Elektronische schaltung mit einem geschuetzten transistor

25-03-1991 дата публикации
Номер:
AT0000392375B
Автор:
Принадлежит: Rca Corp
Контакты:
Номер заявки: 44580
Дата заявки: 28-01-1980

[1]

The invention concerns an electronic circuit with a protected transistor, to which a Basistreiberslrom and a emitter KoUektor tension are supplied, whereby for the protected transistor an over-current protection circuit is intended, which exhibits a second transistor, which is thermally in such a manner coupled with the protected transistor that the Betdebstemperatur of the reference transistor with that of the protected transistor drinks. Normally an over-current protection is usually planned by or two fundamental protection principles, which contain both a current feeling resistance in row with the Hauptslromslrecke of the protected transistor. During the nonlinear against-coupled circuit the voltage drop at a Slromfühlwiderstand, which is positioned in series with the collector emitter distance of the protected transistor, is supplied to a SchweUwertdetektor, which reacts if the SpannungsabfaU exceeds a pre-determined threshold value, and which the protected transistor the available basis driver stream lowers. During the nonlinear limiting circuit the combined tensions over the base-emitter diode of the protected transistor and a Slromfühlwiderstand on one, being positioned in series thereby, become by a limiter determined maximum value limited. For application with an achievement amplifier a current feeling resistance being positioned in series with the collector emitter distance of the protected transistor is however unwanted. The voltage drop at the feeling resistance reduced unwanted-proves the tension modification range, which is available over the collector emitter distance of the protected transistor, and thus by an amplifier, the transistor protected in soft is used, available achievement. In the feeling resistance some achievement is also used, if by the protected transistor higher normal river flows. This achievement is to be regarded as Verlusfleistung, yields the efficiency of the amplifier unwanted lowers. Another problem arises with monolithic integrated circuits, since the current feeling resistances in an appropriate small part of the integrated circuit cannot be trained, because it low of resistances (typically a fraction of an ohm) to have had and substantial river to bear have (typically some ampere). There is from there a large need after an over-current protection circuit, which gets along without Stromffihlwiderstände in row with the KoUektor emitter Slrecken of the protected transistors. The inventor that invention which can be described here found out that the internal emitter resistance of the transistor can be consulted as current feeling resistance for a Überslromschutz, so that a separate current feeling resistance is no longer necessary. A problem here consists of it that the internal emitter resistance has only a relatively small linear component, thus that term, for which the SpannungsabfaU stands in firm relation to the emitter current of the gesehfitzten transistor. The predominating component of the internal emitter resistance is a logarithmic expression, thus a term, with which the voltage drop stands in firm relation to the logarithm of the emitter current of the protected transistor. Thereby it becomes very difficult - and in the practical sense indeed not possibly - changes of potential at this internal emitter resistance by usual bi-threshold detectors or limiter attitudes festzusW31en, since such circuits use generally elements with semiconductor junctions, whose conductance input voltage characteristic runs anti-logarithmically, so that they are not sufficient sensitive or exact, in order to offer a predetermineable over-current protection. A predetermineableness and reproductibility of the result are particularly important with Überslromschutzsehaltungen in monoüthischer integrated training, since the use of components, which are for an accurate value selected or adjusted, is to be avoided, where always possible. A further problem consists of that the internal emitter resistance of the protected transistor has a particularly strong dependence on the operating temperature of the protected transistor. This feature one must consider, if one determines the threshold value, with which the transistor over-current protection to be ordered is. Task of the invention is it to create a circuit of the initially stated kind which avoids the disadvantages of conventional circuits described above. This task is solved according to invention thereby that the second transistor is a reference transistor connected with a power source, how its KoUektor emitter distance a river of pre-determined value leads, and which supplies second transistor an emitter basis reference potential that is supplied a difference comparison circuit, the D! e emitter basis Spanmmg of the protected transistor with that of the second transistor compares