JP2009261044A - Switching power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and high-efficient switching power supply unit using a metal base substrate, which can suppress a switching noise current to be leaked to an input power supply side. <P>SOLUTION: The switching power supply unit has a serial circuit consisting of a high-side switch element Q1 connected to an input power supply E, a primary winding T1p of an output transformer T1 and a low-side switch element Q2. The unit is provided with a control section CONT2 for outputting a predetermined pulsewidth modulation signal based on an output voltage and for driving to turn on/off both the switch elements Q1, Q2. The control section CONT2 is set at a value in which the maximum value of on-duty of the pulsewidth modulation signal to be outputted exceeds 50%. A pair of potential variation patterns 44a, 44b on which terminals having potential varying due to switching are each mounted among the terminals of both the switch elements Q1, Q2 are provided on a metal base substrate 42. Wiring capacitances CQ1, CQ2 formed between the potential variation patterns 44a, 44b and a metal base 42a of the metal base substrate 42 are the same as each other. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply device mounted on a metal base substrate, and more particularly to a switching power supply device having a structure that suppresses the outflow of switching noise current.

  As a conventional switching power supply device, for example, as disclosed in Patent Document 1, at least one switch element on a high-side side or a low-side side, and a terminal whose potential is changed by switching, A two-stone forward switching power supply unit is disclosed in which a heat sink that fixes an element is coupled via a capacitor. This is because if there is an imbalance in each parasitic capacitance formed between each terminal of both switch elements whose potential varies due to switching and a heat sink on which the switch element is attached via an insulating sheet or the like, both switching elements This is made in view of the problem that the voltage generated at both ends of each switch element is unbalanced when the switch is off and the total loss of both switch elements increases, and a capacitor is connected in parallel with at least one parasitic capacitance. This technique corrects the imbalance of the parasitic capacitance.

In addition, the switching power supply device disclosed in Patent Document 2 includes a chopper circuit that generates a pulse voltage in the input side winding of the high-frequency transformer, and a smoothing that smoothes the pulse voltage induced in the output side winding and converts it into DC. A switching power supply device mounted on a metal base substrate, each of which has two output-side windings, a terminal whose potential varies due to switching, and a metal base which is a ground potential Discloses a switching power supply device in which each wiring pattern is formed so that wiring capacitances formed between the two are equal to each other. This is a technique that uses the fact that a voltage having a phase opposite to 180 degrees is applied to each wiring capacitance and makes the wiring capacitances equal to each other, thereby canceling the switching noise current and obtaining a power output with less noise components.
Japanese Unexamined Patent Publication No. 7-177741 Japanese Patent Laid-Open No. 3-169259

  However, the two-stone forward type switching power supply device of Patent Document 1 has a variation in the thickness of the insulating sheet and a variation in the tightening of the screw when the two switch elements are screwed to the heat sink via the insulating sheet. Each parasitic capacitance does not have a constant value. Moreover, if a capacitor connected in parallel with the parasitic capacitance is selected from general-purpose discrete components, individual differences in capacitance, temperature fluctuations, etc. cannot be ignored. That is, the parasitic capacitance imbalance could not be stably corrected due to the variation factor.

  In addition, in the switching power supply device of Patent Document 2, each wiring capacitance formed between a terminal whose potential changes due to switching in a chopper circuit connected to the input side winding of the high frequency transformer and the metal base Is not considered. For example, in a switching power supply device that steps down a high voltage of 200 to 400V DC to a low voltage of several tens of volts or less used for general industrial equipment, it operates at a high voltage on the input side of a high-frequency transformer. The wiring capacity of the chopper circuit has a higher influence on switching noise than the wiring capacity of a smoothing circuit that operates at a low voltage on the output side. However, in this switching power supply device, it is impossible to interrupt the operation in which the main switching noise current generated by the chopper circuit passes through the wiring capacitance on the chopper circuit side and returns to the input power supply side of the switching power supply device. It was a thing.

