Control circuit for a boost converter under dcm

Abstract

A control circuit for a boost converter, wherein the control circuit comprises switching means configured to switch the boost converter to perform a cycle, wherein each cycle comprises an energy charging state in which an inductance stores energy provided by an input voltage and an energy discharging state in which the inductance provides energy to an output of the boost converter; comparison means configured to determine whether a frequency of switching events is lower than a predetermined minimum frequency; and on-time signal generation means configured to generate an on-time signal based on whether the frequency of switching events is lower than the predetermined minimum frequency, wherein the on-time signal determines a duration of a charging state of a next switching event, and wherein the switching means are configured to switch the boost converter based on the generated on-time signal.

Description

[0001] This application claims priority to the European application with the filing date of 17 December 2021, application number 21215690.5, entitled “Control circuit for a boost converter in DCM” to the European Patent Office, the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present invention relates to a control circuit for a boost converter. The present invention also relates to a boost converter circuit comprising said control circuit and to a method of operating said boost converter circuit comprising said control circuit. BACKGROUND

[0003] Energy harvesting is the process of energy acquisition, capture and storage from external sources for small wireless autonomous devices such as wearable electronic devices and devices used in wireless sensor networks. Direct current to direct current (DC-DC) converter circuits, for example boost converter circuits, are electronic circuits that convert a direct current (DC) power source from one voltage level to another by first charging an energy storage element with the input voltage and then discharging the energy storage element to provide energy at the output of the DC-DC converter. DC-DC converters can be used to increase the energy harvested from an energy source. Constant-on-time (COT) boost converters are popular due to their simplicity and high performance. When operating in discontinuous conduction mode (DCM), if the switching frequency of the boost converter drops below a certain frequency, audible noise can be generated or the audio signal patch on the chip can be disturbed causing distortion.

[0004] This problem can be avoided by using only continuous conduction mode (CCM), thus keeping the boost converter switching. However, this solution results in higher energy dissipation and thus lower efficiency at low loads.

[0005] Alternatively, a virtual load can be added at the output of the boost converter, thus guaranteeing a minimum load current and thus a minimum switching frequency in DCM. The dissipation in the virtual load again results in lower efficiency.

[0006] Another possible solution can be to force a transition from DCM to CCM, where each burst ends when DCM is activated again due to low load. Since bursts in CCM require more switching events than in DCM, this also results in lower efficiency. SUMMARY

[0007] It is an object of the present invention to realize an efficient control arrangement for a boost converter for reducing noise and / or interference.

[0008] According to the present invention, a control circuit for a boost converter is provided, wherein the control circuit comprises switching means configured to switch the boost converter to perform cycles, wherein each cycle comprises an energy charging state in which an inductance stores energy provided by an input voltage and an energy discharging state in which the inductance provides energy to an output of the boost converter; comparison means configured to determine whether a frequency of switching events is lower than a predetermined minimum frequency; and on-time signal generating means configured to generate an on-time signal based on whether the frequency of switching events is lower than the predetermined minimum frequency, wherein the on-time signal determines a duration of a charging state of a next switching event, and wherein the switching means are configured to switch the boost converter based on the generated on-time signal. This arrangement provides an efficient control system for a boost converter in which interference and distortion is reduced. By controlling the duration of the charging state, the boost converter is forced to increase the switching frequency when the switching frequency of the boost is lower than a minimum value in order to deliver the same amount of energy to the output. By increasing the switching frequency, it is possible to avoid that the switching frequency of the boost converter falls within the range of the human audible spectrum, thereby avoiding audible noise or interference within an on-chip audio signal patch.

[0009] In examples of the present disclosure, the comparison means are further configured to determine whether the frequency of switching events is higher than a first predetermined maximum frequency, and the on-time signal generating means are configured to generate the on-time signal based on whether the frequency of switching events is higher than the first predetermined maximum frequency. This allows the switching frequency of the boost converter to be lower than a threshold value and provides a return path for the algorithm, so that the switching frequency can be increased or decreased.

[0010] In examples of the present disclosure, the comparison means are further configured to determine whether the frequency of switching events is higher than a second predetermined maximum frequency, and the on-time signal generating means are configured to generate the on-time signal based on whether the frequency of switching events is higher than the second predetermined maximum frequency as well. This allows the switching frequency of the boost converter to be lower than a threshold value and provides a return path for the algorithm, so that the switching frequency can be increased or decreased; wherein the second predetermined maximum frequency is greater than 2.25 times the first predetermined maximum frequency. In this way, it is avoided that the algorithm switches between two values within the duration of the on-time signal.