and with Uberslromzustand of the protected transistor an announcement supplies, if its emitter base voltage exceeds the emitter base voltage of the second transistor around a pre-determined amount, and that by a limiting circuit a further rise of the Basislreiberslromes for the protected transistor is limited as a function of the announcement of the Überstmmzustandes. In this way avoided that a reference resistance is necessary, at that a tension is abffdlt, which indicates a overcurrent condition. Contrary to the state of the art an emitter basis reference potential of a reference transistor is set on a comparator, in order to compare it with the emitter basis potential of the protected transistor. The KoUektor emitter river is firmly adjusted, so that the exit of the comparator makes a direct announcement possible of the collector emitter current condition in the protected transistor. If the output signal of the Vergieichers results in a overcurrent condition in the protected transistor, that is limited for the protected transistor supplied Basisslrom. Since the overcurrent condition is seized by an RK 392,375 B comparison of the basis emitter tensions of the protected transistor and the reference transistor, the disadvantageous feeling resistance usual with the state of the art (requirement 1) is void. It is particularly expedient, if the Vergleieher contains a pair of transistors switched as emitter coupled Gegentaktstufe. This lets sees reaching, as a transistor of the pair in normal operation leads less than the other transistor, however in the Uberstromzustand the overcurrent announcement takes over. This solution results in the special advantage that an emitter coupled Gegentaktstufe represents a relatively simple circuit, which however äu in relation to changes in the difference that their entrances supplied basis emitter tensions is rst sensitive. If in addition the transistors are so arranged that they seize the temperature of the protected transistor and the reference transistor, then the change between the relationship of the led rivers and the difference of the basis emitter tensions of the protected transistor and the reference transistor in the emitter coupled Gegentakt Transistorenpaar can be compensated, with which the temperature independence of the overcurrent announcement is improved (requirement 2). The level, on which the emitter coupled Gegentaktstufe indicates the overcurrent condition, can be raised, by adding it the sum of the basis emitter tension of the reference transistor and a pre-determined further tension, instead of supplying only the basis emitter tension. The pre-determined additional tension can be produced, by scolding a resistance in series with the reference transistor, so that the resistance is flowed through by a pre-determined river. This resistance does not correspond from the conditions to the technology admitted feeling resistance, since it does not lead the variable Ansgangsstrom of the protected transistor. Thus also the disadvantage of a loss at power output or the necessity does not result to dimension the circuit on larger amperages. The tension dropping at the resistance changes not with the river flowing by the protected transistor and does not change also with the occurrence of the overcurrent condition, with which a further tension is produced in optimal way (requirement 3). For the maintenance of the temperature independence of the overcurrent announcement sees the tension over the resistance should proportionally to the operating temperature changing. This is reached by that the pre-determined river is regulated in such a way that it is proportional to that river, which flows by a resistance, at which a potential will maintain, which the difference between the basis emitter tensions of two transistors corresponds. The potential at the resistance specified last is from there proportionally too kT/q. The resistance can be thereby an additional resistance (requirement 4). For a simple circuit design it is however particularly favourable, if one uses f'ür the purpose the first resistance specified above, with which construction unit can be saved (Ansprneh 5). The invention is in detail described in the enclosed designs. Fig show. 1 the diagram of a quasi-linear amplifier with a pair Aus.Bangstransistoren, which heads for a load in the eating differential mode, whereby for the output transistors a Uberstromschutz is ordered by one over-current protection circuit each in accordance with the invention; Fig. 2, 3, 4 and 5 diagrams of further Überstromsehutzsehaltungen in accordance with the invention, which or others of the protective circuits in accordance with Pig. 1 to replace can do; Fig. 6, 7 and 8 diagrams of modifications, those with in the Fig. 1 to 5 remarks shown of the invention to be met can do; Fig. 9 a block diagram of a Slyomversorgungsschaltung, which favourable-proves that with circuits be used according to invention can; and the Fig. 10 a Sehaltbild of another current