DE9411601U1 - Current limiting switch - Google Patents

Description

GR 93 G 3476 EN

Description
Current limiting switch

The invention relates to a current-limiting switch with at least one semiconductor region with an electron donor (source), an electron collector (drain) and an electrode that controls the electron flow (gate), in detail according to the generic term of claim 1.

Electrical systems must be connected to a network or disconnected from the network. There are optimized solutions for mechanical switches that meet the technical requirements, for example for drives, motor protection switches and circuit breakers with regard to overload and short-circuit protection in practice. For protective switching devices in general, which include circuit breakers, motor protection switches or circuit breakers, it is desirable to quickly detect any overload currents that occur, especially short-circuit currents, and to limit them to small values and finally switch them off. Disadvantages of mechanical protective switching devices are wear on 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 operate without wear and switch quickly; they have low switching losses and they can be controlled variably. The disadvantages of semiconductor switches, on the other hand, are:

- high costs,

- high space requirement and

- relatively high transmission losses.

In general, it is often desirable to quickly limit alternating currents or direct currents to certain values and finally switch them off.

·

GR 93 G 3476 EN

The invention is based on the object of developing an advantageous current-limiting switch based on semiconductor technology, which enables a favorable switch-off behavior in practice.
5

The solution to the problem described is achieved by a current-limiting switch according to claim 1. With source and drain electrodes lying flat against each other, the gate electrode is arranged centrally between them and is provided with at least one external connection. When made from silicon carbide, the objectives are met in practice, whereby the symmetrical structure allows both alternating currents and direct currents to be limited regardless of polarity and interrupted when the gate-source voltage is continuously changed accordingly. A high blocking capacity is achieved on both sides with correspondingly large-area drain and source contacts and a low on-state resistance with a high blocking capacity on the other hand, depending on a suitable geometry.

For a given thickness L of the gate electrodes and a given distance of the source-drain path D, the current limitation increases as a result of a field confinement effect with decreasing distance between the gate electrodes.

It is advantageous if the gate electrode, which can consist of connected island areas or of an area with hole recesses, has a ring connection.

The semiconductor region can be integrated into a microchip or as a discrete component. It can

Have structural features of creation by "wafer bonding". Such features are achieved by a corresponding known process of "wafer bonding technology".
35

The invention will now be explained in more detail using embodiments shown schematically in the drawing:

GR 93 G 3476 EN

The current limiting switch is shown in principle in FIG 1.

FIG 2 shows an operating diagram of the current-limiting switch.

In FIG 3, an embodiment of the semiconductor region is shown in perspective as a sector breakout from a ring-shaped structure.

The current-limiting switch according to FIG. 1 has a semiconductor region 1 which has an electron donor (source; 2), an electron collector (drain; 3) and gate electrodes 4. A load circuit to be protected or a consumer to be switched can be connected between the source electrode 2 and the drain electrode 3. The drain-source current, Ids, ^ ^e ~ can be limited by suitable gate-source voltages, Uqs^ and, as the blocking voltage at the gate electrode continues to rise, can be reduced in the direction of the abscissa in the characteristic field according to FIG. 2. The gate electrodes 4 are arranged centrally between source-drain electrodes 2 and 3 which are flatly opposite one another. The gate electrodes 4 are electrically connected and have an external connection, electrode connection 4 according to FIG. 1. It is advantageous if the gate electrodes 4 have a ring connection, as can be seen from FIGS. 1 and 3. Depending on the geometry, the thickness L of the gate electrodes 4, the distance d between the gate electrodes and the source-drain section D, increasing current limitation is achieved as the distance d becomes smaller due to the field constriction. For example, the semiconductor region can have the following values:

L = 2 um, d = 2 um and D = 18 um

This gives an operating range for 23 0 V normal operation and a current limitation for overvoltages, up to about 700 V,

GR 93 G 3476 EN

if the semiconductor region is made on the basis of silicon carbide.

In the diagram in FIG 2, the drain-source voltage U^g is plotted on the abscissa and the drain-source current log on the ordinate. In the characteristic field in FIG 2 for alternating voltage, a linear operating range is obtained in the first and third quadrants and for direct voltage a linear operating range in one of the quadrants. The linear operating range corresponds to the so-called ON resistance, Ron*· The linear operating range is designated 9. For gate-source voltages, characteristic curves limiting the drain-source current are obtained roughly parallel to the abscissa. For the sake of simplicity, it is assumed that the semiconductor region has an η channel and is self-blocking. A desired drain-source current can be set or limited in the event of overvoltages by using a suitable gate-source voltage as a parameter in the characteristic field. One then works in a horizontal area in the characteristic field at a constant I^g. If the upper voltage is too high, a breakdown would eventually occur in an end region, leading to increasing drain-source currents at a constant drain-source voltage. The dimensions and operating range must be selected so that this end region cannot be reached. In the embodiment shown in FIG. 3, a broken-out sector of a semiconductor region 1 is shown in perspective. It is closed off with a source electrode 2 and drain electrode 3 and has embedded gate electrodes 4, which in the embodiment have finger-like recesses, so that peninsula-like regions are created for the gate electrodes 4. The gate electrodes are jointly contacted in an outer ring, since the individual gate electrodes are also connected to one another.

Claims (3)

GR 93 G 3476 DE 5 Protection claims 1. Current-limiting switch with at least one semiconductor region 1 with electron donor (source; 2), electron collector (drain; 3) and electrode controlling the electron flow (gate; 4), wherein, in the case of source and drain electrodes (2; 3) lying flat against one another, the gate electrode (4) is arranged centrally between them and has at least one external connection,
characterized in that the semiconductor region is formed from silicon carbide (SiC). 2. Switch according to claim 1, characterized in that the gate electrode (4) has a ring connection. 3. Switch according to claim 1,
characterized in that the semiconductor region (1) has structural features of being produced by wafer bonding.