Electronic fuse for a power supply

Abstract

An electronic fuse for a power supply includes at least two switching elements and a regulation unit, wherein a first switching element is arranged in a main branch, where the regulation unit is switches off the first switching element when a predetermined threshold value is exceeded by a prevailing current value, and a second switching element that is also actuated by the regulation unit, which is arranged in an auxiliary branch parallel to the first switching element and assumes a substantial proportion of a resulting power loss when an overload occurs, and the second switching element, which is arranged in at least one auxiliary branch, is configured or optimized for linear operation, and where the at least two switching elements are configured such that the line resistance of the second switching element is at least twice the line resistance of the first switching element.

Claims

1. An electronic fuse for a power supply at least comprising: at least two switching elements, a first switching element of the at least two switching elements being arranged in a main branch via which a supply voltage is supplied to at least one output; and a regulation unit configured to switch a current of the first switching element when a predetermined threshold value is exceeded by a prevailing current value; wherein at least one second switching element, which is actuated by the regulation unit, is arranged in an auxiliary branch parallel to the first switching element and assumes a substantial proportion of a resulting power loss in the event of an overload, the first switching element and the at least second switching element being produced using different technology; wherein the at least second switching element is configured for linear operation; and wherein the at least two switching elements are configured such that a line resistance of the second switching element has at least twice the amount of a line resistance of the first switching element; wherein the measurement of the prevailing current value is galvanically isolated by a Hall-effect sensor or a magnetoresistive sensor.

2. The electronic fuse as claimed in claim 1, wherein the regulation unit is further configured such that the first switching element is switched on again after an overload in an event of the prevailing current value falling below the predetermined threshold value.

3. The electronic fuse as claimed in claim 2, wherein the regulation unit is configured such that the at least two switching elements are switched off in an event of tripping.

4. The electronic fuse as claimed in claim 1, wherein the regulation unit is configured such that the at least two switching elements are switched off in an event of tripping.

5. The electronic fuse as claimed in claim 1, wherein the at least second switching element has a higher voltage limit than the first switching element.

6. The electronic fuse as claimed in claim 1, wherein the first switching element comprises a field-effect transistor.

7. The electronic fuse as claimed in claim 1, wherein the at least second switching element comprises one of (i) a planar field-effect transistor, (ii) a trench field-effect transistor and (iii) as a bipolar transistor with insulated gate electrode (IGBT).

8. The electronic fuse as claimed in claim 1, further comprising: at least one current measuring resistor for a measuring a prevailing current value, said at least one current measuring resistor being arranged in series with a connection point of the at least two switching elements arranged in parallel.

9. The electronic fuse as claimed in claim 1, further comprising: a current measuring resistor arranged in series for measuring the prevailing current value for each of the at least two switching elements.

10. The electronic fuse as claimed in claim 1, wherein the regulation unit comprises at least one first regulator for actuating the first switching element and a second regulator for actuating the at least second switching element.

11. The electronic fuse as claimed in claim 1, wherein the regulation unit is constructed from analog regulator units, as a cascade of analog and digital regulator units or of digital regulator units.

12. The electronic fuse as claimed in one claim 1, wherein a voltage supply of the regulation unit is isolated or galvanically isolated from the supply voltage of the power supply.

13. The electronic fuse as claimed in claim 1, further comprising: an activation unit for switching the first switching element, said activation unit comprising one of (i) a microcontroller and (ii) an analog comparator unit with hysteresis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained hereinafter in an exemplary manner with reference to the accompanying figures, in which:

(2) FIG. 1 shows a diagrammatic and exemplary configuration of the electronic fuse in accordance with the invention;

(3) FIG. 2 shows an exemplary and diagrammatic view of a regulation concept for the at least two switching elements of the electronic fuse in accordance with the invention;

(4) FIG. 3a shows an exemplary and diagrammatic view of a time profile of the prevailing current during a transition from an overload to normal operation of the electronic fuse in accordance with the invention; and

(5) FIG. 3b shows an exemplary and diagrammatic view of a time profile of the prevailing current when an overload occurs during normal operation of the electronic fuse according to the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(6) FIG. 1 shows an exemplary and diagrammatic view of an electronic fuse for a power supply with a supply voltage Uv (for example, 24 V DC voltage). The electronic fuse comprises at least one first switching element SE1 and at least one second switching element SE2, and a regulation unit RE for regulating and actuating the at least two switching elements SE1, SE2. The first switching element SE1 is arranged in a main branch HZ. The supply voltage Uv is conducted via the main branch HZ to at least one output of the power supply or to a load V, at which an output voltage UA then drops. A main branch stream I.sub.HZ flows through the main branch HZ. The load V can have capacitive components which, for example when the power supply is connected, can lead to inrush currents which briefly exceed a predetermined threshold value I.sub.target for the current and thus represent an overload for a short time.

(7) A basic function of such an electronic fuse is to prevent an arbitrarily large current I.sub.actual from flowing through a branch of the circuit. A complete interruption of the power supply (for example, in the event of a short circuit, idling and persistent overload) still assumes an operating state in which the current I.sub.actual is limited to a predetermined threshold value I.sub.target. This limiting operation is also used, for example, in the event of a short-term overload such as, for example, when a capacitive load is connected.

(8) For this purpose, an auxiliary branch BZ is provided that is connected in parallel to the main branch HZ. The at least second switching element SE2 is arranged in the auxiliary branch BZ, through which a limiting current I.sub.BZ flows. The second switching element SE2 is thus arranged parallel to the first switching element SE1 in the main branch and, in the event of an overload or limiting operation, takes over a substantial proportion of the current I.sub.actual flowing in the circuit or a resulting power loss.

(9) In the electronic fuse in accordance with the invention, the first switching element SE1 and the at least second switching element SE2 are manufactured using different technologies, where the second switching element SE2 is configured or optimized for linear operation (i.e., the second switching element SE2 is used, for example, as a controlled current source). Furthermore, the at least two switching elements SE1, SE2 are configured such that a line resistance of the at least second switching element SE2 has at least twice the amount of line resistance of the first switching element SE1. Ideally, the at least second switching element SE2 also has a higher rated voltage, in particular a higher Voltage Breakdown Limit, than the first switching element SE1.

(10) Here, for example, a Trench FET can be used as the first switching element SE1 in the main branch HZ, which trench FET is optimized, for example, for a switching operation. Such a transistor has, for example, a relatively low line resistance (for example, 5 mOhm). In the auxiliary branch, a planar FET, which is set up for linear operation and has, for example, a line resistance value of approximately 50 mOhm, can be used as a second switching element SE2. Alternatively, Trench FETs or IGBTs which have been optimized for linear operation can also be used as a second switching element SE2. Due to the use of switching elements SE1, SE2 with different construction technology and different line resistances, a current distribution between the main branch HZ and auxiliary branch BZ is produced, keeping the power loss as low as possible during normal operation. For limiting operation, however, a transistor can be selected in the auxiliary branch as the second switching element SE2, which limits the prevailing current I.sub.actual in the event of an overload and can absorb a large part of the power loss, at least for a short time.

(11) Moreover, the electronic fuse comprises at least one current measuring resistor R.sub.m, from which a prevailing current value I.sub.actual is measured and forwarded to the regulation unit RE. For this purpose, the current measuring resistor R.sub.m is arranged, for example, in series with a connection point of the main branch HZ and of the auxiliary branch BZ.

(12) Alternatively, the current measurement can also be performed with the aid of two current measuring resistors, where a first current measuring resistor is arranged in the main branch in series with the first switching element SE1 and a second current measuring resistor is arranged in the auxiliary branch in series with the second switching element SE2. Here, the current measuring resistor should be dimensioned such that a measurement with as little interference as possible and with corresponding amplification is possible, but influencing the current distribution and regulation by the regulation unit RE is kept as low as possible. In the case of a current measurement in the two branches HZ, BZ, the respective prevailing currents I.sub.HZ, I.sub.BZ are then measured in the branches HZ, BZ, from which the entire prevailing current value I.sub.actual can then be determined.

(13) Alternatively, the prevailing current value I.sub.actual can also be measured in a galvanically isolated manner via a Hall-effect sensor or via a magnetoresistive sensor. Alternatively, these sensors can also be arranged in the branches HZ, BZ in order, for example, to measure the currents I.sub.HZ, I.sub.BZ. The prevailing current value I.sub.actual is then determined as the sum of these currents I.sub.HZ, I.sub.BZ.

