![]() The zener’s non-destructive reverse bias breakdown merely cuts off voltage above a certain level based on choice of the diode. But there are problems in this bare-bones voltage regulator because the output cannot be adjusted or set. In some non-critical circuits where the supply current never rises above a specified level, a simple zener diode will do. One application of the emitter follower amplifier circuit is as part of a voltage regulator, taking advantage of its capability as a buffer. It is easy to note this point by setting voltage cursors on the scope to the 70.7% point. We adjust the output frequency of the waveform generator until the output of the amplifier falls to 70.7% of its normal output. Similarly, it should be easy to see the amplifier frequency response on the scope display. ![]() ![]() So, too, should be the fact that there is no voltage gain in the output. The inverted nature of the amplifier output should be evident from the scope display. If the amplifier is fed from a waveform generator, apply both the amplifier output and the waveform generator output to separate channels of the scope. Oscilloscopes can be useful in displaying some of the qualities that emitter followers exhibit. The small output impedance of the emitter follower reduces any loading of the subsequent stage. Because voltage gain is close to one, the circuit has substantial power gain. For this reason, an emitter follower has current gain. Accordingly, less power is required from the input to drive the output if there were a straight-through connection rather than the emitter follower circuit. The answer is that its value lies in the fact that its input impedance is far greater than its output impedance. Because there is no voltage amplification in this circuit, one may wonder if it has a purpose. In an emitter follower amplifier circuit, the output in addition to being inverted, is just a little less than one because the emitter voltage is pegged at the diode drop of about 0.6 V below the base. If there is an even number of stages, the overall output is not inverted. This is not at all a disadvantage, provided it is taken into account. And second, the output is the inverse of the input. The circuit is characterized by two important attributes: The gain is close to unity at all times, regardless of changes in bias, individual manufacturing variations, thermal effects, loading in a subsequent stage or value of any collector resistor. Because the emitter voltage is a function of the input difference, the device is usually called an emitter follower. In the common collector arrangement, the input voltage is applied between base and collector, and the output voltage comes from the differential that exists between emitter and collector circuits. In other words, the transistor is a robust voltage buffer. Moreover, the output impedance is low, so it is not destabilized by the following circuit if that happens to be a heavy load. being virtually invisible, to the previous circuit. What’s good about it is its high input impedance, which has the effect of not loading, i.e. ![]() In the old world of vacuum tubes, they were common cathode, common grid and common plate.) This particular classification derives from the external circuit configuration.Īn emitter follower circuit, also known as a common-collector amplifier, is the quintessential negative feedback device. (For field-effect transistors, the analogous circuit configurations are common source, common gate and common drain. There are three bipolar junction transistor amplifier topologies: common emitter, common base and common collector. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |