CONTROL CIRCUIT AND CONTROL METHOD FOR LLC RESONANCE CONVERTER CIRCUIT

Abstract

A control circuit (30) for an LLC resonant converter circuit comprises a driver control circuit (50) that outputs driver signals with a switching frequency corresponding to a voltage level of a frequency control terminal and a duty cycle corresponding to a voltage level of a duty cycle control terminal to a driver circuit, a detection circuit (40) that detects an output voltage from the LLC resonant converter circuit, a voltage divider circuit (60) that divides an input voltage and applies the divider voltage as a duty cycle control voltage to a duty cycle control terminal, and an matching circuit (70) that is connected to the voltage divider circuit and the detection circuit, is configured to match the duty cycle control voltage and a frequency control voltage, and changes the duty cycle control voltage so that the duty cycle of the driver signals increases, and changes the frequency control voltage so thatthat the switching frequency of the driver signals decreases, specifically during the switch from the first command signal to the second command signal.

Description

TECHNICAL AREA

[0001] The present invention relates to an LLC resonant converter circuit. TECHNICAL BACKGROUND

[0002] In an LLC resonant converter circuit, frequency control is performed using a feedback signal that corresponds to the output current from a secondary 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 and smoothing circuit connected to a secondary winding of the converter transformer, which rectifies and smooths current obtained in the secondary winding and supplies it to a load; a converter control circuit, which regulates an ON / OFF frequency of the first and second switching elements; an operational amplifier, which detects and amplifies a load voltage supplied to the load; and an optical coupling means, which detects a change in an output voltage of the operational amplifier and feeds it back to the converter control circuit.In this device, the amplification characteristics or the gain curve are stabilized from the light load to the heavy load by adjusting the gain of the operational amplifier depending on the output of the load current sensing circuit, which detects the load current flowing through the load, and preventing abnormal oscillations due to the increase in gain with heavy loads. 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 resonant 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 this resonance shift, the switching frequency (operating frequency) of the switching element is regulated at or above the resonant frequency such that it never falls below the resonant frequency.

[0005] Fig. Figure 3 is a diagram illustrating the output characteristics in a typical LLC resonant converter circuit.

[0006] In the example of Fig. 3. The operating frequency is regulated such that it lies within a frequency range from a lower cutoff frequency fmin to an upper cutoff frequency fmax, both of which are higher than the resonant frequency.

[0007] However, in the typical LLC resonant converter circuit, as in Fig. Figure 3 illustrates how difficult it is to reduce the converter output below a certain level, even when the operating frequency is increased.

[0008] The present invention was made with such problems in mind and provides a control technique for an LLC resonant converter circuit that makes an output voltage continuously variable over a wide range. MEANS TO SOLVENT THE PROBLEM

[0009] According to the present invention, it is possible to provide a control circuit for an LLC resonant converter circuit, wherein the control circuit is configured to regulate a switching frequency to a frequency of at least one resonant frequency of a series resonant circuit, wherein the LLC resonant converter circuit comprises: the series resonant circuit; a driver circuit connected to the series resonant circuit and causing each of several switching elements to perform a switching operation based on a driver signal; a transformer in which a resonant coil, which is part of the series resonant circuit, serves as the primary winding; and a rectifier circuit that rectifies and smooths alternating current generated with a secondary winding of the transformer, wherein the control circuit comprises: a driver control circuit,which has a frequency control terminal and a duty cycle control terminal and outputs driver signals to the driver circuit with a switching frequency corresponding to a voltage level of the frequency control terminal and a duty cycle corresponding to a voltage level of the duty cycle control terminal; a detection circuit that detects an output voltage from the LLC resonant converter circuit and stabilizes the output voltage to a set voltage level; a voltage divider circuit that divides an input voltage from a power supply terminal and applies the divider voltage as a duty cycle control voltage to the duty cycle control terminal; and an matching circuit connected to the voltage divider circuit and the detection circuit, configured to adjust the duty cycle control voltage and configured to apply a frequency control voltage to the frequency control terminal.depending on the input voltage and an output voltage detected by the sensing circuit, the matching circuit changes the duty cycle control voltage to increase the duty cycle of the driver signals and changes the frequency control voltage to decrease the switching frequency of the driver signals when switching from a first command signal to a second command signal.

[0010] According to the present invention, it is further possible to provide a control method for an LLC resonant converter circuit comprising: a series resonant circuit; a driver circuit connected to the series resonant circuit, causing each of several switching elements to perform a switching operation based on a driver signal; a transformer in which a resonant coil, which is part of the series resonant circuit, serves as the primary winding; a rectifier circuit that rectifies and smooths alternating current generated by a secondary winding of the transformer; a driver control circuit having a frequency control terminal and a duty cycle control terminal, which outputs driver signals to the driver circuit with a switching frequency corresponding to a voltage level of the frequency control terminal and a duty cycle corresponding to a voltage level of the duty cycle control terminal.a detection circuit that detects an output voltage from the rectifier circuit and stabilizes the output voltage to a set voltage level, a voltage divider circuit that divides an input voltage from a power supply terminal and applies the divider voltage as a duty cycle control voltage to the duty cycle control terminal, and an matching circuit connected to the voltage divider circuit and the detection circuit to adjust the duty cycle control voltage, and a frequency control voltage applied to the frequency control terminal to adjust depending on the input current and an output voltage detected by the detection circuit, wherein the method comprises: causing the matching circuit to change the duty cycle control voltage upon switching from a first command signal to a second command signal,that the duty cycle of the driver signals increases, and the frequency control voltage changes so that the switching frequency of the driver signals decreases. IMPACT OF THE INVENTION

[0011] According to the above aspect, it is possible to provide a control technique for an LLC resonant converter circuit that makes an output voltage continuously variable over a wide range. 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. Figure 2 is a graph that conceptually illustrates a change over time of a voltage at points A, B, C and D in a matching circuit and of a driver signal at point E. Fig. Figure 3 is a graph illustrating the output characteristics in a typical LLC resonant converter circuit. DESCRIPTION OF THE EXECUTION FORMS

[0012] 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. [Circuit layout]

[0013] Fig. Figure 1 is a circuit diagram of an LLC resonant converter circuit (hereinafter also abbreviated as "converter circuit") 1 according to one embodiment.

[0014] 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 receives alternating current (AC) from the primary-side circuit 10 via the transformer 3, and a control circuit 30.

