LLC resonant converter circuit

Abstract

An LLC resonant converter circuit (1) comprises: a resonant capacitor (Cr); a resonant coil (Np), which is a primary winding of the transformer (3) and, together with the resonant capacitor, forms the series resonant circuit (11); an inverter circuit (12); and a frequency control circuit (15) which outputs a driver signal to the inverter circuit, the frequency of which is changed according to a voltage of a feedback signal. The LLC resonant converter circuit (1) further comprises a circuit (30) which detects the output current of a secondary-side circuit (20) and generates the feedback signal; a circuit (40) which detects a phase difference between a resonant signal of the series resonant circuit and the driver signal; and a circuit (50) which performs voltage control of the feedback signal such that a decrease in the frequency of the driver signal by the frequency control circuit (15) according to the phase difference is suppressed.

Description

TECHNICAL AREA

[0001] The present invention relates to an LLC resonant converter circuit that performs frequency control using a feedback signal corresponding to the output power of a secondary-side circuit. TECHNICAL AREA

[0002] An LLC resonant converter circuit performs frequency control using a feedback signal that corresponds to the output current from a secondary-side circuit.For example, patent document 1 discloses a current resonant converter device comprising: a DC power supply, a converter transformer, a series connection of a first and a second switching element, a series connection of a primary winding of the converter transformer and a resonant capacitor, a rectification / smoothing circuit connected to a secondary winding of the converter transformer, which rectifies and smooths current obtained in the secondary winding and supplies the current to a load, a converter control circuit which controls the ON / OFF frequencies of the first and second switching elements, an operational amplifier which detects and amplifies a load voltage supplied to the load, and a photocoupler which detects a change in the output voltage of the operational amplifier and feeds the detected change in output voltage back to the converter control circuit.Furthermore, this device adjusts the gain of the operational amplifier depending on the sensing output of a load current sensing circuit, which detects a load current flowing in the load, so that the gain characteristics or the gain curve is stabilized from a light load to a heavy load and abnormal oscillations due to the increase in gain at a heavy load are prevented. CITATION LIST PATENT DOCUMENTS

[0003] Patent document 1: JP 2005 - 39 975 A OVERVIEW OF THE PROBLEM THAT THE INVENTION IS INTENDED TO SOLVE.

[0004] It is known that in an LLC resonant converter, deviations from the intended resonance conditions can lead to a breakdown current due to the recovery current of the body diode of the switching elements. This can result in an increase in switching losses and ultimately damage or destruction of the switching element. This phenomenon is called resonance shift. To prevent resonance shift, the switching frequency is controlled within a predetermined range higher than the resonant frequency, ensuring that the switching frequency (operating frequency) of the switching element does not fall below the resonant frequency.

[0005] However, if a load or transformer is replaced by one with different properties in the LLC resonant converter, the resonance characteristics may change unexpectedly and still cause the phenomenon of resonance shift.

[0006] The present invention was made with regard to such a problem and provides a circuit technology of an LLC resonant converter which is able to suppress the phenomenon of resonance shift even when a load or transformer is replaced by one with different properties. MEANS TO SOLVENT THE PROBLEM

[0007] According to the present invention, an LLC resonant converter circuit is provided, comprising: a primary-side circuit connected to a DC power supply and comprising a series resonant circuit; a transformer; and a secondary-side circuit that rectifies and smooths an alternating current received from the primary-side circuit via the transformer and outputs direct current, wherein the primary-side circuit comprises a resonant capacitor, a resonant coil which is a primary winding of the transformer and together with the resonant capacitor forms the series resonant circuit, and an inverter circuit comprising several switching elements connected in a half-bridge or full-bridge configuration, and which is configured such that the several switching elements perform switching operations according to a driver signal, thereby reversing the direction of a current flowing through the resonant coil.and a frequency control circuit that outputs the driver signal to the inverter circuit, the frequency of which is changed according to a voltage of a feedback signal, wherein the secondary-side circuit comprises a secondary-side coil, which is a secondary winding of the transformer, and a rectifier circuit that rectifies and smooths alternating current generated in the secondary-side coil, wherein the LLC resonant converter circuit further comprises: a sensing circuit that detects the output current of the secondary-side circuit and generates the feedback signal; a phase comparator circuit that detects a phase difference between a resonant signal of the series resonant circuit and the driver signal; and a feedback control circuit that performs voltage control of the feedback signal such thatthat a decrease in the frequency of the driver signal is suppressed by the frequency control circuit according to the phase difference detected by the phase comparator circuit. IMPACT OF THE INVENTION

[0008] With the aspect described above, it is possible to provide a circuit for an LLC resonant converter that is able to suppress the phenomenon of resonance shift even when a load or transformer is replaced by one with different characteristics. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 is a circuit diagram of an LLC resonant converter circuit (converter circuit) according to one embodiment. Fig. 2A is a diagram that conceptually illustrates signals at points A, B, C and D in a phase comparator circuit in a case where there is a large phase difference between a resonant signal and a driver signal. Fig. 2B is a diagram that conceptually illustrates signals at points A, B, C and D in the phase comparator circuit in a case where the phase difference between the resonant signal and the driver signal is small. Fig. Figure 3 is a circuit diagram in which an inverter circuit in the LLC resonant converter circuit (converter circuit) is modified according to the embodiment. DESCRIPTION OF THE EXECUTION FORMS

