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From: Sherlock Holmes on 13 May 2010 21:39
As i understand, transformers are meant to pass A/C currents, and
block DC currents. How then is a pulse transformer created that passes
digital pulses through.
From: Michael Black on 13 May 2010 22:37
On Thu, 13 May 2010, Sherlock Holmes wrote:

> As i understand, transformers are meant to pass A/C currents, and
> block DC currents. How then is a pulse transformer created that passes
> digital pulses through.
>
Because a pulse is not a DC voltage.

It's a pulse, a momentary change from low to high and then back to low.

Michael

From: Jamie on 13 May 2010 22:49
Sherlock Holmes wrote:

> As i understand, transformers are meant to pass A/C currents, and
> block DC currents. How then is a pulse transformer created that passes
> digital pulses through.

Transformers produce a magnetic field when DC current is applied. Since
transformers are inductive, the magnetic field builds as the inductor
gets nearer to saturation. This building effect is producing a moving
field, and the secondary of the transformer is with in this same field.

If you have ever taken a coil of wire attached to a volt meter and
passed a magnet through it or passed the wire over the magnet, you'd
noticed that the meter is giving you an indication that its generating
electrical energy.

You can think of the transformer windings on the primary side as
being the magnet and the secondary side as the coil of wire.. In this
example, the magnetic field is moving because the wire in the primary
side is an inductor. As time goes by after you initially applied the DC
source on the primary side, current will start to build, the non instant
building of current is generating this moving field I spoke of...

In your question of a pulse transformer.. The primary side is
energized with DC for a short time. This initial signal applied to
the primary side will not appear on the secondary side rite away
because it needs to build current in the primary which generates the
magnetic field you need.. Once the transformer becomes saturated, you'll
no longer see output on the secondary side...

Example..
A square wave pulse of lets say 100 ms on the primary side, may
generate a <= 1 ms pulse on the secondary side. This is taken into
account for the transformer primary windings to saturate with in this
1 ms window and stop producing this moving field.. Keep in mind that
the magnetic field is still there how ever, the level of it is not
changing and there for, its not seen on the secondary side, until
you remove the DC which is maintaining this field.. You then will get
and response on the secondary side in a reverse polarity. This is
because you are now allowing the magnetic field to dissipate off, which
again causes a moving field. If the release of the DC current is not
properly controlled, you can get dangerous levels of voltage.


This is the simplest way I can explain it, there is more detailed
way of explaining this but at the level of how you asked it, I don't
think that is what you're looking for ...

You'll get lectures of B fields, reluctance, lines of force, Eddy
currents. mutual inductance, inductance leakage, laminated plates
etc., current transformers, signal types, and the list goes on.


have a good day..

From: Bob Eld on 14 May 2010 10:27

"Sherlock Holmes" <physics.curio(a)gmail.com> wrote in message
news:39a18e7a-d548-4ae0-a3de-73805d8327a7(a)k17g2000yqf.googlegroups.com...
> As i understand, transformers are meant to pass A/C currents, and
> block DC currents. How then is a pulse transformer created that passes
> digital pulses through.

Pulse transformers are designed to not saturate on the DC offset created by
a train of pulses. Capacitance is often used to block the DC component of
the train. The voltage output on the secondary side will have no DC
component in the pulse train. This means that the average positive pulse
value of voltage times time will exactly equal the negative pulse value.
Depending on the pulse pattern the pulse height will wander up and down
maintaining this condition. A DC restoring circuit, usually just a diode can
clamp the output train to a fixed voltage, usually ground. Elementary my
dear Watson!


From: John Larkin on 14 May 2010 11:51
On Thu, 13 May 2010 18:39:07 -0700 (PDT), Sherlock Holmes
<physics.curio(a)gmail.com> wrote:

>As i understand, transformers are meant to pass A/C currents, and
>block DC currents. How then is a pulse transformer created that passes
>digital pulses through.

I don't think that you are really Sherlock Holmes.

John

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