CH641298A5 - CURRENT SWITCHING CIRCUIT COMPRISING A THYRISTOR. - Google Patents

Description

The subject of the present invention is a circuit comprising a thyristor and, more particularly but not exclusively,

an integrated semiconductor device comprising a thyristor.

Thyristors are semiconductor devices having a p-n-p-n structure and which have a gate allowing a relatively high power load to be controlled by a relatively low power gate pulse. They include silicon rectifiers which are generally only conductive in one direction, and triacs which are conductive in both directions. In both cases, the device is made conductive by the application, to the door, of an initiating current, the device then remaining conductive until the main current falls below a current level. minimum (holding current) necessary to maintain the regenerative action which keeps the device in the conducting state. Such devices are widely used for the switching of alternating currents but cannot be used for the switching of direct currents when they are used in complex switching circuits because there is no mechanism to cut the device. The gain and response time of such a circuit are limited. It has been proposed to produce a device which can be triggered, that is to say cut by a pulse of polarities opposite to the switching pulse. However, such devices require a recovery time of 10 to 20 microseconds after tripping, during which the device can be made back conductive by an increase in the main current; moreover, the trigger gain as well as the trigger time proved to be disappointing (approximately 5 to 10 and approximately 10 to 20 microseconds, respectively).

The present invention provides a thyristor circuit capable of switching direct current, for example in a chopper (vibrator-switch) or rectifier and capable of being produced so as to have a gain of the order of 100, and a cut-off time. or triggering on the order of a few microseconds.

According to the invention, a circuit is produced by incorporating a thyristor having first and second electrodes as well as a common gate electrode area for initiating the flow of a main current between the first and second electrodes, characterized by the common door area is also arranged to cut off the main current flow, the circuit further comprising switching means which, when actuated, produce a sufficiently low impedance circuit in parallel with the current flow thyristor between the door and the second electrode so that the main current flow decreases below the level necessary for it to be maintained by regenerative action.

This circuit will preferably be an integrated semiconductor device whose different circuit elements are formed on a single semiconductor substrate, the circuit being provided with first and second terminals for conducting the main current, with a first door terminal to receive an energizing pulse to initiate the main current flow, and a second door terminal to receive an interrupting or tripping pulse to interrupt the flow of the main current. The device can be made using standard techniques.

The switching means may include at least one bipolar transistor producing a high current gain. For example, the switching means may comprise two bipolar transistors with the emitter of one connected to the base of the other which, in turn, has its collector / emitter circuit in parallel with the gate / second electrode circuit of the thyristor, the whole so that the application of a suitable trigger pulse to the base of said transistor produces the saturation of the other, thus producing a circuit to

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sufficiently low impedance in parallel with the circuit effectively increases the requirement to maintain the current te / second electrode to trigger the thyristor. dynamics of the device up to a level above

The circuit will advantageously also include that used to conduct the main current by reducing controllable bypass means capable of producing a step of the impedance between gate and cathode.

wise of alternating current between two adjacent zones of the thy- 5 The circuit also comprises a third bi-transistor transistor, of opposite polarities, of which none is the polar zone T3 which ensures a passage of alternating current but carries, so making said sensitive door zone when controllable between the p and n zones of SCR1 adjacent to triggering, thereby improving the time to trigger the anode. This transistor T3 thus serves to ensure that the process is working. trigger is preferably in the n-p-n area of

Gate amplifying means can be provided 10 SCRl. As a result, the gate area of SCRl is rendered to apply a latching signal to the highly sensitive electrode and is capable of breaking the common main gate current so as to produce a latching pal in a very fast response time . R5 resistance per fast. puts the gain control of the p-n-p area of SCRl and

The main thyristor could be a rectifier combining the dv / dt capacity and the tripping time.

mended with silicon or a triac. In the first case, a diode 15 According to the particular device, namely regenerative, of conductive inversion can be provided to allow the chopper, or rectifier, a conductive diode with current return to flow between the cathode terminal and the current terminal d2 can be connected in antiparallel with SCRl of anode in a direction opposite to that of current to allow current to flow in opposite direction to the main direction. of the main current in SCRl. R3 and R4 resistors