  Here, in order to reduce the size and increase the integration of the switching power supply device, the inventor examined a switching power supply device configured on a metal base substrate having a two-stone forward type circuit and excellent in heat dissipation. It was.

  The switching power supply device 10 initially examined will be described with reference to the drawings. The configuration of the circuit is substantially the same as the circuit disclosed in the conventional patent document 1 as shown in FIG. In parallel with the capacitor C1 connected to the input terminal 12, a high-side switch element Q1 using a field effect transistor, a primary winding T1p of an output transformer T1, and a low-side switch using a field effect transistor. A series circuit of the element Q2 is connected. Further, in this series circuit, a regenerative diode SS1 that allows current to flow from the drain terminal side of the switch element Q2 toward the positive side of the input capacitor C1, and a current from the negative side of the input capacitor C1 to the source terminal side of the switch element Q1. A regenerative diode SS2 for flow is connected.

  A rectifying / smoothing circuit including diodes D1 and D2, an inductor L1, and a capacitor C2 is connected to the secondary winding T1s of the output transformer T1.

  A control unit CONT1 that outputs a predetermined pulse width modulation signal based on the output voltage Vo generated across the capacitor C2 is connected to the gate terminals of the switch elements Q1 and Q2. The control unit CONT1 is configured to drive the switch elements Q1 and Q2 on and off in the same phase by a pulse width modulation signal, and the variable range of the on-duty is limited to a range of 50% or less.

  An input power supply E is connected to the input terminal 12 of the switching power supply device 10, and the negative side of the input power supply E is connected to the ground potential FG via a capacitor CY1 for preventing electric shock. On the other hand, a load LD is connected to the output terminal 14, and the minus side of the load LD is similarly connected to the ground potential FG via a capacitor CY2 for preventing electric shock. A metal base 16a of the metal base substrate 16 described later is also connected to the ground potential FG.

  Next, the mounting structure of the switching power supply device 10 will be described with reference to FIGS. The switching power supply device 10 includes a metal base substrate 16 having a wiring pattern 16c formed through a thin insulating layer 16b on one surface of the metal base 16a, and includes a transformer T1, switch elements Q1, Q2, As shown in FIG. 6, the regenerative diodes SS1 and SS2 and the input smoothing capacitor C1 are soldered and mounted on the wiring pattern 16c. The control unit CONT1 and the rectifying / smoothing circuit are also mounted in the same manner, but are omitted here.

  As shown in FIG. 7A, the switch elements Q1 and Q2 are surface mount packages compliant with the standard code SC-83 defined by JEITA (Japan Electronics and Information Technology Industries Association). The SC-83 package has a structure in which a metal frame on which a semiconductor chip is mounted is sealed with an epoxy resin or the like, and terminals for external connection are exposed from the epoxy resin. Of the terminals connected on the wiring pattern 16 c, the drain terminal D has a larger area than the gate terminal G and the source terminal S. As a result, the drain terminal D and the wiring pattern are solder-connected in a wide area, so that the heat generated from the internal semiconductor chip can be efficiently radiated.

  As the regenerative diodes SS1 and SS2, SC-83 having the same package as the switching elements Q1 and Q2 was selected. In SC-83, as shown in FIG. 7B, two diode elements are formed in one package, and the anode of each diode element is connected to a separate terminal A and the cathode is connected to a common terminal K. ing. Of the terminals connected to the wiring pattern 16 c, the cathode terminal K has a larger area than the anode terminal A.

  As shown in FIG. 8A, the layout of the wiring pattern 16c on the metal base substrate 16 is implemented by mounting one terminal of the primary winding T1p, the source terminal S of the switch element Q1, and the cathode terminal K of the regenerative diode SS1. The potential variation pattern 18a integrally formed by connecting the terminals to the same potential, the other terminal of the primary winding T1p, the drain terminal D of the switch element Q2, and the anode terminal A of the regenerative diode SS1 And a potential variation pattern 18b integrally formed by connecting the terminals to the same potential.

