Controlling reverse conducting IGBT

1. A method for controlling a first switch and a second switch, wherein each switch is an RC-IGBT and wherein both switches are arranged as a half-bridge circuit, the method comprising:

controlling the first switch in an IGBT-mode;

controlling the second switch such that it becomes desaturated when being in a DIODE-mode;

wherein controlling the second switch starts before and lasts at least as long as the first switch changes its IGBT-mode from blocking state to conducting state,

wherein the first switch and the second switch are controlled in a pulse-width-modulation at a switching frequency that is higher than a frequency of a load current.

2. The method according to claim 1 , further comprising:

controlling the second switch such that its desaturation phase ends between a time the current conveyed across the second switch becomes 0 and a time when the current reaches a maximum of a reverse recovery current.

3. The method according to claim 2 , wherein the end of the desaturation phase is determined by sensing the current in the second switch or in the first switch.

4. The method according to claim 1 , wherein the step of controlling the gate of the second switch further comprises:

controlling the gate of the second switch with at least one voltage such that it becomes desaturated when being in the DIODE-mode.

5. The method according to claim 4 , wherein the at least one voltage amounts to 0V or to substantially 0V.

6. The method according to claim 4 , wherein the at least one voltage comprises a first voltage for a first time period and a second voltage for a second time period.

7. The method according to claim 6 , wherein the first voltage is higher than the second voltage.

8. The method according to claim 4 , further comprising:

controlling the gate of the second switch with an enhancement voltage that allows the second switch to enter an enhancement state when being in the DIODE-mode,

wherein the enhancement voltage is applied prior to the at least one voltage that desaturates the second switch when being in the DIODE-mode.

9. The method according to claim 1 , wherein each of the first switch and the second switch is a 3-level switch that is arranged to be controlled by at least three different input voltages or three different input voltage ranges applied to its gate.

10. The method according to claim 1 , wherein the first switch and the second switch are controlled such that at one time only one of them is in the conducting state when in IGBT-mode.

11. The method according to claim 1 , wherein the first switch and the second switch are each controlled by a driver or by a controller, wherein the voltage applied to the respective gate is generated via a digital or analog interface.

12. A computer program product directly loadable into a memory of a digital processing device, comprising software code portions for performing the steps of the method according to claim 1 .

13. The method according to claim 1 , wherein the first switch and the second switch each is a semiconductor device comprising:

a barrier region sandwiched between a drift region and a charge carrier transfer region, the barrier and charge carrier transfer regions forming a pn junction and the barrier and drift regions forming a homojunction, wherein an impurity concentration in the barrier region is at least ten times as high as an impurity concentration in the drift region; and

a control structure configured to form an inversion layer in the drift and barrier regions in an inversion state and to form no inversion layer in the drift and barrier regions in a non-inversion state.

14. The method according to claim 13 , wherein the semiconductor device is configured not to form, through the charge carrier transfer region, a path for minority charge carriers in an inversion layer along the control structure between the drift region and a load electrode.

15. The method according to claim 13 ,

wherein the control structure extends from a first surface of a semiconductor body comprising the charge carrier transfer region into the semiconductor body down to at least the drift region, and

wherein the charge carrier transfer region directly adjoins the first surface at the control structure.

16. The method according to claim 13 ,

wherein the control structure extends from a first surface of a semiconductor body comprising the charge carrier transfer region into the semiconductor body down to at least the drift region, and

wherein the control structure comprises a control electrode, a control dielectric sandwiched between the harrier and drift regions on a first side and the control electrode at a second side opposite to the first side, and a top dielectric between the first surface and the control electrode overlaps the charge carrier transfer region in a vertical direction perpendicular to the first surface.

17. The method according to claim 13 , wherein the semiconductor device is an insulated gate bipolar transistor comprising a field effect transistor cell.

18. The method according to claim 17 , wherein the transistor cell comprises a body region forming pn junctions with a source region and the drift region, and a gate structure configured to form an inversion layer in the body region during an on state and to form no inversion layer in the body region outside the on state of the transistor cell.

19. The method according to claim 1 , wherein the first switch and the second switch each is a semiconductor device comprising:

a body zone in a semiconductor mesa formed between neighboring control structures that extend from a first surface into a semiconductor body;

a drift zone forming a first pn junction with the body zone and comprising, in the semiconductor mesa, a first drift zone section that comprises a constricted section of the semiconductor mesa, wherein a minimum horizontal width of the constricted section parallel to the first surface is smaller than a maximum horizontal width of the body zone; and

an emitter layer between the drift zone and a second surface parallel to the first surface, the emitter layer comprising at least one first zone of a conductivity type of the drift zone.

20. A device for operating a first switch and a second switch, wherein each switch is an RC-IGBT and wherein both switches are arranged as a half-bridge circuit, said device comprising a processing unit configured to:

control the first switch in an IGBT-mode;

control the second switch such that it becomes desaturated when being in a DIODE-mode;

wherein control of the second switch starts before and lasts at least as long as the first switch changes its IGBT-mode from blocking state to conducting state,

wherein the first switch and the second switch are controlled in a pulse-width-modulation at a switching frequency that is higher than a frequency of a load current.

21. A device for controlling a first switch and a second switch, wherein each switch is an RC-IGBT and wherein both switches are arranged as a half-bridge circuit, the device comprising:

means for controlling the first switch in an IGBT-mode;

means for controlling the second switch such that it becomes desaturated when being in a DIODE-mode;

wherein controlling the second switch starts before and lasts at least as long as the first switch changes its IGBT-mode from blocking state to conducting state,

wherein the first switch and the second switch are controlled in a pulse-width-modulation at a switching frequency that is higher than a frequency of a load current.