JP2004274996A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply of high flexibility of the design, easy to produce at a low cost, moreover with a small loss at switching. <P>SOLUTION: A ringing choke converter generates voltage in a feedback winding 1b added to the control terminal of a main switching element 2 to cause self excitated oscillation so as to obtain DC voltage by generating a pulse in a secondary winding 1c rectified and smoothed. A series circuit comprising a first capacitor 4, a first resistor 5, and a sub-switching element 7, is inserted into a line connecting the control terminal of the main switching element 2 and the feedback winding 1b. An integrating circuit constituting a second resistor 8 and a second capacitor 9 is connected in parallel to between both ends of the feedback winding 1b, and a control terminal of a sub-switching element 7 is connected to the connection point of these second resistor 8 and second capacitor 9. On-operation of the sub-switching element 7 is delayed by the time constant of the integrating circuit, so as to delay turning on of the main switching element 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a switching power supply, and more particularly, to a technique for improving the efficiency of a switching element in a ringing choke converter.

  FIG. 8 shows an example of a ringing choke converter type (RCC type) switching power supply device. The switching power supply device shown in FIG. 8 is a power supply device that uses a DC power supply (DC 140 V) obtained by rectifying and smoothing a commercial power supply (AC 100 V) (not shown) as an input power supply Vin.

  The switching power supply includes a transformer 1 having a primary winding 1a, a feedback winding 1b, and a secondary winding 1c, and a main switching element (N-channel in the illustrated example) connected in series to the primary winding 1a. MOS type FET) 2 and a control transistor 3 for controlling ON / OFF of the main switching element 2, and applies a voltage generated in the feedback winding 1 b to a control terminal (gate terminal) of the main switching element 2. As a result, self-excited oscillation occurs, and a pulse-like voltage generated in the secondary winding 1c at this time is rectified and smoothed by a rectifying and smoothing circuit such as a diode (not shown) to generate a DC voltage. It is configured to supply.

  By the way, in the switching power supply device having such a configuration, if the turn-on of the main switching element 2 is fast, the current (drain current) Id flowing through the drain terminal of the main switching element 2 as shown in FIG. And a voltage (drain-source voltage) Vds between the drain and source terminals (a portion indicated by hatching in the figure), which results in power loss (switching loss).

  Therefore, recently, the drive circuit of the control terminal (the first capacitor 4 and the first resistor 5 inserted in series in a line connecting the control terminal of the main switching element 2 and the feedback winding 1b of the transformer 1) includes: A saturable inductor 6 having a predetermined voltage-time product is inserted, thereby delaying a turn-on signal to the control terminal. As shown in FIG. 9B, the drain current Id and the drain-source voltage Vds are reduced. A switching power supply device having a so-called zero cross waveform with reduced overlap has been provided (see Patent Document 1). That is, by inserting the saturable inductor 6 as delay means for the turn-on signal, a switching power supply device with small switching loss is provided.

  In FIG. 8, a resistor 14 is a starting resistor for turning on the main switching element 2 when the input voltage Vin is applied, and a resistor 15 is a surge absorber for the main switching element 2. Is shown. Further, the feedback circuit (and the elements connected to the feedback circuit) in the figure is for controlling the operation of the control transistor 3 and has no direct relation to the present invention described later. Omitted.

JP 2000-209857 A

  However, such a configuration in which the saturable inductor is inserted into the drive circuit of the control terminal has the following problems, and its improvement has been desired.

  That is, although the saturable inductor used in the above-described circuit has the effect of delaying the turn-on of the main switching element to reduce the switching loss, the cost as a component is high, so such a saturable inductor is used. If the switching power supply is used for the drive circuit of the control terminal, the manufacturing cost of the entire switching power supply increases, and there is a problem that the switching power supply cannot be provided at low cost. In particular, at the present time when switching power supply devices are frequently used in power supply circuits of electronic devices, it is desired to provide cheaper switching power supply devices.