[0015] The primary-side circuit 10 includes, for example, the series resonant circuit 11, switching elements Q11 and Q12, a driver circuit 13, a capacitor C10 and an input capacitor C11.

[0016] The primary-side circuit 10 is connected to an external DC power supply via an input terminal (DCVin).

[0017] The series resonant circuit 11 is formed by a 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 switching elements Q11 and Q12 are controlled by the driver circuit 13 to perform switching operations. The direction of the current flowing through the resonant coil (primary coil Np) of the series resonant circuit 11 is reversed by the switching operations of the switching elements Q11 and Q12.

[0019] For example, field-effect transistors (FETs) can be used for the switching elements Q11 and Q12, and in Fig. Figure 1 illustrates N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). Therefore, the switching elements Q11 and Q12 will also be referred to as transistors Q11 and Q12 in the following.

[0020] The drain of transistor Q11 is connected to the input terminal (DCVin) of the DC power supply, the source of transistor Q11 is connected to the drain of transistor Q12, and the source of transistor Q12 is connected to the ground wire of the ground terminal (GND).

[0021] As described above, in Fig. 1 For example, switching elements Q11 and Q12 are used, which are connected in a half-bridge circuit, but these can be replaced by two or more switching elements connected in a full-bridge circuit.

[0022] The driver circuit 13 is connected to transistors Q11 and Q12 in such a way that gate-source voltages (hereinafter also referred to as VGS voltages) can be applied to transistors Q11 and Q12.

[0023] The driver circuit 13 alternately applies a VGS voltage to transistor Q11 and transistor Q12, 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 Q11 and Q12 on and off according to a pulse period and duty cycle of the driver signals (VCOoutCH1 and VCOoutCH2) from the driver control circuit 50.

[0024] The series resonant circuit 11 is connected to the source of transistor Q11 and positioned between the drain and source of transistor Q12. Consequently, if transistor Q11 is ON and transistor Q12 is OFF, the load current can flow through the drain-source path of transistor Q11, through the primary-side coil Np, and through the resonant capacitor Cr. Conversely, if transistor Q11 is OFF and transistor Q12 is ON, the load current can flow through the resonant capacitor Cr, through the primary-side coil Np, and through the drain-source path of transistor Q12 due to the energy stored in the resonant capacitor Cr.

[0025] Thus, the direction of the current flowing through the primary-side coil Np is switched by the switching operations of transistors Q11 and Q12.

[0026] The capacitor C10 absorbs voltage fluctuations in the DC power supply and is connected between the input terminal (DCVin) and the ground terminal (GND).

[0027] The input capacitor C11 is connected to the drain of transistor Q1 and the source of transistor Q2, i.e., connected in parallel to transistors Q11 and Q12, and smooths the input voltage.

[0028] The transformer 3 comprises the primary-side coil Np and a secondary-side coil Ns, which are electrically isolated from each other, and a core, wherein the primary-side coil Np and the secondary-side coil Ns are magnetically coupled to each other. Fig. Figure 1 does not illustrate 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 switching elements Q11 and Q12 described later.

[0029] 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. Loads with various characteristics can be connected to the output terminals.

[0030] The secondary-side circuit 20 further comprises the 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 the alternating current generated by the secondary-side coil Ns. The rectifier circuit 21 includes, for example, a bridge rectifier circuit with rectifier diodes D21, D22, D23, and D24, and a capacitor C20. 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.

[0031] The control circuit 30 is configured to control the switching frequency of the switching elements Q11 and Q12 with at least the resonant frequency of the series resonant circuit 11, as well as to control the duty cycle of the switching operations of the switching elements Q11 and Q12. That is, the control circuit 30 can perform pulse frequency modulation (PFM) control and pulse width modulation (PWM) control, thereby allowing the output voltage of the converter circuit 1 (secondary-side circuit 20) to be continuously varied over a wide range.

[0032] Here, the "wide range" is a voltage range that includes a low output range of a converter output, which is difficult to achieve by frequency control alone in a band higher than the resonant frequency of the LLC resonant converter circuit, and a high output range, which is achievable by frequency control alone.

[0033] More precisely, the control circuit 30 sets the voltage level to a predetermined lower limit voltage level within a predetermined low-voltage range and stabilizes the voltage level from there to a set voltage level. The set voltage level is a level higher than the predetermined low-voltage range. In the present embodiment, an example is shown in which the predetermined lower limit voltage level is set to zero, and the control circuit 30 sets the output voltage of the converter circuit 1 from zero and stabilizes the output voltage to a predetermined set voltage level. However, the predetermined lower limit voltage level is not limited to zero and can also be set to a different voltage level within the predetermined low-voltage range.

[0034] Here, the "predetermined low-voltage range" refers to a low output range of the LLC resonant converter circuit, which is difficult to achieve solely through frequency control in a band higher than the resonant frequency, with this voltage range encompassing zero. For example, in an LLC resonant converter circuit with an output power of at least 500 watts (W) operating under normal design conditions (not impractical conditions where efficiency is significantly degraded or during operation with circuit element losses), the predetermined low-voltage range is typically between 0 V and 5 V.

[0035] The control circuit 30 includes, for example, a detection circuit 40, a driver control circuit 50, a voltage divider circuit 60, an adaptation circuit 70 and an input terminal block CN.

[0036] In the example of Fig. 1 The input terminal block CN includes power supply connections (a first connection and a second connection), a command signal connection (a third connection) and ground connections (a fourth connection, a fifth connection and a sixth connection).

[0037] A voltage supplied by a power supply is inserted into the power supply terminals, an OFF signal (corresponding to a first command signal) or an ON signal (corresponding to a second command signal) is inserted into the command signal terminal, and a ground wire is connected to the ground terminals.

[0038] The driver control circuit 50 includes a frequency control terminal (VCOin terminal), a duty cycle control terminal (DTin terminal), and output terminals (VCOoutCH1 terminal, VCOoutCH2 terminal) for driver signals of two channels. It outputs driver signals to the driver circuit 13 with a switching frequency corresponding to a voltage level at the frequency control terminal and a duty cycle corresponding to a voltage level at the duty cycle control terminal. Hereinafter, the voltage applied to the frequency control terminal is also referred to as the frequency control voltage or VCO voltage, and the voltage applied to the duty cycle control terminal is also referred to as the duty cycle control voltage or DT voltage.

[0039] In the example of Fig. 1 The driver control circuit 50 is configured to decrease the pulse frequency of the output driver signal as the VCO voltage increases within a predetermined range, to increase the pulse frequency of the output driver signal as the VCO voltage decreases within the predetermined range, to increase the duty cycle of the output driver signal as the DT voltage increases within a predetermined range, and to decrease the duty cycle of the output driver signal as the DT voltage decreases within the predetermined range.

[0040] The driver control circuit 50 preferably comprises a frequency control connection (VCOin connection), a duty cycle control connection (DTin connection), and output connections for driver signals of two or more channels and is configured to control the pulse frequency and duty cycle of the driver signals as described above. There are no restrictions regarding the specific configuration for this purpose.

[0041] The voltage divider circuit 60 divides an input voltage from the power supply terminals of the input terminal block CN and applies the divider voltage as a duty cycle control voltage (DT voltage) to the duty cycle control terminal (DTin terminal) of the driver control circuit 50.

[0042] In the example of Fig. The voltage divider circuit 60 comprises resistors R8 and R9 and a variable resistor VR2, which are connected in series between the power supply terminals and the ground terminals. A line connected to the duty cycle control terminal of the driver control circuit 50 is connected to a node between resistor R8 and resistor R9. As a result, the voltage input from the power supply terminals is divided by the ratio of the resistance of resistor R8 to the combined resistance of resistors R8 and R9 and the variable resistor VR2, and applied to the duty cycle control terminal.

[0043] Thus, the upper limit level of the DT voltage applied to the duty cycle control terminal is determined by the resistance values ​​of resistors R8 and R9 and the variable resistor VR2, and corresponds to the upper limit of the duty cycle controlled by the driver control circuit 50 (i.e., the upper limit of the duty cycle). In other words, the voltage divider circuit 60 determines the upper limit level of the DT voltage, which corresponds to the upper limit of the duty cycle (maximum duty cycle).

[0044] The detection circuit 40 detects an output voltage of the secondary-side circuit 20 and stabilizes the output voltage at a set voltage level. In the example of Fig. 1 The detection circuit comprises 40 capacitors Cd and Cf, resistor elements R41, R42, R43, R44, R45, R46 and R47, a variable resistor VR1 and a shunt regulator IC.

[0045] Capacitor Cd and resistors R41 and R42 are connected in series between the output terminals (VOUT+) and (VOUT-) of the secondary circuit 20. A series connection of resistor R43, variable resistor VR1, and resistor R44, as well as a series connection of resistors R46 and R47 and the shunt regulator IC, are connected in parallel to capacitor Cd. A branch line extending from a node between resistor R47 and the cathode of the shunt regulator IC is connected, via capacitor Cf and resistor R45 (connected in series), to the slider terminal (terminal connected to the slider) of variable resistor VR1. Furthermore, a line extending from the reference terminal of the shunt regulator IC is connected to a node between resistor R45 and the slider terminal of variable resistor VR1.

[0046] The variable resistor VR1 is provided so that the set voltage level of the output voltage (voltage between the output terminals (VOUT+) and (VOUT-)) of the secondary-side circuit 20 can be adjusted within a voltage range higher than the predetermined low-voltage range. 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 set by the ratio of the resistances of resistor element R43 and resistor element R44, as well as the variable resistor VR1, according to the position of the slider. Consequently, the output voltage of the converter circuit 1 can be variably adjusted.This means that resistors R43 and R44 and variable resistor VR1 can be considered an output adjustment circuit, configured to variably adjust the output voltage level of converter circuit 1. The level of the output voltage set by the output adjustment circuit is also referred to as the "set voltage level".

[0047] As described above, in the detection circuit 40, the output voltage from the secondary-side circuit 20 is detected at both ends of capacitor Cd. The detected output voltage is divided by the resistances of the variable resistor VR1 according to the positions of the slider and the resistors R43 and R44, and applied to the reference terminal of the shunt regulator IC. The division voltage is controlled so that it corresponds to the reference voltage (for example, 2.5 V). Therefore, the circuit, which includes, for example, the shunt regulator IC and the resistors R46 and R47, can be considered a stabilization circuit that stabilizes the output voltage of the converter circuit 1 to a set voltage level by comparing the divided voltage of the detected output voltage with the reference voltage.

[0048] The matching circuit 70 is connected to the voltage divider circuit 60 and the detection circuit 40, and is configured to adjust the DT voltage applied to the duty cycle control terminal (DTin terminal) and the VCO voltage applied to the frequency control terminal (VCOin terminal) based on the input voltage from the power supply terminals and the output voltage detected by the detection circuit 40.

[0049] In the example of Fig. 1 The matching circuit 70 includes, for example, photocouplers PC1 and PC2, a switching element QS, a rectifier diode D1, a capacitor Cs, as well as resistor elements R1, R2, R3, R4, R5 and R6.

[0050] The photocouplers electrically isolate a primary and a secondary side from each other and each comprises a light-emitting diode on the primary side and a phototransistor on the secondary side. Photocoupler PC1 comprises a light-emitting diode HD1 on the primary side and a phototransistor PQ1 on the secondary side. Photocoupler PC2 comprises a light-emitting diode HD2 on the primary side and a phototransistor PQ2 on the secondary side.

[0051] Each of the photocouplers PC1 and PC2 switches to an ON state (a light-emitting state of the light-emitting diodes HD1 and HD2 on the primary side) by applying an input voltage exceeding the non-light-emitting forward voltage. The output impedance of the phototransistors PQ1 and PQ2 on the secondary side can be increased or decreased by increasing or decreasing the current flowing through the light-emitting diodes HD1 and HD2 on the primary side in the ON state. In the following description, the current flowing through the light-emitting diode on the primary side of the photocoupler can also be referred to as the "photocoupler diode current".

[0052] The light-emitting diode HD1 of the photocoupler PC1 is connected in parallel with the resistor R47. This means that the anode of the light-emitting diode HD1 is connected to a node or connecting line between the resistor R46 and the resistor R47, and its cathode is connected to a node between the resistor R47, a cathode of the shunt regulator IC, and the capacitor Cf.

[0053] The collector terminal of the phototransistor PQ1 of the photocoupler PC 1 is connected to a node or connecting line between a cathode of the rectifier diode D1 and the resistor element R3 (this corresponds to a photocoupler output line), and its emitter terminal is connected to a ground line.

