Control circuit and control method of LLC resonant converter circuit

Abstract

A control circuit (30) of an LLC resonant converter circuit includes: a drive control circuit (50) that outputs a drive signal indicating a switching frequency corresponding to a voltage level of a frequency control terminal and a duty ratio corresponding to a voltage level of a duty ratio control terminal to a drive circuit; a detection circuit (40) that detects an output voltage from the LLC resonant converter circuit; a voltage division circuit (60) that divides an input voltage and applies the divided input voltage to the duty control terminal as a duty control voltage; and an adjustment circuit (70) that is connected to the voltage division circuit and the detection circuit, can adjust the duty control voltage and the frequency control voltage, and varies the duty control voltage so as to increase the duty indicated by the drive signal in response to switching from the input of the first instruction signal to the input of the second instruction signal. The frequency control voltage is varied so that the switching frequency indicated by the drive signal is reduced.

Description

Technical Field

[0001] This invention relates to LLC resonant converter circuits. Background Technology

[0002] In LLC resonant converter circuits, frequency control is performed using a feedback signal corresponding to the output power from the secondary side circuit. For example, Patent Document 1 discloses a current resonant converter device comprising: a DC power supply; a converter transformer; a rectifier smoothing circuit connected to a series circuit of first and second switching elements, a primary winding of the converter transformer, a series circuit of a resonant capacitor, and a secondary winding of the converter transformer, for rectifying and smoothing the power obtained in the secondary winding and supplying it to the load; a converter control circuit that controls the on / off frequency of the first and second switching elements; an operational amplifier that detects and amplifies the load voltage supplied to the load; and an optocoupler unit that detects changes in the output voltage of the operational amplifier and feeds them back to the converter control circuit. Furthermore, this device adjusts the gain of the operational amplifier based on the detection output of a load current detection circuit that detects the load current flowing through the load, thereby stabilizing the gain characteristics from light load to heavy load and preventing abnormal oscillations caused by gain increases under heavy load conditions.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-39975 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] It is known that when deviating from the intended resonance conditions in an LLC resonant converter circuit, a follow-through current based on the recovery current of the body diode of the switching element is generated, leading to increased switching losses and damage to the switching element. This is called resonance deviation. To prevent this resonance deviation, the switching frequency is controlled above the resonant frequency, ensuring that the switching frequency (operating frequency) of the switching element is not lower than the resonant frequency.

[0008] Figure 3 This is a graph showing the output characteristics of a typical LLC resonant converter circuit.

[0009] exist Figure 3 In the example, the operating frequency is controlled within a frequency range from the lower limit frequency fmin, which is higher than the resonant frequency, to the upper limit frequency fmax.

[0010] However, in typical LLC resonant converter circuits, such as Figure 3As shown, no matter how much the operating frequency is increased, it is difficult to make the converter output fall below a certain level.

[0011] This invention was made in view of the following problem: to provide a control technique for an LLC resonant converter circuit that enables the output voltage to be continuously variable over a wide range.

[0012] Methods for solving problems

[0013] According to the present invention, a control circuit for an LLC resonant converter circuit is provided. This control circuit controls the switching frequency of the LLC resonant converter circuit at a frequency higher than the resonant frequency of the series resonant circuit. The LLC resonant converter circuit includes the series resonant circuit, a drive circuit, a transformer, and a rectifier circuit. The drive circuit is connected to the series resonant circuit and causes multiple switching elements to switch according to a drive signal. The transformer uses the resonant coil constituting the series resonant circuit as its primary winding. The rectifier circuit rectifies and smooths the AC power generated in the secondary winding of the transformer. The control circuit includes a drive control circuit comprising a frequency control terminal and a duty cycle control terminal, which transmits a drive signal representing the switching frequency corresponding to the voltage level of the frequency control terminal and the duty cycle corresponding to the voltage level of the duty cycle control terminal to the series resonant converter circuit. The drive circuit outputs; a detection circuit that detects the output voltage from the LLC resonant converter circuit and stabilizes the output voltage to a set voltage level; a voltage divider circuit that divides the input voltage from the control power supply terminal and applies it as a duty cycle control voltage to the duty cycle control terminal; and an adjustment circuit connected to the voltage divider circuit and the detection circuit, capable of adjusting the duty cycle control voltage and adjusting the frequency control voltage applied to the frequency control terminal according to the input voltage and the output voltage detected by the detection circuit. The adjustment circuit changes the duty cycle control voltage to increase the duty cycle represented by the drive signal and changes the frequency control voltage to decrease the switching frequency represented by the drive signal according to the switching from the input of the first indication signal to the input of the second indication signal.

[0014] Furthermore, according to the present invention, a control method for an LLC resonant converter circuit can also be provided, the LLC resonant converter circuit comprising: a series resonant circuit; a drive circuit connected to the series resonant circuit, which causes multiple switching elements to switch according to a drive signal; a transformer, which uses the resonant coil constituting the series resonant circuit as a primary winding; a rectifier circuit, which rectifies and smooths the AC power generated in the secondary winding of the transformer; a drive control circuit including a frequency control terminal and a duty cycle control terminal, which outputs a drive signal representing a switching frequency corresponding to the voltage level of the frequency control terminal and a duty cycle corresponding to the voltage level of the duty cycle control terminal to the drive circuit; and a detection circuit that detects signals from the rectifier circuit. The system includes: an output voltage and a detection circuit that stabilizes the output voltage to a set voltage level; a voltage divider circuit that divides the voltage of the input power from the control power supply terminal and applies it as a duty cycle control voltage to the duty cycle control terminal; and an adjustment circuit connected to the voltage divider circuit and the detection circuit, capable of adjusting the duty cycle control voltage and adjusting the frequency control voltage applied to the frequency control terminal according to the input power and the output voltage detected by the detection circuit. The control method causes the duty cycle control voltage to change to increase the duty cycle of the drive signal and causes the frequency control voltage to change to decrease the switching frequency of the drive signal based on a switching from the input of a first indication signal to the input of a second indication signal.

[0015] Invention Effects

[0016] Based on the above method, a control technology can be provided for LLC resonant converter circuits that allow the output voltage to be continuously variable over a wide range. Attached Figure Description

[0017] Figure 1 This is a circuit diagram of the LLC resonant converter circuit (converter circuit) according to the implementation method.

[0018] Figure 2 It is a conceptual diagram showing the time-dependent voltage changes at points A, B, C, and D in the adjustment circuit, as well as the curve of the drive signal at point E.

