current A1 of the switching power supply device 100 when the output current is approximately 3 A or more. It can be seen that the operation of the setting circuit 1 is effective. Further, the peak value of the drain current A1 of the switching power supply device 100 continues to increase linearly with respect to the output current, but the peak value of the drain current A2 of the switching power supply device 11 increases when the output current becomes 4A or more. It can be seen that is suppressed.

  As described above, the switching power supply device 11 includes the off-period setting circuit 1 that can arbitrarily shorten the off-period of the MOSFET Q1 regardless of the change in the output current. As described above, the peak value of the drain current A2 of the switching power supply device 11 can be made smaller than the peak value of the drain current A1 of the switching power supply device 100. As a result, it is possible to suppress the heat generation of its own component parts. Further, since driving in the continuous current mode is possible, smaller ones such as the size of the transformer T1, the current rating of the MOSFET Q1, and the current rating of the diode D1 can be adopted, and a significant cost reduction can be expected.

  Next, FIG. 5 shows the output current dependency of the efficiency of the switching power supply device 11. In addition, the thick line in a figure has shown the efficiency of the conventional switching power supply apparatus 100, and the dashed-two dotted line and the dotted line in the figure have shown the efficiency of the switching power supply apparatus 11. FIG. Specifically, the one-dot chain line indicates the efficiency when the output current is 3 A or more and the switching frequency f2 is about 75 kHz, and the dotted line indicates the efficiency when the output current is 2 A or more and the switching frequency f2 is about 120 kHz. .

  As shown in the figure, as indicated by the one-dot chain line and the dotted line, when the output current is 2 A or more, or the output current is 1 A or more, the switching power supply device 11 operates according to the frequency control of this embodiment regardless of ringing. It is clear that

  Further, when the output current is 5 A or more, the loss due to copper loss or the like is a region that becomes dominant as compared with the loss due to switching of the MOSFET Q1. It can be seen that the switching power supply device 11 provided with the off-period setting circuit 1 is more efficient than the conventional one in a region where loss due to copper loss or the like becomes significant.

  Finally, FIG. 6 shows the output current dependence of the switching frequency f2 of the switching power supply device 11. In addition, the thick line in a figure has shown the switching frequency f1 of the conventional switching power supply apparatus 100, and the dashed-two dotted line and the dotted line in the figure have shown the switching frequency f2 of the switching power supply apparatus 11. FIG. Specifically, the two-dot chain line shows a case where the output current is 3 A or more and the switching frequency f2 is about 75 kHz, and the dotted line shows a case where the output current is 2 A or more and the switching frequency f2 is about 120 kHz.

  From the figure, as indicated by the two-dot chain line and the dotted line, when the output current is 2 A or more, or the output current is 1 A or more, the switching power supply 11 operates according to the frequency control of this embodiment regardless of ringing. As a result, it can be seen that the two switching frequencies f2 of the switching power supply device 11 are higher than the switching frequency f1 of the switching power supply device 100. In addition, the switching frequency f1 of the switching power supply device 100 continues to decrease as the output current increases, but the two switching frequencies f2 of the switching power supply device 11 are prevented from decreasing even if the output current increases. I understand. Thereby, it is understood that the operation of the off period setting circuit 1 is effective.

  As described above, the switching power supply 11 according to the present embodiment uses the drain voltage generated at the drain of the MOSFET Q1 when the MOSFET Q1 is turned off, so that the MOSFET Q1 can be turned on before the MOSFET Q1 is turned on with the ringing voltage. A period setting circuit 1 is provided.

  Thereby, since the off period of MOSFETQ1 can be shortened arbitrarily, it can control arbitrarily so that switching frequency f2 may be made high irrespective of change of output load VR1. As a result, the effects as described above can be achieved. Conventionally, in order to solve the problem of the present invention, an auxiliary winding (additional winding) is provided in the transformer (see Patent Document 1). However, in this case, since the number of transformer pins used increases, there arises a new problem that the degree of freedom of transformer pin arrangement is reduced. However, the switching power supply device 11 according to the present embodiment can solve the above problems without causing the above problems.

[Embodiment 2]
Another embodiment as a reference embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 shows a circuit configuration of the switching power supply device 21 according to the present embodiment. The switching power supply device 21 includes an off period setting circuit 2 (off period setting means) that controls the off period of the MOSFET Q1 (main switching element) included in the switching power supply device 100 in addition to the switching power supply device 100 described in the above prior art. This is an added circuit. Therefore, here, the off period setting circuit 2 will be described. Moreover, in the figure shown below, the member which attached | subjected the code | symbol same as the switching power supply device 100 shown in FIG. 13 shall have the same function unless it demonstrates especially.

