Current detection device and method for sensing an electric current

Abstract

The invention relates to a method and a device for detecting a current in a measuring path, the current in said measuring path corresponding to a current in a power path. An electric current is detected by a current measuring instrument in the measuring path, while simultaneously part of the electric current is conducted parallel to the current measuring instrument by a bypass device, in order to reduce the load on the current measuring instrument.

Claims

1. A current detection device (10) for detecting an electric measuring current (I.sub.s) on a measuring path, the electric measuring current (I.sub.s) corresponding to an electric current (I.sub.E) on a power path, the current detection device comprising: a current measuring device (11) which is arranged on the measuring path and which is designed to provide an output signal which corresponds to an electric current which flows through the current measuring device (11), and a bypass device (12) including a current mirror circuit arranged in parallel with the current measuring device (11) and a resistor (R.sub.0) arranged in series with the current measuring device (11), wherein the bypass device (12) is designed to adjust an electric bypass current (I.sub.B) in dependence on the electric measuring current (I.sub.s) by activating the current mirror circuit when the voltage drop across the resistor (R.sub.0) is greater than a predetermined reference voltage.

2. The current detection device (10) as claimed in claim 1, wherein the bypass device (12) is designed so that no electric bypass current flows through the bypass device (12) when the electric measuring current (I.sub.s) drops below a predetermined first threshold value.

3. The current detection device (10) as claimed in claim 1, wherein the bypass device (12) is designed to adjust an electric bypass current (I.sub.B) in parallel with the current measuring device (11) when the electric measuring current (I.sub.s) exceeds a predetermined second threshold value.

4. The current detection device (10) as claimed in claim 1, wherein the bypass device (12) is designed to adapt the electric bypass current (I.sub.B) in dependence on the output signal of the current measuring device (11).

5. The current detection device (10) as claimed in claim 1, wherein the bypass device (12) is designed to limit the electric current through the current measuring device (11) to a predetermined maximum limit value.

6. The current detection device (10) as claimed in claim 1, wherein the bypass device (12) further includes a reference voltage source (U.sub.Ref) which is designed to provide the predetermined reference voltage and the bypass device (12) is designed to compare the voltage drop across the resistor (R.sub.0) with the predetermined reference voltage provided by the reference voltage source (U.sub.Ref) and to adjust the electric bypass current (I.sub.B) in parallel with the current measuring device (11) in dependence on the comparison.

7. A circuit arrangement (1) for providing an electric current (I.sub.E), comprising: a current control device (20) which is designed to provide an electric current (I.sub.E) on a power path and to provide an electric measuring current (I.sub.s) corresponding to the provided electric current (I.sub.E) on a measuring path, and a current detection device (10) as claimed in claim 1.

8. The circuit arrangement (1) as claimed in claim 7, wherein the current control device (20) comprises a bipolar transistor having an insulated gate, IGBT.

9. A method (100) for detecting an electric current on a measuring path, the electric current corresponding to an electric current on a power path, the method comprising: arranging (110) a current measuring device (11) on a measuring path, arranging (120) a bypass device (12) on the measuring path, the bypass device including a current mirror circuit arranged in parallel with the current measuring device (11) and a resistor (R.sub.0) arranged in series with the current measuring device (11), wherein the bypass device is designed to adjust an electric bypass current (I.sub.B), adjusting (130) an electric current (I.sub.B) which flows through the bypass device (12) in dependence on the electric current which flows on the measuring path by activating the current mirror circuit when the voltage drop across the resistor (R.sub.0) is greater than a predetermined reference voltage, and detecting (140) an electric current which flows through the current measuring device (11).

10. The current detection device (10) as claimed in claim 1, wherein the output signal is scaled in order to compensate for the bypass current not detected by the current measuring device (11) and to infer the electric current (I.sub.E) on the power path by means of a suitable transfer factor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and embodiments of the present invention are apparent in the subsequent description, referring to the attached drawings.

