System and method for regulating a switching converter

Abstract

The invention relates to a system and method for regulating a switching converter. The invention relates to a method for regulating a switching converter having at least one switching element, wherein the switching converter is operated in quasi-resonant operation and the switching element is switched at a predetermined stable switching frequency in the regulated state of the switching converter. The switch-on time point of the switching element is predetermined by a switching signal of a switching regulator unit, and the switching signal is generated by a sawtooth signal loaded with a valley detection signal reaching or exceeding a switch-on threshold. The current cycle duration of the switching signal is determined by a unit for cycle duration detection, and is compared by the regulator unit with a predetermined reference cycle duration of a cycle duration reference unit. From this comparison, a control variable is generated by the regulator unit, by which the distance between the sawtooth signal and the switch-on threshold is changed until the reaching of a stable switching frequency is confirmed with the help of the determined current cycle duration.

Description

Technical Field

[0001] The invention generally relates to the field of electronic technology, in particular to the field of power electronics and power electronic circuits. In particular, the invention relates to a method and a system for regulating a switching converter, the switching converter having at least one switching element, wherein the switching converter is operated in quasi-resonant operation and at least one switching element of the switching converter is switched at a predetermined stable switching frequency in the regulated state of the switching converter. In this case, the switch-on time of the switching element is predetermined by a switching signal of a switching regulator unit, which is generated by a sawtooth signal reaching or exceeding a switch-on threshold. In this case, a valley detection signal is applied to the sawtooth signal, whereby the switch-on time of at least one switching element falls into the valley of the oscillating voltage applied to the switched-off switching element. In addition, the invention relates to a control system for executing the method according to the invention. Background Art

[0002] Switching converters are used in many fields (e.g., automation, automotive, etc.) and represent a technology for voltage and / or current conversion as a basis for supplying power to loads or consumers, such as electrical devices or components with mostly constant and often predeterminable voltages. For this purpose, switching converters usually convert an input voltage (e.g., a DC or AC voltage from a power supply) into a constant output voltage. The constancy of the output voltage is usually achieved by controlling the energy flow, which is controlled by means of at least one periodically timed or working switching element and by means of at least one energy storage device (e.g., a coil, a transformer, a capacitor). Depending on the application, different switching converter topologies (e.g., buck converter, boost converter, buck-boost converter, flyback converter, etc.) can be used for supplying power to the load in order to generate an output voltage that is greater than, less than, or, if necessary, equal to the input voltage.

[0003] Switching elements, such as transistors, like coils, transformers or chokes, contain parasitic capacitances, which in the case of so-called hard-switching converters (i.e., in the case of converters with a fixed switching frequency) lead to switching losses and / or interference emissions (e.g., in the form of noise / or electromagnetic radiation - so-called EMC interference). In the case of a discontinuous or intermittent operating mode (DCM) of a switching converter, for example, at least one switching element of the switching converter is turned on after the inductance or coil of the switching converter has been demagnetized, resulting in a dead time. During this dead time, in the case of a hard-switching converter, the parasitic capacitances oscillate with the inductance of the converter near the input voltage or the intermediate circuit voltage and can be charged to a correspondingly high voltage before the next switch-on time point. When the switching elements of the converter are turned on in the next clock cycle, these parasitic capacitances are discharged or recharged, for example, via the switching elements (e.g., transistors, etc.), and hereby generate more or less high current peaks depending on the applied voltage, which lead to correspondingly high switching losses in the case of correspondingly high voltages. In addition, such current peaks are rich in harmonics, which additionally increase interference radiation or EMI.

[0004] In order to minimize these switching losses and interference radiation, the switching converter can be operated in a so-called quasi-resonant mode, or a so-called quasi-resonant switching can be sought for at least one switching element of the converter. In the case of quasi-resonant switching, the minimum value (also called "valley") of the drain-source voltage of at least one switching element of the converter is effectively detected, for example, by means of an identification loop or an identification circuit, and the switching element is turned on at this point in time. Since the parasitic capacitance is charged to the minimum voltage, the peak value of the on-current is minimized in this way and the reduction of switching losses and interference radiation is achieved. This type of switching of a switching element or a switching converter is generally referred to as valley switching, zero-crossing switching or quasi-resonant switching. Each minimum value of the oscillating voltage applied to the switched-off switching element of the converter is called a valley. Here, the valley that first appears in time during the switching cycle is called the first valley. The subsequent valleys are called the second, third, fourth, etc. valleys according to their time sequence.