supply circuit favourable-proves with the represented execution forms of the invention is usable. In Fig. to become input signals at the port (SIG IN), which can be intensified, supplied and arrive to 1 represented quasi-linear amplifier at a driver (DS). The driver (DS) supplies river (I1) and (12) for eating enterprise, which have same positive quiescent component. With amplitudes of the input signal in a direction has (I1) positively arranged amplitudes, which are overlaid its positive quiescent component, and with input signal amplitudes in the other direction has (I2) positively arranged amplitudes, which are likewise its positive quiescent component overlaid. The driver (DS) can be for example from the kind, as they besehrieben in the US-PS 3,573,645 are. The driver (DS) supplies the river (11) with one relatively gro to n with source impedance to the base electrode of a npn Verstärkertransistors (Q1), operated in collector basic attitude, which is currentsteered thereby, and to the npn power transistor (Q2), which is headed for at its basis by the emitter current supplied from the transistor (Q1), which flows due to its base current (11). The driver (DS) supplies the river (12) from a relatively high source impedance to the basis of the nlm Verstärkertransistors (Q3), operated in Kollektorgrandschaltung, which is currentsteered thereby, and to the npn Leisttmgstransistor (Q4), which is headed for at its basis by the emitter current of the transistor (Q2), whereby this emitter current flows due to the base current (I2). The collector emitter circles of the transistors (Q2) and (Q4) are switched into row for operating voltage supplied between the Ansehlüssen the mass and (B+), and they are switched furthermore so that they supply at the connection (SIG OUT) a Gegentakttreibersignal, to which over a Gleiehspannungsblockkondensator (el) a load (LM) are attached. (B+) a booster circuit with a booster condenser (C2) to RK with 392,375 B between the ports (SIG OUT) and (B+ BOOST) and a resistance (g 1) between the connections (B+) and (B+ BOOST) supply a tension to the collector of (Q1) and the driver (DS), which with positive Sigualamplimden at the port (SIG OUT) over OB+) rises, so that the transistor (Q2) into the state of saturation to be steered can. By the connection of the collector of (Q3) with the emitter of (Q1) can arrive (Q4) into the saturation. The so far described Verstärkerschaltung is well-known in principle. The NPN transistor (Q5) is the Bezngstransistor, which supplies the emitter basis Offsetspanunng (VBEQ5), opposite which the emitter basis offset voltage (VBEQ4) of the transistor (Q4), which the same emitter tension as (QA) has, one compares. The transistor (QA) is provided with a direct collector BasisRüekführung, by which its emitter base voltage is stopped in such a way that its Kollektorstrom is practical equal to the direct current (13), which of a power source (1S1) to a knot (10) is supplied, to which the collector of the transistor (Q5) over the ports (tl) and (T2) isL the NPN transistor (Q7) is attached the reference transistor, which supplies the emitter basis offset potential (VBEQ7), with which the emitter base voltage (VBEQ2) of the transistor (Q2) is compared, which has the same Basispotenüal as (QT). (QT) an amplifier transistor is in Kollektorgrundschaltung, whose emitter current flows to large part, in order to supply the KoUektorstrombedarf of the NPN transistor (Q8), which is supplied to the emitter of the transistor (QT) over Ansehlüsse (T3) and (T4). (Q8) and the NPN transistor (Qg) are auxiliary mirror transistors in a double output current mirror amplifier with the transistor (QA) as Hauptspiegeltmnsistor and an input terminal with (11) as well as output terminals with (12) and (13) and a reference connection with (14). On the assumption that the effective surfaces of their respective emitter basis transitions are made directly, as this by the indications (1) with their respective Emitterelektroden is suggested, has the transistors (Q7) and (QA) resembles emitter basis offset potentials (VBEQ7) and/or. (VBEQS). (This is valid because of the current mirror amplifier effect between (QA) and (Q7) and the Emittergrundschaltung of the transistor (Q8), that on the emitter of the transistor (QT), working for it as collector load, works.) Everyone the Leismngstransistoren (Q2) and (Q4) is trained in practice by an appropriate majority of paraUelgeschalteter transistors in monolithic integrated circuit way, whereby the equivalent effective surface of the emitter basis transition of the power transistor is equal to the sum of the effective surfaces of the emitter basis transitions of the Einzeltmnsistoren joined in parallel. In each case the äqtüvalenten effective surfaces of the emitter basis practicing suppl. are ge of the transistors (Q2) and (Q4) as m-times as largely represented as the effective surfaces of the emitter basis transitions of the transistors (Q7) and/or (Q5), whereby m is a positive number. Thus