The off period setting circuit 2 is a circuit having the same effect as the off period setting circuit 1 shown in the first embodiment. However, in order to arbitrarily shorten the off period of the MOSFET Q1, the MOSFET Q1 is turned off when the MOSFET Q1 is turned off. The voltage V1 induced in the control winding N3 of the transformer T1 when the MOSFET Q1 is turned on is used instead of the drain voltage generated at the drain of the transistor T1.

  First, the configuration of the off period setting circuit 2 will be shown.

  The off period setting circuit 2 includes diodes D5 to D8, capacitors C10 and C11, a transistor Q5 (NPN type), and resistors R14 to R16. The diodes D5 to D7, the capacitors C10 and C11, the transistor Q5, and the resistors R14 to R16 constitute potential raising means.

  The anode side of the diode D5 is connected to one end of the control winding N3 of the transformer T1, and the resistor R14 and one end of the capacitor C10 and the anode side of the diode D6 are connected to the cathode side of the diode D5.

  The other end of the resistor R14 is connected to the collector of the transistor Q5 via the diode D7, and one end of the capacitor C11 and the anode side of the diode D8 are connected to the connection point between the cathode side of the diode D7 and the collector of the transistor Q5. Has been. The gate of MOSFET Q1 is connected to the cathode side of diode D8.

  A resistor R15 connected to the cathode side of the diode D6 is connected to the base of the transistor Q5. Note that one end of the resistor R16 is connected to a connection point between the base of the transistor Q5 and the resistor R15.

  The emitter of the transistor Q3 is connected to the source of the MOSFET Q1, the other end of the capacitor C11, the other end of the resistor R16, and the other end of the capacitor C10.

  Next, the operation of the off period setting circuit 2 will be described.

  First, when the switching power supply 21 is turned on, the input AC voltage is noise-removed by the line capacitor C1 and the line filter L1 via the fuse F1, and then via the bridge diode BD1 and the smoothing capacitor C4. Is rectified and smoothed and converted to a DC voltage. When the DC voltage of the smoothing capacitor C4 rises, the main power supply voltage rises. When the divided voltage value at the starting resistors R2, R3, and R5 becomes equal to or higher than the operating voltage of the MOSFET Q1, the MOSFET Q1 is turned on, and the transformer T1 Excitation energy is accumulated in the primary winding N1.

  At the same time, a voltage V1 in the same direction as the primary winding N1 of the transformer T1 is induced in the control winding N3 of the transformer T1, and the induced current is given to the gate of the MOSFET Q1 via the bias resistor R4 and the capacitor C5. As a result, the MOSFET Q1 is kept on.

  The induced current flows through the diode D5 of the off-period setting circuit 2 to the resistors R15 and R16 via the capacitor C10, the resistor R14, the diode D7, the capacitor C11, and the diode D6. As a result, charges are accumulated in the capacitors C10 (first predetermined location) and C11 (second predetermined location). However, the divided voltage value divided by the resistance value of the resistor R15 and the resistance value of R16 is supplied to the base of the transistor Q5 to turn on the transistor Q5.

  As a result, the charge that should be accumulated in the capacitor C11 via the resistor R14 and the diode D7 is released via the transistor Q5, and the voltage of the capacitor C7 does not become a voltage that acts on the MOSFET Q1. That is, the operation of the off period setting circuit 2 does not affect the on period of the switching power supply device 21.

  The induced current is charged to the capacitor C3 via the phototransistor of the photocoupler PC1, and when the charged voltage becomes equal to or higher than the operating voltage of the control transistor Q2, the control transistor Q2 is turned on. As a result, the gate potential of the MOSFET Q1 is lowered and the MOSFET Q1 is turned off. At this time, a high drain voltage equivalent to the DC voltage of the smoothing capacitor C4 is generated at the drain of the MOSFET Q1, and the control winding N3 of the transformer T1 has a reverse direction to the voltage V1 induced when the MOSFET Q1 is turned on. Voltage V3 is induced. When the voltage V3 is induced, a current flows through the resistor R1, the charge of the capacitor C3 is extracted, and preparation for the next ON operation of the MOSFET Q1 is performed.

  When the MOSFET Q1 is turned off and a voltage V3 opposite to the voltage V1 is induced, the anode side of the diode D5 of the off period setting circuit 2 becomes negative. At this time, the resistance values of the resistors R15 and R16 are set so that the transistor Q5 is instantaneously turned off.

  The electric charge accumulated in the capacitor C10 is gradually discharged through the diode D6 and the resistors R15 and R16, and the voltage of the capacitor C10 gradually decreases. On the other hand, charge is accumulated in the capacitor C11 via the resistor R14 and the diode D7, and the voltage of the capacitor C11 rises. When the voltage of the capacitor C11 exceeds the operating voltage (predetermined potential) of the MOSFET Q1, the MOSFET Q1 is turned on. That is, the off period of MOSFET Q1 ends. Note that the voltage of the capacitor C11 increases depending on the resistance values of the resistors R14 to R16, the capacitances of the capacitors C10 and C11, the current ratings of the diodes D5 to D7, and the time constant determined by the transistor Q5.

  Similarly to the off period setting circuit 1, the off period of the MOSFET Q1 ends when the excitation energy stored in the primary winding N1 of the transformer T1 is released to the secondary side, and the 1 of the transformer T1 is terminated. A ringing voltage generated between the parasitic capacitance generated in the secondary winding N1 and the inductor of the primary winding N1 of the transformer T1 is transmitted to the control winding N3 of the transformer T1, via the bias resistor R4 and the capacitor C5. Before being given to the gate of MOSFETQ1.

  Further, the off period setting circuit 2 changes the time constant by changing the resistance values of the resistors R14 to R16, the capacitances of the capacitors C10 and C11, the current ratings of the diodes D5 to D7, and the transistor Q5. The OFF period of the MOSFET Q1 can be arbitrarily shortened. As a result, it is possible to arbitrarily control the switching frequency f2 to be high regardless of the change in the output load VR1.

  As described above, the switching power supply device 21 according to the present embodiment uses the voltage V1 induced in the control winding N3 of the transformer T1 when the MOSFET Q1 is turned on, so that the off period of the MOSFET Q1 is arbitrarily shortened. A setting circuit 2 is provided.

  Thereby, since the off period of MOSFETQ1 can be shortened arbitrarily, it can control arbitrarily so that switching frequency f2 may be made high irrespective of change of output load VR1. As a result, the same effect as that produced by the off-period setting circuit 1 can be obtained.

[Embodiment 3]
Another embodiment of the present invention will be described below with reference to the drawings.

  FIG. 8 shows a circuit configuration of the switching power supply device 31 according to the present embodiment. Note that the switching power supply 31 changes the time constant for determining the off period of the MOSFET Q1 in accordance with the magnitude of the output load VR1 of the switching power supply 31 in the off period setting circuit 1 described in the first embodiment. The time constant changing circuit 3 (time constant changing means) is added. Therefore, here, the time constant changing circuit 3 will be described. Moreover, in the figure shown below, the member which attached | subjected the code | symbol same as the switching power supply device 11 shown in FIG. 1 shall have the same function unless it demonstrates in particular.

  First, the configuration of the time constant changing circuit 3 is shown.

  The time constant changing circuit 3 includes a Zener diode D9, a diode D10, a capacitor C12, a photocoupler PC2, and resistors R17 and R18.

  One end of the resistor R17 is connected to one end of the control winding N3 of the transformer T1, and the other end of the resistor R17 is connected to the anode side of the Zener diode D9 via the photocoupler PC2 (light emitting element). The cathode side of the diode D10 is connected to the cathode side. The other end of the control winding N3 of the transformer T1 is connected to the anode side of the diode D10, and between the connection point between the Zener diode D9 and the diode D10 and one end of the control winding N3 of the transformer T1. A capacitor C12 is connected.

  The resistor R18 and the photocoupler PC2 (phototransistor) are connected in series between the connection point between the diode D2 and the resistor R9 of the off period setting circuit 1 and the base of the transistor Q4. A photocoupler PC2 (phototransistor emitter) is connected to the base of the transistor Q4.

  Next, the operation of the time constant changing circuit 3 will be described.

  First, when the switching power supply 31 is turned on, the input AC voltage is noise-removed by the line capacitor C1 and the line filter L1 through the fuse F1, and then passed through the bridge diode BD1 and the smoothing capacitor C4. Is rectified and smoothed and converted to a DC voltage. When the DC voltage of the smoothing capacitor C4 rises, the main power supply voltage rises. When the divided voltage value at the starting resistors R2, R3, and R5 becomes equal to or higher than the operating voltage of the MOSFET Q1, the MOSFET Q1 is turned on, and the transformer T1 Excitation energy is accumulated in the primary winding N1.

