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QRZ Forums. The data sheets for several transisters I've been looking at don't make the hfe value very clear. Without a curve tracer, how can you design a class A amp to compensate for variations in parameters such as hfe and hie?
Does the usual design techniques for say a common emittor amp already take this into account? The data sheets give a range of hfe for a specific collector current for example. How would I know what hfe value to use? Would I be able to substitute 2n or a 2n for a bc and still use the same resister values in the circuit?
Some people don't like to hear the word read However, that would be the best bet. This particular book goes through lots of theory and how things work. It is hard to tell you how to design something, when we don't know exactly what you have, what your intentions are Nor will I get into it. As far as changing types, the A is an NPN device. Do not remember what the is and never heard of the other device. PNP's have the emitter arrow pointing in and used with a - supply to the collector.
W0LPQ , Apr 20, George - All of the transistors you mentioned are small signal AF. Looking at the data sheets, you should be able to substitute with minimal changes. W9GB , Apr 20, Just stick it in and see if it works transistors only. K8ERV , Apr 20, Making hFE less relevant The traditional low frequency amplifier with an emitter degneration resistor is designed so that hFE, as long as it's above a nominally low value such as ten, does not matter.
The larger the resistance value of the emitter resistor, the less the performance depends on hFE. Write out the equations for the circuit at DC and you'll be able to tell. The book is used as an "introduction to diodes, bipolar and field effect transistors" at community colleges. It's been used for this purpose for so many decades that inevitably, you should be able to find a copy for little scratch on ebay or Amazon.
You're right - hFE varies a tremendous amount, depending on Ic and temperatures. When you see a parameter like that which appears poorly-controlled then there's only one possible answer - common circuits are available whose performance is independent of the parameter.
W8NF , Apr 20, NTE on-line cross reference If you have a part number, it is quite easy to cross reference semiconductors. NTE has a crossreference source on-line. OpenForm Good luck with your project. Last edited: Apr 20, In a class-A feedback amplifier, Hfe makes little difference. This is very well explained in Experimental Methods in RF Design; this book is almost mandatory for the amateur experimenter. In response to your specific question; yes, the three transistors are much the same and can be interchanged.
Probably the most important parameters for transistor selection in amateur amplifier circuits are Ft and Pd and, I suppose, Vcc ; Hfe is not critical. Smoke Test. W8NSI , Apr 20, Show Ignored Content. Share This Page. Your name or email address: Password: Forgot your password? Register for a free QRZ account.
BC347 Datasheet, Equivalent, Cross Reference Search
transister substitution question
BC347 TRANSISTOR. Datasheet pdf. Equivalent