[0005] The switching-on time point is usually predetermined for at least one switching element of the converter by means of a switching signal of a switching regulator unit. Usually, a pulse width modulation or PWM switching regulator is used to generate the switching signal. Here, a switch-on pulse (e.g., a rising edge of a rectangular signal) is generated for the switching element in the switching signal by reaching a switch-on threshold value by a sawtooth signal. In order to switch on at least one switching element of the converter in a trough, a trough detection signal can be applied to the sawtooth signal, for example, as described in document EP 2 173 026 B1. This achieves that the switch-on time point of the switching element falls into a trough of the oscillating voltage applied to the switched-off switching element.

[0006] The switching on during the valley causes a continuous reset (pulse reset) of the cycle start and thus an adaptation of the switching frequency that is independent of the load or the intermediate circuit voltage at that point in time. If the switching element is always switched on in the same (e.g., first) valley, for example, the switching frequency increases as the load decreases until the maximum frequency is reached at no-load. However, as the frequency increases, the switching losses also increase because more loss-inducing switching processes are performed per time unit. In order to avoid too high a switching frequency under low load or at no-load, for example, when the maximum switching frequency predetermined by the dimensioning of the switching converter is reached, the switch-on time point of at least one switching element of the switching converter is usually moved to a later valley. That is, when the output power of the converter is reduced or the load is reduced, for example, the switch-on time point of the switching element is moved from the current valley to a later valley—for example, from the third valley to the fourth valley.

[0007] Similarly, in the case of an increased power demand or an increased load at the output of the converter, the switching frequency begins to decrease until a minimum switching frequency predetermined by the dimensioning of the switching converter is reached. In order to prevent the switching frequency from falling below a predetermined minimum value, the switch-on time of at least one switching element is shifted to an earlier valley. That is, in the case of an increased output power or an increased load of the converter, the switching element is switched on in an earlier valley instead of in the current valley, for example, in the third valley instead of in the fourth valley.

[0008] By switching between the valleys after a load change (e.g. from no load to full load), it can be achieved, for example, that the switching converter or at least one switching element of the switching converter can be switched at approximately the same stable switching frequency in the regulated state. That is, at this stable switching frequency, the switching converter operates at a stable operating point. The stable switching frequency is usually predetermined by the inductance and capacitance of the switching converter and the efficiency, and can be determined, for example, from the maximum and minimum values ​​of the switching frequency (e.g. arithmetic mean).

[0009] However, changes in the power demand or load at the output of the switching converter and the switching between valleys that are necessary as a result thereof may cause unstable states of regulation. A change in the load at the output of the switching converter, for example, results in a change in the output voltage of the switching converter, which results in a change in the manipulated variable used to regulate the output voltage and a change in the switch-off time point of the switching element of the switching converter. Due to the change in the switch-off time point of the switching element, for example, in the case of an increase in load, the valley recognition signal is applied to the sawtooth signal of the switching regulator unit at a later time point. In the case of a decrease in load, the time point at which the valley recognition signal is applied to the sawtooth signal will, for example, be shifted forward in time.

[0010] Since the switch-on time of the switching element is determined by the sawtooth signal loaded with the valley detection signal reaching or exceeding the switch-on threshold, the load change may result in, for example, two valley detection signals reaching or exceeding the switch-on threshold. This means that the switch-on time of the switching element is switched from the current valley to an earlier or later valley according to the load change by the switching regulator unit. This causes a change in the switching frequency and thus a jump-like change in the power transmitted by the switching converter. In order to compensate for the power change, the output voltage is called back by the voltage regulator of the switching converter and switched back to the previous current valley when necessary. In this case, the switch-on behavior of the switching element may lead to an unstable state of regulation of the output voltage of the switching converter, thereby forcing the pulse-modulated switching regulator unit to continuously jump back and forth between two consecutive valleys, for example, between the third and fourth valleys in an uncontrolled manner. This effect is called "valley skipping" or "valley hopping". Due to valley jumping, a limit cycle oscillation occurs in the control loop, which has an oscillation frequency in the audible range (e.g., 5 kHz to 15 kHz) and a higher power loss. Summary of the invention

[0011] The object of the present invention is to specify an improvement over the prior art for quasi-resonantly switching switching converters in such a way that uncontrolled valley jumps are avoided.

[0012] According to the invention, this object is achieved by a method for regulating a switching converter having at least one switching element in quasi-resonant operation and by a system for regulating a switching converter having at least one switching element.

[0013] The invention is based on the fact that a switching converter having at least one switching element is operated in a quasi-resonant operation or mode. At least one switching element is switched at a predetermined, stable switching frequency in the regulated state of the switching converter. In addition, a switch-on time is predetermined for at least one switching element by a switching signal, which is generated by reaching a switch-on threshold by a sawtooth signal loaded with a valley recognition signal, wherein the corresponding switch-on time of at least one switching element falls into the valley of the oscillating voltage applied to the switched-off switching element by the valley recognition signal. In addition, for example, the current cycle duration of the switching signal is continuously determined and the determined current cycle duration of the switching signal is compared with a predetermined reference cycle duration. A control variable is derived from the comparison of the determined current cycle duration with the reference cycle duration, and when the load at the output of the switching converter changes, the distance between the sawtooth signal loaded with the valley recognition signal and the switch-on threshold is changed by the control variable until the reaching of the predetermined stable switching frequency is confirmed by means of the determined current cycle duration.

[0014] The main aspect of the solution proposed according to the invention is that, in the case of a load change at the output of the switching converter, a jump-like switchover between the current valley for deriving the switch-on time of the switching element to an earlier or later valley is implemented (depending on the corresponding load change). In this case, in the case of a load change at the output of the switching converter, the control variable derived from the respectively current cycle duration influences the distance between the switch-on threshold and the sawtooth signal of the PWM control device loaded with the valley detection signal, so that the switch-on point is determined by the current valley until, depending on the load change, a safe switchover to the previous or subsequent valley is made to determine the switch-on time without jumping back to the current valley. In other words, the change in the distance between the switch-on threshold and the sawtooth signal of the switching regulator unit loaded with the valley detection signal produces a hysteresis, thereby preventing uncontrolled valley jumps or valley jumps.

[0015] Advantageously, the change in the distance between the sawtooth signal loaded with the valley detection signal and the switch-on threshold is carried out via the control variable in proportion to the change in the load at the output of the switching converter. This means, for example, that in the case of an increase in load, the distance between the switch-on threshold and the sawtooth signal loaded with the valley detection signal is enlarged, or in the case of a decrease in load, the distance is reduced.

[0016] A preferred embodiment of the invention provides, for example, that the distance between the sawtooth signal loaded with the trough detection signal and the switch-on threshold value is changed by changing the inclination or the slope of the ramp of the sawtooth signal as a function of the control variable.

[0017] Alternatively, the distance between the sawtooth signal loaded with the valley detection signal and the switch-on threshold can be changed, for example, by changing the switch-on threshold as a function of the control signal. In this case, for example, the switch-on threshold is lowered or increased as a function of the corresponding load change.

[0018] It is also advantageous if the control variable is reset to a predetermined output value when a predetermined stable switching frequency is reached. For example, the control variable is reset abruptly when a predetermined stable switching frequency or a correspondingly associated cycle duration of the switching signal is determined. If the control variable assumes the output value again, the distance between the sawtooth signal of the switching regulator unit, which is loaded with the valley detection signal, and the switch-on threshold value is no longer influenced or changed. The output value of the control variable results, for example, from a predetermined stable switching frequency or an associated cycle duration of the switching converter.

[0019] Depending on how the detection of the current cycle duration is implemented, the current cycle duration of the switching signal can ideally be determined in the form of a digital value or an analog value. In order to determine the cycle duration as a digital value, for example, a microcontroller can be used, by which the current cycle duration of the switching signal is measured. Alternatively, the cycle duration of the switching signal can be determined with the aid of an analog circuit, by which the current cycle duration of the switching signal is output as an analog voltage average value of a sawtooth auxiliary voltage that is synchronized with the sawtooth signal of the switching regulator unit. However, in order to determine the current cycle duration of the switching signal, a frequency-voltage converter can also be used, by which the current frequency of the usually rectangular switching signal is converted into a frequency-dependent or frequency-proportional DC voltage.