[0019] Figure 3 This is a graph showing the output characteristics of a typical LLC resonant converter circuit. Detailed Implementation

[0020] The embodiments of the present invention will now be described. Furthermore, the embodiments listed below are illustrative, and the present invention is not limited to the structures of these embodiments.

[0021] (Circuit structure)

[0022] Figure 1 This is a circuit diagram of the LLC resonant converter circuit (hereinafter, sometimes simply referred to as the converter circuit) 1 according to the implementation method.

[0023] The converter circuit 1 has at least a primary side circuit 10 connected to a DC power supply and including a series resonant circuit 11, a transformer 3, a secondary side circuit 20 that receives AC power from the primary side circuit 10 via the transformer 3, and a control circuit 30.

[0024] The primary circuit 10 includes a series resonant circuit 11, switching elements Q11 and Q12, a drive circuit 13, a capacitor C10, an input capacitor C11, etc.

[0025] The primary circuit 10 is connected to an external DC power supply via an input terminal (DCVin).

[0026] The series resonant circuit 11 is formed by the primary coil Np of the transformer 3 and the resonant capacitor Cr connected in series. Therefore, the primary coil Np can also be referred to as the resonant coil.

[0027] Switching elements Q11 and Q12 are controlled by drive circuit 13 to perform switching operations. By switching elements Q11 and Q12, the direction of the current flowing in the resonant coil (primary coil Np) of the series resonant circuit 11 is switched.

[0028] Switching elements Q11 and Q12 utilize, for example, a FET (Field Effect Transistor). Figure 1 The diagram illustrates an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Therefore, the switching elements Q11 and Q12 are sometimes referred to as transistors Q11 and Q12.

[0029] 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 from the ground terminal (GND).

[0030] Thus, in Figure 1 The example shows switching elements Q11 and Q12 connected in a half-bridge configuration, but it can also be replaced by two or more switching elements connected in a full-bridge configuration.

[0031] The drive circuit 13 is connected to transistors Q11 and Q12 in a manner that allows the application of gate-source voltages (hereinafter sometimes referred to as VGS voltages) to transistors Q11 and Q12.

[0032] The drive circuit 13 alternately applies a VGS voltage exceeding the threshold voltage to transistors Q11 and Q12, causing the on / off states of transistors Q11 and Q12 to switch alternately (perform a switching action). At this time, the drive circuit 13 switches the on / off states of transistors Q11 and Q12 according to the pulse period and duty cycle of the drive signals (VCOoutCH1 and VCOoutCH2) from the drive control circuit 50.

[0033] The series resonant circuit 11 is connected to the source of transistor Q11 and is disposed between the drain and source of transistor Q12. Thus, when transistor Q11 is in the on state and transistor Q12 is in the off state, the load current can flow to the drain and source of transistor Q11, the primary winding Np, and the resonant capacitor Cr. Conversely, when transistor Q11 is in the off state and transistor Q12 is in the on state, the load current can flow to the resonant capacitor Cr, the primary winding Np, and the drain and source of transistor Q12 through the power stored in the resonant capacitor Cr.

[0034] In this way, the direction of the current flowing in the primary coil Np is switched by the switching action of transistors Q11 and Q12.

[0035] Capacitor C10 absorbs voltage changes in the DC power supply connected between the input terminal (DCVin) and the ground terminal (GND).

[0036] The input capacitor C11 is connected to the drain of transistor Q1 and the source of transistor Q2, that is, it is connected in parallel with transistors Q11 and Q12 to smooth the input voltage.

[0037] Transformer 3 consists of a primary winding Np and a secondary winding Ns that are electrically insulated from each other, as well as an iron core, allowing the primary winding Np and the secondary winding Ns to be magnetically coupled. Figure 1 In this diagram, there are no parasitic elements such as the magnetizing inductance (Lm) and leakage inductance (Lr) of transformer 3, the output capacitors in switching elements Q11 and Q12 described later, or parasitic diodes.

[0038] The secondary circuit 20 includes output terminals (VOUT+) and (VOUT-) from which DC power is output. There are no particular restrictions on how the output DC power is utilized. Loads of various characteristics can be connected to these output terminals.

[0039] The secondary circuit 20 also includes a secondary winding Ns, which serves as the secondary winding of the transformer 3, and a rectifier circuit 21 connected to the secondary winding Ns to rectify and smooth the AC power generated in the secondary winding Ns. The rectifier circuit 21 includes a bridge rectifier circuit composed of rectifier diodes D21, D22, D23, and D24, and a capacitor C20. The AC power generated in the secondary winding Ns is converted into DC power through half-wave rectification based on the bridge rectifier circuit and smoothing based on the output capacitor C20.

[0040] The control circuit 30 can control the switching frequency of switching elements Q11 and Q12 at a frequency higher than the resonant frequency of the series resonant circuit 11, and can also control the duty cycle of the switching operation of switching elements Q11 and Q12. That is, the control circuit 30 can perform PFM (Pulse Frequency Modulation) control and PWM (Pulse Width Modulation) control, thereby making the output voltage from the converter circuit 1 (secondary side circuit 20) continuously variable over a wide range.

[0041] Here, "wide range" refers to the voltage range that includes the low output region of the converter output, which is difficult to achieve in an LLC resonant converter circuit by frequency control in a frequency band higher than the resonant frequency alone, and the high output region that can be achieved by frequency control alone.

[0042] More specifically, the control circuit 30 adjusts the voltage level starting from a predetermined lower limit voltage level within a predetermined low voltage region, stabilizing it at a set voltage level. This set voltage level is set to a level higher than the predetermined low voltage region. In this embodiment, an example is shown where the predetermined lower limit voltage level is set to zero, and the control circuit 30 adjusts the output voltage from the converter circuit 1 from zero to stabilize it at the predetermined set voltage level. However, the predetermined lower limit voltage level is not limited to zero; it can be set to a voltage level within the predetermined low voltage region.

[0043] The "specified low voltage region" here refers to the low output region of an LLC resonant converter circuit that is difficult to achieve solely through frequency control in a frequency band higher than the resonant frequency; it is a voltage region including zero. In an LLC resonant converter circuit operating under typical design conditions with an output power of 500 watts (W) or more, which are not impractical design conditions such as significantly poor efficiency or circuit component losses, this specified low voltage region is, for example, a range of 0 (V) or higher and 5 (V) or lower.

[0044] The control circuit 30 includes a detection circuit 40, a drive control circuit 50, a voltage divider circuit 60, an adjustment circuit 70, and an input terminal block CN, etc.

