(A PNP BJT would have a P+ emitter, N-type base, and P-type collector.) NPN transistors exhibit higher transconductance and T Huch08v3. 81a), a P-type base, and an N-type collector. (usually about 100 times R2 which assumes a minimum gain of 100 for the transistor). 8.1 INTRODUCTION TO THE BJT A BJT is made of a heavily doped emitter (see Fig. Typical values for R1 would be in the thousands to tens of thousands of Ohms. The early double-diffused transistors were known as mesa transistors, because the transistor itself was formed on a raised part of the substrate² (Or possibly parts of the substrate were etched away after the transistor was formed Im having trouble finding clear sources). The value of the resistor depends upon the curent needed - more current, smaller value. Typical values for R2 would be in the range of a few hundred Ohms to a couple of thousand Ohms depending upon supply voltage. When a small voltage is applied to the base terminal of the transistor, it allows a current to flow from the emitter to the collector which is much larger than the base current. The voltage at the emitter follows the voltage at the base (but about 0.6V less. A: The working principle of an NPN transistor circuit is based on the amplification of a small input current to a much larger output current. The circuit you have used is called an emitter follower it is not using the transistor as a switch. This is bad design.Īdding series resistance will prevent damage due to excessive current as the voltages are increased. You haven't destroyed the transistor and/or LED because your voltages are too low to do any damage (i.e. The voltage at the collector needs to be higher than the base, when fully turned ON this is at least another 0.2 volts so the minimum in this circuit should be 2.6V (V1) The minimum voltage (V2) that needs to supply the base is 0.6 + 1.8 = 2.4V There are so many things you just got wrong.įor an NPN (silicon) transistor to turn ON the base needs to be at least 0.6V more positive than the emitter.įor a (red) LED to turn ON you need at least 1V8 across it.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |