Switched-mode power supply and method for operating a switched-mode power supply

Abstract

A switch-mode power supply includes a control element in a primary circuit for controlling a transformer for transmitting electric energy from the primary circuit to a secondary circuit, a first regulating element in the secondary circuit for regulating an electric output variable of the secondary circuit, and a second regulating element in the primary circuit for regulating an electric controlled variable of the control element as a function of a temperature of the primary circuit, the second regulating element being thermally coupled to an element of the primary circuit whose temperature is to be ascertained.

Claims

1. A switch-mode power supply, having: a control element situated in a primary circuit for controlling a transformer with the aid of an electric controlled variable; an ascertainment device that is situated in a secondary circuit for ascertaining an electric output variable of the secondary circuit; a first regulating element that is situated in the secondary circuit, functionally connected with the control element, and configured to regulate the electric output variable of the secondary circuit; a coupling element, interconnected between the primary circuit and the secondary circuit, functionally connecting the ascertainment device with the control element for transmitting the ascertained electric output variable of the secondary circuit to the control element of the first circuit; and a second regulating element that is situated in the primary circuit for regulating the electric controlled variable of the control element as a function of a temperature of an element of the primary circuit ascertained by the second regulating element, wherein the second regulating element is connected in parallel to the coupling element.

2. The switched-mode power supply of claim 1, wherein the electric controlled variable is an electric current, an electric voltage, or a digital variable.

3. The switched-mode power supply of claim 2, wherein a switching rate of one or more switches of the control element for the electric controlled variable of the control element is adjustable.

4. The switched-mode power supply of claim 1, wherein the second regulating element is configured to influence the electric controlled variable of the control element to ensure that a specifiable temperature threshold value for the element of the primary circuit is not exceeded.

5. The switched-mode power supply of claim 1, wherein the second regulating element is a resistor.

6. The switched-mode power supply of claim 5, wherein the resistor is an NTC thermistor interconnected in the primary circuit in such a way that it provides an electric regulating current in a control direction.

7. The switched-mode power supply of claim 5, wherein the resistor is a PTC thermistor interconnected in the primary circuit in such a way that it provides an electric regulating current in a control direction.

8. The switched-mode power supply of claim 1, wherein the switched-mode power supply is a resonance converter.

9. A method for operating a switched-mode power supply, the method comprising: a. ascertaining an electric output variable of a secondary circuit of the switched-mode power supply; b. changing a first electric controlled variable based on the ascertained electric output variable; c. ascertaining a temperature of an element in a primary circuit of the switched-mode power supply; d. changing a second electric controlled variable based on the ascertained temperature in the primary circuit; e. adapting a control by a control element based on a sum of the first electric controlled variable and the second electric controlled variable; and f. changing an electric power output that is transmitted in a transformer based on the ascertained temperature of the element of the primary circuit; wherein steps a and b are performed in succession, steps c and d are performed in succession, and the performance of the pair of steps of a and b is simultaneous to the performance of the pair of steps of c and d.

10. The method of claim 9, wherein the adapting of the control by the control element is performed in a manner by which electric power transmitted from the primary circuit to the secondary circuit is reduced when the temperature of the element in the primary circuit exceeds a predefined threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of a provided switched-mode power supply according to an example embodiment of the present invention.

(2) FIG. 2 is a block diagram of a switched-mode power supply according to another example embodiment of the present invention.

(3) FIG. 3 is a flowchart illustrating a method according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(4) Example embodiments of the present invention provide a switched-mode power supply, which regulates a controlled variable for a transformer based on a temperature ascertained on the primary side.

(5) In a known derating function, the temperature is detected only on the secondary side of the switched-mode power supply. This means that in the case of monitoring a temperature on the primary side (e.g., a primary side of the transformer, cooling body, switch element, etc.), a precise derating function or ascertainment of the temperature (reduction of the power output without switching the switched-mode power supply off completely) is not possible.

