|
A linear audio power amplifier can exhibit an effect called "crossover
distortion," caused by nonlinearities when the signal crosses zero.
In a class AB amplifier, such as Circuit A, below, the output transistors
must be biased so that one or the other is on, even for small voltages
near zero. If Q1 and Q2 are both off for some small voltage range,
the result will be a zero-voltage interval at the zero crossing,
as shown in Figure 1.
A circuit called a VBE multiplier can be used to adjust the output
stage bias for lowest crossover distortion. The VBE multiplier is
comprised of transistor Q3, resistor R1 and potentiometer R2 in
both Circuit A and Circuit B below. It is placed on the same heatsink
as transistors Q1 and Q2 to provide thermal tracking.
Both of these circuits will work, providing an adjustable
bias for the output stage. However, one is the preferred solution.
The other has a serious flaw.
Questions:
1. Which is the preferred solution?
2. Why is the other solution undesirable?
Answer
See all EE-Quiz Questions
|
