transistors to switch 24V drive inputs?

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello, I am trying to interface my arduino to a 24V AC drive control circuit via transistors. I do not know whether to use PNP or NPN, or how to wire that either way. I have used TIP120s before to switch relay coils, so I know how that should be wired (with the load between Vs and collector) but I do not understand which part of the 24V control circuit is the "load" or if there even IS a "load" (would it be the input itself?). I'm thoroughly confused. I have a couple options here on the drive. Refer to page 74 of the manual: http://www.yaskawa.com/site/dmdrive.nsf/link2/MNEN-5JLRKP/$file/TM.V7.01.pdf -or- this excerpt:

I guess if all else fails I could just use my TIP120s that I already have to control relays that I already have to do the switching, but I really would like this to not look like a kludge.

Thanks!

2

You would use the left hand wiring diagram with switch SW1 set to NPN mode. S1 to S4 would wire to four NPN transistor collector leads. All the NPN transistor's emitter leads would wire together and then to the SC terminal and also to a Arduino ground pin. Each NPN transistor needs a series current limiting base resistor between each base and each Arduino output pin, 1k ohm should work fine.

Good luck.

Lefty

3

Are you two saying that with the switch in "NPN mode", 24V goes from s1-s4**(+), down to SC (-); opposite of when the switch is in "PNP mode", where +24V comes up from SC(-)** to s1-s4 (+)? If so, I understand and I will take your suggestions and implement them. If not, I'm still confused. Thanks guys!

here's a pic to make to make sure I got what you are saying..

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4

Assuming the diagram above is correct, I still do not 100% understand, as per my understanding a transistor has to switch a "Load" in order to function. Am I mistaken? in order to create a "load" should I add a resistor between S1-S4 and the collectors?

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5

Yes. That is correct. In the "NPN mode" you are sinking current OUT of the controller. In the "PNP mode" you are sourcing current into the controller. Sinking is easier than sourcing.

The controller itself is the "load".

Thank you very much sir (s).
It can be taught!