Output stabilization circuit and DC / DC converter circuit

Abstract

To provide a self-oscillation circuit technique for stabilizing an output voltage in simple circuit configuration.SOLUTION: An output stabilization circuit (1) comprises: a primary-side circuit (2) including a self-oscillation circuit (10) connected to a DC power source (BT); and a secondary-side circuit (3) which obtains an output voltage by oscillating the self-oscillation circuit. The self-oscillation circuit includes: a drive transformer (DT) in which a secondary-side coil is respectively connected to a gate electrode of each of a plurality of half-bridge-connected or full-bridge-connected switching elements; a feedback transformer (CT) in which a primary-side coil is connected to a power transmission coil (L11); and a phase shift filter (F10) connected between a secondary-side coil of the feedback transformer and a primary-side coil of the drive transformer. The phase shift filter includes a primary-side control coil (Lc1) having a characteristic that inductance is changed in accordance with a current flowing in a secondary-side control coil (Lc31) of the secondary-side circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a self-oscillating circuit and a DC-DC converter circuit. [Background technology]

[0002] Current-resonant DC-DC converters use a separate excitation method in which a control circuit such as a control IC provides an on / off signal to the switching element. Patent Document 1 listed below discloses a DC-DC converter in which a series circuit of switch elements 1 and 2 is connected to a DC power supply, and a series circuit of a capacitor 3 and a primary winding 5 of a transformer 4 is connected in parallel to switch element 2. In this DC-DC converter, a tertiary winding 6 and a quaternary winding 7 are further added to transformer 4, an on / off signal is applied to switch element 2 via tertiary winding 6, and quaternary winding 7 is used as a power supply winding for control circuit 18. This control circuit 18 detects the timing of the positive / negative switch of the quaternary winding voltage and applies an on / off signal to switch element 1 at this timing. By shortening the on time of switch element 1 in this way, reactive current is reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-209381 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned separately excited oscillation circuit requires a control circuit, which makes the circuit complicated. The present invention provides a series resonant self-oscillating circuit technology that stabilizes an output voltage with a simple circuit configuration. [Means for solving the problem]

[0005] According to the present invention, there is provided an output stabilization circuit including a primary side circuit including a self-excited oscillation circuit connected to a DC power supply, and a secondary side circuit that obtains an output voltage by oscillation of the self-excited oscillation circuit, wherein the self-excited oscillation circuit includes a power transmitting coil, a resonant capacitor that is connected in series with the power transmitting coil and that forms a series resonant circuit together with the power transmitting coil, a switching circuit that includes a plurality of switching elements connected in half bridge connection or full bridge connection and that is configured so that the direction of current flowing through the power transmitting coil is switched depending on the on / off states of the plurality of switching elements, and a secondary side An output stabilization circuit is provided which comprises a drive transformer having coils connected thereto, a feedback transformer having a primary coil connected to the power transmission coil, and a phase shift filter connected between the secondary coil of the feedback transformer and the primary coil of the drive transformer, wherein the secondary circuit comprises a receiving coil magnetically coupled to the power transmission coil and a secondary control coil in which the magnitude of the current flowing therethrough is controlled in accordance with the magnitude of the output voltage, and the phase shift filter includes a primary control coil which is magnetically coupled to the secondary control coil and has a characteristic that its inductance changes in accordance with the current flowing through the secondary control coil. [Effects of the Invention]

[0006] According to the above aspect, it is possible to provide a series resonant self-oscillating circuit technology that stabilizes an output voltage with a simple circuit configuration. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a circuit diagram of a power supply circuit according to the first embodiment. [Figure 2] FIG. 10 is a circuit diagram of a power supply circuit according to a second embodiment. [Figure 3] FIG. 2 is a circuit diagram of a secondary side circuit of the power supply circuit according to the first embodiment. [Figure 4] 4 is a graph showing the results of simulating voltage changes at various points in the power supply circuit of the first embodiment. [Figure 5]4 is a graph showing the results of simulating voltage changes at various points in the power supply circuit of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present invention (hereinafter referred to as the present embodiments) will be described below. Note that the following embodiments are merely examples, and the present invention is not limited to the configurations of the following embodiments.

