Push/pull from different rails query

Hi,

I have a query regarding transistors in push/pull configuration for switching between +ve/-ve rails.

Referencing the example at the top of this page http://www.ecircuitcenter.com/Circuits/pushpull/pushpull.htm


In my application, VS1 will be a 0 to 3V3 digital signal, which I want to convert to +/-5V (eg 0V becomes -5V, 3V3 becomes +5V).

I understand 3V3 to saturate the NPN b-e, resulting in output +5. However I'd need -0.7V instead of 0V input to saturate the PNP side because the output is referenced to 0V. Correct?

How would I go about resolving this? I thought I could perhaps add a potential divider to the output to replace the 0V with ~1.5V. I haven't seen any diagrams online that do this, so I would guess that's because it's a bad idea.

I'd prefer to use basic components if possible (no op-amp, comparator or ICs etc).

Can anyone point me in the right direction?

Thank you!

 

Thanks. I do know that the circuit wont work, I'm hoping to get some advice to design it so it is working.

Ok, do you mean configured as two darlington or Sziklai pairs? One for the push and one pair for the pull? If so, I still cant see how I'd achieve the -V switching.

I can understand that if Vin=0 then Vout = 0. How do you get 2.6V though?

Thank you, I will study it now.

 

Aha, thank you! I've downloaded LTSpice and found the source of my misunderstanding. I was following the "transistors are like switches" analogy too closely. I was treating it a bit like a relay switch.

Resolved, thank you!