  In the metal base substrate 16, as shown in FIG. 8B, the potential variation patterns 18a and 18b and the metal base 16a face each other through a thin insulating layer 16b, and the wiring capacitance as shown in FIG. 8C. CQ1 and CQ2 are formed. Here, since the switching elements Q1 and Q2 and the regenerative diodes SS1 and SS2 are unified into the SC-83 of the same package, the potential variation patterns 18a and 18b are formed in substantially the same area without any special effort, and the wiring capacitance CQ1 and CQ2 are balanced and approximately equal values. The electrical behavior of the potential fluctuation patterns 18a and 18b and the operation of the wiring capacitors CQ1 and CQ2 will be described later in the description of the circuit operation.

  Next, the circuit operation of the switching power supply device 10 will be described with reference to FIG. FIG. 9 shows waveforms of the voltage VT, the switching current id, the voltage VQ1 of the switch element Q1, and the voltage VQ2 of the switch element Q2 of the primary side winding T1p of the output transformer T1. The waveforms of the voltages VQ1 and VQ2 are shown in a direction with the stable potential side where the potential is not changed by switching as a reference (ground).

  When a predetermined input voltage Vi is applied to the input terminal 12 of the switching power supply 10, the switch elements Q1 and Q2 are driven on and off in the same phase by a pulse width modulation signal output from the control unit CONT1. At this time, the control unit CONT1 forms a pulse width modulation signal so as to stabilize the output voltage Vo to a predetermined value according to the equation (1), and determines the on-duty of the switch elements Q1 and Q2.

ここで、Ｎｐは１次側巻線Ｔ１ｐの巻数、Ｎｓは２次側巻線Ｔ１ｓの巻数、Ｄｕｔｙはオンデューティ、Ｖｆは整流平滑回路のダイオードＤ１，Ｄ２の順方向電圧である。

Here, Np is the number of turns of the primary winding T1p, Ns is the number of turns of the secondary winding T1s, Duty is the on-duty, and Vf is the forward voltage of the diodes D1 and D2 of the rectifying and smoothing circuit.

  The period A is a period in which the switch elements Q1 and Q2 and the diode D1 are on. The input voltage Vin is applied to the primary winding T1p, and excitation energy is accumulated in the output transformer T1.

  The period B is a period in which the switch elements Q1, Q2 and the diode D1 are turned off and the regenerative diodes SS1, SS2 are turned on. Since the output transformer T1 emits the excitation energy accumulated in the period A, an electromotive force is generated in the reverse direction. Then, the voltage VT of the primary winding T1p is fixed to −Vi by the regenerative diodes SS1 and SS2 being conducted, and is kept constant.

  In the period C, since the excitation energy has already been released, the voltage VT of the primary winding T1p decreases and the regenerative diodes SS1 and SS2 are turned off.

  When the above operation is repeated at a constant period T, it is found that when the movements of the voltages VQ1 and VQ2 indicating the change in potential of the potential variation patterns 18a and 18b are compared, voltages having the same amplitude are generated in the opposite directions. . Accordingly, since the same switching noise currents flow in the opposite directions in the same wiring capacitances CQ1 and CQ2, they cancel each other and do not flow out to the input power source side.

  As described above, according to the switching power supply device 10 examined by the inventor, it has been found that the outflow of the switching noise current can be suppressed by the action of the wiring pattern on which the regenerative diodes SS1 and SS2 are mounted without any particular ingenuity. .

  However, in the switching power supply device 10, the presence of the regenerative diodes SS1 and SS2 hinders downsizing of the device. Further, since the effective value of the switching current id is large, resistance loss generated by the resistance component of the primary side winding T1p, the on-resistance components of the switch elements Q1 and Q2, and the like are increased, and high efficiency cannot be obtained. .

