Class AB Audio Power Amplifier.
Class
AB amplifier is an amplifier configuration that stands somewhere
between Class A and Class B configurations. A small diode biasing
voltage keeps the output transistors ON even if there is no input
signal. The transistors will operate normally in their active region for
any small input signal.In simple words, one transistor will be ON for
more than one half cycle of the input signal.? This avoids crossover
distortion. Anyway, a small amount of collector current will flow in the
idle condition, but it is negligible when compared to the Class A
configuration. .?A simple, high quality audio power amplifier that can
be operated from 12V dc is shown below. Such an amplifier is very
suitable for car audio applications. The circuit is very straightforward
and uses commonly available components. Power output of this amplifier
is around 10W.
Description.
The
circuit is purely based on transistors. The first stage of the circuit
is the long tailed pair (LTP) built around the transistors Q1 and Q2.
Transistors Q10, Q11 and associated components form a constant current
source for the long tailed pair. Resistors R15 and R3 are biasing
resistors. The second stage of the circuit is built around transistor
Q3. Transistors Q9 and Q6 form a constant current source for the second
stage. Resistor R8 is the feedback resistor and it plays a vital role in
reducing distortion. The final power amplification stage of the circuit
is based on the complimentary pairs Q8 and Q5. Q7 and Q4 are the driver
transistors for Q8 and Q5 respectively. Audio output is coupled to the
loud speaker through capacitor C3.?D1 and D2 are biasing diodes. C4 is
the power supply filter capacitor. This amplifier circuit can be
operated from anything between 12 to 16 volts.
Circuit diagram.
Class AB amplifier
Notes.
- Use 12V DC for powering the amplifier.
- An optional 10K POT can be added in series to the input for volume control.
- Use a 4 ohm/20W speaker as the load.
- Transistors Q8 and Q5 must be fitted to a proper sink.
No comments:
Post a Comment