WO2015075010A2

WO2015075010A2 - Switch-mode power supply and a method for controlling an output voltage of a switch-mode power supply

Info

Publication number: WO2015075010A2
Application number: PCT/EP2014/074832
Authority: WO
Inventors: Klaus Schürmann; Michael Buschkamp
Original assignee: Weidmüller Interface GmbH & Co. KG
Priority date: 2013-11-25
Filing date: 2014-11-18
Publication date: 2015-05-28
Also published as: EP3075066A2; CN105745830A; WO2015075010A3; DE102013113012A1

Abstract

The invention relates to a switch-mode power supply (1) for converting an input voltage (U_EIN) into an output voltage (U_A), which comprises at least one switching stage (4) controlled by a pulse width modulation circuit (9) in a clocked manner, and a control circuit (8) being provided which acts on said pulse width modulation circuit (9) in order to alter the output voltage (U_A) level. The switch-mode power supply (1) is characterised in that the control circuit (8) has a temperature sensor (S) provided to measure a load-dependent temperature (T) of the switch-mode power supply (1), said control circuit (8) being configured such that the output voltage (U_A) is lowered as the temperature (T) increases. The invention also relates to a method for controlling an output voltage (U_A) of a switch-mode power supply (1).

Description

Switching power supply and method for regulating an output voltage

Switching power supply

The invention relates to a switching power supply for converting an input voltage into an output voltage, the at least one of a

Pulse width modulation circuit clocked controlled switching stage, wherein a control circuit is provided which acts on the pulse width modulation circuit for changing the height of the output voltage. The invention further relates to a method for regulating an output voltage of a

Switching power supply.

In a switching power supply usually an input AC voltage is first rectified and then converted with a switching stage in an AC voltage considerably higher frequency. This input-side high-frequency AC voltage is, for example by means of a transformer, transformed into an output-side high-frequency AC voltage smaller or larger amount and rectified again. To the won so

Stabilize output DC voltage, such switching power supplies have a control circuit that controls the DC output voltage regardless of a load connected to a constant value as possible. This is due to a change in the frequency and / or the pulse width or the

Duty cycle of the clocked control of the switching stage in one

Pulse width modulation (PWM) possible. For this purpose, the switching power supply to a PWM switching stage, which is influenced by the control loop.

Depending on the application, a switching power supply instead of the

Input-side switching stage also have an output side arranged switching stage, or it is provided both the input side and the output side, a switching stage for converting a rectified AC voltage into an AC voltage higher frequency. In order to supply a load with a sufficiently large power, it is known to connect several power supplies in parallel, so that the load is higher

Output current is available. In such a parallel connection, it is important that the power supplies are loaded evenly. This is usually not the case without additional control, since even identical power supplies with nominally equal output voltage in their actual

Output voltages are at least slightly different, which may have greatly divergent output currents of the individual power supplies result.

Without any additional regulation then usually takes one of the power supplies, the full load up to its current limit, while the other or the other power supplies take over only the remaining required load. The heavily loaded power supply then works permanently at its power limit, which significantly reduces its life.

It is therefore known, the output current of each of the parallel connected

To measure power supplies, and to regulate the output voltage with an external control depending on the flowing output current in each case so that the power supplies provide the same proportion of electricity. The power supplies are loaded very evenly in this solution. Because of the required external circuitry, however, this solution is expensive.

It is therefore an object of the invention to provide a switched mode power supply, with which in parallel with another, in particular

identical switching power supply a uniform current load is achieved without an external wiring is required.

The object is achieved with a switching power supply and a method for controlling an output voltage of a switching power supply with the features of the respective independent claim. Advantageous embodiments are described in the dependent claims. An inventive switching power supply of the type mentioned above is characterized in that the control circuit has a temperature sensor which is provided for measuring a load-dependent temperature of the switching power supply, wherein the control circuit is arranged so that the output voltage is lowered with increasing temperature.

