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13-18 Amplifier: Audio power: Amplifier

The audio signal output of the electronic reducer leaves the IC circuit of output 2 and is applied to a high frequency compensation network (173 R) and
(174 C), then they are connected via C173 to the input of the power amplifier in pole 3, and the output of the power amplifier from pole 6 - and from here it is connected capacitively to the capacitor 182 C to the speaker (speaker) - and the speaker's impedance must be (32 ohms) To avoid large power dispersion of the integrated circuit IC.

Protection with Dispersion Bypass:

Overdissipation protection The power amplifier is protected from overdissipation in two ways:

1- Determine the current.

2- Shutdown circuit for thermal protection.

Voltage Regulator:

The voltage regulator adjusts the voltage in all the circuits of the IC, as well as it provides from pole 8 the regulated voltage to feed it to the volume control circuit.

18-14 Audio output circuit by push and pull method:

It is possible to secure the operation of the audio output amplifier (or the preamplifier) ​​using a transistor circuit as in the figure. The diagram shows one transistor for the preamplifier 2030 Q and operates the push-pull amplifier circuit with two transistors (2010 - 2020) - connected
(speaker) with impedance (16 ohms) from the common emitter output of the two transistors (2010 Q and 2020 Q) via capacitor 2040 to line (26 volts).

Speaker impedance. In some circuits, the speaker is connected from the common radiator output through a capacitor and then to the ground. It is noted that there is no need for an output transformer - because the low emitter output impedance of the 2010 and 2020 Q transistors works in a compatibility process with which is (16) ohms). The output circuit consisting of two complementary transistors, one PNP and the other NPN, are connected in series between the supply point and ground - in this way one transistor is sufficient in the amplifier's inductive circuit. As for the output circuit, which consists of two transistors that are completely identical in the push and pull circuit. It takes two transistors, opposite in type, to generate the actuation or trigger voltage

How the circuit works:

The circuit shown in the figure is a push-pull output amplifier of class B, and this means that when one of the output transistors is in the conducting state, the other is in the cut-off state, and vice versa - if we assume that the audio signal at the Q2030 output is moving in the positive direction, and this applies The signal is on my bases Q2020 and Q2010 - but Q2020 is a PNP transistor it cuts and Q2010 is an NPN transistor it connects to the positive half of the base signal. The case is reversed when the stimulus signal is in the negative direction. That is, Q2020 becomes a conductor and Q2010 becomes a cutter, and AC currents from each transistor reach the speaker, through the capacitor 2040 C. In this capacitor and the speaker, the two halves of the audio signal are combined to form the sound. The output power of the speaker is equal to twice the collector dispersion of each transistor. The resistance R2040 in the base of the catalyst 2030 Q regulates this transistor against temperature changes, and it does so by applying feedback from (2010-2020) to the base of Q2030 - small resistances with a value of

(1 or 2 ohms) in series with each radiating terminal - these stabilize and regulate the output stage, against temperature changes. The output (push) - pull method gives the largest capacity and the highest yield, as it works in class B. However, the output becomes nonlinear when approaching the cut-off point radiators.

Therefore, sound distortion may occur when there is a defect in the circuit. To reduce this distortion, it applies a small forward bias to each transistor - the base of the Q2010 NPN transistor is positively polar to its emitter - and the base of the Q2020 PNP is negatively polar to its emitter