US-12627137-B2 - Crowbar circuit, in particular for a voltage transformer, in explosion-protected applications

US12627137B2US 12627137 B2US12627137 B2US 12627137B2US-12627137-B2

Abstract

A crowbar circuit for a voltage transformer, comprising: a triggering device for triggering a short circuit via input terminals depending on control voltage; a comparator configured to trigger the triggering device depending on a comparator voltage at a comparator input and a reference voltage threshold value, a Zener diode with a breakdown voltage in series with a fifth resistor, connected between an input terminal and the comparator input, such that when the input voltage exceeds the breakdown voltage, the comparator voltage triggers the short circuit; a series connection of a seventh resistor, an eighth resistor, the fifth resistor and a sixth resistor, wherein load current at an output flows through the seventh and sixth resistors and wherein the comparator input is connected to a node between the fifth and eighth resistors, and the series connection is connected between the input terminals, such that upon exceeding a predetermined threshold current, the comparator voltage triggers the short-circuit.

Inventors

Martin Jung

Assignees

PEPPERL+FUCHS SE

Dates

Publication Date: 20260512
Application Date: 20240528
Priority Date: 20230606

Claims (10)

1 . A crowbar circuit, for use in a voltage converter, comprising: a triggering device configured to trigger or cause a short circuit across input terminals depending on a control voltage; a comparator configured to trigger the triggering device for triggering the short circuit depending on a comparator voltage at a comparator input of the comparator and depending on a predetermined reference voltage threshold value, a Zener diode with a predetermined breakdown voltage in series with a first resistor, which are connected between one of the input terminals and the comparator input, such that when an applied input voltage exceeds the predetermined breakdown voltage, the comparator voltage exceeds or falls under the predetermined reference voltage threshold value, thus triggering or causing the short circuit; a series connection of a second resistor, an third resistor, the first resistor and a fourth resistor, wherein a load current at an output of the crowbar circuit flows through the second and fourth resistors and the comparator input is electrically connected to a node between the first and eighth third resistors, and the series connection is connected between the input terminals, such that when a predetermined threshold current is exceeded, the comparator voltage exceeds or falls under the predetermined reference voltage threshold value, thus triggering the short circuit.
2 . The crowbar circuit according to claim 1 , wherein the comparator comprises a shunt reference with the predetermined reference voltage threshold value or a bipolar transistor in which the predetermined reference voltage threshold value is determined by a base-emitter-voltage of the bipolar transistor.
3 . The crowbar circuit according to claim 1 , wherein a further Zener diode is connected in series with the third resistor in a reverse direction.
4 . The crowbar circuit according to claim 1 , wherein a low-pass filter is provided between the triggering device and the comparator, such that a time delay is provided when triggering the short circuit if it is detected that the comparator voltage exceeds or falls below the predetermined reference voltage threshold value.
5 . The crowbar circuit according to claim 1 , wherein the comparator input is directly connected via the first resistor to one of two output terminals at which a high and a low output potential is provided.
6 . The crowbar circuit according to claim 5 , wherein the fifth first resistor is connected to the output terminal for the low output potential, wherein a resistance value of the second resistor is greater than a resistance value of the fourth resistor.
7 . The crowbar circuit according to claim 5 , wherein the first resistor is connected to the output terminal for the high output potential, in particular, wherein a resistance value of the second resistor is lower than a resistance value of the fourth resistor.
8 . The crowbar circuit according to claim 1 , wherein the Zener diode and the fourth resistor are connected in series between the input terminals.
9 . The crowbar circuit according to claim 1 , wherein a current limitation is realized within a load current-carrying line, which limits a flowing load current when the comparator voltage is detected to exceed or fall below the predetermined reference voltage threshold value.
10 . The crowbar circuit according to claim 1 , wherein one of the input terminals is provided with a safety fuse which interrupts a current flow when the short circuit is triggered.

Description

TECHNICAL FIELD The invention relates to crowbar circuits for limiting overvoltages and overcurrents in applications in explosion-protected environments. The invention relates in particular to measures for reducing the power rating of Zener diodes and resistors of the crowbar circuit. TECHNICAL BACKGROUND Crowbar circuits are often used to safely prevent overvoltage and overcurrent events of a device/equipment that provides electrical energy in the explosion-protected area. The principle of crowbar circuits is to short-circuit the input voltage source by means of a semiconductor switch (MOSFET, thyristor) when an overvoltage and/or overcurrent is detected, thus quickly triggering a safety fuse connected in series to the input voltage source. Since the response time of the circuit as a whole (including comparator, filtering etc.) is usually several microseconds to milliseconds due to the triggering time of the semiconductors and due to EMC or functional requirements, crowbar circuits are often combined with Zener diodes in parallel with the output in order to further limit the voltage transient of the output voltage of any overvoltage. For example, document U.S. Pat. No. 5,144,517 A discloses a protective barrier device comprising a DC voltage source at a first and a second input terminal and a first and a second output terminal, wherein the first output terminal is in a first low-impedance series path with the first input terminal and the second output terminal is in a second low-impedance series path with the second input terminal. Current detection means are provided for detecting current in at least one of the first and second series paths. Further, an overcurrent level signal generating means is provided for generating an overcurrent level signal in accordance with a detected overcurrent level consisting of a current exceeding a preselected level. An overcurrent level signal generating means is provided for amplifying the overcurrent level signal provided by the overcurrent level signal generating means to form a trigger signal by means of an amplifying device fed at least partially by the excess current in at least one of the first and second series paths. A crowbar circuit for switching a low-resistance current path between the first and second series paths in accordance with the trigger signal is also provided. Furthermore, as disclosed in document EP 1 388 192 B1, a further impedance is provided in series with the Zener diode between the output terminals, such that a higher output voltage than intended is present at the output terminals until the semiconductor switching element is closed. When using Zener diodes for voltage limiting and resistors for current limiting, high power losses occur in the event of a fault, which leads to increased design effort due to the provision of additional cooling elements, limits the possible packing density and places high demands on the thermal load capacity of these components. When using a crowbar, in which an overvoltage or overcurrent is switched off using a power semiconductor switch, voltage and current transients can occur within the crowbar circuit and at the output terminals of the device, which can be critical for use in explosion-protected application areas. The device must therefore undergo extensive testing to ensure explosion safety. Likewise, a distance must be maintained between the functionally available output voltage and the available output current and the maximum output voltages and output currents relevant for the test in the event of a fault. It is therefore the object of the present invention to provide an improved crowbar circuit which suppresses a propagation of high voltage and current transients to the output side of the device or prevents their occurrence. DISCLOSURE OF THE INVENTION This problem is solved by the crowbar circuit for a device according to claim 1, in particular for use in explosion-protected applications. Further embodiments are given in the dependent claims. According to a first aspect, a crowbar circuit is provided, in particular for use in an electronic device, for example, comprising: a triggering device for triggering a short circuit across input terminals depending on a control voltage;a comparator which is configured to trigger the triggering device for triggering the short circuit depending on a comparator voltage at a comparator input of the comparator and depending on a predetermined reference voltage threshold value,a Zener diode with a predetermined breakdown voltage in series with a fifth resistor, which are connected between one of the input terminals and the comparator input, such that when the breakdown voltage is exceeded by the applied input voltage, the comparator voltage exceeds or falls below the reference voltage threshold value, thus triggering the short circuit;a series connection of a seventh resistor, an eighth resistor, the fifth resistor and a sixth resistor, wherein a load current at an outp