it results that the offset voltages over the emitter basis transitions of the transistors (Q2) and (Q4) around the factor (KT/q) LN m at same current values smaller than the offset voltages at the emitter basis transitions of the transistors (QT) and/or (Q5) are. One receives this result by a view of the well-known equation for the transistor impact VBE = T/q LN (I/AJs) whereby VBE K T q is ON BEHALF JS the emitter base voltage of the transistor, the Boltzmann constant, the absolute temperature of the emitter basis transition, the load of an electron, the output current of the transistor; the effective surface of the transistor emitter basis transition, and the middle current density by the emitter basis transition of the transistor, if (VBE) has the zero value. The transistors (QA) and (Q7) are arranged in close thermal coupling with the transistors (Q4) and/or (Q2), so that the operatings temperature of the transistors (QA) and (QT) run with those of the transistors (Q4) and/or (Q2). The respective emitter basis potentials (VBEQ2) and (VBEQ7) the transistors (Q2) and (QT) become differenzmäl] industrial union by a pair NPN transistors (Q10) and (QU) in so-called Long Tail Sehaltung (emitter coupled Gegentaktstufe) compared, whereby the collector of the transistor (Qg) withdraws the so-called Tail river from the interconnect point of the two emitters. During the represented circuit this Tail river is essentially identical (13), however can also different circuits for the production of the Tall river be used. With normal Ausgangsstrombedingangen is substantially smaller (VBEQ2) than (VBEQ7). Thus that stretches the basis of the transistor (Qll) supplied Emitterpotenüal of the transistor (Q2), the positive than that the RK 392,375 B basis of the transistor (Q10) (over the Ansehlüsse (T4) and (T3)) supplied emitter potential of the transistor (QT) is, the transistor (QU) so forwards that it feels as Kollektorstrom of (Q9) flowing Tail river and is linked up (Q10) into the blocking state. If however with the transistor (Q2) a overcurrent condition before-triumphs, in such a way then it rises (VBEQ2) and links up (QU) that he leads less and is linked up (Q10) into the line condition. The line condition of (Q10) shows the overcurrent condition of the transistor (Q2) thus. The collector of (Q10) is attached to the basis of (Q1) and limits its basis driver stream as a function of the announcement of the overcurrent condition for the transistor (Q2), whereby collector requirements of electric current of the transistor (Q10), if these lead, one satisfies by the branching of a part of the river (I1) from the basis driver stream to (Q1) and thus too (Q2). A synchronisation of the operatings temperature of the transistors (Q2, Q7, QI0 and Qll) lets the overcurrent sensing from these operatings temperature becomes insensitive. This is case, because a straight certain difference between the emitter base voltages of the transistors (Q2) and (Q7), which proportionally too (KT/q) and thus too (T) is, a certain firm relationship between their output currents over a large modification range of (T) is assigned, and this same difference, which proportionally (KT/q) between the emitter base voltages of (Q10) and (QU) is, is assigned to a firm Verhälmis between their Ausgangsstr0men. By use of NPN transistors (Q10) and (Qll) in a Long Tail Sehaltung to the difference comparison of (VBEQ2) and (VBEQT) a direct supply of collector requirements of electric current of the transistor (Q10) becomes the I1 - exit of the driver (DS) facilitates, without in addition a shift in level would be chaltung nödg. The respective emitter basis Potenfiale (VBEQ4) and (VBEQ$) the transistors (Q4) and (Q5) become difference moderate by a pair pnp transistors (Q12) and (Q13) in Long Tail circuit compared. The power source (IS2) supplies a direct current (14) as Tail river to the interconnect point between the Emittem of the transistors (Q12) and (13). (13) and (14) equally large can be made, so that an adjustment of the Überstromsehutzeigenschaften is facilitated for that the transistors (Q2) and (Q4) protecting circuits. With normal output current conditions is substantially smaller (VBEQ4) than (VBEQS). In the comparison to the basis potential of (Qb'), (over the ports (tl) and (T2)) of (Q12), is less positive that is supplied to the basis up the basis of (Q13) supplied basis potential of (Q4) and links so the transistor (Q12) into the blocking state. In such a way with Überslrombedingungen for the transistor (Q4) it rises however (VBEQ4) and links up (Q13) that this leads less and comes (Q12) into the line condition. Then flowing the Kollektorstrom of (Q12) shows the Uberstromzustand in (Q4). This announcement arrives at the input terminal (21) of a current mirror amplifier with the NPN transistors (Q14) and (Qlb'), which has an output terminal (22) for the basis of the transistor (Q3) and a reference connection (23) to the ground connection. Under control by the KoUektorstrom