Matrix stages solid state ultrafast switch

Abstract

A semiconductor switching device for switching high voltage and high current. The semiconductor switching device includes a control-triggered stage and one or more auto-triggered stages. The control-triggered stage includes a plurality of semiconductor switches, a breakover switch, a control switch, a turn-off circuit, and a capacitor. The control-triggered stage is connected in series to the one or more auto-triggered stages. Each auto-triggered stage includes a plurality of semiconductor switches connected in parallel, a breakover switch, and a capacitor. The control switch provides for selective turn-on of the control-triggered stage. When the control-triggered stage turns on, the capacitor of the control-triggered stage discharges into the gates of the plurality of semiconductor switches of the next highest stage to turn it on. Each auto-triggered stage turns on in a cascade fashion as the capacitor of the adjacent lower stage discharges or as the breakover switches of the auto-triggered stages turn on.

Claims

1. A semiconductor switching device comprising: a control-triggered stage comprising: an input; an output; a plurality of first semiconductor devices connected in parallel, each first semiconductor device comprising a power input connected to the input of the control-triggered stage, a power output connected to the output of the control triggered stage, and a control input; a control switch coupled to the control input of each first semiconductor device, the control switch configured for turning on each first semiconductor device; and one or more auto-triggered stages, each respective auto-triggered stage comprising: an input; an output; a plurality of second semiconductor devices connected in parallel, each second semiconductor device of the respective auto-triggered stage comprising a power input connected to the input of the respective auto-triggered stage, a power output connected to the output of the respective auto-triggered stage, and a control input; and a breakover switch comprising a first end and a second end, the first end of the breakover switch of the respective auto-triggered stage coupled to the power input of each second semiconductor device of the respective auto-triggered stage, the second end of the breakover switch of the respective auto-triggered stage coupled to the control input of each second semiconductor device of the respective auto-triggered stage, wherein the input of the control-triggered stage is connected to the output of one of the one or more auto-triggered stages, thereby effecting a series connection between the control-triggered stage and the one of the one or more auto-triggered stages, and wherein the one or more auto-triggered stages are configured to turn on after the control-triggered stage turns on.

2. The semiconductor switching device of claim 1, wherein the control-triggered stage further comprises: a breakover switch comprising a first end and a second end, the first end of the breakover switch coupled to the power input of each first semiconductor device of the control-triggered stage, the second end of the breakover switch coupled to the control input of each first semiconductor device of the control-triggered stage; and a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each first semiconductor device of the control-triggered stage, the second end of the suppressor coupled to the control input of each first semiconductor device of the control-triggered stage.

3. The semiconductor switching device of claim 2, wherein: the control-triggered stage further comprises a resistor; and the first end of the breakover switch of the control-triggered stage is coupled to the power input of each first semiconductor device of the control-triggered stage via the resistor of the control-triggered stage.

4. The semiconductor switching device of claim 2, wherein the control-triggered stage further comprises a turn-off circuit connected across the suppressor.

5. The semiconductor switching device of claim 2, wherein each breakover switch is a breakover diode.

6. The semiconductor switching device of claim 1, wherein each respective auto-triggered stage further comprises: a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each second semiconductor device of the respective auto-triggered stage, the second end of the suppressor coupled to the control input of each second semiconductor device of the respective auto-triggered stage.

7. The semiconductor switching device of claim 6, wherein: each respective auto-triggered stage further comprises a resistor; and the first end of the breakover switch of each respective auto-triggered stage is coupled to the power input of each second semiconductor device of the respective auto-triggered stage via the resistor of the respective auto-triggered stage.

8. The semiconductor switching device of claim 1, wherein each breakover switch is a breakover diode.

9. The semiconductor switching device of claim 1, wherein the control-triggered stage further comprises a capacitor having a first end and a second end, the first end of the capacitor coupled to the power output of each first semiconductor device of the control-triggered stage and the second end of the capacitor coupled to the control input of each second semiconductor device of the one of the one or more auto-triggered stages, the capacitor configured to discharge into the control input of the each second semiconductor device of the one of the one or more auto-triggered stages to turn on the each second semiconductor device of the one of the one or more auto-triggered stages in response to the control switch closing.

10. The semiconductor switching device of claim 1, wherein the one or more auto-triggered stages comprise a plurality of the auto-triggered stages, and wherein the input of each auto-triggered stage except for a highest one of the auto-triggered stages is connected to the output of a next higher one of the auto-triggered stages, thereby effecting series connections among the plurality of auto-triggered stages.

11. The semiconductor switching device of claim 10, wherein each respective auto-triggered stage comprises a capacitor having a first end and a second end, the first end of the capacitor of the respective auto-triggered stage coupled to the power output of each second semiconductor device of the respective auto-triggered stage; wherein for each respective auto-triggered stage except a highest one of the plurality of auto-triggered stages the second end of the capacitor of the respective auto-triggered stage is coupled to the control input of each second semiconductor device of a next higher one of the plurality of auto-triggered stages; and wherein the second end of the capacitor of the highest one of the plurality of auto-triggered stages is coupled to the power input of each second semiconductor device of the highest one of the plurality of auto-triggered stages.

12. The semiconductor switching device of claim 1, wherein each first and second semiconductor device has a low output impedance.

