Control circuit for a switch unit of a clocked power supply circuit, and resonance converter

• US 20060285366A1
• Filed: 05/18/2006
• Published: 12/21/2006
• Est. Priority Date: 05/23/2005
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., Infineon Technologies AG
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., Infineon Technologies AG
• Inventors: Radecker, Matthias, Herfurth, Michael, Bisogno, Fabio
• Granted Patent: US 7,746,671 B2
• Time in Patent Office: Days
• US Class Current: 363/16
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A control circuit for a switch unit of a clocked power supply circuit, the switch unit being designed to effect input-side excitation of a resonant transformer arrangement, comprises an input for receiving an auxiliary signal from the resonant transformer arrangement. The auxiliary signal exhibits an essentially fixed phase relation to a load alternating current flowing through a resonant circuit of the transformer arrangement. The control circuit further comprises a phase detector designed to detect reference crossing moments when the auxiliary signal crosses a predefined reference value, a driver controllable to switch the switch unit, and a synchronizer designed to synchronize a turn-on of the switch unit by the driver with regard to a phase position with the auxiliary signal so as to achieve a turn-on of the switch unit within a predetermined time interval around a zero crossing of a voltage present across the switch unit, or of a current flowing through the switch unit. The synchronizer is further designed to receive information about the reference crossing moments from the phase detector, and to provide a turn-on signal to the driver with a fixed phase delay at the reference crossing moments, so as to define turn-on moments at which the driver is to turn on the switch unit. The control circuit further comprises a detector designed to determine an amplitude information which depends on an amplitude or a mean value of the auxiliary signal, and a regulator designed to change an operating frequency in dependence on the amplitude information supplied by the detector, and to determine a period duration between turn-off moments at which the driver is to turn off the switch unit as a reciprocal of the operating frequency. An inventive resonance converter enables independent control of frequency and turn-on moments, or duty cycle, and thus enables a particularly efficient operation of the resonance converter, and a particularly precise regulation.

Claims

1. A control circuit for a switch unit of a clocked power supply circuit, the switch unit being designed to effect input-side excitation of a resonant transformer arrangement, the control circuit comprising:

an input for receiving an auxiliary signal from the resonant transformer arrangement, the auxiliary signal exhibiting an essentially fixed phase relation to a load alternating current flowing through a resonant circuit of the transformer arrangement;

a phase detector designed to detect reference crossing moments when the auxiliary signal crosses a predefined reference value;

a driver controllable to switch the switch unit;

a synchronizer designed to synchronize a turn-on of the switch unit by the driver with regard to a phase position with the auxiliary signal so as to achieve a turn-on of the switch unit within a predetermined time interval around a zero crossing of a voltage present across the switch unit, or of a current flowing through the switch unit,

the synchronizer being designed to receive information about the reference crossing moments from the phase detector, and to provide a turn-on signal to the driver with a fixed phase delay at the reference crossing moments, so as to define turn-on moments at which the driver is to turn on the switch unit;

a detector designed to determine an amplitude information which depends on an amplitude or a mean value of the auxiliary signal; and

a regulator designed to change an operating frequency in dependence on the amplitude information supplied by the detector, and to determine a period duration between turn-off moments at which the driver is to turn off the switch unit as a reciprocal of the operating frequency.

2. The control circuit according to claim 1, wherein the synchronizer is designed to provide the turn-on signal such that the driver turns on the switch unit with a phase delay of between 60°

and 90°

relative to the reference crossing moments.

3. The control circuit according to claim 1, wherein the predetermined time interval starts one twelfth of a period duration of the operating frequency prior to the zero crossing of the voltage present across the switch unit or of the current flowing through the switch unit, ends with the zero crossing of the voltage present across the switch unit, or of the current flowing through the switch unit, and also includes associated interval limits.

4. The control circuit according to claim 1, wherein the synchronizer includes a delayer designed to delay the turn-on signal by a phase delay in a range between 50°

and 80°

, based on a period of the operating frequency, relative to the reference crossing moments.

5. The control circuit according to claim 1, wherein the synchronizer includes a delayer designed to delay the turn-on signal by a phase delay in a range between 60°

and 70°

, based on a period of the operating frequency, relative to the reference crossing moments.

6. The control circuit according to claim 1, wherein the driver is designed such that a sum of phase delays of the switch unit and of the driver, based on a period of the operating frequency, amounts to between 10°

and 40°

.