(2) FIG. 1: shows a diagrammatic representation of a circuit diagram for a circuit arrangement for providing an electric current with a current detection device according to one exemplary embodiment,

(3) FIG. 2: shows a diagrammatic representation of a voltage/current diagram having a characteristic and forms the basis of a current detection device according to one exemplary embodiment; and

(4) FIG. 3: shows a diagrammatic representation of a flow chart for a method for detecting an electric current as forms the basis of an exemplary embodiment.

DETAILED DESCRIPTION

(5) Although the present invention will be described in the text which follows with reference to a bipolar transistor and having an insulted gate (IGBT) which has a sense terminal for providing a measuring current, the invention can also be applied additionally to further circuit arrangements for providing an electric current in which an electric current on a power path is to be evaluated by means of a further current on a measuring path.

(6) FIG. 1 shows a diagrammatic representation of a circuit arrangement 1 for providing an electric current. The circuit arrangement 1 comprises a current control device 20, for example an IGBT. The IGBT has then a control terminal G. On the basis of a control signal present at this control terminal G, an electric current I.sub.E can be adjusted on a power path between the input C and the output E of the IGBT. At a sense terminal S, the IGBT outputs a measuring current which corresponds to the electric current I.sub.E on the power path. With constant boundary conditions such as, for example, constant temperature and identical substrate characteristics, a fixed transfer ratio exists between the current I.sub.E on the power path and the measuring current I.sub.s on the measuring path. However, this requires that identical voltage ratios are set at output E and the sense terminal S of the IGBT.

(7) To adjust these identical voltage ratios at the output E and sense terminal S of the IGBT, the circuit arrangement 1 comprises a compensation circuit 30. In the exemplary embodiment shown in FIG. 1, the compensation circuit 30 comprises, for example, the two voltage sources U.sub.B.1 and U.sub.B.2 and the current source I.sub.0. Furthermore, the compensation circuit 30 comprises transistors T.sub.1 to T.sub.5. Other compensation circuits which are suitable for adjusting the required voltage ratios at output E and sense terminal S of the IGBT are additionally also possible.

(8) In this context, the detection of the electric current I.sub.s on the measuring path is effected by the current detection device 10. The measuring current I.sub.S here flows initially through the transistor T.sub.5 of the compensation circuit 30 and the resistor R.sub.0 of the current detection device 10, and through the current measuring device 11. In the example shown here, the current measuring device 11 is formed by the shunt resistor R.sub.s. Across a shunt resistor R.sub.s, a voltage U.sub.s which is proportional to the current flowing through this resistor is dropped. This voltage drop U.sub.s can here be provided as output signal which represents a measuring quantity corresponding to the current I.sub.s. Optionally, the voltage U.sub.s can also be converted by the shunt resistor R.sub.s into a digital signal by means of an analog/digital converter 13. Thus, digital further processing of the measuring quantity detected is also possible. Furthermore, the current I.sub.E on the power path can be inferred from the analog or digital signal detected in this manner by means of, for example, suitable scaling. The complete measuring current I.sub.s, and thus also the current I.sub.E in the power path, can also be inferred by suitable downstream scaling in the case of analog processing of the output signal, for example of the voltage U.sub.s via the shunt resistor R.sub.s.

