Circuits, methods, and systems with optimized operation of double-base bipolar junction transistors

Abstract

The present application teaches, inter alia, methods and circuits for operating a B-TRAN (double-base bidirectional bipolar junction transistor). Exemplary base drive circuits provide high-impedance drive to the base contact region on the side of the device instantaneously operating as the collector. (The B TRAN is controlled by applied voltage rather than applied current.) Current signals operate preferred implementations of drive circuits to provide diode-mode turn-on and pre-turnoff operation, as well as a hard ON state with low voltage drop (the transistor-ON state). In some preferred embodiments, self-synchronizing rectifier circuits provide adjustable low voltage for gate drive circuits. In some preferred embodiments, the base drive voltage used to drive the c-base region (on the collector side) is varied while base current at that terminal is monitored, so no more base current than necessary is applied. This solves the difficult challenge of optimizing base drive in a B-TRAN.

Claims

1. A method for power switching, comprising: driving a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations in proximity to the respective emitter/collector regions, by in a transistor-ON mode, using one of a pair of first drive circuits to supply an adjustable voltage, relative to a collector voltage, to the one of the base contact regions which is closest to whichever of the emitter/collector regions is instantaneously acting as the collector, as defined by externally applied voltage polarity, and adjusting the voltage to thereby minimalize voltage drop across the transistor; and in a diode-ON mode, using one of a pair of second drive circuits to clamp one of the base contact regions to the respectively nearest one of the emitter/collector regions; whereby a diode drop is imposed on current passing through the device; and in a preturnoff mode, using both of the pair of second drive circuits to clamp each of the base contact regions to the respectively nearest one of the emitter/collector regions.

2. A method for power switching, comprising: driving a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations in proximity to the respective emitter/collector regions, by in a transistor-ON mode, using one of a pair of first drive circuits to supply an adjustable voltage, relative to a collector voltage, to the one of the base contact regions which is closest to whichever of the emitter/collector regions is instantaneously acting as the collector, as defined by externally applied voltage polarity, and adjusting the voltage to thereby minimalize voltage drop across the transistor; and in a diode-ON mode, using one of a pair of second drive circuits to clamp one of the base contact regions to the respectively nearest one of the emitter/collector regions; whereby a diode drop is imposed on current passing through the device.

3. A method for power switching, comprising: driving a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations in proximity to the respective emitter/collector regions, by in a transistor-ON mode, using one of a pair of first drive circuits to supply an adjustable voltage, relative to a collector voltage, to the one of the base contact regions which is closest to whichever of the emitter/collector regions is instantaneously acting as the collector, as defined by externally applied voltage polarity, and adjusting the voltage to thereby minimalize voltage drop across the transistor.

4. The method of claim 1, wherein the first conductivity type is n-type.

5. The method of claim 1, further comprising two additional drive circuits, respectively connected in parallel with the first drive circuits, and each comprising a Schottky diode in series with a normally-off switch.

6. The method of claim 2, wherein the first conductivity type is n-type.

7. The method of claim 2, further comprising two additional drive circuits, respectively connected in parallel with the first drive circuits, and each comprising a Schottky diode in series with a normally-off switch.

8. The method of claim 3, wherein the first conductivity type is n-type.

9. The method of claim 3, further comprising two additional drive circuits, respectively connected in parallel with the first drive circuits, and each comprising a Schottky diode in series with a normally-off switch.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments and which are incorporated in the specification hereof by reference, wherein:

(2) FIG. 1A shows one exemplary embodiment of a base drive circuit according to the present inventions.

(3) FIG. 1B shows one sample embodiment of a base drive circuit according to the present inventions.

(4) FIG. 1C shows exemplary waveforms during operation of the embodiment of FIG. 1A.

(5) FIG. 2 shows one sample embodiment of a variable-voltage self-synchronous rectifier.

(6) FIGS. 3A, 3B, 3C, 3D, 3E, and 3F show sample equivalent circuits for an exemplary B-TRAN in various stages of operation.

(7) FIG. 4 shows a partial device model according to one sample embodiment of the present inventions.

(8) FIG. 5 shows how the base current I.sub.CB on the c-base varies with c-base bias V.sub.CB under operating conditions.