[0009] [First embodiment] FIG. 1 is a circuit diagram of a power supply circuit 1 according to the first embodiment. The power supply circuit 1 is a circuit that includes a primary side circuit 2 having a battery device BT and a secondary side circuit 3 that obtains power from the primary side circuit 2, and provides a stable output to a load connected to the secondary side circuit 3. In the first embodiment, the battery device BT is a battery device that supplies DC power, the secondary side circuit 3 includes a DC conversion circuit, and an example is shown in which the power supply circuit 1 functions as a DC-DC converter circuit as a whole.

[0010] [Primary side circuit] The primary circuit 2 includes a battery device BT, a fuse FU, a capacitor C1, and a self-oscillating circuit 10. The fuse FU separates the battery BT from the primary circuit 2 when an excessive current occurs due to an abnormality in the self-excited oscillation circuit 10 of the primary circuit 2. This prevents the battery BT from being abnormally heated due to the excessive current. The capacitor C1 absorbs the change in voltage caused by the charging and discharging of the battery device BT.

[0011] The self-oscillating circuit 10 includes resistors R11, R12, R13, and R14 connected in series. The resistors R11, R12, R13, and R14 are connected in parallel to the battery BT and apply a bias voltage to the gates of the transistors Q11 and Q12. The resistors R11, R12, R13, and R14 can be called a bias circuit. A capacitor C11 is connected in parallel to the resistor R12, and a capacitor C12 is connected in parallel to the resistor R14. Capacitors C11 and C12 act as bypass capacitors, bypassing the AC components of the power (drive signal) induced in drive coils Ld1 and Ld2, which are the secondary coils of a drive transformer DT (described later), and applying a stable voltage to the gates of transistors Q11 and Q12.

[0012] The self-oscillating circuit 10 further includes two half-bridge connected transistors Q11 and Q12. The transistors Q11 and Q12 are FETs (Field Effect Transistors) and are switching elements. The source of the transistor Q11 and the drain of the transistor Q12 are connected together, the drain of the transistor Q11 is connected to the positive terminal of the battery BT, and the source of the transistor Q12 is connected to the negative terminal of the battery BT. The gates of transistors Q11 and Q12 are connected to the bias circuit via the secondary coil of a drive transformer DT (described later). Specifically, the output terminal of resistor R11 is connected to resistor R12 and a drive coil Ld1, which is the secondary coil of drive transformer DT, and the output terminal of resistor R13 is connected to resistor R14 and a drive coil Ld2, which is the secondary coil of drive transformer DT. In addition, resistors R15 and R16 are connected between the gate and source of transistors Q11 and Q12. Resistors R15 and R16 discharge the gate-source capacitance (Ciss) of transistors Q11 and Q12, thereby shortening the OFF time of transistors Q11 and Q12. In this way, the direction of the current flowing through the power transmission coil L11 (described later) is switched depending on the on / off states of the transistors Q11 and Q12, and the self-oscillating circuit 10 can be described as having a switching circuit including the transistors Q11 and Q12.

[0013] The self-oscillating circuit 10 further includes a power transmitting coil L11 and a resonant capacitor C15 connected in series. The power transmitting coil L11 and the resonant capacitor C15 together form a series resonant circuit. This series resonant circuit is connected to the source of transistor Q11 and is provided between the drain and source of transistor Q12. As a result, when transistor Q11 is on and transistor Q12 is off, current flows from resonant capacitor C15 to transmitting coil L11, whereas when transistor Q11 is off and transistor Q12 is on, current flows from transmitting coil L11 to resonant capacitor C15 due to the power stored in resonant capacitor C15. The transmitting coil L11 is magnetically coupled to the receiving coil L31 of the secondary circuit 3, and constitutes the main transformer MT. As a result, the oscillating power generated by the self-excited oscillator circuit 10 is transmitted from the transmitting coil L11, which is the primary coil of the main transformer MT, to the receiving coil L31, which is its secondary coil.

