Current sensing circuit and current sensing method

Abstract

The invention relates to a current sensing circuit and a current sensing method. A method for measuring current in a conductor, a current measurement circuit, and a power converter are disclosed. The method comprises measuring the current (IL) in the conductor in successive measurement periods using a current measurement circuit (2). Measuring the current (IL) in each measurement period comprises adjusting an initial measurement value of the measurement circuit (2) based on a measurement value obtained in a previous measurement period.

Description

Technical Field

[0001] The present disclosure relates generally to current sensing, and more particularly to current sensing in power converters such as, for example, DC-DC converters. Background Art

[0002] Operating a power converter such as a switch mode power converter includes sensing current flowing through the power converter during operation. The sensed current can be used to regulate the output voltage or output current of the power converter, can be used to protect the power converter from overcurrent, etc. Sensing the current can include coupling a current sensing circuit to a load current path through which the current to be sensed flows, or coupling a current sensing circuit to a sensing circuit path through which the sensed current flows. The sensed current can be obtained using a current mirror, a current sensing transistor, etc. For example, the current sensing circuit can be directly coupled to the load current path or the sensing circuit path using a sensing transistor, or can be indirectly coupled to the second path, for example, using an inductive current sensor.

[0003] Due to the switch mode operation of the power converter, ringing may occur in the current and / or may occur at the input of the current sensing circuit, wherein such ringing may have a negative impact on the current sensing. According to conventional solutions, the current sensing circuit is only activated during a predefined time period to reduce the ringing. After the current sensing circuit is activated, the current sensing circuit may require a period of time to provide correct sensing (measurement) results. The stabilization time between the moment when the current sensing circuit is activated and the moment when the current sensing circuit provides a reasonable sensing result may have a negative impact on functions such as the current or voltage regulation function of the power converter.

[0004] There is therefore a need for improved current sensing, such as in power converters. Summary of the invention

[0005] One embodiment is directed to a method. The method includes measuring current in a conductor in successive measurement cycles using a current measurement circuit. Measuring the current in each measurement cycle includes adjusting a starting measurement value of the measurement circuit based on a measurement value obtained in a previous measurement cycle.

[0006] Another embodiment relates to a current measurement circuit configured to measure current in a conductor in successive measurement cycles. The current measurement circuit is further configured in each measurement cycle to adjust a starting measurement value based on a measurement value obtained in a previous measurement cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following examples are explained with reference to the accompanying drawings. The accompanying drawings are used to illustrate certain principles and therefore only show aspects necessary for understanding these principles. The accompanying drawings are not drawn to scale. The same reference numerals in the accompanying drawings indicate similar features.

[0008] Figure 1 shows a signal diagram illustrating a conventional method for measuring current in a continuous measurement cycle;

[0009] Figure 2 shows a signal diagram illustrating an example of a method for measuring current in consecutive measurement cycles, wherein the method includes adjusting a starting measurement value in each measurement cycle based on a measurement value obtained in a previous measurement cycle;

[0010] Figure 3 shows a block diagram of a current measurement circuit according to one example;

[0011] Figure 4 The diagram shows Figure 3 An example of a current sensing circuit included in a current measurement circuit;

[0012] Figure 5 The diagram shows Figure 3 An example of a control circuit included in a current measurement circuit;

[0013] Figure 6 shows a signal diagram illustrating the Figure 5 An example of an operation control circuit;

[0014] Figure 7 An example of a power converter including a current measurement circuit is shown;

[0015] Figure 8 shows a signal diagram illustrating the Figure 7 The power converter includes a current measurement circuit and the operation of the power converter. DETAILED DESCRIPTION

[0016] In the following detailed description, reference is made to the accompanying drawings. The accompanying drawings form part of the specification and show examples of how the invention may be used and implemented for illustrative purposes. It should be understood that the features of the various embodiments described herein may be combined with each other unless otherwise specifically stated.

[0017] Figure 1 A signal diagram is shown which illustrates a conventional method for measuring the current IL in a conductor in a plurality of consecutive measurement cycles. In each of these measurement cycles, the current in the conductor is measured (sensed) to obtain a measurement signal Is representing the conductor current IL and, in an ideal case, proportional to the conductor current IL. The conductor current IL is also referred to as the load current hereinafter.

[0018] According to one example, the conductor current IL is generated by a switching process that includes alternately turning on and off an electronic switch connected in series with an inductor. The conductor connects the electronic switch and the inductor to, or connects a series circuit including the electronic switch and the inductor to, a power supply or other device in an electronic circuit. In a switching process of this type that may typically occur in a power converter, the conductor current IL increases when the electronic switch is in an on state (on state), and decreases when the electronic switch is in an off state (off state). Therefore, according to one embodiment, the conductor current IL is a current in a power converter, specifically, a current passing through an inductor in a power converter.

[0019] exist Figure 1 In the method shown in , measuring the conductor current IL includes measuring the conductor current IL during those time periods when the conductor current IL increases. This may include measuring the conductor current IL during those time periods when the electronic switch is in the on state. Figure 1 In the method shown in , the conductor current IL is measured during a measurement window having a duration Tmw. The measurement cycle comprises a measurement window and a pause window after the measurement window, wherein the conductor current is interrupted (paused) during the pause window.

[0020] Measuring the conductor current IL during the measurement window and providing the measurement signal Is includes using a current measurement circuit. Figure 1 In the method, the measurement circuit is reset after each measurement window so that the measurement signal Is is zero at the beginning of a new measurement window. The measurement signal then increases to reach a signal value representing the conductor current IL, and for the remaining measurement window, this signal value tracks the conductor current IL. The higher the conductor current IL, the longer it takes for the measurement signal Is at the beginning of the measurement window to reach the signal value representing the load current IL. The time period between the beginning of the measurement window and the moment when the measurement signal Is starts to represent the conductor current IL can be referred to as the stabilization time. Therefore, the higher the conductor current IL, the longer the stabilization time. Figure 1 As shown in , the conductor current IL increases with time, thereby increasing the stabilization time Tset from measurement window to measurement window.

[0021] What is needed is a method for measuring current through a conductor in a plurality of consecutive measurement cycles, each consecutive measurement cycle comprising a measurement window and a pause window following the measurement window, such that the measured current is associated with a reduced settling time. Figure 2 A signal diagram illustrating one example of such an approach is shown.

[0022] More specifically, Figure 2 The signal diagram of the load current IL to be measured and the signal of ( Figure 2Figure 1 is a signal diagram of a measurement signal Is generated by a measurement circuit (not shown) based on the load current IL. Figure 2 The method includes measuring the load current IL in a plurality of consecutive measurement cycles. Each measurement cycle includes a measurement window in which the load current IL is measured and a pause window in which the measurement of the load current IL is paused (interrupted).

[0023] Figure 2 Three consecutive measurement cycles are shown, wherein Tmw(k), Tmw(k+1), Tmw(k+2) indicate the duration of the measurement window of the measurement cycle, and Tpau(k), Tpau(k+1), Tpau(k+2) indicate the duration of the pause window of the measurement cycle. In the following, Tmw generally indicates the duration of the measurement window, and Tpau generally indicates the duration of the pause window.

[0024] The duration Tmw of the measurement window and the duration Tpau of the pause window can vary. That is, the duration Tmw of the measurement window does not need to be the same in each measurement cycle, and the duration Tpau of the pause window between the measurement windows does not need to be the same in each measurement cycle. The following further explains examples for defining the measurement window and the pause window in this article. Hereinafter, the duration Tmw of the measurement window is referred to as the measurement duration and the duration Tpau of the pause window is referred to as the pause duration.

[0025] according to Figure 2 The method comprises, at the beginning of each measurement window, adjusting the starting measurement value of the measurement circuit based on the measurement value obtained in the previous measurement cycle. The measurement value obtained in the previous measurement cycle is the measurement value obtained in the measurement window of the previous measurement cycle. According to an example, with respect to a certain measurement cycle, the previous measurement cycle is the measurement cycle directly before the certain measurement cycle. In this example, the starting measurement value at the beginning of the measurement window of a certain measurement cycle is based on the measurement value obtained in the measurement cycle ending at the beginning of the measurement window of the certain measurement cycle. However, this is only an example. According to another example, there is at least one measurement cycle between the previous measurement cycle and a certain measurement cycle in which the starting measurement value is generated using the measurement value from the previous measurement cycle. This will be briefly explained below.

