WO1995007548A1

WO1995007548A1 - Current limiting device

Info

Publication number: WO1995007548A1
Application number: PCT/DE1993/000823
Authority: WO
Inventors: Reinhard Maier; Hermann Zierhut; Heinz Mitlehner
Original assignee: Siemens Aktiengesellschaft
Priority date: 1993-09-08
Filing date: 1993-09-08
Publication date: 1995-03-16
Also published as: AU4942993A; EP0717880A1

Abstract

The invention pertains to a current limiting device with at least one semiconductor region (1) with electron donor (source;2), electron acceptor (drain;3) and electron flow controlling electrode (gate;4) without its own drive. The semiconductor region has a characteristic curve like that old field effect transistors. As needed, a current breaker (5) can be connected in series to the drain-source path. The gate electrodes (4, 4a, 4b) are dimensioned with respect to their thickness (L), their spacing (d) and the source-drain distance (D) so that a limitation is activated at a predetermined intensity of current.

Description

Current limiter

The invention relates to a current limiter with at least one semiconductor region with electron donor (source), electron collector (drain) and electrodes controlling the electron flow (gate).

It is often desirable to quickly limit currents, in particular alternating currents, to certain values so that overcurrents become compatible or there is therefore time to switch off.

The disadvantage of mechanical protective switching devices is the wear of the contacts, frequent maintenance and a relatively slow switching time in the event of a short circuit, as well as a relatively low temporal accuracy of the switching time.

Semiconductor switches, on the other hand, can work without wear and switch quickly; they have low switching losses and they can be controlled variably. Disadvantages of semiconductor switches are: high costs, high space requirements and relatively high transmission losses.

The object of the invention is to develop a current limiter using semiconductor technology, in which the disadvantages of the semiconductors which have been customary hitherto are reduced to a technically useful extent.

According to the invention, the object described is achieved by a current limiter according to claim 1. The semiconductor region operates without its own control, and it has a characteristic curve such as that which field effect transistors (FETs) have. If necessary, a current interrupter device can be connected in series to the drain-source path be used in order to protect the semiconductor area as an overload relay or also to enable a shutdown during operation. It is essential that the gate electrodes are dimensioned with respect to their thickness L, their distance d from one another and the source-drain path D in such a way that there is a limit at a given current strength. The gate electrodes are at floating potential, which is also known as "floating." referred to as. The semiconductor region can be embodied integrated in a microchip or as a discrete component.

A rapid short-circuit current limitation is achieved above an overload limit and thus equipment or electrical distributions can be protected quickly. With regard to circuit breakers, the advantage of a strong and rapid current limitation is achieved, and the usual burn-up problems are avoided. Compared to mechanical Li¬ miters a rapid high current limitation is achieved without affecting intact parallel circuits of a consumer network. In comparison to PTC thermistors, a more stable characteristic is achieved.

The semiconductor region may ^• be designed as a vertical "Junction" -Feld¬ effect transistor (J-FET). It is particularly advantageous to form the semiconductor region from a substrate material made of silicon carbide.

When using a current interrupter device, this can be designed as a switch contact with a tripping device.

According to a further development, the semiconductor region is designed with embedded gate electrodes. The semiconductor region can also be developed in such a way that gate electrodes are arranged on the source electrode and others on the drain electrode with an electrically conductive connection to the source or drain electrode. The drain-source path can then be compared to fully embedded gate electronics. which are roughly halved, with the operating conditions remaining the same.

It is expedient to arrange coolants on the source electrode and on the drain electrode which can be dimensioned such that the limiting current can be reduced in the current-time diagram as a result of a positive temperature coefficient which is established. Such a lowering is also advantageous for a semiconductor region which is operated as a unipolar component. The pn junction between the gate and the drain-source path then does not come into play as a diode, since the threshold voltage, for example 2.8 volts at SiC, is used. In other words: the permissible load current density remains below the diode pass characteristic. You then work in the ohmic area.

The invention will now be explained in greater detail on the basis of exemplary embodiments shown roughly schematically in the drawing:

1 shows a first exemplary embodiment using a semiconductor region with embedded gate electrodes. 2 shows a current limiter as shown in FIG. 1 with a semiconductor region, the gate

Has electrodes that are electrically connected to the source electrode and gate electrodes that are connected to the drain electrode. 3 shows a characteristic of the current limiter in a diagram, on the ordinate of which the drain-source current is plotted and on the abscissa of which the drain-source voltage is plotted. This diagram illustrates, by way of example, the mode of operation of a current limiter according to FIG. 1. FIG. 4 shows a diagram as shown in FIG. 3, which exemplifies the mode of operation of a current limiter according to FIG. 5 shows a characteristic curve in the current-time diagram for current limiters with additional developments. For this purpose, the semiconductor region is operated as a unipolar component or, or and, and coolants are used.