[0014] The self-oscillating circuit 10 further includes a feedback transformer CT and a drive transformer DT. The feedback transformer CT is composed of a feedback coil Lf1 as a primary coil and a feedback coil Lf2 as a secondary coil, that is, the feedback coils Lf1 and Lf2 are magnetically coupled. The feedback coil Lf1 is connected in series with the power transmission coil L11 and the resonant capacitor C15. The feedback transformer CT is a current transformer that detects the AC current generated on the primary side of the main transformer MT by the feedback coil Lf1 and transmits it to the feedback coil Lf2. In the feedback transformer CT, the number of turns of the feedback coil Lf1, which is the primary winding, is smaller than the number of turns of the feedback coil Lf2, which is the secondary winding, so that the current flowing through the feedback coil Lf1 is converted to a smaller current and induced in the feedback coil Lf2. The feedback coil Lf2 is connected to a phase-shift filter F10.

[0015] The drive transformer DT is composed of a drive coil Ld3 as a primary coil and drive coils Ld1 and Ld2 as secondary coils. That is, the drive coil Ld3 is magnetically coupled to the drive coils Ld1 and Ld2. The drive coil Ld3 is connected to the phase-shift filter F10. One end of the drive coil Ld1 is connected to the gate of the transistor Q11, and the other end is connected to the output end of the resistor R11 and the input end of the resistor R12. One end of the drive coil Ld2 is connected to the gate of the transistor Q12, and the other end is connected to the output end of the resistor R13 and the input end of the resistor R14. As shown in FIG. 1, the polarities of the drive coils Ld1 and Ld2 are connected to the gate of the transistor Q11 or Q12 so as to be opposite to each other. In this manner, in this embodiment, the output of the drive transformer DT is applied to the gates of the transistors Q11 and Q12, and the drive transformer DT determines the switching timing of the transistors Q11 and Q12.

[0016] The phase-shift filter F10 is connected between the feedback coil Lf2, which is the secondary coil of the feedback transformer CT, and the drive coil Ld3, which is the primary coil of the drive transformer DT. The phase-shift filter F10 is composed of a resistor Rf, a control coil Lc1, and a capacitor Cf, and can also be referred to as an RLC filter. In the example of Fig. 1, the resistor Rf and the control coil Lc1 are connected in parallel to the feedback coil Lf2 and the drive coil Ld3, and the capacitor Cf is connected in series to the feedback coil Lf2 and the drive coil Ld3. With this configuration, the phase-shift filter F10 shifts the phase of the AC voltage applied to the resistance element Rf in accordance with the AC current generated in the feedback coil Lf2 and applies it to the drive coil Ld3, which is the primary coil of the drive transformer DT.

[0017] Here, the phase of the AC voltage applied to the drive coil Ld3 is shifted relative to the phase of the secondary coil output of the feedback transformer CT by an amount of phase shift that depends on the polarity of the feedback coil Lf2 and the drive coil Ld3, the filter constant of the phase-shift filter F10, etc. The amount of phase shift by the phase shift filter F10 is variable depending on the filter constants of the phase shift filter F10, such as the resistance value of the resistive element Rf, the inductance of the control coil Lc1, the capacitance of the capacitor Cf, etc. In this embodiment, the inductance of the control coil Lc1 is variable depending on the output voltage of the secondary side circuit 3, and therefore the amount of phase shift by the phase shift filter F10 is also variable. Specifically, the control coil Lc1 of the phase-shift filter F10 forms a control transformer FT together with a control coil Lc31 (described later) of the secondary-side circuit 3, and has the characteristic that its inductance changes depending on the current flowing through the control coil Lc31. Hereinafter, the control coil Lc1 of the phase-shift filter F10 included in the primary-side circuit 2 may be referred to as the primary-side control coil Lc1, and the control coil Lc31 included in the secondary-side circuit 3 may be referred to as the secondary-side control coil Lc31.

[0018] [Secondary side circuit] The secondary circuit 3 includes a receiving coil L31, a rectifier circuit SR30, a reference voltage circuit RV30, and the like. As described above, the receiving coil L31 constitutes the main transformer MT as a secondary coil with the transmitting coil L11 as a primary coil, and generates an induced electromotive force due to the current in the transmitting coil L11.

[0019] The rectifier circuit SR30 is connected to the receiving coil L31. The rectifier circuit SR30 has a bridge rectifier circuit formed by diodes D31, D32, D33, and D34, and a smoothing filter formed by a coil L32 and a capacitor C31, and functions as a full-wave rectifier circuit. In other words, the rectifier circuit SR30 full-wave rectifies and smoothes the AC voltage generated in the receiving coil L31 to convert it into a DC voltage.