[0011] In summary, this allows first to detect when the minimum frequency in DCM is reached, then to reduce the on-time to increase the generated switching frequency in DCM. Then, when the load current further decreases and the frequency limit is reached again, the action can be repeated. For the reverse path, as the current increases, the on-time can be increased again when a different, higher frequency limit is reached. This introduces a hysteresis in the control behavior to ensure a stable behavior. To detect fast increasing load current transients, a third frequency limit allows to reset the DCM minimum frequency regulation.

[0012] In examples of the present disclosure, the on-time signal generating means further comprises a control value, and is configured to increase the control value if the frequency of the switching event is lower than the predetermined minimum frequency, and / or to decrease the control value if the frequency of the switching event is higher than the first predetermined maximum frequency, and / or to reset the control value if the frequency of the switching event is higher than the second predetermined maximum frequency, and wherein the on-time signal is generated based on the control value. This is a very effective way to control the duration of the charging state of the boost converter based on the switching frequency. For example, a parameter determining the duration can be a function of the control value.

[0013] In examples of the present disclosure, the control circuit further comprises a measuring means configured to receive a reference clock signal from a reference clock, and to count a number of clock cycles during the switching event, and to determine the frequency of the switching event based on the number of clock cycles. This is a very effective way to measure the switching frequency of the boost converter.

[0014] In examples of the present disclosure, the on-time signal generating means comprises a feedback circuit, wherein the feedback circuit comprises a feedback input and is configured to receive a charging current at the feedback input, and to generate the on-time signal based on the charging current, and wherein the switching means is configured to switch the boost converter based on the on-time signal.

[0015] In examples of the present disclosure, the on-time signal generating means is configured to generate the charging current based on the determined duration of the charging state of the next switching event and the current in the inductance. This is a suitable way to control the duration of the charging state of the boost converter based on the switching frequency, as the charging current has a direct influence on the duration.

[0016] In examples of the present disclosure, the control circuit is configured to generate the charging current based on the control value and the current in the inductance. This allows to effectively control the charging state time based on the switching frequency, as the charging current can be a function of the current in the inductance of the boost converter and the control value.

[0017] In examples of the present disclosure, the feedback circuit further comprises a capacitor and a comparison circuit, wherein the capacitor is configured to store a voltage based on the charging current, wherein the comparison circuit comprises a first input, a second input, wherein the comparison circuit is configured to receive a reference voltage at the first input, to receive the capacitor voltage at the second input, and to generate the on-time signal by comparing the reference voltage and the capacitor voltage.

[0018] In examples of the present disclosure, the capacitor comprises a variable capacitor, which is controlled based on the determined duration of the charging state of the next switching event. This allows to effectively increase or decrease the duration of the charging state by controlling the capacitor.

[0019] In another example of the present disclosure, the reference voltage is generated by a variable voltage source, which is controlled based on the determined duration of the charging state of the next switching event.

[0020] According to the present invention, there is also provided a boost converter circuit comprising the control circuit, an inductance, an input configured to receive an input voltage, and an output configured to provide an output voltage, and a method.

[0021] The person skilled in the art will understand that the above-mentioned features can be combined in any way deemed useful. Moreover, modifications and variations described in relation with the system can equally apply to a method of operating the boost converter circuit. BRIEF DESCRIPTION OF DRAWINGS

[0022] In the following, aspects of the present invention will be elucidated by way of example with reference to the accompanying drawings. The drawings are diagrammatic and not to scale.

[0023] Figure 1A A known boost converter circuit is shown.

[0024] Figure 2 A known circuit for generating an on-time signal is shown, and Figure 1B - C shows a time waveform diagram of several signals of a boost converter circuit comprising Figure 2 the circuit for generating an on-time signal of

[0025] Figure 3A - E and Figure 4 shows a time waveform diagram of several signals of a boost converter circuit comprising Figure 1A the circuit for generating an on-time signal of

[0026] Figure 5 A schematic diagram of a control circuit for a boost converter according to an embodiment of the present invention is shown.

[0027] Figure 6A schematic diagram of a measuring device according to an embodiment of the present invention is shown.

[0028] Figure 7A -D shows that includes Figure 5 The waveform diagram of several signals of the boost converter of the control circuit, wherein the control circuit includes Figure 6 The measuring device.

[0029] Figure 8 A circuit comprising a conduction time signal generation device and a switching device according to an embodiment of the present invention is shown.

[0030] Figure 9 A flowchart of a method for operating a control circuit according to an embodiment of the present invention is shown.

[0031] Figure 10 , 11A -F, 12A-F, 13A-F, 14A-F, and 15A-F illustrate embodiments of the present invention including Figure 5 , 6 Waveform diagrams of several signals of the boost converter of the control circuit shown in Figure 8.

[0032] Figure 16 A flowchart is shown of a method for operating a control circuit for a boost converter circuit. Detailed Implementation

[0033] In the figures, the same reference numerals indicate elements with similar structures and functions.

