JP2009118730A - Resonance-type switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a resonance-type switching power supply that realizes stable operations. <P>SOLUTION: In this switching power supply, a load RL is connected to the output side of a piezoelectric transducer, and a drive circuit 12 is connected to the input side thereof. An impedance inverter circuit 13, that gives inductivity to impedance as the piezoelectric transducer side is viewed from the drive circuit, is provided. The impedance conversion circuit is configured by an internal capacitance that subsists in a power conversion element, a capacitance element that configures a parallel circuit together with the load, and an inductance element that is connected to this parallel circuit in series, and the capacitance element selects electrostatic capacity C2 so as to satisfy the condition of the formula: (X/(1+X<SP>2</SP>))-(2πfL1/RL)<0 (where, X= 2πfL(Co + C2)RL), if the internal capacitance is Co, an inductance value of an inductance element is L1, the resistance value of the load is RL, and frequency f is the frequency of the drive voltage from the drive circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply device using a power conversion element including a resonance element such as a piezoelectric element or a magnetostrictive element.

  In this type of switching power supply device, a transformer that insulates the primary side from the secondary side is used as a power conversion element that constitutes an inverter. However, in an electromagnetic transformer that uses a conventional ferrite core and windings, a switching frequency is used. With the increase in frequency, the copper loss increased significantly due to the skin effect and proximity effect, and the leakage flux increased due to the reduction in thickness, which was an obstacle to the increase in frequency and thickness of the switching power supply. . As an alternative to this, recently, a piezoelectric transformer using a piezoelectric element that can be electrically insulated by energy transmission by mechanical vibration has been proposed. Piezoelectric transformers are polarized in the thickness and length directions of ferroelectric materials such as barium titanate and lead zirconate titanate (PZT). When an alternating voltage is applied, the power conversion element outputs a high voltage from a power generation unit formed on the other side in the length direction of the dielectric due to an electrostrictive effect and a piezoelectric effect.

  FIG. 6 shows a simple equivalent circuit of the piezoelectric transformer 1 having a piezoelectric element. In the figure, a piezoelectric transformer 1 surrounded by a broken line is configured as an input side configuration in addition to a transformer portion T constituting a transducer portion and a series circuit 2 composed of an inductance Lm and a capacitance Cs as resonance elements thereof. Braking capacity Cd1 and a braking capacity Cd2 as an output side configuration. A series circuit of an AC power supply 11 and an inductance element 6 is connected between the input terminals 3 and 4 of the piezoelectric transformer 1, and a load RL is connected between the output terminals 5 and 6 of the piezoelectric transformer 1.

  In the configuration of FIG. 6, the reason why the inductance element L1 is connected to the input side of the piezoelectric transformer 1 is to extract a large output power from the output terminals 5 and 6 of the piezoelectric transformer 1. That is, when the piezoelectric transformer 1 is driven alone, even if the frequency of the drive voltage supplied from the AC power supply 11 to the piezoelectric transformer 1 is made to coincide with the resonance frequency of the series circuit 2, the braking capacity Cd1 that is inherent in the piezoelectric transformer 1 , Cd2 reduces the power that can be extracted to the load RL. On the other hand, when an inductance element L1 is connected between one end of the AC power supply 11 and one input terminal 3 of the piezoelectric transformer 1, the capacitance of the input impedance when the piezoelectric transformer 1 is viewed from the input side is canceled and the pure resistance To increase the output power to the load RL. The effect of the resonance circuit between the inductance element L1 and the capacitance existing in the piezoelectric transformer 1 is also disclosed in, for example, Japanese Patent Application Laid-Open No. 9-74744.

  On the other hand, a problem associated with the higher frequency and thinner thickness of the switching power supply device is an increase in loss when the switching element is turned on / off. As a fundamental solution for reducing such switching loss, a resonance type switching power supply device is known in which the current flowing through the switching element or the voltage applied between both ends is reduced while the switching element is turned on or off.