  Further, in the configuration in which the saturable inductor is inserted into the drive circuit of the control terminal as described above, when the adjustment for reducing the switching loss is performed, the characteristic value (voltage-time product ) Is a fixed value, so the values of the other delay time determining factors must be changed. That is, in order to insert a saturable inductor, the inductance of the primary winding, the capacitance of the resonance capacitor 15, and the turn ratio of the feedback winding to the primary winding must be changed. Since it affects other factors such as the amount and switching noise, there is a problem that circuit design becomes difficult.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a switching power supply device that has a high degree of freedom in design, can be manufactured at low cost, and has a small switching loss. To provide.

  In order to achieve the above object, a switching power supply according to claim 1 of the present invention comprises a transformer having a primary winding, a feedback winding, and a secondary winding, and a main switching device connected in series to the primary winding. A ringing choke converter that generates self-excited oscillation by applying a voltage generated in the feedback winding to a control terminal of the main switching element, and rectifies and smooths a pulse generated in the secondary winding to obtain a DC voltage. A sub-switching element is inserted in series into a line connecting a control terminal of the main switching element and the feedback winding, and an integrating circuit including a resistor and a capacitor is connected in parallel between both ends of the feedback winding. And a control terminal of the sub-switching element is connected to a connection point between the resistor and the capacitor.

  The switching power supply according to claim 2 of the present invention includes a transformer having a primary winding, a feedback winding, and a secondary winding, and a main switching element connected in series to the primary winding, A ringing choke converter that generates self-excited oscillation by applying a voltage generated in the feedback winding to a control terminal of the main switching element and rectifies and smooths a pulse generated in the secondary winding to obtain a DC voltage, A series circuit composed of a first capacitor, a first resistor, and a sub-switching element is inserted in series into a line connecting a control terminal of the main switching element and the feedback winding, and between both ends of the feedback winding. An integrating circuit including a second resistor and a second capacitor is connected in parallel, and a control terminal of the sub-switching element is connected to the second resistor and the second capacitor. Wherein the connected to.

  According to a third aspect of the present invention, there is provided the switching power supply according to the first or second aspect, wherein the sub-switching element is formed of a bipolar transistor, and a second switching element is provided between a base and an emitter of the transistor. 3 is connected.

  According to a fourth aspect of the present invention, in the switching power supply according to any one of the first to third aspects, the sub-switching element is a bipolar transistor. A rectifying element through which current flows from the emitter side to the collector side is connected between the emitter and the collector.

  A switching power supply according to a fifth aspect of the present invention is the switching power supply according to any one of the first to fourth aspects, wherein a control terminal of the sub-switching element and a resistor constituting the integration circuit are provided. A Zener diode is inserted into a line connecting the capacitor and a connection point of the capacitor such that a control terminal side of the sub-switching element becomes an anode.

  A switching power supply according to a sixth aspect of the present invention is the switching power supply according to any one of the first to fourth aspects, wherein a control terminal of the sub-switching element and a resistor forming the integration circuit. A fourth resistor is connected to a line connecting the capacitor and a connection point with the capacitor.

  The switching power supply according to claim 7 of the present invention is the switching power supply according to any one of claims 1 to 4, wherein a diode is inserted in parallel with a resistor constituting the integration circuit, A discharge charge from a capacitor constituting an integration circuit is caused to flow to the feedback winding via the diode.

  According to the switching power supply device of the present invention, the sub-switching element is connected to the drive circuit of the control terminal of the main switching element, and an integrating circuit including a resistor and a capacitor is connected between both ends of the feedback winding. Since the control terminal of the sub-switching element is connected to the connection point between the resistor and the capacitor, a voltage (turn-on signal) is applied to the control terminal of the main switching element after a predetermined time elapses according to the time constant of the integrating circuit. Is applied, the main switching element can be switched with a so-called zero-cross waveform, and an efficient switching power supply device with small switching loss can be provided.