13. A semiconductor switching device comprising: a control-triggered stage comprising: an input; an output; a plurality of first semiconductor devices connected in parallel, each first semiconductor device comprising a power input connected to the input of the control-triggered stage, a power output connected to the output of the control triggered stage, and a control input; a breakover switch comprising a first end and a second end, the first end of the breakover switch coupled to the power input of each first semiconductor device, the second end of the breakover switch coupled to the control input of each first semiconductor device; and a control switch connected across the breakover switch, the control switch configured for turning on each first semiconductor device; and one or more auto-triggered stages, each respective auto-triggered stage comprising: an input; an output; a plurality of second semiconductor devices connected in parallel, each second semiconductor device of the respective auto-triggered stage comprising a power input connected to the input of the respective auto-triggered stage, a power output connected to the output of the respective auto-triggered stage, and a control input; and a breakover switch comprising a first end and a second end, the first end of the breakover switch of the respective auto-triggered stage coupled to the power input of each second semiconductor device of the respective auto-triggered stage, the second end of the breakover switch of the respective auto-triggered stage coupled to the control input of each second semiconductor device of the respective auto-triggered stage, wherein the input of the control-triggered stage is connected to the output of one of the one or more auto-triggered stages, thereby effecting a series connection between the control-triggered stage and the one of the one or more auto-triggered stages, and wherein the one or more auto-triggered stages are configured to turn on after the control-triggered stage turns on.

14. The semiconductor switching device of claim 13, wherein the control-triggered stage further comprises: a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each first semiconductor device of the control-triggered stage, the second end of the suppressor coupled to the control input of each first semiconductor device of the control-triggered stage.

15. The semiconductor switching device of claim 14, wherein: the control-triggered stage further comprises a resistor; and the first end of the breakover switch of the control-triggered stage is coupled to the power input of each first semiconductor device of the control-triggered stage via the resistor of the control-triggered stage.

16. The semiconductor switching device of claim 14, wherein the control-triggered stage further comprises a turn-off circuit connected across the suppressor.

17. The semiconductor switching device of claim 14, wherein each breakover switch is a breakover diode.

18. The semiconductor switching device of claim 13, wherein each respective auto-triggered stage further comprises: a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each second semiconductor device of the respective auto-triggered stage, the second end of the suppressor coupled to the control input of each second semiconductor device of the respective auto-triggered stage.

19. The semiconductor switching device of claim 18, wherein: each respective auto-triggered stage further comprises a resistor; and the first end of the breakover switch of each respective auto-triggered stage is coupled to the power input of each second semiconductor device of the respective auto-triggered stage via the resistor of the respective auto-triggered stage.

20. The semiconductor switching device of claim 13, wherein each breakover switch is a breakover diode.

21. The semiconductor switching device of claim 13, wherein the control-triggered stage further comprises a capacitor having a first end and a second end, the first end of the capacitor coupled to the power output of each first semiconductor device of the control-triggered stage and the second end of the capacitor coupled to the control input of each second semiconductor device of the one of the one or more auto-triggered stages, the capacitor configured to discharge into the control input of the each second semiconductor device of the one of the one or more auto-triggered stages to turn on the each second semiconductor device of the one of the one or more auto-triggered stages in response to the control switch closing.

22. The semiconductor switching device of claim 13, wherein the one or more auto-triggered stages comprise a plurality of the auto-triggered stages, and wherein the input of each auto-triggered stage except for a highest one of the auto-triggered stages is connected to the output of a next higher one of the auto-triggered stages, thereby effecting series connections among the plurality of auto-triggered stages.

23. The semiconductor switching device of claim 22, wherein: wherein each respective auto-triggered stage comprises a capacitor having a first end and a second end, the first end of the capacitor of the respective auto-triggered stage coupled to the power output of each second semiconductor device of the respective auto-triggered stage; wherein for each respective auto-triggered stage except a highest one of the plurality of auto-triggered stages the second end of the capacitor of the respective auto-triggered stage is coupled to the control input of each second semiconductor device of a next higher one of the plurality of auto-triggered stages; and wherein the second end of the capacitor of the highest one of the plurality of auto-triggered stages is coupled to the power input of each second semiconductor device of the highest one of the plurality of auto-triggered stages.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For the purpose of illustration, there are shown in the drawings certain embodiments of the present invention. In the drawings, like numerals indicate like elements throughout. It should be understood, however, that the invention is not limited to the precise arrangements, dimensions, and instruments shown. In the drawings:

(2) FIG. 1 illustrates an exemplary embodiment of a system for providing pulsed power to a load, the system comprising a power source, an energy storage device, and a semiconductor switching device, in accordance with an exemplary embodiment of the present invention;

(3) FIG. 2 illustrates an exemplary embodiment of the semiconductor switching device of FIG. 1, in accordance with an exemplary embodiment of the present invention;

(4) FIG. 3 illustrates exemplary waveforms for voltage and current provided by the energy storage device of FIG. 1 during turn-on of the semiconductor switching device, in accordance with an exemplary embodiment of the present invention; and

(5) FIG. 4 illustrates exemplary waveforms for voltage and current provided by the energy storage device of FIG. 1 during turn-off of the semiconductor switching device, in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) As described above, various conventional high voltage, high current solid state switches have been proposed. Some of the conventional high voltage, high current solid state switches comprise one or more solid state devices, such as thyristors, across which a snubber circuit is coupled. The snubber circuit facilitates turn-on of the solid state device but limits using an insulated-gate bipolar transistor (IGBT) or a metal oxide field effects transistor (MOSFET) as the solid state devices because IGBTs and MOSFETs are normally used in snubberless circuits.