7. The control circuit according to claim 1, wherein the driver is designed such that a sum of phase delays of the switch unit and of the driver, based on a period of the operating frequency, amounts to between 20°

and 30°

.

8. The control circuit according to claim 1, wherein the detector is designed to obtain a first detector reference value crossing moment when the auxiliary signal crosses a predetermined first detector reference value, and to obtain a second detector reference value crossing moment when the auxiliary signal crosses a predetermined second detector reference value, to determine a detector phase shift between the first detector reference value crossing moment and the second detector reference value crossing moment, and to determine an approximate value for an amplitude of the auxiliary signal from the detector phase shift, which forms the amplitude information.

9. The control circuit according to claim 8, wherein the detector is designed to receive the first detector reference value crossing moment from the phase detector, and to receive the second detector reference value crossing moment from a detector reference value comparator designed to compare the auxiliary signal with a detector reference voltage value or with a detector reference current value, the detector reference value crossing moments being defined as moments when the comparison result of the phase detector or of the detector reference value comparator changes.

10. The control circuit according to claim 9, wherein the detector is designed to detect first detector reference value crossing moments when the auxiliary signal has a zero crossing, and to determine the approximate value for the amplitude of the auxiliary signal by evaluating the relation

$U_{\mathrm{RR}}=\frac{{\mathrm{UI}}_R}{}$

 

⁢

0 sin ⁡

( Δ

φ

)

wherein UI_R0 designates the detector reference voltage value or the detector reference current value, wherein sin designates a sinusoidal function and wherein Δ

φ

designates the detector phase shift.

11. The control circuit according to claim 1, wherein the regulator is designed to compare the amplitude information with an amplitude reference value, to obtain an amplitude comparison result, and to change the operating frequency by a change step towards a resonance frequency of the resonant transformer arrangement, when the amplitude information is smaller than the amplitude reference value, and to change the operating frequency by a change step away from the resonance frequency of the resonant transformer arrangement, when the amplitude information is higher than the amplitude reference value.

12. The control circuit according to claim 11, wherein the regulator is designed to determine the change step in dependence on the detector phase shift, such that the higher the detector phase shift, the smaller the change step.

13. The control circuit according to claim 11, wherein the amplitude reference value is a fixed predetermined value.

14. The control circuit according to claim 8, wherein the regulator is designed to determine a variable amplitude reference value based on a load-dependent correction of a fixed amplitude reference value by using the detector phase shift, and to regulate the operating frequency to minimize a deviation of the amplitude information from the variable amplitude reference value.

15. The control circuit according to claim 1, wherein the regulator is designed to regulate the operating frequency in dependence on a relation between the amplitude information and an amplitude reference value or on a difference between the amplitude information and the amplitude reference value, and to adjust the amplitude reference value such that the amplitude reference value decreases with increasing load resistance at an output of the transformer arrangement.

16. The control circuit according to claim 15, wherein the regulator is designed to adjust the amplitude reference value in dependence on a turn-off angle between a zero crossing of the auxiliary signal and a moment when the switch unit is turned off.

17. The control circuit according to claim 1, wherein the detector is designed to obtain a first detector reference crossing moment when the auxiliary signal crosses a predetermined first detector reference value, to obtain a second detector reference crossing moment when the auxiliary signal crosses a predetermined second detector reference value, to determine a detector phase shift between the first detector reference crossing moment and the second detector reference crossing moments, to compare the detector phase shift with a minimum allowable detector phase shift limit, and to limit a change of the operating frequency towards a resonance frequency of the resonant transformer arrangement, when the detector phase shift reaches the detector phase shift limit or falls below the same.

18. The control circuit according to claim 1, wherein the regulator is designed to determine an updated operating frequency by determining an associated updated period duration, wherein the regulator is further designed to determine the updated period duration by incrementing or decrementing a previous period duration associated to a previous operating frequency.

19. The control circuit according to claim 1, wherein the regulator is designed to regulate the operating frequency in dependence on a relation between the amplitude information and an amplitude reference value, wherein the regulator is further designed to provide a measure for a load resistor connected to an output of the resonant transformer arrangement, and to adjust the amplitude reference value based on the measure for the load resistor such that the amplitude reference value depends on a logarithm of a value of the load resistor according to the linear context.

