DE102015014588A1 - Device for limiting the voltage of a consumer - Google Patents

Abstract

There is provided a device (100) for limiting the voltage of a load (200). The device has a first connection element (102) for receiving an electrical potential (10) and a second connection element (105) for outputting an electrical potential to the consumer. Furthermore, the device has a first field effect transistor, FET, (Q4) and a second FET (Q3), which are each designed as a self-conducting FET on. The first FET (Q4) and the second FET (Q3) are connected in series between the first terminal (102) and the second terminal (105).

Description

Field of the invention

The invention relates to a device for limiting the voltage of a consumer and a test system for testing a voltage source with a device for limiting the voltage.

Background of the invention

Voltage limiting devices are used to cause a potential difference across the device and a voltage drop across the device, respectively.

A device with such a function may, for example, be necessary if a voltage source is used which provides a voltage which is too high for a consumer. The device is switched in such a case between the voltage source and the consumer, so that there is a voltage divider and the voltage applied to the load voltage is reduced.

In the case of a voltage source having a variable output voltage, it may be necessary to vary the voltage drop across the voltage limiting device so that a voltage at the load remains constant.

If the voltage drop across the voltage limiting device is varied, voltage fluctuations may occur for a transitional time since the device must stabilize. In this context, one speaks of necessary stabilization times of the device.

Summary of the invention

It can be regarded as an object of the invention to provide a device for limiting the voltage of a consumer, which is characterized by short stabilization times and high dielectric strength.

This object is solved by the subject matter of the independent claims. Further developments of the invention will become apparent from the dependent claims and from the following description.

According to a first aspect of the invention, a device for limiting the voltage of a consumer, in particular an electrical consumer, specified. The device has a first connection element for receiving an electrical potential and a second connection element for outputting an electrical potential to the consumer. Furthermore, the device has a first field effect transistor, FET, and a second FET, which are each designed as a self-conducting FET. The first FET and the second FET are connected in series between the first connection element and the second connection element.

The device is designed to be connected to the first connection element to a voltage source and with the second connection element to the consumer. Depending on the configuration of the device results in a potential difference or a voltage drop between the first connection element and the second connection element, so that thereby the voltage applied to the load voltage is reduced or limited.

The fact that the two series-connected field-effect transistors are designed to be self-conducting has the advantage that they require no active and thus circuit-complex control. Rather, the field effect transistors without applied control voltage structurally conductive.

By connecting two field-effect transistors in series, the dielectric strength of the device increases or higher potential differences between the first connection element and the second connection element can be caused than would be the case for a single field-effect transistor. The withstand voltage may be, for example, up to 10 kV or more.

The voltage range in which the device can be used, d. H. the voltage that can be dissipated through the device can be between 0 volts and several kilovolts.

According to one embodiment of the invention, a drain of the first FET is connected to the first connection element. A source of the first FET is connected to a drain of the second FET. A source of the second FET is connected to the second terminal.

The outflow of the first FET may be indirectly or directly connected to the first connection element. In particular, the source of the first FET is directly connected to the outflow of the second FET. Alternatively, other components (such as resistors or diodes) may be connected in between. The source of the second FET may be connected directly or indirectly to the second connection element. These compounds are electrical connections, for example by means of an electrically conductive element.

In the case of an indirect connection, apart from an electrical connection element (electrical conductor, conductor track, etc.), one or more active or passive electrical or electronic components may be arranged between the indirectly connected elements. A direct connection is a connection between two elements which, apart from an electrical connection element, has no further components between the directly connected elements.

An electrical connection in the sense of this application is a connection which allows a current flow between the connected elements.

The structure of a field effect transistor is known per se. In connection with this description, all field effect transistor types can be used as long as they are present in a self-conducting embodiment. A field effect transistor, FET, usually has at least three connection elements: the control electrode (also referred to as gate), the drain (also referred to as sink or drain) and the source (also referred to as inflow or source).

According to another embodiment of the invention, the first FET is a metal oxide semiconductor field effect transistor, MOSFET.

MOSFETs offer a high withstand voltage of several hundred volts up to over 1000 V and thus are advantageously suitable for a device as described herein.