of (Q12) by the transistor (Q15) at the point (22) a Kollektorstrom of same size is required. This amplitude equality of the Kollektorströme of (Q12) and (Q15) results due to the effect of the current mirror with the transistors (Q14) and (Q15), whose Stromverstärkung is essentially identical to -1, because the effective surfaces of the emitter basis Ülx of courses of (Q14) and (Q15) in the relationship 1: stand for 1, like the encircled one with their respective Emitterelektroden suggest. The Kollektorstrombedaff of the transistor (Qlb') satisfactory by a part of (12), so that a further rise of the Basistreiberslroms for (Q3) and thus for (Q4) is limited. Fig. an alternative over-current protection circuit for a power transistor, for instance the transistor (Q2) of the Gegentaktverstärkers shows 2 in accordance with Fig. 1, using pnp transistors (Q16) and (Q17) instead of the NPN transistors (Q10) or (Qll) in the Long Tail circuit, for the comparison of the tensions C¢BEQ2) and (VBEQ1) by difference formation. Positive Tail river is supplied to the zusammengesehalteten emitters of the transistors (Q16) and (Q17), for example using a current mirror amplifier circuit of the transistors (Q18) and (Q19) for inverting the Kollektorstroms of (Q9), as this is shown. With normal output current conditions the smaller tension (VBEQ2) links the basis up of the transistor (Q17) to a considerably more positive value, than the larger tension (VBEQ7) the basis of the transistor (Q16) links up. Thus leads (Q16) the entire rope stream of the KoUektor of the transistor (Q19), and (Q17) becomes closed. However is present with (Q2) overcurrent conditions, in such a way then it increases (VBEQ2) and links up (Q16) that this leads less and comes (Q17) into the line condition. The Kollektorstrom of the transistor (Q17) is supplied to the Eingangsanschlaß (31) of a current mirror amplifier with NPN transistors (Q20) and (Q21), whose output terminal (32) is connected with mass with the basis of the transistor (QI) and its reference connection (33). In dependence Kollektorstrom of the transistor (Q17) stands in front collector requirements of electric current of the transistor (Q21), which is satisfied through (11) and a further rise of the basis driver stream for (Q1) and thus for (Q2) limits. RK 392,375 B a further altemaüve Überstromschutzschalmng for a power transistor like the transistor (Q2) of the Gegentaktverstärkers in accordance with Fig. 1 is in Fig. 3 represented. Just as the transistors (Q10) and (Qll) in Fig. 1 NPN transistors (Q22) become and (Q23) for the comparison of the emitter base voltage (VBEQ2) of the geschiitzten transistor (Q2) with the emitter base voltage of the npn Bezugstransistors (24), gesehalteten as diode, uses. However the transistors (Q22) compare and (Q23) the base voltages of the transistors (Q2) and (Q24) instead of their emitter tensions, which are on the same potential, because they are hooked up without inserted elements. A current mirror amplifier attitude with pnpTransistoren (25) and (26) has an input terminal (41), which the Kollektorstrombedaff of the transistor (Q8) is supplied, and an output terminal (42), a passage pre-loading stream (proportional to the KoUektorstrombedaff of the transistor (QA)) to the reference transistor (24), switched as diode, supplies, and the reference connection of the circuit is on (B+) attached. In such a way at normal current values in the transistor (Q2) it is (Q22) linked up that he leads all Tail requirements of electric current at the collector of the transistor (Q9) and these with 01÷) connects. If a overcurrent condition is present with the transistor (Q2), then the increased tension (VBEQ2) links the transistor up (Q23) into the line condition, the transistor (Q22) against it in such a way that it leads less. The collector of (Q23) is attached to the basis of (Q1), and its Kollektorstrombexlarf supplied by branching of a part of the river ('11) of the basis of the transistor (Q1), in order to limit a further rise of the basis driver stream for (Q1) and thus ffir (Q2). A modification of the circuit in accordance with Fig. 3 is in Fig. 4 shown. Here replaces pnpEmitteffolgertransistor (Q28) the NPN transistor (Q24), switched as diode, as reference transistor. Thus the portion of the Kollektorstroms of the transistor (Q26) is reduced, which leads by the port (SIG OUT). Because of the KollektorgrtmdschaItung the transistor (Q28) can be a so-called vertical transistor, whose collector in the substrate of a usual monolithisehen integrated circuit lies and which an isolation uses in relation to other circuit elements by means of closed semiconductor junctions, instead of one using a transistor with lateral structure, if this is desired. Fig. a further modification shows 5 using pnp Differenzvergleiehstransistoren (Q29) and (030) instead of from NPN transistors (Q22) and (Q23). The hooked up emitters of the transistors (Q29) and (Q30) receive river in same Welse as the hooked up emitters of