20. The control circuit according to claim 19, which is further designed to adjust the amplitude reference value in dependence on a forward current time period, during which a current flows in forward direction through a switch of the switch unit, and a reverse current time period, during which a current flows in a reverse direction through a switch of the switch unit, such that the amplitude reference value decreases with increasing ratio between reverse current time period and forward current time period.

21. The control circuit according to claim 20, which is further designed to adjust the amplitude reference value to a final value independent of the forward current time period and the reverse current time period, when the reverse current time period is higher than or equal to the forward current time period.

22. The control circuit according to claim 19, which is further designed to determine a reverse-time/forward-time ratio between a reverse current time period, during which a current flows in a reverse direction through a switch of the switch unit, and a forward current time period, during which a current flows in forward direction through a switch of the switch unit, and to adjust the amplitude reference value based on the reverse-time/forward-time ratio such that a large amplitude reference value is associated to a small reverse-time/forward-time ratio, and that a smaller amplitude reference value is associated to a larger reverse-time/forward-time ratio.

23. The control circuit according to claim 22, wherein the control circuit is designed to determine the amplitude reference value as linear function of the reverse-time/forward-time ratio, if the reverse-time/forward-time ratio is smaller than a predetermined value.

24. The control circuit according to claim 23, wherein the control circuit is further designed to determine the amplitude reference value independent of the reverse-time/forward-time ratio, if the reverse-time/forward-time ratio is higher than the predetermined value.

25. The control circuit according to claim 22, wherein the control circuit is designed to determine a source voltage of the energy source, and to adjust the amplitude reference value in dependence on the source voltage and the reverse-time/forward-time ratio.

26. The control circuit according to claim 25, wherein the control circuit is designed to map the reverse-time/forward-time ratio to the amplitude reference value by a linear functional context, wherein the control circuit is designed to adjust parameters of the linear functional context in dependence on the source voltage in such a manner that for a maximum allowable value of the source voltage, a predetermined reverse-time/forward-time ratio in a range between 0.4 and 0.7 is mapped to a predetermined amplitude reference value,

that for a minimum allowable value of the source voltage, a reverse-time/forward-time ratio in a range between 0.0 and 0.2 is mapped to the predetermined amplitude reference value,

that at a maximum allowable value of the source voltage, a reverse-time/forward-time ratio in a range between 0.9 and 1.0 is mapped to a minimum amplitude reference value, and

that at a minimum allowable value of the source voltage, a reverse-time/forward-time ratio in a range between 0.9 and 1.0 is mapped to the minimum amplitude reference value.

27. The control circuit according to claim 26, wherein the control circuit is designed to adjust the amplitude reference value such that a ratio between a maximum amplitude reference value and the minimum amplitude reference value lies in a range between 2.0 and 2.3.

28. The control circuit according to claim 1 which is further designed to determine a reverse-time/forward-time ratio between a reverse time, during which a current flows through a switch of the switch unit in a reverse direction, and a forward-current time duration, during which a current flows through the switch of the switch unit in a forward direction, and to activate a burst mode, during which the control circuit controls the switch unit to generate separate packets of switching sequences, when the reverse-time/forward-time ratio is larger than 0.9.

29. The control circuit according to claim 1, which is further designed to determine a turn-off phase difference between a turn-off of the driver and a zero crossing of the auxiliary signal, and to activate a burst mode, during which the control circuit controls the switch unit to generate separate packets of switching sequences, when the turn-off phase difference exceeds or falls below a first turn-off phase difference boundary value.

30. The control circuit according to claim 29, wherein the first turn-off phase difference boundary value ranges between 50°

and 80°

.

31. The control circuit according to claim 29, wherein the first turn-off phase difference boundary value ranges between 60°

and 70°

.

32. The control circuit according to claim 29, further designed to determine, in the burst mode, the turn-off phase difference, and to return from the burst mode to a continuous operation wherein the control circuit controls the switch unit to generate a continuous switching sequence, when the turn-off phase difference exceeds or falls below a second turn-off phase difference boundary value.

33. The control circuit according to claim 32, wherein the second turn-off phase difference boundary value ranges between 45°

and 75°

.

34. The control circuit according to claim 32, wherein the second turn-off phase difference boundary value ranges between 55°

and 65°

.