(7) Other conventional high voltage, high current solid state switches use pulse transformers to drive the one or more solid state devices. Pulse transformers, however, are not desirable as they increase the inductance of the solid state switches. Further, the primary winding wire of the trigger transformer conducts the same current that the one or more solid state devices conduct. With wide pulse duration and high load current, the primary winding wire becomes very thick, and the trigger transformer becomes very big and insufficient.

(8) The conventional solid state switches which use snubber circuits or pulse transformers are disadvantageous for additional reasons. Typically, a solid state switch operates in a very narrow range of voltage, usually between V.sub.switchV.sub.switch/N.sub.levels and V.sub.switch. The value of the snubber parameters and the design of the trigger transformer must be selected to avoid auto triggering of the switch during the charging phase. Unwanted turn-on may happen if any unexpected voltage spikes in initial dv/dt occur.

(9) In all of the above-mentioned switches, pulse transformers, multiple phototransistors, and other components are required for each high power solid state device being triggered. With many semiconductors in series and in parallel, the multitude of triggering devices required become very large, thereby increasing the cost, size, and expense of the solid state switch. The size and expense may become impractical if the number of solid state devices is large. Furthermore, if pulse transformers are use, the pulse transformers must be shielded to avoid external magnetic field pick-up, which could create unwanted low-level gate pulses and, as a result, cause misfiring and destroy the solid state devices. Shielding further increases the size and expense of the solid state switch.

(10) Referring now to FIG. 1, there is illustrated a system 100 for use in a pulsed power application, in accordance with an exemplary embodiment of the present invention. The system 100 comprises a power source 110, an energy storage device 120, a load 130, and a switch 200. The power source 110 is coupled to the energy storage device 120 and to ground 140. The switch 200 is coupled to the energy storage device 120 and to ground 140. The load is coupled to the energy storage device 120 and to ground 140.

(11) During use of the system 100, the switch 200 is initially open, and the power source 110 charges the energy storage device 120. When the energy storage device 120 has been charged to a desired level, the power source 110 may be disabled or disconnected from the device 120.

(12) When power is desired to be delivered to the load 130, the switch 200 is closed, and the charge stored in the energy storage device 120 discharges into the load 130. The charging time of the energy storage device 120 may be two or more orders of magnitude greater than the discharge time thereof. Thus, the current supplied to the load via the switch 200 may be many times that of the current supplied to the energy storage device 120 during charge up by the power source 110. Exemplary embodiments of the energy storage device 120 include one or more capacitors, one or more transmission lines, or a pulse forming network. Exemplary values of the voltage and current provided by the energy storage device 120 during discharge are, respectively, tens of kilovolts and ten of kiloamperes, making the system 100 a high voltage, high current circuit.

(13) In the system 100, each of the power source 110, the switch 200, and the load 130 is connected to ground 140. It is to be understood from FIG. 1 that alternative embodiments of the system 100 are contemplated. For example, in an exemplary alternative embodiment, the positions of the switch 200 and the energy storage device 120 are switched.

(14) Illustrated in FIG. 2 is a circuit diagram for the switch 200 of FIG. 1, in accordance with an exemplary embodiment of the present invention. The switch 200 is used for switching a current I.sub.S provided by the energy storage device 120 at a voltage V.sub.S. As noted above, the current I.sub.S may be tens of kiloamperes, and the voltage V.sub.S may be tens of kilovolts.

(15) The switch 200 comprises a plurality of levels or stages, respectively designated as 210.sub.1, 210.sub.2, . . . , 210.sub.n, connected in series. In the exemplary embodiment of the switch 200 illustrated in FIG. 2, there are n stages 210.sub.1 through 210.sub.n. By using a plurality of stages 210.sub.1 through 210.sub.n, the switch 200 divides the source voltage V.sub.S over n stages so that V.sub.S/n is less than the maximum permissible voltage across any of the stages 210.sub.1 through 210.sub.n. Thus, the switch 200 has a higher voltage hold-off capability than it would have had it had only one stage, and each stage is protected from overvoltage.

(16) Each stage comprises a plurality of solid state semiconductor switches or devices, respectively designated as S.sub.x,y, connected in parallel, where x refers to any of stages 210.sub.1 through 210.sub.n and y refers to the semiconductor devices in each stage. In the exemplary embodiment of the switch 200 illustrated in FIG. 2, the first stage 210.sub.1 comprises m semiconductor devices S.sub.1,1 through S.sub.1,m connected in parallel (herein, S.sub.1 is used as shorthand to refer to the plurality of semiconductor devices S.sub.1,1 through S.sub.1,m in the stage 210.sub.1); the second stage 210.sub.2 comprises m semiconductor devices S.sub.2,1 through S.sub.2,m connected in parallel (herein, S.sub.2 is used as shorthand to refer to the plurality of semiconductor devices S.sub.2,1 through S.sub.2,m in the stage 210.sub.1); and the nth stage 210.sub.n comprises m semiconductor devices S.sub.n,1 through S.sub.n,m connected in parallel (herein, S.sub.n is used as shorthand to refer to the plurality of semiconductor devices S.sub.n,1 through S.sub.n,m in the stage 210.sub.n). By using a plurality of m semiconductor devices in each stage, the switch 200 divides the input current I.sub.S by m. Thus, each stage 210.sub.1 through 210.sub.n and, specifically, each semiconductor device S.sub.x,y is protected from overcurrent.