[0045] exist Figure 1 In the example, the input terminal block CN includes control power terminals (terminals 1 and 2), indicator signal terminals (terminal 3), and ground terminals (terminals 4, 5, and 6).

[0046] The voltage supplied by the control power supply is input to the control power supply terminal, and a disconnect signal (equivalent to the first indicator signal) or a connect signal (equivalent to the second indicator signal) is input to the indicator signal terminal. A grounding wire is connected to the grounding terminal.

[0047] The drive control circuit 50 includes a frequency control terminal (VCOin terminal), a duty cycle control terminal (DTin terminal), and output terminals for dual-channel drive signals (VCOoutCH1 terminal, VCOoutCH2 terminal). It outputs drive signals to the drive circuit 13, representing the switching frequency corresponding to the voltage level of the frequency control terminal and the duty cycle corresponding to the voltage level of the duty cycle control terminal. Hereinafter, the voltage applied to the frequency control terminal will sometimes be referred to as the frequency control voltage or VCO voltage, and the voltage applied to the duty cycle control terminal will be referred to as the duty cycle control voltage or DT voltage.

[0048] exist Figure 1 In the example, the drive control circuit 50 is configured such that: the higher the VCO voltage is within the specified range, the lower the pulse frequency of the output drive signal; the lower the VCO voltage is within the specified range, the higher the pulse frequency of the output drive signal; the higher the DT voltage is within the specified range, the higher the duty cycle of the output drive signal; and the lower the DT voltage is within the specified range, the lower the duty cycle of the output drive signal.

[0049] The drive control circuit 50 includes a frequency control terminal (VCOin terminal), a duty cycle control terminal (DTin terminal), and output terminals for drive signals with two or more channels. As long as the pulse frequency and duty cycle of the drive signal can be controlled as described above, its specific structure is not limited.

[0050] Voltage divider circuit 60 divides the input voltage from the control power supply terminal of input terminal block CN and applies it as the duty cycle control voltage (DT voltage) to the duty cycle control terminal (DTin terminal) of drive control circuit 50.

[0051] exist Figure 1In this example, the voltage divider circuit 60 consists of resistors R8 and R9 connected in series between the control power supply terminal and the ground terminal, and a variable resistor VR2. A line connecting resistors R8 and R9 is connected to the duty cycle control terminal of the drive control circuit 50. Thus, the voltage input from the control power supply terminal is divided according to the ratio of the resistance of resistor R8 to the combined resistance of resistors R8, R9, and the variable resistor VR2, and then applied to the duty cycle control terminal.

[0052] 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 variable resistor VR2, which corresponds to the upper limit of the duty cycle (duty cycle upper limit value) controlled by drive control circuit 50. That is, voltage divider circuit 60 determines the upper limit level of the DT voltage corresponding to the upper limit value of the duty cycle (maximum duty cycle).

[0053] The detection circuit 40 detects the output voltage from the secondary side circuit 20 and stabilizes the output voltage to a set voltage level. Figure 1 In the example, the detection circuit 40 includes capacitors Cd and Cf, resistive elements R41, R42, R43, R44, R45, R46 and R47, a variable resistor VR1, a shunt regulator IC, etc.

[0054] A capacitor Cd, resistors R41 and R42 are connected in series between the output terminals (VOUT+) and (VOUT-) of the secondary circuit 20. The series connection lines of resistors R43, variable resistor VR1, and resistor R44, and the series connection lines of resistors R46, R47, and the shunt regulator IC are connected in parallel with capacitor Cd. Furthermore, a branch line from the connection line between resistor R47 and the cathode of the shunt regulator IC connects to the slider terminal (the terminal connected to the slider) of variable resistor VR1 via the series-connected capacitor Cf and resistor R45. Additionally, a line extending from the reference terminal of the shunt regulator IC connects to the connection line between resistor R45 and the slider terminal of variable resistor VR1.

[0055] The variable resistor VR1 is provided to adjust the set voltage level of the output voltage (the voltage between the output terminals (VOUT+) and (VOUT-)) from the secondary circuit 20 in a voltage region higher than the specified low voltage region. Since the voltage applied to the slider of the variable resistor VR1 is controlled as a reference voltage by the shunt regulator IC, the output voltage is set according to the resistance ratio of the resistor elements R43 and R44 and the variable resistor VR1 corresponding to the position of the slider. Thus, the output voltage of the converter circuit 1 can be variably set. That is, the resistor elements R43 and R44 and the variable resistor VR1 can be described as an output variable circuit capable of variably setting the voltage level of the output voltage from the converter circuit 1, and the level of the output voltage set by this output variable circuit is described as the set voltage level.

[0056] As described above, in the detection circuit 40, the output voltage from the secondary side circuit 20 is detected across the capacitor Cd. This detected output voltage is divided by resistors R43 and R44 and the variable resistor VR1 corresponding to the position of the slider, and applied to the reference terminal of the shunt regulator IC. The divided voltage is controlled to a reference voltage (e.g., 2.5V). Therefore, the circuit including the shunt regulator IC, resistors R46 and R47, etc., can be described as a stabilization circuit. This stabilization circuit stabilizes the output voltage from the converter circuit 1 to a set voltage level by comparing the divided voltage of the detected output voltage with the reference voltage.

[0057] The adjustment circuit 70 is connected to the voltage divider circuit 60 and the detection circuit 40. It can adjust the DT voltage applied to the duty cycle control terminal (DTin terminal) and adjust the VCO voltage applied to the frequency control terminal (VCOin terminal) according to the input voltage from the control power supply terminal and the output voltage detected by the detection circuit 40.

[0058] exist Figure 1 In the example, the adjustment circuit 70 includes optocouplers PC1 and PC2, switching element QS, rectifier diode D1, capacitor Cs, and resistors R1, R2, R3, R4, R5, and R6.

[0059] The primary and secondary sides of an optocoupler are electrically isolated, and it consists of a light-emitting diode (LED) on the primary side and a phototransistor on the secondary side. Optocoupler PC1 consists of an LED HD1 on the primary side and a phototransistor PQ1 on the secondary side, while optocoupler PC2 consists of an LED HD2 on the primary side and a phototransistor PQ2 on the secondary side.

[0060] Optocouplers PC1 and PC2 are turned on (the primary-side LEDs HD1 and HD2 emit light) by being supplied with an input voltage exceeding the non-emitting forward voltage. In the on-state, the output impedances of the secondary-side phototransistors PQ1 and PQ2 can be increased or decreased according to the increase or decrease of the current flowing in the primary-side LEDs HD1 and HD2. In the following description, the current flowing in the primary-side LEDs of the optocoupler will sometimes be referred to as the diode current of the optocoupler.