[0009] The following describes embodiments of the present invention. It should be noted that the following embodiments are merely examples and the present invention is not limited to the configurations of the following embodiments. <schaltungskonfiguration>

[0010] Fig. Figure 1 is a circuit diagram of an LLC resonant converter circuit (hereinafter also abbreviated as "converter circuit") 1 according to one embodiment.

[0011] The converter circuit 1 comprises at least a primary-side circuit 10, which is connected to a DC power supply and has a series resonant circuit 11, a transformer 3, a secondary-side circuit 20, which rectifies and smooths alternating current obtained from the primary-side circuit 10 via the transformer 3 and outputs direct current, a sensing circuit 30, a phase comparator circuit 40 and a feedback control circuit 50.

[0012] The secondary-side circuit 20 includes output terminals (VOUT+) and (VOUT-) and outputs direct current from these terminals. There are no restrictions on how the output direct current can be used. The output terminals can be connected to loads of various characteristics.

[0013] Furthermore, the secondary-side circuit 20 comprises a secondary-side coil Ns, which is a secondary winding of the transformer 3, and a rectifier circuit 21, which is connected to the secondary-side coil Ns and rectifies and smooths alternating current generated in the secondary-side coil Ns. The rectifier circuit 21 comprises a bridge rectifier circuit and a capacitor C20, wherein the bridge rectifier circuit includes rectifier diodes D1, D2, D3, and D4. The alternating current generated in the secondary-side coil Ns is converted into direct current by half-wave rectification by the bridge rectifier circuit and smoothing by the output capacitor C20.

[0014] The transformer 3 comprises a primary-side coil Np, the secondary-side coil Ns and a core, which are electrically isolated from each other, wherein the primary-side coil Np and the secondary-side coil Ns are magnetically coupled. Fig. Figure 1 does not illustrate any parasitic elements such as a magnetizing inductance (Lm) or a leakage inductance (Lr) of the transformer 3 or output capacitances or parasitic diodes in the transistors Q1 and Q2 described later.

[0015] The primary-side circuit 10 includes, for example, the series resonant circuit 11, an inverter circuit 12, a VCO circuit (voltage-controlled oscillator) 15, an input capacitor C10, and resistor elements R1 and R2.

[0016] The primary-side circuit 10 is connected to an external DC power supply via an input terminal (DCVin). Additionally, the primary-side circuit 10 also includes an input terminal (Vcc) for a DC voltage.

[0017] The series resonant circuit 11 is formed by the primary-side coil Np of the transformer 3 and a resonant capacitor Cr connected in series. Therefore, the primary-side coil Np can also be referred to as a resonant coil.

[0018] The inverter circuit 12 comprises several switching elements connected in a half-bridge configuration or a full-bridge configuration and is configured to cause the switching elements to perform switching operations according to a driver signal (VCOout) from the VCO circuit 15 described later, so that the direction of the current flowing through the resonant coil (primary coil Np) of the series resonant circuit 11 is switched.

[0019] More precisely, the inverter circuit 12 comprises a driver circuit 13 and two transistors Q1 and Q2, which serve as switching elements. For example, field-effect transistors (FETs) can be used for transistors Q1 and Q2. In the example of Fig. 1 The transistors Q1 and Q2 are N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) and form a half-bridge circuit.

[0020] The driver circuit 13 is connected to transistors Q1 and Q2 in such a way that gate-source voltages (hereinafter also referred to as VGS voltages) can be applied to transistors Q1 and Q2. Furthermore, the drain of transistor Q1 is connected to the input terminal (DCVin) of the DC power supply.

[0021] The driver circuit 13 alternately applies a VGS voltage to transistor Q1 and transistor Q2, exceeding a threshold voltage, thereby switching transistors Q1 and Q2 alternately on and off (causing them to perform a switching operation). The driver circuit 13 switches transistors Q1 and Q2 on and off according to a pulse period of the driver signal (VCOout) from the VCO circuit 15.

[0022] The series resonant circuit 11 is connected to the source of transistor Q1 and positioned between the drain and source of transistor Q2. Thus, when transistor Q1 is ON and transistor Q2 is OFF, a load current can flow between the drain and source of transistor Q1, through the primary-side coil Np and the resonant capacitor Cr. Conversely, when transistor Q1 is OFF and transistor Q2 is ON, the load current can flow between the drain and source of transistor Q2, through the resonant capacitor Cr and the primary-side coil Np, due to the energy stored in the resonant capacitor Cr.

[0023] Thus, the direction of the current flowing through the primary-side coil Np is switched by the switching operations of transistors Q11 and Q12 of the inverter circuit 12.

[0024] The input capacitor C10 is connected in parallel to transistors Q1 and Q2. More precisely, the input capacitor C10 is connected to the drain of transistor Q1 and the source of transistor Q2, thus smoothing the input voltage.

[0025] The VCO circuit 15 outputs a driver signal to the driver circuit 13, the frequency of which changes according to the voltage of the feedback signal. The VCO circuit 15 can also be referred to as a frequency control circuit. The VCO circuit 15 has an input terminal (VCOin terminal) for a feedback signal, and the input terminal is connected via resistor R1 to the input terminal (Vcc) of the DC voltage and via resistor R2 to a collector terminal of a phototransistor of a photocoupler PC of the sensing circuit 30.

[0026] Therefore, the “feedback signal voltage” means a voltage applied to the VCOin terminal via a line connected from the collector terminal of the phototransistor of the photocoupler PC of the sensing circuit 30 to the VCOin terminal of the VCO circuit 15.

[0027] In the example of Fig. The VCO circuit 15 is configured to lower the frequency of the output driver signal when the voltage of the feedback signal (VCOin terminal) is higher within a predetermined range, and to increase the frequency of the output driver signal when the voltage of the feedback signal (VCOin terminal) is lower within the predetermined range. There are no restrictions regarding the specific design of the VCO circuit 15.

[0028] The detection circuit 30 detects the output current from the secondary-side circuit 20 and generates a feedback signal (outputs the feedback voltage). In the example of Fig. 1 The detection circuit includes 30 capacitors Cd and Cf, resistor elements R5, R6, R7, R8 and R9, a variable resistor VR1, a shunt regulator IC, and a photocoupler PC.

[0029] Between the output terminals (VOUT+) and (VOUT-) of the secondary circuit 20, capacitor Cd is provided. Resistors R8, R9, and VR1 are connected in series. Resistors R5, R6, and the shunt regulator IC are connected in series and in parallel with capacitor Cd. Furthermore, the line branching off between resistor R6 and the cathode of the shunt regulator IC is connected to a slider terminal (terminal connected to the slider) of variable resistor VR1. Resistor R7 and capacitor Cf are connected in series in this line. Finally, the line extending from a reference terminal of the shunt regulator IC is connected to a point between resistor R7 and the slider terminal of variable resistor VR1.

[0030] The photocoupler PC electrically isolates the primary and secondary sides and comprises a photodiode on the primary side and a phototransistor on the secondary side. The photocoupler PC is switched to an ON state (light-emitting state of the photodiode on the primary side) by applying an input voltage exceeding the non-light-emitting forward voltage. It is then able to increase or decrease the output impedance of the phototransistor on the secondary side by increasing or decreasing the current flowing through the photodiode on the primary side in the ON state. In the following description, the current flowing through the photodiode on the primary side of the photocoupler PC can also be referred to as the "photocoupler PC diode current".

[0031] The photodiode on the primary side of the photocoupler PC is connected in parallel with resistor R6. That is, the photodiode of the photocoupler PC has a cathode connected to a point between resistors R5 and R6, and an anode connected to a point between resistor R6 and the cathode of the shunt regulator IC and one end of capacitor Cf.

[0032] The collector terminal of the phototransistor on the secondary side of the photocoupler PC is connected via the resistor element R2 to the input terminal (VCOin terminal) for the feedback signal of the VCO circuit 15, and the emitter terminal is connected to ground (GND).

[0033] Thus, in the detection circuit 30, a DC voltage is obtained from the output current of the secondary-side circuit 20 via the capacitor Cd, the DC voltage is divided by the resistance of the resistor element R8, the resistance of the resistor element R9 and the resistance of the variable resistor VR1 according to the position of the slider and applied to the reference terminal of the shunt regulator IC, and the divided voltage is controlled so that it is a reference voltage (for example, 2.5 V).

[0034] If the voltage across the slider of the variable resistor VR1 exceeds the reference voltage, the diode current of the photocoupler PC consequently increases, and if the voltage across the slider of the variable resistor VR1 falls below the reference voltage, the diode current of the photocoupler PC decreases.

[0035] When the diode current of photocoupler PC increases, the output impedance of photocoupler PC decreases, and consequently the voltage at the input terminal (VCOin terminal) for the feedback signal of VCO circuit 15 decreases. Conversely, when the diode current of photocoupler PC decreases, the output impedance of photocoupler PC increases, and consequently the voltage at the VCOin terminal of VCO circuit 15 increases.

[0036] In the present embodiment, when the voltage at the VCOin terminal of the VCO circuit 15 decreases, the frequency of the driver signal output by the VCO circuit 15 increases, and when the voltage at the VCOin terminal of the VCO circuit 15 increases, the frequency of the driver signal output by the VCO circuit 15 decreases.

[0037] The variable resistor VR1 is designed to allow variable adjustment of the output voltage (voltage between the output terminals (VOUT+) and (VOUT-)) from the secondary-side circuit 20. Since the voltage applied to the slider of the variable resistor VR1 is controlled by the shunt regulator IC to serve as the reference voltage, the output voltage is adjusted by the ratio of the resistance of resistor R8, the resistance of resistor R9, and the resistance of the variable resistor VR1, according to the position of the slider.

[0038] Thus, the output voltage of converter circuit 1 can be variably adjusted.

[0039] The phase comparator circuit 40 detects a phase difference between the resonant signal of the series resonant circuit 11 and the driver signal. Since the phase of a resonant current changes in the same way as the voltage phase of the resonant capacitor, in the example of Fig. 1 a voltage signal applied to the resonant capacitor Cr is recorded as the resonant signal of the series resonant circuit 11.

[0040] The phase comparator circuit 40 includes, for example, a half-wave rectifier circuit 41, a phase comparator 42, and a filter circuit 43.

[0041] The half-wave rectifier circuit 41 detects the voltage signal applied to the resonant capacitor Cr from a point between the resonant capacitor Cr and the primary-side coil Np (resonant coil) and subjects the voltage signal to half-wave rectification.

[0042] The phase comparator 42 compares the phases of the voltage signal rectified by the half-wave rectifier circuit 41 with the driver signal output by the VCO circuit 15 and outputs a phase difference signal indicating the phase difference.

[0043] The filter circuit 43 smooths the phase difference signal output by the phase comparator 42 and outputs a DC signal. Since the DC signal output by the filter circuit 43 is a DC voltage signal indicating the phase difference, it can be said that the filter circuit 43 is a circuit that smooths the signal indicating the phase difference and outputs a phase difference voltage. Although there are no restrictions regarding the specific design of the filter circuit 43, it can, for example, be implemented as a CR filter with a resistor and a capacitor.

[0044] The feedback control circuit 50, for example, includes a differential amplifier circuit 60 and a diode D5 and performs voltage control of the feedback signal in such a way that a decrease in the frequency of the driver signal from the VCO circuit 15 is suppressed according to the phase difference detected by the phase comparator circuit 40.

[0045] In this context, “voltage control of the feedback signal”, which is carried out by the feedback control circuit 50, means that the voltage applied to the VCOin terminal of the VCO circuit 15 is controlled.

[0046] The cathode of diode D5 is connected to an output terminal of the differential amplifier circuit 60, and the anode of diode D5 is connected to a branch of a line connecting the collector terminal of the phototransistor in the photocoupler PC and the VCOin terminal of the VCO circuit 15. Depending on the differential voltage output by the differential amplifier circuit 60, diode D5 can be either ON (current flowing) or OFF (no current flowing). Consequently, when diode D5 is ON, the voltage of the feedback signal output by the sensing circuit 30 decreases due to the action of the feedback control circuit 50, and this reduced voltage is fed into the VCOin terminal of the VCO circuit 15.If, on the other hand, diode D5 is in the OFF state, the feedback control circuit 50 does not affect the voltage of the feedback signal output by the detection circuit 30, and the voltage control of the feedback signal by the detection circuit 30 becomes dominant.

[0047] The differential amplifier circuit 60 is provided between the filter circuit 43 and the cathode of the diode D5 and outputs a differential voltage corresponding to the difference between the phase difference voltage output by the filter circuit 43 and a reference voltage.

[0048] In the example of Fig. 1 The differential amplifier circuit 60 includes, for example, resistor elements R11, R12, R13 and R14, a variable resistor VR2 and an operational amplifier OP.

[0049] Resistors R11 and R12 are connected in series between the output terminal of filter circuit 43 and the output terminal of operational amplifier OP. The inverting input terminal of operational amplifier OP is connected to a point between resistors R11 and R12. The output terminal of operational amplifier OP is connected to the cathode of diode D5. Furthermore, the non-inverting input terminal of operational amplifier OP is connected to one end of resistor R13, and the other end of resistor R13 is connected to a slider terminal of variable resistor VR2.One end of the resistance in the variable resistor VR2 is connected to one end of the resistor element R14, the other end of the resistor element R14 is connected to an input terminal (Vcc) into which the DC current is input, which is also supplied to the VCO circuit 15, and the other end of the variable resistor VR2 is connected to ground (GND).

[0050] With this configuration, the differential amplifier circuit 60 obtains a differential voltage by subtracting the phase difference voltage from the reference voltage, amplifies this voltage according to the ratio between the resistance of resistor R11 and the resistance of resistor R12, and outputs the amplified differential voltage. The output differential voltage is applied to the cathode of diode D5. Furthermore, the reference voltage of the differential amplifier circuit 60 is a voltage obtained by dividing the DC voltage supplied from the input terminal (Vcc) by the resistance of resistor R14 and the resistance of variable resistor VR2 according to the position of the slider of variable resistor VR2, and then reducing this value by resistor R13.

