Power converter and method of operating power converter

Abstract

A power converter and a method of operating a power converter are disclosed. A power converter includes: a converter circuit having a first electronic switch and a first inductor connected in series with the first electronic switch; a control circuit configured to control operation of the first electronic switch and including a first input node; and a sensing circuit. The sensing circuit includes a sensing resistor connected in series with the first electronic switch; a second inductor inductively coupled with the first inductor and coupled to a first input node of the control circuit; and a first coupling circuit coupling the sense resistor to a first input node of the control circuit. The first coupling circuit includes a first resistor coupled between the sense resistor and the first input node, and a second electronic switch connected in parallel with the first resistor. The control circuit is further configured to control operation of the second electronic switch.

Description

Technical Field

[0001] The present disclosure relates generally to power converters and methods of operating the same, and more particularly to switch-mode power converters including a sense resistor and a sense inductor and methods of operating the same. Background Art

[0002] A switch mode power converter may include an electronic switch and an inductor connected in series with the electronic switch, a sense resistor connected in series with the electronic switch, and an auxiliary inductor inductively coupled with the inductor. The sense resistor may be used to sense the current through the electronic switch, and the auxiliary inductor may be used to detect the magnetization state of the inductor. Information about the current through the electronic switch and information about the magnetization state of the inductor may be used to control the operation of the electronic switch so as to adjust the output current or output voltage of the power converter.

[0003] The power converter may further include a control circuit configured to control operation of the electronic switch and configured to receive current information from the current sensing resistor and magnetization information from the auxiliary inductor.

[0004] What is needed is a power converter in which the same input pin of a controller can be used to reliably receive both current sensing information and magnetization information. Summary of the invention

[0005] An example of the present disclosure relates to a power converter. The power converter includes: a converter circuit having a first electronic switch and a first inductor connected in series with the first electronic switch; a control circuit configured to control the operation of the first electronic switch and including a first input node; and a sensing circuit. The sensing circuit includes: a sensing resistor connected in series with the first electronic switch; a second inductor inductively coupled to the first inductor and coupled to the first input node of the control circuit; and a first coupling circuit that couples the sensing resistor to the first input node of the control circuit. The first coupling circuit includes: a first resistor coupled between the sensing resistor and the first input node, and a second electronic switch connected in parallel with the first resistor. The control circuit is also configured to control the operation of the second electronic switch.

[0006] Another example of the present disclosure relates to a method for operating a power converter. The method includes operating a sensing circuit in a power converter in a first operating mode or a second operating mode. The power converter includes: a converter circuit having a first electronic switch and a first inductor connected in series with the first electronic switch. The sensing circuit includes: a sensing resistor connected in series with the first electronic switch; a first coupling circuit that couples the sensing resistor to a first input node of a control circuit; and a second inductor that is inductively coupled to the first inductor and coupled to the first input node of the control circuit. The first coupling circuit includes: a first resistor that is coupled between the sensing resistor and the first input node, and a second electronic switch that is connected in parallel with the first resistor. Operating the sensing circuit in the first operating mode includes operating the second electronic switch in an on state, and operating the sensing circuit in the second operating mode includes operating the second electronic switch in an off state. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following examples are described with reference to the accompanying drawings. The accompanying drawings are used to illustrate certain principles, and therefore only aspects necessary for understanding these principles are shown. These drawings are not drawn to scale. In the accompanying drawings, the same reference numerals represent similar features.

[0008] Figure 1 One example of a power converter including a converter circuit having a first electronic switch, a control circuit, and a sensing circuit having a second electronic switch is shown;

[0009] Figure 2 An example of a sensing circuit is shown in more detail;

[0010] Figure 3A and Figure 3B An example for implementing a first electronic switch and a second electronic switch is shown;

[0011] Figure 4 An example of a converter circuit including a boost converter topology is shown;

[0012] Figure 5 An example of a converter circuit including a flyback converter topology is shown;

[0013] Figure 6 An example of a feedback circuit is shown;

[0014] Figure 7 An example for generating a rectified AC voltage based on an AC voltage is shown;

[0015] Figure 8 shows a signal diagram illustrating one example for operating a power converter in continuous conduction mode (CCM);

[0016] Fig. 9 shows a signal diagram illustrating one example for operating a power converter in critical conduction mode (CrCM); and

[0017] Fig.10 A signal diagram illustrating one example for operating a power converter in quasi-resonant mode (QRM) is shown. DETAILED DESCRIPTION

[0018] In the following detailed description, reference is made to the accompanying drawings. The accompanying drawings form a part of the specification and, for illustrative purposes, show examples of how the invention may be used and implemented. It should be understood that the features of the various embodiments described herein may be combined with each other unless otherwise specifically indicated.