[0061] The LED HD1 of the optocoupler PC1 is connected in parallel with the resistor R47. That is, the anode of the LED HD1 is connected to the connection line of the resistors R46 and R47, and the cathode is connected to the connection point of the resistor R47, the cathode of the shunt regulator IC, and the capacitor Cf.

[0062] The collector terminal of the phototransistor PQ1 of the optocoupler PC1 is connected to the cathode of the rectifier diode D1 and the connecting line of the resistor element R3 (equivalent to the output line of the optocoupler), and the emitter terminal is connected to the ground wire.

[0063] The optocoupler PC2 consists of an LED HD2, resistor R4, and resistor R5 connected in series on a line extending from the control power terminal and connected to the ground wire. The cathode of LED HD2 is connected to resistor R4, and the anode is connected to resistor R5. Furthermore, the series-connected LED HD2, resistor R4, and resistor R5 are connected in parallel with the voltage divider circuit 60.

[0064] A rectifier diode D1 and a resistor R3 are connected in series on a branch line that branches off from the output line of the self-dividing circuit 60 to the duty cycle control terminal DT voltage. This branch line is connected to the cathode of the light-emitting diode HD2 and the connection line of the resistor R4. The cathode of the rectifier diode D1 is connected to the resistor R3, and the cathode of the light-emitting diode HD2 is connected to the connection line of the resistors R3 and R4.

[0065] In addition, a capacitor Cs is placed between the duty cycle control terminal and the ground wire. The capacitor Cs is used to achieve soft start of the PFM control and PWM control of the control circuit 30.

[0066] In optocoupler PC2, phototransistor PQ2 and resistor R6 are connected in series on a line extending from the frequency control terminal and connected to the ground wire. The collector terminal of phototransistor PQ2 is connected to the frequency control terminal via resistor R6, and the emitter terminal is connected to the ground wire. Additionally, a branch line from the connection between the collector terminal of phototransistor PQ2 and resistor R6 is connected to the ground wire via resistor R7.

[0067] The switching element QS is switched on or off based on the indication signal input from the indication signal terminal (terminal 3). The collector terminal of the switching element QS is connected to a line extending from the collector terminal of the phototransistor PQ1 (optocoupler output line), and the emitter terminal is connected to the ground line. The gate terminal of the switching element QS is connected to the ground line via resistor R1, and on the other hand, it is connected to the indication signal terminal (terminal 3) via resistor R2 and the NOT circuit NT.

[0068] Switching element QS, for example, utilizes FET (Field Effect Transistor). Switching element QS is sometimes also referred to as transistor QS.

[0069] exist Figure 1 In the example, when a cutoff signal is input from the indicator signal terminal, the cutoff signal is inverted by the NOT circuit NT and input to the gate terminal, thereby turning on the transistor QS. Conversely, when a turn-on signal is input from the indicator signal terminal, the turn-on signal is inverted by the NOT circuit NT and input to the gate terminal, thereby turning on the transistor QS.

[0070] When transistor QS is turned on, the line extending from the collector terminal of phototransistor PQ1 (the optocoupler output line) and the cathode side of rectifier diode D1 falls back to ground level. As a result, as described later, the voltage DT applied to the duty cycle control terminal becomes the voltage level corresponding to the lower limit of the duty cycle.

[0071] Here, "duty cycle lower limit value" refers to a value of zero or more of the duty cycle that enables the output voltage from converter circuit 1 (secondary side circuit 20) to reach a specified lower limit voltage level. In this embodiment, an example of a duty cycle lower limit value of zero is shown.

[0072] In addition, capacitors C1 and C2 are provided in the control circuit 30.

[0073] Capacitors C1 and C2 are connected in parallel between the line connected to the control power supply terminals (terminals 1 and 2) and the grounding line connected to the grounding terminals (terminals 4, 5, and 6) to smooth the input voltage from the control power supply terminals.

[0074] (action)

[0075] The converter circuit 1 with this circuit structure operates as follows.

[0076] The drive circuit 13 switches the on / off states of transistors Q11 and Q12 according to the pulse period and duty cycle of the drive signal from the drive control circuit 50. Specifically, the drive circuit 13 switches the on / off state of transistor Q11 according to the drive signal output from the VCOoutCH1 terminal of the drive control circuit 50, and switches the on / off state of transistor Q12 according to the drive signal output from the VCOoutCH2 terminal of the drive control circuit 50.

[0077] This reverses the direction of the current flowing in the primary winding Np of transformer 3. When transistor Q11 is on and transistor Q12 is off, the load current flows through the path of transistor Q11 between its drain and source, through the primary winding 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 flows in the opposite direction through the charging power applied to the resonant capacitor Cr, through the path of transistor Q12 between its drain and source, through the resonant capacitor Cr, and through the primary winding Np.

[0078] In the primary circuit 10, the switching action of transistors Q11 and Q12 induces a resonant current in the series resonant circuit 11, generating AC power in the secondary coil Ns of transformer 3. In the secondary circuit 20, the AC power generated by the secondary coil Ns is rectified and smoothed in the rectifier circuit 21, converting it into DC power for output.

[0079] The detection circuit 40 detects the output voltage from the secondary side circuit 20 and stabilizes the output voltage to a set voltage level. Specifically, the output voltage from the secondary side circuit 20 is detected across the capacitor Cd. This detected output voltage is divided by the resistors R43 and R44 and the variable resistor VR1 corresponding to the position of the slider, and then applied to the reference terminal of the shunt regulator IC. The divided voltage is controlled to a reference voltage (e.g., 2.5V).

[0080] Therefore, when the voltage of the slider of the variable resistor VR1 is about to be higher than the reference voltage, the diode current of the optocoupler PC1 increases, and when the voltage of the slider of the variable resistor VR1 is about to be lower than the reference voltage, the diode current of the optocoupler PC1 decreases.

[0081] According to optocoupler PC1, the output impedance on the secondary side increases or decreases depending on the magnitude of the diode current on the primary side. Therefore, when transistor QS is in the off state, the voltage across resistor R3 changes, causing a change in the diode current of optocoupler PC2. This results in fluctuations in the VCO voltage applied to the frequency control terminal (VCOin terminal) of the drive control circuit 50.

[0082] On the other hand, in the voltage divider circuit 60, the input voltage from the control power supply terminal is divided and applied to the duty cycle control terminal (DTin terminal) (DT voltage) of the drive control circuit 50.