[0020] Furthermore, the stated object is achieved by a system for regulating a switching converter in quasi-resonant operation, the switching converter having at least one switching element, wherein the system is configured to carry out the method according to the invention and for this purpose comprises at least:

[0021] a switching regulator unit for generating a switching signal which specifies a switch-on time for at least one switching element of the switching regulator, wherein the switching regulator unit comprises an oscillator unit for generating a sawtooth signal which is compared with a switch-on threshold value in order to generate the switching signal;

[0022] - a valley recognition unit for generating a valley recognition signal which is applied to the sawtooth signal, whereby the corresponding switch-on time point of at least one switching element falls into a valley of the oscillating voltage applied to the switched-off switching element;

[0023] - a unit for period duration detection, which determines the current period duration of the switching signal;

[0024] - a cycle duration reference unit for predefining a reference cycle duration (Tref); and

[0025] a control unit which generates a control variable for changing the distance between the sawtooth signal loaded with the trough detection signal and the switch-on threshold value from the current period duration determined by the unit for period duration detection and the reference period duration of the period duration reference unit.

[0026] In the system according to the invention, a further control loop is superimposed on the control device of the switching converter by means of a switching regulator. By means of this further control loop, in addition to regulating the output voltage to a predetermined constant output voltage value in the event of a load change at the output of the switching regulator, the distance between the sawtooth signal of the switching regulator unit, which is loaded with a valley detection signal, and a switch-on threshold value for defining a switch-on time of a switching element of the switching converter is changed or influenced, so that uncontrolled jumping back and forth between valleys or uncontrolled valley jumps are ideally prevented or suppressed.

[0027] To realize the system according to the invention, the unit for period detection can be realized, for example, by means of a microcontroller or a frequency-voltage converter which determines the respectively current period duration of the switching signal. A more cost-effective realization variant of the unit for period detection is, for example, an analog circuit which determines the current period duration of the switching signal as an analog voltage average value of a sawtooth auxiliary voltage which is synchronized with the sawtooth signal of the switching regulator unit.

[0028] Ideally, the regulator unit is designed as a proportional-integral regulator, which generates a control variable for changing the distance between the sawtooth signal, which is acted upon by the trough detection signal, and the switch-on threshold value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention is explained below in an exemplary manner with the aid of the accompanying drawings. In the drawings:

[0030] Figure 1 The schematic and exemplary structure of the system for regulating a quasi-resonant switching switching converter according to the present invention is shown,

[0031] Figure 2 The sequence of the method according to the invention for regulating a switching converter is shown by way of example and schematically.

[0032] Figure 3 An analog implementation variant of the system according to the invention for regulating a quasi-resonant switching converter is shown by way of example and schematically. DETAILED DESCRIPTION

[0033] Figure 1 By way of example and in a schematic manner, a system for adjusting a quasi-resonant switching switching converter SN according to the present invention is shown. The system comprises a switching converter SN having at least one switching element, which is controlled by means of a rectangular switching signal PWM. Here, the switch-on time point of the switching element is predetermined, for example, by means of a rising edge of the rectangular switching signal PWM. In the regulated state of the switching converter SN, the switching element is usually switched at a predetermined, stable switching frequency. This stable switching frequency or the associated cycle duration is predetermined by the dimensioning of the switching converter SN, in particular the inductance and capacitance, and the efficiency to be achieved.

[0034] In order to generate the switching signal PWM, the system according to the invention has a switching regulator unit RE, which is designed, for example, as a pulse width modulated switching regulator RE. The switching regulator unit RE includes an oscillator unit OS (for example, a sawtooth wave generator), which generates a sawtooth signal. The sawtooth signal is used to generate the switching signal PWM.

[0035] Furthermore, a valley detection unit VE (for example a zero crossing detector) is provided, by which a valley detection signal V is generated. To generate the valley detection signal V, the valley detection unit VE measures, for example, an oscillating voltage present at the switched-off switching element of the switching converter SN. If a voltage minimum or a so-called valley is detected at the switched-off switching element by means of a voltage measurement in the voltage curve, the valley detection unit VE can generate, for example, a pulse as the valley detection signal V. This valley detection signal V is then supplied to the switching regulator unit RE and there impinges on the sawtooth signal generated by the oscillator unit OS.