  At the same time, a voltage V1 in the same direction as the primary winding N1 of the transformer T1 is induced in the control winding N3 of the transformer T1, and the induced current is given to the gate of the MOSFET Q1 via the bias resistor R4 and the capacitor C5. As a result, the MOSFET Q1 is kept on.

  Next, the induced current induced in the control winding N3 of the transformer T1 is charged in the capacitor C3 via the phototransistor of the photocoupler PC1, and when the charged voltage becomes equal to or higher than the operating voltage of the control transistor Q2, the control is performed. Transistor Q2 is turned on. As a result, the gate potential of the MOSFET Q1 is lowered and the MOSFET Q1 is turned off.

  At this time, a high drain voltage equivalent to the DC voltage of the smoothing capacitor C4 is generated at the drain of the MOSFET Q1, and the control winding N3 of the transformer T1 has a reverse direction to the voltage V1 induced when the MOSFET Q1 is turned on. Voltage V3 is induced. When the voltage V3 is induced, a current flows through the resistor R1, the charge of the capacitor C3 is extracted, and preparation for the next ON operation of the MOSFET Q1 is performed.

  By the way, the voltage V3 increases as the output load VR1 increases, and decreases as the output load VR1 decreases. Using such a voltage V3, the time constant changing circuit 3 changes the time constant for determining the off period of the MOSFET Q1 in accordance with the magnitude of the output load VR1, thereby changing the off period of the MOSFET Q1 to the output load VR1. Control arbitrarily according to the size.

  Specifically, when the voltage V3 is induced, the voltage V3 is rectified and smoothed by the diode D10 and the capacitor C12 of the time constant changing circuit 3. Note that the rectified and smoothed voltage V3, that is, the voltage of the capacitor C12 is negative at one end of the control winding N3 of the transformer T1, and the voltage of the control winding N3 of the transformer T1, as indicated by the capacitor C12 in FIG. The other end is positive.

  When the voltage of the capacitor C12 is applied to the Zener diode D9 and the voltage of the capacitor C12 exceeds the Zener voltage of the Zener diode D9, the other end side of the control winding N3 of the transformer T1 as shown by the arrow in FIG. If a large amount of current flows in the direction from one end to the other end of the control winding N3 of the transformer T1, and the voltage of the capacitor C12 falls below the Zener voltage of the Zener diode D9, the current does not flow.

  That is, if the output load VR1 is large, the voltage of the capacitor C12 increases, and thus a current flows in the direction of the arrow. Accordingly, the photodiode of the photocoupler PC2 emits light, and the light emitted by the photodiode of the photocoupler PC2 is received by the phototransistor of the photocoupler PC2 connected in the off period setting circuit 1.

  As a result, a current also flows through the time constant changing circuit 3 in the off period setting circuit 1, and the current of the capacitor C6 is passed through the resistance value of the diode D2 and the resistors R9 and R18 connected in parallel. It flows through resistor R12 and is applied to the base of transistor Q4. As a result, when the output load VR1 is large, the MOSFET Q1 can be turned on earlier than the timing when it is turned on by the off period setting circuit 1, and the switching frequency f4 can be increased.

  On the other hand, if the output load VR1 is small, the voltage of the capacitor C12 becomes small, so that a small amount of the current flows and the light emitting element of the photocoupler PC2 emits light weakly, or the current does not flow and the photodiode of the photocoupler PC2 Stops emitting light. In this case, since the phototransistor of the photocoupler PC2 connected in the off period setting circuit 1 cannot receive light, no current flows through the time constant changing circuit 3 in the off period setting circuit 1, and the base of the transistor Q4 has The voltage of the capacitor C6 is divided and applied by the resistance values of the resistors R9 and R12.

  As a result, when the output load VR1 is small, the MOSFET Q1 is turned on at the same timing as when the off-period setting circuit 1 is turned on, so that the off-period of the MOSFET Q1 is longer than when the output load VR1 is large. That is, the switching frequency f4 can be made lower than when the output load VR1 is large.

  As in the first and second embodiments, the MOSFET Q1 off period ends when the excitation energy accumulated in the primary winding N1 of the transformer T1 is released to the secondary side and the transformer T1 A ringing voltage generated between the parasitic capacitance generated in the primary winding N1 and the inductor of the primary winding N1 of the transformer T1 is transmitted to the control winding N3 of the transformer T1, via the bias resistor R4 and the capacitor C5. Before being applied to the gate of MOSFETQ1.