  FIG. 7 shows an example of an active clamp resonant switching power supply. In the figure, a series circuit of first and second switching elements Q1, Q2 each made of a MOS FET and a capacitor Cr is connected between both ends of a DC power supply 21 for supplying a DC input voltage Vi. The first and second switching elements Q1 and Q2 include control switches S1 and S2 which are original FET portions, and body diodes D1 and D2 connected in antiparallel thereto. Of course, the body diodes D1 and D2 can be externally provided without being incorporated. A series circuit of the primary winding N1 of the main transformer T1 and a partial resonance inductance Lr is connected between both ends of the series circuit of the second switching element Q2 and the capacitor Cr. The partial resonance inductance Lr may use the leakage inductance of the main transformer T1. Further, Lp indicated by a broken line in the figure is an excitation inductance Lp equivalently connected in parallel with the primary winding N1 of the main transformer T1. Further, capacitors C11 and C12 are connected between both ends of the first and second switching elements Q1 and Q2. These capacitors C11 and C12 together with the partial resonance inductance Lr form a partial resonance circuit for reducing the switching loss when the first and second switching elements Q1 and Q2 are turned off.

  In the secondary winding N2 of the main transformer T1, the anode of the rectifier diode D11 is connected to one end (dot side terminal) of the secondary winding N2, and the other end (non-dot side terminal) of this secondary winding is connected. A rectifying / smoothing circuit in which the anode of the current diode D12 is connected, the rectifier diode D11 and the cathode of the commutation diode D12 are connected, and a series circuit of the choke coil L11 and the capacitor C13 is connected between both ends of the commutation diode D12. Provided. The DC output voltage Vo generated across the capacitor C13 is supplied to the load RL.

  A control circuit 22 controls the PWM (pulse width) of the first and second switching elements Q1, Q2 while monitoring the DC output voltage Vo. At that time, the first and second switching elements Q1 and Q2 are alternately turned on and off while having a dead time to turn off.

  When the first switching element Q1 is turned on, a closed circuit is formed of the DC power supply 21 → the first switching element Q1 → the primary winding N1 → the resonance inductance Lr → the DC power supply 21. Since the diode D1 is already conducting when the first switching element Q1 is turned on and the voltage across the first switching element Q1 is zero, the switching loss when the first switching element Q1 is turned on is small. Become. Thereafter, when the first switching element Q1 is turned off, the second switching element Q2 is turned on after a predetermined dead time. During this dead time, the partial resonance inductance Lr and the capacitor C11 resonate, and the capacitor The voltage of C11, that is, the voltage across the first switching element Q1, rises in a gentle sine wave shape. Thereby, the switching loss at the time of turn-off in the first switching element Q1 is also reduced.

  The voltage across the first switching element Q1 reaches the sum of the input voltage Vi and the flyback voltage, but is clamped by the capacitor Cr. When the capacitor C12 is discharged, the diode D2 becomes conductive. When the second switching element Q2 is turned on at this point, the voltage across the second switching element Q2 is zero, so the first switching Switching loss at turn-on in the element Q2 is reduced. Thereafter, when the second switching element Q2 is turned off, the first switching element Q1 is turned on after a predetermined dead time. During this dead time period, the partial resonance inductance Lr and the capacitor C12 resonate, and the capacitor The voltage of C12, that is, the voltage across the second switching element Q2, rises in a gentle sine wave shape. Thereby, the switching loss at the time of turn-off in the second switching element Q2 is also reduced.

  By repeating the above operation, forward and reverse currents alternately flow in the primary winding N1 of the main transformer T1. As a result, the DC output voltage Vo is supplied to the load RL via the output rectifying / smoothing circuit.

By the way, when the piezoelectric transformer 1 is incorporated in a switching power supply device or the like, a technique such as zero volt switching as described above is used in order to reduce switching loss. In the circuit shown in FIG. 7, when a piezoelectric transformer is used as the transformer T1, the first and second switching elements Q1, Q2 have an on / off repetition frequency higher than the resonance frequency fo of the piezo element constituting the piezoelectric transformer. It is necessary to control the frequency for turning on and off alternately. FIG. 8 is a characteristic curve showing the relationship between the on / off frequency f of the first and second switching elements Q1 and Q2 and the power P on the secondary side of the main transformer T1, which is apparent from this characteristic curve. As described above, the maximum power P can be extracted when the resonance frequency fo coincides with the on / off frequency f, and the supply amount of the power P changes depending on the on / off frequency f on both sides of the resonance frequency fo.

  In the inductive region having a frequency higher than the resonance frequency fo at which the power P reaches a peak, the supply amount of the power P decreases as the on / off frequency f increases, so that constant voltage control of the output voltage Vo is possible. However, in a capacitive region having a frequency lower than the resonance frequency fo at which the power P reaches a peak, the supply amount of the power P increases as the on / off frequency f increases, and constant voltage control of the output voltage Vo is performed. Cannot be done. Therefore, in practice, the range from fa to fb in the inductive region, which is higher than the resonance frequency fo, is the normal control range of the on / off frequency f of the first and second switching elements Q1, Q2. However, in the inductance element L1 shown in FIG. 6, since the input impedance when the piezoelectric transformer 1 is viewed from the AC power supply 11 is reduced to a pure resistance, there is a problem that a stable operation as a resonance type switching power supply device is not performed. is there.