[0036] In order to determine the switch-on time of the switching element of the switching converter SN, the sawtooth signal loaded with the valley recognition signal V is compared with a predefined switch-on threshold value in the switching regulator unit RE. If the sawtooth signal loaded with the valley recognition signal V reaches or exceeds the predefined switch-on threshold value, a rising edge is generated in the switching signal PWM, for example, and the switch-on time of at least one switching element of the switching converter SN is thus defined. By loading the sawtooth signal with the valley recognition signal V, it is achieved that the switch-on time of at least one switching element of the switching converter SN falls into the minimum value or valley of the oscillating voltage applied to the switched-off switching element.

[0037] Furthermore, the system comprises a unit PE for period duration detection, which determines the current period duration T of the switching signal PWM as an analog or digital value. A possible implementation variant of the unit PE for period duration detection is shown in FIG. Figure 3 , the instantaneous period duration T of the switching signal PWM is determined as an analog value by means of the implementation variant. Here, for example, the period duration T is determined as an analog voltage mean value of the respective sawtooth of a sawtooth auxiliary voltage that is synchronous with the sawtooth signal of the switching regulator unit RE but is separated.

[0038] Alternatively, the unit PE for period duration detection can be implemented, for example, by means of a microcontroller, which measures the current period duration T of the switching signal PWM. Furthermore, the unit PE for period duration detection can also be implemented, for example, by means of a frequency-voltage converter, by means of which, for example, the current frequency of the usually rectangular switching signal PWM is converted into a frequency-dependent or frequency-proportional DC voltage.

[0039] Furthermore, a period duration reference unit PEref is provided, which provides a predetermined reference period duration Tref. Figure 3 A possible implementation variant of the cycle duration reference unit PEref is explained in more detail. The reference cycle duration Tref or the voltage value Uref corresponding to the reference cycle duration Tref can be set, for example, by calibrating the control system, for example during initial commissioning, for example based on the dimensioning of the switching regulator unit RE and the switching converter SN (e.g. maximum and minimum values ​​of the switching frequency, inductance, etc.).

[0040] In addition, the system includes a regulator unit PI, which can be implemented as a proportional integral or PI regulator, for example. The regulator unit PI is fed with a predetermined reference cycle duration Tref provided by a cycle duration reference unit PEref as a rated value and the current cycle duration T of the switching signal PWM determined by a unit PE for cycle duration detection as an actual value. The currently determined cycle duration T is compared with the reference cycle duration Tref by the regulator unit PI, or a difference is formed between the reference cycle duration Tref and the current cycle duration T. The control variable SG is then derived from the comparison result by the regulator unit PI, which control variable can be amplified, for example, with an amplification factor K. Here, the amplification factor K is predetermined, for example, by the implementation or dimensioning of the PI regulator. The control variable SG is then forwarded to the switching regulator unit RE and can there change the distance between the input threshold value and the sawtooth signal of the oscillator unit OS, which is loaded with the valley detection signal V, in the event of a change in the load at the output of the switching converter SN, until the achievement of a predetermined stable switching frequency of the switching converter SN has been confirmed with the aid of a current cycle duration T determined by the unit PE for cycle duration detection or by comparing the determined current cycle duration T with a reference cycle duration Tref.

[0041] Figure 2 An exemplary sequence of the method according to the invention for regulating a quasi-resonantly switched switching converter SN is shown. For this purpose, the current period duration T of the switching signal PWM of the switching regulator unit RE is determined by the unit PE for period duration detection in a determination step 101. The current period duration T can be determined here in the form of a digital value or an analog value depending on the implementation of the unit PE for period duration detection (for example, by means of a microcontroller, by means of a frequency-voltage converter or as an analog circuit).

[0042] For comparison step 102, the determined current cycle duration T is supplied as an actual value to the regulator unit PI. In comparison step 102, the determined current cycle duration T is compared with a predefined reference cycle duration Tref. The predefined reference cycle duration Tref is, for example, predefined as a rated value by a cycle duration reference unit PEref. The comparison between the determined current cycle duration T and the predefined reference cycle duration Tref can be performed by the regulator unit PI, for example, by subtracting the actual value or cycle duration T from the rated value or from the reference cycle duration Tref.

