converting signal to ttl logic voltage level

[ptewright]

Hi,
I have this weird output. When the signal is true, the voltage is 5.0V, but when it is false, the voltage is 3.3V. I need to convert this to a ttl logic level, so that it remains 5.0V when it's true, but it changes the 3.3V to 0V when it is false. Does anyone know if there is a component that does this? I really need suggestions.
Thanks :shock:

 

[Exo]

A zener...

 

[Gaston]

a schmitt trigger?

 

[Sebi]

A possible solution...

 

[crust]

another choice, a comparator (maybe an lm311)

 

[John Sorensen]

How's about a PNP with a pullup to +5 on the emitter (collected grounded, signal to base)? The pull up also limits base current.

j.

 

[Roff]

Below is a 2-transistor solution which is noninverting. Sebi's circuit will invert. John's circuit is an emitter follower, and the output will swing from 4v to 5v as the input swings from 3.3v to 5v. A comparator such as LM311 or LM393 will work.

 

[John Sorensen]

John's circuit is an emitter follower, and the output will swing from 4v to 5v as the input swings from 3.3v to 5v.

I'm so embarrassed

j.

 

[ptewright]

Below is a 2-transistor solution which is noninverting. Sebi's circuit will invert. John's circuit is an emitter follower, and the output will swing from 4v to 5v as the input swings from 3.3v to 5v. A comparator such as LM311 or LM393 will work.

What would the circuit for the comparator look like?

 

[Sebi]

Solution with comparator...

 

[Roff]

Sebi, the input swings from 3.3V to 5V, so the threshold should be 4.15V.

See below.

 

[Sebi]

Right, Ron... I'm wrong in mathematics...