TTL Current Switching

[ScottyStills]

haha yes at 2AM i was connecting the transistor backwards. Both PNP and NPN should work (from my recalling old electronics courses), just that the PNP will switch the power to the load, and the NPN will switch the ground from the load. If NPN will work that much easier, I'll HAPPILY switch over. This has been way too much work remembering forgotten uni courses!

 

[Nigel Goodwin]

Check my tutorial 'hardware extras' page at this shows how to source switch 12V from a TTL/CMOS output, the last circuit on the outputs section.

 

[ScottyStills]

Scott,
Read my post again, I didnt suggest that you leave the 470R permanently connect its just to to try to convince you that the 741 is NOT suitable.
Find an OPA that is and your circuit will WORK!

Oh no I completely agree. In fact I'd much prefer if I could just user a normal feedback resistance circuit for the biasing, and not have to worry about an op amp at all. To tell you the truth I couldn't be happier if I never even saw one again!

 

[audioguru]

The max allowed output current of a PIC is 25mA which is plenty to drive an NPN darlington through a 180 ohm resistor in series with its base.
Then the base current is about 17mA. The darlington saturates well with 8mA or more.

 

[on1aag]

Hi Scotty,

Try this:

on1aag.

 

[audioguru]

Hi Scotty,

Try this:

on1aag.

The first transistor doesn't need to be a power transistor. Any little NPN will work (2N2222, 2N3904, BC547).

 

[ScottyStills]

Guys, can't thank you enough for all the help! I'll be trying everything out when I get home from work this evening, I'll let you know if I can finally get it to work!

Thanks again,
Scott