  In view of the above problems, an object of the present invention is to provide a resonance type switching power supply device that can realize a stable operation in a case where a power conversion element including a resonance element is incorporated.

  In order to achieve the above object, a resonance type switching power supply device according to claim 1 incorporates a power conversion element incorporating a resonance element in which a load is connected to the output side and a drive circuit is connected to the input side. In the switching power supply device, the switching power supply device includes an impedance conversion circuit that imparts inductivity to an impedance when the power conversion element side is viewed from the drive circuit, and the impedance conversion circuit includes an internal capacitance and the load inherent in the power conversion element And a capacitance element forming a parallel circuit, and an inductance element connected in series with the parallel circuit, wherein the internal capacitance is Co, the inductance value of the inductance element is L1, the resistance value of the load is RL, and the drive circuit When the frequency f of the drive voltage from the capacitor element is The capacitance C2 that satisfies the formula is selected.

  In this way, the impedance when the capacitance conversion element sees the power conversion element side from the drive circuit becomes inductive, and the switching element is turned on / off in an inductive region having a frequency higher than the resonance frequency of the power conversion element. And stable operation is realized.

  In this case, there is also an advantage that the output power to the load can be increased by adding a capacitance element even if the value of the combined capacity or the load becomes small.

  According to the resonant switching power supply device of claim 1 of the present invention, when the power conversion element side is viewed from the drive circuit, the impedance becomes inductive, and the power conversion element incorporating the resonance element is incorporated. Can be realized. In addition, the output power to the load can be increased.

1 is a block diagram illustrating a schematic configuration of a resonant switching power supply device according to an embodiment of the present invention. It is a circuit diagram of the principal part at the time of resonance which shows another modification of a present Example. It is a circuit diagram of the principal part at the time of the conventional resonance. It is a circuit diagram of the principal part at the time of resonance of a present Example. It is a circuit diagram of the principal part at the time of resonance which shows another modification of a present Example. It is a circuit diagram of the piezoelectric transformer which shows a prior art example, and its periphery. It is a circuit diagram of the resonance type switching power supply device which shows a prior art example. It is the graph of the characteristic curve which showed the relationship between the on-off repetition frequency of a switching element, and output electric power.

  Hereinafter, an embodiment of a resonant switching power supply device according to the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same part as a prior art example, and since detailed description of the common location overlaps, it abbreviate | omits.

  FIG. 1 is a block diagram showing a configuration of a main part of a switching power supply device according to the present invention. In the figure, reference numeral 1 denotes a piezoelectric transformer as a power conversion element of the resonant switching power supply device, and RL denotes a load connected to the output terminals 5 and 6 of the piezoelectric transformer, as described in the conventional example. The drive circuit 12 drives the piezoelectric transformer 1 and thus the load RL. Specifically, the drive circuit 12 corresponds to the configuration of the primary side of the main transformer T1 shown in FIG. That is, the frequency of the drive voltage supplied from the drive circuit 12 to the piezoelectric transformer 1 matches the on / off frequency f of the switching elements Q1, Q2. An impedance conversion circuit 13 is provided between the drive circuit 12 and the piezoelectric transformer 1 to give a slight inductivity to the input impedance when the drive circuit 12 is viewed from the piezoelectric transformer 1 side.

  FIG. 2 shows a more detailed circuit configuration. Here, the drive circuit 12 is equivalently represented as an alternating current source 14. The frequency f of the drive voltage supplied to the piezoelectric transformer 1 matches the resonance frequency of the series circuit 2 shown in FIG. 6, and the internal structure of the piezoelectric transformer 1 is the impedance of the inductance Lm and the capacitance Cs which are resonance elements. Minutes become zero. The combined electrostatic capacity of the braking capacities Cd1 and Cd2 in this case (= Cd1 + Cd2 / n2: n is the ratio of the primary winding to the secondary winding of the transformer T) is expressed as Co. That is, the equivalent circuit of the piezoelectric transformer 1 is the sum of the load RL and the combined capacitance Co.