[0043] In a derivation step 103, a control variable SG is derived from the comparison result between the determined current cycle duration T and a predetermined reference cycle duration Tref. The control variable SG can be amplified by the regulator unit PI, if necessary, with an amplification factor K predetermined by the dimensioning or implementation of the regulator unit PI. The control variable SG is then forwarded to the switching regulator unit RE.

[0044] If a change in the load occurs at the output of the switching converter SN or the power demand at the output and thus the output voltage of the switching converter SN changes, the distance between the sawtooth signal loaded with the valley recognition signal V and the switch-on threshold of the oscillator unit OS of the switching regulator unit RE is changed by the control variable SG in the regulation step 104. Here, the control variable SG can, for example, realize the distance between the sawtooth signal loaded with the valley recognition signal V and the switch-on threshold in proportion to the change in the load at the output of the switching converter SN. That is, for example, in the case of an increase in the load, the distance is enlarged by the control variable SG, and, for example, when the load is reduced, the distance is reduced by the control variable.

[0045] In the regulating step 104, the change in the distance between the sawtooth signal loaded with the trough detection signal V and the switch-on threshold value can be realized, for example, by influencing the inclination of the sawtooth or ramp of the sawtooth signal by means of a control variable as a function of the load change or a change of the current cycle duration T of the switching signal PWM triggered by the load change. Alternatively, in the case of a load change at the output of the switching converter SN, the level of the switch-on threshold value can be changed in the regulating step 104 by means of a control variable as a function of the corresponding load change or the current cycle duration T.

[0046] The distance between the sawtooth signal loaded with the valley detection signal V and the switch-on threshold is varied in a control step 104 by means of a controlled variable SG until in a test step 105 it is confirmed by means of the determined current cycle duration T that a predefined stable switching frequency of the switching converter SN has been reached.

[0047] This means that, for example, in the case of an increased load at the output of the switching converter SN, the current period duration T of the switching signal PWM is first increased by a corresponding adjustment of the output voltage of the switching converter SN. In the derivation step 103, a control variable SG is generated by the regulator unit PI, for example, which decreases in proportion to the increased period duration T. The control variable SG can then influence the distance between the sawtooth signal loaded with the valley detection signal V and the switch-on threshold, for example, in the following way: the inclination or slope of the sawtooth ramp of the sawtooth signal of the oscillator unit OS is also reduced in proportion to the increased period duration T. That is, the sawtooth ramp becomes flatter and the switch-on time point of the switching element of the switching converter SN is also determined by the current valley of the voltage oscillating at the switched-off switching element. If the changed sawtooth signal loaded with the valley detection signal V reaches or exceeds the switch-on threshold at the time of the previous valley, then in test step 105 it is detected with the aid of the determined current cycle duration T that the switching frequency has returned abruptly to a predetermined stable switching frequency value, which enables stable switch-on or reaches a stable operating point of the switching converter SN at the switching frequency.

[0048] In the case of a reduced load at the output of the switching converter SN, for example by correspondingly adjusting the output voltage of the switching converter, the current cycle duration T of the switching signal PWM becomes smaller. Due to the reduction in the current cycle duration T, the control variable SG derived from the current cycle duration T determined in the derivation step 103 increases. The control variable SG can then influence the distance between the sawtooth signal loaded with the valley detection signal V and the switch-on threshold, for example, in the following way: the inclination or slope of the sawtooth ramp of the sawtooth signal of the oscillator unit OS is also increased in proportion to the reduced cycle duration T. That is, the sawtooth ramp becomes steeper and the switch-on time point of the switching element of the switching converter SN is also determined by the current valley of the voltage oscillating at the switched-off switching element. If the changed sawtooth signal loaded with the valley detection signal V reaches or exceeds the switch-on threshold at the time of the subsequent valley, it is detected in test step 105 with the aid of the determined current cycle duration T that the switching frequency has returned abruptly to a predetermined stable switching frequency value, which enables stable switch-on or reaches a stable operating point of the switching converter SN at the switching frequency.

