techguideline

  The Darlington Transistor configuration of two bipolar transistors offers increased current switching for a given base current. The  Darlington Transistor  named after its inventor, Sidney Darlington is a special arrangement of two standard NPN or PNP bipolar junction transistors (BJT) connected together. The Emitter of one transistor is connected to The base of the other to produce a more sensitive transistor with a much larger current gain being useful in applications where current amplification or switching is required. Darlington Transistor  pairs can be made from two individually connected bipolar transistors or one single device commercially made in a single package with the standard: Base, Emitter and Collector connecting leads and are available in a wide variety of case styles and voltage (and current) ratings in both NPN and PNP versions. As we saw in our  Transistor as a Switch  tutorial, as well as being used as an amplifier, the bipolar ...

  Current Transformers produce output in proportion to the current flowing through the primary winding as a result of a constant potential on the primary. The  Current Transformer  (  C.T.  ), is a type of “instrument transformer” that is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary.  Current transformers   reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a standard ammeter.  The principle of operation of a basic current transformer is slightly different from that of an ordinary voltage transformer. Unlike the voltage or power transformer looked at previously, the current transformer consists of only one or very few turns as it is primary winding.  This primary winding can be of either a single flat turn, a coil of heavy-duty wire w...

  We saw previously, that the N-channel, Enhancement-mode MOSFET (e-MOSFET) operates using a positive input voltage and has an extremely high input resistance (almost infinite) making it possible to interface with nearly any logic gate or driver capable of producing a positive output. We also saw that due to this very high input (Gate) resistance we can safely parallel together with many different MOSFET until we achieve the current handling capacity that we required. While connecting together various MOSFETS in parallel may enable us to switch high currents or high voltage loads, doing so becomes expensive and impractical in both components and circuit board space. To overcome this problem  Power Field Effect Transistors  or  Power FET’s  where developed. We now know that there are two main differences between field-effect transistors, depletion-mode only for JFET’s and both enhancement-mode and depletion-mode for MOSFETs. In this tutorial, we will look ...