According to a further embodiment of the invention, the device has a third FET which is connected directly or indirectly in series with the first FET and the second FET (ie that no other components are arranged in the series connection between the FETs or that further components in the series connection between the FETs are arranged), so that a drain of the third FET is connected to a source of the second FET and a source of the third FET to the second connection element.

The second FET is thus connected via the third FET indirectly or directly to the second connection element. By providing the third FET, the voltage resistance of the arrangement is further increased or there may be a higher potential difference between the first connection element and the second connection element without damaging or destroying the components therebetween, ie the first, second and third FETs.

The device may also have more than three FETs connected in series so as to increase the device withstand voltage or the maximum voltage drop across the device. In this case, each of the FETs can be designed as a MOSFET in a self-conducting configuration.

According to a further embodiment of the invention, as described herein, the device furthermore has a first semiconductor element with a defined breakdown voltage, this semiconductor element being arranged between a control electrode of the first FET and the first connection element.

Alternatively, instead of the first semiconductor element, the device may have another component at which a defined voltage drops or which causes a voltage drop.

According to a further embodiment of the invention, the semiconductor element with a defined breakdown voltage is a Zener diode.

The Zener diode thus supplies a required voltage to the control electrode of the first FET in order to put it from the conducting state into the blocking state. Depending on the required voltage, one or more Zener diodes can be connected in series.

According to a further embodiment of the invention, the device furthermore has a second semiconductor element with a defined breakdown voltage, which is connected in series with the first semiconductor element between the control electrode of the first FET and the first connection element.

In one embodiment, the zener diodes (the breakdown breakdown voltage semiconductor elements) associated with each individual FET are sized such that the breakdown voltage or the sum of the breakdown voltages of a plurality of serially connected zener diodes is the same for all FETs. In one embodiment, the number of Zener diodes associated with each FET may be the same for each FET, and their respective breakdown voltage is identical, e.g. 200V. The plurality of Z-diodes connected in series and assigned to a FET may be referred to as a voltage step. The device may have multiple voltage levels, which may be different from their sizing and dimensioning ago. The sum of the breakdown voltages of a voltage stage must not be greater than the maximum permissible voltage at the FET.

In one embodiment, instead of zener diodes, resistors, e.g. As ohmic resistors are used to limit the voltage. Then the voltage is evenly distributed to the gates of the FETs.

According to a further embodiment of the invention, the device further comprises a fourth FET, which is connected in parallel to the first FET.

The fourth FET may also be a MOSFET having the same specification as the other MOSFETs. This fourth FET connected in parallel with the first FET increases the current capability of the voltage limiting device.

According to another aspect of the invention, a test system is given. The test system includes a voltage source, a voltage limiting device for a consumer as described above, and an electrical load. The device is designed to limit a voltage applied to the electrical load voltage to a predetermined value.

In particular, the test system may be designed to test the voltage source, the consumer, together with the voltage limiting device, serving to simulate a load connected to the voltage source and its behavior.

The device for limiting the voltage for a consumer allows by their construction with self-conducting FETs low stabilization times and high voltage resistance, so that a dynamic behavior of the load can be simulated advantageous with rapid operating point changes and, for example, the number of test cases per unit time can be increased can reduce the total time required to perform multiple test cases one after the other.

According to a further embodiment of the invention, the electrical load is a current load which is designed to simulate the behavior of a traveling wave tube.

In this way, power supplies of a traveling-wave tube can be tested with the test system in this embodiment.

In the following, the function of the test system and the device for limiting the voltage is described by way of example with reference to this embodiment, wherein the use of MOSFETs is mentioned as FET, for example. It should be noted, however, that the device is not limited to this use.

For commissioning a power supply and the subsequent tests, a traveling wave tube is simulated by means of an electronic load and test cases are carried out. In the event that an electronic load fluctuates in its behavior and requires long stabilization times, the duration for performing the test cases is increased, which may be undesirable. This behavior of the electronic load can be attributed to an adverse dynamic behavior and a long duration for setting an operating point.

It has been recognized that a great deal of effort is required to drive individual MOSFETs when, for example, several series-connected MOSFETs or self-locking power MOSFETs are used as the load. The main challenge may be that a control voltage must be available for the control of the individual self-blocking MOSFETs connected in series at the respective voltage level. This must be generated either from the high voltage applied to the load module itself or from a potential-free voltage source. Both variants are technically complex. Furthermore, it has been recognized that electronic loads from load stages with normally-off power MOSFETs have a non-voltage-independent load current and an unsatisfactory dynamic behavior. When only a single MOSFET is used, the withstand voltage of a corresponding device is limited to the withstand voltage of that single MOSFET, typically several hundred volts to about 1000 volts, depending on the design of the MOSFET.

The device as described herein takes into account these findings and enables a high dielectric strength with simultaneously short stabilization times.

This is achieved by making the series-connected MOSFETs self-conducting to achieve the required dielectric strength. The advantage is that the self-conducting MOSFETs do not require any active and therefore circuitry-consuming control. The MOSFETs are structurally conductive without an applied control voltage. The required gate voltage for blocking the MOSFETs can be generated very easily by a respective branch connected in parallel to the load stages with one or more series-connected Zener diodes or resistors.

This eliminates the need for a complex power supply of each load level, ie every MOSFET. The electronic load is characterized in that the load current of a few volts, for example 10 V, linearly to the target specification behaves up to the kilovolt range, has substantially no drift and the load current, if necessary, to a frequency range of about 1 MHz sinewave can be modulated. This means that a setpoint for a load current can be specified which remains constant over the entire voltage range. Furthermore, the device is characterized by a very simple and economically advantageous construction using elements usually available as standard components. An actively controlled load stage, downstream of the voltage limiting device in the test system, may be extended by any number of passive load stages (the number of MOSFETs in the device) so that the demand for the withstand voltage of the electronic load is very high can be easily taken into account. The current capability of the electronic load (referred to as the combination of the device and the load as described with reference to the test system) can be arbitrarily increased by connecting load stages in parallel. The device is characterized by a low effort for matching. Since the load described is characterized by short stabilization times, the elimination of times for adjusting and stabilizing the electronic load, the test and measurement times can be significantly reduced.

In the following, embodiments of the invention will be described with reference to the figures.

Brief description of the drawings

1 shows a device for limiting the voltage for a consumer according to an embodiment of the invention.

2 shows a device for limiting the voltage for a consumer according to another embodiment of the invention.

3 shows a test system according to another embodiment of the invention.

Detailed description of embodiments

The illustrations in the figures are schematic and not to scale. If the same reference numbers are used in the following description of the figures, they refer to the same or similar elements.

1 shows a device 100 to limit the voltage for the consumer 200 , The device 100 is by means of the first connection element 102 to a potential 102 or a voltage source connected. The second connection element 105 the device 100 is with the consumer 200 electrically connected. The consumer is in turn with mass 20 connected. In this construction, the device 100 and the consumer 200 a voltage divider.

2 shows a device 100 which with the consumer 200 connected is. The consumer in this case is a power load. An operational amplifier receives a setpoint of the current through resistor R2 via terminal JP6. The voltage dropping across the resistor R2 is likewise fed back to the operational amplifier via the resistor R3 and can be converted into a current value with the known resistance value of R2. By comparing the current flowing through R2 and the setpoint value, the operational amplifier outputs a signal which serves as the gate voltage for the MOSFET Q1 so as to adjust, if necessary, the current flowing through R2.

It should be noted for the sake of completeness that it is the consumer 200 can be any load that requires a specified voltage.

The consumer 200 is the device 100 , which is characterized by the dashed rectangle, upstream. The device 100 indicates a first load level 110 , a second load level 120 and a third load level 130 on. The load stages can also be referred to as voltage stages or voltage limiting stages. The load levels 110 . 120 . 130 are advantageously constructed identically, but can also be constructed differently. It is also conceivable that the voltage levels are constructed differently in one and the same device.

It will be exemplified the first load level 110 described in this respect, the relevant explanations are analogously the same for the second and third load stage 120 . 130 or other load stages connected in series for this purpose. At the first connection element 102 there is a high voltage. The number of load stages or voltage limiting stages can be increased or reduced depending on the applied high voltage. The high voltage can vary, whereas the voltage applied to the load remains constant regardless of the load current consumed.

