Method of operating power converter, control circuit and power converter

Abstract

A method of operating a power converter, a control circuit, and a power converter are disclosed. The method comprises operating a power converter comprising an inductor and an electronic switch (22) connected in series with the inductor (21) in one of a first mode of operation and a second mode of operation. Operating the power converter in the first mode of operation comprises activating a snubber circuit (3) connected in parallel with the electronic switch (22), and operating the power converter in the second mode of operation comprises deactivating the snubber circuit (3).

Description

Technical Field

[0001] The present disclosure generally relates to methods for operating a power converter, particularly a switched-mode power converter. Background Art

[0002] A switched-mode power converter typically includes an electronic switch and an inductor connected in series with the electronic switch, and is configured to regulate an output voltage or an output current provided by the power converter based on a switching-mode operation of the electronic switch. The switched-mode power converter can operate in different types of operating modes. Examples of different operating modes include continuous conduction mode (CCM) and critical conduction mode (CrCM). In CCM, the power converter is operated such that there is a continuous current flowing through the inductor, such that the current through the inductor does not decrease to zero. In CrCM, the power converter is operated such that in each of a plurality of consecutive drive cycles of the electronic switch, the inductor current decreases to zero, where the electronic switch is turned on again when the inductor has demagnetized.

[0003] A switched-mode power converter capable of operating in CCM and CrCM can operate in CCM under normal load conditions or high load conditions, and can operate in CrCM under low load conditions. Under low load conditions, for example, the power consumption of a load receiving a regulated output voltage or output current is below a specific threshold.

[0004] Operating the power converter in CrCM may cause harmonics in the input current received by the power converter. It is desirable to reduce harmonics in a switched-mode power converter capable of operating in CCM and CrCM. Summary of the Invention

[0005] One example relates to a method of operating a power converter. The method includes operating a power converter including an inductor and an electronic switch connected in series with the inductor in one of a first operating mode and a second operating mode. Operating the power converter in the first operating mode includes activating a buffer circuit connected in parallel with the electronic switch, and operating the power converter in the second operating mode includes deactivating the buffer circuit.

[0006] Another example relates to a control circuit. The control circuit is configured to operate a power converter including an inductor and an electronic switch connected in series with the inductor in one of a first operating mode and a second operating mode. Operating the power converter in the first operating mode includes activating a buffer circuit connected in parallel with the electronic switch, and operating the power converter in the second operating mode includes deactivating the buffer circuit.

[0007] Another example relates to a power converter including such a control circuit. The power converter further includes a converter circuit having an inductor and an electronic switch connected in series with the inductor, and a buffer circuit connected in parallel with the electronic switch. Description of the Drawings

[0008] Examples will be described below with reference to the drawings. The drawings are used to illustrate certain principles and show only aspects necessary for understanding these principles. The drawings are not drawn to scale. In the drawings, the same reference numerals denote the same features.

[0009] Figure 1 An example of a power converter is shown, which includes a converter circuit having an inductor and an electronic switch, and a buffer circuit, where the buffer circuit can be activated and deactivated;

[0010] Figure 2 An example of a power converter according to Figure 1 is shown, where the electronic switch in the converter circuit and the electronic switch in the buffer circuit are each implemented as a MOSFET;

[0011] Figure 3 A timing diagram showing an input voltage implemented as a rectified sinusoidal voltage is shown;

[0012] Figure 4 An example of a rectifier circuit configured to generate a rectified sinusoidal voltage based on a sinusoidal voltage according to Figure 3 is shown;

[0013] Figure 5 A signal diagram showing the operation of a power converter of the type shown in Figure 1 in critical conduction mode (CrCM) according to one example is shown;

[0014] Figure 6 A signal diagram showing the operation of a power converter of the type shown in Figure 1 in critical conduction mode (CrCM) according to another example is shown;

[0015] Figure 7 A signal diagram showing the operation of a power converter of the type shown in Figure 1 in continuous conduction mode (CCM) according to another example is shown;

[0016] Figure 8 An example of a control circuit including a CCM controller and a CrCM controller and configured to control the operation of a power converter of the type shown in Figure 1 is schematically shown;

[0017] Figure 9Schematically shows an example of a CCM controller with PFC (Power Factor Correction) function;

[0018] Figure 10 Schematically shows an example of a CrCM controller with PFC function; and

[0019] Figure 11 Shows a signal diagram showing examples for changing the operation of a power converter between CrCM and CCM. Detailed Description

[0020] Reference is made to the accompanying drawings in the following detailed description. The accompanying drawings form a part of the specification and show, for illustrative purposes, examples of how to use and implement the present invention. It should be understood that the features of the various embodiments described herein can be combined with each other unless otherwise specifically stated.

[0021] Figure 1 Shows a power converter according to an example. Referring to Figure 1 , the power converter includes an inductor 21 and a first electronic switch 22 connected in series with the inductor 21. In addition, the power converter includes a buffer circuit 3 connected in parallel with the first switch 22 and which can be activated and deactivated.

[0022] According to an example, the buffer circuit 3 includes a capacitor. When the capacitor 31 is connected in parallel with the first switch 22, the buffer circuit 3 is activated, and when the capacitor 31 is disconnected from the first switch 22, the buffer circuit 3 is deactivated. To connect the capacitor 31 in parallel with the first switch 22 and to disconnect the capacitor 31 from the first switch 22, the buffer circuit 3 may include a second electronic switch 32 connected in series with the capacitor 31. The series circuit including the capacitor 31 and the second switch 32 of the buffer circuit 3 is connected in parallel with the first switch 22.

