WO2017202569A2 - Primary-pulsed switching power supply - Google Patents

Abstract

The invention relates to a primary-pulsed switching power supply (1) for converting an input voltage (Ue) into an output voltage (Ua), comprising at least: - a fuse (5) arranged in the circuit branch (2) on the primary side, which is designed to interrupt a current flow on the primary side so that the circuit branch (2) on the primary side is substantially voltage-free; - a first switching element (6) that can be switched by a control signal and is arranged in the circuit branch (2) on the primary side relative to the fuse (5) such that it triggers the fuse (5) on the primary side when it is switched by the control signal; - a first feedback element (7) which is designed to guide the control signal from the circuit branch (4) on the secondary side via galvanic separation (3) to the first switching element (6) arranged on the primary side and, in the event of a fault, in particular in the event of an overvoltage, to switch the first switching element (6) on the basis of the control signal so that the circuit branch (2) on the primary side is substantially voltage-free.

Description

 Primary switched switching network

The invention relates to a primary-switched switching power supply and a field device with such a switching power supply.

Switched-mode power supplies are used today in virtually all electronic devices, both in the private consumer sector, for example in a television, as well as in industrial environments, for example in a field device of automation technology.

Such field devices of automation technology are used for detecting and / or influencing process variables. Examples of such field devices are level gauges, mass flowmeters, pressure and temperature measuring devices, pH redox potential measuring devices,

Conductivity meters, etc., the sensors as the corresponding

 Enter process variable level, flow, pressure, temperature, pH value or conductivity value. For influencing process variables serve so-called actuators, z. As valves that control the flow of a liquid in a pipe section or pumps that change the level in a container. In principle, all devices that are used close to the process and supply or process the process-relevant information are referred to as field devices. Under the term field device used in connection with the invention are thus all types of

Subsume measuring devices and actuators. Furthermore, the term field device also includes e.g. a gateway, a radio adapter or other bus users integrated / integrable into a bus system.

A large number of such field devices are manufactured and distributed by the Endress + Hauser group of companies.

As already mentioned, such field devices require a power supply. For this purpose, so-called primary switched-mode power supplies are used today, which typically have a galvanic isolation between a primary side, to which an input voltage can be applied, and a Secondary side, at which an output voltage can be tapped. The energy is transmitted by a high clocking of a transformer to the secondary side. In case of failure, a shutdown of the switching power supply and so destruction of a downstream device, in particular a field device, too

Prevent security measures are implemented in the switching power supply.

For this purpose, so-called crowbar circuits are used today, which limit the output voltage of the switching power supply as a last resort. In such crowbar circuits, a secondary-side thyristor is triggered in the event of a fault, in particular in the case of an overvoltage, which causes a short circuit between the output voltage and a ground. As a result, the secondary-side current rises to such an extent that a fuse blows and the secondary-side current is interrupted, so that the circuit to be supplied to the downstream device from the primary side of

 Switching power supply is disconnected. At the same time but also a control loop, which also typically has a switching power supply, of the

Separated primary side of the switching power supply, so that the switching power supply

detects on the primary side that the secondary-side output voltage is too low and controls accordingly. This in turn has the consequence that due to the open secondary side, the output voltage increases up to several 100 volts. However, the introduced power can only be dissipated via a primary-side circuit branch region with an additional primary winding of the transformer, whereby this primary-side

Schaltungszweigbereich is extremely loaded. As a result, the components involved become very hot and therefore specific

Temperature classes for intrinsic safety, in particular the

Temperature class 6, according to which a maximum surface temperature may not rise above 85/80 ° C, can not be met. Furthermore, there is dangerous voltage in the circuit of the switching power supply, although it is supplied with only relatively low voltages.

It is therefore an object of the invention to provide a switching power supply, which has safety precautions in order to shutdown the case of failure Switching power supply to allow and still a maximum

Surface temperature does not exceed.

The object is achieved by a Primäraktaktetes switching power supply and a field device of automation technology.

With regard to the primary-clocked switched-mode power supply, the object is achieved by a primary-clocked switched-mode power supply for converting an input voltage into an output voltage, wherein the switched-mode power supply comprises at least the following:

 - A primary-side circuit branch to which the input voltage can be applied;

 - One of the primary-side circuit branch separated by a galvanic isolation secondary-side circuit branch to which the output voltage can be tapped;

 - A arranged in the primary-side circuit branch fuse, which is adapted to interrupt a primary-side current flow, so that the primary-side circuit branch substantially

 is tension-free;

 a first switch element which can be switched by a control signal and which is arranged in the primary-side circuit branch in such a way that it triggers the primary-side fuse when switching by the control signal;

 - A first feedback element, which is designed such that it leads the control signal from the secondary-side circuit branch via the galvanic isolation to the primary side arranged first switching element and in case of failure, especially in the case of an overvoltage, the first switching element based on the control signal, so that the primary side Circuit branch is essentially de-energized.