(6) If this known derating function, however, is implemented via the imprecise secondary temperature measurement, then this may have the following disadvantageous effects. If the derating function reduces the power output insufficiently, the components on the primary side may overheat, resulting in a reduced service life or a non-fulfillment of safety standards, etc. Additionally, if the derating function reduces the electric power output too much, the switched-mode power supply is unable to supply the full possible electric power output, even if the temperature is still within the normal range. Ultimately, this means performance losses of the switched-mode power supply.

(7) The two mentioned problems are particularly pronounced in charging devices, in which the electric charging current is regulated on the secondary side and in which thus the temperature of the secondary side varies little. The mentioned problems are even more pronounced if the switched-mode power supply is a resonance converter (e.g., an LLC converter), in which the temperature of the primary side varies greatly with the AC line voltage.

(8) A regulating element is therefore provided having the functionality of a temperature-measuring element, which is thermally coupled to an element of the primary side, the temperature of which is to be monitored, and which influences an electric control element on the primary side.

(9) This can be seen in principle in the representation of a provided switched-mode power supply 100 in FIG. 1. Using a control element 10 of a primary circuit 1, an electric signal is generated, which controls a transformer 30 that transmits electric power from primary circuit 1 to secondary circuit 2. In secondary circuit 2 of switched-mode power supply 100, an ascertainment device 20 ascertains an electric output variable (e.g., the electric current and/or the electric voltage on the output of secondary circuit 2). With the aid of a first regulating element 40, which is functionally connected to ascertainment device 20, the ascertained electric variable is transmitted via a coupling element 50 (e.g., an octocoupler), which is interconnected between primary circuit 1 and secondary circuit 2, to control element 10 of primary circuit 1. A derating element 41 is interconnected with regulating element 40, which performs the derating function explained above.

(10) Coupling element 50 is functionally connected to control element 10, which by way of first regulating element 40 produces a first control loop, which regulates an electric controlled variable for the control element 10 as a function of an electric output variable on secondary circuit 2.

(11) A second regulating element 60 is thermally coupled to an element (not shown) of primary circuit 1 whose temperature is to be monitored and also to connect second regulating element 60 functionally to control element 10. In this manner, second regulating element 60 is used to produce a second control loop, which regulates a electric controlled variable for control element 10 as a function of the temperature of the element of primary circuit 1.

(12) FIG. 2 shows a further possible example embodiment of the provided switched-mode power supply 100, in which the second regulating element 60, in the form of an NTC thermistor, is connected in parallel to coupling element 50. The NTC thermistor has a negative temperature coefficient, which means that with rising temperature the resistance decreases and as a result the electric current I.sub.NTC through the NTC resistor increases.

(13) Ultimately, with rising temperature of the second regulating element 60 in the form of an NTC thermistor, an electric current I.sub.Reg for control element 10 is increased, as a result of which the electric power output generated by transformer 30 is reduced. In the end, the electric power transmitted via transformer 30 at increased temperature is thereby reduced again, which ultimately lowers the temperature in primary circuit 1 and thus also of the element of primary circuit 1 whose temperature is ascertained.

(14) By way of the NTC thermistor in primary circuit 1, it is thus advantageously possible to ascertain the temperature of primary circuit 1 very precisely. It is advantageously possible to position the NTC thermistor in a simple manner on any element whose temperature is to be ascertained, for example on a cooling body, a component, an element of transformer 30 etc. The NTC thermistor in this instance acts like an additional temperature control loop, which acts in addition to the control loop implemented in the first regulating element 40. Here too, a derating element 41 is interconnected with regulating element 40, which helps perform the derating function explained previously.

(15) FIG. 2 shows that an NTC thermistor is interconnected parallel to the primary side of coupling element 50 in the form of the optocoupler. An electric current I.sub.NTC flows through the NTC thermistor which is added to the electric coupler current I.sub.Opto that flows through the optocoupler. This electric current increases with the primary temperature in accordance with the reduction of the resistance of the NTC thermistor.

(16) The total regulating current I.sub.Reg is therefore increased by a temperature-dependent component, whereby, at an excessively high temperature, the maximum available electric power is reduced (derating function). At normal temperature, this component is so low that the secondary control loop including first regulating element 40 is able to compensate for it and that the electric power output of switched-mode power supply 100 is thus not reduced.