  The impedance conversion circuit 13 includes a capacitance element C1 electrically connected in series to the input terminals 3 and 4 of the piezoelectric transformer 1, and an inductance element L3 electrically connected in parallel to the input terminals 3 and 4 of the piezoelectric transformer 1. Thus, by adjusting the capacitance of the capacitance element C1, a slight inductivity is given to the input impedance when the piezoelectric transformer 1 is viewed from the current source 14.

  Here, in order to help the understanding of the circuit of FIG. 2, an equivalent circuit in the case where the impedance conversion circuit is configured by only the conventional inductance element L1 is shown as a comparison in FIG.

  As an example, in FIGS. 2 and 3, the characteristics of each element are L1: = 395 × 10−6H, L3: = 210 × 10−6H, C1: = 3.8 × 10−9F, Co: = 3.56 × 10. The one of −9F, RL = 1331Ω was used. The frequency of the current source 14 was f = 130 × 10 3 Hz.

  First, attention is focused on the parallel circuit of the piezoelectric transformer 1 (the combined capacitance Co) and the load RL. The admittance Y of this parallel circuit is 1 / RL + j · X, but when normalized by the value of the load RL, it becomes 1 + j · X · RL. That is, the admittance Y can be expressed by the following formula 2.

  In order to convert this admittance Y into impedance, the reciprocal thereof may be taken. That is, it can be expressed by the following formula 3.

  In FIG. 3, by adding the inductance element L1 so as to cancel the imaginary part (−0.242 · j) of the impedance Z, the impedance viewed from the input side of the impedance conversion circuit 13 becomes zero, that is, a pure resistance. The conversion ratio is its real part. That is, the impedance Z decreases to 0.062. The value of the inductance element L1 at this time can be expressed by the following equation 4.

  Next, consider the case of FIG. Here, an inductance element L3 is further added to the parallel circuit of the combined capacitor C and the load RL, and the combined admittance Y1 can be complex conjugate with the admittance Y. That is, the following equation 5 is obtained.

  This can be achieved by setting the inductance element L3 to the value of the following equation (6).

  When the synthesized admittance Y1 in the above equation 6 is converted into the impedance Z1, the value becomes the following equation 7, which is the complex conjugate with the impedance Z obtained in the equation 3.

  Therefore, in order to make the impedance viewed from the input side of the impedance conversion circuit 13 in the circuit of FIG. 2 pure resistance, the capacitance element C1 in which the imaginary part of the impedance Z1 is made zero is replaced with the inductance element L1, the combined capacity Co, and the load RL. It may be connected in series with the parallel circuit. The value of the capacitance element C1 at this time can be expressed by the following formula 8.

  The inductance elements L1 and L3 and the capacitance element C1 can also be obtained from ordinary circuit equations. When the inductance element L1 of FIG. 3 is obtained, the admittance Y by the parallel circuit of the composite capacitor Co and the load RL is expressed by the following formula 9 when normalized by the value of the load RL.

  When this admittance Y is converted into impedance, the following equation 10 is obtained.

  The combined impedance Z ′ in a state where the inductance element L1 of FIG. 3 is connected to this parallel circuit can be expressed by the following equation (11).

Here, assuming that the imaginary part of the impedance Z is X1: = X / (1 + X ² ), the value of the inductance element L1 at which the combined impedance Z ′ becomes a pure resistance is obtained by the following equation (12).

  If X1 is shown more specifically, the above equation 12 becomes the following equation 13.

  In particular, when the value of the combined capacitance Co and the load RL is large, the value of the inductance element L1 of the above equation 13 can be approximately expressed by the following equation 14.

  On the other hand, the combined admittance Y1 when the inductance element L3 is added to the parallel circuit of the combined capacitor C and the load RL in the circuit of FIG.

  Here, the condition that the combined admittance Y1 becomes a complex conjugate of the admittance Y is expressed by the following equation (16).

  Therefore, the value of the inductance element L3 is obtained by the following equation (17).

  More specifically, it can be expressed by the following equation (18), and the equation on the right side at this time is half (1/2) of the approximate equation of the inductance L1 obtained by equation (14).

  Further, the combined impedance Z1 'when the capacitance element C1 is connected in series with the parallel circuit of the inductance element L3, the combined capacitance Co, and the load RL can be expressed by the following equation (19).

  Therefore, the condition that the imaginary part of the combined impedance Z1 'becomes zero is the following equation 20.

  More specifically, the following equation 21 is obtained.

