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electrodoc

Beginners Transistor Help

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When using a transistor as a buffer/inverter I find a simple way of remembering the rules for these jobs are as follows..

To remember the transistor type when looking at schemetics
I use Point iN Please and Not Point iN, these are for the emitter arrow directions and the voltage polaritys for them to work.

For the polaritys i use the emitter as my reference and proceed by using each junctions P or N initial as the (P)ositive or (N)egative supply they need to get to switch through between Emitter and Collector.

therefore a PNP to switch needs a positive current or feed to the emitter and a negative (Lower current) feed on the base for the collector to be positive.

Hope this helps.

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For the polaritys i use the emitter as my reference and proceed by using each junctions P or N initial as the (P)ositive or (N)egative supply they need to get to switch through between Emitter and Collector.

therefore a PNP to switch needs a positive current or feed to the emitter and a negative (Lower current) feed on the base for the collector to be positive.



Electrodoc,
I am sorry, but those statements are either very confusing or just plain backwards.
Just remember that with the emitter as the reference, an NPN transistor needs a Positive voltage for its base and collector, and a PNP transistor needs a Negative voltage for its base and collector.
The voltage polarity that is required is the same as the transistor type's middle letter (its base), see?

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Should I use half power to get VCE? I want the beta to have maximum range and still be constant.


Kevin,
A transistor is usually used at a power level that is much less than half of its maximum power rating, to avoid excessive heat and uneccessarily high power supply current.
However, to obtain its maximum dynamic range between cutoff and saturation, a transistor is biased so that its collector voltage idles half-way between its emitter voltage and the collector resistor's supply voltage.
Maybe you are worried that a transistor's beta changes with changes in its collector current. If that change is not acceptable because it causes distortion, then adding negative feedback will reduce it.
The only situation where a transistor's beta remains constant is when its collector resistor is replaced by a fixed true current source, like in opamps. Then its output impedance is very high and it requires an output buffer so that its load impedance does not also require to be as high.

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