(14) In addition, an inductance L can optionally be connected upstream of the load V, via which inductance L a maximum current increase and thus the entire dynamics of the circuit can be determined. Here, the current increase that can be predetermined by the inductance L is, for example, decisive for a configuration of the electronic fuse and can also determine, for example, the parameterization of the regulation unit RE or its components.

(15) The regulation unit RE is provided for regulation and actuation of the switching elements SE1, SE2, and compares the predetermined threshold value I.sub.target for the current with the currently measured current value I.sub.actual in the circuit for actuation. The predetermined threshold value I.sub.target is higher than a maximum operating current I.sub.b,max to be expected in normal operation. The regulation unit RE is set up to switch off the first switching element SE1 when the predetermined threshold value I.sub.target is exceeded by the prevailing current value I.sub.actual, i.e., in the event of extreme overload, such as short-circuiting or idling, but also in the event of short-term overload, such as by connecting an at least partial capacitive load V. If, for example, after an overload by connecting an at least partial capacitive load V, the prevailing current value I.sub.actual again fall short of the predetermined current value I.sub.target, then the first switching element SE1 is switched on again via the regulation unit RE.

(16) In addition, the regulation unit RE is set up to switch off the first switching element SE1 and the second switching element SE2 in the event of tripping, i.e., in the event of extreme overloads, such as a short circuit or idling, if necessary with a time delay.

(17) For this purpose, FIG. 2 shows a diagrammatic and exemplary view of regulation for the at least two switching elements SE1, SE2 of the electronic fuse in accordance with an embodiment of the invention, which can be combined to form the regulation unit RE. Both the main branch HZ and the auxiliary branch BZ each have a regulator R1, R2 with a separate current value comparison and a driver unit GT1, GT2 for actuating the respective switching element SE1, SE2. Here, the first switching element SE1 is actuated by a first regulator R1 and a first driver unit GT1, where the first regulator R1 becomes active, for example, as soon as the prevailing current value I.sub.actual falls below the predetermined threshold value I.sub.target, such as when a capacitive load V is connected or if, for example, an overload occurs during normal operation, which exceeds the predetermined threshold value I.sub.target. The first regulator R1 and the first driver unit GT1 can, for example, be formed as analog circuits or digital units (for example, microcontrollers, FPGA) or, if appropriate, as an analog-digital combination.

(18) In addition, a switching unit A can be provided in the main branch HZ, which is connected upstream, for example, from the comparison of predetermined threshold value I.sub.target with the respective prevailing current value I.sub.actual. The switching unit A can be formed, for example, as a microcontroller or as an analog comparator unit with hysteresis and can support switching of the first switching unit SE1.

(19) In the auxiliary branch BZ, a second regulator R2 and a second driver unit GT2 are provided for actuating and regulating the second switching unit SE2. In the event of limitation, or when the prevailing current I.sub.actual is to be limited, the second regulator R2 always becomes active. That is, the second controller R2 regulates the second switching element SE2, for example, when starting up an at least partial capacitive load V or in the event of a load jump. The second regulator R2 and the second driver unit GT2 can also be formed, for example, as analog circuits or digital units (for example, microcontrollers, FPGA) or, if appropriate, as an analog-digital combination.

(20) A voltage supply of the regulators R1, R2 or the regulation unit RE can, for example, be isolated or galvanically isolated from the supply voltage Uv of the power supply. This voltage supply or auxiliary supply is potentially above the supply voltage for the load V so that the switching elements SE1, SE2 can be actuated or switched correctly.

(21) Furthermore, a digitally configured regulator unit (for example, microcontroller, FPGA) can be connected upstream of the regulation unit RE shown in FIG. 2, which performs regulation to the predetermined threshold value I.sub.target as precisely as possible. This digital regulator unit has, for example, its own current measurement, such as via a Hall-effect sensor or magnetoresistive sensor, and is used to compensate for temperature drift or offset deviations of the regulation unit RE.

(22) FIG. 3a shows an exemplary and diagrammatic view of a graphical plot of a time profile of the prevailing current I.sub.actual in the event of a transition from an overload, such as when an at least partial capacitive load V is connected or in the event of a load jump to normal operation of the electronic fuse according to the invention. A time t is plotted on a horizontal axis and a current I is plotted on a vertical axis. The prevailing current value I.sub.actual in each case is shown as a solid line. The main branch current I.sub.HZ flowing in the main branch HZ is shown as a dashed line and the limiting current I.sub.BZ flowing in the auxiliary branch is shown as a dotted line.

