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How can I build a 555 timer equivalent circuit out of transistors? Answered

I want to go old school and do things the hard way by building an equivalent circuit of the classic 555 timer. There are equivalent circuits on just about any 555 timer data sheet. Such as here... http://www.national.com/ds/LM/LM555.pdf  That schematic is for a LM555. 

First, what would be a good, easy to find, NPN and PNP transistors to use uniformly in the circuit? Preferably something I could get a pack of at Radio Shack just to make this project easier.

Also I can't figure out what Q5, and Q6, and Q22 are? Please help. They look like transistors, but each of those ones have an extra lead coming out of it? Is that extra lead just a doubled up (collector) ? Also Q22 has no base, or is the base that horizontal line, but in the opposite direction?
I am thoroughly confused already, any help would be great! Thanks in advance.

Discussions

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steveastrouk

Best Answer 8 years ago

Q5,6 and 22 are unique devices implemented only in ICs. They have no discrete equivalents. They cannot be replaced by multiple discrete devices, because they work by being perfectly matched.

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WayneL84

4 months ago

Download LTSPICE and open the example 555. It is a full blown descrete solution of the 555

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erickgra000

1 year ago

they are npns or pnps

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pongpak

7 years ago

Try using NE555's schematics
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000479.pdf

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bart245

8 years ago

Wow! Thanks for the quick responses! @ RickHarris - Yes, I've seen that page also, a good informational reference page however Q19 on the diagram is another one of those pesky "what's it" components. @ Steveastrouk - So I guess you couldn't really use those diagrams to make an equivalent circuit without re-engineering something from scratch? I'm glad I asked on here before messing around with my breadboard! Thanks!

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kelseymhbart245

Answer 8 years ago

So who are you going to mark as Best Answer?

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bart245kelseymh

Answer 8 years ago

It was a tough call, however I'd say that Steveastrouk was probably the closest since I didn't know that I can't really do what I wanted anyway, at least not from that schematic. I never knew that parts within the chip couldn't be directly replicated, especially from the equivalent datasheet circuit.

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steveastroukbart245

Answer 8 years ago

That's right. IC designers have some VERY clever tricks that we can't do in discrete techniques.

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rickharris

8 years ago

I guess you could emulate the functionality - here - http://www.electronics.dit.ie/staff/mtully/555%20folder/555%20timer.htm - is a site with a block diagram of the 555 and a full description of it's functionality.