I would like to ask how a Class AB amplifier is biased. In other words, is there an established procedure which is known to give good results? In simulations under LTSpice my amplifier was optimally biased but when I modified the circuit according to the optimal values under LTSpice, my amplifier is underbiased.
Coincidentally, I recently wrote an article. http://www.edgrochowski.com/articles4/classab.html
The lowest distortion occurs at around 22mV across the emitter resistor.
The real difficulty is in staying at optimum bias as the output transistors heat up. Expect the bias current to increase by several times.
Ed
The lowest distortion occurs at around 22mV across the emitter resistor.
The real difficulty is in staying at optimum bias as the output transistors heat up. Expect the bias current to increase by several times.
Ed
I usually measure distortion and adjust, and also measure the voltage drop over the emitter resistors at the same time to see that I'm not going too far. You can measure distortion with ARTA or REW with decent sound card and PC,
This is usually stated as 26mV, but there are just too many counterexamplesof either for the theory to be credible. Two amps I have on the bench at the moment want 15mV and 5mV respectively, and I've seen as high as 40mV.
The theory is indisputable, but it applies only to a pair of output transistors driven by a voltage source. Its applicability depends on how closely the rest of the amplifier approximates a voltage source (my amplifier is close).
Ed
Ed