[0023] Hereinafter, the first switch 22 is also referred to as the power switch, the second switch 32 is also referred to as the buffer switch, and the capacitor 31 of the buffer circuit 3 is also referred to as the buffer capacitor.

[0024] The power converter can operate in a first operation mode and a second operation mode. The first operation mode is the operation mode in which the buffer circuit 3 is activated, and the second operation mode is the operation mode in which the buffer circuit 3 is deactivated. This will be further described in detail below.

[0025] Referring to Figure 1, the power converter may further include input nodes 11, 12 configured to receive an input voltage Vin and an input current Iin, and output nodes 13, 14 configured to provide an output voltage Vout and an output current Iout. According to one example, the power converter is configured to regulate the output voltage Vout such that the power converter operates as a voltage source. According to another example, the power converter is configured to regulate the output current Iout such that the power converter operates as a current source.

[0026] According to one example, the power converter is a boost converter. In this example, a series circuit including an inductor 21 and a power switch 22 is connected between the input nodes 11, 12 such that the series circuit having the inductor 21 and the power switch 22 receives the input voltage Vin. Additionally, the power converter may include a rectifier 23, and the rectifier 23 is coupled between the series circuit including the inductor 21 and the power switch 22 on one side and the output nodes 13, 14 on the other side. More specifically, the rectifier 23 may include an input connected to the power switch 22 and an output connected to the output nodes 13, 14 of the power converter.

[0027] For illustrative purposes only, according to Figure 1 the rectifier 23 includes a rectifier element 231 (e.g., a diode) and a capacitor 232 connected in series, wherein the series circuit including the rectifier element 231 and the capacitor 232 is connected in parallel with the power switch 22 and the buffer circuit 3. The capacitor 232 (hereinafter also referred to as the output capacitor) is connected to the output nodes 13, 14 such that the output voltage Vout is available across the output capacitor 232. However, implementing the rectifier 23 in the Figure 1 manner shown is only an example. Other types of rectifiers may also be used, such as rectifiers that include an inductor in addition to a capacitor and a rectifier element.

[0028] Referring to Figure 1 , the power converter may further include a control circuit 4 configured to control the operation of the power converter. More specifically, the control circuit 4 is configured to control the operation of the power switch 22 and the buffer switch 32. To this end, the control circuit 4 is configured to provide a first drive signal S22 at a first node (pin) 41 and a second drive signal S32 at a second node (pin) 42. The first drive signal S22 is provided to the power switch 22 and is configured to turn on or off the power switch 22. The second drive signal S32 is provided to the buffer switch 32 and is configured to turn on or off the buffer switch 32 to activate or deactivate the buffer circuit 3.

[0029] According to one example, the control circuit 4 is configured to generate the first drive signal S22 and the second drive signal S32 at least based on a feedback signal Vout' and an auxiliary signal Vaux.

[0030] The auxiliary signal Vaux represents the magnetization state of the inductor 21. According to one example, the auxiliary signal Vaux is the voltage across an auxiliary inductor 24 that is inductively coupled to the inductor 21. According to one example, the auxiliary signal Vaux is provided to the third node (pin) 43 of the control circuit 4.

[0031] The feedback signal Vout' represents the output signal to be regulated. The feedback signal Vout' is substantially proportional to the regulated output signal and can be obtained by measuring the output signal using an appropriate sensor. Referring to the above, for example, the output signal to be regulated is the output voltage Vout or the output current Iout. Thus, when the output voltage Vout is to be regulated, the feedback signal Vout' can be obtained by measuring the output voltage Vout, or when the output current Iout is to be regulated, the feedback signal Vout' can be obtained by measuring the output current Iout. The feedback signal Vout' is received at the fourth node (pin) 44 of the control circuit 4.

[0032] According to one example, in each of the first and second operating modes, operating the power converter includes operating the power switch 22 in a switching mode such as the PWM mode. This can include operating the power switch 22 in a plurality of consecutive drive cycles, where, in each drive cycle of the drive cycles, the electronic switch is in the on state (closed state) during the on-time and in the off state (open state) during the off-time. The durations of the on-time and the off-time can vary to regulate the output signal (e.g., the output voltage Vout or the output current Iout).

[0033] In each drive cycle, during the on-time, the input voltage Vin is applied to the inductor 21 such that the inductor 21 is magnetized. During the off-time, the inductor 21 is demagnetized and forces the current to pass through the rectifier 23 to the output nodes 13, 14.

[0034] The electronic switch, i.e., the power switch 22 and the buffer switch 32, can be implemented in various ways. For example, the electronic switches 22, 32 are transistor devices. According to Figure 2 one example shown in, the transistor device is a MOSFET, such as an N-type enhancement MOSFET, which can be based on silicon (Si) or silicon carbide (SiC), for example. However, this is only an example. Other types of transistor devices can also be used, such as, IGBT, JFET, or GaN-HEMT (gallium nitride high electron mobility transistor) or other types of MOSFETs. According to one example, the two switches 22, 32 are the same type of transistor device, such as an N-type enhancement MOSFET. According to another example, the two switches 22, 32 are different types of transistor devices.

[0035] According to an example, the input voltage Vin received by the power converter is a rectified input voltage, such as a rectified sinusoidal voltage. Figure 3 A timing diagram of the input voltage as a rectified sinusoidal voltage is schematically shown, and Figure 4 an example of a rectifier circuit configured to generate a rectified voltage based on an AC input voltage Vac is shown. For example, the AC input voltage is a sinusoidal voltage. The RMS value of the AC voltage is, for example, 110 Vrms or 230 Vrms. For example, the frequency is 50 Hz or 60 Hz.