[0020] The reference voltage circuit RV30 includes resistor elements R31 and R32 and a shunt regulator element Ic31, and is a circuit that stabilizes the output voltage from the secondary side circuit 3 to a reference voltage or higher. The shunt regulator element Ic31 receives the input of the voltage obtained by dividing the output voltage using resistor elements R31 and R32 at its reference terminal, and controls the voltage between the reference and anode to be the reference voltage. The reference voltage circuit RV30 further includes a secondary control coil Lc31. A current flows through the secondary control coil Lc31 in accordance with the voltage control of the shunt regulator element Ic31. That is, when the output voltage becomes higher than the reference voltage, the current flowing through the secondary control coil Lc31 increases, and when the output voltage becomes lower than the reference voltage, the current flowing through the secondary control coil Lc31 decreases.

[0021] As described above, the secondary control coil Lc31 is magnetically coupled to the primary control coil Lc1 by the control transformer FT, and the inductance of the primary control coil Lc1 is made variable by the amount of current flowing through the secondary control coil Lc31. The primary-side control coil Lc1 and the secondary-side control coil Lc31 form a transformer with one magnetic path, with the primary and secondary windings wound around a common core. This transformer is configured to have an inductance DC superposition characteristic such that the greater the DC current flowing through the secondary-side control coil Lc31, the greater the inductance reduction rate of the primary-side control coil Lc1. As a result, in the phase-shift filter F10, due to the RLC filter characteristics, the greater the inductance value of the primary-side control coil Lc1, the greater the amount of phase shift.

[0022] With this configuration, the amount of phase shift of the phase-shift filter F10 can be increased or decreased in accordance with the output voltage from the secondary-side circuit 3. The accompanying change in the drive timing of the transistors Q11 and Q12 brings the oscillation frequency on the primary side of the main transformer MT closer to or farther away from the resonant frequency, thereby stabilizing the output voltage from the secondary-side circuit 3.

[0023] [Operation] The operation of the power supply circuit 1 in the first embodiment having the above-described configuration will be described below.

[0024] In the primary circuit 2, when DC power is supplied from the battery BT to resistor elements R11, R12, R13, and R14 that function as a bias circuit, voltages divided by the resistor elements of the bias circuit are applied to the gates of transistors Q11 and Q12 as bias voltages, causing either transistor Q11 or Q12 to turn on first. At this time, when transistor Q11 is on and transistor Q12 is off, power supplied from battery BT causes current to flow through the drain-source path of transistor Q11, capacitor C15, power transmission coil L11, and feedback coil Lf1. This current becomes a resonant current through the primary leakage inductance of main transformer MT and capacitor C15, and at this time, capacitor C15 is charged.

[0025] When a current flows through the transmitting coil L11, which is the primary coil, a magnetic field is generated in the main transformer MT, and an induced electromotive force is generated in the receiving coil L31, which is the secondary coil. The output impedance of the induced electromotive force generated in the receiving coil L31 can be set according to the winding ratio of the transmitting coil L11 and the receiving coil L31. In addition, current flowing through the feedback coil Lf1, which is the primary coil of the feedback transformer CT, also induces current in the feedback coil Lf2, which is the secondary coil of the feedback transformer CT. A voltage is applied to the resistive element Rf in response to the current induced in the feedback coil Lf2, and the phase of this voltage is shifted by the phase-shift filter F10 before being applied to the drive coil Ld3.

[0026] When power is supplied to the drive coil Ld3, which is the primary coil of the drive transformer DT, a magnetic field is generated in the drive transformer DT, and an induced electromotive force is generated in the secondary coils, the drive coils Ld1 and Ld2. As described above, the drive coils Ld1 and Ld2 have opposite polarities relative to the gate of the transistor Q11 or Q12, so the voltages induced in the drive coils Ld1 and Ld2 are of opposite phases. As a result, a negative voltage is applied to transistor Q11, the bias voltage applied to transistor Q11 becomes equal to or lower than the threshold voltage, and transistor Q11 is turned off. On the other hand, a positive voltage is applied to transistor Q12, the bias voltage applied to transistor Q12 becomes higher than the threshold voltage, and transistor Q12 is turned on. In other words, the on / off states of transistors Q11 and Q12 are switched.

