A class b amplifier is biassed so that it conducts over half the waveform. Two devices provide combined current drive for the load. This implies that only half of the input signal is processed in. On the other hand, class b amplifiers cannot produce a clean audio signal. It is created using two active devices which conduct half of the actual cycle, ie 180 degrees of the cycle. To obtain an input signal for this amplifier to amplify, just connect it to the output of a radio or other audio device like this. When an input signal is present across the secondary of the driver. Electronics tutorial about the class ab amplifier circuit that is forward biased to. The emitters are shorted and the collectors are given the v cc supply through the primary of the output transformer t r2. Department of electrical engineering national institute of technology, rourkela odisha, india769008 certificate this is to certify that the thesis entitled design of high. Join paul as he explains the differences between these different amplifier classes.
Since the active device is switched off for half the input cycle, the active device dissipates less power and hence the efficiency is improved. The main difference with the class a is that class b amplifiers have a conduction angle of 180. Pushpull class b and class ab amplifiers analog devices wiki. Class b amplifier is a type of power amplifier where the active device transistor conducts only for one half cycle of the input signal. Efficiency of class b amplifier is higher than class a amplifier, as it consists of two transistors npn and pnp. Ingram school of engineeringtexas state universitysan marcos, txdecember 5th, 2011 2. Class ab and class c power amplifiers tutorialspoint. Electronics tutorial about class b amplifier and class b power amplifiers including its.
Class b amplifier the class b amplifier is a bit different from the class a. Class b audio amplifier analog integrated circuits electronics. By using adblocking software, youre depriving this site of revenue that is needed. The class b amplifier has a significant advantage over their class a amplifier cousins in that no current flows through the transistors when they are in their quiescent state i. To achieve this, two active devices are used and input waveform is split so that one active device conducts during half of an input cycle, the other during the other half. By using two amplifiers, each conducting our half the waveform, the complete signal can be covered.
The figure below shows the input and output waveforms during class b. Complementary devices are each used for amplifying the opposite halves of the input signal, which is then recombined at the output. Class b amplifiers are greatly preferred over class a designs for highpower applications such as audio power amplifiers and pa systems. The circuit of a pushpull class b power amplifier consists of two identical transistors t 1 and t 2 whose bases are connected to the secondary of the centertapped input transformer t r1. Class ab and class c power amplifiers the class a and class b amplifier so far discussed has got few limitations. This type of amplifier therefore requires two amplifying elements to produce a full sine wave at its output. Like the classa amplifier circuit, one way to greatly boost the current gain a i of a class b pushpull amplifier is to use darlington transistors pairs instead of single transistors in its output circuitry. For a sine wave, the positive portion of the signal is the positive 180 degree. So, when the signal is applied, only the positive half cycle is amplified at the output.
High efficiency high gain pushpull transistors power amplifier. Classb amplifiers are also favoured in batteryoperated devices, such as transistor radios. Let us now try to combine these two to get a new circuit which would have all the ad. Understanding amplifier operating classes electronic. Pushpull class b and class ab amplifiers analog devices. Output current collector current flows for only half the cycle of the input signal. Therefore, the output transistors or the transformer dissipate no power when there is no signal present. Engineering, software engineering amplifier of class.
One active device conducts during half of an input cycle, the other during the other half. What are the differences between class a, ab, and class d. Class b amplifier is the actual pushpull amplifier. The class b amplifier circuit is biased in such a way that each transistor will work on one half cycle of the input waveform. A practical circuit using classb elements is the pushpull stage, such as the very simplified complementary pair arrangement shown at right. An ideal class b amplifier has a conduction angle of 180 degrees, or one half cycle of a sine wave. Class b amplifier and the classb transistor amplifier. What are the system applications of a class b amplifier. Push pull amplifier circuit diagram class a, class b and.
501 683 300 829 952 177 1546 505 1595 900 1025 832 1238 294 1223 702 1049 204 942 469 1335 78 944 149 1122 412 529 890 470 855