  As a means for reducing the effective value of the switching current id, for example, a method of performing a switching operation with a wide on-duty is conceivable. For this purpose, the turn ratio Ns / Np of the output transformer T1 is reduced based on the equation (1). That's fine. However, in the switching power supply device 10, as shown in FIG. 9, in the period B, the voltage VT of the primary winding T1p is fixed to −Vi by the operation of the regenerative diodes SS1 and SS2. If becomes longer than a certain length, there arises a problem that it becomes impossible to complete the release of excitation energy within the period T. That is, when the on-duty duty exceeds 50%, the voltage / time product (area of the hatched portion) in the period A of the waveform of the voltage VT becomes larger than the voltage / time product (area of the hatched portion) in the period B. The excitation energy is gradually accumulated in the output transformer T1, and eventually becomes magnetically saturated and cannot operate normally. Therefore, in order to avoid such magnetic saturation due to the bias of the output transformer T1, it is necessary to always operate in the range of on-duty duty 50% or less.

  Accordingly, the inventor has made a design change in which the turn ratio Ns / Np of the output transformer T1 is reduced and the regenerative diodes SS1 and SS2 are deleted so that the on-duty operates normally within a range of 50% or more. It was investigated. As shown in FIG. 10, the mounting structure includes an output transformer T1, switching elements Q1 and Q2, and an input smoothing capacitor C1 mounted on a metal base substrate 22 in the same manner as the switching power supply device 10. The layout of the wiring pattern 20c on the metal base substrate 20 is reduced in size by the amount that the regenerative diodes SS1 and SS2 are deleted. On the other hand, as shown in FIG. Are not equal, and the wiring capacitors CQ1 and CQ2 are unbalanced. Therefore, the switching noise currents flowing through the wiring capacitors CQ1 and CQ2 are not offset each other, and the switching noise current flows out to the input power source side.

  In order to suppress the switching noise current, for example, as shown in FIG. 12, a method of blocking the outflow of the switching noise current itself by forming a shield layer 26 between the potential fluctuation patterns 24a and 24b and the metal base 22b. Though conceivable, there are problems such as a decrease in heat dissipation due to the distance between the switch elements Q1 and Q2 and the metal base 22a and an increase in the cost of the metal base substrate 24.

  The present invention has been made in view of the above-described background art, and is a small, high-efficiency, two-stone forward type switching power supply device using a metal base substrate, which suppresses a switching noise current leaking to the input power supply side. It is an object of the present invention to provide a switching power supply device that can be used.

  The present invention is connected to a series circuit of a high-side switch element connected to an input power source, a primary-side winding of an output transformer, and a low-side switch element, and a secondary-side winding of the output transformer. A rectifying / smoothing circuit for rectifying and smoothing an AC voltage generated in the secondary winding by switching of a switch element to obtain a DC output voltage; and outputting a predetermined pulse width modulation signal based on the output voltage; A switching power supply device in which both the switch elements are mounted on a wiring pattern on a metal base substrate, and the control section has a maximum on-duty value of a pulse width modulation signal to be output. It is set to a value exceeding 50%, and on the metal base substrate, among the terminals of both the switch elements, the potential fluctuates due to switching. Each of the wiring patterns on which the terminals are mounted, each of which is provided with at least a pair of potential fluctuation patterns corresponding to each of the terminals, and is formed between each of the potential fluctuation patterns and the metal base of the metal base substrate. This is a switching power supply device formed so that the wiring capacitances are equal to each other.

  The potential variation pattern of the high-side switch element is formed by connecting an additional pattern to the mounting pattern to which the terminal is connected, and the wiring capacitance is set to be equal by adjusting the area of the additional pattern. It is a switching power supply device.

  According to the switching power supply device of the present invention, since the two-stone forward type switching power supply device is operated in the range where the on-duty exceeds 50%, the effective value of the switching current can be reduced in a wide input voltage range. Loss due to the resistance component of each part can be reduced.