[0034] Figure 1A A known boost converter circuit 100 is shown. Figure 3A -E indicates the operation period Figure 1A The time waveform diagram of several signals of the boost converter circuit. Figure 4 This explains that in Figure 1A In the boost converter circuit, the DCM as a function of time, I COIL The value of I. COIL yes Figure 1A The diagram shows the inductor L BST The current.

[0035] Now refer to Figure 1A , 2 3A-E and 4 illustrate the operation of the boost converter circuit.

[0036] like Figure 4 As shown, during the time interval 400, switch S L Close the switch S H Disconnect so that Figure 1A Inductance L BST Connect to ground. When inductor LBST When grounded, the boost converter circuit 100 enters a charging state in which current flows through the inductor L BST and the inductor L BST stores some energy by generating a magnetic field. The current I BST in the inductor L COIL increases during a time interval 400, as shown. The switching device 124 sends a control signal S L to open the switch 128 to disconnect the inductor L BST from ground and sends a control signal S H to close the switch 126 to connect the inductor L BST to the output V BST . The boost converter circuit enters a discharging state in which the energy previously accumulated in the inductor L BST is transferred to the output V BST during a time interval 402, as shown, and the current I BST in the inductor L COIL begins to decrease. In this case, the time intervals 400 and 402 are part of a discontinuous mode event in which the circuit has performed a complete switching cycle. A new discontinuous mode event starts at a time interval T BST .

[0037] Figure 1A The target output boost voltage V BST of the boost converter of SH is set by choosing an appropriate value for the current I BST using the adjustable current source 114, as follows:

[0038]

[0039] In the boost converter of Figure 1A , under periodic steady-state conditions with constant load, the switch 128 is closed with a frequency f and a duty cycle D, where the duty cycle D depends on the output voltage V BAT and the input voltage V ON , as follows:

[0040]

[0041] Figure 1A The on-time signal T ON , i.e. the time period 400, of the boost converter of BAT is related to the switching frequency f and the duty cycle D as follows:

[0042]

[0043] This means that, for the on-time signal T BSTGiven a fixed value, the frequency f will depend on the duty cycle D, and therefore on the input voltage V. BAT and output voltage V BST This is generally undesirable. Therefore, the conduction time signal T ON It is typically chosen based on the input voltage V. BAT Output voltage V BST and the expected switching frequency f TARGET As shown below:

[0044]

[0045] The actual switching frequency f will be equal to the expected frequency f. TARGET And with input voltage V BAT and output voltage V BST It is irrelevant; the method is as follows:

[0046]

[0047] Figure 2 An example for generating the conduction time signal T is shown. ON The pulse generator circuit 200 and Figure 1A The switching device 124. Figure 3A The on-time signal T is shown. ON The time waveform diagram. Figure 3B and Figure 3C They are shown respectively Figure 1A The timing waveforms of the start and ready signals of the boost converter 100 are shown. Finally, Figure 3D and Figure 3E The first switching signal and the second switching signal S of the same boost converter 100 are shown respectively. L and S H The time waveform diagram. Switching device 124 also controls switches 128 and 126 to open / close based on a zero-current signal (e.g., ...). Figure 3A -C is shown).

[0048] Figure 2 The signal shown is used to generate the on-time signal T. ON The pulse generator circuit 200 includes a current source 202, a capacitor 204, and a comparator 206. The comparator 206 includes a first input terminal 208 and a second input terminal 210. The switching device 124 is configured to receive a start signal and generate a reset signal, such that when the start signal goes high, the reset signal goes low, causing the switch 220 to close and the voltage V across the capacitor 204 to decrease. C As time increases linearly, until the first input terminal 208 of comparator 206 reaches the reference voltage V received at the second input terminal 210 of comparator 206. REFAt this time, comparator 206 generates a ready signal, which opens switch 220 and sets voltage V. C Reset to zero. Switching device 124 generates a control signal based on the start signal and the ready signal to drive switch S. H and S L .

[0049] For the output voltage V BST and input voltage V BAT Given a combination and a sufficiently high load current I LOAD Inductor L BST Current I in COIL It exhibits a switching frequency f TARGET The periodic stable state, such as Figure 1B As shown. This operating mode is often called continuous conduction mode (CCM) because current is constantly flowing into the inductor.

[0050] For the output voltage V BST and input voltage V BAT The same combination, but the load current I LOAD Lower, inductance L BST Current I in COIL Behavior such as Figure 1C As shown. Note that in this case, the inductance L BST Current I in COIL It can also be negative. For zero-load current I LOAD Average inductor current I COIL,average It is also zero; the converter simply transfers charge from the battery to the output capacitor and back, with no net effect other than power consumption.