(9) FIG. 6 shows one sample embodiment of a B-TRAN.

DETAILED DESCRIPTION OF SAMPLE EMBODIMENTS

(10) The numerous innovative teachings of the present application will be described with particular reference to presently preferred embodiments (by way of example, and not of limitation). The present application describes several inventions, and none of the statements below should be taken as limiting the claims generally.

(11) Published US application US 2014/0375287 A1 (which is hereby incorporated by reference) disclosed (inter alia) novel bidirectional bipolar transistors known as B-TRANs. As discussed above, the operating cycle of a B-TRAN includes, in succession, a diode turn-on (or diode-ON) state, a low-V.sub.ce or transistor-ON state, a pre-turnoff state, and an active OFF state. Preferably the B-TRAN also has a passive-OFF state, which keeps its blocking voltage high when normal operation is not happening.

(12) The present application describes improvements in the operation of these devices. One area of improvement has been in the fully ON state (the transistor-ON state). An important advantage of the B-TRAN is its low voltage drop V.sub.CE when fully on. However, it is desirable to maintain a high value for device gain. It is also desirable to keep the device's switching speed and reverse recovery fast. These improvements have been achieved by a better understanding of the device's behavior in the fully ON state.

(13) For simplicity, the following description will assume that an NPN B-TRAN is being used. In this case the physical base is provided by the bulk of the p-type semiconductor die, and the base contact regions are p-type (with p+ contact doping). The two emitter/collector regions are n+, and whichever emitter/collector region sees a more positive external voltage will be the collector side. (The principles of operation are the same for PNP B-TRAN devices, with opposite polarity; in such devices the side which sees the more negative external voltage will be the collector side.)

(14) The base contact region on the collector side will be referred to as the c-base, and the other base contact region (on the emitter side) will be referred to as the e-base. These base contact regions are not physically different, but behave very differently when an externally applied voltage is present.

(15) The fully ON state (transistor-on) is reached by applying elevated drive voltage to the c-base. This provides a low on-state voltage drop with good gain, without reducing the breakdown voltage. Device gain is measured as beta, i.e. the ratio of emitter current to base current, but the behavior of the transistor under c-base drive is very different from that of other power bipolar junction transistors.

(16) FIG. 4 shows a partial device model, with a table of values for c-base bias V.sub.CB and corresponding voltage drop V.sub.CE across the external terminals. In this figure, the collector/emitter terminal at the top of the figure is assumed to be the collector (i.e. connected to the more positive external voltage), so the base contact which is shown connected to the variable voltage source is the c-base.

(17) FIG. 5 shows how the base current I.sub.CB on the c-base varies with c-base bias V.sub.CB under operating conditions. It should be noted that current I.sub.CB is nearly flat over a wide range of values for V.sub.CB.

(18) The combination of FIGS. 4 and 5 shows important features of operation. The device's voltage drop V.sub.CE will come down to its desired low value when c-base bias V.sub.CB gets up to its optimal operating point (defined as described below), but the current on the c-base stays nearly constant as c-base bias is increased to this point. To put this differently, the c-base terminal has a very high impedance until its bias is increased to the point where the impedance drops. At this point, the device's series resistance is low, as desired.

(19) In the transistor-on state, the e-base is essentially at a constant voltageit varies only about 0.1 V from a low drive to a high drive condition. The c-base, in contrast, is a nearly constant current drive, even as the voltage is varied from 0 V above the collector to about 0.6V above the collector. Instead of the c-base current changing with c-base voltage, V.sub.CE changes. At a c-base bias of 0V (c-base shorted to collector), there is a certain gain that depends on the emitter current density, and Vce is nominally 0.9 V over a large range of current density. Raising the c-base bias to 0.1 V above the collector does not change the gain, but it lowers V.sub.CE by nominally 0.1 V. Raising c-base bias to 0.6V drops Vce to about 0.2 or 0.3 V. Thus, when driving the c-base, a voltage source is advantageously used, as in the sample embodiment of FIG. 1A, not a current source.

(20) This is a very significant difference from the way BJTs are normally driven, which is from a current source into the base.