  In addition, the predetermined terminal of each switch element on the high side and the low side is connected, and the potential variation pattern in which the potential varies by switching is formed so that the wiring capacitances formed between the metal bases are equal to each other. Therefore, the switching noise currents flow equally in the opposite directions to each wiring capacitance and cancel each other, and do not flow out to the input power source side. Therefore, the adverse effect on the outside of the switching power supply device can be greatly reduced.

  In addition, by providing an additional pattern to adjust the balance of each wiring capacity, it is possible to form only on one switch element side and using the space below the other large components, In particular, the switching power supply device can be downsized without using an expensive multilayer substrate.

  In addition, since the balance of each wiring capacity can be adjusted by appropriately changing only the area of the additional pattern, for example, a predetermined shape such as a pad shape set to improve the solder connection reliability of the terminals of the mounted component. Noise reduction performance can be improved while the wiring pattern layout is fixed.

  Further, the thickness of the insulating layer of the metal base substrate varies from one substrate to another, but it can be said that the thickness is almost uniform within one substrate. Therefore, even if the thickness of the insulating layer varies from substrate to substrate due to mass production, the shape of the wiring pattern is fixed, so that the balance of each wiring capacity is accurately maintained. Furthermore, even when the insulation layer temperature, moisture absorption, etc. change due to changes in the usage environment of the switching power supply device, and the wiring capacitance fluctuates, the wiring capacitances increase or decrease equally, so that the balance of the capacitance is maintained. . Therefore, stable noise reduction performance can be realized.

  Hereinafter, a switching power supply device 40 according to an embodiment of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated for the structure similar to the above-mentioned switching power supply apparatuses 10 and 20. FIG.

  As shown in FIG. 1, the circuit has a high-side switch element Q1 using a field effect transistor in parallel with a capacitor C1 connected to the input terminal 12, and a primary winding T1p of the output transformer T1. A series circuit of a low-side switch element Q2 using a field effect transistor is connected. Here, the regenerative diodes SS1 and SS2 included in the switching power supply device 10 are not provided.

  A rectifying / smoothing circuit including diodes D1 and D2, an inductor L1, and a capacitor C2 is connected to the secondary winding T1s of the output transformer T1.

  A control unit CONT2 that outputs a predetermined pulse width modulation signal based on the output voltage Vo generated across the capacitor C2 is connected to the gate terminals of the switch elements Q1 and Q2. The control unit CONT2 is configured so that the switch elements Q1 and Q2 can be driven on and off in the same phase by a pulse width modulation signal, and the on-duty can be varied to a range exceeding 50%. Here, the upper limit is set to about 80%.

  The input power supply E is connected to the input terminal 12 of the switching power supply device 40, and the negative side of the input power supply E is connected to the ground potential FG via a capacitor CY1 for preventing electric shock. On the other hand, a load LD is connected to the output terminal 14, and the minus side of the load LD is similarly connected to the ground potential FG via a capacitor CY2 for preventing electric shock. A metal base 42a of the metal base substrate 42 described later is also connected to the ground potential FG.

  Next, the mounting structure of the switching power supply device 40 will be described with reference to FIGS. The switching power supply device 40 includes a metal base substrate 42 having a wiring pattern 42c formed on one surface of a metal base 42a via a thin insulating layer 42b, and includes an output transformer T1 and switch elements Q1, Q2 as main components. The input smoothing capacitor C1 is soldered and mounted on the wiring pattern 42c as shown in FIG. The control unit CONT2 and the rectifying / smoothing circuit are also mounted in the same manner, but are omitted here.

  The size of the metal base substrate 42 has a power industry standard outer shape (width 117 mm, depth 61 mm) called, for example, FuLL-Brick size. The metal base 42a is a metal plate having a thickness of about 1 to 2 mm, and the material is iron, aluminum, stainless steel, copper, or the like. The insulating layer 42b is formed by applying an epoxy resin to an appropriate thickness on one surface of the metal base 42a. This thickness is set in consideration of the insulation performance between the wiring pattern 42c and the metal base 42a, the heat dissipation performance of the mounted components, and the like. This epoxy resin is filled with an inorganic filler or the like and has high thermal conductivity, and has a relative dielectric constant of about 4 to 8. The wiring pattern 42c is a copper foil having a thickness of about 35 to 200 μm, and the surface is plated. In addition, on the back surface side of the metal base substrate 42, heat sink fins having an arbitrary shape are attached and assembled so as to be cooled by forced ventilation.