(17) In the exemplary embodiment illustrated in FIG. 2, the first stage 210.sub.1 is a control-triggered stage used to control the turn-on and turn-off of the stages 210.sub.2 through 210.sub.n and thereby of the switch 200. FIG. 2 illustrates that the control-triggered stage 210.sub.1 is the first or bottommost stage and connected to ground 140. It is to be understood that the control-triggered stage 210.sub.1 need not be so located and could be positioned in the place of any of the other stages 210.sub.2 through 210.sub.n in the switch 200.

(18) The control-triggered stage 210.sub.1 comprises the semiconductor devices S.sub.1,1 through S.sub.1,m having respective control inputs CI.sub.1,1 through CI.sub.1,m, power inputs PI.sub.1,1 through PI.sub.1,m and power outputs PO.sub.1,1 through PO.sub.1,m. The power outputs PO.sub.1,1 through PO.sub.1,m are connected to an output 211.sub.1 of the control-triggered stage 210.sub.1 which is at ground 140. The control-triggered stage 210.sub.1 further comprises a capacitor C.sub.1, a turn-off circuit 215, and a suppressor Z.sub.1. A first side or end of the suppressor Z.sub.1 is connected to the output 211.sub.1, as is a first side or end of the capacitor C.sub.1 and a first end 215A of the turn-off circuit 215. A second side or end of the capacitor C.sub.1 is connected to the control inputs CI.sub.2,1 through CI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m of the second stage. A second side or end of the suppressor Z.sub.1 is connected to the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m, as is a second end 215B of the turn-off circuit 215.

(19) The control-triggered stage 210.sub.1 further comprises a breakover switch BOS.sub.1, a second side or end of which is coupled to the second side of the suppressor Z.sub.1. A first side or end of the breakover switch BOS.sub.1 is coupled to the power inputs PI.sub.1,1 through PI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m via a resistor R.sub.1. The power inputs PI.sub.1,1 through PI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m are connected to an input 212.sub.1 of the control-triggered stage 210.sub.1. A switch SW.sub.1 is disposed in the control-triggered stage 210.sub.1 across the breakover switch BOS.sub.1.

(20) In an exemplary embodiment, the suppressor Z.sub.1 is a Zener diode, the breakover switch BOS is a breakover diode, the switch SW.sub.1 is a MOSFET, and the turn-off circuit 215 is a MOSFET. The first side of the Zener diode Z.sub.1, its anode, is connected to the output 211.sub.1 of the stage 210.sub.1, and the second side of the Zener diode Z.sub.1, its cathode, is connected to the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m. The first side of the breakover switch BOS.sub.1, its anode, is connected to the resistor R.sub.1, and the second side of the breakover switch BOS.sub.1, its cathode, is connected to the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m.

(21) In this exemplary embodiment, the collector of the MOSFET SW.sub.1 is connected to the anode of the breakover diode BOS.sub.1, and the emitter is connected to the cathode of the breakover diode BOS.sub.1. The gate of the MOSFET SW.sub.1 serves as a control input to selectively turn on the switch 200. The collector of the MOSFET 215 is connected to the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m, and the emitter is connected to the output 211.sub.1 of the control-triggered stage 210.sub.1. The gate of the MOSFET 215 serves as a control input to selectively turn off the switch 200. The control inputs into the MOSFETS SW.sub.1 and 215 are low-power inputs, which allows for low-power control of the switch 200.

(22) Still referring to FIG. 2, the second through nth stages, 210.sub.2 through 210.sub.n, are auto-triggered stages triggered by the control-triggered stage 210.sub.1. The stages 210.sub.2 through 210.sub.n are constructed similarly to the stage 210.sub.1 but differ in that they do not include the switch SW.sub.1 or the turn-off circuit 215.

(23) The second stage 210.sub.2 comprises the semiconductor devices S.sub.2,1 through S.sub.2,m having respective control inputs CI.sub.2,1 through CI.sub.2,m, power inputs PI.sub.2,1 through PI.sub.2,m, and power outputs PO.sub.2,1 through PO.sub.2,m. The second stage 210.sub.2 further comprises a capacitor C.sub.2, a suppressor Z.sub.2, a breakover switch BOS.sub.2, and a resistor R.sub.2. The power outputs PO.sub.2,1 through PO.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m are connected to an output 212.sub.1 of the second stage 210.sub.2. The output 211.sub.2 of the second stage 210.sub.2 is the input 212.sub.1 of the first stage 210.sub.1. Thus, the second stage 210.sub.2 is connected in series to the first stage 210.sub.1.