[0051] To minimize dissipation under low load conditions, discontinuous operating mode (DCM) is typically used, such as... Figure 4 As shown. In this mode, the inductor current I is detected. COIL The zero-crossing occurs at the start of cycle 490, when both switches 128 and 126 are open, therefore no current flows through inductor L. BST Once the boost voltage drops below the desired level, switch 128 is turned on for a period of time T. ON This initiates the next switching event. For low loads, this significantly reduces the number of switching events, thus minimizing power consumption and increasing efficiency. The switching frequency in the DCM will be lower than the (target) switching frequency in the CCM.

[0052] Figure 5A control circuit 500 for a boost converter according to an embodiment of the present invention is shown. The control circuit 500 includes a comparator 502, a conduction time signal generation device 504, and a switching device 506.

[0053] like Figure 5 The comparison device 502 of the control circuit 500 shown includes a first input terminal 520, a second input terminal 522, and an output terminal 528. The first input terminal 520 is configured to receive information about the switching frequency of the boost converter, where the switching frequency is the frequency at which a switching event occurs. The second input terminal 522 is configured to receive a first threshold indicating a predetermined minimum frequency. The comparison device 502 is configured to determine whether the frequency of the switching event is lower than the predetermined minimum frequency by comparing the information about the switching frequency received at the first input terminal 520 with the first threshold received at the second input terminal 522. The comparison device 502 may optionally include a third input terminal 524 and / or a fourth input terminal 526. The third input terminal 524 may be configured to receive a second threshold indicating a first predetermined maximum frequency, and the fourth input terminal 526 may be configured to receive a third threshold indicating a second predetermined maximum frequency. The comparison device 502 may be configured to determine whether the frequency of the switching event is higher than the first predetermined maximum frequency by comparing the information about the switching frequency received at the first input terminal 520 with the second threshold received at the third input terminal 524. Furthermore, the comparator 502 can be configured to determine whether the frequency of a switching event is higher than a second predetermined maximum frequency by comparing information about the switching frequency received at the first input 520 with a third threshold received at the third input 526. The comparator 502 can generate a signal at the output 528 indicating whether the frequency of the switching event is lower than the first threshold and / or higher than the second threshold and / or higher than the third threshold.

[0054] Figure 5 The control circuit 500 shown includes an on-time signal generation device 504 comprising an input terminal 530 and an output terminal 532. The input terminal 530 is configured to receive a signal generated at the output terminal 528 by the comparator device 502. The on-time signal generation device 504 is also configured to generate an on-time signal at the output terminal 532. The on-time signal is generated based on the signal received at the input terminal 530. The on-time signal will be used to generate the charging state of the boost converter for the next switching event, and a switching device is configured to switch the boost converter based on the generated on-time signal.

[0055] like Figure 5The switching device 506 of the control circuit 500 shown includes an input terminal 534 and an output terminal 536. The input terminal 534 of the switching device 506 is configured to receive an on-time signal at the output terminal 532 of the on-time signal generator 504. The switching device 506 is configured to switch the boost converter to perform a cycle, wherein each cycle includes an energy charging state where the inductor stores energy supplied by the input voltage at the input terminal of the boost converter, and an energy discharging state where the inductor supplies energy to the output terminal of the boost converter. Each time the on-time signal is activated, a new switching event, i.e., a cycle, begins. The boost converter will remain in the charging state until the on-time signal is deactivated. Then, the boost converter will enter the discharging state. When the on-time signal is activated again, the cycle or switching event will begin.

[0056] The conduction time signal generation device 504 may also include control values ​​( Figure 5 (Not shown in the diagram), the control value is configured to increase if the frequency of the switching event is lower than a predetermined minimum frequency. The on-time signal at output 532 can be generated based on this control value. The control value can also be configured to decrease if the frequency of the switching event is higher than a first predetermined maximum frequency, and the on-time signal is generated based on this control value, and / or reset if the frequency of the switching event is higher than a second predetermined maximum frequency, and the on-time signal is generated based on this control value. The control value can be increased by adding one to a previously stored value and / or decreased and / or reset to zero. However, the control value can be increased / decreased / reset to any suitable value. The on-time signal generation device may include a register configured to store the control value.

[0057] Figure 5 The control circuit 500 may include Figure 6 The measuring device 600 shown. Figure 6 The measuring device 600 shown includes a first input terminal 602, a second input terminal 604, and an output terminal 608. The first input terminal 602 is configured to receive a reference clock signal from a reference clock 606. The second input terminal 604 can be configured to receive signals indicating the start and end of a switching event. The measuring device can be configured to count the number of clock cycles of the reference clock 606 received at the first input terminal 602 during the duration of the switching event, as indicated by the signal received at the second input terminal 604. In this way, the measuring device 600 can generate information about the frequency of the switching event based on the number of clock cycles and send this information to the output terminal 608. Figure 6 The output terminal 608 of the measuring device 600 shown can be coupled to Figure 5 The first input terminal 520 of the comparison device 502 shown.