52. The resonance converter according to claim 1, wherein a voltage rectified at the output load and proportional to the output voltage, or a rectified current proportional to the output current is used via a direct current feedback, such as a galvanically separating optocoupler, to provide a reference value, and thus to regulate the output voltage or the output current, present at the output-side resistive load, to have a constant value.

53. The resonance converter according to claim 1, wherein a voltage rectified at the output load and proportional to the output voltage, or a rectified current proportional to the output current is used via a direct current feedback, such as a galvanically separating optocoupler, to be initially compared with a reference value, and wherein the comparison result is thereafter supplied to the direct current feedback to provide, from the feedback output thereof, a signal which is directly supplied to a voltage-controlled oscillator to regulate the output voltage to have a constant value, and wherein an auxiliary signal obtained from the resonant transformer arrangement is additionally used to operate a synchronizer designed to synchronize a turn-on of the switch unit by the driver with regard to a phase position with the auxiliary signal.

54. The resonance converter according to claim 1, wherein a voltage rectified at the output load and proportional to the output voltage, or a rectified current proportional to the output current is used via a direct current feedback, such as a galvanically separating optocoupler, to be initially compared with a reference value, and wherein the comparison result is thereafter supplied to the direct current feedback to provide, from the feedback output thereof, a signal which is directly supplied to a voltage-controlled oscillator to regulate the output voltage to have a constant value, and wherein, additionally, the duty cycle of the switch unit is set, in a fixed relation to the frequency of the voltage-controlled oscillator, such that the duty cycle is preferably in a linear relation to the frequency of the voltage-controlled oscillator.

55. The resonance converter according to claim 54, wherein the duty cycle takes on a value of between 0.3 and 0.6 at a minimum frequency of the voltage-controlled oscillator, and wherein the duty cycle takes on a value of between 0,05 and 0.25 at a maximum frequency of the voltage-controlled oscillator.

56. The resonance converter according to claim 1, designed such that a voltage rectified at the output load and proportional to the output voltage, or a rectified current proportional to the output current is initially compared with a reference variable, a result of the comparison is supplied to a regulator, an output signal of the regulator is fed back via a galvanically separating feedback element to control a voltage-controlled oscillator.

57. The resonance converter according to claim 56, wherein the feedback element is an optocoupler.

58. The resonance converter according to claim 56, designed to control the voltage-controlled oscillator such that a higher output voltage or a higher output current results in a higher frequency of the voltage-controlled oscillator, and that a smaller output voltage or a smaller output current results in a lower frequency of the voltage-controlled oscillator.

59. The resonance converter according to claim 1, the resonance converter being designed such that an inductance of the switch unit forms, with an input capacitance of a load network, a resonant frequency which has a ratio of between 0.75 and 1.25 to a resonant frequency of an alternating current source.

60. The resonance converter according to claim 1, the resonance converter being designed such that an inductance of the switch unit forms, with an input capacitance of a load network, a resonant frequency which has a ratio of between 0.1 and 1.0 to a resonant frequency of an alternating current source.

35. A resonance converter for providing an output voltage or an output current for a load network based on an energy supplied by an energy source, the resonance converter comprising:

a resonant transformer arrangement having an input for receiving an input-side excitation, an output for providing the output voltage or the output current for the load network, and an auxiliary output for transformationally providing an auxiliary signal, the amplitude of which is essentially proportional to a load alternating current flowing through a resonant circuit of the resonant transformer arrangement, and which exhibits an essentially fixed phase relation to the load alternating current flowing through the resonant circuit of the resonant transformer arrangement;

a switch unit designed to generate the input-side excitation of the resonant transformer arrangement from the energy of the energy source; and

a control circuit for a switch unit of a clocked power supply circuit, the switch unit being designed to effect input-side excitation of a resonant transformer arrangement, the control circuit comprising;

an input for receiving an auxiliary signal from the resonant transformer arrangement, the auxiliary signal exhibiting an essentially fixed phase relation to a load alternating current flowing through a resonant circuit of the transformer arrangement;

a phase detector designed to detect reference crossing moments when the auxiliary signal crosses a predefined reference value;

a driver controllable to switch the switch unit;

a synchronizer designed to synchronize a turn-on of the switch unit by the driver with regard to a phase position with the auxiliary signal so as to achieve a turn-on of the switch unit within a predetermined time interval around a zero crossing of a voltage present across the switch unit, or of a current flowing through the switch unit,