[0051] Furthermore, the differential amplifier circuit 60 outputs a differential voltage that does not allow a current to flow through the diode D5 when the phase difference voltage is higher than the reference voltage, and outputs the differential voltage that allows a current to flow through the diode D5 when the phase difference voltage is lower than the reference voltage.

[0052] As described above, the feedback control circuit 50, due to the rectification of diode D5 according to the differential voltage output by the differential amplifier circuit 60, is configured to switch between a state in which the voltage of the feedback signal output by the sensing circuit 30 is reduced and fed into the VCOin terminal of the VCO circuit 15, and a state in which the voltage of the feedback signal output by the sensing circuit 30 is fed directly into the VCOin terminal. If the phase difference voltage is higher than the reference voltage, the voltage control by the feedback control circuit 50 has no effect on the feedback signal, so that the frequency of the driver signal is controlled by the feedback signal output by the sensing circuit 30 as a function of the output current of the secondary-side circuit 20.If the phase difference voltage is lower than the reference voltage, a decrease in the frequency of the driver signal by the voltage control is suppressed by the feedback control circuit 50 relative to the feedback signal output by the sensing circuit 30.

[0053] Here, based on the differential voltage output by the differential amplifier circuit 60, it is determined whether a decrease in the frequency of the driver signal, i.e., a decrease in the switching frequency (operating frequency) of the inverter circuit 12, is limited or not, and this differential voltage corresponds to a difference between the phase difference voltage output by the filter circuit 43 and the reference voltage of the differential amplifier circuit 60. Therefore, the reference voltage of the differential amplifier circuit 60 is a threshold for determining whether a decrease in the operating frequency should be limited or not, and is variable depending on the position of the slider of the variable resistor VR2.

[0054] Therefore, it can be said that the variable resistor VR2 is a circuit element that can variably adjust the phase difference threshold to determine whether or not the voltage control by the feedback control circuit 50 acts on the feedback signal; in other words, a circuit element that can variably adjust a condition for triggering a limitation of the operating frequency decay, depending on how close the operating frequency approaches the resonant frequency in a frequency range higher than the resonant frequency of the series resonant circuit 11. Accordingly, it can be stated that the feedback control circuit 50 includes a circuit element with which the phase difference threshold can be variably adjusted to determine whether or not voltage control of the feedback signal should be performed to suppress a decay of the driver signal frequency by the VCO circuit 15.It should be noted that this circuit element is not limited to a variable resistor. <betrieb>

[0055] The converter circuit 1 with such a circuit configuration is operated as follows.

[0056] Inverter circuit 12 switches transistors Q1 and Q2 on and off depending on the pulse period of the driver signal from VCO circuit 15. This reverses the direction of the current flowing through the primary-side coil Np of transformer 3. When transistor Q1 switches ON and transistor Q2 switches OFF, a load current flows through a path between the drain and source of transistor Q1, through the primary-side coil Np, and through the resonant capacitor Cr, charging the resonant capacitor Cr. When transistor Q1 switches OFF and transistor Q2 switches ON, a load current flows through the path between the drain and source of transistor Q2, through the resonant capacitor Cr, and through the primary-side coil Np in the opposite direction to that described above, due to the energy stored in the resonant capacitor Cr.

[0057] In the primary-side circuit 10, such switching operations of the inverter circuit 12 cause a resonant current to flow through the series resonant circuit 11, thereby inducing an alternating current in the secondary-side coil Ns of the transformer 3. In the secondary-side circuit 20, the alternating current generated by the secondary-side coil Ns is rectified and smoothed by the rectifier circuit 21 and is thereby converted into output direct current.

[0058] The sensing circuit 30 detects the output current of the secondary circuit 20 and generates a feedback signal. More precisely, a DC voltage is derived from the DC current output by the secondary circuit 20 via the capacitor Cd. The shunt regulator IC ensures that the DC voltage, divided by the resistances of resistor element R8, resistor element R9, and variable resistor VR1 according to the position of the slider, assumes a reference voltage (for example, 2.5 V). That is, when the voltage across the slider of variable resistor VR1 exceeds the reference voltage, the diode current of the photocoupler PC increases, and when the voltage across the slider of variable resistor VR1 falls below the reference voltage, the diode current of the photocoupler PC decreases.

[0059] The photocoupler PC increases or decreases the output impedance according to the magnitude of the diode current on the primary side and consequently increases or decreases the voltage at the VCOin terminal (feedback signal) of the VCO circuit 15.

[0060] By operating the detection circuit 30 in this way, if the power of the DC current output by the secondary-side circuit 20 decreases, the voltage of the feedback signal input to the VCO circuit 15 increases, and if the power of the DC current output by the secondary-side circuit 20 increases, the voltage of the feedback signal decreases.

[0061] The VCO circuit 15 lowers the frequency of the output driver signal the higher the voltage of the feedback signal is within a predetermined range, and increases the frequency of the output driver signal the lower the voltage of the feedback signal is within the predetermined range.

