US2759111A - Transistor trigger circuit - Google Patents

Description

Aug. 14, 1956 R. WIDERE 2,759,111 TRANSISTOR TRIGGER CIRCUIT Filed June 2e, 1952 o11+ I+ Fi g'mi 'mh 3 V 4 f E; Z Jl@ f, #MIF MMIV e A4h29. 3M "4 Lf@ V 1f z/ 5 "zlllllllllN/VENTOR.

ATTORNEYJ United States Patent Q TRANSISTOR TRIGGER Rolf` Widexe,. Ennethaden, Switzerland, assignorI to Akltilgesellschaft Brown, Roveri & Cie, Baden, Swit- The invention concerns a trigger circuit where triggering occurs in dependence'on arcontrol voltage which acts at leastfor a short time' and exceeds a minimum value.

According to the invention the control voltage is transmitted to the control electrode circuit of a transistor, and an interrupting contact and the switching element provided for utilizing the impulses are located in the collector electrode circuit of the transistor, a resistor being located in the common lead of both circuits in series with the base electrode.

The invention is now explained by means of the circuit diagrams shown in the drawing, Figs. 2 and 3 being modified arrangements of the basic circuit shown in Fig. 1.

In Fig. l reference numeral 1 indicates the block-shaped semi-conductor of the transistor, for instance a germanium plate, 2 is the base electrode, 3 the control electrode and 4 the collector electrode. In the control electrode circuit is a bias voltage source 5, for instance a battery, and the input circuit element 7 for introducing the control voltage, for instance the secondary winding of a transformer. The circuit of the collector electrode 4 contains a source of D. C. potential 6 and the output circuit element 8 for utilizing the triggering impulses, for instance the coil of a relay, as well as the interrupting Contact 10. Both circuits are connected by means of the common resistor 9 to the base electrode 2. When a control voltage occurs at element 7, such voltage being of a polarity which, in eiect, increases, i. e. adds to the voltage of the bias voltage source 5, a current will ow through control electrode 3 to base electrode 2, whereby a relatively large change in current strength occurs in the circuit of the collector electrode due to the amplilication eect of the transistor.

This increase in current strength becomes noticeable at resistor 9 where a higher potential drop occurs which adds itself to the control voltage. There will thus be an increase in amplification, that is to say a feed-back to the control circuit. The feed-back increases with the magnitude of the resistance 9. If the resistance continues to be increased a point will be reached where the amplication process changes over to a triggering process. The increased current which ows over the collector electrode may in some cases continue to flow, even when the control voltage has ceased. In order to stop this current, contact 10 has to be opened for a short time, whereupon the original condition is restored. Triggering is thus to a great extent dependent on the magnitude of resistor 9.