[0026] Hereinafter, Isr generally indicates a starting measurement value and Isr(k) indicates a starting measurement value of the kth measurement cycle. In addition, Ism(ki) indicates a measurement value obtained in a previous measurement cycle (the (ki)th measurement cycle) based on which the starting measurement value is obtained, such that

[0027] Isr(k)=f(Ism(ki)) (1),

[0028] Where i is an integer, i>0, and f(.) is a function that generates the starting measurement value Isr(k) based on the measurement value Ism(ki) obtained in the previous measurement cycle. If the previous measurement cycle is the immediately previous measurement cycle, then i_1, such that

[0029] Isr(k)=f(Ism(k-1)) (2).

[0030] According to one embodiment, the starting measurement value Isr(k) is proportional to the measurement value obtained in the previous measurement cycle, such that

[0031] Isr(k)=p·Ism(k-1) (3),

[0032] wherein p indicates a proportionality factor. According to one embodiment, the proportionality factor is equal to one, p=1. In this case, the starting measurement value Isr(k) is equal to the measurement value Ism(k-1) obtained in the previous measurement cycle.

[0033] exist Figure 2 In the embodiment, tm(k), tm(k+1), tm(k+2) indicate the measurement moments within the measurement window. At each of these measurement moments tm(k), tm(k+1), tm(k+2), a measurement value for generating a corresponding starting measurement value can be obtained. According to one example, the measurement values ​​in each measurement window are obtained, and the starting measurement value for the directly subsequent measurement cycle is generated based on the measurement values ​​obtained in a measurement window. However, this is only an example. It is also possible to obtain the measurement values ​​in a measurement window and generate the starting measurement values ​​for two or more subsequent measurement cycles based on the measurement values ​​obtained in the measurement window.

[0034] According to an example, each of the measurement moments tm(k), tm(k+1), tm(k+2) is spaced from each other from the start and the end of the respective measurement window. According to an example, there is a predefined time period between the start of the measurement window and the respective measurement moment tm(k), tm(k+1), tm(k+2). An example for defining the measurement moments tm(k), tm(k+1), tm(k+2) within the measurement window is further explained herein below.

[0035] like Figure 2As can be seen in FIG. 1 , the load current IL can change within the measurement window. Therefore, the measurement signal Is changes within the measurement window. Thus, the starting measurement value does not need to represent the load current IL at the beginning of a new measurement window. However, in particular in those operating scenarios in which the load current IL is not zero at the beginning of each measurement window, the measurement value obtained in the previous measurement cycle is a good approximation of the measurement signal at the beginning of the new measurement window, so that the stabilization time is significantly reduced compared to the conventional method in which the measurement signal Is starts from zero at the beginning of each new measurement window.

[0036] Figure 3 The example shows a system configured according to Figure 2 An example of a measurement circuit 2 operating in accordance with the method shown in FIG. Figure 3 The measuring circuit is configured to measure the load current IL flowing through the conductor 1 in a plurality of consecutive measurement cycles and is configured to provide a measurement signal Is at least towards the end of each measurement window, the measurement signal Is being representative of the load current IL. Figure 3 , the measurement circuit 2 comprises a current sensing circuit 3. The current sensing circuit 3 is coupled to the conductor 1 and is configured to provide a measurement signal Is. Furthermore, the current measurement circuit 2 comprises a controller 4, which is configured to receive the measurement signal Is and to provide a starting measurement value at the beginning of each new measurement cycle based on the measurement values ​​obtained in the previous measurement cycle.

[0037] Figure 3 The load current IL shown may be flowing through ( Figure 3 2 . However, this is merely an example. According to another example, the load current IL sensed by the current measurement circuit 2 is a copy of the current flowing through the load. In this case, the load current IL may be proportional to the current flowing through the load. A load current IL proportional to the current flowing through the load may be obtained using a current mirror, a current sensing transistor, or the like.

[0038] Figure 4 An example of a current measurement circuit 2 is shown in more detail. More specifically, Figure 4 A more detailed example of the current sensing circuit 3 is shown. The controller 4 is as follows Figure 4 The following reference will be made to the circuit modules in FIG. Figure 4 An example of the controller 4 is explained.