(24) A first side or end of the suppressor Z.sub.2 is connected to the output 211.sub.2 of the second stage 210.sub.2, as is a first side or end of the capacitor C.sub.2. A second side or end of the suppressor Z.sub.2 is connected to the control inputs CI.sub.2,1 through CI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m and to a second side or end of the breakover switch BOS.sub.2. A first side or end of the breakover switch BOS.sub.2 is coupled to the power inputs PI.sub.2,1 through PI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m via the resistor R.sub.2. A second side or end of the capacitor C.sub.2 is connected to the control input of the semiconductor devices of the next higher stage. The power inputs PI.sub.2,1 through PI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m are connected to the input 212.sub.2 of the auto-triggered stage 210.sub.2, which input 212.sub.2 is an output 211.sub.3 of the next higher stage.

(25) Each next higher stage through to stage n1 is configured the same as the stage 210.sub.2 (stage 2). The last stage, stage 201.sub.n comprises the semiconductor devices S.sub.n,1 through S.sub.n,m having respective control inputs CI.sub.n,1 through CI.sub.n,m, power inputs PI.sub.n,1 through PI.sub.n,m, and power outputs PO.sub.n,1 through PO.sub.n,m. The stage 201 further comprises a capacitor C.sub.n, a suppressor Z.sub.n, a breakover switch BOS.sub.n, and a resistor R.sub.n. These components are connected in the same manner as those in the auto-triggered stage 210.sub.2, except that the second side or end of the capacitor C.sub.n is not connected to the control input of the semiconductor devices of the next higher stage as there is no next higher stage. Rather, the second side or end of the capacitor C.sub.n is connected to the input 212.sub.n of the auto-triggered stage 210.sub.n. This input 212.sub.n is connected to an input 220 of the switch 200. As with the other auto-triggered stages, the output 211.sub.n of the auto-triggered stage 201.sub.n is connected to the input of the next lowest stage, in this case an input 212.sub.n-1 of the auto-triggered stage 210.sub.n-1 (not illustrated).

(26) In an exemplary embodiment, for each of the stages 210.sub.2 through 210.sub.n, the suppressors Z.sub.2 through Z.sub.n are Zener diodes, and the breakover switches BOS.sub.2 through BOS.sub.n are breakover diodes. The first side of each of the Zener diodes Z.sub.2 through Z.sub.n, its anode, is connected to the respective output 211.sub.2 through 211.sub.n of the respective stage 210.sub.2 through 210.sub.n, and the second side of each of the Zener diodes Z.sub.2 through Z.sub.n, its cathode, is connected to the respective control inputs of the respective semiconductor devices S.sub.2 through S.sub.n. The first side of each of the breakover diodes BOS.sub.2 through BOS.sub.n, its anode, is connected to the respective resistor R.sub.2 through R.sub.n, and the second side of each of the breakover diodes BOS.sub.2 through BOS.sub.n, its cathode, is connected to the respective control inputs of the respective semiconductor devices S.sub.2 through S.sub.n.

(27) As further shown in FIG. 2, the breakover switches BOS.sub.1 through BOS.sub.n are identical, as are the respective components among the stages 210.sub.1 through 210.sub.n. The breakover switches BOS.sub.1 through BOS.sub.n have a breakover voltage equal to V.sub.S/n+V, where V.sub.S is the maximum voltage seen across the switch 200, n is the number of stages, and V is a minimum acceptable difference in blocking voltage between a stage and its breakover switches. The breakover voltage of each of the breakover switches BOS.sub.1 through BOS.sub.n is desirably V greater than V.sub.S/n, so that the switch 200 does not automatically turn on when V.sub.S is applied at its input 220. For example, if the switch 200 comprises 5 levels, and V.sub.S is 5,000V, the maximum voltage across each stage is 1,000V, and each breakover switches BOS.sub.1 through BOS.sub.n desirably has a breakover voltage greater than 1,000V. For example, the breakover voltage may be 1,007V so that V=7V.

(28) Turn-on and turn-off of the control-triggered stage 210.sub.1 is now described. In its initial state, the switch 200 is open and a voltage V.sub.S is present at its input 220 by the energy storage device 120. The voltage drop across each stage is equal to V.sub.S/n, and each capacitor C.sub.1 through C.sub.n is fully charged. Each breakover diode BOS.sub.1 through BOS.sub.n desirably has a breakover voltage greater than V.sub.S/n but less than V.sub.S(n1), so that once one stage turns on, all stages turn on. The voltage drop V.sub.S/n across each stage is distributed over the suppressor, the breakover switch, and the resistor of each respective stage.

(29) Turn-on of the control-triggered stage 210.sub.1 and the auto-triggered stages 210.sub.2 through 210.sub.n is now described. In the description below, the voltage across each stage 210.sub.1 through 210.sub.n is, respectively, V.sub.S1 through V.sub.Sn, each of which is equal to V.sub.S/n when the switch 200 is off. Current I.sub.S is then zero because the switch 200 is off because the stages 210.sub.1 through 210.sub.n are in a non-conducting (off) state. The voltage V.sub.S1 through V.sub.Sn across each stage 210.sub.1 through 210.sub.n when the switch 200 is turned on is, respectively V.sub.Saturation-1 through V.sub.Saturation-n, the voltages across each of the semiconductor devices S.sub.1 through S.sub.n while in saturation. Current I.sub.S is then non-zero because the switch 200 is on because all of the stages 210.sub.1 through 210.sub.n are conducting, i.e., in an on state. The switch 200 is not turned on until each stage 210.sub.1 through 210.sub.n is conducting (turned on).