[0019] Figure 1 An example of a power converter, in particular a switch mode power converter, is shown. More specifically, Figure 1 A circuit diagram of a power converter according to an example is schematically shown. The power converter comprises a converter circuit 1, a sensing circuit 2 and a control circuit 3. The converter circuit 1 comprises a first electronic switch 11 and a first inductor 12 connected in series with the first electronic switch 11. The control circuit 3 is configured to control the operation of the power converter by controlling the operation of the first electronic switch 11, and comprises a first input node 31 connected to the sensing circuit 2.

[0020] Reference Figure 1 , the sensing circuit 2 includes: a sensing resistor 21 connected in series with the first electronic switch 11; a second inductor 22 inductively coupled with the first inductor 12; a first coupling circuit 23 coupling the sensing resistor 21 to the first input node 31 of the control circuit 3; and a second coupling circuit 24 coupling the second inductor 22 to the first input node 31 of the control circuit. The first coupling circuit 23 includes: a first resistor 25 coupled between the sensing resistor 21 and the first input node 31, and an electronic switch 26 connected in parallel with the first resistor 25. In addition to controlling the operation of the first electronic switch 11, the control circuit 3 is also configured to control the operation of the second electronic switch 26 of the second coupling circuit 24.

[0021] According to an example, the first inductor 12 and the second inductor 22 have the same winding direction, so that the voltage V22 across the second inductor 22 has the same polarity as the voltage V12 across the first inductor 12. The voltage V22 across the second inductor 22 is substantially proportional to the voltage V12 across the first inductor 12, wherein the proportionality factor is given by the winding ratio of the first inductor 12 and the second inductor 22.

[0022] Each of the first electronic switch 11 and the second electronic switch 26 includes a control input terminal and a load path. The first electronic switch 11 is configured to be turned on or off according to the first drive signal S11 received at its control input terminal, and the second electronic switch 26 is configured to be turned on or off according to the second drive signal S26 received at its control input terminal. The load path of the first electronic switch 11 is a circuit path connected in series with the first inductor 12 and the sense resistor 21. The load path of the second electronic switch 26 is a circuit path connected in parallel with the first resistor 25 and connected between the sense resistor 21 and the first input node 31 of the control circuit 3.

[0023] In order to control the first electronic switch 11 and the second electronic switch 26, the control circuit 3 includes an output node 30, which may also be referred to as a driver output terminal. The control circuit 3 is configured to provide a switch drive signal S30 at the driver output terminal 30, wherein the first electronic switch 11 and the second electronic switch 26 are driven based on the switch drive signal S30. This includes generating a first drive signal S11 and a second drive signal S26 based on the switch drive signal S30. The first drive signal S11 and the second drive signal S26 may be identical and identical to the switch drive signal S30, such as Figure 1 However, this is only an example. Other examples for generating the first drive signal S11 and the second drive signal S26 based on the switch drive signal S30 are further described below.

[0024] Reference Figure 1 The converter circuit 1 comprises input terminals 13, 14 configured to receive an input voltage Vin and an input current Iin, and output terminals 15, 16 configured to provide an output voltage Vout and an output current Iout. Within the converter circuit 1, a series circuit comprising a first inductor 12 and a first electronic switch 11 is connected to the input terminals 13, 14, such that the first inductor 12 is magnetized when the first electronic switch 11 is in an on-state (conducting state), and the first inductor 12 is demagnetized when the first electronic switch 11 is subsequently in an off-state (off-state). Different examples for interconnecting the series circuit with the first electronic switch 11 and the first inductor 12 within the converter circuit 1 are further described below.

[0025] Magnetizing the first inductor 12 during the on-state of the first electronic switch 11 is associated with storing energy received from the input terminals 13, 14 in the first inductor 12, and demagnetizing the first inductor 12 during the off-state of the first electronic switch 11 is associated with transferring at least a portion of the energy stored in the first inductor 12 to the output terminals 15, 16. The control circuit 3 is configured to operate the first electronic switch 11 in a switching mode. This includes operating the first electronic switch 11 in a plurality of consecutive drive cycles, wherein each drive cycle includes an on-time during which the first electronic switch 11 is in the on-state and an off-time during which the first electronic switch 11 is in the off-state. The duty cycle d of the switch-mode operation of the first electronic switch 11 is given by the duration Ton of the on-time divided by the duration T of one drive cycle as shown in equation (1):

[0026]

[0027] In the converter circuit 1 , the power flow from the input terminals 13 , 14 to the output terminals 15 , 16 may be controlled by controlling the duty cycle of the switch mode operation of the first electronic switch 11 .