  Moreover, since the circuit for delaying the turn-on signal is composed of elements (switching elements, resistors, and capacitors) that can be obtained relatively inexpensively without using a conventional saturable inductor, The switching power supply can be manufactured at low cost. In addition, since the adjustment of the delay time of the turn-on signal is performed by appropriately selecting the resistors and capacitors constituting the integration circuit and adjusting these time constants, it is not necessary to change other elements. The degree of freedom is improved.

  Further, by configuring the sub-switching element by a bipolar transistor and connecting the third resistor between the base and the emitter of the sub-switching element, the circuit stability of the switching power supply device can be improved.

  Also, by connecting a rectifying element between the emitter and the collector of the sub-switching element so that a current flows from the emitter terminal side to the collector terminal side, a current also flows through the rectifying element when the main switching element is turned off. Therefore, the drain current Id can quickly fall, and the switching loss at the time of turning off can be reduced.

  Furthermore, by inserting a Zener diode in the line connecting the control terminal of the sub-switching element and the connection point between the resistor and the capacitor forming the integrating circuit, it is possible to prevent the main switching element from turning on at low input. Thus, the stability of the circuit can be improved.

  Further, by connecting a fourth resistor to a line connecting a control terminal of the sub-switching element and a connection point between a resistor and a capacitor constituting the integration circuit, a current flowing to the control terminal of the sub-switching element is limited. can do. Thereby, the rating of the sub-switching element can be prevented from being exceeded, and the package size of the sub-switching element can be reduced.

  In addition, a diode is inserted in parallel with the resistor constituting the integration circuit, and the discharge charge from the capacitor of the integration circuit is caused to flow through the feedback winding through the diode to control the sub-switching element. The current flowing to the terminal can be limited. Thereby, the rating of the sub-switching element can be prevented from being exceeded, and the package size of the sub-switching element can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1
FIG. 1 shows an example of a circuit configuration of the switching power supply device according to the first embodiment of the present invention. The switching power supply device shown in FIG. 1 is obtained by modifying the configuration of a drive circuit for applying a turn-on signal to the control terminal of main switching element 2, and the other configuration is the same as that of the conventional example shown in FIG. Therefore, portions having the same configuration are denoted by the same reference numerals, and description thereof is omitted.

  That is, in the conventional switching power supply device, as described above, the saturable inductor 6 is used as a means for delaying the turn-on signal of the main switching element 2, but in the first embodiment, the saturable inductor 6 is used. As an alternative circuit replacing the type inductor 6, a delay circuit 10 including a sub-switching element 7, a second resistor 8, and a second capacitor 9 is used.

  The delay circuit 10 is configured so that a turn-on signal (bias) is applied to the control terminal of the main switching element 2 when the sub-switching element 7 is turned on. The second capacitor 9 forms an integrating circuit, and the turn-on of the main switching element 2 is delayed by delaying the ON time of the sub-switching element 7 by the time constant of the integrating circuit.

  Specifically, the control terminal of the main switching element 2 and the feedback winding 1b are connected by connecting the sub-switching element 7 in series to a series circuit including the first capacitor 4 and the first resistor 5. A series circuit including the first capacitor 4, the first resistor 5, and the sub-switching element 7 is inserted in series to the connecting line. Then, an integrating circuit composed of a second resistor 8 and a second capacitor 9 is connected in parallel between both ends of the feedback winding 1b, and the control terminal of the sub-switching element 7 is connected to the second resistor 8 It is connected to the connection point with the second capacitor 9.

  In this embodiment, an NPN bipolar transistor is used for the sub-switching element 7, the emitter terminal of this transistor is connected to the first resistor 5, and the collector terminal is connected to the feedback winding 1b. . A base terminal is connected to a connection point between the second resistor 8 and the second capacitor 9.

  Note that the delay time of the turn-on signal supplied to the control terminal of the main switching element 2 via the sub-switching element 7 is equal to the drain current Id and the drain-source voltage Vds when the main switching element 2 is turned on. The setting is made so that the overlap is reduced (that is, the switching loss is reduced). This setting is made by appropriately selecting the second resistor 8 and the second capacitor 9 constituting the integration circuit, and This is done by adjusting the time constant. That is, in the present invention, the delay time of the delay circuit 10 is mainly determined by the time constant of the second resistor 8 and the second capacitor 9, so that the zero cross Points can be changed freely.

  As described above, according to the switching power supply device of the first embodiment, when the potential at the point a in the drawing becomes positive, the time constant of the second resistor 8 and the second capacitor 9 (integrating circuit) After a predetermined time has elapsed, a voltage is applied to the control terminal of the sub-switching element 7 to turn on the sub-switching element 7, whereby a voltage (turn-on signal) is applied to the control terminal of the main switching element 2 and the main switching element 7 is turned on. Since the switching element 2 is turned on, the main switching element 2 can be switched with a so-called zero-cross waveform, so that an efficient switching power supply device with small switching loss can be provided.

Embodiment 2
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a modified example of the delay circuit 10 shown in the first embodiment. Therefore, portions having the same configuration as the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The switching power supply device according to the first embodiment employs a configuration in which the timing at which the sub-switching element 7 is turned on is delayed by the time constant of the second resistor 8 and the second capacitor 9. If the switching element 7 does not operate properly, the main switching element 2 and other elements may be damaged.

  In order to solve such a problem, the switching power supply device according to the second embodiment is provided between the base terminal and the emitter terminal (between the base and the emitter) of the bipolar transistor constituting the sub-switching element 7. 3 resistors 11 are connected. Note that the resistance value of the third resistor 11 connected here can be set as appropriate, but a resistance of approximately several kilohms to several tens kilohms is preferably used.

  As described above, in the switching device according to the second embodiment of the present invention, since the third resistor 11 is connected between the base and the emitter of the sub-switching element 7 of the delay circuit 10, the circuit stability of the switching power supply device is improved. Therefore, it is possible to provide an efficient switching power supply device with little switching loss without damaging the main switching element 2 and other elements.

Embodiment 3
Next, a third embodiment of the present invention will be described with reference to FIG. The switching power supply shown in FIG. 3 shows a further modification of the switching power supply shown in the second embodiment. Therefore, portions having the same configurations as those in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

  The switching power supply according to the third embodiment is designed to reduce the switching loss when the main switching element 2 is turned off, and the switching power supply is connected between the emitter terminal and the collector terminal of the sub switching element 7. Between them (between the emitter and the collector), the rectifying element 12 is connected so that a current flows from the emitter terminal side to the collector terminal side.

  That is, in the switching power supply having the above-described conventional configuration, when the main switching element 2 is turned off, the charge remaining at the gate terminal of the main switching element 2 is caused to flow through the path indicated by the arrow b in FIG. However, in this case, the drain current Id cannot be quickly dropped when the main switching element 2 is turned off because only one path of the current flows when the main switching element 2 is turned off. . Therefore, in the conventional switching power supply device, such a delay in the fall of the drain current Id also contributes to the switching loss in the main switching element 2.

  The third embodiment is proposed to improve the switching loss when the main switching element 2 is turned off, and uses a diode as the rectifying element 12 to reduce the switching loss of the sub switching element 7. The anode terminal of the diode is connected to the emitter terminal, and the cathode terminal is connected to the collector terminal of the sub-switching element 7.

  Thus, as a path through which current flows when the main switching element 2 is turned off, a path through the rectifying element 12 (see an arrow c in FIG. 3) is added in addition to the path indicated by the arrow b. As a result, a path through which a current flows when the main switching element 2 is turned off is secured, and the drain current Id can quickly fall.

  Therefore, in the switching power supply device according to the third embodiment, the switching loss when the main switching element 2 is turned off can be reduced, and the efficiency of the entire power supply can be further increased. Further, heat generation of the main switching element 2 can be suppressed.

Embodiment 4
Next, a fourth embodiment of the present invention will be described with reference to FIG. The switching power supply shown in FIG. 4 shows a further modification of the switching power supply shown in the third embodiment. Therefore, portions having the same configuration as those in the first to third embodiments are denoted by the same reference numerals, and description thereof is omitted.

  The switching power supply device according to the fourth embodiment is configured so that the sub-switching element 7 does not turn on when the input voltage Vin is low, and the control terminal of the sub-switching element 7 and the second It is configured by inserting a Zener diode 13 into a line connecting the resistor 8 and the connection point of the second capacitor 9.

  That is, in the switching power supply devices shown in the first to third embodiments, the voltage of the second capacitor 9 is mainly the number of turns of the primary winding 1a and the feedback winding 1b in the transformer 1 with respect to the input voltage Vin. Although determined by the ratio, in the above-described configuration, even when the input voltage Vin is low and the input is low, the sub-switching element 7 is turned on, so that the main switching element 2 may be damaged.

  In the fourth embodiment, the anode terminal of the Zener diode 13 is connected to the base terminal (control terminal) side of the sub-switching element 7 so that the sub-switching element 7 does not turn on at the time of such low input, and the cathode terminal is The Zener diode 13 is connected so as to be on the connection point side between the second resistor 8 and the second capacitor 9.

  Therefore, according to the fourth embodiment, when the input voltage is low and the voltage of the second capacitor 9 is less than the breakdown voltage of the Zener diode 13, a bias is applied to the base terminal of the sub-switching element 7. Since the sub-switching element 7 does not turn on, the main switching element 2 does not turn on at the time of low input, and there is no risk of damage.

  In addition, with this configuration, the on-operation level of the sub-switching element 7 can be adjusted by selecting the Zener diode 13. In the fourth embodiment, the configuration in which the Zener diode 13 is inserted is adopted. However, if the element has a constant voltage characteristic equivalent to that of the Zener diode 13 and is applicable to the present invention, other elements can be used. It is also possible to replace with an element.

Embodiment 5
Next, a fifth embodiment of the present invention will be described with reference to FIG. The switching power supply shown in FIG. 5 shows a further modification of the switching power supply shown in the third embodiment. Therefore, portions having the same configuration as those in the first to third embodiments are denoted by the same reference numerals, and description thereof is omitted.

  The switching power supply according to the fifth embodiment has a circuit configured to limit the base current flowing through the sub-switching element 7 when the main switching element 2 is turned off. It is configured by inserting a fourth resistor 16 into a line connecting a control terminal and a connection point between the second resistor 8 and the second capacitor 9.

  That is, in the switching power supply devices according to the first to third embodiments, when the main switching element 2 is turned off, the polarity of the feedback winding 1b of the transformer 1 is inverted. The charge stored in the second capacitor 9 is released. The current Ic1 flowing through the circuit due to the discharge of the second capacitor 9 flows to one end of the feedback winding 1b having the lowest potential through a path having the lowest resistance.

  By the way, regarding the path of the current Ic1 flowing through the circuit due to this discharge, the second resistor 8 and the third resistor 11 usually have a resistance value of about 100 ohm to several kilo ohms. Ic1 flows to the control terminal (base terminal) of the sub-switching element 7. On the other hand, as shown in FIG. 6, an equivalent diode 17 having an anode on the base terminal side is inserted between the base-emitter terminal and the base-collector terminal of the sub-switching element 7, and the base-emitter terminal Since the rectifier diode 12 is connected after the equivalent diode 17 on the intermediate side, the path with the lowest resistance is the path on the side between the base and collector terminals. However, in the above-described first to third embodiments, In the switching power supply device shown, since there is no element that limits the current flowing during this period, there is a problem that a transistor having a large base current rating must be selected as the sub-switching element 7.

  The switching power supply device according to the present embodiment includes a control terminal of the sub-switching element 7, the second resistor 8, and the second capacitor 9 in order to limit the base current flowing through the sub-switching element 7. A fourth resistor 16 is inserted in a line connecting the connection point of the second switching element 7 and the fourth resistor 16 restricts a current flowing through the sub-switching element 7.

  Therefore, according to the fifth embodiment, by setting the resistance value of the fourth resistor 16 to an appropriate value, the current flowing through the sub-switching element 7 is reduced (so as not to exceed the rating of the transistor). As a result, there is an advantage that the package size of the sub-switching element 7 does not need to be unnecessarily large.

Embodiment 6
Next, a sixth embodiment of the present invention will be described with reference to FIG. The switching power supply shown in FIG. 7 shows a further modification of the switching power supply shown in the fifth embodiment. Therefore, portions having the same configuration as the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

  The switching power supply according to the sixth embodiment has a circuit configured to limit the base current flowing through the sub-switching element 7 when the main switching element 2 is turned off. , A diode 18 is inserted in parallel with the second resistor 8 constituting the integration circuit, and the discharge charge from the second capacitor 9 is transferred through the diode 18 to the transformer 1. It is configured to flow through the feedback winding 1b.

  That is, in the above-described fifth embodiment, the configuration in which the fourth resistor 16 is provided to limit the current flowing through the sub-switching element 7 is employed. Since the time constant of the integrating circuit including the second resistor 8 and the second capacitor 9 changes, it is necessary to newly adjust the timing at which the sub-switching element 7 turns on.

  In the present embodiment, in order to make such adjustment unnecessary, a diode 18 is inserted in parallel with the second resistor 8 constituting the integration circuit, and the discharge charge from the second capacitor 9 is transferred to the diode 18. Through the feedback winding 1 b of the transformer 1. Specifically, an anode terminal of the diode 18 is connected to a connection point between the second resistor 8 and the second capacitor 9, and a cathode terminal is connected to one end of the feedback winding 1 b of the transformer 1. .

  Therefore, according to the sixth embodiment, when the main switching element 2 is turned off, the electric charge released from the second capacitor 9 flows to the transformer 1 via the diode 18, so that the sub switching The current flowing through the element 7 can be almost eliminated. As a result, similarly to the fifth embodiment, there is an advantage that the package size of the sub-switching element 7 does not need to be made larger than necessary.

  It should be noted that the above-described embodiments merely show preferred embodiments of the present invention, and the present invention is not limited to these embodiments, and various design changes can be made within the scope.

  For example, in the above-described embodiment, for convenience of explanation, the second embodiment is a modification of the first embodiment, the third embodiment is a modification of the second embodiment, and the fourth embodiment is a fourth modification. Although the embodiments have been described as the modifications of the third embodiment, the respective embodiments can be combined as appropriate. For example, as a modification of the first embodiment, the configuration shown in the third embodiment (the rectifying element 12 The configuration shown in the fourth embodiment (the configuration using the Zener diode 13) may be adopted. Similarly, the configuration shown in the fourth embodiment (the configuration using the Zener diode 13) may be adopted as a modification of the second embodiment.

  In the above-described embodiment, the switching power supply of the present invention uses a DC power supply (DC 140 V) obtained by rectifying and smoothing a commercial power supply as an input power supply. It can be changed as appropriate according to the environment in which the power supply is used. Further, in the above-described embodiment, the so-called line-operated type has been described, but it is also possible to use it as an offline converter.

  In the above-described embodiment, the first capacitor 4 and the first resistor 5 are connected in series from the main switching element 2 side as a series circuit inserted into a line connecting the control terminal of the main switching element 2 and the feedback winding 1b. Although the case where the respective elements are arranged in the order of the sub-switching elements 7 is shown, these arrangements can be appropriately changed without being limited to the above-described embodiment.

  Further, the present invention is characterized by including the delay circuit 10 shown in each of the above-described embodiments, so that the configuration of the drive circuit of the control terminal of the main switching element 2 can be appropriately changed.