the synchronizer being designed to receive information about the reference crossing moments from the phase detector, and to provide a turn-on signal to the driver with a fixed phase delay at the reference crossing moments, so as to define turn-on moments at which the driver is to turn on the switch unit;

a detector designed to determine an amplitude information which depends on an amplitude or a mean value of the auxiliary signal; and

a regulator designed to change an operating frequency in dependence on the amplitude information supplied by the detector, and to determine a period duration between turn-off moments at which the driver is to turn off the switch unit as a reciprocal of the operating frequency,

wherein the input of the control circuit is coupled to the auxiliary output of the resonant transformer arrangement, and wherein the driver is designed to generate a control signal to switch the switch unit.

36. The resonance converter according to claim 35, wherein the resonant transformer arrangement includes a first transformer and a second transformer, the first transformer and the second transformer being connected in series on the input side,

wherein an output of the first transformer is coupled in an electrically conducting manner to the output of the transformer arrangement, and

wherein an output of the second transformer is coupled in an electrically conducting manner to the auxiliary output of the transformer arrangement.

37. The resonance converter according to claim 36, wherein the output of the second transformer has a capacitance connected in parallel with it which is designed to cause the auxiliary voltage to exhibit a phase shift ranging between 80°

and 100°

relative to an input-side current.

38. The resonance converter according to claim 37, wherein the first transformer and the second transformer are two piezoelectric transformers or parts of one single piezoelectric transformer.

39. The resonance converter according to claim 35, wherein the switch unit, the driver, and the synchronizer are designed such that a sum of the phase delay of the synchronizer, of the driver and of the switch unit ranges between 80°

and 100°

, the phase delay of the driver describing a time delay between a turn-on signal and a generation of the control signal for turning on the switch of the switch unit, and the phase delay of the switch describing a time delay between generating the control signal for turning on the switch, and an actual turn-on of the switch.

40. The resonance converter according to claim 35, wherein the switch unit, the driver, and the synchronizer are designed such that a sum of the phase delay of the synchronizer, of the driver and of the switch unit ranges between 85°

and 95°

, the phase delay of the driver describing a time delay between a turn-on signal and a generation of the control signal for turning on the switch of the switch unit, and the phase delay of the switch describing a time delay between generating the control signal for turning on the switch, and an actual turn-on of the switch.

41. A resonance converter for providing an output voltage or an output current for a load network based on an energy supplied by an energy source, the resonance converter comprising:

a resonant transformer arrangement having an input for receiving an input-side excitation, an output for providing the output voltage or the output current for the load network, and an auxiliary output for transformationally providing a signal which is essentially proportional to the output voltage provided by the resonant transformer arrangement, or to the output current provided by the resonant transformer arrangement;

a switch unit designed to generate the input-side excitation of the resonant transformer arrangement from the energy of the energy source, the switch unit comprising a switch; and

a control circuit designed to set or to regulate an operating frequency, with which the switch unit is switched, in dependence on a phase shift between a current flowing through the switch or a current flowing from the switch unit to the input of the resonant transformer arrangement, on the one hand, and on the signal present at the auxiliary output, on the other hand.

42. The resonance converter according to claim 41, wherein the auxiliary output is designed to provide an auxiliary signal which is essentially proportional to the output voltage,

which further includes an output current detector for determining a load current information about the output current or a current in the load network,

a logarithmizer for taking the logarithm for determining a logarithmized load current information by forming a logarithm of the load current information,

a phase reference value provider for deriving a phase reference value from the logarithmized load current information by applying a linear function to the logarithmized load current information, and

a regulator,

the regulator being designed to regulate the operating frequency so as to minimize a difference between the phase shift and the phase reference value.

43. The resonance converter according to claim 42, wherein the logarithmizer and the phase reference value provider are designed to provide, with a higher output current or current in the load network, a smaller phase reference value than with a smaller output current or current in the load network.

46. The resonance converter according to claim 41, wherein the auxiliary output is designed to provide an auxiliary signal essentially proportional to the output voltage,

which includes a first reference value comparator designed to detect zero crossing moments of the auxiliary signal,

a second reference value comparator designed to compare the auxiliary signal with a predefined reference value different from zero, and to provide an output signal which indicates whether the auxiliary signal is smaller or larger than the reference value, and

a zero crossing detector designed to detect zero crossing moments at which the current flowing through the switch, or the current flowing from the switch unit to the input of the resonant transformer arrangement, comprises zero crossings, and

wherein the control circuit is designed to determine a phase shift between the zero crossing moments of the auxiliary signal and the zero crossing moments of the current,

to generate a phase reference value as a function of the output signal of the second reference value comparator, and

to regulate the operating frequency based on the phase shift and the phase reference value.