  In particular, when the value of the combined capacitance Co and the load RL is large, the value of the capacitance element C1 of the above equation 21 can be approximately expressed as the following equation 22.

As described above, the impedance conversion circuit 13 in FIG. 2 connects the inductance element L3 in parallel that the input impedance when the piezoelectric transformer 1 is viewed from the current source 14 becomes capacitive by the combined capacitance Co inside the piezoelectric transformer 1. Thus, the circuit is converted to inductivity, and the capacitance element C1 is connected in series to the parallel circuit, thereby realizing a circuit equivalent to FIG. Therefore, the impedance conversion values in FIGS. 2 and 3 are exactly the same, and the voltage values between the inductance elements L1 and L3 and between the capacitance elements Co are equal. When the output voltage across the load RL and rose to a times the resonance, the output power is increased to ^twice a. On the contrary, the impedance Z becomes smaller by the reciprocal thereof. That is, the real part of the impedance Z (same as the combined impedance Z ′) can be expressed by the following Expression 23.

  In the conventional impedance conversion circuit 13 shown in FIG. 3, since the output power is set only by the inductance element L1, when the combined capacitance Co of the load resistor RL and the piezoelectric transformer 1 is reduced, the real part of the combined impedance Z ′ is The output power that can be taken out increases and decreases.

  In order to solve this, the piezoelectric element body of the piezoelectric transformer 1 may be stacked to increase the combined capacitance Co, but there is a structural limit. As shown in FIG. 4, the simplest method for extracting a large output power is to connect an external capacitance element C <b> 2 between both ends of the input terminals 3 and 4 of the piezoelectric transformer 1. As a result, the value of the real part of the combined impedance Z ′ decreases, and the output voltage increases.

  Also, in the imaginary part in Equation 11, when the capacitance element C2 is connected, the value of 1 / (1 + X2) that controls the capacitance becomes small and approaches zero, and the entire combined impedance Z ′ shifts from capacitive to inductive. Therefore, in the resonance type switching power supply device in which the first and second switching elements Q1, Q2 are turned on and off in an inductive region having a frequency higher than the resonance frequency fo of the piezo element, the impedance conversion circuit 13 shown in FIG. By adopting, the value of the capacitance element C2 can be appropriately selected, and the impedance viewed from the current source 14 can be made inductive, which is convenient.

  As described above, in the circuit of FIG. 3, the value of the inductance element L1 increases as the combined capacitance Co and load RL of the piezoelectric transformer 1 decreases. The inductance element L3 in the impedance conversion circuit 13 of FIG. 2 of the example can be reduced to about half that of the conventional inductance element L1, and the creation of the inductance element is facilitated. In this case, contrary to the capacitance element C2 in FIG. 4, as the inductance value of the inductance element L3 is reduced, the output power can be increased even if the combined capacitance Co and the load RL are small.

  Further, in the impedance conversion circuit 13 of FIG. 2, since the input impedance when the piezoelectric transformer 1 is viewed from the current source 14 except for the capacitance element C1 is originally inductive, it has a frequency higher than the resonance frequency fo of the piezo element. In the resonance type switching power supply device in which the first and second switching elements Q1, Q2 are turned on and off in the inductive region, it is only necessary to change the value of the capacitance element C1, and the adjustment is very easy. Further, depending on how the inductance element L3 is selected, even when the capacitance element C1 is not required as shown in FIG. 5, the input impedance when the piezoelectric transformer 1 is viewed from the current source 14 is maintained at an appropriate value of inductivity. be able to. That is, in FIG. 5, the value of the inductance L3 for making the input impedance when the piezoelectric transformer 1 is viewed from the current source 14 inductive is given by the following equation (24).

  Therefore, if the inductance value of the inductance element L3 is selected to be as small as Equation 20, even if the capacitance element C1 in FIG. 2 is not required, the resonant switching power supply device can be operated normally. If this condition is not satisfied, it means that the input impedance when the piezoelectric transformer 1 side is viewed from the current source 14 in FIG. 2 does not become inductive regardless of the value of the capacitance element C1. In FIG. 5, the capacitance element C1 is not provided, and the inductance element L3 having a value smaller than that of the inductance element L1 can be selected, so that the circuit configuration is simplified.

  Further, in the circuit of FIG. 4, the condition that the combined impedance Z ′ viewed from the current source 14 when viewed from the piezoelectric transformer 1 is inductive is given by the following equation 25 from the above equation 11.