[0062] By such frequency control of the VCO circuit 15, the switching frequency (operating frequency) is controlled within a predetermined range, which is higher than the resonant frequency of the series resonant circuit 11, in such a way that the switching frequency of the inverter circuit 12 does not fall below the resonant frequency.

[0063] If the load connected to transformer 3 or the output terminals (VOUT+) (VOUT-) of the secondary circuit 20 is replaced by one with different characteristics, the output current of the secondary circuit 20 is affected, and the resonant frequency of the series resonant circuit 11 changes. If the output current of the secondary circuit 20 is reduced by such a load change, the voltage of the feedback signal is increased by the control described above via the sensing circuit 30, and the frequency of the driver signal output by the VCO circuit 15 becomes progressively lower. If the resonant frequency changes due to such a load change, and if the control range of the switching frequency remains unchanged, then the switching frequency after the change may become lower than the resonant frequency, and the phenomenon of so-called resonance shift may occur.

[0064] In the present embodiment, the feedback control circuit 50 therefore performs a voltage control of the feedback signal such that a decrease in the frequency of the driver signal by the VCO circuit 15 is suppressed according to the phase difference detected by the phase comparator circuit 40.

[0065] More precisely, the phase comparator circuit 40 outputs a phase difference voltage indicating a phase difference between a voltage signal and a driver signal. The voltage signal is obtained by half-wave rectification of a voltage signal applied to the resonant capacitor Cr, and the driver signal is output by the VCO circuit 15. In the feedback control circuit 50, the differential amplifier circuit 60 amplifies a differential voltage obtained by subtracting the phase difference voltage from the reference voltage and applies the amplified differential voltage to the cathode of diode D5.A differential voltage that prevents current from flowing through diode D5 is output when the phase difference voltage is higher than the reference voltage, and a differential voltage that allows current to flow through diode D5 is output when the phase difference voltage is lower than the reference voltage.

[0066] If the phase difference voltage is higher than the reference voltage, the voltage control of the feedback signal by the detection circuit 30 becomes dominant, and if the phase difference voltage is lower than the reference voltage, a decrease in the frequency of the driver signal is suppressed by the effect of the feedback control circuit 50 on the feedback signal output by the detection circuit 30 (the frequency of the driver signal is maintained or increased).

[0067] Fig. 2A and Fig. 2B are diagrams that conceptually illustrate signals at points A, B, C and D in the phase comparator circuit 40. Fig. Figure 2A illustrates a case where the phase difference between the resonant signal and the driver signal is large, and Fig. 2B illustrates a case where the phase difference is small.

[0068] The signal at point A is a voltage signal that is rectified and output by the half-wave rectifier circuit 41, the signal at point B is a driver signal output by the VCO circuit 15, the signal at point C is a phase difference signal output by the phase comparator 42, and the signal at point D is a phase difference voltage signal output by the filter circuit 43.

[0069] Additionally, illustrate Fig. 2A and Fig. 2B is a mode in which the phase comparator 42 includes an exclusive-OR (EXOR) circuit. However, the phase comparator 42 is not limited to such a configuration.

[0070] As the phase difference between the driver signal and the resonant signal (voltage signal applied to the resonant capacitor Cr) increases, the following applies: Fig. 2A and Fig. 2B the phase difference voltage output by the filter circuit 43, whereas the phase difference voltage decreases when the phase difference decreases.

[0071] If in the example of Fig. 2A and Fig. 2B As the switching frequency (operating frequency) approaches the resonant frequency of the series resonant circuit 11, the phase difference voltage decreases, so that a decrease in the frequency of the driver signal is suppressed by the voltage control with the feedback control circuit 50 on the feedback signal, and as the switching frequency (operating frequency) moves away from the resonant frequency, the phase difference voltage increases, so that the voltage control of the feedback signal by the sensing circuit 30 becomes dominant.

[0072] If the load or transformer 3 is replaced by one with different properties, then even if the switching frequency decreases more and more according to a decrease in the output current, a decrease in the switching frequency is suppressed when the switching frequency approaches the resonant frequency, so that the phenomenon of resonance shift can be prevented from occurring. [Modification]

[0073] The content of the embodiments described above can be modified as needed.

[0074] Fig. Figure 3 is a circuit diagram in which the inverter circuit 12 is modified in the converter circuit 1 according to the embodiment described above.

[0075] The arrangement of the inverter circuit 12 according to the embodiment described above, which is in Fig. As illustrated in Figure 1, this arrangement can also be modified to a configuration in which the switching elements are connected in a full bridge configuration, as shown in Figure 1. Fig. 3 illustrated.

[0076] In the example of Fig. The inverter circuit 12 comprises four transistors Q1, Q2, Q3, and Q4, connected in a full-bridge configuration as switching elements. For example, a field-effect transistor (FET), an N-channel MOSFET, or the like can be used as transistors Q3 and Q4, just as transistors Q1 and Q2 can be.