[0058] Figure 6The measuring device 600 shown allows the use of a reference clock 606 at a clock frequency f clk Measure the switching frequency f BST , where f clk >>f BST In this way, the switching period T of the boost converter is... BST It can be achieved by using the conduction time signal T ON After the switching event begins, clock cycles are counted to achieve measurement. In the next switching event, the count performed by the measuring device 600 represents the switching frequency f. BST The period. The count can then be reset, for example, to zero, and the on-time signal T can be determined by the on-time signal generation device 504 based on the measured frequency. ON The new value. This will result in a modified switching frequency f. BST The process repeats in the next switching event. The counting action can be a function performed in the digital domain available to the reference clock 606. Figure 6 The measuring device 600 may include a register (not shown) to store the counting results.

[0059] This process is in Figure 7A The -D specification shows that it includes... Figure 5 The waveform diagram of several signals of the boost converter of the control circuit 500 shown is illustrated, wherein the control circuit includes... Figure 6 The measuring device 600 shown. Figure 7A The waveform of the reference clock signal for an example of reference clock 606 is shown. Figure 7B The waveform of the count performed by the measuring device 600 is shown. Figure 7C The current I is shown COIL The waveform diagram shows the current I. COIL By utilizing Figure 5 and 6 The inductor of the boost converter in the control device shown. For example... Figure 7A and Figure 7B As shown, each time the reference clock 606 executes a cycle 702, the measuring device 600 increments the count by one step 704. The result of this count is sent to the on-time generation device 504, and the duration of the charging state of the boost circuit is modified based on this count, as... Figure 7C As shown, where T' ON Less than T ON . Figure 7D The diagram illustrates the change of waveform 702 corresponding to the inductor current over time when the present invention is applied, and the change of waveform 704 corresponding to the inductor current over time when the present invention is not applied. Figure 7D As shown, by reducing the charging T ON The duration of the switching frequency f is increased.BST This is because the boost converter needs to switch more times to charge the same amount of energy. In this way, the frequency f... BST The conduction time T can be used ON To control. Figure 7C In the middle, the duration of the conduction time is from T ON Reduce to T' ON By reducing the duration of the on-time period, the amount of charge transferred per switching event is reduced, and for the same load current I... LOAD This will require more switching events, resulting in a higher switching frequency f' BST T ’BST =1 / F ’BST For example, consider Figure 7C In this case, the duration of the conduction time period is reduced by a factor of 2. Since the area under the triangular current pulse is proportional to the square of its height, this will reduce the amount of charge transported in a single pulse by a factor of 4. Therefore, the frequency will increase by a factor of 4, such as... Figure 7D As shown.

[0060] Figure 8 An example of a conduction time signal generation apparatus 504 and a switching apparatus 506 according to an embodiment of the present invention is shown. The conduction time signal generation apparatus 504 receives the result generated by the comparison apparatus 502 at its input terminal 530, and generates a conduction time signal at its output terminal 532 based on the result. The conduction time signal generation apparatus 504 may further include a feedback circuit 840, which is similar to the feedback circuit 506 described above. Figure 2 The circuit shown and explained. Figure 8 The feedback circuit shown includes a feedback input terminal 310 and is configured to receive a charging current I at the feedback input terminal 310. CHARGE And based on the charging current I CHARGE Generate a conduction time signal of 532. Note that I... CHARGE With output voltage V BST Proportional to the reference voltage V REF With V BST -V BAT Proportional to the desired target frequency in continuous conduction mode (CCM).

[0061] The on-time signal generation device 504 is configured to generate a charging current I based on the duration of the charging state of the determined next switching event and the current in the inductor. CHARGE . Figure 8 The on-time signal generation device 504 shown may further include a register 802, which is configured to store the control value N. SET The control value N SETis the signal 528 generated at the output 528 of the comparison device 502 and indicates whether the frequency of the switching event is below a first threshold and / or above a second threshold and / or above a third threshold.

[0062] Figure 8 The on-time signal generator 504 is configured to generate the on-time signal 532 based on a control value N SET The on-time signal 532 is modified to change the switching frequency. Figure 8 The on-time signal generator 504 comprises a current digital analogic converter (DAC) 810 configured to generate N SET times the reference current I . Instead of a DAC, any other suitable circuit can be used. The current DAC 810 can be configured to scale the charging current I CHARGE by using a correction factor. The correction factor depends on the control value N SET , which in this example is a 3-bit signal. However, the control value N SET may comprise any other number of bits. In other embodiments, the capacitor 204 can be a variable capacitor and the on-time signal generating device 504 can be configured to scale the capacitance value of the capacitor 204 based on the control value N SET . Alternatively, the reference voltage V REF may be based on N SET by scaling using for example a variable voltage source to generate the reference voltage V REF , i.e. to manipulate the on-time signal 532 T ON . An alternative way to scale the on-time signal 532 T REF is to scale the capacitor size or to scale V by a factor of 1 / 2.

