Assembly for switching a resistor

Abstract

An assembly, comprising a heat-dissipating first resistor, control device for controlling the first resistor, as well as a grounded component, which lies on a potential without direct relation to a control voltage. The first resistor is arranged in spatial vicinity of the grounded component and comprising a first and a second connection. The control device comprises a first switching device and a second switching device. The first switching device, first resistor and second switching device form a series connection. A compensation device is configured such that in the On-state of the first resistor a voltage is applied between the first and second connection, wherein the resistor in the off-state is held on an in-between potential that lies between the first and the second potential and/or the control device is configured to trigger the first resistor in a pulse width modulated fashion, such that the first as well as the second switching device are switched synchronously.

Claims

1. An arrangement comprising a heat-emitting first resistor, a control device for switching the first resistor, and a grounded housing or chassis that is at a potential without direct reference to a driving voltage, wherein the first resistor is arranged in a spatial vicinity of the housing or chassis, and has a first and a second terminal, wherein the control device comprises a first switching device and a second switching device, wherein the first switching device, the first resistor and the second switching device are connected in series in said order and thus form a series circuit, wherein a compensation apparatus is provided and configured such that, in the on state of the first resistor, a voltage is present between the first and the second terminal, such that the first terminal is at a first potential and the second terminal is at a second potential, wherein the resistor in the off state is kept at an intermediate potential that lies between the first and the second potential, and wherein the control device is configured to drive the first resistor using pulse width modulation, wherein the first and the second switching device are switched substantially synchronously, wherein the compensation apparatus comprises a high-resistance second resistor, a high-resistance third resistor and a connecting line, wherein the second and the third resistor are connected in series with one another and are connected in parallel with the series circuit formed of the first switching device, the first resistor and the second switching device, wherein the connecting line connects a point between the second and the third resistor to a point between the two switching devices.

2. The arrangement as claimed in claim 1, wherein a resistance of the second resistor and a resistance of the third resistor differ from one another by at most 10%.

3. The arrangement as claimed in claim 1 wherein the first and/or second switching device comprises a transistor based on silicon and/or silicon carbide and/or gallium arsenide.

4. The arrangement as claimed in claim 1, further comprising a support apparatus comprising one or more capacitors in parallel with a second and/or third resistor, for supporting a voltage corresponding to the intermediate potential.

5. The arrangement as claimed in claim 1, further comprising a microcontroller and/or FPGA for controlling the switching of the first and/or second switching device to hone a switching time of the first and second switching device.

6. The arrangement as claimed in claim 1, further comprising a voltage supply.

7. The arrangement as claimed in claim 1, wherein a time lag between a switch-on time of the first switching device and a switch-on time of the second switching device or a time lag between a switch-off time of the first switching device and a switch-off time of the second switching device is less than 20% of a switched-on time of the first switching device.

8. A control method using the arrangement as claimed in claim 1, for switching a heat-emitting first resistor having a first and a second terminal and arranged in a spatial vicinity of a grounded housing or chassis, which is at a potential without direct reference to a driving voltage, wherein the first terminal in an on state of the first resistor is at a first potential and the second terminal in an on state is at a second potential, wherein the resistor in an off state is kept at an intermediate potential, which lies between the first and the second potential, and/or wherein the first resistor is driven using pulse width modulation, wherein a first switching device associated with the first terminal and a second switching device associated with the second terminal are switched synchronously.

9. The control method as claimed in claim 8, wherein a time lag between a switch-on time of the first switching device and a switch-on time of the second switching device and/or a time lag between a switch-off time of the first switching device and a switch-off time of the second switching device is less than 20% of a switched-on time of the first switching device.

10. An electrical heating apparatus comprising an arrangement as claimed in claim 1.

11. The arrangement as claimed in claim 1, wherein a resistance of the second resistor and a resistance of the third resistor are substantially the same.

