TWI867701B - Resonant converter and method of operation the same - Google Patents

Abstract

A resonant converter converts a DC voltage into an output voltage, and the resonant converter includes a transformer, a primary side circuit and a control module. The primary side circuit receives a DC voltage and includes a resonant circuit. The resonant circuit is coupled to a primary winding of the transformer to form a resonant module. The control module controls the primary side circuit to convert the DC voltage to generate a winding voltage at the two terminals of the resonant module. When the control module detects that an output current of the resonant converter is within a current interval between a predetermined current and a rated current, the control module adjusts a duty cycle of the winding voltage by adjusting a variable amount, so as to control an EMI value of the resonant converter to comply with a standard by adjusting the duty ratio.

Description

Resonance converter and method of operating the same

The present invention relates to a resonant converter and an operating method thereof, and in particular to a resonant converter with a frequency dithering function and an operating method thereof.

With the rapid development of the information industry, power supplies have played an indispensable role. The input voltage of information and household appliances is divided into AC voltage and DC voltage, and power supplies can generally be divided into two levels. The front stage is usually an AC/DC converter, a power factor corrector or a DC/DC converter, and the back stage is usually a resonant converter. As shown in Figure 1A, when the power supply is applied to the AC mains voltage Vac input, the output voltage Vo of the front stage AC/DC converter has a double frequency mains voltage Vac characteristic. In order to adjust the output voltage, the operating frequency of the post-stage DC/DC converter will change within the frequency range of ±6kHz R1 at a rated power of approximately 85kHz, as shown in Figure 1B. This frequency variation of ±6kHz is similar to the characteristics of frequency gitter. Such characteristics can evenly disperse the EMI energy generated by the DC/DC converter within the frequency range of ±6kHz R1 and the double frequency range of approximately 170kHz±12kHz. Therefore, better EMI suppression characteristics can be obtained.

However, as shown in Figure 1C, when the power supply is applied to the DC voltage Vdc input, the double-frequency mains voltage will not appear in the output voltage Vo of the front-stage DC/DC converter. Therefore, the adjusted operating frequency of the rear-stage resonant converter (as shown in Figure 1D) will show a small change in the frequency range R2 of ±0.2kHz. Since the operating frequency variation is very small, the EMI energy generated by the DC/DC converter will be concentrated on N times the current operating frequency (N=1, 2, 3...). Since there is no frequency jitter characteristic, the effect of suppressing EMI is extremely poor.

Therefore, the existing methods of solving the above problems in the known technology are: 1. Enhance the EMI attenuation capability, but this will make the design of the resonant converter more difficult, and it will not be possible to reduce the circuit size and circuit cost. 2. By adjusting the operating frequency of the resonant converter, avoid the minimum safety limit specification value (150kHz). For example, if the operating frequency is designed at 70kHz, the double frequency is 140kHz, which is still less than the specification value of 150kHz. Therefore, the resonant converter will be limited in design. 3. Deliberately generate a frequency gitter effect. This approach is to fix the front-stage output voltage Vout and deliberately change the operating frequency of the resonant converter by ±6kHz. However, since the operating frequency is deliberately changed, a low-frequency voltage ripple will occur in the DC/DC output voltage Vout.

Therefore, how to design a resonant converter and its operation method so that the resonant converter has a better EMI suppression effect and the EMI value measured by the resonant converter meets the standard value is a major topic that the creator of this case wants to study.

In order to solve the above problems, the present disclosure provides a resonant converter to overcome the problems of the prior art. Therefore, the resonant converter of the present disclosure converts a DC voltage into an output voltage, and the resonant converter includes a transformer, a primary side circuit and a control module. The transformer includes a primary side winding, and the primary side circuit receives the DC voltage. The primary side circuit includes a resonant circuit, and the resonant circuit is coupled to the primary side winding to form a resonant module. The control module is coupled to the primary side circuit and controls the primary side circuit to convert the DC voltage to generate a winding voltage at both ends of the resonant module. When the control module detects that the output current of the resonant converter is between the predetermined current and the rated current, the control module adjusts the duty cycle of the winding voltage by a variable amount, so as to control the EMI value of the resonant converter to meet the standard value by adjusting the duty cycle.

In order to solve the above problems, the present disclosure provides an operating method of a resonant converter to overcome the problems of the prior art. Therefore, the resonant converter disclosed in the present disclosure includes a transformer and a primary side circuit, and the primary side circuit includes a resonant circuit. The resonant circuit is coupled to the primary side winding of the transformer to form a resonant module, and the operating method of the resonant converter includes the following steps: (a) controlling the primary side circuit to convert a DC voltage to control the resonant converter to convert the DC voltage into an output voltage, and generating a winding voltage at two ends of the resonant module. (b) Detect the output current of the resonant converter, and when it is determined that the output current is between the predetermined current and the rated current, adjust the duty cycle of the winding voltage by a variable amount. (c) Control the operating frequency of the resonant converter to change within a frequency range by adjusting the duty cycle, and the frequency range is positively correlated with the variable amount.

