SU1243085A1 - Power amplifier - Google Patents

Description

The invention relates to radio engineering, in particular, to power amplifiers of signals of low and high frequencies, and can be used in public address and notification devices.

The purpose of the invention is to increase the efficiency by reducing the power loss.

Fig. 1 shows a structural electrical power amplifier circuit; in fig. 2 is a timing diagram of the amplified signal and bias current.

The power amplifier contains a preliminary cascade of 1 amplification, about

Incomplete push-pull amplifier stage 2, bias resistors 3 and 4, keys 5 and 6, comparators 7 and 8, transistors 9 and 10, and power supply 11.

The power amplifier works as follows.

In the absence of a useful signal, the keys 5 and 6 are open, the transistors 9 and 10 are not biased, so their collector and main circuits do not consume power from the 1T power supply, and the final two-stroke cascade 2 amplifiers are in cutoff mode (class mode C) is closed to low level noise and interference.

Under the action of the half-waves of the amplified signal, the comparators 7 and 8 alternately work. At the output of one comparator 7, a rectangular voltage pulse is generated at the output of a positive half-wave signal — the switch 5 of the base bias of the transistor 9j and the output of the other comparator 8, under the action of a negative half-wave of the signal, another rectangular voltage pulse 5 is formed that controls the closure of the switch 6 in the base-bias transistor circuit. ra 10.

The duration of the control pulses at the outputs of the comparators 7 and 8 and the duration of the closure of the keys 5 and 6 associated with these comparators is equal (with high accuracy) to the duration of the positive and negative half-waves of the signal, respectively, at the instants of their zero crossing.

When alternately closing the switches 5 and 6 to the transistors 9 and 10, respectively, through the resistors 3 and 4, the bias is applied.

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the operation of the push-pull terminal stage 2 amplification on these transistors in the AB mode. The transistor 9 is converted to AB for the duration of the half-wave of the TiinbHbix signal, and the transistor 10 is switched to the same relay only for the amplification time of the negative half-wave of the signal; due to the successive operation of the comparators 7 and 8, the collector circuit of transistor 9 and its base circuit, which is closed through the switch 5 and the bias resistor 3, in the AV mode, consume the bias current from the power source 11 only during each positive half-period of the signal . Similarly, the collector circuit of transistor 10 and its base circuit, which closes via key 6 and bias resistor 4, in AV mode, draws bias current from power source 11 only during the operation of each negative half-period of the signal.

Thus, the energy of the power source 11, which is necessary for the operation of transistors 9 and 10 in the AB mode, consumes only half the period of the amplified signal and, respectively, half the time of action of this signal in each arm of the main shell. ,

In the collector-emitter circuit of a transistor of one arm for one half-period of a sinusoidal signal, the current pulse of one half-wave of the amplified signal (curve 12) and the rectangular pulse current 13 of the mixing mode AB operate.

Since the amplitude of the pulse 13 in amplifiers with an output power of 50-200 VA and more is an insignificant value - no more than 0.2 of the amplitude of the amplified signal, the distortion of the form of this signal (mode switching noise) is only a small amount The portion of the square impulse 13 that does not coincide with the area bounded by the half-period curve 12 of the signal. The remainder of the largest part of the energy r of Empulse 13 is summed with the impulse of signal 12 and this total energy is transferred to the load. At the same time, the control circuit of the smelting, working strictly synchronously with the amplified signal, provides additional amplification

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This is due to the fact that the displaced 11 is almost completely - with the half-wave base - the power of the power supply, engendered to provide j of the push-pull cascade, is basic to the extra, which is allocated in the load of the signal and not on the transistors of this)

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The relative value of the power loss to ensure the mode AB in the collector-emitter circuit of the transistor of the terminal push-pull stage 2. the amplification for one working half-period of the amplified signal is only an insignificant part — about 1-2% of the area of the rectangular impulse. 13 The form of the amplified signal is distorted by the same amount (1-2%), but the magnitude of these distortions can be easily reduced by negative feedback. In addition, these distortions are manifested in the form of high-order harmonics, which in most cases of amplifiers can be easily filtered in the load.

Editor N. Yatsola Order 3716/55

Compiled by N. Dubrovska

Tehred O. SopkoCorrector S. Shekmar

Circulation 816

Subscription

VNIIPI USSR State Committee

for inventions and discoveries 13035, Moscow, Zh-35, Raushsk nab., 4/5

J.

Production and printing company, Uzhgorod, st. Design. four .

Claims (1)

Invention Formula A power amplifier containing a series-connected pre-amplifier stage, having a symmetrical output, and a terminal two-stroke amplifier stage, implemented transistors, as well as two bias resistors, each of which is connected to the input by a single pin. of the end arm of the push-pull amplification stage, and the bias control circuit, whose input is connected to the symmetrical output of the pre-amplification cascade, characterized in that, in order to increase efficiency by reducing the power loss, the bias control circuit contains two keys, each of which is turned on between the other output of the bias resistor of the corresponding arm of the terminal push-pull amplification stage and the power bus of the terminal push-pull amplification stage, and between the input of each shoulder of the terminal push-pull On the gain stage and the control input of each key, a corresponding comparator is inserted, the input of each of which is the input of the bias control circuit. Subscription