[0054] The light-emitting diode HD2 and the resistors R4 and R5 of the photocoupler PC2 are connected in series in a line extending from the power supply terminals and connected to the ground line. The light-emitting diode HD2 has a cathode connected to resistor R4 and an anode connected to resistor R5. Furthermore, the light-emitting diode HD2 and the resistors R4 and R5, connected in series, are connected in parallel to the voltage divider circuit 60.

[0055] Rectifier diode D1 and resistor R3 are connected in series in a branch line that branches off from an output line of the DT voltage, which leads from voltage divider circuit 60 to the duty ratio control terminal. The other end of this branch line is connected to a node between the cathode of light-emitting diode HD2 and resistor R4. The cathode of rectifier diode D1 is connected to resistor R3, and the cathode of light-emitting diode HD2 is connected to a node, or connecting line, linking resistor R3 and resistor R4.

[0056] Furthermore, capacitor Cs is provided between the duty cycle control terminal and the ground line. A soft start for both the PFM and PWM control by the control circuit 30 is achieved due to the effect of capacitor Cs.

[0057] Phototransistor PQ2 of photocoupler PC2 and resistor R6 are connected in series in a line extending from the frequency control terminal and connected to ground. The collector terminal of phototransistor PQ2 is connected to the frequency control terminal via resistor R6, and its emitter terminal is connected to ground. Furthermore, a branch line from the connecting line linking the collector terminal of phototransistor PQ2 and resistor R6 is connected to ground via resistor R7.

[0058] Depending on the command signal applied to the command signal terminal (third terminal), the switching element QS enters an ON state or an OFF state. The collector terminal of switching element QS is connected to a line (photocoupler output line) extending from the collector terminal of phototransistor PQ1, and its emitter terminal is connected to ground. The gate terminal of switching element QS is connected to ground via resistor R1 and to the command signal terminal (third terminal) via resistor R2 and a NOT circuit NT.

[0059] It is also possible to use a field-effect transistor (FET) as the switching element QS, and the switching element QS can also be referred to as transistor QS.

[0060] In the example of Fig. 1. When an OFF signal is input from the command signal terminal, the OFF signal from the NOT circuit NT is inverted and input to the gate terminal, causing transistor QS to switch to the ON state. Conversely, when an ON signal is input from the command signal terminal, the ON signal from the NOT circuit NT is inverted and input to a gate terminal, causing transistor QS to switch to the OFF state.

[0061] When transistor QS is switched on, the voltage on the line extending from the collector terminal of phototransistor PQ1 and the cathode side of rectifier diode D1 (photocoupler output line) drops to ground level. As a result, as described later, the DT voltage applied to the duty cycle control terminal becomes a voltage level corresponding to the lower limit of the duty cycle.

[0062] Here, the "lower duty cycle limit" specifies a duty cycle value equal to or greater than zero at which the output voltage of converter circuit 1 (secondary-side circuit 20) can be set to a predetermined lower limit voltage level. In the present embodiment, an example is shown in which the lower duty cycle limit is zero.

[0063] The control circuit 30 also includes capacitors C1 and C2.

[0064] Capacitors C1 and C2 are arranged in parallel to each other between a line connected to the power supply terminals (the first terminal and the second terminal) and the ground line connected to the ground terminals (the fourth terminal, the fifth terminal and the sixth terminal), and smooth an input voltage from the power supply terminals. [Operation]

[0065] The converter circuit 1 with this circuit arrangement is operated as follows.

[0066] The driver circuit 13 switches transistors Q11 and Q12 on and off according to a pulse period and duty cycle of the driver signals from the driver control circuit 50. More precisely, the driver circuit 13 switches transistor Q11 on and off depending on the driver signal output by the VCOoutCH1 terminal of the driver control circuit 50, and switches transistor Q12 on and off depending on the driver signal output by the VCOoutCH2 terminal of the driver control circuit 50.

[0067] As a result, the direction of the current flowing through the primary-side coil Np of transformer 3 is reversed. When transistor Q11 is ON and transistor Q12 is OFF, a load current flows through a path between the drain and source of transistor Q11, through the primary-side coil Np, and through the resonant capacitor Cr, charging the resonant capacitor Cr. When transistor Q11 is OFF and transistor Q12 is ON, the load current, due to the energy stored in the resonant capacitor Cr, flows in the opposite direction to the case described above, through a path between the drain and source of transistor Q12, through the resonant capacitor Cr, and through the primary-side coil Np.

[0068] In the primary-side circuit 10, a resonant current flows through the series resonant circuit 11 due to the switching operations of transistors Q11 and Q12, 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 then converted into direct current and output.

[0069] The detection circuit 40 detects the output voltage of the secondary circuit 20 and stabilizes the output voltage at a set voltage level. More precisely, the output voltage of the secondary circuit 20 is detected at both ends of the capacitor Cd, and this detected output voltage is divided by the resistors R43 and R44 and the variable resistor VR1 according to the position of the slider, applied to the reference terminal of the shunt regulator IC, and controlled so that the divider voltage assumes a reference voltage (for example, 2.5 V).

[0070] Consequently, when the voltage across the slider of the variable resistor VR1 is about to exceed the reference voltage, the diode current of the photocoupler PC1 increases, and when the voltage across the slider of the variable resistor VR1 is about to fall below the reference voltage, the diode current of the photocoupler PC1 decreases.

[0071] According to photocoupler PC1, the output impedance on the secondary side increases or decreases in response to the magnitude of the diode current on the primary side. Consequently, when transistor QS is in the OFF state, the voltage across resistor R3 changes, and the diode current of photocoupler PC2 changes, thus increasing or decreasing the VCO voltage applied to the frequency control terminal (VCOin terminal) of driver control circuit 50.

[0072] On the other hand, in the voltage divider circuit 60, the input voltage at the power supply terminals is divided and applied to the duty cycle control terminal (DTin terminal) of the driver control circuit 50 (DT voltage).

[0073] Thus, the DT voltage applied to the duty cycle control terminal and the VCO voltage applied to the frequency control terminal are adjusted by the matching circuit 70, depending on whether an ON signal or an OFF signal is input at the command signal terminal.

[0074] The following describes the adaptation operation of the DT voltage and the VCO voltage by the adaptation circuit 70 with reference to Fig. 2 described in detail. Fig. Figure 2 is a diagram that conceptually illustrates the time-dependent change of a voltage at points A, B, C, and D in the matching circuit 70 and a driver signal at point E. Here, the voltage at point C is equal to the voltage of the duty cycle control terminal (DTin terminal), and the voltage at point D is proportional to the voltage of the frequency control terminal (VCOin terminal).

[0075] As indicated by the diagram for point A, an OFF signal is input at the command signal terminal until time T1, at time T1 the signal input at the command signal terminal is switched from an OFF signal to an ON signal, and after time T1 the input of an ON signal continues.

[0076] In a state where the OFF signal is input, the OFF signal is inverted by the NOT circuit NT and input into the gate terminal of transistor QS, causing transistor QS to assume the ON state.

[0077] When transistor QS is in the ON state, the line extending from the collector terminal of phototransistor PQ1 and the cathode side of rectifier diode D1 (photocoupler output line) drops to ground level. As a result, the voltage at point B becomes ground level (0 V), and the voltage at point C reaches its lower limit. Thus, the driver signal output by driver control circuit 50 has a duty cycle of zero, and consequently, the output current from converter circuit 1 becomes zero.

[0078] In the example of Fig. 1 the lower limit of the voltage at point C is determined by the forward voltage of the rectifier diode D1 and the collector-emitter saturation voltage of the transistor QS when it is in the ON state, and corresponds to the DT voltage, which specifies the lower limit of the duty cycle (a duty cycle of zero in the present embodiment).

[0079] Since the diode current of photocoupler PC2 reaches its maximum and the output impedance on the secondary side reaches its minimum, the voltage at point D also reaches its lower limit at this time, and the VCO voltage likewise reaches its lower limit. The switching frequency of the driver signals output by the driver control circuit 50 assumes the upper limit frequency of a predetermined frequency range.

[0080] When the OFF signal is switched to the ON signal at time T1, the ON signal is inverted by the NOT circuit NT, causing the transistor QS to assume the OFF state.

[0081] When transistor QS is switched off, the voltages at points B and C increase, and the DT voltage also increases, thus increasing the duty cycle of the output driver signal. The voltage at point C rises with the time constant of resistor R8 and capacitor Cs, and the voltage at point B also rises across rectifier diode D1. As a result, the output current of converter circuit 1 also increases.

[0082] On the other hand, the current flowing through the light-emitting diode HD2 of the photocoupler PC2 (diode current) decreases when the voltages at points B and C increase. Consequently, the output impedance on the secondary side of the photocoupler PC2 increases, the voltage at point D increases due to the current flowing from the frequency control terminal (VCOin terminal) of the driver control circuit 50, and the VCO voltage also increases. As a result, the switching frequency of the output driver signal is controlled to decrease from the upper cutoff frequency.

[0083] As described above, in the present embodiment, in response to the input of an OFF signal (this corresponds to a “first command signal”), the matching circuit 70 sets the DT voltage to a voltage level corresponding to the lower limit of the duty cycle (in the present embodiment, this is a duty cycle of 0), and sets the VCO voltage to a voltage level corresponding to a predetermined high frequency (upper cutoff frequency) that is higher than the resonant frequency of the series resonant circuit 11, and in response to the switching from the OFF signal to an ON signal (this corresponds to a “second command signal”), the matching circuit changes the DT voltage so that the duty cycle of the driver signals increases, and changes the VCO voltage so that the switching frequency of the driver signals decreases.

[0084] Thus, according to the present embodiment, by setting the duty cycle to the lower limit (i.e., a duty cycle of zero in the present embodiment) while adjusting the operating frequency in a frequency range higher than the resonant frequency, the output voltage of the converter circuit 1 can be set to the predetermined lower limit voltage level (zero in the present embodiment), which is difficult to achieve solely with frequency control by the LLC resonant converter circuit. Furthermore, by gradually increasing the duty cycle from the lower limit, the output voltage of the converter circuit 1 can be gradually increased from the predetermined lower limit voltage level, and thus the output voltage can be stabilized at the set voltage level from the predetermined lower limit voltage level in a low-voltage range that includes zero.

[0085] The voltage at point C and the DT voltage gradually increase from time T1 and reach their upper limit at time T2. Consequently, after time T2, the duty cycle of the driver signals also reaches its upper limit (the maximum duty cycle). As described above, the upper limit levels of the voltage at point C and the DT voltage are determined by the resistance values ​​of resistors R8 and R9 and the variable resistor VR2. As described above, the rise time of the voltage at point C and the DT voltage (i.e., the time from time T1 to time T2) is determined by the time constant of resistor R8 and capacitor Cs, and this rise time is the period during which PWM (duty cycle) control is performed.

[0086] On the other hand, the voltage at point B continues to increase even when the voltage at point C and the DT voltage reach the upper limit.

[0087] The voltage at point D and the VCO voltage continue to increase, and consequently, the switching frequency of the output driver signals is also controlled so that it decreases from an upper limit frequency. The duty cycle of the driver signals is the upper limit, and the output voltage of converter circuit 1 increases.

[0088] Thus, when the output voltage detected by the sensing circuit 40 increases and the voltage across the slider of the variable resistor VR1 is about to exceed the reference voltage, the diode current of the photocoupler PC1 increases, thereby reducing the output impedance on the secondary side and limiting the voltage increase at point B. Consequently, due to the action of the photocoupler PC2, the increase in voltage at point D and the VCO voltage are also limited, and as a result, the reduction in the switching frequency of the output driver signals is also limited.

[0089] This point in time is represented by time T3 in the diagram of Fig. T2 is displayed, and then the change in switching frequency is stabilized, and the output voltage of converter circuit 1 is stabilized at a predetermined set voltage level. That is, the time from time T1 to time T3 is a period during which PFM control is performed.

[0090] As described above, in the present embodiment, when the second command signal (ON signal) is applied, the matching circuit 70 suppresses any change in the frequency control voltage (VCO voltage) if the divider voltage (voltage across the slider of the variable resistor VR1) is about to exceed the reference voltage. That is, in the present embodiment, the output voltage is set by the PFM control to a constant voltage within a specific output range.

[0091] Thus, according to the present embodiment, the output voltage of the converter circuit 1 is stabilized from the predetermined lower limit voltage level in a low-voltage range that includes zero to a set voltage level that is higher than this low-voltage range.

