# Inductance ratio

Discussion in 'Feedback and Suggestions' started by debjit625, Aug 26, 2010.

1. ### debjit625 Thread Starter Well-Known Member

Apr 17, 2010
790
186
Isnt it a error at http://www.allaboutcircuits.com/vol_2/chpt_9/7.html

Here the Inductance ratio is given as (N secondary/N primary)^2 which should be (Number of primary turns / Number of secondary turns)^2

Now in example, for a step up transformer 125V to 250V is given

And how this ratio could be 2:1 it should be 1:2 as per Primary:Secondary .

EDIT :: here is another thing
Should both be same?

Last edited: Aug 26, 2010
2. ### Wendy Moderator

Mar 24, 2008
21,425
2,949
Seems OK to me...

That last sentence covers it, "N = number of turns in winding".

3. ### debjit625 Thread Starter Well-Known Member

Apr 17, 2010
790
186
How a step up transformer which step up 125V to 250V have 2:1 ratio rather 1:2, as it should have low primary turns w.r.t secondary turns.

4. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
523
Remember

Turns ratio = voltage ratio = 1/current ratio = N2/N1

Where N2 is the secondary turns N1 is the primary turns.

Thus there are twice as many secondary turns as primary to step up 125 volts primary to 250 volts secondary.
Thus the turns ratio = 2/1 = 2:1

Of course the current ratio is the reciprocal ie 1/2 = 1:2 and the secondary current is half the primary.