  As shown in FIG. 3A, the layout of the wiring pattern 42c is a mounting pattern 44a1 in which one terminal of the primary winding T1p and the source terminal S of the switch element Q1 are mounted, and both terminals are connected to the same potential. In addition, a potential variation pattern 44a formed integrally by connecting the additional pattern 44a2 is provided. Here, it is considered that the additional pattern 44a2 is connected in a narrow pattern so that the temperature increase of the solder paste of the mounting pattern 44a1 is not hindered in the reflow soldering process. Further, the other terminal of the primary winding T1p and the drain terminal D of the switch element Q2 are mounted, and a potential variation pattern 44b is formed integrally with both terminals having the same potential. Here, the additional pattern 44a2 is added to the mounting pattern 44a1 having a small area to increase the area of the potential fluctuation pattern 44a, and the potential fluctuation pattern 44a is adjusted to have the same area as the potential fluctuation pattern 44b. Therefore, as shown in FIG. 3B, the wiring capacitances CQ1 and CQ2 are balanced and equal values. Further, since the additional pattern 44a2 is provided at a position hidden under the output transformer T1, there is no useless space above the additional pattern 44a2 in the mounted state.

  Next, the circuit operation of the switching power supply device 40 of this embodiment will be described with reference to FIG. When a predetermined input voltage Vi is applied to the input terminal 12 of the switching power supply 40, the switch elements Q1 and Q2 are driven on and off in the same phase by a pulse width modulation signal output from the control unit CONT2. At this time, the control unit CONT2 forms a pulse width modulation signal so as to stabilize the output voltage Vo to a predetermined value, and determines the on-duty of the switch elements Q1, Q2.

  The turn ratio Ns / Np of the output transformer T1 of this embodiment is set smaller than that of the switching power supply device 20 shown in FIG. Therefore, as apparent from the equation (1), when the input voltage Vi and the output voltage Vo are equal, the on-duty becomes wider than that of the switching power supply device 20.

  The period A is a period in which the switch elements Q1 and Q2 and the diode D1 are on. The input voltage Vin is applied to the primary winding T1p, and excitation energy is accumulated in the output transformer T1.

  The period B is a period in which the switch elements Q1, Q2 and the diode D1 are off. The output transformer T1 generates an electromotive force in the reverse direction in order to release the excitation energy accumulated in the period A. At that time, the voltage VT of the primary winding T1p is a voltage lower than −Vin and is lowered to a voltage determined by the relationship with the parasitic capacitance formed in the output transformer T1 and the like. That is, unlike the switching power supply device 20, it is not fixed to -Vin by the regenerative diodes SS1 and SS2. Therefore, even if excitation energy is accumulated in the output transformer T1 with an on-duty exceeding 50% in the period A, the emission of excitation energy can be completed during the period B.

  In period C, since the excitation energy has already been released, the voltage VT of the primary winding T1p is decreased.

  When the above operation is repeated at a constant period T, it is understood that a voltage having the same amplitude is always generated in the reverse direction when the potential changes of VQ1 and VQ2 indicating the operation of the potential variation patterns 44a and 44b are compared. . Accordingly, since equal switching noise currents flow in the opposite directions in the same wiring capacitances CQ1 and CQ2, they cancel each other and do not flow out to the input power source side.

  In addition, the switching current id has an average value Iin substantially equal to that of the switching power supply device 10 shown in FIG. 6, but the peak value becomes lower and the effective value becomes smaller as the on-duty is wider. Accordingly, resistance loss caused by the resistance component of the primary winding T1p, the on-resistance components of the switch elements Q1 and Q2, and the like is reduced. Further, each part can be reduced in size as the loss is reduced.