[0092] Furthermore, as described above, the voltage at point C and the DT voltage gradually increase from time T1 and are limited to the upper limit level after time T2, and the voltage at point D and the VCO voltage gradually increase from time T1, continue to increase after time T2, and are only limited at time T3. Consequently, after time T1, the duty cycle of the driver signals reaches its upper limit (the maximum duty cycle) after time T2, and the switching frequency of the driver signals reaches its lower limit (a frequency higher than the resonant frequency) after time T3.

[0093] That is, in the present embodiment, the matching circuit 70 is configured such that the first change time of the duty cycle control voltage (DT voltage) after switching from the first command signal (OFF signal) to the second command signal (ON signal) is shorter than the second change time of the frequency control voltage (VCO voltage) after this switch. The first change time is the time required to change the duty cycle control voltage (DT voltage) from a voltage level corresponding to the lower limit of the duty cycle (which in the present embodiment is a duty cycle of zero) to a voltage level corresponding to the upper limit of the duty cycle.The second change time is a period from the time the frequency control voltage (VCO voltage) changes from a voltage level corresponding to a predetermined high frequency (upper cutoff frequency) until the frequency control voltage is suppressed.

[0094] The point in time at which the frequency control voltage (VCO voltage) is suppressed is approximately the point in time at which the output voltage reaches a predetermined set voltage level.

[0095] By making the first change time of the DT voltage shorter than the second change time of the VCO voltage, it is possible to control the output voltage in such a way that the PWM (duty-rate control) stops at a certain output level, and the PFM (proportional frequency control) maintains a constant, set voltage, while the PWM control achieves a low output range. The PWM control performs a hard switch, but because it is limited to the low output range, no particular problems arise in the circuit. [Example of variation]

[0096] The content of the embodiments described above can be modified as needed. That is to say, the present embodiment is not limited to the one described in Fig. The circuit arrangement shown is limited to one illustration.

[0097] In Fig.Figure 1 illustrates an arrangement in which the switching elements Q11 and Q12 are connected in a half-bridge configuration; however, the arrangement can also be modified to an arrangement in which four switching elements are connected in a full-bridge configuration. In such a modified example, the driver control circuit 50 can have output terminals for driver signals for four channels or output terminals for driver signals for two channels. In the former case, the driver circuit 13 can control the operation of the switching elements corresponding to each individual channel depending on the driver signals of each channel. In the latter case, the driver circuit 13 can control the operation of a pair of switching elements corresponding to that one channel depending on the driver signal of that channel.

[0098] Additionally, the embodiment described above can be modified such that the switching element QS assumes the ON state upon input of the ON signal, and the switching element QS assumes the OFF state upon input of the OFF signal. In this case, the NOT circuit NT is unnecessary.

[0099] Furthermore, the driver control circuit 50 can be configured, by modifying the embodiment described above, to output a driver signal indicating a lower duty cycle as the DT voltage increases within a predetermined range, and to output a driver signal indicating a higher duty cycle as the DT voltage decreases within the predetermined range. Additionally, the driver control circuit 50 can be configured to output a driver signal with a switching frequency that increases as the VCO voltage increases within a predetermined range, and to output a driver signal with a switching frequency that decreases as the VCO voltage decreases within the predetermined range.In this case, the matching circuit 70 can be configured to decrease the DT voltage so that the duty cycle of the driver signals increases, and to decrease the VCO voltage so that the switching frequency of the driver signals decreases towards a switch from the first command signal (OFF signal) to the second command signal (ON signal).

