how to test and define Volt * Sec for power inductor?

[szhighstar]

how to test and define Volt * Sec for power inductor?

 

[tronitech]

A little more information would be nice?

Are you talking about Webers?

 

[szhighstar]

for power inductor, a electrical parameter Volt * Sec needs to be define.

 

[ronv]

Maybe this will help.

**broken link removed**

 

[dr pepper]

Sounds like your talking about inductor charge capacity or saturation limit.
Depends whether your asking a homework question or you have a specific application.
By far the best way to develop inductors and trannys for switching supplies is to build a test jig, theres an article on the web, google 'switching supplies for nixie tubes', theres a good explantion of power inductors.
Building a test jig with variable pwm on time shows you on a 'scope the exact saturation point of a particular inductor, I use this method every time.

 

[MrAl]

Henry: V*s/A
Joule: W*s


Hi,

In designing circuits with inductors the unit of volt seconds (V*s) is sometimes used as a substitute for energy. This can simplify some problems involving inductors such as in power supplies and other circuits as an example below will illustrate.

To show how this works most basically, the following abbreviations will be used:
V for Volt
A for Ampere
J for Joule
W for Watt
s for seconds
H for Henry

so W*s for example means "watt seconds".

As you probably know, the energy in an inductor is:
E=(1/2)*L*I^2

The inductor is rated in the unit of the Henry. So in units we can rewrite that equation as:
J=K*H*A^2

where K is just the dimensionless constant 1/2.

Now the Henry H can also be defined as:
H=V*s/A

which is simply volt seconds per Ampere.

Now inserting this into the previous equation for energy we end up with this:
J=K*(V*s/A)*A^2

which can be simplified because of the A's to this:
J=K*(V*s*A)

or in terms of the dimensions alone:
J=V*A*s

Dividing both sides by A we get:
J/A=V*s

So talking about inductors in terms of V*s means talking about the energy per Ampere.

Example:

We have a relay coil that we energize with 100 volts DC. After it has been on for a
while we want to turn it off. When we disconnect the power, the coil inductance causes
current to flow out of the inductor into the external circuit which is usually a diode.
The diode conducts at about 0.7 volts.
Now lets say this particular coil discharges in 10 seconds with that 0.7v diode.
How fast will it discharge if we instead use a 7v zener diode?

Well, since it discharged in 10 seconds at 0.7 volts, that in volt seconds is:
0.7*10=7 V*s

and that is simply the voltage times the time it took to discharge V*t.
Ok, so we know we have 7 volt seconds of 'energy' to discharge, so if we use a 7v
zener instead of the diode we will be able to discharge faster:
V*t=7
but now we have 7 volts so we have:
7*t=7
and dividing both sides by 7 we get:
t=1

So now we can discharge that coil in 1 second instead of it taking 10 seconds.

There are better examples in the data sheets for some switching regulator ic chips
which you can look up on the web. Sometimes the inductor is chosen based on the required volt seconds.