the transistors (Q16) and (Q17) in Fig. 2 and a current mirror amplifier with the transistors (Q21) and (Q22) one uses, in order to supply the Kollektorstrom of the transistor (Q29) with Colonel Rome conditions of the basis of the transistor (Q1). The Long Tail Schaltnngen used as difference comparison circuits is represented with symmetrical transistors (Q10 and QU, Q12 and Q13, Q16 and Q17, as well as Q22 and Q23), with which it concerns in each pair adapted transistors. However the effective surface of the emitter basis transition of the transistor (Qll) can be made as n times largely as the emitter footpoint of the transistor (Q10), whereby n is a number grölMr as unity, and thus receives one an asymmetrical Long TailSchaltung, yields the value, at which the over-current protection for the protected transistor (Q2) is given, in relation to the level of the collector emitter current in the comparison transistor (Q7) raises. Other Long TailPaare can be made similarly asymmetrical the same purpose: Another procedure for the raising of the level, with which the Uberstromschutz for the protected transistor enters, exists in relation to the level of the river flowing by the reference transistor in the imitation of the decrease of the surface of the reference transistor, and one can reach this by adding the SpannungsabfaUs by means of a resistance for the basis emitter tension of the transistor. Fig. the Einfügang of a resistance (g 1) shows 6 between the ports (tl) and (T2) for the increase of the emitter base voltage (VBEQ5) of the reference transistor (QA) during the circuit in accordance with Fig. 1. Fig. the Eirlfügung of a resistance (R2) shows 7 between the ports (T3) and (T4) for the increase of the emitter base voltage (VBEQ7) of the reference transistor (Q7) in the circuits in accordance with Fig. 1 or Fig. 2. Fig. the insertion of a resistance (R3) shows 8 between the ports (TS) and (T6) for the increase of the emitter base voltage (VBEQ24) of the reference transistor (24) in the circuit in accordance with Fig. 3 or for the increase of the emitter base voltage (VBEQ.28) of the Bezagstransistors (Q28) in the circuits in accordance with Fig. 4 or 5. the independence of the Uberstromschatzes from the operating temperature it can be maintained if one provides the river (I3) with such Temperaturkoeffmient that the Spannungsahfall at a resistance such as 0il, 112 or R3) proportionally with the absolute temperature changes, at which the carved and the reference transistor are operated. A good possibility for this exists in the use of a power source (ISl), with which the supplied river (13) the river in a resistance is proportional, at which a tension proportionally KT/q one holds, by being held equal the difference between the emitter base voltages of two transistors claimant at equivalent temperature, and with which the resistance is operated at equivalent temperature and the same temperature coefficients as dfe of resistances 0il, R2 or R3) has. One port current automatic controllers of this fundamental kind are among other things described RK 392,375 B a) in the US-PS 3,629,691, b) in the US-PS 3,911,353, c) in the US-PS 3,930,172, and tl) in the US-PS 4,063,149. Fig. possibly one this one port current automatic controller (IREG) shows 9, that with a connection to the port (T2) of the quasi-linear amplifier in accordance with Fig. 1 is attached and with its other connection to the entrance (51) of a current mirror amplifier (CMA) and then over its entrance circle to its reference connection (53) and thus to the operating voltage (B+). The exit (52) of the current mirror amplifier (CMA) supplies a Tailstrom (4) proportionally too (I3) to the hooked up emitters of the transistors (Q12) and (Q13). One can produce also one proportionally to KT/q running tension at one of the resistances (g 1, R2 and R3), if one lets a voltage drop develop at these equal the difference of the emitter base voltages of two transistors. Fig. 10 a circuit shows lthnlich in the US-PS 3,629,691 described circuit for the production of a tension equal the difference between the emitter basis potentials (VBEQ5) and (VBEQ6) the NPN transistors (QA) and (Q6) over (g 1). The specialist will find easily numerous circuit modifications on the basis understanding revealing in the context of the invention, and which enclosed requirements are to cover with their save area all such over-current protection circuits in the sense of the understanding invention.



[2]

No current sensing resistor is used for sensing overcurrent condition in a power transistor in the disclosed overcurrent protection circuit, avoiding the power loss and reduction of available output potential range for the power transistor associated with the use of such sensing resistor. Instead, a differential comparator means is used to sense when the emitter-to-base potential of the power transistor exceeds that of a reference transistor sufficiently to indicate an overcurrent condition in the power transistor.



