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For how many degrees of an input sine wave does a class B amplifier conduct?
Wiki User
∙ 13y ago
The actual answer is 360 degrees, that is, a class B amplifier will conduct for the entire 360 degrees of an input sine wave. However, the interesting part is how this is accomplished.
For a "pure" class B amplifier, each of the two output power devices will conduct for 180 degrees of the total 360 degrees of a complete sine wave. This is because in a class B amplifier, each of the output devices is biased so that it is off when the input signal is zero. When the input signal goes positive, one of the output devices will conduct. Assuming there is no overall phase inversion in the amplifier, this would be the "upper" device that is connected to the positive voltage rail. In a typical solid state audio power amplifier, this device is usually an NPN transistor or power MOSFET.
The "lower" device, typically connected to the negative voltage rail, will conduct when the input signal goes negative. This device will typically be a PNP transistor in a solid state amplifier, or a power MOSFET.
There are many possible configurations for class B amplifiers. For example, with vacuum tube amps, there is usually only a positive voltage supplied to the output stage, and the two output tubes are identical types. Instead of connecting the lower tube to a negative rail, it is usually connected to ground, but since we are interested in AC amplification, and also since an output transformer is required to couple tube output stages to low impedance loads such as loudspeakers, this doesn't present a problem. The output transformer will have a center tap where the positive output stage voltage is connected, and each of the output tubes will conduct in alternating fashion, similarly to the output of a solid state amp.
In fact, early solid state audio amps also used output Transformers, and they typically also used two NPN transistors for output devices, in contrast to modern designs that use symmetrical matched pairs of NPN/PNP. At that time it was difficult to obtain high power matched pairs, whereas high power NPNs were relatively easy to obtain.
A variation that is often used to obtain more power is the doubling of output devices by operating them in parallel to obtain higher current gain. It is possible to see six, eight, or even more devices operating in this way, but it will almost always be in multiples of two.
Nevertheless, no matter what the variations, a class B amplifier will always conduct for 360 degrees of an input sine wave. There is an important qualification on this, however. A true class B amplifier is almost never seen, due to a problem called "crossover distortion." This occurs because any output device has a nonlinear region during turn-on from zero conduction. While the input signal is beginning to go positive, for example, the output device will not "follow" the input signal in a proportional manner. To overcome the distortion caused by this, most audio amps are operated in class AB, where each of the output devices is biased slightly on all the time. This technique virtually eliminates crossover distortion.
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∙ 13y ago
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What is non inverting amplifier?
The amplifier whose output is inphase with it input means if we consider voltage amplification then there is zero phase shift in input and output
What is the phase relationship between the input and output voltage of a common emitter amplifier?
In common emitter amplifier circuit, input and output voltage are out of phase. When input voltage is increased then ib is increased, ic also increases so voltage drop across Rc is increased. However, increase in voltage across RC is in opposite sense. So, the phase difference between the input and the output voltages is 180 degrees.
Am amplifier that inverts the signal between input and output is called a what?
common emitter
Circuit diagram of RC coupled amplifier?
One of the several uses of an RC coupled amplifier is to amplify the given input signal. It makes use of a sinusoidal input signal.
In a multistage amplifier input impedance is high and output impedance is low justify the statement?
no. input impedance is low & output impedance is high
What is Class b power amplifier?
When we get amplifier output current for 180 degrees of input. then it's called B class amplifier. In a push pull class B amplifier one of the two power transistors or other amplifying elements handles the positive half of the waveform and the other element handles the negative half of the waveform. In practice, push pull audio amplifiers are usually class AB; each power transistor handles slightly more than 180 degrees of input. This minimizes distortion (crossover distortion) when one of the two transistors ceases output and the other takes over.
What is the ideal dc value of output signal when there is no input signal in class b amplifier?
A: If the input is zero the desire output is zero no matter what class it is.
Which BJT amplifier has the phase shift between input and output voltage is 180 degree?
The Class A common emitter BJT design has input on the base and output on the collector. This design is inverting, or 180 degrees phase shift.
What is Class B push-pull amplifier?
When we get amplifier output current for 180 degrees of input. then it's called B class amplifier. In a push pull class B amplifier one of the two power transistors or other amplifying elements handles the positive half of the waveform and the other element handles the negative half of the waveform. In practice, push pull audio amplifiers are usually class AB; each power transistor handles slightly more than 180 degrees of input. This minimizes distortion (crossover distortion) when one of the two transistors ceases output and the other takes over.
What is a transformer-coupled class A amplifier?
A transformer-coupled class A amplifier is just what it says it is. You'll recall that a class A amp is one that has an output that varies through all 360 degrees of an input signal. As regards the manner in which the signal is coupled to or from the stage, a transformer is used, complete with the non-linearity that it will introduce because of the characteristics of the (untuned) inductive component.
Why efficiency of class c amplifier is high?
It conducts for less than one half cycle of the input.
What is class c tuned amplifier?
Class C tuned amplifier is a large signal tuned amplifier that amplifies high power signals of the radio frequency range. The amplifier is said to be Class C if the output cycle obtained is less than half a cycle of the full input cycle. This means the transistor remains active for less than half a cycle so that only that much part of the input waveform is reproduced at the output with amplification. For the remaining part, the transistor remains inactive.
What is invertion?
An inverting amplifier is one where the output is an inverted function of the input. The Class A transistor amplifier, also known as common-emitter, is inverting. As you increase the voltage on the base, the output voltage on the collector decreases. The operational amplifier has an inverting and a non-inverting input. In typical bridge mode, the output is inverted with respect to the (inverting) input, and the non-inverting input is used to reject common-mode input signals by moving the virtual ground point as needed.
Input impedance of voltage amplifier?
In audio the input impedance of an amplifier is between 10 kiloohms and 20 kiloohms.
Input impedance of current shunt feedback amplifier?
The input impedance of a current shunt feedback amplifier is the open loop impedance of the amplifier divided by 1+(A*beta)
What effect does an amplifier have on the frequency of the signal?
A; An amplifier will have no effect on the input frequency however its output may not follow the input frequency at the hi end due to the amplifier limitations
What amplification is done by class c amplifier?
a class c amplifier conducts only for a small fraction of the period ( cycle ) of the input signal. hence its use is normally limited to circuits called oscillators where the high efficiency & power gain inherent of class C is utilised together with tuned circuits. As a matter of information, high fidelity amplifiers used for professional audio etc. use class A amplifier, where the amplifier works continoulsy over the full period of the input signal. Then there is class B type where the amplifier works for about 50% of the input signal period. This type of amplifier is used especially in High frequency circuits where the use of a Tuned circuit enables a full cycle to be generated even though the amplifier is working as class B A variation of clss B used especially in audio systems is with Two class B circuits each operating synchronously over a particular half of the signal, the two halves being combined to generate a whole signal cycle. Then there are inbetween variations called class AB etc. Modern digital technology has introduced Class D type amplifiers which are a different lot altogether.