[0027] When transistor Q11 is turned off and transistor Q12 is turned on, the power charged in capacitor C15 causes a current to flow in the opposite direction to the above through the drain-source path of transistor Q12, feedback coil Lf1, power transmission coil L11, and capacitor 15. This current also becomes a resonant current through the primary leakage inductance of main transformer MT and capacitor 15. In this way, in the primary side circuit 2, the transistors Q11 and Q12 are alternately turned on and off, causing currents to flow alternately in opposite directions through the power transmission coil L11 and the feedback coil Lf1.

[0028] Such an operation of the primary circuit 2 generates a magnetic field in the main transformer MT, and an AC voltage is induced in the power receiving coil L31, which is a secondary coil in the secondary circuit 3. In the secondary side circuit 3, the AC voltage generated in the receiving coil L31 in this manner is input to the rectifier circuit SR30, where it is converted into a DC voltage by full-wave rectification and smoothing, and this DC voltage is input to the reference voltage circuit RV30, where the shunt regulator element Ic31 controls the output voltage to be the reference voltage and outputs it. At this time, a current corresponding to the output voltage flows through the secondary control coil Lc31. The inductance value of the primary control coil Lc1, which is magnetically coupled to the secondary control coil Lc31, changes depending on the current. The change in the inductance value of the primary control coil Lc1 changes the amount of phase shift of the phase shift filter F10.

[0029] In this embodiment, when the output voltage becomes higher than the reference voltage, the current flowing through the secondary-side control coil Lc31 increases, the inductance value of the primary-side control coil Lc1 decreases, and the phase shift amount of the phase-shift filter F10 increases. On the other hand, when the output voltage becomes lower than the reference voltage, the current flowing through the secondary-side control coil Lc31 decreases, the inductance value of the primary-side control coil Lc1 increases, and the phase shift amount of the phase-shift filter F10 decreases. When the phase shift amount of the phase shift filter F10 increases, the timing at which the transistors Q11 and Q12 are driven by the output of the drive transformer DT advances (the self-oscillation frequency increases), causing the oscillation frequency on the primary side of the main transformer MT to deviate from the resonance frequency, resulting in a decrease in the output voltage from the secondary side circuit 3. On the other hand, when the phase shift amount of the phase shift filter F10 decreases, the timing at which the transistors Q11 and Q12 are driven by the output of the drive transformer DT delays (the self-oscillation frequency decreases), causing the oscillation frequency on the primary side of the main transformer MT to approach the resonance frequency, resulting in an increase in the output voltage from the secondary side circuit 3.

[0030] Therefore, according to this embodiment, it is possible to realize a series resonant self-oscillating circuit that can stabilize the output voltage with a simple circuit configuration without requiring a control circuit like an externally excited oscillator circuit. For this reason, the power supply circuit 1 in this embodiment can be referred to as an output stabilization circuit.

[0031] [Second embodiment] FIG. 2 is a circuit diagram of the power supply circuit 1 according to the second embodiment. The power supply circuit 1 in the second embodiment differs from the first embodiment in that the switching circuit in the primary side circuit 2 includes full-bridge connected transistors Q11, Q12, Q21 and Q22. The following description of the power supply circuit 1 in the second embodiment will focus on the differences from the first embodiment, and the same details as those in the first embodiment will be omitted as appropriate.

[0032] In the second embodiment, the self-oscillating circuit 10 further includes resistors R21, R22, R23, and R24 connected in series. The resistors R21, R22, R23, and R24 are connected in parallel to the battery BT and apply a bias voltage to the gates of the transistors Q21 and Q22. The resistors R21, R22, R23, and R24 can also be called a bias circuit, similar to the resistors R11, R12, R13, and R14. Capacitor C21 is connected in parallel to resistor R22, and capacitor C22 is connected in parallel to resistor R24. Capacitors C21 and C22 act as bypass capacitors, bypassing the AC components of the power (drive signal) induced in drive coils Ld4 and Ld5, which are the secondary coils of drive transformer DT, and applying a stable voltage to the gates of transistors Q21 and Q22.