(17) Using a single NTC thermistor, it is thus possible in a simple manner to implement an additional primary derating function for an already existing control loop for switched-mode power supply 100. At increased temperature, the power output is thus reduced (derating), the control element 10, however, advantageously not latching, i.e., completely switching off, the switched-mode power supply 100. As a result, advantageously, a basic functionality is preserved for switched-mode power supply 100 at a reduced level. For a battery charger, this means for example that the electric charging function is not completely shut off, but that merely e.g., the electric charging current is reduced.

(18) Another example embodiment of the provided switched-mode power supply 100, which is not shown in the figures, provides for the second regulating element 60 to be a PTC thermistor, which is interconnected in primary circuit 1 in such a way that it provides the electric regulating current I.sub.Reg in the correct control direction. A PCT thermistor can be used as regulating element 60, for example, in the event that the control direction in the switched-mode power supply is reversed (regulating current I.sub.Reg diminishes in order to reduce the power output). In this manner, an alternative additional control loop is provided using the PTC thermistor.

(19) Another example embodiment of the switched-mode power supply 100, which is not shown in the figures, provides for the electric controlled variable to be a digital controlled variable for control element 10, for example a control signal for control element 10 having an adjustable relationship between turn-on time and turn-off time as a function of the ascertained temperature. For this purpose, the second regulating element 60 is preferably developed as an electronic circuit (not shown), which provides the mentioned function.

(20) The provided switched-mode power supply 100 is preferably a resonance converter, in which the temperature monitoring of the primary circuit has a high priority. In this manner, it is advantageously possible to achieve a maintenance and/or monitoring of technical safety standards and/or norms.

(21) FIG. 3 is a flowchart of an example embodiment of a method of the present invention. In a step 200, an electric output variable of a secondary circuit 2 of switched-mode power supply 100 is ascertained. In a step 210, a first electric controlled variable I.sub.Opto is changed as a function of the ascertained electric output variable. In a step 220, a temperature of an element in the primary circuit 1 is ascertained. In a step 230, a second electric controlled variable I.sub.NTC is changed as a function of the ascertained temperature in primary circuit 1. In a step 240, the control of a control element 10 is adapted as a function of a sum of first electric controlled variable I.sub.Opto and of second electric controlled variable I.sub.NTC. In a step 250, the electric power output that is transmitted in transformer 30 is changed as a function of the ascertained temperature of the element of primary circuit 1, steps 200 and 210 being performed in succession, steps 220 and 230 being performed in succession, and steps 200 and 210 being performed simultaneously with performance of steps 220 and 230. Steps 200, 210 are performed using a first regulating element 40, and steps 220, 230 are performed using a second regulating element 60.

(22) First electric controlled variable (step 210) is an electric controlled variable that is changed as a function of the ascertained electric output variable (step 200) and with the aid of coupling element 50.

(23) In the example embodiment of the switched-mode power supply 100, as shown in FIG. 2, it is the current I.sub.Opto that is changed by the optocoupler. The optocoupler changes this current I.sub.Opto as a function of the signal that is produced by regulating element 40 on the secondary side.

(24) Second electric controlled variable (step 230) is an electric controlled variable that is changed as a function of the ascertained temperature on the primary side (step 220).

(25) In the example embodiment of switched-mode power supply 100 from FIG. 2, it is current I.sub.NTC that is changed by the NTC thermistor (the resistance value of the NTC thermistor changes with the temperature and thus this current I.sub.NTC is changed).

(26) FIG. 2 shows that these two electric controlled variables are added together. This yields a current I.sub.Reg (I.sub.Reg=I.sub.Opto+I.sub.NTC) as a function of which the control of control element 10 is adapted (step 240).

(27) In summary, the present invention provides a switched-mode power supply having a primary-side temperature regulation in addition to a secondary-side regulation.

(28) Although the present invention was described above with reference to concrete examples of use, one skilled in the art is also able to implement embodiments that were not disclosed above or that were disclosed above only partially, without deviating from the essence of the invention.