Power amplifier with balanced differential input stage. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers
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The amplifier has the following main technical characteristics:
Rated output power ...... 55 W
Harmonic distortion .......... 0,07%
Operating frequency band .......... 20... 50 Hz
Signal-to-noise ratio .................... 89 dB
Supply voltage ........... ±36 V
Quiescent current .......... 100 mA
One of the features of this power amplifier is its power supply from a bipolar source. This allows you to turn on the load between the outputs of the amplifier and the common wire without a transition capacitor. Another feature is the use of a balanced differential input stage with good thermal stability.
Rice. 1 (click to enlarge)
Schematic diagram of the amplifier is shown in fig. 1. It consists of an input stage (transistors VT1. VT2}, a voltage amplification stage (VT3) and an output stage (VT4-VT7) and protection elements for output transistors (VD3-VD6). The input stage is made according to the differential stage circuit with an unbalanced output. the signal enters the base of the transistor VT1 through a decoupling capacitor C1. The OOC signal is fed from the output through the resistor R6 to the base of the transistor VT2. The differential stage compares the output voltage with the zero voltage of the common wire, and if for some reason the constant voltage at the output of the amplifier becomes different from zero, the error signal from the output of the differential stage is fed to the output stage, thereby providing zero voltage at the output of the amplifier.From the output of the differential stage, the signal is fed to the voltage amplifier and through the resistor D7 to the output stage.The output stage is made on composite complementary transistors VT4, VT6 and VT5, VT7, with a large input and a very small output resistance.
Diodes VD1 and VD2 create the initial bias of the output stage and provide temperature stabilization of the quiescent current of the output transistors. Through the voltage boost capacitor C5, the PIC is connected to the target. collector load of the transistor VT3, thereby ensuring the maximum output voltage swing. Diodes VD3, VD4 and VD5, VD6 protect the output transistors by shunting the transistor junctions in case of overload. Elements C3, C6, R.14, C7, L1 prevent self-excitation of the amplifier at high frequencies.
For temperature stabilization of the quiescent current of the output transistors, diodes VD1 and VD2 are installed on a heat sink common with transistors VT6 VT7. Coil L1 is wound on a resistor R15 (MLT-2) and contains 25 turns of PEV-2 0,8 wire. Resistors R12 and R13 are made of high-resistance wire (manganin, constantan).
The adjustment of the amplifier consists in checking the correct installation. With proper installation and the use of serviceable elements, additional settings are not required. To power the amplifier, a bipolar source is required that provides a current of at least 36 A at a voltage of ± 1,2 V.
Literature
DI. Ataev, V.A. Bolotnikov. Practical schemes for high-quality sound reproduction. M. Radio and communication. 1986
Publication: cxem.net
See other articles Section Transistor power amplifiers.
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