1 is a circuit diagram illustrating an example of a circuit configuration of a first embodiment in a switching power supply device according to the present invention. FIG. 9 is a circuit diagram showing a second embodiment of the switching power supply device, specifically showing a modified example of the delay circuit. It is a circuit diagram showing an example of a circuit configuration of a third embodiment in the switching power supply device. FIG. 9 is a circuit diagram illustrating an example of a circuit configuration of a fourth embodiment in the switching power supply device. FIG. 13 is a circuit diagram illustrating an example of a circuit configuration of a fifth embodiment in the switching power supply device. FIG. 3 is a circuit diagram showing a configuration of an equivalent diode in a sub-switching element in the switching power supply device. It is a circuit diagram showing an example of a circuit configuration of a sixth embodiment in the switching power supply device. 1 shows a circuit configuration of a conventional switching power supply device, specifically, a case where a saturable inductor is used as delay means for a turn-on signal given to a main switching element. FIG. 9A is an explanatory diagram showing the relationship between the drain current Id and the drain-source voltage Vds in the main switching element. FIG. 9A shows a case where the turn-on is too fast and there is a switching loss, and FIG. (b) shows the case where the turn-on is delayed to suppress the switching loss.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Transformer 1a Primary winding 1b Feedback winding 1c Secondary winding 2 Main switching element 3 Control transistor 4 First capacitor 5 First resistor 6 Saturable inductor 7 Secondary switching element 8 Second resistor 9 Second capacitor Reference Signs List 10 delay circuit 11 third resistor 12 rectifier (diode)
13 Zener diode 16 Fourth resistor 18 Diode

Claims (7)

A transformer having a primary winding, a feedback winding, and a secondary winding, and a main switching element connected in series to the primary winding, wherein a voltage generated in the feedback winding is supplied to a control terminal of the main switching element. A ringing choke converter that generates self-excited oscillation by adding the pulse, rectifies and smoothes a pulse generated in the secondary winding to obtain a DC voltage,
A sub-switching element is inserted in series into a line connecting the control terminal of the main switching element and the feedback winding,
An integrating circuit including a resistor and a capacitor is connected in parallel between both ends of the feedback winding,
A switching power supply device, wherein a control terminal of the sub-switching element is connected to a connection point between the resistor and the capacitor. A transformer having a primary winding, a feedback winding, and a secondary winding, and a main switching element connected in series to the primary winding, wherein a voltage generated in the feedback winding is supplied to a control terminal of the main switching element. A ringing choke converter that generates self-excited oscillation by adding the pulse, rectifies and smoothes a pulse generated in the secondary winding to obtain a DC voltage,
A series circuit including a first capacitor, a first resistor, and a sub-switching element is inserted in series into a line connecting a control terminal of the main switching element and the feedback winding,
An integrating circuit including a second resistor and a second capacitor is connected in parallel between both ends of the feedback winding,
A switching power supply device, wherein a control terminal of the sub-switching element is connected to a connection point between the second resistor and the second capacitor.   3. The switching power supply according to claim 1, wherein the sub-switching element is formed of a bipolar transistor, and a third resistor is connected between a base and an emitter of the transistor.   4. The device according to claim 1, wherein the sub-switching element is a bipolar transistor, and a rectifying element through which a current flows from the emitter side to the collector side is connected between the emitter and the collector of the transistor. A switching power supply according to one of the preceding claims.   A zener diode is inserted into a line connecting a control terminal of the sub-switching element and a connection point between a resistor and a capacitor forming the integration circuit so that the control terminal side of the sub-switching element becomes an anode. The switching power supply according to any one of claims 1 to 4.   5. The circuit according to claim 1, wherein a fourth resistor is connected to a line connecting a control terminal of the sub-switching element and a connection point between a resistor and a capacitor forming the integration circuit. 6. 3. The switching power supply device according to any one of the above. 2. A device according to claim 1, wherein a diode is inserted in parallel with a resistor constituting said integrating circuit, and discharge charge from a capacitor constituting said integrating circuit is caused to flow to said feedback winding via said diode. 5. The switching power supply device according to any one of items 1 to 4.

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