In the event of a sustained high power output, the switched-mode power supply unit heats up or at least heats up at least individual components (components) of the power supply unit

Switching power supply. According to the invention, the temperature sensor detects this

Warming and acts on the control circuit such that the

Output voltage is lowered with increasing temperature. If the power supply operates in parallel with other power supplies, it will be replaced by the

Temperature-controlled lowering of the output voltage causes less damage to the power supply. Consequently, subsequently, with a certain time delay, due to the thermal inertia of the power supply, the measured temperature again decreases. The output voltage increases, and the power supply is again heavily loaded. With suitable slope of the

Temperature dependence of the output voltage, however, results in no repetitive temperature increase and decrease, but it turns a largely constant and on the parallel-connected power supplies

uniform load and thus temperature distribution. Without the need for external wiring, the load is distributed in a parallel connection of several power supply units to the interconnected power supply units.

In an advantageous embodiment of the switching power supply is the

Output voltage with increasing temperature only lowered when the temperature is above a predetermined threshold temperature. The control circuit can, for example, an evaluation circuit for the

Temperature sensor comprising a threshold switch. In this way, a variation of the output voltage in a low power range is prevented and also an unwanted dependence of the output voltage on the ambient temperature. Only when a component has a significantly increased temperature due to load, which suggests a load inequality distribution, the temperature-dependent control mechanism begins. Preferred is a Threshold temperature selected between 70 and 100 ° C (degrees Celsius), and more preferably between 85 and 95 ° C.

In a further advantageous embodiment of the switching power supply is the

Output voltage linearly lowered with increasing temperature. Preferably, the lowering of the output voltage between 0.005 and 0.025 V / K (volts / Kelvin, corresponds to V / ° C) and more preferably between 0.015 and 0.02 V / K. The reduction can be relatively easily implemented, for example, by the fact that the control circuit has an evaluation circuit with a

includes counter-coupled operational amplifier for the temperature sensor. A linear functional relationship between the measured temperature and the output voltage can be easily implemented circuitry and leads to a good-natured control behavior in a parallel circuit of multiple power supplies, in which a swing in a control situation in which constantly another power supply is excessively loaded.

In a preferred embodiment, the control circuit comprises a

Voltage regulation. Also preferably, the control circuit is additionally or alternatively designed as a current control.

In a further advantageous embodiment of the switching power supply is the

Temperature sensor a temperature-dependent resistor. This can as

Thermistor or be designed as a PTC thermistor. In principle, however, are also designed as a switching transistor or as semiconductor temperature sensors

Temperature sensors usable.

The temperature sensor is preferably arranged on an output side of the switched-mode power supply and is in thermal contact with a component of the switched-mode power supply. For example, the temperature sensor with a

be coupled output side rectifier. But it is also an arrangement on an input side of the switching power supply conceivable, if there is a

load-dependent temperature is measurable. The switching power supply is preferred as a so-called wide-range power supply

educated. The height of the input voltage is preferably in the range of 10 to 300V, more preferably in the range of 15 to 265V.

The object is further solved by a method for controlling a

Output voltage of a switching power supply in which a load-dependent temperature of a component of the switching power supply is measured and the

Output voltage is adjusted depending on the measured temperature. Preferably, the output voltage is lowered with increasing temperature and lowered in particular linearly with the temperature. More preferably, the output voltage is lowered with increasing temperature when the temperature is greater than a predetermined threshold temperature. This results in the advantages described in connection with the switching power supply.

In the following the invention with reference to an embodiment using figures is described in more detail. The figures show:

Figure 1 is a schematic diagram of a switching power supply;

Figure 2 is a more detailed circuit diagram of a portion of the switched mode power supply; and

Figure 3 is a schematic representation of the dependence of a

Output voltage of an evaluation circuit of a temperature measured within the switching power supply; and

FIG. 4 shows a more detailed circuit diagram of an evaluation circuit of FIG

Switching power supply.