According to the invention, a primary-side fuse is destroyed instead of the secondary-side fuse. Since both the electrical safety as well as for the Ex area a galvanic isolation is required, is a Control signal from the secondary side via the galvanic isolation led to the primary side and in case of failure, for example

secondary side overvoltage, a primary side arranged switching element connected so that the primary-side fuse is triggered. As a result, the switched-mode power supply is switched directly completely de-energized so that no further consequential errors and / or thermal loads can occur any more.

An advantageous development of the invention provides that the first

Switching element comprises a thyristor, a field effect transistor or a relay.

A further advantageous development of the invention provides that the galvanic isolation comprises a transformer which has at least on the primary side a first primary winding and wherein the first

Primary winding is arranged in a first circuit branch region of the primary-side circuit branch. In particular, the development provides that the first circuit branch region has a second switching element which is in series with the first primary winding and the first

Primary winding is clocking. Furthermore, the development can provide that the first circuit branch region is a control unit for driving the second

Has switching element.

Yet another advantageous development of the invention provides that the transformer has a second primary winding, which is arranged in a second circuit branch region and the second

 Schaltungszweigbereich essentially for powering the

Control unit is used. In particular, the training provides that the

Fuse in the first circuit branch area of the primary side

Circuit branch is arranged so that the first circuit branch region is substantially free of stress.

Yet another advantageous development of the invention provides that a start-up circuit is provided in the first circuit branch region, which supplies the control unit with the required energy when starting. Yet another advantageous development of the invention provides that the switching power supply further comprises a second feedback element, which is designed such that it is a feedback signal from

secondary-side circuit branch leads via the galvanic isolation to the primary side arranged control unit, so that the control unit controls the second switching element for clocking the first primary winding according to the feedback signal.

Yet another advantageous development of the invention provides that the first and / or the second feedback element comprises at least one optical coupling element, preferably an optocoupler.

As an alternative to this development, the first and / or second

Feedback element comprise a capacitive or inductive coupler. With regard to the field device, the object is achieved by a field device of

 Automation technology, which has a trained according to one of the embodiments described primary switched mode power supply solved. The invention will be explained in more detail with reference to the following drawings. It shows:

1 shows a circuit of a primary-switched switching power supply without security measures according to the invention,

Fig. 2 shows an example of a circuit of the invention

Security measures, and

Fig. 3: shows an example of the current through the invention in the

primary-side circuit branch arranged fuse at different input voltages. FIG. 1 shows a primary-clocked switched mode power supply 1, which has a

Has primary-side circuit branch 2 and separated by a galvanic separation 3 thereof secondary side circuit branch 4. The primary-side circuit branch 2 of the illustrated in Fig. 1

 Switching power supply 1 comprises a first circuit branch region with at least one input connection 14, a rectification unit 15, a

Start-up circuit 12, a first primary winding of a transformer 16, a second switching element 9 and a control unit 10th

The input terminal 14 serves to connect or apply a

Input voltage U _a to the switching power supply 1. Depending on the design of the switching power supply 1, both an AC wide-range input voltage of typically 80 to 253 V AC and a DC input voltage of typically 18 to 65 V DC can be applied to the input terminal 14.

The input voltage U _e , in the case of being an AC voltage, is rectified by the rectifying unit 15. Such rectifying units 15 generally comprise a bridge rectifier, which consists of four diodes 18. The rectified input voltage is then fed to a start-up circuit 12, which in the starting phase, typically only the first clock cycles, for the switching power supply 1, the required electrical

Energy provides. Based on the electric power provided by the starting circuit 12, the control unit 10 is operated, which serves to drive the second switching element 9 with a corresponding clock frequency. Usual clock frequencies lying after power, between 20 and 300 kHz. Modern control units or control blocks are due to the high clock frequencies and duty cycles of up to 80% capable of correspondingly high performance to drive. The second switching element 9, for example a transistor, is connected in series with a first primary winding 8 of the transformer 16 and clocks the first primary winding 8

in accordance with the predetermined by the control unit 10 clock frequency, so as to remove energy portions of the input voltage U _e and to a Secondary winding 17 of the transformer 16 in the secondary side

Circuit branch 4 to transmit or transform. On the basis of these transmitted energy portions, a consumer who is at the

secondary-side circuit branch can be connected to provide energy.