[0100] Some or all of the embodiments and variations described above can also be specified as follows. However, the embodiments and variations described above are not limited to the following. <1> Control circuit for an LLC resonant converter circuit, wherein the control circuit is configured to regulate a switching frequency to a frequency of at least one resonant frequency of a series resonant circuit, wherein the LLC resonant converter circuit comprises: the series resonant circuit; a driver circuit connected to the series resonant circuit causing each of several switching elements to perform a switching operation based on a driver signal; a transformer in which a resonant coil, which is part of the series resonant circuit, serves as the primary winding; and a rectifier circuit that rectifies and smooths alternating current generated by a secondary winding of the transformer, wherein the control circuit comprises: a driver control circuit which has a frequency control terminal and a duty cycle control terminal and outputs driver signals to the driver circuit with a switching frequency corresponding to a voltage level at the frequency control terminal and a duty cycle corresponding to a voltage level at the duty cycle control terminal; a detection circuit that detects an output voltage of the LLC resonant converter circuit and stabilizes the output voltage at a set voltage level, a voltage divider circuit that divides an input voltage from a power supply terminal and applies the divider voltage as a duty cycle control voltage to the duty cycle control terminal, and an matching circuit connected to the voltage divider circuit and the detection circuit is set up to adjust the duty cycle control voltage, and a frequency control voltage applied to the frequency control terminal is set up to adjust depending on the input voltage and the output voltage detected by the detection circuit; wherein wherein the matching circuit changes the duty cycle control voltage in such a way that the duty cycle of the driver signals increases, and changes the frequency control voltage in such a way that the switching frequency of the driver signals decreases, in order to switch from a first command signal to a second command signal. <2> Control circuit for the LLC resonant converter circuit according to <1> , wherein, upon input of the first command signal, the matching circuit sets the duty cycle control voltage to a voltage level corresponding to a lower limit of the duty cycle, and sets the frequency control voltage to a voltage level corresponding to a predetermined frequency higher than the resonant frequency. <3> Control circuit for the LLC resonant converter circuit according to <2> , the detection circuit has the following features: an output adjustment circuit designed to variably adjust the voltage level of the output voltage of the LLC resonant converter circuit, and a stabilization circuit that stabilizes the output voltage of the LLC resonant converter circuit by comparing a divided voltage of the detected output voltage with a reference voltage to the voltage level set by the output adjustment circuit, and wherein the matching circuit, in a state where the second command signal is input, suppresses a change in the frequency control voltage if the divider voltage is about to exceed the reference voltage. <4> Control circuit for the LLC resonant converter circuit according to <3> , The matching circuit is set up such that the first change time of the duty cycle control voltage after switching from the first command signal to the second command signal is shorter than the second change time of the frequency control voltage after switching. The first change time is the time required to change the duty cycle control voltage from a voltage level corresponding to the lower limit of the duty cycle to a voltage level corresponding to the upper limit of the duty cycle. The second change time is a period of time from the moment the frequency control voltage changes from the voltage level corresponding to the predetermined high frequency until the frequency control voltage is suppressed. <5> Control circuit for the adaptation circuit according to <3> or <4> , the matching circuit has the following features: a first light-emitting diode in which a current flowing through it increases when the divider voltage is about to exceed the reference voltage, a first phototransistor, which together with the first light-emitting diode forms a first photocoupler, a rectifier diode and a first resistor element, which are provided in series in a branch line that branches off from an output line of the duty cycle control voltage, which leads from the voltage divider circuit to the duty cycle control terminal and is connected to a ground line, a second resistor element and a second light-emitting diode, connected in parallel to the voltage divider circuit in a line extending from the power supply terminal to the ground line, and a second phototransistor, which together with the second light-emitting diode forms a second photocoupler, wherein a line in which the second light-emitting diode and the second resistor element are provided in series is connected to the branch line on the cathode side of the second light-emitting diode, the second phototransistor is provided in a line that extends from the frequency control terminal and leads to the ground line. an emitter terminal of the first phototransistor is connected to the ground line, and a photocoupler output line extending from a collector terminal of the first phototransistor is connected to a node in the branch line between a cathode of the rectifier diode and the first resistive element. <6> Control circuit for the LLC resonant converter circuit according to <5> , wherein the matching circuit further comprises a switching element in which an emitter terminal is connected to a ground line, a collector terminal is connected to the photocoupler output line, and the switching element assumes an ON state upon input of the first command signal and an OFF state upon input of the second command signal, and When the switching element is in the ON state, the photocoupler output line and one cathode side of the rectifier diode drop to a ground level, so that the duty cycle control voltage applied to the duty cycle control terminal assumes a voltage level corresponding to the lower limit of the duty cycle. <7> LLC resonant converter circuit, which features the following: the control circuit according to one of <1> until <6> , the series resonant circuit, the driver circuit, the transformer, and the rectifier circuit. <8> Control method for an LLC resonant converter circuit that has the following features: a series resonant circuit, a driver circuit connected to the series resonant circuit that causes each of several switching elements to perform a switching operation based on a driver signal, a transformer in which a resonant coil, which is part of the series resonant circuit, serves as the primary winding, A rectifier circuit that rectifies and smooths alternating current generated by a secondary winding of the transformer. a driver control circuit which has a frequency control terminal and a duty cycle control terminal and outputs driver signals to the driver circuit with a switching frequency corresponding to a voltage level at the frequency control terminal and a duty cycle corresponding to a voltage level at the duty cycle control terminal; a detection circuit that detects an output voltage of the rectifier circuit and stabilizes the output voltage at a set voltage level, a voltage divider circuit that divides an input voltage from a power supply terminal and applies the divider voltage as a duty cycle control voltage to the duty cycle control terminal, and A matching circuit connected to the voltage divider circuit and the sensing circuit is provided to adjust the duty cycle control voltage, and a frequency control voltage applied to the frequency control terminal is adjusted depending on the input current and the output voltage detected by the sensing circuit; the method comprises the following: switching from a first command signal to a second command signal, changing the duty cycle control voltage so that the duty cycle of the driver signals increases, and changing the frequency control voltage so that the switching frequency of the driver signals decreases. <9> Control procedure for the LLC resonant converter circuit according to <8> , which further exhibits the following: Upon input of an initial command signal, the duty cycle control voltage is set to a voltage level corresponding to a lower limit of the duty cycle, and the frequency control voltage is set to a voltage level corresponding to a predetermined frequency higher than a resonant frequency of the series resonant circuit. <10> Control procedure for an LLC resonant converter circuit according to <9> , wherein the detection circuit comprises: an output setting circuit configured to variably adjust a voltage level of an output voltage of the LLC resonant converter circuit, and a stabilization circuit configured to stabilize the output voltage of the LLC resonant converter circuit to the voltage level set by the output setting circuit based on a comparison between a divided voltage of the detected output voltage and a reference voltage, and wherein the method further comprises: In a state where the second command signal is entered, suppressing a change in the frequency control voltage when the divider voltage is about to exceed the reference voltage. <11> Control method for an LLC resonant converter circuit according to <10> , where where the first change time of the duty cycle control voltage after switching from the first command signal to the second command signal is shorter than the second change time of the frequency control voltage after switching. The first change time is the time required to change the duty cycle control voltage from a voltage level corresponding to the lower limit of the duty cycle to a voltage level corresponding to the upper limit of the duty cycle. The second change time is a period of time from the moment the frequency control voltage changes from the voltage level corresponding to the predetermined high frequency until the frequency control voltage is suppressed. REFERENCE MARK LIST 1 LLC resonant converter circuit (converter circuit) 3 Transformer 10 Primary-side circuit 11 Series Resonant Circuit 13 Driver circuit 20 Secondary-side circuit 21 Rectifier circuit 30 Control circuit 40 Detection circuit 50 driver control circuit 60 Voltage divider circuit 70 Adaptive circuit VR1, VR2 Variable Resistance IC shunt regulator PC1, PC2 photocoupler QS, Q11, Q12 Switching element (transistor) NT NOT circuit HD1, HD2 Light-emitting diode PQ1, PQ2 Phototransistor 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]