Triggering can be improved when rectiers are provided in the control circuit as indicated in Fig. 2. For this purpose an asymmetrically conducting device such as for example a rectiiier 11 is connected in series with the transformer which transmits the control voltage. The method of operation is as follows: When a control voltage occurs at element 7, during the positive half wave thereof a current will ow over rectilier 11 so as to increase the polarisation voltage at electrode 3. The function of rectifier 11 is to eect a substantial reduction in the reactive elect on the input circuit after the triggering action is completed, the rectifier serving as a block for the reactive voltage 2` which'occurs at such time. Increase in polarization voit age atl e'lec'trtydeV 3 results in a triggering current int-he collector electrode'circuitiwliicli atr'esistor 9 has the effeet of-a feed-back to the control circuit.. inthe-central circuit there is anv increase of current over the aon-trol electrode'- 3. This current rise produces an eecff over rectifier 12, whereby switch e'ltl=`,1'r1e'z'1tl 7' remains unloaded. Rectifier IZ' or an equivalenti asymmetrically conducting device isconnectedf in series` with the circuit which in eludesbattery 5', control electrode 3' andj resisfox' 9 and is so poled, as' shownon the drawing-, y that'` in thefabsence of any input voltage pulse appearing on transfoifmrsecondary 7, a very low amplitude-current will ownil circuit. Thefvolt'age in eiernent 7 may be; of very-short duration, but even then-theteedback current over recte'r 12 will continue to ow. expedient-has; afavourable eliect' on the initiation of the' current rise/anti ilse-helps to-maint'ain itl- The introduction of the control Voltage into the control circuit can of course also occur at any other point in the circuit in an electrically equivalent manner. Due to the coupling of the circuits, any Voltage which is introduced will always have an effect on the control circuit so that triggering is started, although there will be a diminution in power amplification. The improvement in the effect of the rectiiier is thus also maintained. A point for the introduction of the voltage is for instance at the resistor 9. The input voltage can then become eiective either in series or in parallel with the resistor. Such an arrangement is shown in Fig. 3. The network 17 in which the control voltage occurs is connected in series with a rectifier 11 and across the feed-back resistor 9. Resistor 9 also has a rectifier 13 arranged in series with it. This rectifier 13 prevents the control voltage which acts on the resistor 9 from being short circuited over load resistor 8, battery 6 and the transistor. During its effective phase the polarity of the control voltage is opposed to that of battery 6. If the voltage of the battery 6 predominates, a voltage occurs at electrode 4 which would act in the forward direction of the transistor and cause a short circuit. No triggering could occur in this case. As in the case of the Fig. 2 circuit, rectiiier 11, in series between transformer secondary 17, to which the triggering impulse or control voltage is applied, and resistor 9, serves to reduce any reactive effect on the input circuit element 17 following the triggering action of the transistor circuit. Rectifier 13, corresponding in function to rectilier 12 in the Fig. 2 circuit, is placed in series in the circuit which includes the collector electrode 4, battery 6, output clement 8, switch 10, resistor 9 and base electrode 2, and is so poled, as indicated on the drawing, that a very low amplitude current flows through this circuit in the absence of a triggering voltage impulse at transformer secondary 17.

In order to improve the triggering of the circuit still further, it can be an advantage to arrange separate bias voltages in series with the individual rectiiiers.

Instead of the rectiers or the resistors it is also possible to use voltage-dependent resistances, for example silit rods or the like, silit being the trade name for a material made by exposing mixed silicon, silicon carbide, and carbon, to the action of carbon monoxide at 1500" C.

The advantage of this circuit compared with a trigger circuit employing electronic tubes is that the life of the transistor is practically unlimited. The circuit is thus particularly suitable where trigger circuits are required in connection with supervisory devices for electrical plants. A very useful application of the circuit is for impedance protective devices where short impulses have to produce a tripping effect with absolute certainty.

I claim:

1. In a control circuit, the combination comprising a transistor having a control electrode, a collector electrode input circuit including an input element therein by which v a triggering voltage can be introduced, said input circuit including a iirst asymmetrical conducting device in series with said input element, means connecting said input circuit with one of said transistor circuits, and a second asymmetrically conducting device connected in one of said transistor circuits poled to establish a low resistance path for ow of positive emitter and base electrode current, said first asymmetrical conducting device being poled to establish a low resistance path therethrough for current owing through said input element and a high resistance path through said second asymmetrical conducting device.

2. A control circuit as defined in claim l wherein said second asymmetrical conducting device is connected in said tirst transistor circuit, and said series connected input element and rst asymmetrical conducting device constituting said input circuit are connected in parallel with said second asymmetrical conducting device.

3. A control circuit as dened in claim 1 wherein said series connected input element and rst asymmetrical conducting device constituting said input circuit are connected in parallel with said resistor.

4. A control circuit as dcn'ned in claim 3 wherein said.

second asymmetrical conducting device is connected in said lead common to both of said transistor circuits.

References Cited in the iile of this patent UNITED STATES PATENTS 2,584,990l Dimond Feb. 12, 1952 2,595,208 Bangert Apr. 29, 1952 2,622,211 Trent Dec. 16, 1952 2,628,310 Wood Feb. 10, 1953 2,629,833 Trent Feb. 24, 1953 2,629,834 Trent Feb. 24, 1953 2,670,445 Felker Feb. 23, 1954

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