# Guessing Pulse Transformer Turns Ratio

#### alfred75

Joined Feb 7, 2013
4
Hi guys! Is it possible to determine the turns ratio of a pulse transformer by looking at its inductance (H) values?

I'm trying to find the replacement of the faulty transformer but the part number is really blur, it's impossible to read it. It is used in the servo drive and serves as isolation transformer to fire the IGBT.

#### crutschow

Joined Mar 14, 2008
25,647
The inductance is proportional to the square of the number of turns so the turns ratio would be equal to the square-root of the inductance ratios.
Thus for the measured values you show in the picture, the turns ratio would be √(47/0.87) = 7.35:1.

#### eetech00

Joined Jun 8, 2013
2,040
HI

You can use a sine wave signal generator and input a 1v rms signal in one side of the transformer and measure output on the other side.
For example, if the ratio is 7.35:1 (pri=7.31, Sec =1), input 1vrms into the secondary and measure the primary. The primary should output approx. 7.35 vrms.

eT

#### crutschow

Joined Mar 14, 2008
25,647
You can use a sine wave signal generator and input a 1v rms signal in one side of the transformer and measure output on the other side.
For example, if the ratio is 7.35:1 (pri=7.31, Sec =1), input 1vrms into the secondary and measure the primary. The primary should output approx. 7.35 vrms.
I would suggest a test frequency of at least 10kHz and an input of 100mV to minimize the chance of saturating the core.