[0028] According to an example, the control circuit 3 is configured to control the operation of the power converter so that one of the output voltage Vout and the output current Iout is regulated. To this end, the control circuit receives a current sensing signal V21 from the sensing resistor 21 and a magnetization signal V22 from the second inductor 22. The current sensing signal V21 is the voltage across the sensing resistor 21, and the magnetization signal is the voltage V22 across the second inductor 22. The current sensing signal V21 includes information about the current level of the current I11 passing through the first electronic switch 11 when the first electronic switch 11 is in the on state. The magnetization signal includes information about the magnetization state of the first inductor 12. In particular, the magnetization signal includes information about the moment when the first inductor 12 has been demagnetized. Both the current sensing signal V21 and the magnetization signal V22 are received at the first input terminal 31 of the control circuit 3.

[0029] Optionally, the control circuit 3 may also receive a feedback signal Sout at the feedback input terminal 32. The feedback signal Sout represents the output voltage Vout or the output current Iout to be adjusted. According to an example, the feedback signal Sout is proportional to the output voltage Vout or the output current Iout to be adjusted.

[0030] Based on the current sensing signal V21 , the magnetization signal V22 and the optional feedback signal Sout, the control circuit 3 adjusts the duty cycle of the switch mode operation of the first electronic switch 11 so as to adjust the output voltage Vout or the output current Iout.

[0031] Referring to the above, the current sensing signal V21 and the magnetization signal V22 are received by the control circuit 3 at the first input terminal 31. The current sensing signal V21 represents the current I11 through the first electronic switch 11 during the on-state of the first electronic switch 11. During the off-state of the electronic switch 11, the sensing signal S31 represents the magnetization signal V22.

[0032] The current sensing signal V21 may be used to detect overcurrent and / or regulate the output voltage Vout or the output current Iout. This is further described below.

[0033] Reference Figure 1 , the input voltage Vin is a voltage with reference to a reference node GND, which is also referred to as a ground node hereinafter. The voltage across the second inductor 22 representing the magnetization signal V22 and the voltage across the sensing resistor 21 representing the current sensing signal V21 are also voltages with reference to the ground node GND. According to an example, the control circuit 3 is connected to the ground node at the reference node 34, and the first input node 31 is coupled to the reference node 34 with high ohm, so that the sensing signal S31 is a voltage with reference to the ground node GND.

[0034] In accordance with Figure 1 In the power converter, the sensing circuit 2 is configured to operate in the first operation mode or the second operation mode.

[0035] When the first electronic switch 11 and the second electronic switch 26 are in the on state, the sensing circuit 2 is in the first operation mode. In this operation mode, the electronic switch 26 bypasses the first resistor 25 and directly connects the sensing resistor 21 to the first input node 31 of the control circuit 3, so that the sensing signal S31 received at the first input node 31 is substantially equal to the current sensing signal V21. As further detailed below, the second coupling circuit 24 is configured to decouple the second inductor 22 from the first input node 31 in the first operation mode, so that in the first operation mode, the sensing signal S31 received at the first input node 31 of the control circuit 3 is controlled by the current sensing signal V21. The sensing circuit 2 is in the first operation mode at least during a portion of the time period when the first electronic switch 11 is in the on state, so that when the sensing circuit 2 is in the first operation mode, the current sensing signal V21 represents the current I11 through the electronic switch 11.

[0036] When the first electronic switch 11 and the second electronic switch 26 are in the off state, the sensing circuit 2 is in the second operating mode. In this operating mode, the series circuit including the second coupling circuit 24, the first resistor 25 of the first coupling circuit 23 and the sensing resistor 21 couples the second inductor 22 to the ground node GND. According to an example, the resistance R25 of the first resistor 25 is significantly higher than the resistance R21 of the sensing resistor 21. According to an example, the resistance R25 of the first resistor 25 is at least 10 times, at least 100 times, or at least 1000 times the resistance R21 of the sensing resistor 21. In order to reduce conduction losses, it is desirable to implement a sensing resistor 21 with a low resistance R21. According to an example, the resistance R21 of the sensing resistor is selected from a range between 100 milliohms and 500 milliohms.

[0037] The first resistor 25 with a high resistance R25 ensures that in the off-state of the first electronic switch 11 the second inductor 22 provides a sufficiently high signal level of the sense signal S31 at the first input node 31 of the control circuit 3 .

[0038] Reference Figure 1 The control circuit 3 may further include a power supply node 33 configured to receive a power supply voltage Vcc for supplying power to the control circuit 3. For example, the power supply voltage Vcc is referenced to a ground node GND.

[0039] Figure 2 An example of the second coupling circuit 24 is shown in more detail. Figure 2 In the example shown, the second coupling circuit 24 comprises a second resistor 27 and a rectifier element 28 connected in series between the second inductor 22 and the first coupling circuit 23. The resistance of the second resistor 27 is selected from the same range as the resistance of the first resistor 25, for example.