(30) Turn-on of the control-triggered stage 210.sub.1 begins with each of the semiconductor devices S.sub.1,1 through S.sub.1,m in a non-conducting (off) state such that the stage 210.sub.1 is in a non-conducting (off) state. The control-triggered stage 210.sub.1 operates as follows during turn-on:

(31) a) In response to a control signal, for example supplied to the switch SW.sub.1, the switch SW.sub.1 across the breakover switch BOS.sub.1 is closed, thereby shorting the first side of the breakover switch BOS.sub.1 to its second side.

(32) b) The voltage drop V.sub.S1 across the stage 210.sub.1 instantaneously decreases slightly and is redistributed over the resistor R.sub.1 and the suppressor Z.sub.1.

(33) c) The voltage at the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m instantaneously increases, i.e., a positive voltage pulse is provided to control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m.

(34) d) The positive voltage pulse at the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m turns on the semiconductor devices S.sub.1,1 through S.sub.1,m and places them into saturation. The control-triggered stage 210.sub.1 is thereby turned on.

(35) Because the semiconductor devices S.sub.1,1 through S.sub.1,m turn on and go into saturation, the voltage at the power inputs PI.sub.1,1 through PI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m decreases, thereby pulling down the voltage at the input 212.sub.1 of the control-triggered stage 210.sub.1 and at the output 211.sub.2 of the auto-triggered stage 210.sub.2. The voltage V.sub.S1 across the stage 210.sub.1 is V.sub.Saturation-1 after turn-on. Because the remaining stages 210.sub.2 through 210.sub.n are still in the off state and the total voltage V.sub.S across the switch 200 remains the same, the voltages V.sub.S2 through V.sub.Sn across respective stages 210.sub.2 through 210.sub.n increase after the switch SW.sub.1 closes and the semiconductor devices S.sub.1,1 through S.sub.1,m turn on.

(36) After the stage 210.sub.1 is turned on, the voltage V.sub.S2 through V.sub.Sn across each respective stage 210.sub.2 through 210.sub.n is (V.sub.SV.sub.Saturation-1)(n1). In other words, the voltage V.sub.S2 through V.sub.Sn across each respective stage 210.sub.2 through 210.sub.n increases to (V.sub.SV.sub.Saturation-1)(n1), where (V.sub.SV.sub.Saturation-1)(n1)>V.sub.S/n because V.sub.Saturation-1<V.sub.S/n. This increase in voltage V.sub.S2 through V.sub.Sn across each respective stage 210.sub.2 through 210.sub.n causes the stages 210.sub.2 through 210.sub.n to turn on by one of two ways: via turn-on of the breakover switches BOS.sub.2 through BOS.sub.n or via the capacitors C.sub.2 through C.sub.n discharging into the control inputs of their respective semiconductor devices.

(37) Following turn-on of the control-triggered stage 210.sub.1, if the voltage V.sub.S2 through V.sub.Sn across each of the respective stages 210.sub.2 through 210.sub.n causes the voltage V.sub.BOS2 through V.sub.BOSn across each respective breakover switch BOS.sub.2 through BOS.sub.n to exceed the breakover voltage (V.sub.S/n+V) of each of the breakover switches BOS.sub.2 through BOS.sub.n, turn-on of the auto-triggered stages 210.sub.2 through 210.sub.n proceeds as follows (the first auto turn-on procedure):

(38) a) Each of the breakover switches BOS.sub.2 through BOS.sub.n begins conducting at the same time.

(39) b) V.sub.BOS2 through V.sub.BOSn decreases because breakover switches BOS.sub.2 through BOS.sub.n begin conducting.

(40) c) The voltage drops V.sub.S2 through V.sub.Sn across the respective stages 210.sub.2 through 210.sub.n instantaneously redistribute over the respective resistors R.sub.2 through R.sub.n and the suppressors Z.sub.2 through Z.sub.n.

(41) d) The voltages at the control inputs of the semiconductor devices S.sub.2 through S.sub.n instantaneously increase, i.e., positive voltage pulses are provided to control inputs of the semiconductor devices S.sub.2 through S.sub.n.

(42) e) The positive voltage pulses at the control inputs CI.sub.2,1 through CI.sub.2,m of the semiconductor devices S.sub.2 through S.sub.n turn on the semiconductor devices S.sub.2 through S.sub.n and place them into saturation.

(43) f) Because the semiconductor devices S.sub.2 through S.sub.n turn on and go into saturation, the voltages at the power inputs of the semiconductor devices S.sub.2 through S.sub.n decrease, thereby pulling down the respective voltages at the respective inputs 212.sub.2 through 212.sub.n of the respective stages 210.sub.2 through 210.sub.n. The voltages V.sub.S2 through V.sub.Sn across the respective stages 210.sub.1 through 210.sub.n are, respectively, V.sub.Saturation-2 through V.sub.Saturation-n after turn-on.

(44) g) The voltage V.sub.S across the switch 200 decreases to V.sub.Saturation-1+V.sub.Saturation-2+ . . . +V.sub.Saturation-n and I.sub.S increases from zero.