[0049] If it is detected in test step 105 that the current switching frequency has reached the value of a predetermined stable switching frequency, the controlled variable SG assumes the predetermined value again in return step 106. This output value can be specified, for example, by the predetermined stable switching frequency or the associated cycle duration T and a predetermined reference cycle duration Tref.

[0050] exist Figure 3 , by way of example and schematically, shows an implementation variant of a system for controlling a switching converter SN, in particular a unit PE for period duration detection, an analog implementation variant of a period duration reference unit PEref, and a regulator unit PI.

[0051] Here, an exemplary implementation of a unit PE for period duration detection includes a series circuit of a first resistor R1 and a first capacitor C1, which is connected to the base of a transistor TR (e.g., a bipolar transistor). In addition, the base of the transistor TR is connected to a reference potential via a second resistor R2. The emitter of the transistor TR is also connected to the reference potential and a third resistor R3 is connected to the collector of the transistor TR. A second capacitor C2 is arranged in parallel with the transistor TR and the third resistor R3, which second capacitor C2 has a connection with the third resistor R3 in a connection point. The second capacitor C2 is connected to a voltage V+ via a fourth resistor R4, wherein the second capacitor C2 forms an integrator circuit with the fourth resistor. In addition, the second capacitor is also connected to the reference potential.

[0052] In order to determine the current cycle duration, the second capacitor C2 is discharged via the series circuit of the first resistor R1 and the first capacitor C1 and the transistor TR at the rising edge of the switching signal PWM. Here, the rising edge of the switching signal PWM corresponds to the switch-on time point of the switching element of the switching converter SN in the current valley. Via the fourth resistor R4, which acts like a power supply, the second capacitor C2 can be charged again until the second capacitor C2 is discharged again at the next positive edge of the switching signal PWM, that is, the next switch-on time point of the switching element of the switching converter SN. This results in the integration of the current cycle duration T of the switching signal PWM at the connection point between the third resistor R3, the fourth resistor R4 and the second capacitor C2. By connecting the series circuit of the first resistor R1 and the first capacitor C1, the transistor TR and the integrator circuit composed of the second capacitor C2 and the fourth resistor R4, the current cycle duration T of the switching signal PWM is determined as the analog voltage average value of the sawtooth derived from the switching signal PWM related to the current cycle duration T. In this case, for example, a longer period duration T results in a higher mean voltage value than a shorter period duration T, or a shorter period duration T results in a lower mean voltage value than a longer period duration T.

[0053] In addition, Figure 3, a realization variant of a cycle duration reference unit PEref is shown, by which a reference cycle duration Tref or a corresponding reference voltage value is provided. The cycle duration reference unit PEref comprises a fifth and a sixth resistor R5, R6 connected to a reference voltage Uref and a reference potential. In addition, a third capacitor is arranged in parallel with the sixth resistor R6.

[0054] The reference cycle duration Tref or the corresponding reference voltage value is then supplied to the regulator unit PI, for example a proportional integral regulator or PI regulator as a setpoint value. In addition, the current cycle duration T or the analog voltage average value associated with the current cycle duration T is supplied to the PI regulator PI as an actual value. The two values ​​are compared by the PI regulator PI and the control variable SG is derived therefrom and amplified by an amplification factor K, which is related to the dimensioning of the regulator unit PI. The control variable SG is then forwarded to the switching regulator unit RE, in order to, for example, influence the inclination or slope of the sawtooth signal of the oscillator OS according to the current change of the cycle duration T. In addition, the control variable SG is led back to the input of the PI regulator PI via the seventh resistor R7 as feedback, in order to close the control loop, in which the current cycle duration T is supplied to the PI regulator PI.

[0055] Alternatively, instead of the inclination of the ramp of the sawtooth signal of the oscillator unit OS, the switch-on threshold can be influenced by means of a control variable SG as a function of the change in the instantaneous period duration T. For this purpose, the control variable SG can be inverted, for example.

