I have this transistor schematic that has me scratching my head. I was wondering if there is somebody out there that can explain it to me. I know the basics of how a PNP and NPN transistor works but this configuration to me looks like a glorified switch? Also is the circled "A" an ammeter? and shouldn't it be a motor?

Thank you,

 

I think that is H bridge, they often used to power motors because motors need a lot of current.
http://en.wikipedia.org/wiki/H_bridge

 

This is really bad design circuit. PNP transistor will work in "Inverted/reversed" region.
You should swap the emitter with collector.
And "A" for Armature.

 

Thank you for the link shteii. In all my years in field service I never ran across this configuration. I appreciate your quick response to my question,

Have a great day

 

Hi Jony130,

The wikilink explained the theory behind the design (H Bridge) pretty well as far as reversing the polarity of a motor which fits well with robotics. I agree the design isn't the greatest but is all I have to work with at the moment.

 

Jony is correct, it is unusual these days to use this connection, It was more common before the advent of good PNP/NPN power transistor pairs.
However the drive details are not shown. They will be different from modern practice to switch the transistors on at the appropriate half cycles.

Here are some links to modern practice.

http://www.nathandumont.com/blog/h-bridge-tutorial

http://www.youtube.com/watch?v=d90HPrJ4XW8

 

Hi Jony130,

The wikilink explained the theory behind the design (H Bridge) pretty well as far as reversing the polarity of a motor which fits well with robotics. I agree the design isn't the greatest but is all I have to work with at the moment.

Hey what can I say. Try goggle "reverse active region".
And the "correct" diagram should look like this
http://forum.allaboutcircuits.com/attachment.php?attachmentid=71746&stc=1&d=1408034727

And here you have a idiot-proof h-bridge

 

I'm not being critical as a matter of fact I am most appreciative of everyones input on this. To me its all good and useful information.

 

Ok, no problem. Any more question about the circuit?

 

I don't think so I think everything good.