[0077] The source of transistor Q3 is connected to the drain of transistor Q4, the drain of transistor Q3 is connected to the drain of transistor Q1, and the source of transistor Q4 is connected to the source of transistor Q2. Furthermore, the driver circuit 13 is connected to transistors Q3 and Q4 such that the respective VGS voltages can be applied to them. The drain of transistor Q3 is connected to the input terminal (DCVin) of the DC power supply, and the source of transistor Q4 is connected to ground (GND). Additionally, the series resonant circuit 11 is connected along a path from a point between the source of transistor Q1 and the drain of transistor Q2 to a point between the source of transistor Q3 and the drain of transistor Q4. The connection between transistor Q1 and transistor Q2 is as described above.

[0078] The driver circuit 13 causes the transistors Q1, Q2, Q3 and Q4 to switch on and off according to a pulse period of the driver signal from the VCO circuit 15, so that the direction of the current flowing through the primary-side coil Np is reversed.

[0079] Even if the arrangement of the inverter circuit 12 is modified from the half-bridge configuration to the full-bridge configuration as described above, the same operational effects can be achieved as with the embodiment described above.

[0080] Additionally, in a modification of the embodiment described above, the VCO circuit 15 can be configured to increase the frequency of the output driver signal when the voltage of the feedback signal (VCOin terminal of the VCO circuit 15) is higher within a predetermined range, and to decrease the frequency of the output driver signal when the voltage of the feedback signal is lower within the predetermined range. In this case, the sensing circuit 30 is configured such that the voltage of the feedback signal input to the VCO circuit 15 increases when the output current from the secondary circuit 20 is high, and the voltage of the feedback signal decreases when the output current is low.Additionally, the feedback control circuit 50 can be configured not to affect the feedback signal to be input into the VCO circuit 15 if the phase difference voltage is higher than the reference voltage, and to increase the voltage of the feedback signal if the phase difference voltage is lower than the reference voltage.

[0081] Furthermore, in a modification of the embodiment described above, the phase comparator circuit 40 can be configured such that the phase difference voltage output by the filter circuit 43 is lower the greater the phase difference between the resonant signal of the series resonant circuit 11 and the driver signal, and higher the smaller the phase difference. In this case, if the phase difference voltage is higher than the reference voltage, a current flows through diode D5, thereby reducing the voltage of the feedback signal; if the phase difference voltage is lower than the reference voltage, no current flows through diode D5, and the feedback signal is not affected.

[0082] In any case, the feedback control circuit 50 can be configured to perform voltage control of the feedback signal in such a way that a decrease in the frequency of the driver signal is suppressed as the resonant signal of the series resonant circuit 11 approaches the resonant frequency, and if the resonant signal moves away from the resonant frequency, the voltage control of the feedback signal by the sensing circuit 30 becomes dominant.

[0083] Some or all of the embodiments and modifications described above may also be specified as follows. However, the embodiments and modifications described above are not limited to the following.

[0084] <1> LLC resonant converter circuit comprising: a primary-side circuit connected to a DC power supply and comprising a series resonant circuit; a transformer; and a secondary-side circuit that rectifies and smooths alternating current obtained from the primary-side circuit via the transformer and outputs direct current. the primary-side circuit has the following features: a resonant capacitor, a resonant coil, which is a primary winding of the transformer and together with the resonant capacitor forms the series resonant circuit, an inverter circuit comprising multiple switching elements connected in a half-bridge or full-bridge configuration, and configured such that the multiple switching elements perform switching operations according to a driver signal, thereby reversing the direction of a current flowing through the resonant coil, and a frequency control circuit that outputs a driver signal to the inverter circuit, the frequency of which changes depending on the voltage of a feedback signal, the secondary-side circuit has the following features: a secondary-side coil, which is a secondary winding of the transformer, and a rectifier circuit that rectifies and smooths alternating current generated by the secondary-side coil, the LLC resonant converter circuit further comprises the following: a detection circuit that detects the output current of the secondary-side circuit and generates the feedback signal; a phase comparator circuit that detects a phase difference between a resonant signal of the series resonant circuit and the driver signal; and a feedback control circuit that performs voltage control of the feedback signal in such a way that a decrease in the frequency of the driver signal is suppressed by the frequency control circuit depending on the phase difference detected by the phase comparator circuit.

[0085] <2> LLC resonant converter circuit according to <1> , wherein the feedback control circuit includes a circuit element with which the threshold of a phase difference can be variably set to determine whether or not voltage control of the feedback signal is performed by the frequency control circuit to suppress a decrease in the frequency of the driver signal.

[0086] <3> LLC resonant converter circuit according to <1> , wherein the phase comparator circuit includes a filter circuit that smooths a signal indicating the phase difference and outputs a phase difference voltage, the feedback control circuit has the following features: a differential amplifier circuit that outputs a differential voltage between the phase difference voltage from the filter circuit and a reference voltage; and a diode that is provided between an input terminal for the feedback signal of the frequency control circuit and an output terminal of the differential amplifier circuit, and wherein the feedback control circuit is configured to switch between a state in which the voltage of the feedback signal input into the frequency control circuit is reduced and a state in which the voltage of the feedback signal is not reduced, due to a rectifying effect of the diode according to the differential voltage output by the differential amplifier circuit.