6 shows a current limiter according to FIG. 1 with coolants on drain and on source electrodes.

7 shows coolant in a current limiter according to FIG. 2.

The current limiter according to FIG. 1 works with a semiconductor region 1, with source electrode, source electrode 2, drain electrode 3 and gate electrode 4. The gate electrode does not have its own control and is completely embedded. The gate electrode 4 can consist of individual doping islands or can also be produced from a disk-shaped doping region with hole-like interruptions. The gate electrodes 4 are dimensioned with respect to their thickness L, their distance d, from one another and the source-drain path D in such a way that a current limitation is established at a given current strength.

For the values L = 3 μm, d = 1 μm and D = 21 μm and with silicon carbide as the substrate material, the working range entered is obtained with a characteristic according to FIG. 3. Up to 230 volts one works in the linear range 8 and in the case of overvoltages up to about 700 V one remains in the horizontal limitation range, so that the current intensity I- _{Q is set} independently of the voltage U _D g. The linear region 8 corresponds to an ON resistance RON

Optionally, as illustrated in FIG. 1, a current interrupter device 5 with a switch contact 6 can be connected in series with the drain-source path to the semiconductor region 1. In the exemplary embodiment, the circuit breaker device 5 usually has a switch contact 6 with a tripping device 7. The current interrupter device 5 can act as an overload relay to protect the semiconductor area in the event of voltage 3, in which the characteristic curve for high drain-source voltages changes into a region parallel to the drain-source current. The current interrupter device 5 can also be designed for operational shutdown in order to achieve a current limiter with the properties of a circuit breaker, for example in the manner of a circuit breaker. The semiconductor region then works as a particularly good limiter, which makes it unnecessary to provide the current interrupter device with arc extinguishing devices.

In the exemplary embodiment according to FIG. 1, the semiconductor region can be understood as a vertical "junction" field effect transistor, J-FET. It is particularly favorable if the semiconductor region is formed from a substrate material made of silicon carbide.

In the further development according to FIG. 2, gate electrodes 4a are arranged on the source electrode 2 and other gate electrodes 4b on the drain electrode 3 and are connected in an electrically conductive manner to the source or drain electrode. Under otherwise the same conditions as in the exemplary embodiment in FIGS. 1 and 3, the drain-source path can be shortened by approximately half and a steeper linear region 8 of the characteristic curve is obtained, which results in a lower ON resistance RON- * corresponds. With alternating voltage, the first and third quadrants are used, as illustrated in FIGS. 3 and 4. A semiconductor region with a structure according to FIG. 2 can thus be halved in comparison to a semiconductor region in the structure according to FIG. 1 with the same reverse voltage with regard to its drain-source path, and a lower resistance is achieved in normal operation, so that here the already low losses become even lower. Correspondingly, RO _* or the linear region in FIG. 4 runs steeper than in FIG. 3. If the semiconductor region 1 is operated as a unipolar component, a positive temperature coefficient with respect to RON » ^{SO is obtained} since, depending on the external circuit, a load-dependent progressive current limitation results, as is illustrated in the current-time diagram according to FIG. 5. The lowering of the limiting current over time can also be promoted by coolants which are in thermally conductive connection with the drain electrode and with the source electrode, as is illustrated in FIGS. 6 and 7. Here, the coolants 9 are shown as cooling lugs.

In the semiconductor area, with decreasing distance d between the gate electrodes under otherwise identical conditions, a stronger and earlier restriction of the current flow is achieved, so that the current limitation in the horizontal area according to FIGS. 3 and 4 in the case of lower drain-source currents Overload range.

Claims

claims

1. Current limiter in which at least one semiconductor region (1) with an electron donor (source; 2) electron collector (drain; 3) and the electrode controlling the electron flow (gate; 4) without its own control and with a characteristic such as that of field-effect transistors (FETs), optionally a current interrupter (5) is connected in series with the drain-source path, the

Gate electrodes are dimensioned with regard to their thickness (L), their distance (d) from one another and the source-drain path (D) in such a way that a limit is set at a given current strength.

3. Current limiter according to claim 1 or 2, so that the semiconductor region (1) is formed from a substrate material made of silicon carbide (SiC).

4. Current limiter according to one of the claims 1 to 3, so that the current interrupter device (5) is designed as a switching contact (6) with a tripping device (7).

5. Current limiter according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that the semiconductor region (1) with embedded gate electrodes (4) is executed.

6. Current limiter according to claim 5, characterized in that gate electrodes (4a) on the source electrode (2) and gate electrodes (4b) on the drain electrode (2) are arranged with an electrically conductive connection to the source - or to the drain electrode.

7. Current limiter according to one of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that coolant (9) are arranged on the source electrode (2) and on the drain electrode (3).

8. Current limiter according to one of claims 1 to 7, d a d u r c h g e k e n n z e i c h n e t that the semiconductor region (1) is operated as a unipolar component.