The main purpose and effect of this disclosure is that when the control module detects that the output current rises to a certain level, the control module adjusts the duty cycle of the winding voltage by a variable amount to achieve the function of frequency gitter, so as to reduce the EMI value and make the EMI value meet the standard value.

In order to further understand the technology, means and effects adopted by the present invention to achieve the intended purpose, please refer to the following detailed description and attached figures of the present invention. It is believed that the purpose, features and characteristics of the present invention can be understood in depth and concretely. However, the attached figures are only provided for reference and explanation, and are not used to limit the present invention.

100: Resonance converter

1: Transformer

12: Beginner Side Roll Set

122: Resonance module

a: First end

b: Second end

14: Secondary side winding set

2: Primary side circuit

2A: Resonance circuit

22: First bridge arm

Q1: First switch

Q2: Second switch

24: Second bridge arm

Q3: The third switch

Q4: The fourth switch

Cr: resonant capacitor

Lr: resonant inductance

3: Secondary side circuit

4: Control module

42: Comparator

44: Voltage controller

46: Pulse Width Modulator

48: Occupancy ratio adjustment module

5: Driving circuit

200: Preamplifier circuit

300: Load

Vac: Mains voltage

Vdc: Direct current voltage

Vo: output voltage

Vab: Winding voltage

Vref: reference voltage

Io: output current

Io_stop: preset current

Io_max: rated current

Ci: Current range

R1, R2, △fsw: frequency range

fsw: operation frequency

Sc1, Sc2, Sc3, Sc4: control signal

Sfb: Feedback signal

Ser: Error signal

D: Space ratio

Dp: Predetermined value

Dl: critical value

Vpwm: pulse width modulation value

Vm: variable value

M: Variation

I, II, III: interval

Vs: Phase shift

DT: Dead time

(S100)~(S360): Steps

FIG1A is a waveform diagram of a known power supply when applied to an AC mains voltage input; FIG1B is a frequency characteristic diagram of a known resonant converter when applied to an AC mains voltage input; FIG1C is a waveform diagram of a known power supply when applied to a DC voltage input; FIG1D is a frequency characteristic diagram of a known resonant converter when applied to a DC voltage input; FIG2A is a waveform diagram of the present disclosure having FIG. 2B is a current-frequency curve diagram of the first embodiment of the resonant converter disclosed in the present invention; FIG. 3A is a current-frequency curve diagram of the second embodiment of the resonant converter disclosed in the present invention; FIG. 3B is a current-frequency curve diagram of the third embodiment of the resonant converter disclosed in the present invention; FIG. 4A is a current-frequency curve diagram of the first embodiment of the resonant converter with frequency jitter function disclosed in the present invention; FIG. 4B is a signal waveform diagram of the first embodiment of the resonant converter with frequency jitter function disclosed in the present invention; FIG. 4C is a circuit block diagram of the control module of the first embodiment of the resonant converter with frequency jitter function disclosed in the present invention; FIG. 5A is a circuit block diagram of the second embodiment of the resonant converter with frequency jitter function disclosed in the present invention; FIG. 5B is a circuit block diagram of the resonant converter with frequency jitter function disclosed in the present invention; FIG. 5C is a circuit block diagram of a control module of the second embodiment of the resonant converter with frequency jitter function disclosed herein; FIG. 6A is a method flow chart of an operation method of the first embodiment of the resonant converter with frequency jitter function disclosed herein; and FIG. 6B is a method flow chart of an operation method of the second embodiment of the resonant converter with frequency jitter function disclosed herein.

The technical content and detailed description of the present invention are as follows with the accompanying drawings: Please refer to FIG. 2A for a circuit block diagram of the resonant converter with a frequency jitter function disclosed herein, and FIG. 2B for a current-frequency curve diagram of the first embodiment of the resonant converter disclosed herein, and refer to FIG. 1A to FIG. 1D in conjunction. The resonant converter 100 couples the front-end circuit 200 and the load 300, and the front-end circuit 200 can be, for example but not limited to, an AC/DC conversion circuit, a DC/DC conversion circuit, or a DC power source such as a DC input source. The resonant converter 100 converts the DC voltage Vdc into an output voltage Vo, and based on the power demand of the load 300, provides an output current Io to the load 300. The resonant converter 100 includes a transformer 1, a primary side circuit 2, a secondary side circuit 3 and a control module 4, and the transformer 1 includes a primary side winding 12 and a secondary side winding 14. The primary side circuit 2 includes a resonant circuit 2A, the resonant circuit 2A is coupled to the primary side winding 12 to form a resonant module 122, and the secondary side circuit 3 is coupled to the secondary side winding 14. It is worth mentioning that in one embodiment, the resonant circuit 2A includes a resonant capacitor Cr and a resonant inductor Lr, although they are shown in series in the figure, it is only an illustrative example and is not limited thereto. The resonant capacitor Cr and the resonant inductor Lr can also be connected in parallel.