The drawing shows, by way of example, a form of execution used to laterally couple the zones of T2 to the action zones of the object of the invention. ves of SCRl, these resistances being representative of the separation

Fig. 1 is a circuit diagram equivalent to a lateral distribution of these zones in the integrated device.

positive integrated in semiconductor. Tl requires a relatively high tension which is ensured

Fig. 2 is a plan view of the device during its manufacture by the inclusion of resistors ri, ri 'and a diode dl which ser-cation, seen from the bottom of figs. 3 and 4. 25 wind to increase the nominal voltage of the breaking current

Fig. 3 is a section through a part of the device according to the Vceo of Tl to a value close to Vcbo and to improve the line OA 'in FIG. 2. tripping time. T2 requires a relatively low voltage

Fig. 4 is a section of a part of the device according to the sion (10 to 20 volts) which allows some degrees of freedom in line OB 'of FIG. 2, and the design of the device by optimizing certain parameters

Fig. 5 is a graph illustrating the characteristics of 30 so as to produce a high current capacity, a switching of the device. rapid mutation, high gain, and saturation voltage

The device shown can be called a weak rectifier. In order to prevent the flow of the main silicon-controlled current comprising a cut-off gate or through Tl, this is arranged so as to present a small trigger, this device comprising, in fact, an effective zone and to have an abrupt drop in gain above any number of semiconductor components integrated into 35 of its designated maximum current level. A single substrate resistance. The structure and operation of the dis-R2 is connected between the door electrode 3 and the positive cathode 2 can be more easily understood by referring to it to aid in the cut-off or tripping process.

equivalent circuit shown in fig. 1, even though it is Referring to figs. 2 to 4, the various components of the understanding that this diagram is only intended to serve as a model. circuit are produced by diffusion on the two sides of a sub. In practice, various zones of the different components 40 silicon strat 4 of type n. The zone 5 shown in FIG. 3 may not be physically separated and the structure may be obtained by epitaxial growth. A metallic layer

real may be somewhat more complicated. coated with aluminum 6 is produced on each side of the substrate

The circuit shown in fig. 1 includes a rectifier and the current leaks are minimized by a main chamfering SCRl controlled with silicon, of the pnpn type, suitable for the edges of the substrate 5 and by rounding them with one having an anode 1, a cathode 2, and a door electrode 45 passivation material 7. The substrate is sandwiched in common 3 to engage the device and trigger it or between two pressure contacts not shown and is encap-cut. The device is triggered by the application of a conventional insula- tion.

positive impulse at a first door terminal gl, this im- Fig. 2 represents the substrate 4 seen from the lower drive part being “amplified” by a pilot rectifier SCR2 com- of FIG. 3, illustrating the interlocking gate gl and the silicon mandated gate connected to the common gate electrode 3, this trigger g2 50 before metallization. This figure mon-which ensures rapid engagement (high capacity di / dt) of the tre also the conductive diode with current feedback d2 for-device. The rectifier SCR2 trips when the rectifier led to the outer circumference of the substrate 4. SCR1 begins to become conductive. Fig. 3 represents the anode 1 located on one side of the substrate 4

The device is triggered or cut by the application and the cathode 2 located on the other side of it. In practice, the of a positive pulse at a second gate terminal g2, 55 cathode metallization is thicker than the metallization this pulse used to trigger the two bipo- gate transistors in such a way that the cathode contact member , TI and T2 areas of a modified Darlington pair. The agency, acting by pressure, does not come into electrical contact, such that the transistor T2 quickly reaches saturation with the gates. The electrical contact with the doors is made and produces a current flow at low impedance by wires not shown. The areas of the substrate 4 corres-parallel with the common gate / cathode circuit of the rectifier 60 weighting the different elements are indicated by the same SCRl. This is used to derive or shunt a large output from the reference letters and numbers as those used for the main elements by the transistor by means of the electrode of fig. 1. It should be noted that SCRl is of gate 3 shape, with the effect that the current passing between the gate and annular. The transmitters of TI and T2 have a high central cathode areas of the rectifier SCRl decreases below in impurity so as to produce a gain and a return of the level necessary to maintain SCRl conductor by action 65 ment high. It should be noted that the presence of the regenerator door. The main current passing through SCRl is thus triggered does not adversely affect the properties reduced to zero and remains at this level until the terminal gl re- of high voltage of SCRl because the zone n and the zone receive a impulse. The triggering process consists of SCRl anode remain intact. A lateral separation of

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Tl from the basic structure of SCRl produces the required electrical insulation.