[0063] The on-time signal generating device 504 can further comprise a current source 820 configured to generate a reference current I REF , the current DAC 810 being configured to generate the charging current I SET based on the control value N CHARGE as follows:

[0064] I CHARGE = I REF factor

[0065] For ease of illustration, we have chosen a certain function for the factor, although many alternative approaches can be used:

[0066] factor = 1 + N SET / 2

[0067] As Figure 8As shown, the feedback circuit also includes a capacitor 204 and a comparator circuit 206, wherein the capacitor is configured to operate based on the charging current I. CHARGE The storage voltage Vc. The comparator circuit 206 is configured to receive the reference voltage V at the first input terminal 208. REF The capacitor voltage Vc is received at the second input terminal 210, and the conduction time signal 532 is generated by comparing the reference signal and the capacitor voltage.

[0068] If the control value N SET Including 3 bits, for a given V BAT and V BST The combination now has 8 charging currents I. CHARGE Possible values ​​and 8 possible conduction times.

[0069]

[0070] With control value N SET Compared to a value of 0, the corrected on-time is scaled by a factor of 1:

[0071]

[0072] For a given load current, the corrected switching frequency is expressed in factorial. 2 Scale to the uncorrected switching frequency (for control value N) SET =0):

[0073]

[0074] For control value N SET The 3-bit values ​​and example scaling factors are given in Table 1. Using this implementation, the minimum load current can be 20.25 lower than without a regulation system (i.e., factor = 1) before reaching the minimum switching frequency. Maximum N SET The design of the value can take into account the self-load of the boost converter output, so that even if the external I... LOAD The value is zero, and the switching frequency is also higher than the required minimum value.

[0075] I CHARGE / I REF ]]> [CAT ON / T ON,NSET＝0 ]]> f BST / f BST,NSET＝0 ]]> factor 1 / factor Factor 2 ]]>

[00013] N SET ]] (1+N SET / 2)]]> 1 / (1+N SET / 2)]]> 1 / (1+N SET / 2) 2 ]]> 0 1 1.00 1.00 1 1.5 0.67 2.25 2 2 0.50 4.00 3 2.5 0.40 6.25 4 3 0.33 9.00 5 3.5 0.29 12.25 6 4 0.25 16.00 7 4.5 0.22 20.25

[0076] Table 1

[0077] Figure 9 An operation is shown Figure 5 The flowchart describes the method for controlling the circuit. To modify the on-time to change the switching frequency, the on-time T... ON Depends on the multi-bit control value N SET When the boost converter enters DCM, the control value N SETStarting from zero, thus the same as the on-time in CCM. In step 902, the switching frequency f BST is measured. In step 904, if the load current has decreased to a switching frequency f BST below a predetermined minimum frequency f MIN , the method proceeds to step 906, where the value of the control value N SET is increased by one unit, thus decreasing the on-time. Consequently, the switching frequency is increased by one level. The method then proceeds to step 908 to wait for the next switching event. When the next switching event starts, the method proceeds to step 910 and starts counting to measure the switching frequency f BST . In step 912, the counting is ended when the next switching event is detected. The method then proceeds again to step 902, where the switching frequency will be determined using the counting result.

[0078] In step 904, if the switching frequency is not below the predetermined minimum frequency, the method proceeds to step 916, where it is determined whether the switching frequency is above a first predetermined maximum value f MAX . In case the switching frequency is above the first predetermined maximum value f MAX , the control value N SET is reset to zero in step 918 and the method proceeds to step 908. In case the switching frequency is not above the first predetermined maximum value f MAX , the method proceeds to step 920.

[0079] In step 920, if the switching frequency is above a second predetermined maximum frequency f MID , the method proceeds to step 922, where the value of the control value N SET is decreased by one unit, thus increasing the on-time. Consequently, the switching frequency is decreased by one level. The method then proceeds to step 908 to wait for the next switching event.

[0080] In case the switching frequency is not above the second predetermined maximum value f MID , the method proceeds to step 912.

[0081] In this way, the procedure of steps is repeated as long as the load current decreases (and N SET has not reached its maximum value). When the load current increases, the frequency will also increase until f MID is reached. The value of N SET is then decreased by 1 to fall back again to a larger on-time and a lower frequency. With a slowly varying load current, a step-wise behavior will be observed. However, when the load current increases rapidly, the measured frequency will be above the maximum value f MAX , and N SET is reset to 0.