12. The arrangement as claimed in claim 3 wherein the first and/or second switching device comprises a MOSFET or IGBT.

13. The arrangement as claimed in claim 1, wherein a voltage supply is a DC source.

14. The arrangement as claimed in claim 1, wherein a time lag between a switch-on time of the first switching device and a switch-on time of the second switching device or a time lag between a switch-off time of the first switching device and a switch-off time of the second switching device is less than 5% of a switched-on time of the first switching device.

15. The control method of claim 8 wherein the intermediate potential is at least approximately half of a supply voltage.

16. An electrical heating apparatus configured perform the control method of claim 8.

Description

(1) The invention will be described below with reference to an example according to the prior art and a first exemplary embodiment, these being explained in more detail with reference to the drawings. In the figures:

(2) FIG. 1 shows an arrangement for supplying power to and switching a resistor arranged in the vicinity of a housing, according to the prior art;

(3) FIG. 2 shows an arrangement for supplying power to and switching a resistor arranged in the vicinity of a housing, according to a first exemplary embodiment of the invention during a first switching process;

(4) FIG. 3 shows an arrangement according to FIG. 2 during a second switching process; and

(5) FIG. 4 shows an arrangement for switching the supply of power to a resistor arranged in the vicinity of a housing, according to a second exemplary embodiment of the invention.

(6) In the following description, the same reference designations will be used for identical parts and parts of identical action.

(7) FIG. 1 shows a schematic view of an arrangement having an electrical resistor that is to be switched, according to the prior art. The electrical resistor to be switched is in this case depicted symbolically by the resistors R1 to R4. Fundamentally, however, what is involved in this case is just one (continuous) resistor. To this extent, the schematically depicted resistors R1 to R4 may also be understood as resistor sections of the resistor (that is to say individual sections of the resistor that are connected in series). As an alternative, however, resistors that are structurally delimited from one another (for example four of them) may also actually be involved. The resistor R1 to R4 is arranged close to a housing 10 for heat extraction (cooling) purposes.

(8) The capacitors C1 to C5 shown in FIG. 1 correspond to a symbolic depiction of a capacitance of the resistor that results from the close arrangement to the housing. In the sectional view of the resistor R1 to R4 having four sections R1, R2, R3 and R4, these capacitances may then be assigned to individual sections.

(9) Furthermore, a switch M (specifically a transistor, in particular MOSFET or IGBT) is provided, which is able to be switched on and off. If the switch M is switched off, the resistor R1 to R4 is at the supply voltage, which is provided by a voltage supply 11. If the switch M is then (initially) switched on, the voltage across the resistor R1 to R4 changes. The lower end (in FIG. 1) of R1 goes toward 0 V, whereas the upper end (in FIG. 1) of R1 remains at the supply voltage. The result of this is that the capacitor, according to the schematic depiction C1 to C5, is entirely or partly discharged. The capacitor C1 is for example completely discharged, whereas C3 is discharged to half the supply voltage. Half the supply voltage corresponds to the middle voltage across the whole resistor.

(10) On average, the complete capacitance is discharged by half the supply voltage.

(11) If the switch M is then (finally) switched off, the process just described is basically repeated. However, the capacitors are not discharged, but rather charged up to the supply voltage. This charging and discharging of the capacitors C1 to C5 may lead to significant EMC interference (both line-conducted and radiated) depending on the speed of the switching.

(12) The reference sign 12 denotes an intermediate circuit capacitor. Further capacitors 13 and inductors 14 form part of a line impedance stabilization network (LISN) and are not of further importance for the present invention. The reference sign 15 symbolizes a ground connection of the housing 10.

(13) FIG. 2 shows an arrangement analogous to FIG. 1, but with differences according to the invention. The elements/units having the reference signs 10 to 15 correspond to the arrangement according to the prior art according to FIG. 1, such that, in this respect, reference is made to the statements made with respect to the prior art.

(14) In contrast to the prior art, the arrangement according to FIG. 2, however, comprises not just one switch M (cf. FIG. 1), but rather two switches M1, M2 (which are configured as transistors, preferably MOSFETs or IGBTs). Furthermore, two (high-resistance) resistors 16, 17 are provided, which are connected to the first resistor R1 to R4 by way of a connecting line 18.