[0039] exist Figure 4In the example shown in , the current sensing circuit 3 includes a shunt resistor 31 connected to the conductor 1 so that the load current IL flows through the shunt resistor 31. The voltage V31 across the shunt resistor 31 is proportional to the load current IL, wherein the proportionality coefficient between the voltage V31 and the load current IL is given by the resistance R31 of the shunt resistor 31.

[0040] The sensing circuit 3 also includes an input circuit having an operational amplifier 34 such as an operational transconductance amplifier (OTA), and a first transistor 371 driven by the operational amplifier 34. The operational amplifier 34 drives the first transistor 371 so that a current I371 flowing through the first transistor 371 is given by the following formula:

[0041] I371=Is′+q·Ioffs (4).

[0042] The current I371 flowing through the first transistor 371 is hereinafter referred to as the first current. Referring to equation (4), the first current I371 includes a first current portion Is′ proportional to the voltage V31 across the shunt resistor 31, so that the first current portion Is′ is proportional to the load current IL,

[0043] Is′~IL (5).

[0044] The second current portion of the first current I371 is equal to the known offset q·Ioffs.

[0045] Furthermore, the current circuit 3 includes an output circuit coupled to the first transistor 371. The output circuit includes a second transistor 372 driven by the operational amplifier 34 in the same manner as the first transistor 371, so that a second current I372 flowing through the second transistor 372 is proportional to the first current I371.

[0046] I372=m·I371=m·(Is′+q·Ioffs) (6),

[0047] Wherein m is a proportionality coefficient between the first current I371 and the second current I372 and is given by the ratio between the size of the second transistor 372 and the size of the first transistor 371. The output circuit further comprises a current mirror having an input transistor 381 connected in series with the second transistor 372 and an output transistor 382 coupled to the input transistor 381. The current I382 flowing through the output transistor 382 is proportional to the current flowing through the input transistor 381 and the current flowing through the second transistor 372,

[0048] I381=n·I372=n·m·(Is′+q·Ioffs) (7),

[0049] Where n is the proportionality coefficient between the output current I382 of the current mirror and the current flowing through the second transistor 372. The proportionality coefficient n is given by the current ratio of the current mirror. The current mirror ratio is given by the ratio between the size of the output transistor 382 and the size of the input transistor 381.

[0050] refer to Figure 4 , the output current I382 of the current mirror is given as

[0051] I382=m·n·Is′+m·n·q·Ioffs (8)

[0052] And includes a first current part m·n·Is′ proportional to the load current IL, and a second current part m·n·q·Ioffs proportional to the offset q·Ioffs.

[0053] The current source 332 is connected in series with the output transistor 382 of the current mirror and sinks a current equal to the constant second current portion m·n·q·Ioffs of the current mirror output current I382. Thus, at the output of the sensing circuit, which is the circuit node between the current mirror output transistor 382 and the current source 332, a current measurement signal Is is available, which is given as

[0054] Is=m·n·Is′ (9)

[0055] And it is proportional to the load current IL.

[0056] In order to drive the first transistor 371 so that the first current I371 is proportional to the voltage V31 across the shunt resistor 31 and the load current IL, the first input of the operational amplifier 34 is connected to the first circuit node of the shunt resistor 31 through the first resistor 321, and the second input of the operational amplifier 34 is connected to the second circuit node (different from the first circuit node) of the shunt resistor 31 through the second resistor 322. In addition, the circuit node between the first resistor 321 and the first input of the operational amplifier 34 is connected to the offset current source 331. In addition, the second node between the second resistor 322 and the second input of the operational amplifier 34 is connected to the load path of the first transistor 371.

[0057] The input current of the operational amplifier 34 is substantially zero, so that the current flowing through the first resistor 321 is substantially equal to the offset current Ioffs provided by the offset current source 331 and the current flowing through the second resistor 322 is substantially equal to the first current I371. The operational amplifier 34 drives the first transistor 371 so that the voltage between the input nodes of the operational amplifier 34 is substantially zero. In this case, the voltage V322 across the second resistor 322 is given by the voltage V321 across the first resistor 321 plus the voltage V31 across the shunt resistor 31,

[0058] V322=V321+V31 (10a).

[0059] The voltage V31 across the shunt resistor 31 is given by the load current IL multiplied by the resistance of the shunt resistor 31, and the voltage V321 across the first resistor 321 is given by the resistance R321 of the first resistor 321 multiplied by the offset current Ioffs, so that the voltage V322 across the second resistor 322 is given by equation (8)

[0060] V322=R31·IL+R321·Ioffs (10b).