[0083] 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 adjustment circuit 70 according to the on or off signal input from the indicator signal terminal.

[0084] The following uses Figure 2 The adjustment actions of the DT voltage and VCO voltage of the adjustment circuit 70 are explained in detail. Figure 2 This is a conceptual diagram showing the time-varying voltage changes at points A, B, C, and D in the adjustment circuit 70, and the curve of the drive signal at point E. Here, the voltage at point C is equal to the voltage at the duty cycle control terminal (DTin terminal), and the voltage at point D is proportional to the voltage at the frequency control terminal (VCOin terminal).

[0085] As shown in the curve at point A, a disconnect signal is input from the indicator signal terminal before timing T1. At timing T1, the signal input from the indicator signal terminal switches from a disconnect signal to an on signal. After timing T1, the on signal input continues.

[0086] When a disconnect signal is input, the disconnect signal is inverted by the NOT circuit NT and input to the gate terminal of transistor QS, making transistor QS turn on.

[0087] When transistor QS is in the ON state, the line extending from the collector terminal of phototransistor PQ1 (optocoupler output line) and the cathode side of rectifier diode D1 drops to ground level. Therefore, the voltage at point B becomes ground level (0V), and the voltage at point C becomes the lower limit. Furthermore, the drive signal output from drive control circuit 50 indicates a zero duty cycle, resulting in zero output power from converter circuit 1.

[0088] Here, in Figure 1 In the example, 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 in the on state, which corresponds to the DT voltage, which represents the lower limit of the duty cycle (zero duty cycle in this embodiment).

[0089] At this point, the diode current of optocoupler PC2 is at its maximum, and the output impedance on the secondary side is at its minimum. Therefore, the voltage at point D also becomes the lower limit, and the VCO voltage also becomes the lower limit. Furthermore, the switching frequency represented by the drive signal output from the drive control circuit 50 becomes the upper limit frequency of the specified frequency range.

[0090] When timing T1 switches from an off signal to an on signal, the on signal is inverted by the NOT circuit NT, so transistor QS becomes off.

[0091] When transistor QS is turned off, the voltages at points B and C rise, and the voltage at point DT also rises, thus increasing the duty cycle represented by the output drive signal. Here, the voltage at point C rises with the time constant of resistor R8 and capacitor Cs, and the voltage at point B also rises via rectifier diode D1. As a result, the output power from converter circuit 1 also increases.

[0092] On the other hand, as the voltages at points B and C increase, the current flowing through the LED HD2 in the optocoupler PC2 (diode current) decreases. Consequently, the output impedance on the secondary side of the optocoupler PC2 increases, and the voltage at point D rises due to the current flowing from the frequency control terminal (VCOin terminal) of the drive control circuit 50, thus increasing the VCO voltage. As a result, the switching frequency represented by the output drive signal is controlled in a direction decreasing from the upper limit frequency.

[0093] Thus, in this embodiment, the adjustment circuit 70 adjusts the DT voltage to a voltage level corresponding to the lower limit of the duty cycle (zero duty cycle in this embodiment) based on the input of the disconnect signal (equivalent to the first indication signal), and adjusts the VCO voltage to a voltage level corresponding to a predetermined high frequency (upper limit frequency) higher than the resonant frequency of the series resonant circuit 11. Based on the switching from the input of the disconnect signal to the input of the turn-on signal (equivalent to the second indication signal), the DT voltage is changed to increase the duty cycle represented by the drive signal, and the VCO voltage is changed to decrease the switching frequency represented by the drive signal.

[0094] Therefore, according to this embodiment, by setting the operating frequency within a frequency range higher than the resonant frequency and setting the duty cycle to a lower limit (zero in this embodiment), the output voltage from the converter circuit 1 can be made to reach a predetermined lower limit voltage level (zero in this embodiment), which is difficult to achieve solely through frequency control in the LLC resonant converter circuit. Furthermore, by gradually increasing the duty cycle from the lower limit, the output voltage from the converter circuit 1 can be gradually increased from the predetermined lower limit voltage level. Consequently, the output voltage can be adjusted from the predetermined lower limit voltage level within a low voltage region containing zero, and stabilized at the set voltage level.

[0095] The voltages at point C and DT gradually increase from timing T1, reaching their upper limit at timing T2. As a result, after timing T2, the duty cycle represented by the drive signal also becomes its upper limit (maximum duty cycle). As mentioned above, the upper limit levels of the voltages at point C and DT are determined by the resistance values ​​of resistors R8 and R9 and the variable resistor VR2. Furthermore, the rise time of the voltages at point C and DT (the time from timing T1 to timing T2) is determined based on the time constants of resistor R8 and capacitor Cs, as described above; this time constitutes the period for executing PWM control (duty cycle control).

[0096] On the other hand, even if the voltage at point C and the voltage at point DT reach their upper limits, the voltage at point B will rise further.

[0097] At this point, the voltage at point D and the VCO voltage also increase further. As a result, the switching frequency represented by the output drive signal is controlled in a direction that decreases from the upper limit frequency. At this time, the duty cycle represented by the drive signal becomes the upper limit value, and the output voltage from converter circuit 1 increases.

[0098] As a result, the output voltage detected by the detection circuit 40 rises. When the voltage across the slider of the variable resistor VR1 is about to exceed the reference voltage, the diode current of the optocoupler PC1 increases, thereby reducing the output impedance on the secondary side and limiting the rise in voltage at point B. Simultaneously, through the action of the optocoupler PC2, the rise in voltage at point D and the VCO voltage is also limited. Consequently, the reduction in the switching frequency represented by the output drive signal is also limited.

[0099] The timing is Figure 2 The curve is represented by timing T3, after which the switching frequency fluctuation stabilizes, and the output voltage from converter circuit 1 stabilizes at the specified set voltage level. That is, the time from timing T1 to timing T3 is the period for performing PFM control.

[0100] Thus, in this embodiment, when the adjustment circuit 70 is input with the second indication signal (on signal), it suppresses fluctuations in the frequency control voltage (VCO voltage) when the voltage divider voltage (voltage of the slider of the variable resistor VR1) is about to be higher than the reference voltage. That is, in this embodiment, the output is controlled to become a constant set voltage by PFM control in a certain high output range.

[0101] Therefore, according to this embodiment, the output voltage from the converter circuit 1 can be adjusted from a predetermined lower limit voltage level in the low voltage region containing zero, and stabilized at a set voltage level higher than that low voltage region.

