DE2363094A1 - Push-pull amplifier - has high output current and limited short-cct. current - Google Patents

Abstract

A pair of complementary transistors is connected with each other and with the output by their emitters, and their collector-emitter paths are inserted between a supply voltage source terminals. One of them (control transistor) is controlled at its base by an input signal. A third transistor, of the same conduction type as the second, collector-emitter path is also inserted between the voltage source terminals, and its collector is connected through a diode to the output. Output current flows through the second or the third transistor and the diode, depending on the input signal. The third transistor base is connected to the control transistor collector, and its collector to the second transistor base.

Description

2 3 6 3 0 9

TELEFUNKEN COMPUTER GmbH, Constance

Ik, December 1973 PT-KN Za / ro

Push-pull amplifier with high output and limited short-circuit current

The present invention relates to a push-pull amplifier, which on the one hand delivers high output currents and on the other hand only with a limited one when idle Short-circuit current is loaded.

Push-pull amplifiers are known per se and, according to the example shown in FIG. 1, usually consist of one complementary transistor pair, the transistors of which depend on whether there is a positive or a negative input voltage at input E, are alternately controlled to be conductive. the two complementarily connected diodes connected to the circuit input are used to generate a bias voltage for the Base connections of the transistors and are responsible for ensuring that the quiescent current flowing in the push-pull amplifier is via the Transistors flows. The diodes that are arranged on the output side and are also connected in a complementary manner are used for thermal purposes Stabilization and ensure that the current negative feedback is still effective even at high operating temperatures.

KN 73/31 509827/033 B _{/ 2}

AL INSPECTED

The disadvantage of the known push-pull amplifier ^ that despite the measures mentioned, the quiescent current (short-circuit current) is difficult to stabilize. This is particularly true for push-pull stages built in discrete technology, in which, for example, as shown in FIG. 1, the stabilization of the short-circuit current by means of the between the emitter connections the transistors of the complementary transistor pair arranged resistors is realized. In case of The power output of the push-pull amplifier shown increases however, due to the temperature increase associated with the power output, the short-circuit current increases very sharply.

The object of the present invention is to provide a simply constructed push-pull amplifier, the optimal one has dynamic and static properties, and in particular can be used in an excellent manner in terms of thermal stability.

The object on which the invention is based is achieved by the measures specified in claim 1 achieved.

The details of the invention are illustrated in FIG illustrated push-pull amplifier according to the invention in more detail explained.

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The push-pull amplifier stage shown in FIG. 2 according to the invention consists of a complementary transistor pair with an npn transistor 1 and a pnp transistor 2, both of which are connected to one another with their emitter connections and to the output connection A of the circuit with regard to their common emitter point. The collector connection of the npn transistor 1 is with the positive pole + U; the collector connection of the pnp transistor 2 to the negative Pole -U connected to a supply voltage source.

The features according to the invention of that shown in FIG Push-pull amplifiers consist in that only one transistor of the complementary transistor pair is controlled and this in turn controls the second transistor. For this purpose, a lock is further provided according to the invention, which consists of a further third transistor 3 and causes only one of the two transistors 1, 2 of the complementary Transistor pair is conductive and the other is held in the blocked state.

Corresponding to the push-pull amplifier shown in FIG the npn transistor 1 is the transistor controlled by the input signal applied to input E and is accordingly referred to as a control transistor. According to the special voltage conditions, the transistor 3 is a pnp transistor chosen. This is connected on the emitter side to the positive pole + U of the supply voltage source and is located

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on the base side at the collector connection of the control transistor 1. The transistor 3 is also connected to its collector connection to the base of the second transistor 2 of the complementary transistor pair and via a resistor 4 to the negative Pole -U connected to the supply voltage source.

In addition, there is between the collector connection of the transistor and the common emitter point of the complementary transistor pair a diode 7 is inserted, the cathode terminal being connected to the mentioned emitter point. This diode has the task of protecting transistor 3 from being driven into saturation.

Between the collector connection of the control transistor 1 and the positive pole + U of the supply voltage source lies a collector resistor 5 «

According to the function of the push-pull amplifier stage according to the invention As an impedance converter, the circuit can be used as a voltage-controlled current amplifier and should be used as such are explained in more detail.

It should be said in advance that the circuit arrangement according to the invention shown in FIG. 2 between input E and Output A has an offset voltage that corresponds to the base-emitter voltage of the control transistor 1 corresponds. This offset voltage can, however, be achieved by connecting a pnp emitter follower can be compensated in a simple manner.

KN 73/31 509827/0335 ^{/ 5}

If a positive output voltage is to be generated at output load 6, then input E must have a positive output voltage Control voltage of the same amplitude (taking into account the offset voltage).

As a result, the control transistor 1 becomes conductive, whereby due to the voltage drop across the resistor 5, the Transistor 3 is controlled to be conductive. This transistor is turned on so far that the required diode 7 Output current flows and the potential at its cathode just assumes the size that the Control transistor 1 remains conductive. The base current for transistor 3 is thus continuously supplied.

For positive output currents, the transistors 1 and 1 form a closed control loop. The transistor 2 remains due to the conductive state of diode 7 blocked (locked)

Should a negative output voltage at the output load 6 are generated, the control voltage at input E must be negative. The effective between input E and output A. Offset voltage must also be taken into account.

In the case of the negative output current, the control loop closes over all transistors 1, 2 and 3, with

the current path is now due to the blocked diode 7 / from the transistor

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locked to transistor 2

and is held in this state (locked)

If the input voltage is negative, the control transistor blocks first 1 and thus also the transistor 3 · The transistor is thereby converted into the conductive state. Will the output voltage at the output load is so negative that the control transistor 1 becomes conductive with reference to the predetermined input voltage, the transistor 3 also becomes conductive again conductive and the base control of transistor 2 is regulated.

In this way, the emitter of transistor 2 follows the input voltage fed to input E. The from Control current flowing from transistor 1 to transistor 2

U__ (transistor 3) ^k R (resistor 5)

If there is no output load 6 at output A, the output voltage is generated in an analogous manner and the above-mentioned one Control current I corresponds to the short-circuit current.

The output currents corresponding to the two active states be

or I _ CZ ¹ Zi ' ^ß 2'

where (b ' _{x is} the current gain for transistors 1, 2 and 3

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It goes without saying that the described inventive Push-pull amplifier stage can also be constructed with complementary active components.

The locking of the current paths is activated in such a way that when power is drawn from the output stage, the receiving path is blocked and that the output path is separated from the withdrawal path when power is output in the final stage. This creates an impermissibly large short-circuit current safely avoided.

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Claims (2)

- 8 patent claims \) Push-pull amplifier with high output and limited short-circuit current, characterized in that a complementary transistor pair (1, 2) is provided which is connected to one another and to the output (A) with respect to the collector-emitter paths between the poles of a supply voltage source only one (hereinafter called control transistor) transistor (1) is driven on the base side with an input signal, and that a third transistor (3) corresponding to the conductivity character of the second transistor (2) of the transistor pair is provided, which is also between with regard to its emitter-collector path the poles of the supply voltage source and is connected on the collector side via a diode (7) to the output (A), so that, depending on the input signal, an output current via the second transistor (2) or via the third transistor (3) and the diode (7 ) flows. 2. Push-pull amplifier according to claim 1, characterized in that the third transistor (3) is connected on the base side to the collector connection of the control transistor (l) and on the collector side to the base connection of the second transistor (2). ^KN 73/31 509827/0335