1 shows a switching power supply 1 is shown in a block diagram. The

Switched-mode power supply 1 of FIG. 1 is provided for converting an input voltage UE, here an input AC voltage, into an output voltage UA (here an output DC voltage). The input voltage U _E , typically a mains voltage, is converted by a rectifier 2 into a pulsating DC voltage Ui, which is smoothed and / or screened by means of a smoothing module 3. For this purpose, the smoothing module 3 has a first smoothing capacitor Ci.

With the DC voltage Ui a primary winding I of a transformer 5 is acted clocked via a switching stage 4 with a switching element 41. With the switching stage 4, the DC voltage Ui is in a higher-frequency

AC voltage U ₂ converted, which has a frequency which is significantly greater than the frequency of the input AC voltage U _E.

The AC voltage U ₃ is smaller with the transformer 5 in a secondary side higher frequency AC voltage U ₃ (or in certain

Use cases also larger) amounts converted. Subsequently, the secondary-side higher-frequency AC voltage U _{3 is} rectified again in a secondary-side rectifier 6 in a secondary-side DC voltage and smoothed in a secondary-side smoothing assembly 7 and / or screened. For this purpose, the secondary-side smoothing module 7 here by way of example has a further smoothing capacitor C ₂ . In principle, however, more complex circuits of a plurality of in particular discrete components (not shown) are preferred for the secondary-side smoothing module 7.

The output voltage of the secondary-side smoothing module 7 is the here positive output voltage U _{A of} the power supply 1 with respect to a reference potential GND.

Thus, the output voltage UA is stable even with changing load 10, a control circuit 8 is provided which compares the output voltage UA with a reference voltage and depending on the comparison to a

Pulse width modulation (PWM) circuit 9 acts. The PWM circuit 9 controls the switching stage 4 and changes according to the specifications of

Control circuit 8, the clock parameters, in particular a clock ratio, but possibly also a clock frequency, the switching stage 4, whereby the output voltage U _{A is} influenced. It is formed so a loop through which the Output voltage U _{A is kept} at a desired, predetermined value. In addition to this voltage regulation, a current regulation, not shown here, can additionally be provided, by means of which the current delivered to the load 110 can be limited.

Such a switching power supply 1 often also has a filter (not shown), with which the input AC voltage U E is filtered before rectification to filter out harmonics, surges and / or network interference.

On the secondary side, the transformer 5 can also have a plurality of secondary windings (not shown) with which secondary-side alternating voltages of different heights can be generated. In this embodiment of the switched-mode power supply 1, a plurality of rectifiers 6 and smoothing assemblies 7 are provided for the different secondary alternating voltages.

According to the invention, the control circuit 8 is set up to measure a temperature of a component which heats up as the load of the switched-mode power supply 1 increases, and to regulate the output voltage U _A as a function of this temperature. This will be explained in more detail below in connection with FIGS. 2 to 4.

FIG. 2 shows the control circuit 8 of the switched mode power supply 1 in more detail. The

Output voltage UA is applied to the inverting input of a voltage divider formed by two resistors Ri and R ₂

Operational amplifier 82 out. The non-inverting input of the

Operational amplifier 82 is acted upon by a reference voltage L provided by a reference voltage source 83. The operational amplifier 82 is connected as a negative feedback amplifier by a

Counter-coupling branch is formed with a negative feedback resistor R ₀ . To suppress vibration tendencies, the negative feedback resistor R _0, a capacitor C ₀ is connected in parallel. The output of the

Operational amplifier 82 is indirectly connected to the input of the PWM circuit 9 via an opto-coupler 84, which serves for galvanic isolation. These just described components of the control circuit 8 are used to set an initially constant output voltage U _{A of} the switching power supply. 1

Further, a temperature sensor S is provided, which is thermally coupled to a component of the switching power supply 1, which heats up during operation and load of the switching power supply 1. This component may be one of the arranged in the load circuit components or assemblies, such as the secondary-side rectifier 6 or even the primary-side rectifier 2 or

Switching element 41 of the switching stage 4. The temperature sensor S is in the illustrated example of Figure 2 is a temperature-dependent resistor R _# , for example, a thermistor or a PTC thermistor. In principle, temperature sensors based on another principle are also suitable, for example semiconductor temperature sensors.