The drain 114 of the MOSFET Q4 is connected to the first terminal 102 connected. As control voltage at the control electrode 112 of the MOSFET Q4 is used at the first connection element 102 applied voltage, which is reduced via four Zener diodes D20, D21, D22, D23 with a breakdown voltage of, for example, in each case 200 V to a total of 800 V and via the resistor R6 to the control electrode 112 is guided. The source 116 of the MOSFET Q4 is connected to the drain of the MOSFET Q3 of the second load stage 120 connected. Between the control electrode 112 and the source 116 is a Z-diode D25 connected. The Zener diode D25 has a protective function and prevents overvoltage between the control electrode 112 and source 116 ,

To increase the current stability of the device 100 For example, MOSFET Q4 may be connected in parallel with a MOSFET. Similarly, the other MOSFETs Q3 and Q2 each have a MOSFET in parallel. The gates of the MOSFETs connected in parallel are connected to the same potential.

3 shows a test system 1 with a voltage source 2 , which is executed, the first connection element 102 the device 100 to limit the voltage for the consumer 200 to apply a potential. It can be seen that the device 100 and the consumer 200 form a voltage divider. The device 100 In particular, it is possible to keep a voltage applied or dropped at the load at a constant value, independently of that at the first connection element 102 applied potential.

LIST OF REFERENCE NUMBERS

1

test system

2

voltage source

10

electrical potential

20

Dimensions

100

Device for limiting the voltage

102

first connection element

105

second connection element

110

first load level

112

Control electrode (gate)

114

Drainage

116

Source

120

second load level

130

third load level

200

consumer

Claims (10)

Contraption ( 100 ) for limiting the voltage of a consumer ( 200 ), comprising: a first connection element ( 102 ) for receiving an electrical potential ( 10 ); a second connection element ( 105 ) for delivering an electrical potential to the consumer; a first field effect transistor, FET, (Q4), which is implemented as a self-conducting FET; a second FET (Q3), which is implemented as a self-conducting FET; wherein the first FET (Q4) and the second FET (Q3) between the first connection element (Q4) 102 ) and the second connection element ( 105 ) are connected in series. Contraption ( 100 ) according to claim 1, wherein an effluent ( 114 ) of the first FET (Q4) with the first connection element ( 102 ) connected is; where a source ( 116 ) of the first FET (Q4) is connected to a drain of the second FET (Q3); wherein a source of the second FET (Q3) is connected to the second terminal element (Q3) 105 ) connected is. Contraption ( 100 ) according to claim 1 or 2, wherein the first FET (Q4) is a metal oxide semiconductor field effect transistor, MOSFET. Contraption ( 100 ) according to any one of the preceding claims, wherein the device ( 100 ) has a third FET (Q2) connected in series with the first FET and the second FET such that a drain of the third FET with a source of the second FET and a source of the third FET with the second connection element ( 105 ) connected is. Contraption ( 100 ) according to one of the preceding claims, further comprising a first semiconductor element (D23) with a defined breakdown voltage which is connected between a control electrode (D23). 112 ) of the first FET (Q4) and the first connection element ( 102 ) is arranged. Contraption ( 100 ) according to claim 5, wherein said semiconductor element (D23) is a Zener diode. Contraption ( 100 ) according to claim 5 or 6, further comprising a second semiconductor element (D22) with a defined breakdown voltage, which is connected to the first semiconductor element (D23) between the control electrode (D23). 112 ) of the first FET (Q4) and the first connection element ( 102 ) is connected in series. Contraption ( 100 ) according to one of the preceding claims, further comprising a fourth FET, which is connected in parallel with the first FET. Test system ( 1 ), comprising: a voltage source ( 2 ); a device ( 100 ) according to any one of claims 1 to 8; an electrical consumer ( 200 ); the device ( 100 ) is designed to limit a voltage applied to the electrical load voltage to a predetermined value. Test system ( 1 ) according to claim 9, wherein the electrical consumer ( 200 ) is a current load designed to simulate the behavior of a traveling wave tube.

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