[0036] Referring to the above, the power converter can operate in a first operating mode or a second operating mode. According to an example, the first operating mode is the critical conduction mode (CrCM), and the second operating mode is the continuous conduction mode (CCM). The following refers to Figures 4 to 6 describe these operating modes, Figures 4 to 6 a signal diagram of the signals that occur in the power converter during operation is shown.

[0037] Figures 5 to 6 The operation of the power converter in CrCM is shown. Figures 5 to 6 Each of the figures in shows a signal diagram of the switching voltage V22 as the voltage across the power switch 22, the auxiliary signal Vaux as the voltage across the auxiliary inductor 24, the input current Iin as the current through the inductor 21, and the first drive signal S22. Figures 5 to 6 Each of the figures in shows a number of consecutive drive signals, where in each of these drive signals, the power switch 22 is turned on during the on-time and turned off during the off-time. During the on-time, the first drive signal S22 has a conduction level that turns on the power switch 22. During the off-time, the drive signal S22 has a turn-off level that turns off the power switch 22. For illustrative purposes only, in Figures 5 to 6 the conduction level of the first drive signal S22 is a high signal level, and the turn-off level is a low signal level. In addition, Ton represents the duration of one on-time, and Toff represents the duration of one off-time.

[0038] Referring to Figures 5 to 6, during the conduction time of the power switch 22, the switch voltage V22 is substantially zero. The auxiliary inductor 24 can be connected in such a way that during the conduction time, the auxiliary voltage Vaux is negative and has a magnitude that is substantially proportional to the inductor voltage VL, which is the voltage across the inductor 21. The proportionality factor is given by the ratio between the number of windings of the inductor 21 and the number of windings of the auxiliary inductor 24. According to one example, the auxiliary inductor 24 is connected such that a first circuit node of the auxiliary inductor 24 is connected to a circuit node having the same potential as one of the input nodes 11, 12, specifically 12, and a second circuit node of the auxiliary inductor 24 is connected to the third node 43 of the control circuit 4.

[0039] During the conduction time, the inductor voltage VL is substantially equal to the input voltage Vin, such that during the conduction time, the magnitude of the auxiliary voltage Vaux is substantially proportional to the input voltage Vin. During the conduction time, the inductor 21 is magnetized, i.e., energy is magnetically stored in the inductor 21.

[0040] Referring to Figures 5 to 6 , when the electronic switch 22 is turned off, the switch voltage V22 rapidly increases to a voltage level that is substantially equal to the voltage level of the output voltage Vout. Due to the voltage drop across the rectifier 23, the switch voltage V22 is slightly higher than the output voltage Vout. As the current provided by the inductor 21 and flowing through the rectifier 23 decreases, the voltage across the rectifier 23 decreases during the turn-off time.

[0041] During the turn-off time, the inductor 21 is demagnetized. When the inductor voltage VL reaches zero, the inductor 21 has been fully demagnetized, such that the switch voltage V22 is equal to the input voltage Vin. In CrCM, once the inductor 21 has been demagnetized, or shortly thereafter, the switch 22 is turned on again. After the inductor 21 has been magnetized, parasitic oscillations of the switch voltage V22 may occur. These parasitic oscillations are due to a parasitic resonant circuit including the output capacitance C22 of the power switch 22. In Figure 1 and Figure 2 , the output capacitance C22 of the power switch 22 is represented by a capacitor connected in parallel with the power switch 22.

[0042] These parasitic oscillations can cause the switch voltage V22 to further decrease after the inductor 21 has been demagnetized. In the example shown in Figure 5 and Figure 6 , after the switch voltage V22 reaches its minimum value due to parasitic oscillations, the power switch 22 is turned on again. Turning on the electronic switch 22 when the switch voltage V22 reaches its minimum value helps to reduce the switching losses that occur during the switching-mode operation of the power switch 22.

[0043] The duration between the moment when the inductor 21 has been demagnetized, i.e., the moment when the switching voltage V22 is equal to the input voltage Vin, and the moment when the switching voltage V22 reaches a (local) minimum value is substantially equal to one - quarter of a period of the parasitic oscillation. The duration of a period of the parasitic oscillation can be obtained through simulation or measurement on a prototype circuit. Thus, according to Figure 5 and Figure 6 In an example shown, after a predefined time period after the inductor 21 has been demagnetized, the off - time expires and the switch 22 is turned on again. According to an example, the predefined time period is substantially equal to one - quarter of a period of the parasitic oscillation of the switching voltage V22 that may occur after the inductor 21 has been demagnetized.

[0044] Referring to Figures 5 to 6 the moment when the inductor 21 has been demagnetized such that the switching voltage V22 is equal to the input voltage Vin is equal to the moment when the auxiliary voltage Vaux reaches zero. Thus, according to an example, the power switch 22 is turned on again after a predefined time period after the auxiliary voltage Vaux has reached zero.

[0045] Figure 5 and Figure 6 show two different scenarios of the switching voltage V22 and the auxiliary voltage Vaux that may occur. In the example shown in Figure 5 the input voltage Vin is greater than 50% of the output voltage Vout, Vin > Vout / 2. In this example, when the inductor has been demagnetized, the switching voltage V22 does not drop to zero. That is, the minimum value that the switching voltage V22 reaches after the inductor 21 is demagnetized is greater than zero. In the example shown in Figure 6 the input voltage is less than 50% of the output voltage Vout, Vin < Vout. In this example, the minimum value that the switching voltage V22 reaches after the inductor 21 has been demagnetized is substantially equal to zero.

[0046] Hereinafter, T CrCM represents the duration of a driving period in CrCM. The duration T CrCM is given by the duration Ton of the on - time plus the duration Toff of the off - time in the corresponding driving period, T CrCM = Ton + Toff. In CrCM, the duration of a driving period and thus the switching frequency f CrCM can vary. The switching frequency f CrCM as the frequency at which the switch 22 is turned on is given by the reciprocal of the driving - period duration T CrCM f CrCM = 1 / T CrCMGiven. Basically, at a given input voltage Vin and a given output voltage Vout, as the duration Ton of the on-time increases, the drive cycle duration T CrCM increases and the switching frequency f CrCM decreases. An example for adjusting the duration Ton of the on-time is further described herein below.

[0047] Figure 7 A signal diagram showing operation of a power converter in CCM is shown. More specifically, Figure 7 a signal diagram of the switch voltage V22, the auxiliary signal Vaux, and the drive signal S22 received by the power switch 22 in CCM is shown.

[0048] According to one example, in CCM, the power converter operates at a fixed switching frequency f CCM . That is, the power switch 22 is turned on at a fixed frequency f CCM . For example, the switching frequency f CCM is defined by a clock signal CLK. According to one example, a new on-time of the power switch 22 starts whenever a pulse of the clock signal CLK appears. The duration Ton of the on-time can vary. An example for adjusting the duration Ton of the on-time is further described herein below.

[0049] In CCM, the duration T of each drive cycle CCM is fixed and given by the reciprocal of the switching frequency T CCM = 1 / f CCM . In addition, the duration T of a drive cycle CCM is given by the duration Ton of an on-time in a corresponding drive cycle plus the duration Toff of an off-time.

[0050] As can be seen from Figure 7 , in CCM, the inductor 21 typically does not fully demagnetize. Thus, during the off-time, the switch voltage V22 is equal to or higher than the output voltage Vout. The switch voltage V22 substantially reduces to zero when the electronic switch 22 is turned on, and increases again to a voltage level equal to or higher than the output voltage Vout when the electronic switch 22 is turned off.

[0051] Referring to the above, the input voltage Vin can be a rectified AC voltage, such as a rectified sinusoidal voltage. In this example, the input voltage Vin varies between zero and a voltage level substantially given by the magnitude of the AC voltage Vac. The frequency of the rectified input voltage is twice the frequency of the AC voltage Vac.

[0052] It should be noted that, in each of CrCM and CCM, the switching frequencies f CrCM and fCCM A frequency much higher than the AC voltage Vac and the rectified input voltage Vin such that the input voltage Vin can be considered to be substantially constant during the corresponding drive cycle. For example, the switching frequency is higher than 10 kHz, higher than 50 kHz, or higher than 100 kHz.

[0053] Referring to the above, in CrCM, the inductor 21 is completely demagnetized in each drive cycle of the device. This may cause a rather high fluctuation in the input current Iin of the power converter. Activating the buffer circuit 3 in CrCM, which adds a capacitor in parallel with the electronic switch 22, can help reduce the harmonics caused by such fluctuations in the input current Iin.

[0054] According to one example, the capacitance of the buffer capacitor 31 is selected between 0.5 nanofarads (nF) and 5 nF, particularly between 0.9 nF and 3 nF.

[0055] When the electronic switch 22 is turned off and the voltage V22 across the switch 22 increases, the buffer capacitor 31 connected in parallel with the power switch 22 in CrCM is charged. When the switch 22 is turned on, the charge stored in the buffer capacitor 31 is transferred to the input capacitor 25 through a resonant process that involves a resonant circuit including the buffer capacitor 31, the output capacitor C22 of the switch 22, the inductor 21, and parasitic inductance. Thus, the energy stored in the buffer capacitor 31 is recovered and not dissipated in the switch 22.

[0056] In addition to reducing the harmonics of the input current Iin in CrCM, the activated buffer circuit 3 also helps reduce the switching losses that may occur in the electronic switch 22.

[0057] Figure 8 An example of the control circuit 4 is shown, which is configured to operate the power converter in CrCM or CCM and is configured to activate the buffer circuit 3 in CrCM and deactivate the buffer circuit 3 in CCM. It should be noted that Figure 8 The block diagram shown shows the functions of the control circuit 4 rather than the specific implementation. The functional blocks shown can be implemented in various ways Figure 8 The functional blocks shown. According to one example, dedicated circuits are used to implement these functional blocks. According to another example, hardware and software are used to implement the control circuit 4. For example, the control circuit 4 includes a microcontroller and software executed by the microcontroller.

[0058] Referring to Figure 8, the control circuit 4 includes a first controller 41, a second controller 42, and a mode selector 43. The first controller 41 is configured to control the operation of the power converter in CCM and is configured to output a CCM drive signal Sccm. The first controller 41 may also be referred to as a CCM controller. The second controller 42 is configured to control the operation of the power converter in CrCM and is configured to output a CrCM drive signal Scrcm. The second controller 42 may also be referred to as a CrCM controller. Both the CCM drive signal Sccm and the CrCM drive signal Scrcm are PWM signals, wherein, in CCM, the CCM drive signal Sccm is provided to the power switch 22 as a first drive signal S22, and in CrCM, the CrCM drive signal Scrcm is provided to the power switch 22 as a first drive signal S22.

[0059] Reference Figure 8 , the control circuit 4 may include a multiplexer 44. The multiplexer 44 receives the drive signals Sccm and Scrcm from the first controller 41 and the second controller 42 as input signals, and receives a mode control signal Smode from the mode selector 43. The multiplexer 44 is configured to output one of the CCM signal Sccm and the CrCM signal Scrcm as the first drive signal S22 according to the mode control signal Smode. According to one example, the mode control signal Smode has two different signal levels, the first signal level indicating CCM and the second signal level indicating CrCM. In this example, the multiplexer 44 is configured to output the CCM drive signal Sccm as the first drive signal S22 whenever the mode control signal Smode has the first signal level indicating CCM, and to output the CrCM drive signal Scrcm as the first drive signal S22 whenever the mode control signal Smode has the second signal level indicating CrCM. According to Figure 8 an example shown in, the control circuit 4 is further configured to output the mode control signal Smode as a second drive signal S32, wherein the second drive signal S32 deactivates the buffer circuit 3 when the second drive signal S32 has the first signal level indicating CCM and activates the buffer circuit 3 when the second drive signal S32 has the second signal level indicating CrCM.

[0060] The first controller 41 may be a conventional controller configured to control the operation of a power converter, such as a power converter having a boost topology as shown in Figure 1 and Figure 2 in, in CCM. Refer to Figure 8, the first controller 41 can receive a clock signal CLK that defines a switching frequency under CCM and an error Verr signal. The error signal Verr represents the difference between the instantaneous signal level of the output signal to be regulated and the desired signal level. According to one example, the output voltage Vout is the output signal to be regulated. In this example, the error signal Verr represents the difference between the instantaneous signal level of the output voltage Vout and the signal level of the reference signal. In this example, as Figure 8 shown in, the error signal Verr can be generated by subtracting the measured output voltage Vout' from the reference voltage Vref using a subtractor 45. The measured output voltage Vout' represents the instantaneous signal level of the output voltage and can be obtained using any kind of conventional voltage sensor. For example, the measured output voltage Vout' is proportional to the output voltage Vout. The reference voltage Vref represents the desired voltage level of the output voltage Vout.

[0061] Referring to the above, under CCM, the power converter operates at a fixed switching frequency defined by the clock signal CLK. The first controller 41 generates a CCM drive signal Sccm according to the Figure 7 first drive signal S22 shown in.

[0062] According to one example, the first controller 41 is configured to increase the duration of the on-time in a continuous drive cycle whenever the error signal Verr indicates that the output voltage Vout is lower than desired, and to decrease the duration of the on-time whenever the error signal Verr indicates that the output voltage Vout is higher than desired. Increasing the on-time duration is equivalent to increasing the duty cycle of the PWM operation of the electronic switch 22, and decreasing the on-time duration is equivalent to decreasing the duty cycle. The duty cycle is given by dividing the duration Ton of the on-time in the corresponding drive cycle by the (fixed) duration T of the drive cycle CCM is given.

[0063] In addition to the clock signal CLK and the error signal Verr, the first controller 41 can also receive a measured input current Iin' and a measured input voltage Vin'. The measured input current Iin' represents the instantaneous current level of the input current Iin and can be obtained by measuring the input current Iin using a conventional current sensor. For example, the measured input current Iin' is proportional to the input current Iin. The measured input voltage Vin' represents the instantaneous voltage level of the input voltage Vin and can be obtained by measuring the input voltage using a conventional voltage sensor. For example, the measured input voltage Vin' is proportional to the input voltage Vin.

[0064] According to one example, the first controller 41 is a PFC controller. In this example, the first controller 41 is configured not only to regulate one of the output signals, such as the output voltage Vout, but also to regulate the signal waveform of the input current Iin such that the signal waveform of the average input current Iin corresponds to the waveform of the input voltage Vin. Thus, if the input voltage Vin is a rectified sinusoidal voltage, the average input current Iin is a rectified sinusoidal current. The "average input current Iin" is the average value of the input current over at least one driving period within the driving cycle. PFC controllers are well-known and thus do not require detailed description in this regard.

[0065] For completeness, Figure 9 an example of the PFC controller 41 is shown. Referring to Figure 9 , the PFC controller 41 includes a latch, such as the SR flip-flop 411 that provides the CCM drive signal Sccm. It should be noted that the signal output by the latch 411 can be a logic signal, and the PFC controller 41 may also include a driver configured to generate a signal level sufficient to drive the power switch 22 of the CCM drive signal Sccm. However, Figure 9 such a driver is not shown in

[0066] In the example according to Figure 9 , the latch 411 is set by the clock signal CLK received at the set input S at the start of each new driving period and reset by the comparator S412 received at the reset input R. The conduction time duration Ton is given by the time period between the moment when the latch 411 is set and the moment when the latch 411 is reset. In the example according to Figure 9 , the comparator signal defines the end of the conduction time based on the error signal Verr, the measured input voltage Vin', and the measured input current Iin. The comparator 412 compares the measured input current Iin' that increases during the conduction time with the multiplier output signal S413 that depends on the measured input voltage Vin' and the error signal Verr. Whenever the increased measured input current Iin' reaches the multiplier output signal S413 given by the multiplication of the error signal Verr and the measured input voltage Vin', the latch 411 is reset to end the conduction time and turn off the power switch. In this way, simultaneously, the output voltage Vout represented by the error signal Verr can be regulated, and the signal waveform of the average input current can be regulated to be equal to the signal waveform of the input voltage Vin represented by the measured input voltage Vin'.

[0067] Referring to Figure 8, the second controller 42 receives an error signal Verr and an auxiliary signal Vaux, and is configured to generate a CrCM drive signal Scrcm based on the auxiliary signal Vaux and the error signal Verr. The second controller 42 generates the CrCM drive signal Scrcm according to Figure 5 and Figure 6 the first drive signal S22 shown in

[0068] According to one example, the second controller 42 is configured to start a new drive cycle according to the auxiliary signal Vaux. According to one example, the second controller 42 is configured to detect the zero-crossing point of the auxiliary signal Vaux, and start a new drive cycle at the first zero-crossing point after the power switch 22 has been turned off or at a predefined time period after the first zero-crossing point. According to one example, the second controller 42 adjusts the duration of the on-time in each drive cycle according to the error signal Verr, where the duration of the on-time can increase when the error signal Verr indicates that the output signal, such as the output voltage Vout, is lower than expected or can decrease when the error signal Verr indicates that the output signal is higher than the expected value.