1. Electronic circuit with a protected transistor, to which a basis driver stream and an emitter collector tension are supplied, whereby ffir the protected transistor an over-current protection circuit is intended, which exhibits a second transistor, which is in such a manner coupled with the protected transistor that the operating temperature of the Bezugswansistors with that of the protected transistor runs, thereby characterized that the second transistor (Q7; Q5) a reference transistor connected with a power source (IS1, Q8) is, whereby its collector emitter distance leads a river of pre-determined value, and which supplies second transistor an emitter basis reference potential, which is supplied a difference comparison circuit (Q10, Qll, Q12, Q13), those the emitter base voltage of the protected transistor (Q2, Q4) with that of the second transistor (Q7, Qb') compares and with Uberstromzustand of the protected transistor an announcement supplies, if its emitter base voltage around a pre-determined amount the emitter base voltage of the second transistor (Q7; Q5) exceeds, and that by a Begrenzerschalmng (Q1, Q3, Q14, Q15) a further rise of the basis driver stream for the protected transistor (Q2, Q4) is limited as a function of the announcement of the overcurrent condition.

2. Over-current protection circuit according to requirement 1, by characterized that the difference comparison circuit two bipolar transistors switched as emitter coupled Gegentaktstnfe (Q10, Qll; Q12, Q13) of same Leitungstyps contains, whereby by a ouple circuit (Q9, IS2) a Teilslrom the interconnect point of the emitters of the two transistors (Q10, QU; Q12, Q13 is supplied), and that the entrance electrode the one of the two transistors (Q10, Q12) with the emitter or the basis of the reference transistor (Q7, QA) and the entrance electrode of the other one of the two transistors (Qll, Q13) with the basis and/or the emitter of the protected transistor (Q2, Q4) is coupled, and that the announcement of the overcurrent condition of the output electrode of that one of the two transistors (Q10, Q12) is deduced, which leads with missing Uberstrom to few.

3. Over-current protection circuit according to requirement 1, by characterized that the difference comparison circuit a resistance (R2; G 1) contains, for that in row with the collector Emilier distance of the reference transistor (QT, Q$) is appropriate and the same pre-determined current value leads and its two ends (“1 ' 2, T4 and/or tl, T3) is so switched that its Spannungsahfall, which depends on the pre-determined current value adds itself to the emitter basis potential of the reference transistor (Q7, QA), so that a Summenspannnng between the first end of the resistance of the Basisoder Emitterelektrode of the reference transistor (QT, Qb”) including a connection other Basisbzw. Emitterelektrode of the reference transistor (QT, QA) with the second end of the resistance develops that two further than emitter coupled Gegentaktstufen switched transistors (Q10, Qll; Q12, Q13) of same Leitungstyps RK 392,375 B are intended, whereby over a Koppelsehaltung (Q9; IS2) the interconnect point of the two connected emitters of the further transistors (Q10, QU; Q12, Q13) a component current is supplied and the entrance electrode one of the two further transistors (Q10, Q12) to the first end (T2, T4) of the resistance (R2, g 1) and the entrance electrode of the other one of the two further transistors (Qll, Q13) at the basis or Emitterelektrode of the gesehUtzten transistor (Q2, Q4) is coupled, so that the further transistors (Q10, Qll; Q12, Q13) the Snmmenspannnng. .mit the basis emitter Potenüal of the protected transistor (Q2, Q4) compares, and that the announcement of a Uberströmens is deduced of the Ausgangseleklxode of that one of the further transistors (Q10, Q12), which leads with missing overcurrent to few.

4. Over-current protection circuit according to requirement 1, 2 or 3, by it characterized that the power source (IS1) a further resistance is switched into series, against its ends a tension rests, which equal to the difference between the emitter base voltages of a pair of transistors (Q5, Q6) is, and that a circuit is intended proportionally to the production of the river of pre-determined value to the river flowing by the resistance. Überstromschutzschaltnng according to requirement 3, by characterized that a circuit with an additional transistor ((Q6), Fig. I0) to the power source (ISl) is coupled, whereby a tension between the ends of the resistance (g 1) lies close, which is equal to the difference between the emitter base voltages of the Bezngstransistors (Q5) and the other transistor.