(45) Following turn-on of the control-triggered stage 210.sub.1, if the voltage V.sub.S2 through V.sub.Sn across each of the respective stages 210.sub.2 through 210.sub.n does not cause the voltage V.sub.BOS2 through V.sub.Bosn across each respective breakover switch BOS.sub.2 through BOS.sub.n to exceed the breakover voltage (V.sub.S/n+V) of each of the breakover switches BOS.sub.2 through BOS.sub.n, turn-on of the auto-triggered stage 210.sub.2 proceeds as follows (the second auto turn-on procedure):

(46) a) After the control-input stage 210.sub.1 turns on, the voltage V.sub.S1 decreases to V.sub.Saturation-1 and the voltages V.sub.S2 through V.sub.Sn across the remaining stages increase to (V.sub.SV.sub.Saturation-1)(n1).

(47) b) The voltages across the resistor R.sub.2, the breakover switch BOS.sub.2, and the suppressor Z.sub.2 increase.

(48) c) The capacitor C.sub.2 discharges into the control inputs CI.sub.2,1 through CI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m.

(49) d) The semiconductor devices S.sub.2,1 through S.sub.2,m turn on and go into saturation. The auto-triggered stage 210.sub.2 is thereby turned on.

(50) Because the semiconductor devices S.sub.2,1 through S.sub.2,m turn on and go into saturation, the voltage at the power inputs PI.sub.2,1 through PI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m, decrease, thereby pulling down the voltage at the input 212.sub.2 of the auto-triggered stage 210.sub.2 and at the output 211.sub.3 of the auto-triggered stage 210.sub.3. The voltage V.sub.S2 across the stage 210.sub.2 is V.sub.Saturation-2 after turn-on. Because the remaining stages 210.sub.3 through 210.sub.n are still in the off state and the total voltage V.sub.S across the switch 200 remains the same, the voltages V.sub.S3 through V.sub.Sn across respective stages 210.sub.3 through 210.sub.n increase after the auto-triggered stage 210.sub.2 turns on.

(51) After the auto-triggered stage 210.sub.2 turns on according to the second auto turn-on procedure, the capacitor C.sub.3 begins to discharge into the control inputs CI.sub.3,1 through CI.sub.3,m of the semiconductor devices S.sub.3,1 through S.sub.3,m. The auto-triggered stages 210.sub.3 through 210.sub.n start to cascade on according to the second auto turn-on procedure. However, turn-on of any of the auto-triggered stages 210.sub.3 through 210.sub.n progresses according to the first turn-on procedure if the voltages across the remaining breakover switches are exceeded. Thus, cascading turn-on may shift to simultaneous turn-on once the breakover voltages of the remaining breakover switches are exceeded.

(52) The suppressors Z.sub.1 through Z.sub.n provide protection for the control-input-to-power-output junctions of the semiconductor devices S.sub.1 through S.sub.n against overcurrent and overvoltage during switching of the switch 200 on and off. The breakover switches BOS.sub.1 through BOS.sub.n also provide protection for each of the levels 210.sub.1 through 210.sub.n from overvoltage when the switch 200 is off and while it is being turned on. Protection from overvoltage during turn-on is desirable as the voltages across levels that are not on increase as other levels are turned on. Thus, the switch 200 is able to handle voltages V.sub.S in the level of 10 s of kilovolts.

(53) As noted above, the semiconductor devices S.sub.1 through S.sub.n are desirably distributed m per stage, although differing numbers of semiconductor devices per stage are contemplated. Thus, the current I.sub.S is divided across m semiconductors in each of stages 210.sub.1 through 210.sub.n. Accordingly, the switch 200 is able to handle currents I.sub.S in the level of 10 s of kiloamps.

(54) Turn-off of the switch 200 proceeds as follows:

(55) a) In response to a control signal, for example supplied to the turn-off circuit 215, the turn-off circuit 215 provides a negative-voltage signal to the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m, for example by pulling the control inputs to ground 140.

(56) b) The negative voltage pulse at the control inputs CI.sub.1,1 through CI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m turns of the semiconductor devices S.sub.1,1 through S.sub.1,m.

(57) c) Because the semiconductor devices S.sub.1,1 through S.sub.1,m turn off, the voltage at the power inputs PI.sub.1,1 through PI.sub.1,m of the semiconductor devices S.sub.1,1 through S.sub.1,m increases, thereby causing the voltage at the input 212.sub.1 of the control-triggered stage 210.sub.1 and at the output 211.sub.2 of the auto-triggered stage 210.sub.2 to rise. The voltage V.sub.S1 across the stage 210.sub.1 increases, and the voltage V.sub.S2 across the stage 210.sub.2 decreases.

(58) d) Negative current from the control inputs CI.sub.2,1 through CI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m charges the capacitor C.sub.1 providing a negative-voltage signal to the control inputs CI.sub.2,1 through CI.sub.2,m of the semiconductor devices S.sub.2,1 through S.sub.2,m.

(59) e) The semiconductor devices S.sub.2,1 through S.sub.2,m turn off.

(60) f) Steps (c) through (e) repeat for each next higher stage, so that the stages 210.sub.3 through 210.sub.n cascade off until all of the stages of the switch 200 are turned off.