[0061] The current I322 passing through the second resistor 322 is given by the voltage V322 across the second resistor 322 divided by the resistance R322 of the second resistor 322,

[0062]

[0063] Based on equation (10b) and equation (11a), it can be seen that the current I322 passing through the second resistor 322, which is equal to the first current I371, includes two current parts as follows,

[0064]

[0065] As can be seen in equation (11b), the proportionality coefficient between the load current IL and the first current portion of the first current I371 is given by the ratio between the resistance R31 of the shunt resistor 31 and the resistance R322 of the second resistor 322. In addition, the proportionality coefficient q between the offset current Ioffs provided by the offset current source 331 and the second portion of the first current I371 is given by the ratio between the resistance R321 of the first resistor 321 and the resistance R322 of the second resistor 322.

[0066] According to an example, the first resistor 321 and the second resistor 322 have the same resistance, such that R321=R322. In addition, the first transistor 371 and the second transistor 372 have the same size, such that m=1, and the input transistor 381 and the output transistor 382 of the current mirror have the same size, such that n=1. In this case, the output signal Is is equal to the first current part of the first current I371, Is=Is', so that the proportionality coefficient between the load current IL and the current measurement signal Is is defined only by the resistance R31 of the shunt resistor 31 and the resistance R322 of the second resistor 322.

[0067] refer to Figure 4 , the sensing circuit 3 further includes a compensation network 35 connected to the output of the operational amplifier 34. The compensation network 35 includes an RC filter, for example, and may include a series circuit having a resistor 351 and a capacitor 352. The compensation network 35 increases the operational stability of the current sensing circuit 2.

[0068] In accordance with Figure 4 In the current measurement circuit 2, the controller 4 is configured to sense the output voltage V34 at the measurement time tm in the previous measurement cycle; store the measurement value representing the output voltage V34 at the measurement time tm; and adjust the output voltage V34 of the operational amplifier 34 based on the stored measurement value at the beginning of the new measurement cycle so that the output voltage V34 is equal to the output voltage V34 at the measurement time tm in the previous measurement cycle. In this way, the measurement signal Is at the beginning of the new drive cycle is equal to the measurement signal Is at the measurement time tm in the previous drive cycle. The measurement value stored in the controller 4 therefore represents the measurement value at the beginning of the new drive cycle.

[0069] Adjusting the output voltage V34 by the controller 4 at the beginning of a new drive cycle includes adjusting the voltage across the filter 35, which includes charging the capacitor 352 of the filter 35. It should be noted that the controller 4 adjusts the output voltage V34 of the operational amplifier 34 only at the beginning of a new measurement cycle so that the measurement signal Is has a desired starting measurement value. After having the pre-charged capacitor 352, the controller 4 allows the operational amplifier 34 to adjust the output voltage V34 based on the load current IL to obtain a corresponding level of the current measurement signal Is.

[0070] Figure 5 An example of the controller 4 is shown in FIG. Figure 5 , the controller 4 includes a capacitor 41, a voltage buffer 46, a plurality of switches 42, 43, 44, 45 and a drive signal generator 47, the capacitor 41 is configured to store ( Figure 5The drive signal generator 47 is configured to provide the drive signals S1, S2 received by the switches 42-45 based on the output voltage V34 of the operational amplifier (not shown) at the measurement time. The drive signal generator 47 may include a microcontroller, a logic signal generator, a finite state machine, etc. An example of a signal diagram of the drive signals S1, S2 provided by the drive signal generator 47 is shown in Figure 6 middle.

[0071] refer to Figure 5 , the controller 4 includes connecting the input of the voltage buffer 46 to ( Figure 5 4. The first electronic switch 42 connects the output of the operational amplifier 34 (not shown) and the filter 35, and the second electronic switch 43 connects the output of the voltage buffer 46 to the capacitor 41. Therefore, when both the first electronic switch 42 and the second electronic switch 43 are turned on (in the on state), the voltage V41 across the capacitor 41 tracks the output voltage V34 of the operational amplifier 34.