The temperature sensor S is connected to an evaluation circuit 81, which depends on a measured temperature T at an output a

Provides voltage U _# . The output of the evaluation circuit 81 is also connected via a resistor R ₃ to the inverting input of

Operational amplifier 82 connected.

In FIG. 3, the dependence of the voltage U _# on the measured one

Temperature T shown in a curve 20. At a temperature T which is between an ambient temperature T ₀ and a threshold temperature T _s , the voltage U _{# is} zero. In this temperature range, the one

Normal temperature or only a slightly elevated temperature of the component to which the temperature sensor S is coupled, is the

Output voltage UA of the switching power supply 1 is thus guided via a voltage divider to the inverting input of the operational amplifier 82, which is composed of the resistor R ₂ and a parallel connection of the resistors Ri and R ₃ . Together with the magnitude of the reference voltage U _ref , the resistance values Ri to R _{3 determine} the nominal level of the output voltage UA. If the temperature T exceeds the threshold temperature Ts, the

Voltage U _# in this embodiment linearly with further increasing

Temperature T on. With unchanged output voltage UA of the switching power supply 1 This temperature increase T leads to an increase in the potential at the non-inverting input of the operational amplifier 82. The control circuit responds to this increased potential by lowering the output voltage UA, the output voltage UA being further lowered the greater the voltage U _# becomes.

In a parallel network of several such switching power supplies 1, in which the switching power supplies 1 are connected in parallel at their outputs, a

Operating situation occur in which one of the switching power supplies 1 is more heavily loaded than the one or the other. If this load inequality is pronounced, the temperature of the more heavily loaded power supply 1 will increase

Temperature sensor S measured temperature T over the

Threshold temperature T _s occur, which leads to a reduction in the

Output voltage UA leads. By lowering the output voltage UA reduces the load of this switching power supply 1, which slowly lowers its temperature T again and the output voltage is in turn slightly increased. In the interaction of at least two or more switching power supplies 1 connected in parallel, an equal distribution of the load of the switched-mode power supply 1 is established. The temperature inertia with which changes the temperature of components of the switching power supply 1, causes a large time constant of a few minutes of this temperature-dependent part of the control loop, the

Counteract vibration tendencies.

Figure 4 shows a suitable structure of the evaluation circuit 81 in more detail. The evaluation circuit 81 comprises an operational amplifier 81 1, which is supplied with an asymmetrical supply voltage (reference potential GND and a positive supply voltage V ₊ ). Accordingly, the

Output of this operational amplifier 81 1 with respect to the reference potential GND assume no negative voltages. The non-inverting input of the operational amplifier 81 1 is connected via the temperature-dependent resistor R # used with the positive reference voltage U _re f and via a resistor R to the reference potential GND. The inverting input of the operational amplifier 81 1 is connected via a resistor R ₆ to the reference potential and via a resistor R ₆ with his Output. The temperature-dependent resistor R # is in the illustrated embodiment, a thermistor whose resistance decreases with increasing temperature T. Accordingly, at the non-inverting input of the operational amplifier 81 1, the potential increases as the temperature T increases. At the threshold temperature T _s , the potential does not exceed

Inverting input the potential at the inverting input, which is formed by the voltage divider from the resistors R ₅ and R ₆ . Due to the negative feedback via the resistor R ₆ , the output voltage of the operational amplifier increases proportionally with increasing temperature T.

Due to the asymmetrical supply voltage acts

Operational amplifier 81 1 in this embodiment as a

Threshold switch which provides a non-zero output voltage U _# only when the temperature T becomes higher than that

Threshold temperature T _s . The negative feedback effects a voltage U _{# which} then increases linearly with a further temperature T. In alternative embodiments, a temperature other than a linear temperature dependence of the voltage U _# may be provided.

LIST OF REFERENCE NUMBERS

1 switching power supply

2 rectifiers

3 smoothing module

4 switching stage

5 transformer

6 output rectifier

7 output-side smoothing module

8 control loop

81 evaluation circuit

81 1 operational amplifier

82 operational amplifiers

83 reference voltage source

84 optocouplers

9 PWM circuit

S temperature sensor

Co capacitor

Ci, C2 smoothing capacitor

R ₀ to R ₆ resistance

temperature-dependent resistance

U _E Input voltage of the power supply

U _A Output voltage of the power supply

U1 DC voltage

u ₂ primary voltage

u ₃ secondary voltage

Uref reference voltage

u ₊ positive supply voltage

GND reference potential

Output voltage of the evaluation circuit temperature

Threshold temperature

Primary side of the transformer / power supply Secondary side of the transformer / power supply

Claims

claims

1 . Switching power supply (1) for converting an input voltage (UEIN) into a

Output voltage (UA), comprising at least one of a

Pulse width modulation circuit (9) clocked controlled switching stage (4), wherein a control circuit (8) is provided, which on the

Pulse width modulation circuit (9) for changing the height of

Output voltage (UA) acts, characterized in that

the control circuit (8) has a temperature sensor (S) which is provided for measuring a load-dependent temperature (T) of the switched-mode power supply (1), wherein the control circuit (8) is set up so that the output voltage (UA) increases with increasing temperature (T ) is lowered.

Second switching power supply (1) according to claim 1, wherein the output voltage (UA) is lowered only above a predetermined threshold temperature (Ts) with increasing temperature (T).

3. Switching power supply (1) according to claim 2, wherein the threshold temperature (T _s )

between 70 and 100 ° C and in particular between 85 and 95 ° C.

4. Switching power supply (1) according to claim 2 or 3, wherein the control circuit (8) comprises an evaluation circuit (81) for the temperature sensor (S) having a

Threshold has.

5. Switching power supply (1) according to one of claims 1 to 4, wherein the

Output voltage (U _A ) with increasing temperature (T) is linearly lowered.

6. Switching power supply (1) according to claim 5, wherein the temperature dependence of the reduction is between 0.005 and 0.025 V / K and in particular between 0.015 and 0.02 V / K.

7. Switching power supply (1) according to claim 5 or 6, wherein the control circuit (8) comprises an evaluation circuit (81) for the temperature sensor (S), which comprises a negative feedback operational amplifier (81 1).

8. Switching power supply (1) according to one of claims 1 to 7, wherein the control circuit (8) comprises a voltage control and / or a current control.

9. Switching power supply (1) according to one of claims 1 to 8, wherein the

Temperature sensor (S) is a temperature-dependent resistor (R #).

10. Switching power supply (1) according to one of claims 1 to 9, wherein the

Temperature sensor (S) is thermally coupled to an input-side component of the switching power supply (1).

1 1. Switching power supply (1) according to one of claims 1 to 9, wherein the

Temperature sensor (S) is thermally coupled to an output-side component of the switching power supply (1).

12. Switching power supply (1) according to claim 1 1, wherein the temperature sensor (S) is thermally coupled to an output rectifier (6) of the switched mode power supply (1).

13. Switching power supply (1) according to one of claims 1 to 12, wherein a

Input voltage (U _E IN) in the range of 10 - 300V, in particular 15 - 265V, is provided.

14. A method for regulating an output voltage (UA) of a switched-mode power supply (1), in particular according to one of claims 1 to 13, with the following steps:

Measuring a load - dependent temperature (T) of a component of the

Switching power supply (1),

- Setting the output voltage (UA) depending on the measured

Temperature (T).

15. The method of claim 14, wherein the output voltage (UA) with

rising temperature (T) is lowered.

1 6. The method of claim 14 or 15, wherein the output voltage (UA) is lowered with increasing temperature (T) when the temperature (T) is greater than a predetermined threshold temperature (Ts).