Inverter transformer question

[Robert W. Mudge Miller]

I'm looking for a transformer (or some other passive device) that will
step-up the 2 volt max. RMS speaker output from my PC to about 70-90
volts RMS. I want to simulate a telephone ringer voltage with about a
60Hz, ~70V sine wave. I know the spec calls for 20Hz at 90V but I
understand that most modern phones -- i.e. ones that have no
mechanical ringer -- will respond to ring signals of 70V or less and
frequencies of 60Hz or more (and draw very little current in ring
state.)

Now, I've already tried the obvious idea of turning around a small
power transformer and driving the secondary winding with my speaker
output. But instead of the appr. 20:1 voltage gain I would expect from
a 120=>6.3volt transformer, I get only about a 4-5X step-up even with
no load. I noticed that the voltage step-up improves to about 10X if I
increase the frequency to 1KHz or more.

So my questions are this: Why don't I get the same step-up ratio when
driving the secondary winding as the step-down ratio I get when
driving the primary with 120VAC 60Hz? Is there any transformer that
can produce a 40:1 voltage step-up that I need for a 2V, 60Hz input?
If so, where can I get it? Is it something that can be made, salvaged
(from old electronics) or can it be purchased?

Any thoughts highly appreciated. Also, is there a better place (usenet
or elsewhere) to ask this question?

Robert Miller
San Jose, CA

 

[Thomas C. Sefranek]

"Robert W. Mudge Miller" <rwm415@pacbell.net> wrote in message
news:484ca614.0401291552.78808365@posting.google.com...

I'm looking for a transformer (or some other passive device)

Not going to happen! (Passive device)
Your transformer is NOT all that efficent running backwards.

that will
step-up the 2 volt max. RMS speaker output from my PC to about 70-90
volts RMS. I want to simulate a telephone ringer voltage with about a
60Hz, ~70V sine wave. I know the spec calls for 20Hz at 90V but I
understand that most modern phones -- i.e. ones that have no
mechanical ringer -- will respond to ring signals of 70V or less and
frequencies of 60Hz or more (and draw very little current in ring
state.)

Now, I've already tried the obvious idea of turning around a small
power transformer and driving the secondary winding with my speaker
output. But instead of the appr. 20:1 voltage gain I would expect from
a 120=>6.3volt transformer, I get only about a 4-5X step-up even with
no load. I noticed that the voltage step-up improves to about 10X if I
increase the frequency to 1KHz or more.

So my questions are this: Why don't I get the same step-up ratio when
driving the secondary winding as the step-down ratio I get when
driving the primary with 120VAC 60Hz?

Because the transformer is NOT bidirectional.
The primary has a MUCH better coupling to the core than the secondary.

Is there any transformer that
can produce a 40:1 voltage step-up that I need for a 2V, 60Hz input?

Telephone ringing is NOT 60 Hz, try 20 Hz.

If so, where can I get it? Is it something that can be made, salvaged
(from old electronics) or can it be purchased?

Any thoughts highly appreciated. Also, is there a better place (usenet
or elsewhere) to ask this question?

Robert Miller
San Jose, CA

 

[GPG]

Not enough power available Transformers have losses.
Google "ring generators"