  The operation of the time constant changing circuit 3 has been described above. Next, the effect produced by the time constant changing circuit 3 will be described in detail with reference to the drawings.

  FIG. 9 shows the output current dependence of the peak value of the drain current A3 of the switching power supply 31. The thick line in the figure indicates the peak value of the drain current A1 of the conventional switching power supply apparatus 100 shown in FIG. 2, and the two-dot chain line in the figure indicates the switching power supply apparatus according to the first embodiment shown in FIG. 11 shows the peak value of the drain current A2, and the dotted line in the figure shows the peak value of the drain current A3 of the switching power supply 31 according to the present embodiment.

  In the first embodiment, the peak value of the drain current A1 of the switching power supply device 100 increases linearly with respect to the output current using FIG. 4, but the peak value of the drain current A2 of the switching power supply device 11 is It has been stated that the increase is suppressed when the output current is 4A or more. However, as is clear from FIG. 9, the peak value of the drain current A3 of the switching power supply device 31 increases more than the drain current A2 of the switching power supply device 11 when the output current is 4 A or more. I understand that. Thereby, it is understood that the operation of the time constant changing circuit 3 is effective.

  Thereby, the heat_generation | fever of an own component can be further suppressed. Further, the size of the transformer T1, the current rating of the MOSFET Q1, the current rating of the diode D1, and the like can be reduced as compared with the switching power supply device 11, and a significant cost reduction can be expected.

  Next, FIG. 10 shows the output current dependence of the switching frequency f4 of the switching power supply 31. In addition, the thick line in a figure has shown the switching frequency f1 of the conventional switching power supply apparatus 100 shown in FIG. 6, and the dashed-two dotted line and a dotted line show the switching frequency f2 of the switching power supply apparatus 11 which concerns on Embodiment 1. FIG. (The two-dot chain line indicates that the output current is 3 A or more and the switching frequency f2 is approximately 75 kHz, and the dotted line indicates that the output current is 2 A or more and the switching frequency f2 is approximately 120 kHz). Moreover, the continuous line has shown the switching frequency f4 of the switching power supply device 31 which concerns on this Embodiment.

  In the description of FIG. 6 in the first embodiment, the switching frequency f1 of the switching power supply device 100 decreases as the output current increases, but the two switching frequencies f2 of the switching power supply device 11 increase the output current. In the present embodiment, the switching frequency f4 of the switching power supply 31 is prevented from decreasing even if the output current is increased, as in the switching frequency f2. It can be seen that when the output current is 3 A or more, the switching frequency f4 is increased. Thereby, it is understood that the operation of the time constant changing circuit 3 is effective.

  As described above, the switching power supply 31 according to the present embodiment has the off-period setting circuit 1 that can arbitrarily shorten the off-period of the MOSFET Q1, and the voltage V3 that varies according to the magnitude of the output load VR1. And a photocoupler PC2 that operates to turn on / off the time constant changing circuit 3 in the off period setting circuit 1 according to the current. A constant changing circuit 3 is provided.

  As a result, when the output load VR1 of the switching power supply 31 is large, the MOSFET Q1 can be turned on earlier than the timing when it is turned on by the off period setting circuit 1, and the switching frequency f4 is arbitrarily controlled. Can do. As a result, when the output load VR1 is large, the switching frequency f4 is not lowered, and higher efficiency than the off-period setting circuit 1 can be obtained.

  On the other hand, when the output load VR1 of the switching power supply 31 is small, the MOSFET Q1 is turned on at the same timing as when it is turned on by the off period setting circuit 1, so that the off period of the MOSFET Q1 is larger than that when the output load VR1 is large. become longer. That is, the switching frequency f4 can be arbitrarily controlled so as to be lower than when the output load VR1 is large. As a result, when the output load VR1 is small, the switching frequency f4 is not increased unnecessarily, and higher efficiency than the off-period setting circuit 1 can be obtained.

[Embodiment 4]
Another embodiment of the present invention will be described with reference to FIG.

  FIG. 11 shows a circuit configuration of the switching power supply device 41 according to the present embodiment. The switching power supply 41 includes an off period modulation circuit 4 (off period modulation means) for causing the off period setting circuit 1 described in the first embodiment to modulate the off period of the MOSFET Q1 included in the off period setting circuit 1. It is a circuit to which is added. Therefore, here, the off-period modulation circuit 4 will be described. Moreover, in the figure shown below, the member which attached | subjected the code | symbol same as the switching power supply device 11 shown in FIG. 1 shall have the same function unless it demonstrates in particular.

  First, the configuration of the off-period modulation circuit 4 is shown.

  The off-period modulation circuit 4 includes resistors R19 and R20, and the resistors R19 and R20 have one end of a capacitor C6 connected to a voltage dividing point between the resistors R6 and R7 of the off-period setting circuit 1 and the resistor R8. The line filter L1 and the input line (L line) between the bridge diode BD1 are connected in series.

  Next, the operation of the off period modulation circuit 4 will be described.

  Resistors R19 and R20 connected to the input line supply charges from the input line to the capacitor C6. Since this amount of charge is determined by the difference between the level of the AC voltage and GND (not shown), it varies depending on the period of the input AC voltage.

  In this way, by periodically changing the period until the base potential of the transistor Q4 reaches the operating voltage of the transistor Q4 by supplying the charge whose amount varies periodically to the capacitor C6, the off period of the MOSFET Q1 Can be modulated. Thereby, since the switching frequency can be modulated, it is possible to prevent the energy of noise depending on the harmonics of the switching frequency from being concentrated on a specific frequency. As a result, the filter of the switching power supply device 41 can be prevented. Configuration can be minimized.

  As described above, the switching power supply device 41 according to the present embodiment supplies the capacitor C6 with a charge whose amount varies periodically to the off period setting circuit 1 that can arbitrarily shorten the off period of the MOSFET Q1. The off-period modulation circuit 4 for modulating the off-period of the MOSFET Q1 is provided.

  Thereby, in addition to the effect produced by the off period setting circuit 1, the off period of the MOSFET Q1 can be modulated, so that the switching frequency can also be modulated, and noise is prevented from concentrating on a specific frequency. Filter configuration can be minimized.

[Embodiment 5]
Another embodiment of the present invention is described below with reference to FIG. FIG. 12 shows a circuit configuration of the switching power supply device 51 according to the present embodiment.

  By the way, the rated input voltage of a power supply apparatus compatible with the whole world needs to correspond to a wide range input of AC100V to AC240V. However, in the conventional RCC switching power supply, in the case of the wide range input as described above, the switching frequency fluctuates over a wide range, and as a result, there is a problem that noise performance is particularly deteriorated.

  Therefore, in order to solve the above problem, the switching power supply 51 receives the time constant for determining the off-period of the MOSFET Q1 from the off-period setting circuit 1 described in the first embodiment. A time constant changing circuit 5 (time constant changing means) for changing according to the magnitude of the voltage is added. Therefore, here, the time constant changing circuit 5 will be described. Moreover, in the figure shown below, the member which attached | subjected the code | symbol same as the switching power supply device 11 shown in FIG. 1 shall have the same function unless it demonstrates in particular.

  First, the configuration of the time constant changing circuit 5 is shown.

  The time constant changing circuit 5 includes a Zener diode D11, a transistor Q6 (NPN type), and resistors R21 to R25. One end of the resistor R21 is connected to the positive terminal of the smoothing capacitor C4, and the other end of the resistor R21. The resistor R22 and the resistor R23 are connected in series. One end of a resistor R24 is connected in series to the other end of the resistor R23 via a Zener diode D11. That is, the resistor R22, the resistor R23, and the Zener diode D11 are connected between the other end of the resistor R21 and one end of the resistor R24.

  The other end of the resistor R24 is connected to the negative terminal of the smoothing capacitor C4, and the base of the transistor Q6 is connected to the connection point between the anode side of the Zener diode D11 and one end of the resistor R24. A resistor R25 is connected between the collector of Q6 and the voltage dividing points of the resistors R6 and R7 and the resistor R8 of the off period setting circuit 1. The emitter of the transistor Q6 is connected to the negative terminal of the smoothing capacitor C4.

  Next, the operation of the time constant changing circuit 5 will be described.

  First, when the switching power supply 51 is turned on, the input AC voltage is noise-removed by the line capacitor C1 and the line filter L1 through the fuse F1, and then passed through the bridge diode BD1 and the smoothing capacitor C4. Is rectified and smoothed and converted to a DC voltage.