(23) If, for example, a load V with a capacitive component is connected to the power supply, in particular a DC voltage source, then on the basis of the capacitive component inrush currents occur, of which the predetermined threshold value I.sub.target would be exceeded. In this case, the auxiliary branch BZ is active, i.e., the first switching element SE1 is switched off and the second switching element SE2 is switched on, and the prevailing current I.sub.actual is kept constant at the predetermined threshold value I.sub.target. That is, the entire current I.sub.actual flows through the auxiliary branch and the limiting current I.sub.BZ corresponds to the I.sub.actual or has the predetermined threshold value I.sub.target. The second switching element SE2 assumes the resulting power loss. In the course of charging the capacitive load component, the prevailing current I.sub.actual drops in accordance with an e-function and approaches a maximum expected operating current I.sub.b,max for normal operation of the electronic fuse. If the prevailing current I.sub.actual begins to drop below the predetermined threshold value I.sub.target, then the first switching element SE1 is switched on at a time t1 or becomes conductive when its threshold voltage is reached. The main branch current I.sub.HZ in the main branch HZ thus increases, i.e. the prevailing current I.sub.actual commutates from the auxiliary branch BZ into the main branch HZ. The limiting current I.sub.BZ decreases proportionally in the auxiliary branch until the current conduction in normal operation is almost completely taken over by the first switching element SE1 in the main branch HZ. Only a small current I.sub.BZ flows through the auxiliary branch BZ and the second switching element SE2, which remains switched on, can cool down.

(24) FIG. 3b shows an exemplary and diagrammatic view of a graphical plot of a time profile of the prevailing current I.sub.actual when an overload occurs (for example, a load jump, a current peak) during normal operation of the electronic fuse according to the invention. The time t is again plotted on a horizontal axis and a current I is plotted on a vertical axis. The prevailing current value I.sub.actual in each case is again shown as a solid line. The main branch current I.sub.HZ flowing in the main branch HZ is shown as a dashed line and the limiting current I.sub.BZ flowing in the auxiliary branch is shown as a dotted line.

(25) The electronic fuse is in normal operation, i.e., the at least two switching elements SE1, SE2 are both conductive or are operated in the ohmic or conductive region. The prevailing current I.sub.actual flowing in the fuse corresponds, for example, to the maximum expected operating current I.sub.b,max for normal operation, where the current I.sub.actual on the main branch HZ and the auxiliary branch BZ is divided up in the ratio of the amounts of the conductive resistances of the at least two switching elements SE1, SE2.

(26) If, for example, an overload (such as current peak, short circuit or idle) occurs at a first time t1, then the prevailing current I.sub.actual in the electronic fuse and thus the currents I.sub.HZ, I.sub.BZ in the main branch HZ and in the auxiliary branch BZ increase until the predetermined threshold value I.sub.target is reached or exceeded at a second time t2. The second regulator R2 and thus the second switching element SE2 in the auxiliary branch BZ become active and the output voltage UA is regulated back or the prevailing current I.sub.actual is limited to the predetermined threshold value I.sub.target. Moreover, the first switching element SE1 is switched off in the main branch HZ, as a result of which the main branch current I.sub.HZ drops to zero. The limiting current I.sub.BZ in the auxiliary branch BZ increases to the predetermined threshold value and the auxiliary branch BZ takes over the resulting power loss (at least in the short term). The switching elements SE1, SE2 can only withstand the load arising from the power loss for a limited time without damage, and the second switching element SE2 is also switched off in the event of a lasting load, i.e., if the electronic fuse trips.

(27) In FIGS. 1 and 2, the electronic fuse in accordance with the disclosed embodiments of the invention is illustrated by way of example with two switching elements SE1, SE2, e.g., a switching element SE1 in the main branch HZ and a switching element SE2 in the auxiliary branch BZ. However, in the case of the fuse in accordance with the disclosed embodiments of the invention, it is possible to provide further parallel auxiliary branches BZ with correspondingly configured second switching elements SE2 and/or further parallel main branches with correspondingly configured first switching elements SE1.

(28) Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.