Transistors common what?

Hello group, Is there a "rule of thumb" to choose which set-up for a transistor........ common base, common emitter, or common collector? Is one better for amplification? another for switching? oscillators? Thanks in advance, Bart

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Most of the time the common emitter is used. The common collector may be found as the next most common but way behind the common emitter. The common base is sometimes used in low power (preamp for a receiver) radio frequency work.

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Ralph Mowery

There are a whole bunch of conflicting rules of thumb that emphasize different things. There are generalities about input and output impedances, generalities about voltage and current gain, and generalities about frequency response. You have to have some idea of how these 3 categories of requirement are prioritized before you can select the best configuration.

For example. Highest input impedance = common collector. Highest output impedance = common base. Lowest input impedance = common base. Lowest output impedance = common collector. Highest voltage gain = common emitter or common base. Lowest voltage gain = common collector. Highest power gain (for low frequencies) = common emitter Highest current gain = common collector. Lowest current gain = common base. Highest frequency capability = common base or common collector.

When you understand at least a bit of why each of these are true, you will be on your way toward selecting a configuration that is appropriate for various needs.

So ask about items on this list that make no sense to you.

Reply to
John Popelish

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