Furthermore, the primary-side circuit branch of the switched-mode power supply shown in FIG. 1 comprises a second circuit branch region, which is shown in FIG

Essentially used to power the control unit 10. The second circuit branch region comprises at least a second primary winding 1 1 of the transformer 16, wherein the second primary winding 1 1 such on other components, for example. A arranged in series with the second primary winding resistor and a likewise arranged in series with the resistor and the second primary winding diode, with the starting circuit 12 is connected, that as soon as enough energy on the second primary winding 1 1 for supplying the Regeleinehit 10 is available, the

 Power supply via the second circuit branch area is done.

The secondary-side circuit branch 4 comprises, as already mentioned, the secondary winding 17 of the transformer 16 and a smoothing means 20 for smoothing the discontinuous energy flow via the transformer 16. In the simplest case, the smoothing means comprises a smoothing diode 20. Further, the secondary-side circuit branch 4 comprises a feedback circuit 19 , which is arranged to galvanically decouple a feedback signal from the secondary-side circuit branch 4 to the primary-side

Return circuit branch 2, so as to adjust the clock frequency of the control unit 10 accordingly. Typically, this includes

Feedback circuit 19 for this purpose, a voltage reference 21, which is designed such that when the voltage applied to its input REF, a predetermined threshold, z. B. exceeds 2.5 V, the voltage reference 21 allows a current flow between its terminals C and A, so as to generate the feedback signal.

The galvanic decoupling may, for example, be realized by the feedback circuit 19, a second feedback element 13, For example, an optocoupler comprises, which connects the secondary-side and primary-side circuit branch with each other. As with the first feedback element 7, the second feedback element 13 may alternatively also comprise a capacitive or inductive coupling element.

Furthermore, the circuit shown in Fig. 1 of the switching power supply 1 is shown greatly simplified and includes, for example. Not known from the prior art and initially mentioned security measures, in particular it does not include, as usual in the art, a secondary side arranged switching element and fuse. Furthermore, the circuit according to FIG. 1 does not include any measures with regard to electromagnetic

Compatibility (EMC).

FIG. 2 shows by way of example a safety circuit according to the invention by which a switched-mode power supply, as shown, for example, in FIG. 1, has to be expanded, so that in the event of an error, for example in the case of an overvoltage, the switched-mode power supply is de-energized on the primary side, so that no further consequential errors occur and / or thermal loads occur more. It should be noted that Fig. 1 shows an AC switching power supply, the

inventive teaching but can be easily transferred to a DC / DC power supply.

According to the circuit of the switching power supply 1 to the

Security circuit extended, which in principle parallel to the

Feedback circuit 19 is connected in the switching power supply 1.

The security circuit comprises at least in the primary-side

Circuit branch 2 a fuse 5, preferably a fuse, which interrupts the primary-side current flow l _P mär when exceeding a defined current for a defined period of time and a first

Switching element 6, which is switchable by a control signal. The first switching element 6 is arranged such that when switching the primary-side fuse 5 is triggered. This can be realized, for example, that the fuse 5 by the series-connected first Switching element 6 is connected to the ground when the first switching element 6 switches, that is conductive.

The first switching element 6, which preferably comprises a thyristor, is electrically isolated by a first feedback element 7

 Control signal supplied from the secondary-side circuit branch, so that it is switched or ignited in the event of an error or in the case of an overvoltage. In addition to the thyristor, the first switching element 6 alternatively a

Field effect transistor or a relay include. The first

Feedback element 7 preferably comprises an optocoupler for galvanically separated transmission of the control signal. Alternatively, the first feedback element 7 may comprise a capacitive or inductive coupling element.

To generate the control signal is used in the secondary side

Circuit branch 4 arranged voltage monitoring, which is realized in the simplest case in the form of a reverse-biased Zener diode, so that when exceeding a defined voltage value, the corresponding

Control signal generated and transmitted by means of the first feedback element 7 to the primary-side circuit branch 2.

FIG. 3 shows, by way of example, a family of measuring curves i) -v), which represent the

Primary-side current flow l _P mär by the present invention arranged in the primary-side circuit branch fuse 5 at different

Indicate input voltages U _e . On the abscissa axis is the

Output voltage U _{a of} the switching power supply 1 plotted, whereas on the ordinate axis of the primary-side current flow l _P mär is represented by the fuse. For secondary-side voltage monitoring, a Zener diode with a Zener voltage of approx. 27.5 V was used.

