DE1762319A1 - Transformerless power amplifier in a bridge circuit, especially for audio frequencies - Google Patents

Description

1762313

! DELEB ¹ TJIiKEH '- Patentverwertungsgesellschaft mbH Ulm / Danube «Elisabethenstr. 3

P 17 62 319.7-31 21.5.1968

PT-N-Hs / rh

Transformerless power amplifier in bridge circuit, especially for audio frequencies.

The invention relates to a transformerless power amplifier in bridge circuit in which two bridge halves are formed by pairs of complementary transistors so that in each Bridge branch the collector-Eaitter path of a transistor is In such a bridge circuit, the bridge diagonal formed by the two connection points of the complementary transistors lies a load resistor, while a supply voltage source is located in the other bridge diagonal. for

Especially * the output stages of audio frequency amplifiers are transformerless Power amplifier in bridge circuit in many variants for Eöhr circuits known (radio technology Kr, 15, 1954-, Page 426, Funktechnik Sr. 21, 1956, page 636). Compared to a power amplifier of conventional design with two amplifier elements in push-pull B mode are obtained in the bridge circuit with approximately twice the cost of switching elements four times the useful power. It is thanks to this high efficiency that the bridge circuit in audio frequency amplifiers with high output power has generally prevailed.

Also transistorized bridge circuits are considered transformerless Power amplifier for audio frequencies known (radio technology No. 3, 1967, page 77 and Funkschau 1967, issue 3, page 178), wherein a right and a left · bridge half through a complementary pair each are formed by transistors.

The disadvantage of these known bridge arrangements with transistors is that a relatively large one is used to control one bridge half Control voltage is required, which must be slightly larger than that applied to the load resistance · useful voltage. This high control voltage is generally applied by a separate driver stage.

The invention is based on the task, in relation to the performance equivalent · circuit · arrangement of a power «-

009819/1606

BATH ORIGINAL

Develop an amplifier with a lower control voltage is needed

In the case of a power amplifier of the type described, the invention consists in that the transistors are thus in the bridge branches lie that at the two connection points of the load resistance assigned bridge diagonal the collectors each one of the transistors are connected to each other

The advantage of this arrangement, in which the collectors each have two mutually complementary transistors are connected together, is that a smaller control voltage is required to control the bridge than in known arrangements, since the Transistors are operated in emitter circuit. For the correct phase and amplitude control of all transistors of such a bridge, in which at least one transistor is controlled by a signal source, it is advantageous if the control electrodes of the remaining transistors are connected to a connection point facing away from the associated collector of the transistor in question Load resistance are connected.

The invention is illustrated in the following with reference to two circuit diagrams Figures 1 and 2 explained in more detail. The same reference symbols correspond to the same parts in the figures.

The bridge circuit of a power amplifier, which is shown in FIG. 1 as a basic circuit or, for example, as a direct current A amplifier, contains four transistors as bridge branches, with transistors 1 and 2 and transistors 3 and 4 being complementary to one another. The transistors 1 to 4 are so arranged in the circuit that the collectors of a complementary pair are connected to one another. The two bridge diagonals are marked by four connection points 5, 6, 7, 8, the load resistor 9 being switched on between connection points 7 and 8, while a fixed voltage source -Ug is located in the other bridge diagonal from connection points 5 to 6. The bridge arrangement is controlled by an input voltage U _£ at the transistor 2, while the other transistors are connected with their control electrodes via resistors R ₂ to the connection points of the air resistance 9 facing away from the collectors concerned for the correct phase and amplitude control. the

009819/1606

other resistors R,, R ^, R ^ of the arrangement are for adjustment the operating points and intended for current limitation for the transistors. To identify the correct phase position of the inputs and Output signals are small arrows on the input and output electrodes of transistors 1 to 4 are shown.

In Fig. 2 a practically tested embodiment of the invention is shown, which is suitable, for example, as an audio frequency amplifier. In this arrangement, transistor 1 is also controlled directly by the input signal TJg, while transistors 3 and 4 are controlled jointly by part of the output voltage at point 7 _{via a voltage divider 10 connected in parallel with load resistor 9 (Rj 4 ■ 4 Q).} In order to obtain a particularly power-saving control for the arrangement according to FIG. 2, an emitter follower stage 11 with a sliding operating point can be provided at the input. The operating point of this emitter follower stage 11 is shifted as a function of the output voltage U. via a feedback Rj. The working resistance 12 of the emitter follower stage is not directly connected to ground but via a resistor Ry. The connection point between the resistors 12 and Ry is the point of engagement for the feedback. The size of the resistances Ry and Ry is determined by the equation Ry-: (Ry + Ry) aU _E : U., Where Ry is chosen to be 100 Q, for example. In addition to the power-saving control of the bridge arrangement, the feedback offers the advantage of a strong reduction in distortion factor.

It can be particularly advantageous to use either the complementary transistor pairs or the entire amplifier arrangement except for to carry out the load resistance in monolith technology and in one to accommodate common housing. This so-called monolith can, for example, be combined with a loudspeaker to form a structural one Unity. For example, the housing of the monolith can be mounted on the housing aoa loudspeaker. Through this On the one hand, cooling of the monolith and, on the other hand, a particularly space-saving arrangement is achieved.

009819/1606

BATH ORIGINAL

Claims (7)

Patent claims: 1.Transformerless power amplifier in a bridge circuit, in which two bridge halves are formed by pairs of complementary transistors in such a way that the collector-emitter path of a transistor is located in each bridge branch, in whose bridge diagonal formed by the two connection points of the complementary transistors a load resistor and in its other bridge diagonal a supply voltage source is located, in particular for increasing the power of audio frequencies, characterized in that the transistors (1 to 4) are located in the bridge branches in such a way that the collectors are at the two connection points (7 »8) of the bridge diagonal assigned to the load resistor (9) two transistors (1, 2 or 3 »Ό are connected to each other. 2. Power amplifier according to claim 1, in which at least one transistor of the bridge is controlled by a signal source , characterized in that the control electrodes of the remaining transistors (1, 3 »4) with one, the associated collector of the relevant transistor (1 or 3 or 4) remote connection point (7 or 8) of the load resistor (9) are connected. 3. Power amplifier according to claim 1, characterized in that «the bridge circuit is controlled by an impedance converter stage (11) whose operating point is shifted as a function of the output signal (TJ ^). 4. Power amplifier according to claim 3, characterized in that the working resistance of the impedance converter stage (11) is divided into two partial resistances (12, By), and that a feedback voltage derived from the output signal (U ^) for regulating the working point at the connection point of the two partial resistances ( 12, Rf) attacks. 5 «Power amplifier according to at least one of the preceding claims, characterized in that the complementary Traneietorpaare executed in monolith technology and built into a common housing. 6. Power amplifier according to at least one dtr claims 1 to 4, characterized in that the whole ampl & rktran- 009819/1606 - y - Order except for the load resistance (Et) in monolith technology is designed and built into a common housing 7. Power amplifier for audio frequencies, in which a loudspeaker is provided as a load resistor, according to claim 5 or 6, characterized in that the common housing is connected to the loudspeaker to form a structural unit. 009819/1608 Blank page