  The DC voltage, that is, the voltage of the smoothing capacitor C4 increases as the input AC voltage increases, and decreases as the input AC voltage decreases. Using such a voltage of the smoothing capacitor C4, the time constant changing circuit 5 changes the time constant for determining the OFF period of the MOSFET Q1 in accordance with the magnitude of the input AC voltage, thereby reducing the OFF period of the MOSFET Q1. It is arbitrarily controlled according to the magnitude of the input AC voltage.

  First, the case where the input AC voltage is small will be described in detail. As described above, when the input AC voltage is small, the voltage of the smoothing capacitor C4 is also small. Along with this, the switching frequency f5 also decreases. Therefore, in this case, the resistance values of the resistors R21 to R24 are selected so that the voltage of the smoothing capacitor C4 does not exceed the Zener voltage of the Zener diode D10, and the transistor Q6 is left off.

  As a result, the MOSFET Q1 is turned on at the same timing as when it is turned on by the off period setting circuit 1, so that the off period of the MOSFET Q1 can be shortened and the switching frequency f5 can be increased.

  On the other hand, when the input AC voltage is large, the voltage of the smoothing capacitor C4 also increases. Along with this, the switching frequency f5 also increases. Therefore, in this case, the resistance values of the resistors R21 to R24 are selected so that the voltage of the smoothing capacitor C4 exceeds the Zener voltage of the Zener diode D10, and the transistor Q6 is turned on.

  When transistor Q6 is turned on, resistor R25 is connected in parallel to resistor R8 among resistors R6, R7, and R8 that determine the voltage of capacitor C6. As a result, the increase in the voltage of the capacitor C6 gradually changes. As a result, the off period of the MOSFET Q1 can be lengthened, and the switching frequency f5 can be lowered.

  As in the first and second embodiments, the MOSFET Q1 off period ends when the excitation energy accumulated in the primary winding N1 of the transformer T1 is released to the secondary side and the transformer T1 A ringing voltage generated between the parasitic capacitance generated in the primary winding N1 and the inductor of the primary winding N1 of the transformer T1 is transmitted to the control winding N3 of the transformer T1, via the bias resistor R4 and the capacitor C5. Before being applied to the gate of MOSFETQ1.

  As described above, the switching power supply device 51 according to the present embodiment allows a current to flow through the off period setting circuit 1 that can arbitrarily shorten the off period of the MOSFET Q1 based on the magnitude of the input AC voltage, or A time constant changing circuit 5 including a Zener diode D11 that does not flow and a transistor Q6 that sets the voltage of the capacitor C6 by turning on and off according to the current is provided.

  Thus, when the input AC voltage is small, the MOSFET Q1 is turned on at the same timing as when the off-period setting circuit 1 is turned on, so that the off-period of the MOSFET Q1 can be arbitrarily shortened. That is, it can be arbitrarily controlled to increase the switching frequency f5, and high efficiency can be obtained.

  On the other hand, when the input AC voltage is large, by setting the voltage of the capacitor C6 of the MOSFET Q1, the increase in the voltage of the capacitor C6 can be moderated and the off period of the MOSFET Q1 can be lengthened. As a result, it is possible to prevent the switching frequency f5 from being increased unnecessarily and to obtain high efficiency.

  That is, the switching power supply device 51 according to the present embodiment adds a dependency opposite to the input voltage dependency of the switching frequency f1 of the switching power supply device 100, so that the switching frequency depends on the magnitude of the input AC voltage. It is possible to obtain a power supply that is prevented from fluctuating and has a relatively small input voltage dependency of the switching frequency.

  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.

  The present invention can be suitably used as an AC-DC converter, a DC-DC converter, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment as a reference form of the present invention, and is a circuit diagram illustrating a main configuration of a switching power supply device. It is a wave form diagram which shows the drain voltage and drain current of MOSFETQ1 with which the conventional switching power supply device is provided. It is a wave form diagram which shows the said drain voltage and drain current of MOSFETQ1 with which the switching power supply device of this embodiment as a reference form is provided. It is a graph which shows the output current dependence of the said drain current peak value of the switching power supply device of this embodiment as a reference form . It is a graph which shows the output current dependence of the efficiency of the switching power supply device of this embodiment as a reference form . It is a graph which shows the output current dependence of the switching frequency of the switching power supply device of this embodiment as a reference form . Another embodiment as a reference form of the present invention is shown, and is a circuit diagram showing a main configuration of a switching power supply device. And shows the implementation form of the present invention, it is a circuit diagram showing a main configuration of a switching power supply device. Is a graph showing the output current dependency of the drain current peak value of the switching power supply of the implementation of the invention. Is a graph showing the output current dependency of the switching frequency of the switching power supply device of the implementation mode of the present invention. FIG. 10, showing another embodiment of the present invention , is a circuit diagram illustrating a configuration of a main part of a switching power supply device. FIG. 32, showing still another embodiment of the present invention, is a circuit diagram illustrating a main configuration of a switching power supply device. It is a circuit diagram which shows the principal part structure of the said conventional switching power supply device.