[0033] In the second embodiment, the self-oscillating circuit 10 further includes four full-bridge connected transistors Q11, Q12, Q21, and Q22. The transistors Q11, Q12, Q21, and Q22 are FETs (Field Effect Transistors) and switching elements. The connection between the transistors Q11 and Q12 and other circuit components is the same as in the first embodiment. The source of the transistor Q21 and the drain of the transistor Q22 are connected together, the drain of the transistor Q21 is connected to the positive terminal of the battery BT, and the source of the transistor Q22 is connected to the negative terminal of the battery BT. The gates of transistors Q21 and Q22 are connected to the bias circuit via the secondary coil of drive transformer DT. Specifically, the output terminal of resistor R21 is connected to resistor R22 and drive coil Ld4, which is the secondary coil of drive transformer DT, and the output terminal of resistor R23 is connected to resistor R14 and drive coil Ld5, which is the secondary coil of drive transformer DT. In addition, resistor element R25 or R26 is connected between the gate and source of transistors Q21 and Q22. Resistor elements R25 and R26 discharge the gate-source capacitance (Ciss) of transistors Q21 and Q22, thereby shortening the OFF time of transistors Q21 and Q22.

[0034] In the second embodiment, the direction of current flowing through the power transmission coil L11 (described later) is switched depending on the on / off states of the transistors Q11, Q12, Q21, and Q22, and the self-oscillating circuit 10 can be described as having a switching circuit including full-bridge connected transistors Q11, Q12, Q21, and Q22.

[0035] The drive transformer DT in the second embodiment is composed of a drive coil Ld3 as a primary coil and drive coils Ld1, Ld2, Ld4, and Ld5 as secondary coils. That is, the drive coil Ld3 is magnetically coupled to the drive coils Ld1, Ld2, Ld4, and Ld5. One end of drive coil Ld4 is connected to the gate of transistor Q21, and the other end is connected to the output terminal of resistor R21 and the input terminal of resistor R22. One end of drive coil Ld5 is connected to the gate of transistor Q22, and the other end is connected to the output terminal of resistor R23 and the input terminal of resistor R24. 2, the polarities of the drive coils Ld4 and Ld5 are connected to be opposite to each other with respect to the gate of transistor Q21 or Q22. Furthermore, so that the pair of transistors Q11 and Q22 and the pair of transistors Q12 and Q21 are in the same on or off state, the pair of drive coils Ld1 and Ld5 are connected to be the same polarity with respect to the gate of transistor Q11 or Q22, the pair of drive coils Ld2 and Ld4 are connected to be the same polarity with respect to the gate of transistor Q12 or Q21, and the pair of drive coils Ld1 and Ld5 and the pair of drive coils Ld2 and Ld4 are connected to be opposite to each other with respect to each gate. As described above, in the second embodiment, the output of the drive transformer DT is applied to the gates of the transistors Q11, Q12, Q21, and Q22, and the switching timing of the transistors Q11, Q12, Q21, and Q22 is determined by the drive transformer DT.

[0036] [Operation] The operation of the power supply circuit 1 in the second embodiment having the above-described configuration will be described below.

[0037] In the primary side circuit 2, when DC power is supplied from the battery BT to resistor elements R11, R12, R13, R14, R21, R22, R23, and R24 that serve as a bias circuit, voltages divided by the resistor elements of the bias circuit are applied as bias voltages to the gates of transistors Q11, Q12, Q21, and Q22, respectively. As a result, either the pair of transistors Q11 and Q22 or the pair of transistors Q12 and Q21 turns on first. At this time, when the pair of transistors Q11 and Q22 is on and transistors Q12 and Q21 are off, power supplied from the battery BT causes a current to flow through the drain-source path of transistor Q11, capacitor C15, power transmission coil L11, feedback coil Lf1, and the drain-source path of transistor Q22. This current becomes a resonant current of the primary leakage inductance of main transformer MT and capacitor C15.

[0038] As in the first embodiment, when power is supplied to the drive coil Ld3, which is the primary coil of the drive transformer DT, a magnetic field is generated in the drive transformer DT, and an induced electromotive force is generated in the secondary coils, the drive coils Ld1, Ld2, Ld4, and Ld5. As described above, the pair of drive coils Ld1 and Ld5 and the pair of drive coils Ld2 and Ld4 are connected so that the polarity with respect to each gate is opposite between the pairs, so the power induced in the pair of drive coils Ld1 and Ld5 and the pair of drive coils Ld2 and Ld4 is of opposite phase. As a result, a negative voltage is applied to the transistors Q11 and Q22, the bias voltage applied to the transistors Q11 and Q22 becomes equal to or lower than the threshold voltage, and the pair of transistors Q11 and Q22 is turned off. On the other hand, a positive voltage is applied to the transistors Q12 and Q21, the bias voltage applied to the transistors Q12 and Q21 becomes higher than the threshold voltage, and the pair of transistors Q12 and Q21 is turned on.

