220V AC present/absent to TTL logic ?

V

vlad777

Member

• Jul 26, 2010

• #1

What is the best way to get
220V AC present/absent to TTL logic representation ?
(open collector, 10-15 mA)

I experimented with cny17-3 and I conclude it takes too much
input current (more then 6 mA) to saturate it's output transistor.
Too much input current means more power for resistors and
bigger cap.

Is there a better solution?

Thanks.

 

Externet

Well-Known Member

• Jul 26, 2010

• #2

Optocoupler. I have done it with neon-to-phototransistor, convenient to have hysteresis/filtering to get rid of the 60 Hz if will drive logic.

 

V

vlad777

Member

• Jul 26, 2010

• #3

Is there an IC or you used discrete components?

 

Externet

Well-Known Member

• Jul 26, 2010

• #4

I used a neon bulb superglued to a phototransistor inside black shrink tubing, sealed ends. Still works after 10+ years.

 

V

vlad777

Member

• Jul 26, 2010

• #5

I think I will use something like this.
SFH628A would have been better choice.
If a signal passes slow enough trough the middle
TTL logic will oscillate because it will amplifie the noise;
so schmitt trigger might have to be used.

 

Attachments

• cny.gif

  10.7 KB · Views: 1,433

Externet

Well-Known Member

• Jul 26, 2010

• #6

Yes, that should work. I used neon because my AC was riding on top of 50V DC and I wanted to recognize the AC presence only.