[0040] The rectifier element 28 is, for example, a diode, wherein the polarity of the rectifier element 28 is such that the rectifier element 28 decouples the auxiliary winding 22 from the first input node 31 of the control circuit 3 when the electronic switch 11 is in the on state. When the first electronic switch 11 is in the on state, the voltage V22 across the second inductor 22 has a value such as Figure 2 In this operating state, the rectifier element 28 blocks and decouples the second inductor 22 from the first input node 31 .

[0041] Reference Figure 2 , the second coupling circuit 24 may further comprise a capacitor 291 connected in parallel with the rectifier element 28. This capacitor 291 is optional and helps to improve the dynamic behavior of the sensing circuit 2.

[0042] In addition, another rectifier element 292 such as a diode may be connected in parallel with the series circuit including the second inductor 22 and the second resistor 27. According to one example, the polarity of the other rectifier element 292 is such that when the first electronic switch 11 is in the on state, the other rectifier element 292 clamps the voltage at the connection point of the other rectifier element 292, the second resistor 27 and the rectifier element 28. In this operating state, the voltage V22 across the second inductor 22 has a voltage V22 of 1 / 20 V. Figure 2 The polarity shown is opposite to the polarity.

[0043] Any type of electronic switch can be used to implement the first electronic switch 11 and the second electronic switch 26. According to one example shown in FIG. 3 , each of the first electronic switch 11 and the second electronic switch 26 is a transistor device, such as, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Figure 3A and Figure 3B In the example shown, each of the first electronic switch 11 and the second electronic switch 26 is an N-type enhancement MOSFET. However, this is only an example. Any other type of transistor device may also be used to implement the first electronic switch 11 and the second electronic switch 26.

[0044] like Figure 3A and Figure 3B As shown, the same type of transistor device can be used to implement the first electronic switch 11 and the second electronic switch 26. However, this is only an example. It is also possible to use a first type of transistor device to implement the first electronic switch 11 and a second type of transistor device to implement the second electronic switch 26.

[0045] exist Figure 3A and Figure 3B In the example shown, the load path of the first electronic switch 11 is the drain-source path of the MOSFET forming the first electronic switch 11, and the control node of the first electronic switch 11 is the gate node of the MOSFET forming the first electronic switch 11. Equivalently, the load path of the second electronic switch 26 is the drain-source path of the MOSFET forming the second electronic switch 26, and the control node of the second electronic switch 26 is the gate node of the MOSFET forming the second electronic switch 26.

[0046] exist Figure 3A In the example shown, the control node of the first electronic switch 11 is connected to the drive node 30 via the first gate resistor 111, and the control node of the second electronic switch 26 is connected to the drive node 30 via the second gate resistor 261. According to an example, the resistance R111 of the first gate resistor 111 and the resistance R261 of the second gate resistor 261 are substantially the same.

[0047] According to another example, the resistance R261 of the second gate resistor 261 is higher than the resistance R111 of the first gate resistor 111. In this example, when the drive signal S30 changes from the off level to the on level, the first electronic switch 11 is turned on faster than the second electronic switch 26. The "off level" of the drive signal S30 is a signal level that turns off the first electronic switch 11 and the second electronic switch 26, and the "on level" of the drive signal S30 is a signal level that turns on the first electronic switch 11 and the second electronic switch 26.

[0048] according to Figure 3B In another example shown, the control node of the first electronic switch 11 is connected to the driving node 30 via the first RC network 112, and the control node of the second electronic switch 26 is connected to the driving node 30 via the second RC network 262. Each RC network in the first RC network 112 and the second RC network 262 includes at least one capacitor and at least one resistor. Each RC network in the RC networks 112 and 262 is configured to generate a drive signal S11 and S26 suitable for driving the corresponding first electronic switch 11 or the second electronic switch 26 based on the drive signal S30 provided by the control circuit 3. As described above, the two electronic switches 11 and 26 can be implemented as different types of electronic switches. In this case, the RC networks 112 and 262 can be implemented in different ways, each RC network being suitable for driving the corresponding electronic switches 11 and 26.

[0049] The converter circuit 1 having the series circuit including the first electronic switch 11 and the first inductor 12 can be implemented in various ways. Figure 4 and Figure 5 Two different examples are described.

[0050] exist Figure 4 In the example shown, the power converter is a boost converter. In this example, a series circuit including a first electronic switch 11, a first inductor 12 and a sensing resistor 21 is connected between a first input node 13 and a second input node 14 at the input end, so that the series circuit receives an input voltage Vin. In this circuit, when the first electronic switch 11 is in an on state, the voltage V12 across the first inductor 12 is substantially equal to the input voltage Vin. In addition to the series circuit having the first electronic switch 11 and the first inductor 12, the converter circuit 1 also includes a rectifier circuit 10 connected in parallel with the first electronic switch 11. More specifically, the rectifier circuit 10 is connected in parallel with the series circuit including the first electronic switch 11 and the sensing resistor 21. The rectifier circuit 10 provides an output voltage Vout and an output current Iout.