(9) To lower the current through the shunt resistor R.sub.s at relatively high measuring currents I.sub.s, the current through the shunt resistor R.sub.s can be reduced by connecting a bypass path in parallel. For this purpose, the current detection device 10 comprises a bypass device 12. The bypass device 12 then comprises the resistor R.sub.0 which is arranged in series with the shunt resistor R.sub.s. The voltage drop across this resistor R.sub.0 is supplied to an input of an operational amplifier OP. The operational amplifier OP compares this voltage drop with the output voltage of a reference voltage source U.sub.Ref. The output signal of the operational amplifier OP is supplied to the control input of a transistor T.sub.6 which can in turn activate a current mirror circuit of transistors T.sub.7 and T.sub.8 and the two resistors R.sub.1 and R.sub.2. If the voltage drop across the resistor R.sub.0 exceeds the voltage provided by the reference voltage U.sub.Ref, the transistor T.sub.6 is activated by the operational amplifier OP as a result of which the current mirror circuit sets a bypass current I.sub.B. This bypass current I.sub.B thus flows in parallel with the current through the shunt resistor R.sub.S. In this manner, the measuring current I.sub.s is divided so that a current through the shunt resistor R.sub.S is correspondingly reduced by the bypass current I.sub.B as soon as the voltage drop across the resistor R.sub.0 is greater than the voltage of the reference voltage source U.sub.Ref. In this case, the voltage U.sub.s across the shunt resistor R.sub.S no longer increases proportionally to the full measuring current I.sub.s with increasing measuring current I.sub.s. Instead, the voltage drop is then reduced by a proportion which is proportional to the bypass current I.sub.B. In this manner, the current through the shunt resistor R.sub.S, and thus also the voltage rise across the shunt resistor R.sub.S is correspondingly reduced with large measuring currents I.sub.s. This flattened curve of the output signal with increasing measuring current I.sub.s can be taken into consideration during a subsequent evaluation of the output signal of the current detection device 10 and compensated for in order to again infer the full measuring current I.sub.s and thus the current I.sub.E on the power path.

(10) FIG. 2 shows a diagrammatic representation of a current/voltage diagram for the relationship between the measuring current I.sub.s and the voltage drop U.sub.s across the shunt resistor R.sub.S. In a first range I, the voltage rise is initially completely proportional to the measuring current I.sub.s. If the measuring current I.sub.s exceeds a predetermined limit value, a bypass current I.sub.B begins to flow in the bypass device 12. The steepness of the current/voltage characteristic is thus reduced in section II. In this manner, it is possible to provide the first section I with a relatively large sensitivity so that with relatively low measuring currents I.sub.s, there is great steepness of the current/voltage characteristic. This provides for very good resolution at relatively low measuring currents I.sub.s, and accurate evaluation of small currents. In addition, the steepness of the current/voltage characteristic can be reduced at relatively large measuring currents I.sub.s in the second area II so that no excessively large output signals occur even with relatively large measuring currents I.sub.s. Thus, a smaller dynamic range of the output signal U.sub.s is obtained over a very large dynamic range of the measuring current I.sub.s, at which, nevertheless, relatively low measuring currents I.sub.s can be resolved very well.

(11) For the purpose of further optimization, it is additionally also possible that, instead of a single kink in the current/voltage characteristic, there are also more than two part areas in which the steepness of the current/voltage characteristic is in each case different. For this purpose, the circuit arrangement according to FIG. 1 can be extended, for example, by using more bypass branches, or there is a comparison of several reference voltages which in each case activate a common bypass branch differently. Further alternatives for adapting the steepness of the current/voltage characteristic in several part areas are additionally also possible.

(12) So that the current detection device 10 is not overloaded too much even at very high measuring currents I.sub.s, the maximum current which flows through the shunt resistor R.sub.S can be limited to a maximum value. In this case, the bypass device 12 is configured in such a manner that a further rise in the measuring current I.sub.s flows completely via the bypass branch and does not lead to further rise of the current through the current measuring device 11.

(13) FIG. 3 shows a diagrammatic representation of a flow chart for a method 100 for detecting an electric current on a measuring path which carries an electric current corresponding to an electric current on a power path as it forms the basis in one embodiment. The method 100 then comprises firstly a step 110 for arranging a current measuring device in a measuring path. In step 120, a bypass device is additionally arranged on the measuring path.

(14) In step 130, an electric current through the bypass device 12 is adjusted in dependence on the current on the measuring path. Following this, an electric current is detected by the current measuring device in step 140. A suitable output signal can be output corresponding to the detected current. The output signal can be scaled thereupon in order to compensate for the bypass current not detected by the current measuring device 11 and to infer the current I.sub.E on the power path by means of a suitable transfer factor.

(15) In summary, the present invention relates to a method and to a device for detecting a current on a measuring path, the current on this measuring path corresponding to a current on a power path. For this purpose, an electric current is detected on the measuring path by a current measuring device whereas, at the same time, a part of the electric current is conducted in parallel to the current measuring device by a bypass device in order to thus relieve the current measuring device.