(61) Turn-on and turn-off of the switch 200 does not require the use of a pulse transformer for each stage 210.sub.1 through 210.sub.n. As noted above, pulse transformers are bulky and require isolation from one another, increasing the size and complexity of the switch. Further, pulse transformers have non-negligible inductance, which is not desirable for high voltage, high current switches. Finally, pulse transformers provide pulses of short time periods, which may not be long enough to turn on the semiconductor devices S.sub.1 through S.sub.n.

(62) By using breakover switches BOS.sub.1 through BOS.sub.n and capacitors connecting the output of one level to the control inputs of the semiconductor devices of another lover, the switch 200 provides for very fast turn-on and turn-off and avoids the use of pulse transformers. Inductance in the switch 200 is reduced and the control inputs of the semiconductor devices S.sub.1 through S.sub.n may be kept at a negative voltage for as long as is needed to turn them on. For a six level device, turn-on time may be 200 nanoseconds.

(63) Various types of semiconductor devices are contemplated for the semiconductor devices S.sub.1 through S.sub.n. For example, in an exemplary embodiment, the semiconductor devices S.sub.1 through S.sub.n are IGBTs. In another embodiment, they are MOSFETs. In yet another embodiment, they are SCRs. In still another embodiment, they are gate turn-off thyristors (GTOs). In a further embodiment, they are MOS controlled thyristors or light-controlled thyristors. It is to be understood that the anodes or collectors of such devices are the power inputs, as that term is used herein, the cathodes or emitters of such devices are the power outputs, as that term is used herein, and the gates of such devices are the control inputs, as that term is used herein.

(64) The semiconductor devices S.sub.1 through S.sub.n desirably have low output impedances when on. For example, in an exemplary embodiment, the semiconductor devices S.sub.1 through S.sub.n desirably have output impedances in the milliohm region, and, when off, they desirably have output impedances greater than 5,000 ohms. The input impedances of the semiconductor devices S.sub.1 through S.sub.n depend on the type of semiconductor device employed. If the semiconductor devices S.sub.1 through S.sub.n are MOSFETs, then the input impedances are in the megohm region. If they are thyristors, then the input impedances are in the milliohm region.

(65) In the embodiments of the switch 200 described herein, the switch 200 may include the suppressors Z.sub.1 through Z.sub.n to protect the semiconductor devices S.sub.1 through S.sub.n against overcurrent and overvoltage during turn-on and turn-off. In an exemplary embodiment, the semiconductor devices S.sub.1 through S.sub.n include gate-to-cathode junctions, and the suppressors Z.sub.1 through Z.sub.n provide protection for these gate-to-cathode junctions against overcurrent and overvoltage during switching of the switch 200 on and off. It is to be understood that other embodiments of the switch 200 are contemplated in which the suppressors Z.sub.1 through Z.sub.n are not included.

(66) It is further to be understood that the breakover switches BOS.sub.1 through BOS.sub.n also provide protection for each of the levels 210.sub.1 through 210.sub.n from overvoltage when the switch 200 is off and while it is being turned on. Protection from overvoltage during turn-on is desirable as the voltages across levels that are not on increase as other levels are turned on. Thus, the switch 200 is able to handle voltages V.sub.S in the level of 10 s of kilovolts.

(67) In an exemplary embodiment, the energy storage device 120 is a capacitor. FIG. 3 illustrates the waves for the voltage V.sub.S across an exemplary embodiment of the energy storage device 120 and the current I.sub.S supplied by the exemplary energy storage device 120 as an exemplary embodiment of the switch 200 is turned on, in accordance with an exemplary embodiment of the present invention. For the example illustrated in FIG. 3, the energy storage device 120 is a 0.15 F capacitor.

(68) Referring to FIG. 3, prior to the exemplary switch 200 closing, V.sub.S is 4.92 kV and I.sub.S is 0 A. At time t.sub.0, corresponding to 0 seconds, a command signal is sent to the switch SW.sub.1 to close, beginning the turn-on process of the exemplary switch 200. At time t.sub.1, corresponding to 40 ns, the exemplary switch 200 is fully turned on, and the exemplary energy storage device 120 begins discharging. I.sub.S increases to a maximum of 2.04 kA at time t.sub.2, corresponding to 48 ns. V.sub.S and I.sub.S then oscillate until settling at zero.

(69) FIG. 4 illustrates the waves for the voltage V.sub.S across another exemplary embodiment of the energy storage device 120 and the current I.sub.S supplied by the exemplary energy storage device 120 as another exemplary embodiment of the switch 200 is turned on and then turned off, in accordance with an exemplary embodiment of the present invention. In FIG. 4, prior to the exemplary switch 200 closing, V.sub.S is about 1.4 kV and I.sub.S is 0 A. At time t.sub.1, the exemplary switch 200 is fully turned on, and the exemplary energy storage device 120 begins discharging. I.sub.S increases to a maximum of 100 A at time t.sub.2, at which time the exemplary switch 200 is provided with a turn-off signal via the turn-off circuit 215. The exemplary switch 200 turns off, as described above. As the exemplary switch 200 turns off, I.sub.S decreases, and V.sub.S spikes to 5.4 kV at time t.sub.3 before returning to 1.4 kV when the exemplary switch 200 is fully closed.

(70) These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it is to be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is to be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention.