[SOLVED] How Can I Implement a Tristate Buffer with Transistors?

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kvnsmnsn

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There are a few places on the Internet that explain how a tristate buffer works, but I haven't been able to find any place that shows how to implement it with transistors. Can anyone tell me how to implement a tristate buffer with transistors?
 

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1) Buy a computer
2) Open the browser
3) Search "tri-state buffer circuit"
4) Look at all the answers.
 

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    kvnsmnsn

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High state = top transistor on, bottom transistor off. (sourcing current)
Low state = top transistor off, bottom transistor on. (sinking current)
Tristate = both transistor off. (no current flows in or out so it is 'disconnected')

There is a fourth state where both top and bottom are on at the same time but it usually only lasts a brief moment before smoke comes out!

Brian.
 

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Tristate discussed in attached.
 

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  • Foundation of Digital Electronics and Logic Design -- De, Asish Kumar; Sarkar, Souvik; Sarkar,...pdf
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TI TTL Data book. Every digital dude had one on their desk back in the day. Check out the level of schematic detail, unheard-of in modern days.
 

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  • IMG_20250306_184200186.jpg
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Apart from using a search engine to find out the answer, @kvnsmnsn should have put this question at the 'Analog Circuit Design' sub-forum!
 

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Every TTL circuit has a standard input threshold voltage of 2 diode drops or 2*Vbe
This compares 74' 74LS' and 74S' inputs and outputs for tri-state buffers
The '244 types are non-inverting and '245 were inverting hex TS buffers... any questions?

 

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