[0082] Figure 10 , 11A -F, 12A-F, 13A-F, 14A-F and 15A-F show several signal waveforms of a boost converter comprising Figure 5 , 6 and the control circuit shown in Fig. 8.

[0083] Figure 10 shows the switching frequency f LOAD as a function of the load current I BST , the predetermined minimum frequency f MIN , the first predetermined maximum frequency f MAX , the second predetermined maximum frequency f MID and the control value N SET . To avoid toggling between the two values of the control value N SET , a hysteresis is established by choosing the second predetermined maximum frequency f MID = 2.5 * f MIN , ensuring that the second predetermined maximum frequency f MID is greater than 2.25 * f MIN . When the control value changes from N SET = 0 to N SET = 1, this ratio is based on a maximum frequency jump of the factor 2.25. The resulting behavior is shown in Fig. Figure 10 . Due to the hysteresis, an increasing load current level will follow the frequency curve limited by the second predetermined maximum frequency f MID , while a decreasing current will follow the curve limited by the predetermined minimum frequency f MIN . The arrows in Fig. Figure 10 indicate which part of the curve is followed when the load current I LOAD is increasing or the load current I LOAD is decreasing. In this way, the hysteresis serves to prevent oscillation.

[0084] Figure 11A -F shows the output voltage V BST , the load current I LOAD , the switching frequency f BST , the inductor current I COIL , the control value N SET and the count of the measuring means as a function of time when the load current is slowly decreasing. Figure 12A -F shows the output voltage V BST , the load current I LOAD , the switching frequency f BST , the inductor current I COIL , the control value N SET and the count of the measuring means as a function of time when the load current is slowly decreasing, the amplification N SET is changed from 2 to 3. InFigure 11A - F and Figure 12A - F, the control behavior during the transient of decreasing load current can be seen. Each time the frequency drops below a predetermined minimum frequency f MIN , the value of the control value N SET is increased. As a result, the peak value of the inductor current I COIL is decreased and the switching frequency is increased. Another benefit is that the ripple amplitude on the output voltage V BST is decreased.

[0085] Figure 13A - F shows the variation over time of the output voltage V BST , the load current I LOAD , the switching frequency f BST , the inductor current I COIL , the control value N SET and the counter of the measuring device when the load current is increased. When N SET is turned from 3 to 2, Figure 14A - F corresponds to Figure 13A - F. Each time the second predetermined maximum frequency f MID is reached, the value of the control value N SET is decreased. As a result, the peak value of the inductor current I COIL is increased and the switching frequency is decreased. When a high load step is applied, the switching frequency exceeds the predetermined maximum frequency f MAX and the control value N SET becomes zero. This happens when the boost converter exits DCM and enters CCM.

[0086] To illustrate the speed limitation of the control method, a step load current variation is used, as shown in Figure 15A - F. Because it takes some time to measure the switching frequency after a step down, the switching frequency drops below the predetermined minimum frequency f MIN for a few cycles, but is corrected by increasing the value of N SET . After the load current is increased, the switching frequency increases to a level above the predetermined maximum frequency f MAX and the control value N SET is reset to zero. After this reset action, the control value N SET reaches the original value again.

[0087] Figure 16A flow chart of a method of operating a control circuit for a boost converter circuit is shown, wherein the method comprises a first step 1602 comprising switching the boost converter by a switching device to perform cycles, wherein each cycle comprises an energy charging state in which an inductance stores energy provided by an input voltage and an energy discharging state in which the inductance provides energy to an output of the boost converter. In step 1604, the method comprises determining by a comparing device whether a frequency of switching events is below a predetermined minimum frequency. Finally, the method proceeds to step 1606 comprising generating by a conduction time signal generating device a conduction time signal based on whether the frequency of switching events is below the predetermined minimum frequency, wherein the conduction time signal determines a duration of the charging state of a next switching event, and wherein the switching device is configured to switch the boost converter based on the generated conduction time signal.

[0088] The examples and embodiments described herein are used to illustrate and not limit the present application. Those skilled in the art will be able to design alternative embodiments without departing from the scope of the claims. The reference signs placed in brackets in the claims shall not be construed as limiting the scope of the claims. Items described as being separately implemented in the claims or the description can be implemented as a single hardware or software item incorporating features of the described items.