[0072] Furthermore, the controller 4 includes a third switch 44 connecting the capacitor 41 to the input of the voltage buffer 46, and a fourth switch 45 connecting the output of the voltage buffer 46 to the filter 35. Therefore, when both the third switch 44 and the fourth switch 45 are turned on (in the on state), the controller 4 adjusts the voltage V34 across the filter 35 to be equal to the voltage V41 across the capacitor 41.

[0073] The following operating state of the controller 4 is referred to as the first operating state hereinafter: the first electronic switch 42 and the second electronic switch 43 are in the on state, so that the capacitor voltage V41 tracks the operational amplifier output voltage V34. The following operating state of the controller 4 is referred to as the second operating state hereinafter: the third switch 44 and the fourth switch 45 are in the on state, so that the operational amplifier output voltage V34 is equal to the capacitor voltage V41.

[0074] exist Figure 5 and Figure 6 In the example shown in FIG. 1 , the first operating state is controlled by a first drive signal S1 driving a first switch 42 and a second switch 43, and the second operating state is controlled by a second drive signal S2 driving a third switch 44 and a fourth switch 45. Each of the first drive signal and the second drive signal has an on-level for turning on a corresponding switch or an off-level for turning off a corresponding switch. For illustration purposes only, the on-level is Figure 6 The high signal level is shown in the Figure 6 Therefore, the controller 4 is in the first operating state when the first drive signal S1 has a high signal level, and is in the second operating state when the second drive signal S2 has a high signal level.

[0075] refer to Figure 6 , at the corresponding measurement time tm (where tm represents Figure 6 Before any one of the measurement times tm(k), tm(k+1), tm(k+2) shown in FIG. 1 ), the controller 4 is in the first operation state for a certain period of time, so that the capacitor voltage V41 tracks the operational amplifier output voltage V34. The first operation state ends at the measurement time tm, so that the voltage level of the operational amplifier output voltage V34 at the measurement time tm is stored as the capacitor voltage. For the purpose of illustration only, Figure 6 In the example shown in FIG. 1 , the first operating state is in the measurement window Tmw (where Tmw represents Figure 6 The first operating state may also start after the start of the measurement window but before the measurement time.

[0076] refer to Figure 6 , before the start of a new measurement cycle, the controller 4 is in a second operating state for a certain period of time, so that a voltage corresponding to the capacitor voltage V41 is provided by the controller 4 to the filter 35 and thus to the first transistor 371. The voltage stored by the capacitor 41 and provided to the filter 35 and the first transistor 371 generates a starting measurement value of the current measurement signal Is at the start of a new measurement cycle. The second operating state in which the voltage V34 across the filter 35 is provided by the controller 4 ends at the start of a new measurement cycle, so that the measurement circuit 2 can start tracking the load current IL. For illustration purposes only, Figure 6 In the example shown in , the controller 4 is in the second operating state during the pause time periods Tpau(k), Tpau(k+1), Tpau(k+2). However, this is only an example. It is also possible to operate the controller 4 in the second operating state in a time period shorter than the pause time periods Tpau(k), Tpau(k+1), Tpau(k+2) and each end with a corresponding new measurement cycle.

[0077] exist Figure 5 and Figure 6 In the example shown in , the first switch 42 and the second switch 43 are driven by the first signal S1, so that the first switch 42 and the second switch 43 are in the same operating state at every time. However, this is only an example. According to another example, the third switch 43 is driven by the first drive signal S1 defining the first operating state, and the second switch 42 is driven by the inverted (inverted) second drive signal S2!, so that each time the controller 4 is not in the second operating state, the first switch 42 is turned on.

[0078] Figure 7 An example of a power converter including a current sensing circuit 2 is shown. Figure 2 According to one example, according to reference Figures 3 to 6 Any of the explained examples implements the current sensing circuit 2. The power converter includes an electronic switch 51 and an inductor 52 connected in series with the electronic switch 51. The electronic switch 51 is connected to a power supply node 55 for receiving an input voltage Vin, and the inductor 52 is connected to an output node 56 providing an output voltage Vout.

[0079] The conductor 1 in which the load current IL is measured by the current measurement circuit 2 connects the electronic switch 51 and the inductor 52. However, this is only an example. It is also possible to measure the load current IL between the power supply node and the electronic switch 51, or between the inductor 52 and the output 56.