[0102] Furthermore, as mentioned above, the voltages at point C and DT gradually increase from timing T1, and are limited to the upper limit level after timing T2. The voltages at point D and VCO gradually increase from timing T1, and continue to increase after timing T2, before being limited at timing T3. Therefore, after the indicator signal switches from an off signal to an on signal at timing T1, the duty cycle represented by the drive signal becomes the upper limit value (maximum duty cycle) after timing T2, and the switching frequency represented by the drive signal becomes the lower limit value (a frequency higher than the resonant frequency) after timing T3.

[0103] That is, in this embodiment, the adjustment circuit 70 is configured such that the first variation time of the duty cycle control voltage (DT voltage) associated with the switching from the input of the first indication signal (disconnect signal) to the input of the second indication signal (connect signal) is shorter than the second variation time of the frequency control voltage (VCO voltage) associated with the switching. The first variation time is the time required for the duty cycle control voltage (DT voltage) to change from the voltage level corresponding to the lower limit of the duty cycle (zero duty cycle in this embodiment) to the voltage level corresponding to the upper limit of the duty cycle. The second variation time is the time for the frequency control voltage (VCO voltage) to change from the voltage level corresponding to the specified high frequency (upper limit frequency) until it is suppressed.

[0104] In addition, the timing when the frequency control voltage (VCO voltage) is suppressed is similar to the timing when the output voltage reaches the specified set voltage level.

[0105] In this way, by making the first fluctuation time of the DT voltage shorter than the second fluctuation time of the VCO voltage, the low output region can be achieved through PWM control (duty cycle control), and PWM control can be stopped in the high output region to control the output to a constant set voltage through PFM control. Although it becomes a hard switch in PWM control, it does not cause any particular problems in the circuit because it is only performed in the low output region.

[0106] [Variation Example]

[0107] The above embodiments can be modified appropriately. That is, this embodiment is not limited to... Figure 1 The circuit structure is illustrated.

[0108] exist Figure 1 The example shown illustrates a structure where switching elements Q11 and Q12 are connected in a half-bridge configuration, but it can also be modified to a structure where four switching elements are connected in a full-bridge configuration. In this modified example, the drive control circuit 50 can have output terminals for four-channel drive signals or output terminals for two-channel drive signals. In the former case, the drive circuit 13 only needs to control the operation of the switching element corresponding to each channel according to the drive signal of each channel. In the latter case, the drive circuit 13 only needs to control the operation of the pair of switching elements corresponding to one channel according to the drive signal of one channel.

[0109] Alternatively, the above implementation can be modified so that the switching element QS is turned on by inputting an on signal and turned off by inputting an off signal. In this case, the NOT circuit NT is not required.

[0110] Alternatively, the above-described embodiment can be modified so that the drive control circuit 50 is configured such that, within a specified range, a higher DT voltage outputs a drive signal representing a lower duty cycle, and a lower DT voltage outputs a drive signal representing a higher duty cycle. Alternatively, the drive control circuit 50 can be configured such that, within a specified range, a higher VCO voltage outputs a drive signal representing a high switching frequency, and a lower VCO voltage outputs a drive signal representing a low switching frequency. In this case, the adjustment circuit 70 only needs to be configured to, based on the switching from the input of the first indication signal (off signal) to the input of the second indication signal (on signal), decrease the DT voltage to increase the duty cycle represented by the drive signal and decrease the VCO voltage to decrease the switching frequency represented by the drive signal.

[0111] Some or all of the above-described embodiments and modifications can also be determined as follows. However, the above-described embodiments and modifications are not limited to the following description.

[0112] <1> A control circuit for an LLC resonant converter circuit, which is a control circuit in the LLC resonant converter circuit that controls the switching frequency at a frequency higher than the resonant frequency of the series resonant circuit. The LLC resonant converter circuit includes the series resonant circuit, a drive circuit, a transformer, and a rectifier circuit. The drive circuit is connected to the series resonant circuit and causes multiple switching elements to switch according to a drive signal. The transformer uses the resonant coil constituting the series resonant circuit as the primary winding. The rectifier circuit rectifies and smooths the AC power generated in the secondary winding of the transformer. The control circuit includes: a drive control circuit, which includes a frequency control terminal and a duty cycle control terminal. The drive control circuit sends a drive signal representing the switching frequency corresponding to the voltage level of the frequency control terminal and the duty cycle corresponding to the voltage level of the duty cycle control terminal to the series resonant converter circuit. The drive circuit outputs; a detection circuit that detects the output voltage from the LLC resonant converter circuit and stabilizes the output voltage to a set voltage level; a voltage divider circuit that divides the input voltage from the control power supply terminal and applies it as a duty cycle control voltage to the duty cycle control terminal; and an adjustment circuit connected to the voltage divider circuit and the detection circuit, capable of adjusting the duty cycle control voltage and adjusting the frequency control voltage applied to the frequency control terminal according to the input voltage and the output voltage detected by the detection circuit. The adjustment circuit changes the duty cycle control voltage to increase the duty cycle represented by the drive signal and changes the frequency control voltage to decrease the switching frequency represented by the drive signal according to the switching from the input of the first indication signal to the input of the second indication signal.

[0113] <2> The control circuit of the LLC resonant converter circuit according to <1>, wherein the adjustment circuit, according to the input of the first indication signal, makes the duty cycle control voltage a voltage level corresponding to the lower limit of the duty cycle, and makes the frequency control voltage a voltage level corresponding to a predetermined high frequency higher than the resonant frequency.

[0114] <3> The control circuit of the LLC resonant converter circuit according to <2>, wherein the detection circuit includes: an output variable circuit capable of variably setting the voltage level of the output voltage from the LLC resonant converter circuit; and a stabilization circuit that stabilizes the output voltage from the LLC resonant converter circuit to the set voltage level set by the output variable circuit by comparing the detected output voltage divider voltage with a reference voltage, wherein the adjustment circuit, when the second indication signal is input, suppresses the fluctuation of the frequency control voltage when the divider voltage is about to be higher than the reference voltage.

[0115] <4> The control circuit of the LLC resonant converter circuit according to <3>, wherein the adjustment circuit is configured such that the first variation time of the duty cycle control voltage accompanying the switching from the input of the first indication signal to the input of the second indication signal is shorter than the second variation time of the frequency control voltage accompanying the switching, the first variation time being the time required for the duty cycle control voltage to change from the voltage level corresponding to the lower limit of the duty cycle to the voltage level corresponding to the upper limit of the duty cycle, and the second variation time being the time for the frequency control voltage to change from the voltage level corresponding to the specified high frequency until it is suppressed.

[0116] <5> The control circuit of the LLC resonant converter circuit according to <3> or <4>, wherein the adjustment circuit comprises: a first light-emitting diode, in which the current flowing through the first light-emitting diode increases when the voltage divider voltage is about to be higher than the reference voltage; a first phototransistor, which together with the first light-emitting diode forms a first optocoupler; a rectifier diode and a first resistive element, which are connected in series on a branch line: the branch line branches off from the voltage divider circuit to the output line of the duty cycle control voltage of the duty cycle control terminal and is connected to a ground line; a second resistive element and a second light-emitting diode, which are connected in series on the second... A light-emitting diode (LED) is connected in parallel with the voltage divider circuit on a line extending from the control power terminal and connected to the ground wire; and a second phototransistor, which together with the second LED forms a second optocoupler, wherein the line in which the second LED and the second resistive element are connected in series is connected to the branch line on the cathode side of the second LED; the second phototransistor is provided on a line extending from the frequency control terminal and connected to the ground wire; the emitter terminal of the first phototransistor is connected to the ground wire; and the optocoupler output line extending from the collector terminal of the first phototransistor is connected between the cathode of the rectifier diode in the branch line and the first resistive element.

[0117] <6> The control circuit of the LLC resonant converter circuit according to <5>, wherein the adjustment circuit further includes a switching element, the emitter terminal of which is connected to the ground line and the collector terminal is connected to the output line of the optocoupler. The switching element is turned on according to the input of the first indication signal and turned off according to the input of the second indication signal. When the switching element is turned on, the output line of the optocoupler and the cathode side of the rectifier diode fall back to the ground level, thereby the duty cycle control voltage applied to the duty cycle control terminal becomes a voltage level corresponding to the lower limit of the duty cycle.

[0118] <7> An LLC resonant converter circuit, comprising the control circuit described in any one of <1> to <6>, the series resonant circuit, the drive circuit, the transformer, and the rectifier circuit.

[0119] <8> A control method for an LLC resonant converter circuit, the LLC resonant converter circuit comprising: a series resonant circuit; a drive circuit connected to the series resonant circuit, which causes multiple switching elements to switch according to a drive signal; a transformer, which uses the resonant coil constituting the series resonant circuit as a primary winding; a rectifier circuit, which rectifies and smooths the AC power generated by the secondary winding of the transformer; a drive control circuit including a frequency control terminal and a duty cycle control terminal, which outputs a drive signal representing a switching frequency corresponding to the voltage level of the frequency control terminal and a duty cycle corresponding to the voltage level of the duty cycle control terminal to the drive circuit; and a detection circuit that detects the output voltage from the rectifier circuit. The output voltage is stabilized to a set voltage level; a voltage divider circuit divides the voltage of the input power from the control power supply terminal and applies it as a duty cycle control voltage to the duty cycle control terminal; and an adjustment circuit connected to the voltage divider circuit and the detection circuit, capable of adjusting the duty cycle control voltage and adjusting the frequency control voltage applied to the frequency control terminal according to the input power and the output voltage detected by the detection circuit, wherein the control method changes the duty cycle control voltage to increase the duty cycle of the drive signal and changes the frequency control voltage to decrease the switching frequency of the drive signal according to the switching from the input of the first indication signal to the input of the second indication signal.

[0120] <9> The control method for the LLC resonant converter circuit according to <8>, wherein the control method further includes: according to the input of the first indication signal, setting the duty cycle control voltage to a voltage level corresponding to the lower limit of the duty cycle, and setting the frequency control voltage to a voltage level corresponding to a predetermined high frequency higher than the resonant frequency of the series resonant circuit.

[0121] <10> The control method for the LLC resonant converter circuit according to <9>, wherein the detection circuit includes: an output variable circuit capable of variably setting the voltage level of the output voltage from the LLC resonant converter circuit; and a stabilization circuit that stabilizes the output voltage from the LLC resonant converter circuit to the set voltage level set by the output variable circuit by comparing the detected output voltage divider voltage with a reference voltage. The control method further includes: suppressing the fluctuation of the frequency control voltage when the voltage divider voltage is about to be higher than the reference voltage under the state of inputting the second indication signal.

[0122] <11> The control method for the LLC resonant converter circuit according to <10>, wherein the first variation time of the duty cycle control voltage accompanying the switching from the input of the first indication signal to the input of the second indication signal is shorter than the second variation time of the frequency control voltage accompanying the switching, the first variation time being the time required for the duty cycle control voltage to change 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, and the second variation time being the time for the frequency control voltage to change from a voltage level corresponding to the specified high frequency until it is suppressed.

[0123] Label Explanation

[0124] 1: LLC resonant converter circuit (converter circuit); 3: Transformer; 10: Primary side circuit; 11: Series resonant circuit; 13: Drive circuit; 20: Secondary side circuit; 21: Rectifier circuit; 30: Control circuit; 40: Detection circuit; 50: Drive control circuit; 60: Voltage divider circuit; 70: Adjustment circuit; VR1, VR2: Variable resistors; IC: Shunt regulator; PC1, PC2: Optocouplers; QS, Q11, Q12: Switching elements (transistors); NT: NOT circuit; HD1, HD2: Light-emitting diodes; PQ1, PQ2: Phototransistors.

Claims

1. A control circuit for an LLC resonant converter circuit, comprising a control circuit that controls the switching frequency at a frequency above the resonant frequency of the series resonant circuit, the LLC resonant converter circuit including the series resonant circuit, a drive circuit, a transformer, and a rectifier circuit, wherein the drive circuit is connected to the series resonant circuit and causes multiple switching elements to switch according to a drive signal, the transformer uses the resonant coil constituting the series resonant circuit as the primary winding, and the rectifier circuit rectifies and smooths the AC power generated in the secondary winding of the transformer, wherein... The control circuit has the following features: A drive control circuit includes a frequency control terminal and a duty cycle control terminal. The drive control circuit outputs a drive signal representing a switching frequency corresponding to the voltage level of the frequency control terminal and a duty cycle corresponding to the voltage level of the duty cycle control terminal to the drive circuit. A detection circuit that detects the output voltage from the LLC resonant converter circuit and stabilizes the output voltage to a set voltage level; A voltage divider circuit divides the input voltage from the control power supply terminal and applies it as the duty cycle control voltage to the duty cycle control terminal. as well as An adjustment circuit, connected to the voltage divider circuit and the detection circuit, is capable of adjusting the duty cycle control voltage and adjusting the frequency control voltage applied to the frequency control terminal based on the input voltage and the output voltage detected by the detection circuit. The adjustment circuit, based on the switching from the input of the first indication signal to the input of the second indication signal, causes the duty cycle control voltage to change so that the duty cycle represented by the drive signal increases, and causes the frequency control voltage to change so that the switching frequency represented by the drive signal decreases.