[0056] The PI regulator PI can be implemented, for example, by means of an operational amplifier with corresponding circuits (e.g. resistors, capacitors), wherein the reference cycle duration Tref or a corresponding voltage value is supplied to the positive input of the operational amplifier and the current cycle duration T or an analog voltage mean value derived from the current cycle duration T by means of the unit PE for cycle detection is supplied to the inverting input of the operational amplifier. The control variable SG is supplied, for example, via the seventh resistor R7 to the inverting input of the operational amplifier or the PI regulator PI.

Claims

1. A method for regulating a switching converter (SN) having at least one switching element in quasi-resonant operation, wherein the at least one switching element is switched at a predetermined stable switching frequency in the regulated state of the switching converter (SN), and wherein the switch-on time of the at least one switching element is predetermined by a switching signal (PWM), the switching signal being generated by a sawtooth signal loaded with a valley detection signal (V) reaching a switch-on threshold, wherein the respective switch-on time of the at least one switching element falls into a valley of an oscillating voltage applied to the switched-off switching element by means of the valley detection signal (V), characterized in that The invention relates to a method for determining a current cycle duration (T) of the switching signal (PWM), comparing the current cycle duration (T) of the switching signal (PWM) with a predetermined reference cycle duration (Tref), deriving a control variable (SG) from the comparison of the current cycle duration (T) with the reference cycle duration (Tref), and changing the distance between the sawtooth signal loaded with the valley detection signal (V) and the switch-on threshold value by the control variable (SG) in the event of a load change at the output of the switching converter (SN) until reaching of the predetermined stable switching frequency is confirmed with the aid of the current cycle duration (T) determined.

2. The method according to claim 1, characterized in that The change in the distance between the sawtooth signal loaded with the valley detection signal (V) and the switch-on threshold is performed by the controlled variable (SG) in proportion to the change in the load at the output of the switching converter (SN).

3. The method according to any one of claims 1 to 2, characterized in that The change in the distance between the sawtooth signal loaded with the valley recognition signal (V) and the switch-on threshold is performed by changing the inclination of the ramp of the sawtooth signal as a function of the control variable (SG).

4. The method according to any one of claims 1 to 2, characterized in that The change in the distance between the sawtooth signal loaded with the valley recognition signal (V) and the switch-on threshold is performed by changing the switch-on threshold in accordance with the control variable (SG).

5. The method according to any one of claims 1 to 2, characterized in that When the predefined stable switching frequency is reached, the controlled variable (SG) is reset to a predefined output value.

6. The method according to any one of claims 1 to 2, characterized in that The current period duration (T) of the switching signal (PWM) is determined in the form of a digital value or an analog value.

7. A system for regulating a switching converter (SN) having at least one switching element, the switching converter being operated in quasi-resonant operation, and wherein the at least one switching element is switched at a predetermined stable switching frequency in the regulated state of the switching converter (SN), the system comprising at least: a switching regulator unit (RE) for generating a switching signal (PWM) which specifies a switch-on time for at least one switching element of a switching regulator (SN), wherein the switching regulator unit (RE) comprises an oscillator unit (OS) for generating a sawtooth signal which is compared with a switch-on threshold value in order to generate the switching signal (PWM); - a valley recognition unit (VE) for generating a valley recognition signal (V) which is applied to the sawtooth signal, whereby the respective switch-on time point of the at least one switching element falls into a valley of the oscillating voltage applied to the switched-off switching element, Characterized in that the system further comprises: - a unit for period duration detection (PE), which determines the current period duration (T) of the switching signal (PWM); - a cycle duration reference unit (PEref) for predefining a reference cycle duration (Tref); and - a control unit which generates a control variable (SG) for changing the distance between the sawtooth signal loaded with the trough detection signal (V) and the switch-on threshold value from a current cycle duration (T) determined by the unit for cycle duration detection (PE) and a reference cycle duration (Tref) of the cycle duration reference unit (PEref).

8. The system according to claim 7, characterized in that The unit for period duration detection (PE) is implemented with the aid of a microcontroller or a frequency-voltage converter.

9. The system according to claim 7, characterized in that The unit (PE) for period duration detection is implemented as an analog circuit which determines the current period duration (T) of the switching signal (PWM) as an analog voltage average value of a sawtooth auxiliary voltage synchronized with the sawtooth signal of the switching regulator unit (RE).

10. The system according to any one of claims 7 to 9, characterized in that The controller unit is designed as a proportional-integral controller.

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