[0080] For illustrative purposes, Figure 7 The power converter shown in is a buck converter. In addition to the switch 51 and the inductor 52, the buck converter also includes a controller 55 configured to control the operation of the electronic switch 51, an output capacitor 54 providing an output voltage Vout across its two ends, and a freewheeling element 53, such as a diode 53 connected in parallel with a series circuit including the inductor 52 and the output capacitor 54. However, implementing the power converter as a buck converter is only an example. The current measurement circuit 2 can also be used in any other type of power converter. These other types of power converters include, but are not limited to, boost converters, flyback converters, buck-boost converters, Sepic converters, Converters, etc.

[0081] In the conventional way, according to Figure 7 The power converter 5 is configured to regulate one of the output voltage Vout or the output current Iout by switch-mode operation of the electronic switch 51. To this end, the controller 55 receives an output signal Sout representing the instantaneous signal level of the output voltage Vout or the output current Iout, whichever is regulated.

[0082] refer to Figure 7 , which shows a signal diagram of a drive signal Sdrv driving the electronic switch 51, a load current IL, and a current measurement signal Is, when the electronic switch 51 is in the on state, the load current IL increases and when the electronic switch 51 is in the off state, the load current IL decreases. When the electronic switch 51 is in the off state, the freewheeling element 53 takes over the load current IL through the inductor 52.

[0083] exist Figure 8In the example shown in , generating the current measurement signal Is includes generating the current measurement signal Is so that the current measurement signal Is during a pause period Tpau after a measurement window and before a new measurement window is substantially equal to a measurement value obtained at a measurement instant tm during the measurement window, so that the starting measurement value Isr at the beginning of the new measurement window is equal to the measurement value. Figure 8 Three consecutive measurement cycles are shown. The starting measurement value at the beginning of the measurement time window Tm(k+1) of the second measurement cycle is, for example, equal to the measurement value Isr(k) obtained at the measurement instant tm(k) in the measurement time window Tm(k) of the first measurement cycle. Figure 6 In a measuring circuit 2 of a controller 4 of the type shown in FIG. 1 , this can be achieved by operating the controller 4 in the second operating state throughout the pause time periods Tpau(k), Tpau(k+1), Tpau(k+2). For this example, the drive signal S2 governing the second operating state of the controller 4 is also shown in FIG. Figure 8 middle.

[0084] According to one example, the second drive signal S2 is generated so that when the electronic switch 51 is disconnected, that is, when the signal level of the drive signal Sdrv changes from the on level (turning on the switch 51) to the off level (turning off the switch 51), the second operating state of the controller 4 begins. After a new drive cycle, that is, after the electronic switch 51 has been turned on for the next time, the second operating state of the controller 4 ends. The delay time between the moment when Sdrv changes from the off level to the on level in order to turn on the electronic switch 51 and the beginning of the new measurement window can be selected so that when the new measurement window begins, the voltage oscillation (voltage noise) that may occur after turning on the electronic switch 51 has been attenuated. According to one example, the controller 55 is configured to generate the drive signal Sdrv so that the drive signal has an on level within a certain time period Tonmin, which can be called the minimum on time. According to one example, the delay time between the moment when the drive signal Sdrv changes to the on level and the beginning of the measurement window is equal to the minimum on time Tonmin. In this example, the same signal may be used to define the minimum on-time of the electronic switch 51 and the delay time between the start of a new drive cycle of the electronic switch 51 and the start of the measurement window.

[0085] exist Figure 7In the example shown, the current measurement circuit 2 is directly coupled to the conductor 1 and the inductor 52 connecting the electronic switch 51, so that the load current IL measured by the current measurement circuit 2 is the current passing through the inductor 52. However, this is only an example. It is also possible to include such a current path in the power converter, through which a copy of the current passing through the inductor 52 flows, and a copy of the inductor current can be measured. Such a copy of the inductor current can be obtained by implementing the electronic switch 51 as a transistor circuit having a load transistor and a sense transistor. The load transistor conducts the current flowing through the inductor 52, and the sense transistor provides a sense current that is substantially proportional to the load current. The sense current can be measured by the current measurement circuit 2 to obtain a current measurement signal Is. The transistor arrangement having a load transistor and a sense transistor is well known, so no further explanation is required in this regard.