2. The control circuit of the LLC resonant converter circuit according to claim 1, wherein, The adjustment circuit, based on the input of the first indication signal, sets the duty cycle control voltage to a voltage level corresponding to the lower limit of the duty cycle and sets the frequency control voltage to a voltage level corresponding to a predetermined high frequency higher than the resonant frequency.

3. The control circuit of the LLC resonant converter circuit according to claim 2, wherein, The detection circuit includes: A variable output circuit is provided, which can variably set the voltage level of the output voltage from the LLC resonant converter circuit. as well as The stabilization circuit, by comparing the divided voltage of the detected output voltage with a reference voltage, stabilizes the output voltage from the LLC resonant converter circuit to the set voltage level determined by the output variable circuit. When the adjustment circuit is input with the second indication signal, it suppresses the fluctuation of the frequency control voltage when the voltage divider is about to be higher than the reference voltage.

4. The control circuit of the LLC resonant converter circuit according to claim 3, wherein, The adjustment circuit is configured such that the first variation time of the duty cycle control voltage accompanying the switching from the input of the first indication signal to the input of the second indication signal is shorter than the second variation time of the frequency control voltage accompanying the switching. The first variation time is the time required for the duty cycle control voltage to vary from the voltage level corresponding to the lower limit of the duty cycle to the voltage level corresponding to the upper limit of the duty cycle. The second variation time is the time from when the frequency control voltage changes from the voltage level corresponding to the specified high frequency until it is suppressed.

5. The control circuit of the LLC resonant converter circuit according to claim 3 or 4, wherein, The adjustment circuit includes: The current flowing through the first light-emitting diode increases when the voltage divider voltage is about to be higher than the reference voltage. The first phototransistor, together with the first light-emitting diode, constitutes the first optocoupler; A rectifier diode and a first resistor element are connected in series on a branch line that branches off from the voltage divider circuit to the output line of the duty cycle control voltage at the duty cycle control terminal and is connected to a ground line. A second resistive element and a second light-emitting diode are connected in parallel with the voltage divider circuit on a line extending from the control power supply terminal and connected to the ground wire; and The second phototransistor, together with the second light-emitting diode, constitutes the second optocoupler. The line connecting the second light-emitting diode and the second resistive element in series is connected to the branch line on the cathode side of the second light-emitting diode. The second phototransistor is disposed on a line extending from the frequency control terminal and connected to the ground wire. The emitter terminal of the first phototransistor is connected to the ground wire. An optocoupler output line extending from the collector terminal of the first phototransistor is connected between the cathode of the rectifier diode and the first resistive element in the branch line.

6. The control circuit of the LLC resonant converter circuit according to claim 5, wherein, The adjustment circuit further includes a switching element, the emitter terminal of which is connected to a ground wire, and the collector terminal of which is connected to the output line of the optocoupler. The switching element is switched on according to the input of the first indication signal and switched off according to the input of the second indication signal. When the switching element is turned on, the output line of the optocoupler and the cathode side of the rectifier diode fall back to ground level, thereby the duty cycle control voltage applied to the duty cycle control terminal becomes a voltage level corresponding to the lower limit of the duty cycle.

7. An LLC resonant converter circuit, wherein, The LLC resonant converter circuit includes the control circuit, the series resonant circuit, the drive circuit, the transformer, and the rectifier circuit as described in any one of claims 1 to 6.

8. A control method for an LLC resonant converter circuit, the LLC resonant converter circuit having: Series resonant circuit: A driving circuit, which is connected to the series resonant circuit, causes multiple switching elements to switch according to the driving signal. A transformer that uses the resonant coils that constitute the series resonant circuit as the primary winding; A rectifier circuit that rectifies and smooths the alternating current generated in the secondary winding of the transformer; A drive control circuit includes a frequency control terminal and a duty cycle control terminal. The drive control circuit outputs a drive signal representing a switching frequency corresponding to the voltage level of the frequency control terminal and a duty cycle corresponding to the voltage level of the duty cycle control terminal to the drive circuit. A detection circuit that detects the output voltage from the rectifier circuit and stabilizes the output voltage to a set voltage level; A voltage divider circuit divides the voltage of the input power from the control power supply terminal and applies it as a duty cycle control voltage to the duty cycle control terminal. as well as An adjustment circuit, connected to the voltage divider circuit and the detection circuit, is capable of adjusting the duty cycle control voltage and adjusting the frequency control voltage applied to the frequency control terminal based on the input power and the output voltage detected by the detection circuit. in, The control method, based on the switching from the input of the first indication signal to the input of the second indication signal, causes the duty cycle control voltage to change so that the duty cycle of the drive signal increases, and causes the frequency control voltage to change so that the switching frequency of the drive signal decreases.

9. The control method for the LLC resonant converter circuit according to claim 8, wherein, The control method further includes: according to the input of the first indication signal, setting the duty cycle control voltage to a voltage level corresponding to the lower limit of the duty cycle, and setting the frequency control voltage to a voltage level corresponding to a predetermined high frequency higher than the resonant frequency of the series resonant circuit.

10. The control method for the LLC resonant converter circuit according to claim 9, wherein, The detection circuit includes: A variable output circuit is provided, which can variably set the voltage level of the output voltage from the LLC resonant converter circuit. as well as The stabilization circuit, by comparing the divided voltage of the detected output voltage with a reference voltage, stabilizes the output voltage from the LLC resonant converter circuit to the set voltage level determined by the output variable circuit. The control method further includes: when the second indication signal is input, suppressing the fluctuation of the frequency control voltage when the voltage divider voltage is about to be higher than the reference voltage.

11. The control method for the LLC resonant converter circuit according to claim 10, wherein, The first variation time of the duty cycle control voltage accompanying the switching from the input of the first indication signal to the input of the second indication signal is shorter than the second variation time of the frequency control voltage accompanying the switching. The first variation time is the time required for the duty cycle control voltage to vary from the voltage level corresponding to the lower limit of the duty cycle to the voltage level corresponding to the upper limit of the duty cycle. The second variation time is the time from when the frequency control voltage changes from the voltage level corresponding to the specified high frequency until it is suppressed.

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