NOT function using transistor

172

02:32:14

A simple circuit which we can use to illustrate the NOT function. when the switch is open, the transistor is able to conduct and current will flow through the lamp. But if the switch is closed, the transistor will have no forward bias and will be cut off, extinguishing the lamp.

Introduction to Digital Electronics p. 8 fig 3.

published 8 years ago

Robert_Kidd

8 years ago

Perhaps NOT! With switch open transistor base sees a ‘1’, in this case around 0.7V). With switch closed base sees a ‘0’ (0V). As the ‘1’ condition lights the LED this is NOT a NOT.

Robert_Kidd

8 years ago

However, if you ignore LED and instead monitor the collector voltage there is an inversion - closing switch pulls base to 0V and collector goes high.

hurz

8 years ago

Robby you mix "light" and "voltage". As long as voltage is our input variable, it suppose to be also the output criterium - Uce. This is a NOT gate demo, sorry sheriff in red cotton.

Robert_Kidd

8 years ago

I said LED, but meant LIGHT. My error. However, the light indicates a condition - what other purpose does it have? I stand by my analysis where I address both scenarios. Our views differ.

hurz

8 years ago

Then compare light with light and its still a NOT gate http://everycircuit.com/circuit/6339809653293056

Robert_Kidd

8 years ago

As I've already said, using voltages it IS a NOT gate demo. @tcab may well have intended this. However, he/she may have been using the lamp as a condition indicator in which case, with the switch providing the condition (i.e. voltage) and the lamp the indicator of output condition, (it being usual that an illuminated lamp is taken as a logic '1' condition) then it is not a NOT gate demo. Until & unless @tcab responds we will not know.

tcab

8 years ago

I copied the circuit from page 8 figure 3. of this book - see https://www.dropbox.com/s/2kzgdm47xhj33nk/Digital%20Electronics%20-%20An%20introduction%20-%20Chapter%202%20extract.pdf?dl=0

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