The control module 4 couples the primary circuit 2 and the secondary circuit 3, and the control module 4 controls the resonant converter 100 to convert the DC voltage Vdc into the output voltage Vo by controlling the primary circuit 2 and the secondary circuit 3. It is worth mentioning that in one embodiment, the control module 4 may include a controller (such as but not limited to a microcontroller, a central processing unit, etc.) and a detection circuit (such as but not limited to an inductive flow sensor, a voltage sensor, etc.) for detecting voltages and currents at various points (such as but not limited to input ends, output ends, etc.) of the resonant converter 100.

In FIG. 2B , Io_min is the output current at no load, and Io_max is the output current (or rated current) at full load. When the output current Io is lower, the operating frequency fsw of the resonant converter 100 is higher. Conversely, when the output current Io is higher, the operating frequency fsw of the resonant converter 100 is lower. Under this variable frequency operation (i.e., the operating frequency fsw varies with the size of the output current Io), when the general resonant converter 100 converts the DC voltage Vdc into the output voltage Vo, a winding voltage Vab (which can be called an effective input voltage) is generated at both ends of the resonant module 122, and the duty cycle D of the winding voltage Vab is usually maintained at a predetermined value Dp (for example, but not limited to, an upper limit of 50%, but can also be 45%, 40%, etc., which can be adjusted according to actual needs). However, as shown in the prior art of FIGS. 1A to 1D , when the power supply is applied to the DC voltage Vdc input and the output current Io rises to a certain level, since the resonant converter 100 does not have the function of frequency gitter, the resonant converter 100 has a very poor effect of suppressing EMI, which easily causes the EMI value measured by the resonant converter 100 to fail to meet the standard value (for example, but not limited to, the international standard of the International Electrotechnical Commission IEC).

Therefore, in order to make the EMI value measured by the resonant converter 100 meet the standard value, the present disclosure uses the function of frequency jitter to reduce the EMI value when the output current Io rises to a certain level, so that the EMI value meets the standard value. Specifically, when the control module 4 detects that the output current Io of the resonant converter 100 is between the current interval Ci of the predetermined current Io_stop and the rated current Io_max, the control module 4 provides the function of frequency jitter. That is, the control module 4 adjusts the duty cycle D of the winding voltage Vab by a variation M so that the duty cycle D does not remain at the predetermined value Dp. When the variation M is larger, the duty cycle D is smaller, and vice versa, the duty cycle D is larger. The variation M varies between the predetermined value Dp and the critical value Dl according to the calculation of the control module 4, and the curve of the critical value Dl can be adaptively adjusted (indicated by a dotted line) according to the requirements of the resonant converter 100. For example, but not limited to, when the variation M is 10% and the duty cycle D is the upper limit of 50%, the duty cycle D will vary between the predetermined value Dp of 50% and the critical value Dl of 40%. Alternatively, when the variation M is 5% and the duty cycle D is 45%, the duty cycle D will vary between the predetermined value Dp of 45% and the critical value Dl of 40%, or between the predetermined value Dp of 45% and the critical value Dl of 50%, and so on.

On the other hand, since the resonant converter 100 uses the frequency jitter function, when the output current Io is a fixed value, the operating frequency fsw of the resonant converter 100 will change accordingly with the change of the variation M. Therefore, when the output current Io is in the current interval Ci, the operating frequency fsw will change within a specific frequency range Δfsw, and the frequency range Δfsw is positively correlated to the variation M. For example, when the output current Io is fixed at 10A (10A is within the current interval Ci) and the current operating frequency fsw is 85kHz, the adjusted variation M varies between the predetermined value Dp and the critical value Dl of the variation M according to the calculation of the control module 4, and the operating frequency fsw varies between 85kHz and 75kHz or 85kHz and 95kHz according to the variation of the variation M.