(21) The differential impedance, in terms of di/dv, of the c-base itself is high. The c-base drive current changes very little with c-base to collector voltage V.sub.CB over a wide range of values, until V.sub.CB gets close to forward biasing the collector/base junction (over 0.6V at 25C in silicon). That is why a voltage-source-type drive is needed. C-base current I.sub.CB changes with emitter current, increasing with increased emitter current even when V.sub.CB remains constant, but not much with changing V.sub.CB (up until a value of V.sub.CB where I.sub.CB begins to increase undesirably).

(22) The impedance of the e-base is very low, as it keeps a nearly constant voltage while the c-base current is varied.

(23) FIG. 1A shows a first example of a complete switch 100, including an NPN B-TRAN transistor 106 as well as diode-mode drive circuitry 110 and transistor-mode drive circuitry 130. The half at the top of the page will be assumed to be the collector side, i.e. to be seeing the positive side of the applied voltage.

(24) FIG. 1C shows an example of waveforms during the operation of the circuit of FIG. 1A. Initially, in the diode-on phase, the gate of NMOS S12 is low, and the gate of NMOS S13 is high. This enables the diode-turn-on mode described e.g. in published application US2014-0375287. NMOS transistors S22 and S23 remain off. During this time the current I.sub.T across the emitter/collector terminals turns on quickly, and voltage V.sub.CE across the emitter/collector terminals, which is assumed to have been ramping up under external drive, is brought down to approximately a diode drop (plus some ohmic drop, for a total of about 0.8V in silicon).

(25) Next, in the transistor-on phase, S12 is turned on while S13 is turned off. S12 is connected to a variable-voltage source 190, which is derived from the collector terminal as described below. This voltage at the c-base drives the transistor into its low-voltage-drop state, where the voltage drop V.sub.CE is 0.3V or less. This phase continues for as long as drive current is needed.

(26) In the pre-off phase, switch S12 is turned off, and switches S13 and S23 are both turned on. This immediately bumps the voltage drop up to a diode drop, but the device current I.sub.T remains at a level determined by emitter current density. If this current is not enough to clamp the voltage of the external load, the applied voltage will increase as shown.

(27) Finally, in the active-off phase, switch S13 is turned off, but switch S23 remains on. This cuts off device current I.sub.T, and the voltage on the device goes up to whatever is dictated by the external connections.

(28) Note that switch S23 was never turned on during this sequence. This switch would be turned on to achieve the transistor-on mode when the external voltage has reversed (so that the emitter/collector terminal node at the top of the page is then the emitter side rather than the collector side).

(29) FIG. 2 shows one sample embodiment of a variable-voltage self-synchronous rectifier, which can be advantageously used in the sample embodiment of FIG. 1A. A variable-voltage supply 210 (which in the example shown is a simple buck converter) provides an adjustable supply voltage to oscillator 220. Oscillator 220 drives a first winding 232 of a transformer 230. A first secondary winding 234 provides complementary outputs A and B, which are synchronous with the transitions of oscillator 220, plus the phase shift due to coupling through the transformer 230. Another secondary winding 236 provides a higher-current and lower-voltage waveform, corresponding to the output of oscillator 220 (with voltage shifted). The output of the two secondary windings is synchronous, so that the control signals A and B can be used to drive the synchronous inverter 240. The control signals A and B are preferably scaled to provide appropriate gate voltages for the four transistors of the synchronous inverter, e.g. 5V. Thus a 24V DC supply has been efficiently translated into a very-low-voltage DC output whose voltage can be varied. By changing the set-point voltage of the buck converter, the voltage applied to the c-base terminal can be adjusted.

(30) Returning now to FIG. 5, the bias on the c-base terminal is optimized by adjusting it to the point where base current is no longer constant.

(31) Unlike the e-base contact, the c-base contact is high impedance, meaning that the current I.sub.CB going into the c-base is nominally constant, when the device is on, until V.sub.CB gets close to forward biasing the base-collector junction. At that point, V.sub.CE is well below a diode drop (nominally 0.2V), and I.sub.CB starts increasing rapidly with small additional increases in V.sub.CB, as shown below.

(32) The present application teaches, among other concepts, that V.sub.CB is dynamically varied, or dithered, to find the Optimal Operating Point. The Optimal Operating Point should fall where I.sub.CB has increased some small but measurable amount above the flat portion of the I.sub.CB/V.sub.CB curve. This is done by finding a V.sub.CB where the slope of the curve is some optimal value.