[0051] The rectifier circuit 10 may be implemented in a variety of ways. For illustration purposes only, Figure 4 An example for implementing the rectifier circuit 10 is shown in FIG. In this example, the rectifier circuit 10 comprises a series circuit including a rectifier element 131 such as a diode and a capacitor 132, wherein the series circuit is connected in parallel with a series circuit including a first electronic switch 11 and a sensing resistor 21. An output voltage Vout is available across the capacitor 132.

[0052] In accordance with Figure 4 In a boost converter, for example, the output voltage Vout can be adjusted by appropriately controlling the input current Iin. The input current Iin can be controlled by controlling the switch mode operation of the electronic switch 11. Figure 4 In the boost converter of FIG. 1 , when the first electronic switch 11 is in the on state, the first inductor 12 is magnetized. In this operating state, the input current Iin is equal to the current I11 through the first electronic switch 11. When the first electronic switch 11 is in the off state, the first inductor 12 is being demagnetized. In this operating state, the input current Iin continues to flow through the rectifier circuit 10 to the output terminals 15, 16. Figure 4 The shown boost converter topology and its function are known, so that no further explanation is required in this regard.

[0053] exist Figure 5 In the example shown, the power converter is a flyback converter. In this example, a series circuit including a first electronic switch 11, a first inductor 12 and a sensing resistor 21 is connected between a first input node 13 and a second input node 14 at the input end. The first inductor 12 is the primary winding of the transformer. The transformer also includes a secondary winding inductively coupled to the primary winding. The primary winding 12 and the secondary winding 14 have opposite winding directions. The rectifier circuit 10 is connected in parallel with the secondary winding 14. The transformer having a primary winding and a secondary winding provides galvanic isolation between the input terminals 13, 14 and the output terminals 15, 16, so that the output voltage Vout is referenced to a reference potential GND', which is different from the reference potential GND to which the input voltage Vin is referenced.

[0054] In accordance with Figure 5 In the flyback converter of , for example, the output voltage Vout can be adjusted by appropriately controlling the input current Iin, wherein the input current Iin is controlled by the switch mode operation of the electronic switch 11. Figure 5In the flyback converter of FIG. 1 , when the first electronic switch 11 is in the on state, the first inductor 12 is magnetized. In this operation mode, the input current Iin is equal to the current I11 through the first electronic switch 11. When the first electronic switch 11 is in the off state, the first inductor 12 is being demagnetized. In this operation state, the input current Iin is zero, and the secondary winding 14 drives the current through the rectifier element 13 to the output terminals 15, 16. Figure 5 The flyback converter topology shown and its function are known, so that no further explanation is required in this regard.

[0055] Reference Figure 1 As described above, the control circuit 3 may receive a feedback signal Sout representing the output signal to be adjusted. That is, the feedback signal Sout represents the output voltage Vout or the output current Iout to be adjusted. The power converter may include a feedback circuit for generating the feedback signal Sout according to the corresponding output signal. Figure 6 An example of a feedback circuit 4 configured to generate a feedback signal Sout according to an output voltage Vout is shown in FIG.

[0056] exist Figure 6 In the example shown, the feedback circuit 4 includes a voltage divider having a first resistor 41 and a second resistor 42 connected in series between the output nodes 15 and 16. The feedback signal Sout is the voltage across one of the two resistors 41 and 42. Optionally, the feedback circuit 4 includes a voltage divider connected between the voltage divider 41 and 42 and the control circuit 3 ( Figure 6 The coupling circuit 43 is configured to transmit the feedback signal Sout across a galvanic isolation (such as a galvanic isolation in a flyback converter). To this end, the coupling circuit 43 includes, for example, an optocoupler.

[0057] However, using a voltage divider connected to the output nodes 15, 16 to generate the feedback signal Sout representing the output voltage Vout is only an example. According to another example (not shown), the feedback signal Sout is generated based on the voltage V22 across the second inductor 22. In a flyback converter, for example, during the off time of the electronic switch 11, the voltage V22 across the second inductor 22 is substantially proportional to the output voltage Vout, so that the voltage V22 across the second inductor 22 can be used to obtain output voltage information.

[0058] According to one example, the input voltage Vin is a direct current voltage (DC voltage).According to another example, the input voltage Vin is a rectified alternating current voltage, such as, for example, a rectified sinusoidal voltage. Figure 7 An example of an input circuit of a power converter is shown, which is configured to generate an input voltage Vin based on an alternating voltage Vac, such as a sinusoidal voltage.

[0059] Reference Figure 7 , the input circuit includes a rectifier 5 having input nodes 51, 52 configured to receive an AC voltage Vac. The rectifier 5 is configured to provide the rectified AC voltage as an input voltage Vin to the input nodes 13, 14. The rectifier 5 may include a conventional passive rectifier bridge. However, this is only an example. Other types of rectifiers 5 configured to rectify the AC voltage may also be used. Optionally, the input circuit also includes an EMI (electromagnetic interference) filter connected between the rectifier 5 and the input nodes 13, 14. The EMI filter 6 is configured to filter high-frequency components included in the input current Iin and the input voltage Vin, wherein such high-frequency signal components may be generated by the switch mode operation of the power converter.

[0060] According to one example, the power converter is a PFC converter. In this example, the control circuit 3 is not only configured to control the operation of the power converter so that one of the output voltage Vout and the output current Iout is regulated, but the control circuit 3 is also configured to control the operation of the power converter so that the waveform of the average input current is consistent with the waveform of the input voltage Vin. The "average input current" is the average value of the input current Iin over one or more drive cycles of the switch mode operation of the power converter. According to one example, the average input current is proportional to the input voltage Vin.

[0061] In the PFC converter, in addition to the sensing signal S31 and the output signal Sout, the control circuit 3 may receive an input signal (not shown in the drawing) representing the input voltage Vin and used by the control circuit 3 to control the input current Iin according to the voltage level of the input voltage Vin. This is basically known in the PFC converter, so no further explanation is needed in this regard.

[0062] The power converter can be operated in different operating modes. Figures 8 to 10 The timing diagrams shown illustrate the three different modes of operation. These timing diagrams involve operating in the three different modes of operation Figure 4 The boost converters of the types shown are continuous conduction mode (CCM), critical conduction mode (CrCM) and quasi-resonant mode (QRM). Each timing diagram shows the drive signal S30 provided by the control circuit 3, the input current Iin, the voltage V22 across the second inductor 22, the sense signal S31 at the first input node 31 of the control circuit 3 and the current sense signal V21.

[0063] Referring to the above, the driving signal S30 for operating the first electronic switch 11 and the second electronic switch 26 has an on-level for turning on the first switch 11 and the second switch 26 or an off-level for turning off the first switch 11 and the second switch 26. Figures 8 to 10 In the example shown, the on level is a high signal level and the off level is a low signal level.

[0064] exist Figures 8 to 10 In each of the different operation modes shown, operating the power converter includes operating the power converter in a plurality of consecutive drive cycles, wherein each drive cycle includes an on-time in which the first electronic switch 11 is in an on-state, followed by an off-time in which the first electronic switch 11 is in an off-state. The different operation states differ with respect to the timing of turning on the first electronic switch 11 again, that is, with respect to the timing of starting a new drive cycle.

[0065] In each of the three operation modes, the duration of the on-time Ton can be adjusted by the control circuit 3 according to the feedback signal Sout. According to an example, the control circuit 3 is configured to detect the power consumption of the load (not shown) connected to the output nodes 15, 16 based on the feedback signal Sout, and is configured to select one of the three operation modes according to the power consumption of the load. According to an example, the power converter operates in CCM under high load conditions, in CrCM under medium load conditions, and in QRM under low load conditions.

[0066] In each of the three operating modes, the current sensing signal V21 can be used by the control circuit 3 to detect an overcurrent scenario. According to one example, the control circuit 3 is configured to switch off the first electronic switch 11 whenever the current sensing signal reaches a predefined current level indicating that an overcurrent scenario has occurred.

[0067] According to another example, the current sensing signal V21 is used to control the output voltage of the output current Vout, Iout. In this example, a current threshold is generated based on the feedback signal Sout, and each time the first electronic switch 11 is turned off, the current I11 causes the first electronic switch 11 to reach the current threshold generated based on the feedback signal Sout. This type of operation mode of the power converter is generally referred to as a current mode.

[0068] Figure 8 A signal diagram showing one example of operating a power converter in CCM is shown. In this operating mode, the input current Iin increases during the on-time and decreases during the off-time. Figure 8In , Ton represents the duration of the on-time in one drive cycle, Toff represents the duration of the off-time in one drive cycle, and T represents the total duration of the drive cycle. Under CCM, a new on-time (a new drive cycle) starts before the input current Iin has decreased to zero during the off-time. Therefore, during the off-time, the first inductor 12 is not completely demagnetized.

[0069] In CCM, during the on-time, the voltage V22 across the second inductor 22 is proportional to the input voltage, and during the off-time, the voltage V22 across the second inductor 22 is proportional to the voltage given by the output voltage Vout minus the input voltage Vin, V22 ˜Vout−Vin.

[0070] In CCM, the control circuit 3 does not need the magnetizing signal V22 to regulate the output voltage Vout or the output current Iout. In addition, the control circuit 3 can operate the power converter at a fixed switching frequency. This includes that the total duration T of each drive cycle is the same.

[0071] Fig. 9 A signal diagram showing an example of operating a power converter under CrCM is shown. In this operating mode, the input current Iin increases during the on-time and decreases during the off-time. In addition, in this operating mode, the duration of the off-time is selected so that the first inductor 12 is completely demagnetized during the off-time, so that the input current Iin is reduced to zero during the off-time. Under CrCM, the control circuit 3 uses the magnetization signal V22 to detect the moment when the first inductor 12 has been completely demagnetized during the off-time. In addition, the control circuit 3 is configured to turn on the first electronic switch 11 again after a predetermined duration after detecting that the first inductor 12 has been demagnetized.

[0072] Fig.10 A signal diagram showing an example of operating a power converter under QRM is shown. In this operating mode, the input current Iin increases during the on-time, decreases during the off-time, and is substantially zero for a specific time period near the end of the off-time. In this operating mode, the first inductor 12 is completely demagnetized during the off-time. After the first inductor 12 has been demagnetized, parasitic oscillations may occur in the voltage V12 across the first inductor 12. Equivalently, parasitic oscillations of the magnetization signal V22 may occur. In this operating mode, the control circuit 3 is configured to start a new drive cycle after a predetermined number of cycles of parasitic oscillations have occurred, that is, after a predetermined number of zero crossings of the magnetization signal V22 have occurred. The number of zero crossings allowed to occur before a new drive cycle begins depends on the power consumption of the load and increases as the power consumption of the load decreases.

[0073] from Figures 8 to 10 It can be seen that during the on-time of the first electronic switch 11, the sensing signal S31 received at the first input node 31 of the control circuit 3 follows the current sensing signal V21. More specifically, the sensing signal S31 is substantially equal to the current sensing signal V21. The first input node 31 has an input capacitance (not shown in the figure). The input capacitance forms an RC element together with the sensing resistor 21. At the beginning of the on-time, the input capacitance is discharged so that the sensing signal S31 is zero. The input capacitance is quickly charged at the beginning of the on-time so that the sensing signal S31 increases rapidly and tracks the current sensing signal V21, wherein there is only a small difference (if any) between the current sensing signal V21 and the sensing signal S31.

[0074] In the power converter described above, the pin count of the control circuit 3 can be reduced by using the same first input pin 31 for receiving both the current sensing signal V21 representing the current I11 through the first electronic switch 11 and the magnetization signal V22 given by the voltage across the second inductor 22. The second electronic switch 26 ensures that the sensing signal S31 received at the first input node 31 during the on-state of the second electronic switch 26 is substantially equal to the current sensing signal V21, so that the sensing signal S31 is not distorted by the presence of the first resistor 25.

[0075] Some aspects of the power converter and method described heretofore are summarized below.

[0076] According to one example, a power converter includes: a converter circuit including a first electronic switch and a first inductor connected in series with the first electronic switch; a control circuit configured to control the operation of the first electronic switch and including a first input node; and a sensing circuit. The sensing circuit includes: a sensing resistor connected in series with the first electronic switch; a second inductor inductively coupled to the first inductor and coupled to the first input node of the control circuit; and a first coupling circuit coupling the sensing resistor to the first input node of the control circuit. The first coupling circuit includes: a first resistor coupled between the sensing resistor and the first input node, and a second electronic switch connected in parallel with the first resistor. The control circuit is also configured to control the operation of the second electronic switch.

[0077] The second inductor may be coupled to the first input node via a second coupling circuit, wherein the second coupling circuit includes a second resistor coupled between the second inductor and the first input node. The second coupling circuit may also include a rectifier element connected in series with the second resistor. The second coupling circuit may also include a capacitor connected in parallel with the rectifier element.

[0078] According to one example, the converter circuit has a boost converter topology.According to another example, the converter circuit has a flyback converter topology.

[0079] The control circuit may be configured to operate the second electronic switch in the on state at least during a portion of the time period in which the first electronic switch is in the on state. According to an example, the control circuit is configured to synchronously turn on and off the first electronic switch and the second electronic switch.

[0080] According to one example, a method for operating a sensing circuit in a power converter includes operating the sensing circuit in a first operating mode or a second operating mode. The power converter includes: a converter circuit having a first electronic switch and a first inductor connected in series with the first electronic switch. The sensing circuit includes: a sensing resistor connected in series with the first electronic switch; a first coupling circuit coupling the sensing resistor to a first input node of a control circuit; and a second inductor inductively coupled to the first inductor and coupled to the first input node of the control circuit. The first coupling circuit includes: a first resistor coupled between the sensing resistor and the first input node, and a second electronic switch connected in parallel with the first resistor. Operating the sensing circuit in the first operating mode includes operating the second electronic switch in an on state, and operating the sensing circuit in the second operating mode includes operating the second electronic switch in an off state.