Therefore, when the variation M calculated by the control module 4 is smaller, in order to keep the winding voltage Vab fixed, the amplitude of the change of the operating frequency fsw is also smaller. Conversely, when the variation M calculated by the control module 4 is larger, in order to keep the winding voltage Vab fixed, the amplitude of the change of the operating frequency fsw will be larger. On the other hand, from the EMI characteristics of the converter (including the DC/DC converter), it can be known that the larger the output current Io, the greater the N-order harmonic energy generated by the current converter. Conversely, the smaller the output current Io, the smaller the N-order harmonic energy generated by the converter. This characteristic is limited by the EMI specification. When the output current Io is larger, the harmonic energy generated is larger, making the EMI value closer to the maximum limit value. On the contrary, when the output current Io is smaller, the generated harmonic energy is smaller, making the EMI value farther from the maximum limit value. Therefore, when the output current Io is larger (i.e. greater than or equal to the predetermined current Io_stop), by adjusting the duty cycle D by a change amount M, the EMI value of the resonant converter 100 can be controlled to meet the standard value.

Please refer to FIG. 3A for the current-frequency curve diagram of the second embodiment of the resonant converter disclosed in the present invention, and refer to FIG. 2A~2B in conjunction. The present invention utilizes the change in the duty cycle D of the winding voltage Vab in response to the difference in the output current Io, in combination with the EMI characteristics of the converter itself, to operate the resonant converter 100. When the output current Io is larger, the harmonic energy generated is also larger. Therefore, in order to comply with regulatory restrictions, the adjustment of the variation M is larger. Conversely, when the output current Io is smaller, the harmonic energy generated is also smaller, and the adjustment of the variation M is smaller or can remain unchanged. Therefore, when the control module 4 detects that the output current Io is less than the predetermined current Io_stop (interval I) or greater than the rated current Io_max (interval III), the control module fixes the duty cycle D to a predetermined value Dp (for example but not limited to 50%), so that the EMI value of the resonant converter 100 meets the standard value. That is, when the output current Io is not in the current interval Ci, the control module 4 controls the variation M to zero, so that the duty cycle D is fixed to the predetermined value Dp. Therefore, in intervals I and III, the operating frequency fsw is variable frequency, which changes according to the increase or decrease of the output current Io, and when the output current Io is a fixed value, the operating frequency fsw is substantially a constant value.

When the control module 4 detects that the output current Io is in the current interval Ci (interval II), the duty ratio D of the winding voltage Vab is the predetermined value Dp minus the variation M, and the control module 4 sets the critical value Dl of the variation M to a fixed value (i.e., the critical value Dl is a horizontal line). Similarly, the frequency range Δfsw corresponds to the critical value Dl and presents a specific range. Therefore, in interval II, the operating frequency fsw is still variable frequency, which changes according to the increase or decrease of the output current Io. In addition, in interval II, when the output current Io is a fixed value, the variation M varies between the predetermined value Dp and the critical value Dl according to the calculation of the control module 4, and the operating frequency fsw varies within a specific range accordingly with the variation of the variation M. Therefore, in interval II, assuming that the predetermined value Dp of the duty cycle is the upper limit of 50%, and the variation M is 10%, the critical value Dl is 40% (i.e., 50% minus 10%). Correspondingly, when the predetermined value Dp is the upper limit of 50%, the corresponding operating frequency fsw is 85kHz, and the frequency range △fsw corresponding to the variation M of 10% is 10kHZ, then the operating frequency fsw varies between 85kHz and 75kHz according to the variation of the variation M. It is worth mentioning that in one embodiment, when the predetermined value Dp of the duty cycle is other values, the above logic can be used by analogy, and no further explanation is given here.

Please refer to FIG. 3B for the current-frequency curve diagram of the third embodiment of the resonant converter disclosed in the present invention, and refer to FIG. 2A to FIG. 3A in conjunction. The difference between this embodiment and the embodiment of FIG. 3A is that when the control module 4 detects that the output current Io is in the current interval Ci (interval II), the control module 4 sets the critical value Dl of the variation M to decrease as the output current Io increases (i.e., the critical value Dl is a curve with a negative slope). Similarly, the frequency range △fsw expands corresponding to the decrease of the critical value Dl. Specifically, the larger the output current Io, the greater the N-order harmonic energy generated by the current converter. Therefore, the critical value D1 of the variation M decreases with the increase of the output current Io, so that when the output current Io is larger, it has a better EMI suppression effect, making the EMI value less likely to approach the maximum limit value. It is worth mentioning that in one embodiment, the technical content not described in FIG3B is the same as FIG3A, and will not be elaborated here.