(33) In one sample embodiment, the optimal value for the transconductance, or the optimal operating point, is when the base drive current is 20% over the base drive current for the c-base to collector shorted condition V.sub.CB=0 V. This point can be found, in practice, by any number of dithering sequences; in one example a baseline value for I.sub.CB can be found in diode mode, and then a target value is calculated, e.g. by increasing the baseline current value by 10% or 20% or 30%. Voltage V.sub.CB is then increased in small steps, e.g. in 1% increments, until the measured collector current reaches the target value. Optionally two limit values can be calculated, and the control voltage V.sub.CB ramped back down when the upper limit value for I.sub.CB is reached during operation. Optionally this dithering process can be repeated at short intervals when the transistor is in the ON state for long periods of time.

(34) FIG. 1B shows an example of a more complete base drive circuit. This is slightly different from the drive circuit of FIG. 1A in that antiparallel diodes are connected with the body diodes in two of the MOS transistors in the diode-mode drive circuitry 110. Moreover, FIG. 1B also shows the JFET plus Schottky branches which form the passive-off protection circuitry 120.

(35) A B-TRAN is in the active off-state when the e-base (base on emitter side) is shorted to the emitter, and the c-base (base on the collector side) is open. In this state with the NPN B-TRAN, the collector is the anode (high voltage side), and the emitter is the cathode (low voltage side).

(36) The B-TRAN is also off when both bases are open, but due to the high gain of the B-TRAN in this state, the breakdown voltage is low. The series combination of a normally-ON JFET and a Schottky diode attached between each base on its respective emitter/collector, as previously disclosed, will significantly increase the blocking voltage in this passive off-state. The JFETs are turned off during normal operation.

(37) One presently-preferred sample embodiment for B-TRAN turn-on is to simultaneously, from the active off-state and blocking forward voltage, open the e-base to emitter short while shorting the c-base to the collector. This immediately introduces charge carriers into the highest field region of the depletion zone around the collector/base junction, so as to achieve very fast, forward biased turn-on for hard switching, very similar to IGBT turn-on.

(38) Another advantageous turn-on method, from the active off-state, occurs when the circuit containing the B-TRAN reverses the polarity of the voltage applied to the B-TRAN, which produces the same base state described in the hard turn-on method, but at near zero voltage. That is, the e-base which is shorted to the emitter becomes the c-base shorted to the collector as the B-TRAN voltage reverses from the active off-state polarity. Again, turn-on is fast.

(39) In a third turn-on method from the active off-state, the e-base is disconnected from the emitter, and connected to a current or voltage source of sufficient voltage to inject charge carriers into the base region. This method is likely slower, since the charge carriers go into the base just below the depletion zone. Also, it is known that carrier injection into the e-base results in inferior gain relative to carrier injection into the c-base.

(40) After turn-on is achieved with either of the methods using the c-base, Vice is more than a diode drop. To drive V.sub.CE below a diode drop, turn-on goes to the second stage of increased charge injection into the c-base via a voltage or current source. The amount of increased charge injection determines how much V.sub.CE is reduced below a diode drop. Injection into the e-base will also reduce V.sub.CE, but the gain is much lower than with c-base injection.

(41) Turn-off can be achieved by any of several methods. The most advantageous method is a two-step process. In the first step, the c-base is disconnected from the carrier injection power supply and shorted to the collector, while the previously open e-base is shorted to the emitter. This results in a large current flow between each base and its emitter/collector, which rapidly removes charge carriers from the drift region. This in turn results in a rising Vce as the resistivity of the drift region increases. At some optimum time after the bases are shorted, the connection between the c-base and the collector is opened, after which Vce increases rapidly as the depletion region forms around the collector/base junction.

(42) Alternately, turn-off can be achieved by simply opening the c-base and shorting the e-base to the emitter, but this will result in higher turn-off losses since the drift region (base) will have a high level of charge carriers at the start of depletion zone formation.

(43) Or, turn-off can be achieved by simply opening the c-base and leaving the e-base open, but this will result in the highest turn-off losses and also a low breakdown voltage.