[0069] According to one example, the second controller 42 is a PFC controller. PFC controllers operating under CrCM are well known, and thus no detailed description is needed in this regard.

[0070] For the sake of completeness, Figure 10 an example of a PFC controller 42 operating under CrCM is shown in Figure 10 The second controller 42 operates with a fixed on-time Ton and a variable off-time Toff. In this controller 42, a latch 421 is set by a zero-crossing detection signal Szcd. The zero-crossing detection signal Szcd is output by a zero-crossing detector 422 that receives the auxiliary signal Vaux, and is generated by the zero-crossing detector 422 such that a new drive cycle starts when the zero-crossing of the auxiliary signal Vaux is detected or after a predefined time period after such a zero-crossing has been detected. A delay element 422 receives the zero-crossing detection signal Szcd, and resets the latch 421 after a predefined time period after the latch 421 has been set by the zero-crossing detection signal Szcd. Thus, the on-time of the drive cycle ends after a predefined time period, where the predefined time period defines the on-time duration Ton. It is well known that the PFC function can be implemented by a second controller 42 of the type shown in

[0071] According to one example, the mode selector 43 is configured to switch between CCM and CrCM based on the clock signal CLK and the auxiliary signal Vaux. More specifically, the mode selector 43 is configured to generate a mode control signal Smode based on the clock signal CLK and the auxiliary signal Vaux to have a first signal level indicating CCM or a second signal level indicating CrCM.

[0072] According to one example, the mode selector 43 is configured to change the operation of the power converter from CCM to CrCM when the auxiliary signal Vaux indicates that the inductor 21 has been fully demagnetized during the off-time of the inductor 21 in CCM. The full demagnetization of the inductor 21 in CCM indicates that the conduction time duration Ton is quite short, such that a small amount of energy is stored in the inductor 21 during the conduction time, causing the inductor 21 to demagnetize quickly during the off-time. For example, a short conduction time duration may occur in a low-power mode, which is an operating mode in which the power consumption of the load connected to the output nodes 13, 14 is quite low. The transition of the power converter from CCM to CrCM may cause an increase in the switching frequency.

[0073] According to one example, the mode selector 43 is configured to change the operation of the power converter from CrCM to CCM when the switching frequency in CrCM becomes lower than the fixed switching frequency defined by the clock signal CLK in CCM. According to one example, the mode selector 43 is configured to obtain the switching frequency in CrCM from the auxiliary signal Vaux. The switching frequency is substantially equal to the frequency at which the zero-crossing of the auxiliary signal Vaux occurs in CrCM.

[0074] According to one example, the mode selector 43 is configured to change the operation mode immediately when the corresponding condition for changing the operation mode is detected. According to another example, the mode selector 43 is configured to change the operation mode of the power converter only at the start of a new cycle of the input voltage Vin. In this example, the mode selector 43 detects the condition for changing the operation mode and waits until the end of the current cycle of the input voltage Vin and the start of a new cycle before changing the operation mode.

[0075] Figure 11 The latter is shown in Figure 11 schematically shows the input current Iin, the output current Iout, and the average input current of the power converter <iin>Signal diagram. Average input current <iin>is the average value of the input current Iin over one or more drive cycles of the switching-mode operation of the power converter. Additionally, Figure 11 The signals CCM and CrCM shown in Figure 11 indicate the operating modes of the power converter, where a high signal level of the signal CCM indicates that the power converter is operating in CCM, and a high signal level of the signal CrCM indicates that the power converter is operating in CrCM.

[0076] For illustrative purposes, it is assumed that the output voltage Vout of the power converter ( Figure 11 not shown in Figure 11 ) is regulated to have a predefined voltage level. The output power of the power converter is given by the output voltage multiplied by the output current Iout. Basically, in the case where the output power received by the load connected to the output nodes 13, 14 is relatively high, the power converter operates in CCM, and in the case where the output power is relatively low, the power converter operates in CrCM. In Figure 11 the example shown in Figure 11 , a change in the output power occurs whenever the output current Iout changes.

[0077] In Figure 11 the example shown in Figure 11 , the power converter first operates in CCM. At a first moment t1, the output power significantly decreases, which causes a reduction in the conduction time duration, where this reduction in the conduction time duration causes the inductor 21 to be fully demagnetized during the off time. However, the mode selector 43 does not immediately change the operating mode from CCM to CrCM, but waits until the end of the instantaneous cycle of the input voltage Vin before changing the operating mode from CCM to CrCM. At a later moment t2, the output power increases again, which may cause the switching frequency in CrCM to be lower than the fixed switching frequency in CCM. Therefore, the mode selector waits until the end of the instantaneous cycle of the input voltage and then changes the operating mode from CrCM back to CCM.

[0078] It should be noted that Figure 11 The scenario where the mode selector shown in changes the operating mode at the start of a new input voltage is merely an example. According to another example (not shown), the mode selector is configured to change the operating mode immediately once the corresponding condition for changing the operating mode is detected. That is, the mode selector changes the operating mode from CrCM to CCM once it detects that the switching frequency in CrCM is lower than the fixed switching frequency in CCM, or changes from CCM to CrCM once it detects that the inductor 21 is fully demagnetized in CCM. The first condition is equivalent to the occurrence of a signal pulse of the clock signal CLK before the zero crossing of the auxiliary signal is detected. The second condition is equivalent to the occurrence of the zero crossing of the auxiliary signal Vaux before the next signal pulse of the clock signal CLK appears. Thus, instead of determining the switching frequency in CrCM, the mode selector can simply compare the clock signal CLK and the auxiliary signal Vaux to detect the corresponding condition for changing the operating mode.