Claims

[1] Control circuit for an LLC resonant converter circuit, wherein the LLC resonant converter circuit comprises the following: a series resonant circuit; a driver circuit connected to the series resonant circuit that causes each of several switching elements to perform a switching operation based on a driver signal; a transformer in which a resonant coil, which is part of the series resonant circuit, serves as the primary winding; and a rectifier circuit that rectifies and smooths alternating current generated in a secondary winding of the transformer, wherein the control circuit is configured to regulate a switching frequency of the LLC resonant converter circuit to a frequency of at least one resonant frequency of the series resonant circuit, the control circuit further comprises the following: a driver control circuit which has a frequency control terminal and a duty cycle control terminal and outputs driver signals to the driver circuit with a switching frequency corresponding to a voltage level at the frequency control terminal and a duty cycle corresponding to a voltage level at the duty cycle control terminal; a detection circuit that detects an output voltage of the LLC resonant converter circuit and stabilizes the output voltage at a set voltage level; a voltage divider circuit that divides an input voltage from a power supply terminal and applies the divider voltage as a duty cycle control voltage to the duty cycle control terminal; and an matching circuit connected to the voltage divider circuit and the detection circuit is set up to adjust the duty cycle control voltage, and a frequency control voltage applied to the frequency control terminal is set up to adjust depending on the input voltage and the output voltage detected by the detection circuit; wherein the matching circuit changes the duty cycle control voltage in such a way that the duty cycle of the driver signals increases, and changes the frequency control voltage in such a way that the switching frequency of the driver signals decreases, in order to switch from a first command signal to a second command signal. [2] Control circuit for the LLC resonant converter circuit according to claim 1, wherein, upon input of the first command signal, the matching circuit sets the duty cycle control voltage to a voltage level corresponding to a lower limit of the duty cycle and sets the frequency control voltage to a voltage level corresponding to a predetermined frequency higher than the resonant frequency. [3] Control circuit for the LLC resonant converter circuit according to claim 2, wherein the detection circuit comprises the following: an output adjustment circuit designed to variably adjust the voltage level of the output voltage of the LLC resonant converter circuit, and a stabilization circuit that stabilizes the output voltage of the LLC resonant converter circuit by comparing a divided voltage of the detected output voltage with a reference voltage to the voltage level set by the output adjustment circuit, and wherein the matching circuit, in a state where the second command signal is input, suppresses a change in the frequency control voltage if the divider voltage is about to exceed the reference voltage. [4] Control circuit for the LLC resonant converter circuit according to claim 3, The matching circuit is set up such that the first change time of the duty cycle control voltage after switching from the first command signal to the second command signal is shorter than the second change time of the frequency control voltage after switching. The first change time is the time required to change the duty cycle control voltage from a voltage level corresponding to the lower limit of the duty cycle to a voltage level corresponding to the upper limit of the duty cycle. The second change time is a period of time from the moment the frequency control voltage changes from the voltage level corresponding to the predetermined high frequency until the frequency control voltage is suppressed. [5] Control circuit for the LLC resonant converter circuit according to claim 3 or 4, wherein the matching circuit comprises: a first light-emitting diode in which a current flowing through it increases when the divider voltage is about to exceed the reference voltage, a first phototransistor, which together with the first light-emitting diode forms a first photocoupler, a rectifier diode and a first resistor element, which are provided in series in a branch line that branches off from an output line of the duty cycle control voltage, which leads from the voltage divider circuit to the duty cycle control terminal and is connected to a ground line, a second resistor element and a second light-emitting diode, connected in parallel to the voltage divider circuit in a line extending from the power supply terminal to the ground line, and a second phototransistor, which together with the second light-emitting diode forms a second photocoupler, wherein a line in which the second light-emitting diode and the second resistor element are provided in series is connected to the branch line on the cathode side of the second light-emitting diode, the second phototransistor is provided in a line that extends from the frequency control terminal and leads to the ground line. an emitter terminal of the first phototransistor is connected to the ground line, and a photocoupler output line extending from a collector terminal of the first phototransistor is connected to a node in the branch line between a cathode of the rectifier diode and the first resistive element. [6] Control circuit for the LLC resonant converter circuit according to claim 5, wherein the matching circuit further comprises a switching element in which an emitter terminal is connected to a ground line, a collector terminal is connected to the photocoupler output line, and the switching element assumes an ON state upon input of the first command signal and an OFF state upon input of the second command signal, and When the switching element is in the ON state, the photocoupler output line and one cathode side of the rectifier diode drop to a ground level, so that the duty cycle control voltage applied to the duty cycle control terminal assumes a voltage level corresponding to the lower limit of the duty cycle. [7] LLC resonant converter circuit, comprising: the control circuit according to one of claims 1 to 6; the series resonant circuit; the driver circuit; the transformer; and the rectifier circuit. [8] Control procedure for an LLC resonant converter circuit which has the following features: a series resonant circuit, a driver circuit connected to the series resonant circuit that causes each of several switching elements to perform a switching operation based on a driver signal, a transformer in which a resonant coil, which is part of the series resonant circuit, serves as the primary winding, A rectifier circuit that rectifies and smooths alternating current generated by a secondary winding of the transformer. a driver control circuit which has a frequency control terminal and a duty cycle control terminal and outputs driver signals to the driver circuit with a switching frequency corresponding to a voltage level at the frequency control terminal and a duty cycle corresponding to a voltage level at the duty cycle control terminal; a detection circuit that detects an output voltage of the rectifier circuit and stabilizes the output voltage at a set voltage level, a voltage divider circuit that divides an input voltage from a power supply terminal and applies the divider voltage as a duty cycle control voltage to the duty cycle control terminal, and a matching circuit connected to the voltage divider circuit and the sensing circuit is configured to adjust the duty cycle control voltage, and a frequency control voltage applied to the frequency control terminal is configured to adjust depending on the input current and output voltage detected by the sensing circuit; the method comprising: switching from a first command signal to a second command signal, changing the duty cycle control voltage so that the duty cycle of the driver signals increases, and changing the frequency control voltage so that the switching frequency of the driver signals decreases. [9] Control method for the LLC resonant converter circuit according to claim 8, further comprising: Upon input of an initial command signal, the duty cycle control voltage is set to a voltage level corresponding to a lower limit of the duty cycle, and the frequency control voltage is set to a voltage level corresponding to a predetermined frequency higher than a resonant frequency of the series resonant circuit. [10] Control method for an LLC resonant converter circuit according to claim 9, wherein the detection circuit comprises: an output adjustment circuit designed to variably adjust the voltage level of an output voltage of the LLC resonant converter circuit, and a stabilization circuit configured to stabilize the output voltage of the LLC resonant converter circuit based on a comparison between a divided voltage of the detected output voltage and a reference voltage to the voltage level set by the output setting circuit, and wherein the method further comprises: In a state where the second command signal is entered, suppressing a change in the frequency control voltage when the divider voltage is about to exceed the reference voltage. [11] Control method for an LLC resonant converter circuit according to claim 10, where the first change time of the duty cycle control voltage after switching from the first command signal to the second command signal is shorter than the second change time of the frequency control voltage after switching. The first change time is the time required to change the duty cycle control voltage from a voltage level corresponding to the lower limit of the duty cycle to a voltage level corresponding to the upper limit of the duty cycle. The second change time is a period of time from the moment the frequency control voltage changes from the voltage level corresponding to the predetermined high frequency until the change is suppressed.

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