Please refer to FIG. 4A for a circuit block diagram of the first embodiment of the resonant converter with a frequency jitter function disclosed herein, and FIG. 4B for a signal waveform diagram of the first embodiment of the resonant converter with a frequency jitter function disclosed herein, and refer to FIG. 2A to FIG. 3B in combination. In FIG. 4A , the resonant converter 100 is a full-bridge resonant converter, and the primary side circuit 2 further includes a first bridge arm 22 and a second bridge arm 24 connected in parallel. The first bridge arm 22 includes a first switch Q1 and a second switch Q2 connected in series, and the second bridge arm 24 includes a third switch Q3 and a fourth switch Q4 connected in series. The first end a of the resonance module 122 is coupled between the first switch Q1 and the second switch Q2, and the second end b of the resonance module 122 is coupled between the third switch Q3 and the fourth switch Q4. The control module 4 provides a first control signal Sc1 to control the first switch Q1, provides a second control signal Sc2 to control the second switch Q2, provides a third control signal Sc3 to control the third switch Q3, and provides a fourth control signal Sc4 to control the fourth switch Q4. Therefore, as shown in FIG. 4A, through the control of the control module 4, the primary side circuit 2 can convert the DC voltage Vdc, and generate a winding voltage Vab between the first end a and the second end b of the resonance module 122.

In the waveform diagram of FIG4B, the signal waveform on the left half corresponds to interval I or III of FIG3A or 3B, and the signal waveform on the right half corresponds to interval II of FIG3A or 3B. Taking the predetermined value Dp of the duty cycle D as 50% as an example, when the control module 4 detects that the output current Io is not in the current interval Ci (i.e., in interval I or III), the control module 4 provides the first control signal Sc1 and the fourth control signal Sc4 with the same phase, and provides the second control signal Sc2 that complements the first control signal Sc1, and provides the third control signal Sc3 that complements the fourth control signal Sc4. Therefore, the winding voltage Vab forms a waveform of positive/negative voltage variation, and there is no dead time. However, the control signal is not limited to complete complementation, and an additional dead time may also be included between the two complementary control signals.

When the control module 4 detects that the output current Io is in the current interval Ci, the control module 4 controls the first control signal Sc1 and the fourth control signal Sc4 to have a phase shift amount Vs of phase change, so that the positive half-cycle duty cycle D of the winding voltage Vab decreases due to the sum of the first control signal Sc1 and the fourth control signal Sc4 (that is, when both are turned on at the same time, there is a current path to generate the winding voltage Vab), and then adjusts the change amount M by adjusting the phase shift amount Vs. Among them, the first control signal Sc1 and the second control signal Sc2 are corresponding opposite signals, and the fourth control signal Sc4 and the third control signal Sc3 are corresponding opposite signals, so controlling the first control signal Sc1 or the fourth control signal Sc4 can make the second control signal Sc2 or the third control signal Sc3 make corresponding adjustments.

On the other hand, when the control module 4 detects that the output current Io is in the current interval Ci, the control module 4 controls the second control signal Sc2 and the third control signal Sc3 to have a phase shift amount Vs of phase change, which can also make the negative half cycle duty cycle D of the winding voltage Vab decrease due to the sum of the second control signal Sc2 and the third control signal Sc3, and then adjust the change amount M by adjusting the phase shift amount Vs. Its operation method is roughly the same as the first control signal Sc1 and the fourth control signal Sc4 mentioned above, and will not be repeated here. In FIG. 4B, although only a schematic example of controlling the first control signal Sc1 to lead the fourth control signal Sc4 by a phase shift amount Vs, or controlling the second control signal Sc2 to lead the third control signal Sc3 by a phase shift amount Vs is disclosed, the possibility of multiple implementation methods is not excluded. That is, we can think in reverse and use the lagging phase to control. The principle is similar and will not be elaborated here.

Please refer to FIG. 4C for a circuit block diagram of the control module of the first embodiment of the resonant converter with frequency jitter function disclosed in the present invention, and refer to FIG. 2A to FIG. 4B in conjunction. The control module 4 includes a comparator 42, a voltage controller 44, a pulse width modulator 46, and a duty cycle adjustment module 48. The comparator 42 compares the feedback signal Sfb corresponding to the output voltage Vo with the reference voltage Vref to provide an error signal Ser, and the voltage controller 44 generates a pulse width modulation value Vpwm and a change value Vm corresponding to the change amount M according to the error signal Ser. Among them, since the pulse width modulation value Vpwm is generated according to the error between the feedback signal Sfb and the reference voltage Vref, the output voltage Vo will change with the output current Io extracted by the load 300, so the pulse width modulation value Vpwm reflects the size of the output current Io. Therefore, the pulse width modulation value Vpwm and the variation value Vm can be changed according to the size of the output current Io.

