what is the component on the top of this circuit that appears to be a back to back zener diode? is it part of the circuit? it doesnt have a value next to it. thank you much!

http://www.maximintegrated.com/app-notes/index.mvp/id/1923

 

I was wrong, so I deleted my stupid answer.

 

Hello,

It is a voltage transient suppressor diode.
http://www.simbologia-electronica.com/index.htm?url=/simbolos_electronicos/simbolos_diodos.htm
The 1N62XX series are a couple.
I have attached a datasheet of the series.

Bertus

 

It's a transient-voltage-suppression diode.

 

Hello,

It is a voltage transient suppressor diode.
http://www.simbologia-electronica.com/index.htm?url=/simbolos_electronicos/simbolos_diodos.htm
The 1N62XX series are a couple.
I have attached a datasheet of the series.

Bertus

This is new to me, both the component and phone systems. what part number would you recommend for this application?

 

According to WIKI the voltage on the telephone line "on-hook" is -50VDC and +90VAC superimposed on that -50V when it's ringing.

90VAC --» 127Vp

That would be 177V maximum voltage between ring and tip. So I would choose a transorb value not less than 200V, e.g. the 1.5KE220CA.

The transorb is always connected to the phone line so it has to support these high voltages. Eventhough I don't know if it would be effective for every imaginable phone line voltage disturbance when S1 is closed (off-hook).

 

According to WIKI the voltage on the telephone line "on-hook" is -50VDC and +90VAC superimposed on that -50V when it's ringing.

90VAC --» 127Vp

That would be 177V maximum voltage between ring and tip. So I would choose a transorb value not less than 200V, e.g. the 1.5KE220CA.

The transorb is always connected to the phone line so it has to support these high voltages. Eventhough I don't know if it would be effective for every imaginable phone line voltage disturbance when S1 is closed (off-hook).

In the link you posted, what is the difference between "reverse standoff voltage" and "breakdown voltage min/max"? Also how much current is expected in a phone line?