  The present invention is not limited to the above embodiment. For example, in the switching power supply 40, the potential variation pattern 44a is formed by separating the mounting pattern 44a1 and the additional pattern 44a2, but there are other adverse effects such as deterioration of the solder connection reliability of the terminals of the mounted components. If it does not occur, the mounting pattern 44a1 may be widened to adjust the balance of each wiring capacity, and the additional pattern 44a2 may be omitted.

  Further, the switch element Q1 may be configured by connecting a plurality of switch elements in parallel to reduce electrical stress per element. The same applies to the switch element Q2. Further, the package shape of each switch element is not particularly limited as long as it can be mounted on a metal base substrate. Further, surge absorbing parts and other circuits may be connected to both ends of each switch element. It is sufficient that at least the areas of the potential fluctuation patterns 44a and 44b are set to be equal.

  Further, the upper limit value of the on-duty set in the control unit CONT2 may be varied during the operation of the switching power supply device. For example, in order to reduce the effective value of the switching current when the input voltage is low, the upper limit value is set to a value exceeding 50%, and when the input voltage is high, the output transformer T1 is protected during a transient operation such as a sudden load change. Therefore, the upper limit value may be varied to a value of 50% or less.

It is a circuit diagram showing one embodiment of a switching power supply device of the present invention. It is a top view which shows the mounting structure of this embodiment. It is the top view (a) and side surface schematic diagram (b) which show the metal base substrate of this embodiment. It is a waveform of each part which shows circuit operation of this embodiment. It is a circuit diagram which shows an example of the conventional switching power supply device. It is a top view which shows the mounting structure of this prior art example. FIG. 4A is a structural diagram for explaining the terminal arrangement of a field effect transistor of an SC-83 package, and FIG. It is the top view (a) which shows this metal base board of a prior art example, AA sectional drawing (b), and a side surface schematic diagram (c). It is a waveform of each part which shows circuit operation of this conventional example. It is a top view which shows the mounting structure of another prior art example. It is the top view (a), BB sectional drawing (b), and side surface schematic diagram (c) which show the metal base substrate of this prior art example. It is a sectional side view which shows the metal base substrate of another prior art example.

Explanation of symbols

10, 20, 40 Switching power supply device 16, 22, 42 Metal base substrate 16a, 22a, 42a Metal base 18a, 18b, 24a, 24b, 44a, 44b Potential variation pattern 42 Metal base substrate CONT2 Control unit CQ1, CQ2 Wiring capacitance E Input power supply Q1, Q2 Switch element SS1, SS2 Regenerative diode T1 Output transformer

Claims (2)

A series circuit of a high-side switch element connected to an input power source, a primary-side winding of the output transformer, and a low-side switch element, and a secondary-side winding of the output transformer, and switching of both the switch elements A rectifying / smoothing circuit for rectifying and smoothing the AC voltage generated in the secondary winding to obtain a DC output voltage, outputting a predetermined pulse width modulation signal based on the output voltage, and driving both the switch elements on and off A switching power supply device, wherein both the switch elements are mounted on a wiring pattern on a metal base substrate.
The control unit is set such that the maximum on-duty value of the output pulse width modulation signal exceeds 50%,
On the metal base substrate, a wiring pattern in which terminals that vary in potential by switching among terminals of the both switch elements are mounted, and includes at least a pair of potential variation patterns corresponding to the terminals,
A switching power supply device, wherein each wiring capacitance formed between each potential variation pattern and the metal base of the metal base substrate is formed to be equal to each other. The potential variation pattern of the high-side switch element is formed by connecting an additional pattern to a mounting pattern to which the terminals are connected, and the wiring capacitance is set to be equal by adjusting the area of the additional pattern. The switching power supply device according to claim 1.

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