(44) In one sample embodiment, the base drive uses only N-channel MOSFETs to drive the B-TRANs. This makes advantageous use of low MOSFET output voltage (less than 0.7V). The input is most preferably variable voltage, which, with current sensing, can be used to determine the optimum base drive voltage.

(45) Another sample embodiment can support higher voltages, but uses both N-channel and P-channel MOSFETs.

(46) Advantages

(47) The disclosed innovations, in various embodiments, provide one or more of at least the following advantages. However, not all of these advantages result from every one of the innovations disclosed, and this list of advantages does not limit the various claimed inventions. High gain; Low ON-state voltage drop; Avoidance of breakdown; Inherent current limiting; Simple circuit implementation; Minimized power dissipation; Adjustable supply voltage.

(48) According to some but not necessarily all embodiments, there is provided: The present application teaches, among other innovations, methods and circuits for operating a B-TRAN (double-base bidirectional bipolar junction transistor). A base drive circuit is described which provides high-impedance drive to the base contact region on whichever side of the device is operating as the collector (at a given moment). (The B-TRAN, unlike other bipolar junction transistors, is controlled by applied voltage rather than applied current.) The preferred implementation of the drive circuit is operated by control signals to provide diode-mode turn-on and pre-turnoff operation, as well as a hard ON state with a low voltage drop (the transistor-ON state). In some but not necessarily all preferred embodiments, an adjustable low voltage for the gate drive circuit is provided by a self-synchronizing rectifier circuit. Also, in some but not necessarily all preferred embodiments, the base drive voltage used to drive the c-base region (on the collector side) is varied while the base current at that terminal is monitored, so that no more base current than necessary is applied. This solves the difficult challenge of optimizing base drive in a B-TRAN.

(49) According to some but not necessarily all embodiments, there is provided: A system for power switching, comprising: a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations; and first and second transistor-mode drive circuits, separately connected to the first and second base contact regions respectively; wherein each drive circuit is configured, as a voltage source, to selectably apply an adjustable voltage between the corresponding base contact region and the emitter/collector region which is nearest to that base contact region; and first and second diode-mode drive circuits, separately connected to the first and second base contact regions respectively; wherein each drive circuit is configured to selectably connect the corresponding base contact region to the emitter/collector region which is nearest to that base contact region.

(50) According to some but not necessarily all embodiments, there is provided: A system for power switching, comprising: a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations; and a pair of transistor-mode drive circuits, separately connected to the first and second base contact regions respectively, wherein each transistor-mode drive circuit is a voltage-mode drive circuit; and a pair of diode-mode drive circuits, separately connected to the first and second base contact regions respectively; wherein each diode-mode drive circuit is configured to selectably connect the corresponding base contact region to the emitter/collector region which is nearest to that base contact region.

(51) According to some but not necessarily all embodiments, there is provided: A system for power switching, comprising: a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations; and a pair of transistor-mode drive circuits, separately connected to the first and second base contact regions respectively; wherein each drive circuit is configured, as a voltage source, to selectably apply an adjustable voltage at a selectable value between the corresponding base contact region and the emitter/collector region which is nearest to that base contact region.

(52) According to some but not necessarily all embodiments, there is provided: A method for power switching, comprising: driving a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations, by, in a transistor-ON mode, when minimal voltage drop is desired, using one of a pair of first drive circuits to supply a selected adjustable voltage to the one of the base contact regions which is closest to whichever of the emitter/collector regions is positioned to act as the collector, as defined by externally applied voltage polarity; and in a diode-ON mode, when a diode drop across the device is acceptable, using one of a pair of second drive circuits to clamp one of the base contact regions to the respectively nearest one of the emitter/collector regions; and in a preturnoff mode, using both of the pair of second drive circuits to clamp each of the base contact regions to the respectively nearest one of the emitter/collector regions.

(53) According to some but not necessarily all embodiments, there is provided: A method for power switching, comprising: driving a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations, by, in a transistor-ON mode, when minimal voltage drop is desired, using one of a pair of first drive circuits to supply a selected adjustable voltage to the one of the base contact regions which is closest to whichever of the emitter/collector regions is positioned to act as the collector, as defined by externally applied voltage polarity; and in a diode-ON mode, when a diode drop across the device is acceptable, using one of a pair of second drive circuits to clamp one of the base contact regions to the respectively nearest one of the emitter/collector regions.