(15) Specifically, the first switching devices M1, the first resistor R1 to R4 and the second switching device M2 are connected in series. The second (high-resistance) resistor 16 and the third (high-resistance) resistor 17 are connected in parallel therewith. The connecting line 18 is connected between the (high-resistance) resistors 16, 17, on the one hand, and to the resistor R1 to R4, on the other hand. Specifically, the connecting line may be connected between a second resistor section R2 and a third resistor section R3 (in the sectional view). However, this is not mandatory. The connecting line could also for example (in FIG. 2) be arranged above R1 or below R3, etc.

(16) I1 and I2 symbolize currents that flow when the switches M1 and M2 are switched on.

(17) The two (high-resistance) resistors 16, 17 have the same value in the present exemplary embodiment (but may also possibly vary, at least slightly). The switches M1, M2 are switched synchronously (at the same time).

(18) When M1 and M2 are switched on synchronously (in particular initially), the current flowing in C5 is (directly) taken up by C1. The same applies for C4 and C2. Ideally, current then no longer flows via the ground connection. In principle, the same occurs (in the reverse direction) if M1 and M2 are switched off synchronously. This is illustrated in FIG. 3. FIG. 3 corresponds to FIG. 2, only in that the currents I1 and I2 that flow upon switching off are shown.

(19) If the switching devices M1 and M2 are not switched on (exactly) synchronously, depending on the switching time and time difference, a particular current flows via the ground connection 15. Even when the switching devices M1 and M2 do not switch (exactly) synchronously, the undesired current is however able to be reduced by at least a factor of 10 (in comparison with the driving according to FIG. 1). Capacitors may also possibly support the mid-voltage that is present at the resistor R1 to R4 in the switched-off state of the switching devices M1 and M2, so as to mitigate the effect of the time difference. These capacitors may for example be arranged in parallel with the two (high-resistance) resistors 16, 17.

(20) The switching devices M1, M2 are controlled by a control apparatus 19 (not shown in detail). The (high-resistance) resistors 16, 17 and the connecting line 18 are elements of a compensation apparatus 20, which ensures (as described above) that a mid-voltage is present at the resistor R1 to R4 in the (finally) switched-off state of the switching devices M1, M2.

(21) A (fast) control unit, such as for example a microcontroller or FPGA, may also possibly hone the switching time (timing) of the two switching devices (MOSFETs) M1 and M2, so as to achieve a comparatively high degree of synchronicity.

(22) FIG. 4 shows an alternative embodiment of the invention. This corresponds to the embodiment according to FIGS. 2 and 3, with the difference that the compensation apparatus (with the resistors 16, 17 and the connecting line 18) is not provided. In this embodiment, the resistor R1-R4 is driven using PWM. In this case, the switching devices are switched synchronously not only upon initial switching on and upon initial switching off, but also during operation of the resistor R1-R4 (that is to say during the on state of the resistor). As a result, interference during the PWM driving of the resistor (in particular heating resistor) during operation is able to be compensated or at least reduced. In the first embodiment according to FIGS. 2-3 as well, PWM driving of the resistor R1-R4 takes place take place (in particular as described with reference to FIG. 4).

(23) It is pointed out at this juncture that all of the above-described parts both individually and in any combination, in particular the details illustrated in the drawings, are claimed as being essential to the invention. Modifications in relation to this are familiar to a person skilled in the art.

REFERENCE SIGNS

(24) C1-C5 Capacitors (as a symbolic depiction of an overall capacitance) M Switching device M1 First switching device M2 Second switching device R1-R4 Resistors (as a symbolic depiction of an overall resistance) 10 Housing 11 Voltage supply 12 Intermediate capacitor 13 Capacitor 14 Inductor 15 Ground connection 16 Second (high-resistance) resistor 17 Third (high-resistance) resistor 18 Connecting line 19 Control apparatus 20 Compensation apparatus