47. The resonance converter according to claim 46, wherein the control circuit is designed to specify the direction of a change in the operating frequency as a function of the phase reference value, and to specify an amount of a change in the operating frequency as a function of the phase shift.

48. The resonance converter according to claim 41, further comprising a pump circuit connected in series to the input of the resonant transformer arrangement, wherein the control circuit is designed to sample a voltage curve across the pump circuit, to determine information about a source voltage, provided by the energy source, or a resonant frequency of the switch unit, and to determine, on the basis thereof, a correction variable and superimpose it onto the phase shift in a linear manner.

49. The resonance converter according to claim 41, which further comprises a pump circuit connected in series to the input of the resonant transformer arrangement,

which includes a driver which is controllable to switch the control unit,

and wherein the control circuit is further designed to generate a reverse detection signal when a current flowing through a switch of the switch unit falls below a predefined current value or flows in a reverse direction,

to provide a turn-on signal to the driver to define turn-on moments at which the driver is to turn on the switch unit,

to compare the voltage present across the pump circuit with a predefined pump voltage reference value,

to generate a pump voltage reference comparison signal indicating whether the voltage present across the pump circuit is larger or smaller than the pump voltage reference value,

to delay the pump voltage reference comparison signal to obtain a delayed pump voltage reference comparison signal, and

to generate the turn-on signal by an OR operation of the reverse detection signal and of the delayed pump voltage reference comparison signal.

50. The resonance converter according to claim 49, wherein the control circuit is designed to delay the pump voltage reference comparison signal by a phase delay ranging between 80°

and 100°

, based on an operating frequency.

44. The resonance converter according to claimed 41, wherein the auxiliary output is designed to provide an auxiliary signal which is essentially proportional to the output voltage,

which includes a reference value comparator designed to compare the auxiliary signal with a predefined reference value and to detect reference crossing moments at which the auxiliary signal crosses the predefined reference value, and

a zero crossing detector designed to detect zero crossing moments at which the current flowing through the switch, or the current flowing from the switch unit to the input of the resonant transformer arrangement, comprises zero crossings,

and wherein the control circuit is designed to determine a phase shift between the reference crossing moments and the zero crossing moments to detect whether at least one reference crossing moment is present within a predefined time interval, so as to set a phase reference as a function of whether at least one reference crossing moment is present in the predefined time interval, and

to regulate the operating frequency as a function of a difference between the phase shift and the phase reference.

45. The resonance converter according to claim 44, wherein the control circuit is designed to regulate the operating frequency so as to minimize the difference between the phase shift and the phase reference.

51. A resonance converter for providing an output voltage or an output current for a load network based on an energy provided by an energy source, the resonance converter comprising:

a resonant transformer arrangement having an input for receiving an input-side excitation, an output for providing the output voltage or the output current, and an auxiliary output for transformationally providing an auxiliary signal, the amplitude of which is essentially proportional to the output voltage provided by the resonant transformer arrangement, the amplitude of which is essentially proportional to the output current provided by the resonant transformer arrangement, or the amplitude of which is essentially proportional to a load alternating current flowing through a resonant circuit of the resonant transformer arrangement;

a switch unit designed to generate the input-side excitation of the resonant transformer arrangement from the energy of the energy source; and

a regulator circuit, the regulator circuit comprising a comparator adapted to receive the auxiliary signal, to compare it with a predefined reference value and to provide comparison information indicating whether the auxiliary signal is larger or smaller than the reference value,

the regulator circuit further including a switching detector designed to detect whether the comparison information changes its state within a predefined time interval, and

the regulator circuit being designed to change an operating frequency, the period duration of which determines time intervals between turn-on moments or turn-off moments of the switch unit, from a resonant frequency of the resonant transformer arrangement when the detector detects that the comparison information has changed its state within the predefined time interval, and to change the operating frequency toward the resonant frequency when the detector detects that the comparison information has not changed its state within the predefined time interval.