[0079] Referring to the above, Figure 8 The block diagram shown in illustrates the function of the control circuit 4 rather than its implementation. The control circuit 4 does not necessarily include two separate controllers, such as Figure 8 the first controller 41 and the second controller 42 shown in. Instead, there may also be a single controller that is controlled by the mode selector 43 and operates in a first operating mode in which a CCM drive signal is output and in a second operating mode in which a CrCM drive signal is output depending on the mode signal provided by the mode selector.

[0080] Some of the aspects described previously in this document are briefly summarized below with reference to numbered examples.

[0081] Example 1. A method of operating a power converter, comprising: operating a power converter including an inductor and an electronic switch connected in series with the inductor in one of a first operating mode and a second operating mode, wherein operating the power converter in the first operating mode includes activating a buffer circuit connected in parallel with the electronic switch, and wherein operating the power converter in the second operating mode includes deactivating the buffer circuit.

[0082] Example 2. The method according to Example 1, wherein the buffer circuit includes a buffer capacitor and another electronic switch connected in series with the buffer capacitor, wherein activating the buffer circuit includes turning on the other electronic switch, and wherein deactivating the buffer circuit includes turning off the other electronic switch.

[0083] Example 3. The method according to Example 1 or 2, wherein the first operating mode is the critical conduction mode, and wherein the second operating mode is the continuous conduction mode.

[0084] Example 4. The method according to Example 3, wherein operating the power converter in the first operating mode includes: operating the electronic switch in a plurality of drive cycles, each drive cycle including an on-time and a subsequent off-time, detecting the magnetization state of the inductor during the off-time, and starting a new on-time based on the detected magnetization state.

[0085] Example 5. The method according to Example 3 or 4, wherein operating the power converter in the second operating mode includes: operating the electronic switch in a plurality of drive cycles, each drive cycle including an on-time and a subsequent off-time, and turning on the electronic switch at a predefined switching frequency to start a new on-time.

[0086] Example 6. The method according to any one of Examples 4 and 5, wherein operating the power converter in the first operating mode includes: adjusting the duration of the on-time to be equal to a fixed value.

[0087] Example 7. The method according to any one of Examples 4 to 6, wherein operating the power converter in the second operating mode includes: adjusting the duration of the on-time according to a feedback signal.

[0088] Example 8. The method according to any one of Examples 3 to 7, further comprising: changing the operation of the power converter from the first operating mode to the second operating mode when a first condition is detected.

[0089] Example 9. The method according to Example 8, wherein the first condition is detected when: the duration of a drive cycle in the first operating mode becomes higher than a predefined duration, or the switching frequency in the first operating mode becomes lower than a fixed switching frequency in the second operating mode.

[0090] Example 10. The method according to Example 9, wherein the predefined duration is the reciprocal of a predefined switching frequency in the first operating mode.

[0091] Example 11. The method according to any one of Examples 8 to 10, wherein the power converter is configured to receive a rectified AC voltage, and wherein changing the operation of the power converter from the first operating mode to the second operating mode includes changing from the first operating mode to the second operating mode at the start of a new cycle of the rectified AC voltage after the first condition has been detected.

[0092] Example 12. The method according to any one of Examples 8 to 10, wherein the power converter is configured to receive a rectified AC voltage, and wherein changing the operation of the power converter from the first operating mode to the second operating mode includes changing from the first operating mode to the second operating mode as soon as the first condition has been detected.

[0093] Example 13. The method according to any one of Examples 3 to 12 further includes: when a second condition is detected, changing the operation of the power converter from a second operation mode to a first operation mode.

[0094] Example 14. The method according to Example 13, wherein the second condition is detected when: a predefined magnetization state of the inductor is detected in the second operation mode.

[0095] Example 15. The method according to Example 14, wherein the predefined magnetization state is a state in which the inductor has been completely demagnetized.

[0096] Example 16. The method according to Example 14 or 15, wherein detecting the predefined magnetization state of the inductor includes detecting a zero crossing of an auxiliary voltage across an auxiliary inductor inductively coupled to the inductor.

[0097] Example 17. The method according to any one of Examples 13 to 16, wherein the power converter is configured to receive a rectified AC voltage, and wherein changing the operation of the power converter from the second operation mode to the first operation mode includes: after the second condition has been detected, changing from the second operation mode to the first operation mode at the start of a new cycle of the rectified AC voltage.

[0098] Example 18. The method according to any one of Examples 13 to 16, wherein the power converter is configured to receive a rectified AC voltage, and wherein changing the operation of the power converter from the second operation mode to the first operation mode includes changing from the second operation mode to the first operation mode as soon as the second condition has been detected.

[0099] Example 19. The method according to any one of Examples 1 to 18, wherein the power converter further includes: an input node configured to receive an input voltage; and an output node configured to provide an output voltage, wherein a series circuit including an inductor and an electronic switch is connected between the input nodes, and wherein the power converter further includes a rectifier circuit connected in parallel with the electronic switch and connected to the output node.

[0100] Example 20. The method according to any one of Examples 2 to 18, wherein the capacitance of the buffer capacitor is selected between 0.5 nF and 5 nF, particularly between 0.9 nF and 3 nF.

[0101] Example 21. A control circuit configured to: operate a power converter including an inductor and an electronic switch connected in series with the inductor in one of a first operation mode and a second operation mode, wherein operating the power converter in the first operation mode includes activating a buffer circuit connected in parallel with the electronic switch, and wherein operating the power converter in the second operation mode includes deactivating the buffer circuit.