[0081] The method may also include operating the first electronic switch in a plurality of drive cycles, each drive cycle including an on-time in which the first electronic switch is in an on-state and an off-time in which the first electronic switch is in an off-state, wherein operating the sensing circuit in the first operating mode further includes operating the sensing circuit in the first operating mode during at least a portion of the on-time of the first electronic switch. The method may also include monitoring a sensing signal received at a first input node of the control circuit during at least a portion of the off-time, and starting a new drive cycle based on the monitored sensing signal.

[0082] According to one example, the method further comprises monitoring a sense signal received at a first input node of the control circuit during at least a portion of the on-time, and turning off the first electronic switch when the sense signal reaches a predetermined threshold.

Claims

1. A power converter, comprising: A converter circuit (1) comprising a first electronic switch (11) and a first inductor (12) connected in series with the first electronic switch (11); a control circuit (3) configured to control the operation of the first electronic switch (11) and comprising a first input node (31); as well as Sensing circuit (2), Wherein, the sensing circuit (2) comprises: a sensing resistor (21) connected in series with the first electronic switch (11); a second inductor (22) inductively coupled to the first inductor (12) and coupled to a first input node (31) of the control circuit (3); and a first coupling circuit (23) coupling the sensing resistor (21) to a first input node (31) of the control circuit (3), The first coupling circuit (23) comprises a first resistor (25) and a second electronic switch (26), wherein the first resistor (25) is coupled between the sensing resistor (21) and the first input node (31), and the second electronic switch (26) is connected in parallel with the first resistor (25), and Wherein, the control circuit (3) is further configured to control the operation of the second electronic switch (26).

2. The power converter according to claim 1, in, The second inductor (22) is coupled to the first input node (31) via a second coupling circuit (24), The second coupling circuit (24) includes a second resistor (27) coupled between the second inductor (22) and the first input node (31).

3. The power converter according to claim 2, wherein: The second coupling circuit (24) further comprises a rectifier element (28) connected in series with the second resistor (27).

4. The power converter according to claim 3, wherein: The second coupling circuit (24) also includes a capacitor (291) connected in parallel with the rectifier element (28).

5. The power converter according to any one of claims 1 to 4, in, The converter circuit (1) has a boost converter topology.

6. The power converter according to any one of claims 1 to 4, in, The converter circuit (1) has a flyback converter topology.

7. A power converter according to any one of the preceding claims, in, The control circuit (3) is configured to operate the second electronic switch (26) in the on state at least during a portion of a time period in which the first electronic switch (11) is in the on state.

8. The power converter according to claim 7, in, The control circuit (3) is configured to synchronously turn on and off the first electronic switch and the second electronic switch.

9. A method of operating a power converter, comprising: operating a sensing circuit (2) in the power converter in a first operating mode or a second operating mode, The power converter comprises a converter circuit (1) having a first electronic switch (11) and a first inductor (12) connected in series with the first electronic switch (11). Wherein, the sensing circuit (2) comprises: a sensing resistor (21) connected in series with the first electronic switch (11); a first coupling circuit (23) coupling the sensing resistor (21) to a first input node (31) of a control circuit (3); and a second inductor (22) inductively coupled to the first inductor (12) and coupled to a first input node (31) of the control circuit (3), The first coupling circuit (23) comprises a first resistor (25) and a second electronic switch (26), wherein the first resistor (25) is coupled between the sensing resistor (21) and the first input node (31), and the second electronic switch (26) is connected in parallel with the first resistor (25). wherein operating the sensing circuit (2) in the first operating mode comprises operating the second electronic switch (26) in an on state, and Wherein, operating the sensing circuit (2) in the second operating mode includes operating the second electronic switch (26) in an off state.

10. The method according to claim 9, further comprising: operating the first electronic switch (11) in a plurality of drive cycles, each drive cycle comprising an on-time during which the first electronic switch (11) is in an on-state and an off-time during which the first electronic switch (11) is in an off-state, Wherein, operating the sensing circuit (2) in the first operating mode further comprises operating the sensing circuit (2) in the first operating mode at least during a portion of the on-time of the first electronic switch (11).

11. The method according to claim 10, further comprising: monitoring a sense signal (S31) received at a first input node (31) of the control circuit (3) during at least a portion of the off time, and A new driving cycle starts according to the monitored sensing signal (S31).

12. The method according to claim 10 or 11, further comprising: monitoring a sense signal (S31) received at a first input node (31) of the control circuit (3) during at least a portion of the on-time, and When the sensing signal (S31) reaches a predetermined threshold, the first electronic switch (11) is turned off.

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