(54) According to some but not necessarily all embodiments, there is provided: A method for power switching, comprising: driving a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations, by, in a transistor-ON mode, when minimal voltage drop is desired, using one of a pair of first drive circuits to supply a selected adjustable voltage to the one of the base contact regions which is closest to whichever of the emitter/collector regions is positioned to act as the collector, as defined by externally applied voltage polarity.

(55) According to some but not necessarily all embodiments, there is provided: A method of providing a variable-voltage low-voltage output, comprising the actions of: a) providing an adjustable voltage to supply an oscillator; b) using the oscillator to apply an AC waveform to a primary winding of a transformer; c) at one secondary winding of the transformer, generating complementary control signals; and d) using the complementary control signals to operate a synchronous rectifier which is connected to another secondary winding of the same transformer, to thereby provide a low-voltage output.

(56) According to some but not necessarily all embodiments, there is provided: A variable-voltage low-voltage power circuit, comprising: an adjustable voltage supply circuit, connected to provide an adjustable voltage; an oscillator circuit, connected to receive the adjustable voltage as a supply voltage, and connected to drive a primary winding of a transformer with an AC waveform; a first secondary winding of the transformer, connected to output complementary control signals; and a second secondary winding of the transformer, having fewer turns than the first secondary winding; and a synchronous rectifier, including at least four transistors which are gated by the complementary control signals and are connected in a bridge configuration, which is connected to rectify the output of the secondary winding; wherein the output of the second secondary winding, after rectification by the synchronous rectifier, provides a substantially DC output which is smaller than a diode drop.

(57) According to some but not necessarily all embodiments, there is provided: A method of operating a bidirectional bipolar transistor which has first and second first-conductivity-type emitter/collector regions in distinct locations separated by a bulk second-conductivity-type base region, and also has two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations, in respective proximity to first and second emitter/collector regions but not to each other, comprising the actions of: a) when low on-state resistance is desired, applying a base drive voltage to whichever of the base contact regions is then on the collector side of the device; and b) varying the base drive voltage while monitoring base current, to thereby find a target base drive voltage where base current begins to increase with base drive voltage; and operating the transistor at approximately the target base drive voltage.

(58) According to some but not necessarily all embodiments, there is provided: A system for power switching, comprising: a bidirectional bipolar transistor which has two first-conductivity-type emitter/collector regions separated by a bulk second-conductivity-type base region, and two distinct second-conductivity-type base contact regions which connect to the bulk base region in mutually separate locations; and a pair of transistor-mode drive circuits, separately connected to the first and second base contact regions respectively; wherein, during the transistor-ON state where low voltage drop is desired, one of the drive circuits, as determined by external voltage polarity, is configured to apply an adjustable voltage to a selected one of base contact regions, and dither the adjustable voltage, to thereby find an operating point voltage where the current at the selected base contact begins to increase with applied voltage, and then keep the adjustable voltage at approximately the operating point voltage.

(59) Modifications and Variations

(60) As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given. It is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

(61) For one example, the main embodiments described above use NPN B-TRAN transistors. However, the same principles apply to PNP B-TRAN transistors, with appropriate inversion of voltages.

(62) For another example, the teachings here can be applied to B-TRAN devices of various sizes, depending on what blocking voltage and current capacity are required.

(63) For another example, a wide variety of other sensors and/or control relationships can be added onto the conceptual circuit relations shown in this application.

(64) For another example, where a B-TRAN is used as part of a larger circuit (e.g. a PPSA converter), a single control module can optionally be connected to apply the appropriate control signals to each of the B-TRANs' drive circuits.

(65) For another example, because voltage-mode drive is used, a single B-TRAN drive circuit can optionally be used to drive multiple B-TRANs in parallel. This is not practical with other bipolar junction transistors.

(66) None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none of these claims are intended to invoke paragraph six of 35 U.S.C. section 112 unless the exact words means for are followed by a participle.

(67) The claims as filed are intended to be as comprehensive as possible, and NO subject matter is intentionally relinquished, dedicated, or abandoned.