It can be seen from FIG. 3 that, given an input voltage U _e = 20 V, a current flow of approximately 2.8 A (measurement curve i)), with an input voltage U _e = 30 V, a current flow of approximately 4.5 A (trace ii)), at a

Input voltage U _e = 40 V is a current flow of approx. 6.0 A (measurement curve iii)), with an input voltage U _e = 50 V a current flow of approx. 7.4 A (measurement curve iv)) and with an input voltage U _e = 60 V on

Current flow of approx. 9.0 A (curve v)).

Thus, according to the field of application of the switching power supply, the primary-side fuse can be selected accordingly.

In the field of automation technology, such a switching power supply can, for example, be used to operate a field device without causing problems in terms of electrical safety and Ex specifications.

LIST OF REFERENCE NUMBERS

1 primary switched mode power supply

 Primary circuit branch

Galvanic separation

 Secondary circuit branch

Primary side fuse

 First switching element

 First feedback element

First primary winding

 Second switching element

 10 control unit

 1 1 Second primary winding

 12 start-up circuit

 13 second feedback element

14 input connection

 15 rectification unit

 16 transformer

 17 secondary winding of the transformer

18 diode for rectification

 19 feedback circuit

 20 smoothing diode

 21 voltage reference

 22 Zener diode as voltage monitoring

I primary primary current flow

 Ue input voltage

 Ua output voltage

Claims

claims 1 . A primary switched mode power supply (1) for converting an input voltage (Ue) into an output voltage (Ua) at least comprising:  - A primary-side circuit branch (2) on which the  Input voltage (Ue) can be applied;  - One of the primary-side circuit branch (2) by a  galvanic isolation (3) separate secondary side  Circuit branch (4) on which the output voltage (Ua) can be tapped off;  - One in the primary-side circuit branch (2) arranged fuse (5), which is adapted to a primary-side current flow  interrupt, so that the primary-side circuit branch (2) in  Essentially stress-free;  a first switching element (6) which can be switched by a control signal,  which is arranged in the primary-side circuit branch (2) for securing (5) such that it triggers the primary-side fuse (5) when switching by the control signal;  - A first feedback element (7) which is designed such that it leads the control signal from the secondary-side circuit branch (4) via the electrical isolation (3) to the primary side arranged first switching element (6) and in case of failure, in particular in the case of an overvoltage, the first switching element (6) based on the  Control signal switches, so that the primary-side circuit branch (2) is substantially de-energized. 2. Switching power supply according to claim 1, wherein the first switching element (6) comprises a thyristor, a field effect transistor or a relay. 3. Switching power supply according to claim 1 or 2, wherein the galvanic isolation (3) comprises a transformer having at least on the primary side a first primary winding (8) and wherein the first primary winding (8) in a first circuit branch region of the primary-side circuit branch (2) is arranged , 4. A switched-mode power supply according to claim 3, wherein the first circuit branch region comprises a second switching element (9) which is in series with the first primary winding (8) and clocks the first primary winding (8). 5. Switching power supply according to claim 4, wherein the first circuit branch region has a control unit (10) for driving the second switching element (9). 6. Switching power supply according to at least one of claims 3 to 5, wherein the transformer has a second primary winding (1 1), which is arranged in a second circuit branch region and the second Schaltungszweigbereich essentially for powering the Control unit (10) is used. 7. Switching power supply according to claim 6, wherein the fuse (5) in the first  Circuit branch region of the primary-side circuit branch (2) is arranged, so that the first circuit branch region is substantially free of stress. 8. Switching power supply according to at least one of claims 3 to 7, wherein in the first circuit branch region, a start-up circuit (12) is provided, which supplies the control unit (10) at start with the required energy. 9. Switching power supply according to at least one of claims 3 to 8, further comprising at least one second feedback element (13) which is designed such that it is a feedback signal from secondary-side circuit branch via the galvanic isolation (3) leads to the control unit arranged on the primary side (10), so that the control unit (10) controls the second switching element (9) for clocking the first primary winding (8) in accordance with the feedback signal. 10. Switching power supply according to claim 1 or 9, wherein the first and / or the second feedback element (7, 13) at least one optical Coupling element, preferably comprises an optocoupler. 1 1. Field device of automation technology comprising a primary-clocked switching power supply (1) according to at least one of the preceding claims.