Claims

1. A control circuit for a boost converter, wherein the control circuit comprises: The switching device (506) is configured to switch the boost converter to perform a cycle, wherein each cycle includes an energy charging state in which an inductor stores energy provided by an input voltage and an energy discharging state in which the inductor provides energy to the output of the boost converter. The comparison device (502) is configured to determine whether the frequency of the switching event is lower than a predetermined minimum frequency; as well as A conduction time signal generating device (504) is configured to generate a conduction time signal based on whether the frequency of the switching event is lower than the predetermined minimum frequency, wherein the conduction time signal determines the duration of the charging state of the next switching event, and wherein the switching device is configured to switch the boost converter based on the generated conduction time signal. The conduction time signal generation device (504) includes a feedback circuit (840), wherein the feedback circuit (840) includes a feedback input terminal (310) and is configured to receive a charging current I at the feedback input terminal. CHARGE The on-time signal is generated based on the charging current, wherein the charging current I... CHARGE With the output voltage V of the boost converter BST Proportional; The feedback circuit (840) further includes a capacitor (204) and a comparator circuit (206), wherein the capacitor is configured to store a capacitor voltage based on the charging current, and wherein the comparator circuit includes a first input (208) and a second input (210), wherein the comparator circuit is configured to receive a reference voltage at the first input, receive the capacitor voltage at the second input, and generate the on-time signal by comparing the reference voltage and the capacitor voltage.

2. The control circuit according to claim 1, wherein the comparison device (502) is further configured to determine whether the frequency of the switching event is higher than a first predetermined maximum frequency, and the conduction time signal generation device (504) is configured to generate the conduction time signal based on whether the frequency of the switching event is higher than the first predetermined maximum frequency.

3. The control circuit according to claim 2, wherein the comparison device (502) is further configured to determine whether the frequency of the switching event is higher than a second predetermined maximum frequency, and the conduction time signal generation device (504) is configured to further generate the conduction time signal based on whether the frequency of the switching event is higher than the second predetermined maximum frequency; wherein the second predetermined maximum frequency is greater than 2.25 times the first predetermined maximum frequency.

4. The control circuit according to claim 1, wherein the conduction time signal generating device (504) further includes a control value configured to increase if the frequency of the switching event is lower than the predetermined minimum frequency, and wherein the conduction time signal is generated based on the control value.

5. The control circuit according to claim 2, wherein the conduction time signal generating device (504) further includes a control value configured to decrease if the frequency of the switching event is higher than the first predetermined maximum frequency, and wherein the conduction time signal is generated based on the control value.

6. The control circuit according to claim 3, wherein the conduction time signal generating device (504) further includes a control value configured to reset if the frequency of the switching event is higher than the second predetermined maximum frequency, and wherein the conduction time signal is generated based on the control value.

7. The control circuit according to any one of claims 1 to 6 further includes a measuring device (600) configured to receive a reference clock signal from a reference clock (606), count the number of clock cycles during the switching event, and determine the frequency of the switching event based on the number of clock cycles.

8. The control circuit according to any one of claims 1 to 6, wherein the on-time signal generating device (504) is configured to generate the charging current I based on the duration of the charging state of the determined next switching event and the current in the inductor. CHARGE .

9. The control circuit according to any one of claims 4 to 6, further comprising generating the charging current based on the control value and the current in the inductor.

10. The control circuit according to any one of claims 1 to 6, wherein the capacitor includes a variable capacitor that is controlled based on the duration of the charging state of the determined next switching event.

11. The control circuit according to any one of claims 1 to 6, wherein the reference voltage is generated by a variable voltage source, the variable voltage source being controlled based on the duration of the charging state of the determined next switching event.

12. A boost converter circuit, comprising: The control circuit according to any one of claims 1 to 11; Inductor L BST ; The input terminal is configured to receive the input voltage V. BAT ;and The output terminal is configured to provide an output voltage V. BST .

13. A method of operating a control circuit for a boost converter circuit, the method comprising: The boost converter is switched by a switching device to perform a cycle, wherein each cycle includes an energy charging state in which the inductor stores energy provided by the input voltage and an energy discharging state in which the inductor provides energy to the output of the boost converter. The comparison device determines whether the frequency of the switching event is lower than a predetermined minimum frequency; as well as A conduction time signal is generated by a conduction time signal generation device based on whether the frequency of the switching event is lower than the predetermined minimum frequency, wherein the conduction time signal determines the duration of the charging state of the next switching event, and wherein the switching device is configured to switch the boost converter based on the generated conduction time signal. The conduction time signal generation device includes a feedback circuit, wherein the feedback circuit includes a feedback input terminal and is configured to receive a charging current I at the feedback input terminal. CHARGE The on-time signal is generated based on the charging current, wherein the charging current I... CHARGE With the output voltage V of the boost converter BST Proportional; The feedback circuit further includes a capacitor and a comparator circuit, wherein the capacitor is configured to store a capacitor voltage based on the charging current, and wherein the comparator circuit includes a first input terminal and a second input terminal, wherein the comparator circuit is configured to receive a reference voltage at the first input terminal, receive the capacitor voltage at the second input terminal, and generate the on-time signal by comparing the reference voltage and the capacitor voltage.

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