[0039] When the pair of transistors Q11 and Q22 is turned off and the pair of transistors Q12 and Q21 is turned on, current flows in the opposite direction to the above through the drain-source of transistor Q12, the drain-source of transistor Q21, feedback coil Lf1, transmitting coil L11, and capacitor 15. This current also becomes a resonant current through the primary leakage inductance of main transformer MT and capacitor 15. In this way, in the primary side circuit 2, the pair of transistors Q11 and Q22 and the pair of transistors Q12 and Q21 are alternately turned on and off, causing currents to flow alternately in opposite directions through the power transmission coil L11 and the feedback coil Lf1. The other operations are the same as those in the first embodiment, and therefore will not be described. Therefore, in the second embodiment, as in the first embodiment, a series resonant self-oscillating circuit can be realized that does not require a control circuit like an externally excited oscillator circuit and that can stabilize the output voltage with a simple circuit configuration.

[0040] The above content will be explained in more detail below with reference to examples, but the following examples do not limit the above content in any way. [Example]

[0041] In the examples, the results of verifying the effects of the first embodiment described above by simulation are shown. FIG. 3 is a circuit diagram of the secondary side circuit 3 of the power supply circuit 1 in the first embodiment. In the simulation of Example 1, the inductance value of the primary control coil Lc1 was set virtually manually without controlling the inductance of the primary control coil Lc1 by magnetic coupling between the primary control coil Lc1 and the secondary control coil Lc31. Therefore, the reference voltage circuit RV30 is not provided in the secondary side circuit 3, and a load resistor RO is connected thereto. The primary side circuit 2 has the same configuration as that of the first embodiment shown in FIG.

[0042] 4 and 5 are graphs showing the results of simulating voltage changes at various points in the power supply circuit 1 of Example 1. In Fig. 5 to Fig. 7, (a) shows the simulation results when the inductance value of the primary side control coil Lc1 is set to a first value, and (b) shows the simulation results when the inductance value of the primary side control coil Lf21 is set to a second value that is smaller than the first value.

[0043] Figures 4(a) and 4(b) show the voltage waveform (thick line) induced in the feedback coil Lf2 and the voltage waveform (thin line) applied to the drive coil Ld3 after the output of the feedback coil Nf2 has been applied (passed through) the phase-shift filter F10. According to FIG. 4(a), when the inductance value of the primary side control coil Lc1 is set to a first value (large), the amount of phase shift of the phase shift filter F10 becomes small, and therefore the phase of the voltage induced in the feedback coil Lf2 is applied to the gates of the transistors Q11 and Q12 without being shifted significantly. On the other hand, in Fig. 4(b), when the inductance value of the primary-side control coil Lc1 is set to a second value (small), the amount of phase shift of the phase-shift filter F10 is larger than in Fig. 4(a), and the phase of the voltage generated in the feedback coil Lf2 is shifted by the phase-shift filter F10 before being applied to the gates of the transistors Q11 and Q12. As a result, as shown in Fig. 4(b), it can be seen that the frequencies of both the voltage waveform generated in the feedback coil Lf2 (thick line) and the voltage waveform applied to the drive coil Ld3 (thin line) are changed from the waveforms shown in Fig. 4(a).

[0044] Figures 5(a) and 5(b) show the voltage waveform at the gate of transistor Q12 (thick line), the voltage waveform between the drain and source of transistor Q12 (thin line), and the DC voltage level applied to the load resistor (approximately straight line). By comparing Figures 5(a) and 5(b), it can be seen that when the inductance value of the primary side control coil Lc1 is set to the first value (large), the oscillation period is longer and the DC voltage level applied to the load resistor, i.e., the output voltage, is larger than when the inductance value is set to the second value (small). This indicates that when the inductance value of the primary side control coil Lc1 is set to a first value (large), the oscillation frequency of the primary side circuit 2 matches or is close to the resonant frequency, resulting in a large output voltage, and when the inductance value of the secondary side control coil Lc1 is set to a second value (small), the oscillation frequency of the primary side circuit 2 moves away from the resonant frequency, resulting in a small output voltage.

[0045] As described above, according to this example, it has been demonstrated that in the power supply circuit 1 of the first embodiment, the output voltage can be controlled by changing the amount of phase shift by the phase shift filter F10 depending on the magnitude of the inductance value of the primary side control coil Lc1, and thus stabilization of the output voltage can be achieved.

[0046] Some or all of the above-described embodiments and modifications can be specified as follows: However, the above-described embodiments and modifications are not limited to the following descriptions.

[0047] (1) An output stabilization circuit comprising: a primary side circuit including a self-oscillating circuit connected to a DC power supply; and a secondary side circuit that obtains an output voltage by oscillation of the self-oscillating circuit, The self-oscillating circuit comprises: A transmitting coil; a resonant capacitor connected in series with the power transmitting coil to form a series resonant circuit together with the power transmitting coil; a switching circuit including a plurality of switching elements connected in a half bridge or full bridge configuration, and configured to switch the direction of a current flowing through the power transmitting coil depending on the on / off states of the plurality of switching elements; a drive transformer having a secondary coil connected to each gate electrode of the plurality of switching elements; a feedback transformer having a primary coil connected to the power transmission coil; a phase-shift filter connected between the secondary coil of the feedback transformer and the primary coil of the drive transformer; and The secondary side circuit includes: a power receiving coil magnetically coupled to the power transmitting coil; a secondary control coil in which the magnitude of a current flowing therethrough is controlled in accordance with the magnitude of the output voltage; and the phase-shift filter includes a primary-side control coil that is magnetically coupled to the secondary-side control coil and has an inductance that changes in response to a current flowing through the secondary-side control coil; Output stabilization circuit. (2) A DC-DC converter circuit including the output stabilization circuit according to (1), The secondary side circuit further includes a DC conversion circuit that converts an AC voltage generated in the power receiving coil into a DC voltage. DC-DC converter circuit. [Explanation of symbols]

[0048] 1 Power circuit 2 Primary circuit 3 Secondary circuit BT Battery Device Q11, Q12, Q21, Q22 transistors L11 transmitting coil L31 receiving coil Lf1, Lf2 feedback coil C15 Resonant capacitor Ld1, Ld2, Ld3, Ld4, Ld5 drive coils Lc1 Primary control coil Lc31 Secondary side control coil R11, R12, R13, R14, R15, R16, R21, R22, R23, R24, Rf, R25, R26, R31, R32 resistive elements C11, C12, C21, C22 bypass capacitors MT main transformer CT feedback transformer DT drive transformer FT Control Transformer F10 Phase Shift Filter SR30 rectifier circuit RV30 Reference Voltage Circuit Ic31 shunt regulator element

Claims

1. An output stabilization circuit comprising: a primary side circuit including a self-oscillating circuit connected to a DC power supply; and a secondary side circuit that obtains an output voltage by oscillation of the self-oscillating circuit, The self-oscillating circuit comprises: A transmitting coil; a resonant capacitor connected in series with the power transmitting coil to form a series resonant circuit together with the power transmitting coil; a switching circuit including a plurality of switching elements connected in a half bridge or full bridge configuration, and configured to switch the direction of a current flowing through the power transmitting coil depending on the on / off states of the plurality of switching elements; a drive transformer having a secondary coil connected to each gate electrode of the plurality of switching elements; a feedback transformer having a primary coil connected to the power transmission coil; a phase-shift filter connected between the secondary coil of the feedback transformer and the primary coil of the drive transformer; and The secondary side circuit includes: a power receiving coil magnetically coupled to the power transmitting coil; a secondary control coil in which the magnitude of a current flowing therethrough is controlled in accordance with the magnitude of the output voltage; and the phase-shift filter includes a primary-side control coil that is magnetically coupled to the secondary-side control coil and has an inductance that changes in response to a current flowing through the secondary-side control coil; Output stabilization circuit.

2. A DC-DC converter circuit including the output stabilization circuit according to claim 1, The secondary side circuit further includes a DC conversion circuit that converts an AC voltage generated in the power receiving coil into a DC voltage. DCDC converter circuit.

Images