- Jul 06, 2017 -
Amplifier type, how to do a recognition?
Depending on the angle, the amplifier can be divided into different categories. Amplifier according to the size of the signal conduction angle can be divided into A, B, C, D, AB class, this article will be introduced one by one.
Class A amplifier
Pure Class A amplifier that is the final amplifier tube work in a state of the amplifier, also known as pure Class A amplifier. Class A amplifiers have a current flowing through the transistor (ie, the conduction angle of 3600) over the entire period of the input signal. This amplifier is called Class A amplifier. Class A amplifier distortion is very small, but its efficiency is low, even in the ideal case, the highest efficiency can only reach 50%, usually only 30% to 40% 0 in the input signal half a cycle of current flow through the transistor (Ie, the conduction angle is 1800), this amplifier is called Class B amplifier. Since the conduction angle is 1800, the other half of the input signal is cut off, so the distortion is great.
The two (or two) transistors of the Class A amplifier (Class A amplifier) are always in a conductive state, that is, they maintain the conduction current regardless of the presence or absence of signal input and make the two currents equal to the peak of the AC When the flow in the case of the largest signal into the load. When there is no signal, the two transistors flow the same amount of current, so there is no imbalance in the output center of the current or voltage, so no current input speaker. When the signal tends to positive, the output transistor above the line allows more current to flow, the lower output transistor is relatively reduce the current, because the current began to imbalance, then flow into the speaker and push the speaker sound. In simple terms, the pure class amplifier is far from working at maximum output power.
Class B amplifier
Due to the presence of the transistor's turn-on voltage and the non-linearity of the initial conduction, there is a crossover distortion in the Class B amplifier, which is clearly not allowed in the field of high-quality HI-FI amplification. Therefore, the push-pull circuit of the two transistors are often applied a small amount of bias, so that the conduction angle is slightly greater than 1800, to avoid cross-distortion. This circuit, conduction angle between the A class and B class, called AB class (class B) amplifier oAB class circuit efficiency is lower than the B class, only 60% to 70%. But it takes into account the advantages of Class A and B (low distortion, high efficiency), it is now widely used.
Class AB amplifiers
Class B amplifier that is the final amplifier tube work in the Class B state of the amplifier. Also known as class AB amplifier. Class AB is a traditional amplifier. It is also the type of most amplifiers. From the power point of view, Class A power values are generally larger. But does not always work in the state of maximum output power, although the amplification type is less than pure Class A, as long as after a high level of debugging and school sound, Class B amplifier can also send a beautiful and moving sound. Countless HIFI manufacturers have proved this point with the fact.
Class C amplifiers
When the input signal exceeds the bias point, only the current flows through the transistor (ie, the conduction angle is less than 1800). This amplifier is called Class C (Class C) Amplifier Class C amplifier is more efficient, but its current waveform distortion too Large, and therefore can not be used for Hi-Fi amplification, can only be used for high-Q tuning circuit as the load of the resonant power amplification. As the tuning loop has the filtering ability, the loop current and voltage are still close to the sine waveform, the distortion is very small.
Class D amplifiers
Class D amplifier refers to the Class D audio power amplifier (sometimes referred to as digital amplifier). By controlling the ON / OFF of the switch unit, the amplifier that drives the loudspeaker is called a Class D amplifier. Class D amplifier for the first time in 1958, in recent years has gradually become popular. Compared with the general linear AB amplifier circuit, D class amplifier is high efficiency, small size and so on.