[0087] <4> LLC resonant converter circuit according to <3> , wherein the frequency control circuit is configured to lower the frequency of the output driver signal as the voltage of the feedback signal is higher within a predetermined range, and to increase the frequency of the output driver signal as the voltage of the feedback signal is lower within the predetermined range, the diode is connected on its cathode side to an output terminal of the differential amplifier circuit, and on its anode side to an input terminal for the feedback signal of the frequency control circuit, and The differential amplifier circuit is configured to output a differential voltage that causes no current to flow through the diode when the phase difference voltage is higher than the reference voltage, and to output a differential voltage that causes a current to flow through the diode when the phase difference voltage is lower than the reference voltage.

[0088] <5> LLC resonant converter circuit according to <3> or <4> , the differential amplifier circuit has a variable resistor with which the reference voltage can be variably adjusted. REFERENCE MARK LIST 1 LLC resonant converter circuit (converter circuit) 3 Transformer 10 Primary-side circuit 11 Series Resonant Circuit 12 Inverter circuit 13 Driver circuit 15 VCO circuit 20 Secondary-side circuit 21 Rectifier circuit 30 detection circuit 40-phase comparator circuit 41 Half-wave rectifier circuit 42 Phase comparator 43 Filter circuit 50 Feedback control circuit 60 Differential amplifier circuit Np Primary side coil Ns secondary side coil Cr resonant capacitor Q1, Q2, Q3, Q4 Transistor PC photocoupler OP operational amplifier D1, D2, D3, D4, D5 Diode IC shunt regulator VR1, VR2 Variable Resistance QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2005 - 39 975 A

[0003] < / betrieb> < / schaltungskonfiguration>

Claims

[1] LLC resonant converter circuit comprising: a primary circuit connected to a DC power supply and comprising a series resonant circuit; a transformer; and a secondary circuit which rectifies and smooths an alternating current obtained from the primary circuit via the transformer and outputs direct current, the primary-side circuit has the following features: a resonant capacitor, a resonant coil, which is a primary winding of the transformer and together with the resonant capacitor forms the series resonant circuit, an inverter circuit comprising several switching elements connected to each other in a half-bridge or full-bridge arrangement, and configured such that the several switching elements perform a switching operation according to a driver signal, so that one direction of a current flowing through the resonant coil is reversed, and a frequency control circuit that outputs a driver signal to the inverter circuit, the frequency of which changes depending on the voltage of a feedback signal, the secondary-side circuit has the following features: a secondary-side coil, which is a secondary winding of the transformer, and a rectifier circuit that rectifies and smooths alternating current generated by the secondary-side coil, the LLC resonant converter circuit further comprises the following: a detection circuit that detects the output current of the secondary-side circuit and generates the feedback signal; a phase comparator circuit that detects a phase difference between a resonant signal of the series resonant circuit and the driver signal; and a feedback control circuit that performs voltage control of the feedback signal in such a way that a decrease in the frequency of the driver signal is suppressed by the frequency control circuit depending on the phase difference detected by the phase comparator circuit. [2] LLC resonant converter circuit according to claim 1, wherein the feedback control circuit comprises a circuit element with which the threshold of the phase difference can be variably set to determine whether or not voltage control of the feedback signal is performed to suppress a decrease in the frequency of the driver signal by the frequency control circuit. [3] LLC resonant converter circuit according to claim 1, wherein the phase comparator circuit includes a filter circuit that smooths a signal indicating the phase difference and outputs a phase difference voltage, the feedback control circuit has the following features: a differential amplifier circuit that outputs a differential voltage between the phase difference voltage from the filter circuit and a reference voltage; and a diode that is provided between an input terminal for the feedback signal of the frequency control circuit and an output terminal of the differential amplifier circuit, and wherein the feedback control circuit is configured to switch between a state in which the voltage of the feedback signal input into the frequency control circuit is reduced and a state in which the voltage of the feedback signal is not reduced, due to a rectifying effect of the diode according to the differential voltage output by the differential amplifier circuit. [4] LLC resonant converter circuit according to claim 3, wherein the frequency control circuit is configured to lower the frequency of the output driver signal as the voltage of the feedback signal is higher within a predetermined range, and to increase the frequency of the output driver signal as the voltage of the feedback signal is lower within the predetermined range, the diode is connected on its cathode side to an output terminal of the differential amplifier circuit, and on its anode side to an input terminal for the feedback signal of the frequency control circuit, and The differential amplifier circuit is configured to output a differential voltage that causes no current to flow through the diode when the phase difference voltage is higher than the reference voltage, and to output a differential voltage that causes a current to flow through the diode when the phase difference voltage is lower than the reference voltage. [5] LLC resonant converter circuit according to claim 3 or 4, wherein the differential amplifier circuit has a variable resistor with which the reference voltage can be variably adjusted.

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