The transistor p-n-p T3 is incorporated into the basic structure p-n-p-n by allowing the selected areas of the substrate to remain of the n type after the main diffusion. R5 is formed by anode short circuits, R2 is formed by gate diffusion short circuits which remain after the cathode diffusion. These cathode short circuits will be larger and more numerous in the areas preceding the trip gate structure. A doping with gold and / or a doping by neutron transmission of the substrate can be used for the control of longevity of the characteristics of release and, also, to allow to use a thinner substrate thus producing tensions in the state engaged weaker.

The switching on and off characteristics of the device described above are illustrated in FIG. 5 which is a graph of the voltage V anode / cathode with respect to time t The current gain of T3 is important because it determines both the trigger delay and the increase in time, FIG. 5 representing the switching on and off voltages for different gains of T3. We see that, by choosing a suitable gain for T3, a load of 1 kw can be triggered with a delay of one microsecond by means of 1 watt, plus a door pulse of 10 volts. We see that the elimination of the door impulse completes and ends the triggering action. The device thus has a response time of 2 to 3 microseconds. In addition, a trigger gain, that is to say the ratio between the main current and the gate current, of more than 100, is obtainable with such a device. A similar device can be made so as to be able to conduct current in both directions. Such a device can be called a door triac triac.

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2 sheets of drawings

Claims (13)

641,298 1. Circuit comprising a thyristor having a first and second electrodes and a common gate electrode area for initiating the flow of a main current between the first and second electrodes, characterized in that the common gate area (3) is also arranged to cut the main current flow, the circuit further comprising switching means (TI, T2) which, when actuated, produce a sufficiently low impedance circuit in parallel with the current flow of the thyristor (SCR1) between the door and the second electrode (2) so that the main current flow decreases below the level necessary for it to be maintained by regenerative action. 2. Circuit according to claim 1, characterized in that it is constituted by an integrated semiconductor device. 2 3. Circuit according to claim 2, characterized in that the different elements of the circuit are formed by diffusion on both sides of a substrate of a semiconductor (4). 4. Circuit according to one of claims 1,2 or 3, characterized in that it comprises first and second terminals (1,2) for conducting the main current, a first door terminal (gl) for receiving an energizing pulse to initiate the main current flow and a second gate terminal (g2) to receive an initiating pulse terminating the main current flow. 5. Circuit according to any one of the preceding claims, characterized in that the switching means comprise at least one bipolar transistor (TI, T2) producing a high current gain. 6. Circuit according to claim 5, characterized in that the switching means comprise two bipolar transistors (TI, T2), the transmitter of one (Tl) is connected to the base of the other (T2), which has its collector / emitter circuit mounted in parallel with the gate / second thyristor electrode circuit (SCR1) so that the application of a suitable trigger pulse at the base of said transistor (Tl) connected to the base of the another produces the saturation of the other transistor (T2) thus producing a low impedance circuit located in parallel with the thyristor current circuit (SCR1). 7. Circuit according to any one of the preceding claims, characterized in that it further comprises controllable bypass means (T3) capable of producing an alternating current circuit between two adjacent regions of the thyristor (SCR1) of opposite polarities , none of which is the door area (3). 8. Circuit according to any one of the preceding claims, characterized in that the door amplifier means (SCR2) are arranged to apply a trigger signal to the common door area electrode (3). 9. Circuit according to claim 8, characterized in that the amplification means are constituted by a controlled silicon rectifier (SCR2). 10. Circuit according to any one of the preceding claims, characterized in that the thyristor is a silicon rectifier (SCR1) controlled. 11. Circuit according to claim 10, characterized in that a conductive inverting diode (d2) is mounted in parallel with the thyristor (SCR1) to allow the current to flow in the opposite direction to that of the main current. 12. Circuit according to any one of claims 1 to 9, characterized in that the thyristor is a triac. 13. Use of a circuit according to any one of the preceding claims in a direct current inverter.