[0102] Example 22. A power converter, comprising: a converter circuit including an inductor and an electronic switch connected in series with the inductor; a buffer circuit connected in parallel with the electronic switch; and a control circuit according to Example 21.

[0103] Example 23. The power converter according to Example 22, wherein the control circuit is further configured to control the operation of the electronic switch.< / iin> < / iin>

Claims

1. A method of operating a power converter, comprising: operating the power converter including an inductor (21) and an electronic switch (22) connected in series with the inductor (21) in one of a first operating mode and a second operating mode, wherein operating the power converter in the first operating mode comprises activating a snubber circuit (3) connected in parallel with the electronic switch (22), and Wherein, operating the power converter in the second operating mode includes disabling the snubber circuit (3).

2. The method according to claim 1, in, The buffer circuit (3) comprises a buffer capacitor (31) and another electronic switch (32) connected in series with the buffer capacitor (31). wherein activating the buffer circuit (3) comprises switching on the other electronic switch (32), and Wherein, deactivating the buffer circuit (3) comprises turning off the other electronic switch (32).

3. The method according to claim 1 or 2, in, The first operating mode is a critical conduction mode, and Wherein, the second operation mode is a continuous conduction mode.

4. The method according to claim 3, in, Operating the power converter in the first operating mode includes: operating the electronic switch (22) in a plurality of drive cycles, each drive cycle comprising an on-time followed by an off-time, and The magnetization state of the inductor (21) is detected during the off-time, and a new on-time is started based on the detected magnetization state.

5. The method according to claim 3 or 4, in, Operating the power converter in the second operating mode includes: operating the electronic switch (22) in a plurality of drive cycles, each drive cycle comprising an on-time followed by an off-time, and The electronic switch (22) is switched on at a predefined switching frequency to start a new on-time.

6. The method according to any one of claims 4 and 5, in, Operating the power converter in the first operating mode includes: The duration Ton of the on-time is adjusted to be equal to a fixed value.

7. The method according to any one of claims 4 to 6, in, Operating the power converter in the second operating mode includes: The duration Ton of the on-time is adjusted according to the feedback signal Vout′.

8. The method according to any one of claims 3 to 7, further comprising: Upon detecting a first condition, operation of the power converter is changed from the first operating mode to the second operating mode.

9. The method according to claim 8, in, The first condition is detected when: The duration of the drive cycle in the first operation mode becomes higher than a predefined duration, or The switching frequency in the first operation mode becomes lower than the fixed switching frequency in the second operation mode.

10. The method according to claim 9, wherein: The predefined duration is the inverse of a predefined switching frequency in the first operation mode.

11. The method according to any one of claims 8 to 10, in, The power converter is configured to receive a rectified AC voltage Vin, and Wherein, changing the operation of the power converter from the first operation mode to the second operation mode comprises: changing from the first operation mode to the second operation mode at the beginning of a new cycle of the rectified AC voltage Vin after the first condition has been detected.

12. The method according to any one of claims 8 to 10, in, The power converter is configured to receive a rectified AC voltage Vin, and Wherein changing the operation of the power converter from the first operation mode to the second operation mode comprises changing from the first operation mode to the second operation mode once the first condition has been detected.

13. The method according to any one of claims 3 to 12, further comprising: Upon detecting a second condition, operation of the power converter is changed from the second operating mode to the first operating mode.

14. The method according to claim 13, in, The second condition is detected when: A predefined magnetization state of the inductor (21) is detected in the second operating mode.

15. The method according to claim 14, wherein: The predefined magnetization state is a state in which the inductor (21) has been completely demagnetized.

16. The method according to claim 14 or 15, in, Detecting the predefined magnetization state of the inductor (21) includes detecting a zero crossing of an auxiliary voltage Vaux across an auxiliary inductor (24) inductively coupled to the inductor (21).

17. The method according to any one of claims 13 to 16, in, The power converter is configured to receive a rectified AC voltage Vin, and Wherein, changing the operation of the power converter from the second operation mode to the first operation mode comprises: changing from the second operation mode to the first operation mode at the beginning of a new cycle of the rectified AC voltage Vin after the second condition has been detected.

18. The method according to any one of claims 13 to 16, in, The power converter is configured to receive a rectified AC voltage Vin, and Wherein changing the operation of the power converter from the second operation mode to the first operation mode comprises changing from the second operation mode to the first operation mode once the second condition has been detected.

19. The method according to any one of the preceding claims, in, The power converter further comprises: an input node (11, 12) configured to receive an input voltage Vin; and an output node (13, 14) configured to provide an output voltage Vout, wherein a series circuit including the inductor (21) and the electronic switch (22) is connected between the input nodes (11, 12), and The power converter further comprises a rectifier circuit (23) connected in parallel with the electronic switch (22) and connected to the output node (13, 14).

20. The method according to any one of claims 2 to 18, in, The capacitance of the buffer capacitor (31) is selected between 0.5 nF and 5 nF, in particular between 0.9 nF and 3 nF.

21. A control circuit, configured to: operating a power converter comprising an inductor (21) and an electronic switch (22) connected in series with the inductor (21) in one of a first operating mode and a second operating mode, in, Operating the power converter in the first operating mode includes activating a snubber circuit (3) connected in parallel with the electronic switch (22), and Wherein, operating the power converter in the second operating mode includes disabling the snubber circuit (3).

22. A power converter comprising: A converter circuit comprising an inductor (21) and an electronic switch (22) connected in series with the inductor (21); a buffer circuit (3) connected in parallel with the electronic switch (22); and A control circuit according to claim 21.

23. The power converter according to claim 22, in, The control circuit is also configured to control the operation of the electronic switch (22).

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