The pulse width modulator 46 modulates the first control signal Sc1, the second control signal Sc2, the third control signal Sc3 and the fourth control signal Sc4 according to the pulse width modulation value Vpwm, and the control signals Sc1, Sc2, Sc3, Sc4 are pulse width modulation signals. The duty cycle adjustment module 48 adjusts the phase shift Vs of the control signals Sc1, Sc2, Sc3, Sc4 according to the change value Vm, so that the duty cycle D of the winding voltage Vab is adjusted by a change amount M so that the duty cycle D does not remain at the predetermined value Dp. The duty cycle adjustment module 48 can be, for example but not limited to, a phase adjustment circuit or the like for phase shifting (i.e. controlling leading/lagging) the control signals Sc1, Sc2, Sc3, Sc4, but is not limited thereto. It is worth mentioning that in one embodiment, a driving circuit 5 may be further included between the pulse width modulator 46 and the primary side circuit 2. The driving circuit 5 is a driving device that smoothly utilizes a weak current signal to drive a high-power switch. When the control signals Sc1, Sc2, Sc3, and Sc4 can smoothly drive the first bridge arm 22 and the second bridge arm 24 without the driving circuit 5, the driving circuit 5 may not be required. In addition, in one embodiment of the present invention, the components in the control module 4 are not limited to be implemented according to this architecture. Any components, circuits or software programs (and the controller controls the resonant converter according to the program by writing the control software program) that can achieve the same function (for example, the comparison function is not limited to the use of only comparators) should be included in the scope of this embodiment.

Please refer to FIG. 5A for a circuit block diagram of the second embodiment of the resonant converter with a frequency jitter function disclosed herein, and FIG. 5B for a signal waveform diagram of the second embodiment of the resonant converter with a frequency jitter function disclosed herein, and refer to FIG. 2A to FIG. 4C in combination. In FIG. 5A , the resonant converter 100 is a half-bridge resonant converter, and the primary side circuit 2 further includes a first bridge arm 22. The first bridge arm 22 includes a first switch Q1 and a second switch Q2 connected in series, and the resonant module 122 is connected in parallel to the second switch Q2. The control module 4 provides a first control signal Sc1 to control the first switch Q1, and provides a second control signal Sc2 to control the second switch Q2. Therefore, as shown in FIG5B , through the control of the control module 4, the primary side circuit 2 can convert the DC voltage Vdc and generate a winding voltage Vab between the first end a and the second end b of the resonance module 122.

In the waveform diagram of FIG5B, the technical content of the signal waveform on the left side is similar to that of FIG4B, and will not be described in detail here. In the signal waveform on the right side, since the first control signal Sc1 and the second control signal Sc2 cannot be phase-shifted, the dead time can be used to adjust the variation M. Specifically, when the control module 4 detects that the output current Io is in the current interval Ci, the dead time DT between the first control signal Sc1 and the second control signal Sc2 is adjusted, so that the duty cycle D of the positive and negative half-cycle of the winding voltage Vab decreases due to the adjustment of the dead time DT, and then the variation M is adjusted by adjusting the dead time DT. Among them, the first control signal Sc1 and the second control signal Sc2 are corresponding opposite signals, so controlling the first control signal Sc1 can make the second control signal Sc2 make corresponding adjustments.

Please refer to FIG. 5C for a circuit block diagram of a control module of a second embodiment of a resonant converter with a frequency jitter function disclosed herein, and refer to FIG. 2A to FIG. 5B in conjunction. The difference between the control module 4 of the embodiment of FIG. 5C and the control module 4 of FIG. 4C is that the pulse width modulator 46 modulates the first control signal Sc1 and the second control signal Sc2 according to the pulse width modulation value Vpwm, and the duty cycle adjustment module 48 adjusts the dead time DT of the control signals Sc1 and Sc2 according to the change value Vm. The duty cycle adjustment module 48 can be, for example but not limited to, a time delay circuit or other circuit for generating the dead time DT, but is not limited thereto. It is worth mentioning that in one embodiment, the technical content not described in FIG. 5C is the same as that in FIG. 4C and will not be described in detail here. On the other hand, in one embodiment, the resonant converter 100 is not limited to the LLC architecture of FIG. 4A and FIG. 5A. Any converter that can use resonance to perform a DC conversion function should be included in the scope of the present disclosure.

Please refer to FIG. 6A for a method flow chart of the operation method of the first embodiment of the resonant converter with frequency jitter function disclosed in the present invention, and refer to FIG. 2A to FIG. 5C in conjunction with the operation method in FIG. 6A. The operation method in FIG. 6A is mainly in conjunction with the curve diagram in FIG. 3A, and the control module 4 of the resonant converter 100 can pre-set parameters such as the predetermined current Io_stop, the predetermined value Dp, and the critical value Dl, and the operation method of the resonant converter 100 includes determining whether the output current is less than the predetermined current (S100). When the control module 4 determines that the output current Io is less than the predetermined current Io_stop (interval I), the control variation is zero (S120). When the control module 4 determines that the output current Io is not less than the preset current Io_stop (interval I), it determines whether the output current is greater than the rated current (S200). When the control module 4 determines that the output current Io is greater than the rated current Io_max (interval III), the control variation is zero (S220). Among them, the order of steps (S100) and (S200) can be reversed, and when the judgment results of steps (S100) and (S200) are both "no", it means that the output current Io is in the current interval Ci. Therefore, the variation is calculated (S320). Finally, the phase shift of the control signal is adjusted to adjust the variation (S340).

Since the variation M in steps (S120) and (S220) is zero, the phase shift control signals Sc1, Sc2, Sc3, Sc4 are not used in step (S340), so that the duty cycle D is fixed at the predetermined value Dp. In step (S320), since the variation M is not zero, in step (S340), the control module 4 adjusts the phase shift Vs of the control signals Sc1, Sc2, Sc3, Sc4 based on the calculated variation Vm (corresponding to the variation M), so that the duty cycle D of the winding voltage Vab changes within the range of the predetermined value Dp minus the variation M and the predetermined value Dp. In this way, the EMI values of the resonant converter 100 from no load to full load can meet the standard values. It is worth mentioning that in one embodiment, the detailed operation method of the resonant converter 100 can be found in conjunction with FIGS. 2A to 5C and will not be described in detail here.

Please refer to FIG. 6B for a flow chart of the method of operating the resonant converter with frequency jitter function according to the second embodiment of the present disclosure, and refer to FIG. 2A to FIG. 6A in conjunction. The operating method in FIG. 6B is mainly in conjunction with the curve diagram of FIG. 3B, and the difference between the operating method in FIG. 6B and the operating method in FIG. 6A is that the dead time of the control signal is adjusted to adjust the variation (S360). In step (S320), since the variation M is not zero, in step (S360), the control module 4 adjusts the dead time DT of the control signals Sc1 and Sc2 based on the calculated variation Vm (corresponding to the variation M), so that the duty cycle D of the winding voltage Vab changes within the range of the predetermined value Dp minus the variation M and the predetermined value Dp. In this way, the EMI values of the resonant converter 100 from no load to full load can meet the standard values. It is worth mentioning that in one embodiment, the steps not described in FIG. 6B are the same as those in FIG. 6A, and the detailed operation method of the resonant converter 100 can also be referred to in conjunction with FIG. 2A to FIG. 5C, and will not be described in detail here.

However, the above is only a detailed description and diagram of the preferred specific embodiment of the present invention, but the features of the present invention are not limited thereto, and are not used to limit the present invention. The entire scope of the present invention shall be subject to the scope of the patent application described below. All embodiments that conform to the spirit of the patent application scope of the present invention and its similar variations shall be included in the scope of the present invention. Any changes or modifications that can be easily thought of by anyone familiar with the art within the field of the present invention can be covered by the patent scope of the following case.

(S100)~(S340): Steps

Claims (19)

A resonant converter converts a DC voltage into an output voltage. The resonant converter includes: a transformer including a primary winding; a primary circuit receiving the DC voltage and including a resonant circuit coupled to the primary winding to form a resonant module; and a control module coupled to the primary circuit and controlling the resonant module. The primary side circuit converts the DC voltage to generate a winding voltage at two ends of the resonant module; wherein, when the control module detects that an output current of the resonant converter is between a predetermined current and a rated current, and the output current is a fixed value, the control module adjusts a duty cycle of the winding voltage to have a variable amount. A resonant converter as described in Item 1 of the patent application, wherein when the control module detects that the output current is less than the predetermined current or greater than the rated current, the control module fixes the duty cycle to a predetermined value. As described in item 1 of the patent application, when the control module detects that the output current is in the current range, the control module controls an operating frequency of the resonant converter to change within a frequency range, and the frequency range is positively correlated to the change amount. As described in item 3 of the patent application scope, the control module sets a critical value of the variable to a fixed value, and the frequency range is a specific range corresponding to the critical value. As described in item 3 of the patent application scope, the control module sets a critical value of the variation amount to decrease as the output current increases, and the frequency range expands according to the decrease of the critical value. The resonant converter as described in item 1 of the patent application, wherein the resonant converter is a full-bridge resonant converter, and the primary-side circuit further comprises: a first bridge arm, comprising a first switch and a second switch connected in series, and a first end of the resonant module is coupled between the first switch and the second switch; and a second bridge arm, connected in parallel with the first bridge arm, and comprising a third switch and a fourth switch connected in series, and a second end of the resonant module is coupled between the third switch and the fourth switch; wherein the control module provides a first control signal to control the first switch A switch is provided, a second control signal is provided to control the second switch, a third control signal is provided to control the third switch, and a fourth control signal is provided to control the fourth switch; and when the control module detects that the output current is in the current range, the control module controls the first control signal and the fourth control signal to have a phase shift amount of phase change and adjusts the change amount; or when the control module detects that the output current is in the current range, the control module controls the second control signal and the third control signal to have a phase shift amount of phase change and adjusts the change amount. As described in item 6 of the patent application scope, the resonant converter, wherein when the control module detects that the output current is not in the current range, the second control signal and the first control signal are complementary signals, and the third control signal and the fourth control signal are complementary signals. The resonant converter as described in item 6 of the patent application scope, wherein the control module includes: a comparator, comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal; a voltage controller, generating a pulse width modulation value and a change value corresponding to the change amount according to the error signal; a pulse width modulator, modulating the first control signal, the second control signal, the third control signal and the fourth control signal according to the pulse width modulation value; and a duty cycle adjustment module, adjusting the phase shift amount according to the change value. As described in item 1 of the patent application scope, the resonant converter is a half-bridge resonant converter, and the primary side circuit further includes: a first bridge arm, including a first switch and a second switch connected in series, and the resonant module is connected in parallel with the second switch; wherein the control module provides a first control signal to control the first switch, and provides a second control signal to control the second switch; when the control module detects that the output current is in the current range, the control module adjusts a dead time between the first control signal and the second control signal to adjust the variation. As described in item 9 of the patent application scope, the resonant converter, wherein when the control module detects that the output current is not in the current range, the second control signal and the first control signal are complementary signals. The resonant converter as described in item 9 of the patent application, wherein the control module includes: a comparator, comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal; a voltage controller, generating a pulse width modulation value and a change value corresponding to the change amount according to the error signal; a pulse width modulator, modulating the first control signal and the second control signal according to the pulse width modulation value; a duty cycle adjustment module, adjusting the dead time according to the change value. A method for operating a resonant converter, the resonant converter comprising a transformer and a primary side circuit, wherein the primary side circuit comprises a resonant circuit, the resonant circuit is coupled to a primary side winding of the transformer to form a resonant module, and the method comprises the following steps: controlling the primary side circuit to convert a DC voltage to control the resonant converter to convert the DC voltage into an output voltage, A winding voltage is generated at two ends of the resonant module; an output current of the resonant converter is detected, and when it is determined that the output current is between a predetermined current and a rated current, a duty cycle of the winding voltage is adjusted to have a variation; and an operating frequency of the resonant converter is controlled to vary within a frequency range by adjusting the duty cycle, and the frequency range is positively correlated with the variation. The operating method described in Item 12 of the patent application further includes the following steps: when the output current is less than the predetermined current or greater than the rated current, the duty cycle is fixed to a predetermined value. The operating method described in item 12 of the patent application further includes the following steps: setting a critical value of the variable to a fixed value, and the frequency range is a specific range corresponding to the critical value. The operating method as described in Item 12 of the patent application further includes the following steps: A critical value of the variable is set to decrease as the output current increases, and the frequency range is expanded according to the decrease of the critical value. As described in the operating method of item 12 of the patent application scope, the primary side circuit includes a first bridge arm and a second bridge arm connected in parallel, the first bridge arm includes a first switch and a second switch, and the second bridge arm includes a third switch and a fourth switch, and the operating method further includes the following steps: providing a first control signal to control the first switch, providing a second control signal to control the second switch, providing a third control signal to control the third switch, and providing a fourth control signal to control the fourth switch; when the output current is in the current range, controlling the first control signal and the fourth control signal to have a phase shift amount of phase change and adjusting the change amount; or when the output current is in the current range, controlling the second control signal and the third control signal to have the phase shift amount of phase change and adjusting the change amount. The operating method described in item 16 of the patent application scope further includes the following steps: comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal; generating a pulse width modulation value and a change value corresponding to the change amount according to the error signal; modulating the first control signal, the second control signal, the third control signal and the fourth control signal according to the pulse width modulation value; and adjusting the phase shift amount according to the change value. As described in the operating method of item 12 of the patent application scope, the primary side circuit includes a first bridge arm, and the first bridge arm includes a first switch and a second switch, and the operating method further includes the following steps: Providing a first control signal to control the first switch, and providing a second control signal to control the second switch; and when the output current is in the current range, adjusting a dead time between the first control signal and the second control signal to adjust the variation. The operating method described in item 18 of the patent application scope further includes the following steps: comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal; generating a pulse width modulation value and a change value corresponding to the change amount according to the error signal; modulating the first control signal and the second control signal according to the pulse width modulation value; and adjusting the dead time according to the change value.

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