1, 2 OFF period setting circuit (OFF period setting means)
3 Time constant changing circuit (time constant changing means)
5 Off-period modulation circuit (off-period modulation means)
4 Time constant changing circuit (Time constant changing means)
6 Main control circuit 11, 21, 31, 41, 51 Switching power supply MOSFETQ1 Main switching element T1 Transformer N1 Primary winding N2 Secondary winding N3 Control winding

Claims (5)

A transformer comprising a primary winding, a secondary winding, and a control winding;
In an RCC type switching power supply comprising a main switching element connected to the primary winding of the transformer and converting the DC voltage into a high frequency AC voltage by turning on and off the DC voltage,
Using a voltage appearing on the high potential side terminal of the main switching element when the main switching element is turned off, and comprising a potential raising means for raising the potential at a predetermined location with a certain time constant,
Before the main switching element in the off state is turned on by ringing, the potential increasing means turns on the predetermined portion at a timing at which the predetermined potential becomes a predetermined potential according to the time constant. An off period setting means for controlling the off period ,
The off period setting means includes time constant changing means for changing the time constant according to the magnitude of the output load of the switching power supply device,
The time constant changing means for changing the time constant according to the magnitude of the output load of the switching power supply is a magnitude of the output load of the switching power supply that appears in the control winding of the transformer when the main switching element is off. A diode and a capacitor for rectifying and smoothing a voltage that fluctuates depending on the length;
A Zener diode that turns on and off according to the level of the voltage rectified and smoothed by the diode and the capacitor;
A photocoupler that is turned on when the Zener diode is turned on and adds a new element to the circuit that determines the time constant, changes the circuit configuration that determines the time constant, and changes the time constant. switching power supply device characterized in that it comprises. A transformer comprising a primary winding, a secondary winding, and a control winding;
  In an RCC type switching power supply comprising a main switching element connected to the primary winding of the transformer and converting the DC voltage into a high frequency AC voltage by turning on and off the DC voltage,
  Using a voltage appearing on the high potential side terminal of the main switching element when the main switching element is turned off, and comprising a potential raising means for raising the potential at a predetermined location with a certain time constant,
  Before the main switching element in the off state is turned on by ringing, the potential increasing means turns on the predetermined portion at a timing at which the predetermined potential becomes a predetermined potential according to the time constant. An off period setting means for controlling the off period,
  The potential increasing means includes off period modulation means for modulating the off period by periodically varying the period until the predetermined location reaches the predetermined potential by the time constant,
  The off-period modulation means includes a resistor that divides the voltage of the input line, and the electric potential increasing means is supplied to the electric potential increasing means as a part of the electric charge that is supplied from the resistor and whose amount changes periodically. A switching power supply device that modulates the off period by supplying. 3. The switching power supply apparatus according to claim 2 , wherein the off period setting means includes time constant changing means for changing the time constant in accordance with a magnitude of an input voltage of the switching power supply apparatus. The off period setting means includes a resistor that divides a voltage appearing on a high potential side terminal of the main switching element when the main switching element is off;
A capacitor that raises the potential of its own high potential side terminal, which is the predetermined location, by accumulating the charge supplied from the voltage dividing point by the resistor with the time constant;
A transistor that is turned on when the predetermined location reaches the predetermined potential and operates to turn on the main switching element;
The switching power supply device according to any one of claims 1 to 3 , wherein the potential raising means includes a circuit including the resistor and the capacitor. The time constant changing means for changing the time constant according to the magnitude of the input voltage of the switching power supply device comprises: a resistor that divides the voltage of a smoothing capacitor that smoothes the rectified voltage of the input voltage;
A Zener diode connected in series to the resistor and turned on / off according to the voltage level of the smoothing capacitor;
The circuit configuration for determining the time constant is changed by turning on the zener diode at the voltage supplied from the voltage dividing point of the resistor and adding a new element to the circuit for determining the time constant. 4. The switching power supply device according to claim 3, further comprising a transistor that changes the time constant.

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