[0086] Briefly summarizing what has been described previously herein, one example relates to a method that includes measuring a current in a conductor in successive measurement cycles using a current measurement circuit. Measuring the current in each measurement cycle includes adjusting a starting measurement value of the measurement circuit based on a measurement value obtained in a previous measurement cycle.

[0087] In the previous measurement cycle, the starting measurement value is obtained at a time different from the beginning of the previous measurement cycle and different from the end of the previous measurement cycle.

[0088] According to one example, measuring the current includes measuring the current in a power converter including at least one electronic switch. Each measurement cycle in the measurement cycle can be during the on-time of the at least one electronic switch and can be shorter than the on-time of the at least one electronic switch. At least one electronic switch can have a minimum on-time, and the starting measurement value can be obtained at the moment when the minimum on-time of the at least one electronic switch expires. According to one example, the power converter is one of a buck converter, a boost converter, a buck-boost converter, a flyback converter, or a Sepic converter.

[0089] Another embodiment relates to a current measurement circuit configured to measure current in a conductor in successive measurement cycles. The current measurement circuit is further configured in each measurement cycle to adjust a starting measurement value based on a measurement value obtained in a previous measurement cycle.

[0090] According to an example, the current measurement circuit is configured to obtain, in a previous measurement cycle, a starting measurement value at a time different from the beginning of the previous measurement cycle and different from the end of the previous measurement cycle.

[0091] The current measurement circuit may be included in the power converter. Thus, another example relates to a device comprising at least one electronic switch, a control circuit configured to control the operation of the at least one electronic switch, and a current measurement circuit. The current measurement circuit is configured to measure a current in a conductor of the power converter and provide a current measurement signal to the control circuit based on the measured current.

[0092] In a power converter, the control circuit can be configured to operate at least one electronic switch in a plurality of consecutive drive cycles each including a minimum on-time, wherein the current measurement circuit can be configured to obtain a starting measurement value at the moment when the minimum on-time expires in each cycle of the plurality of consecutive drive cycles.

Claims

1. A method comprising: The current (IL) in the conductor is measured in successive measurement cycles using a current measuring circuit (2), The measuring of the current (IL) in each measurement cycle comprises: adjusting a starting measurement value of the measurement circuit (2) based on a measurement value obtained in a previous measurement cycle.

2. The method according to claim 1, Wherein in the previous measurement cycle, the start measurement value is obtained at a time (Tm) different from the beginning of the previous measurement cycle and different from the end of the previous measurement cycle.

3. The method according to claim 1 or 2, Wherein measuring the current (IL) comprises measuring the current in a power converter, the power converter comprising at least one electronic switch (51).

4. The method according to claim 3, Each of the measurement cycles is during the on-time of the at least one electronic switch (51) and is shorter than the on-time of the at least one electronic switch (51).

5. The method according to claim 4, wherein the at least one electronic switch (51) has a minimum on-time, and The starting measured value is obtained at the time when the minimum switch-on time (Tonmin) of the at least one electronic switch (51) expires.

6. The method according to any one of claims 3 to 5, wherein the power converter is selected from the group consisting of: Buck converter; Boost converter; Buck-boost converter; Flyback converter; and Sepic converter.

7. A current measurement circuit, the current measurement circuit being configured to measure a current (IL) in a conductor in successive measurement cycles, The current measurement circuit is further configured in each measurement cycle to adjust the starting measurement value based on the measurement value obtained in the previous measurement cycle.

8. The current measuring circuit according to claim 7, The current measurement circuit is configured to obtain the start measurement value in the previous measurement cycle at a time (Tm) different from the beginning of the previous measurement cycle and different from the end of the previous measurement cycle.

9. A power converter comprising: at least one electronic switch (51); a control circuit (55) configured to control the operation of the at least one electronic switch (51); A current measurement circuit according to claim 7 or 8, configured to measure a current (IL) in a conductor of the power converter and to provide a current measurement signal (Is) to the control circuit (55) based on the measured current.

10. The power converter according to claim 9, wherein the control circuit (55) is configured to: operate the at least one electronic switch (51) in a plurality of consecutive drive cycles each including a minimum on-time; and The current measurement circuit is configured to obtain the starting measurement value at a time when the minimum on-time in each cycle of the plurality of consecutive driving cycles expires.

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