  If the capacitance element C2 is selected so as to satisfy the above conditions, the resonant switching power supply device can be operated normally while increasing the output power.

  As described above, in this embodiment, in the resonance type switching power supply device incorporating the power conversion element, that is, the piezoelectric transformer 1, having the resonance element in which the load RL is connected on the output side and the drive circuit 12 is connected on the input side, An impedance conversion circuit 13 is provided for imparting inductivity to the impedance when the piezoelectric transformer 1 side is viewed from the circuit 12.

  Conventionally, as an impedance conversion circuit, in order to extract the maximum output power, the main focus has been on reducing the input impedance when the piezoelectric transformer is viewed from the drive circuit to a pure resistance. However, when such a piezoelectric transformer and an impedance conversion circuit are incorporated in a resonance type switching power supply device, there is a drawback that stable zero volt switching is not performed.

  Therefore, the applicant has found that such a drawback can be solved if there is an impedance conversion circuit 13 that does not dare to make the input impedance pure and makes it somewhat inductive. That is, with the impedance conversion circuit 13 in this embodiment, the impedance when the piezoelectric transformer 1 side is viewed from the drive circuit 12 becomes inductive, and in an inductive region having a frequency higher than the resonance frequency fo of the piezo element. The first and second switching elements Q1, Q2 can be turned on / off, and a stable operation is realized.

  There are several circuit examples that embody the preferred impedance conversion circuit 13. For example, as shown in FIG. 2, the piezoelectric transformer 1 may include an internal capacitor, that is, a composite capacitor Co and an inductance element L3 that forms a parallel circuit with the load RL, and a capacitance element C1 that is connected in series with the parallel circuit. Good. In this case, the inductance element L3 is selected to a value that satisfies the following equation (26).

  In this way, the place where the combined impedance of the piezoelectric transformer 1 and the load RL becomes capacitive by the combined capacitance Co of the piezoelectric transformer 1 is converted into inductive by adding the inductance element L3. In the adjustment, it is only necessary to change the value of the capacitance element C1 instead of the conventional inductance element L1, and the adjustment becomes very easy. Further, as the value of the inductance element L3 is decreased, the impedance of the parallel circuit composed of the composite capacitor Co, the load RL, and the inductance element L3 becomes more inductive. The value can be reduced as compared with the inductance element L1 connected in series. Therefore, the circuit can be simplified.

  In the configuration of FIG. 2, the capacitance element C1 can be eliminated as shown in FIG. 5 by reducing the value of the inductance element L3. In this way, the circuit configuration is further simplified by the absence of the capacitance element C1.

  As another modification of the impedance conversion circuit 13, a circuit configuration shown in FIG. 4 may be selected. The impedance conversion circuit 13 may be constituted by an internal capacitance inherent in the piezoelectric transformer 1, that is, a capacitance element C2 that forms a parallel circuit with the combined capacitance Co and the load RL, and an inductance element L1 that is connected in series with the parallel circuit. . In this case, the inductance element C2 is selected to satisfy the following equation (27).

  In this manner, the impedance when the piezoelectric transformer 1 side is viewed from the drive circuit 12 by the capacitance element C2 becomes inductive, which is preferable for the resonant switching power supply device. In this case, there is also an advantage that the output power can be increased by adding the capacitance element C2 even if the value of the combined capacitance Co or the load RL becomes small.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist of the present invention. In the embodiment, the piezoelectric transformer is taken as an example. However, if the power conversion element has other resonance elements, the same operation and effect are exhibited. Further, the impedance conversion circuit 13 may be connected not to the input side of the piezoelectric transformer 1 but to the output side.

1 Piezoelectric transformer (power conversion element with internal resonance element)
12 Drive circuit
13 Impedance conversion circuit

Claims (1)

In a resonant switching power supply device incorporating a power conversion element having a resonance element in which a load is connected to the output side and a drive circuit is connected to the input side, the impedance when the power conversion element side is viewed from the drive circuit An impedance conversion circuit that imparts inductivity, the impedance conversion circuit comprising: an internal capacitance inherent in the power conversion element; a capacitance element that forms a parallel circuit with the load; and an inductance element that is connected in series to the parallel circuit. When the internal capacitance is Co, the inductance value of the inductance element is L1, the resistance value of the load is RL, and the frequency f of the drive voltage from the drive circuit is Resonance type switch characterized in that the capacitance C2 is selected to satisfy Power supply.

Images