# Should I consider inductance values of the pulse transformer when purchasing?

Thread Starter

#### Dong-gyu Jang

Joined Jun 26, 2015
115
Hello.

I'm now thinking about using pulse transformer to break ground loop as our instruments are all connected with BNC 50 ohm coaxial cable. The transferring signal is TTL signal of 5 V amp and >= 10 us duration.

Currently I'm only considering inter-winding capacitance, rising time (to ensure original rising time as much as possible), rated voltage, turn ratios.

However, all datasheet what I've seen shows inductances of primary and secondary.

Should I consider these values also? If so, what consequences are from these values?

Thanks to read this and happy new year!

#### crutschow

Joined Mar 14, 2008
29,796
The inductance determines that magnetizing current that is generated during the pulse duration.
This magnetizing current cannot exceed the saturation dc current value for the transformer.

Thread Starter

#### Dong-gyu Jang

Joined Jun 26, 2015
115
The inductance determines that magnetizing current that is generated during the pulse duration.
This magnetizing current cannot exceed the saturation dc current value for the transformer.
Am...could you give me the details?

Could you show me the formula to determine magnetizing current and what is saturation DC current?
(It may be current above which magnetic core is saturated?)

#### crutschow

Joined Mar 14, 2008
29,796
When you apply a pulse the the transformer the (magnetizing) current will increase according to the formula V= L di/dt or di = V/L dt Where V is the applied pulse voltage and dt is the pulse width.

Yes, the saturation current is that which saturates the magnetic core material. It should be listed in the transformer specifications.

Thread Starter

#### Dong-gyu Jang

Joined Jun 26, 2015
115
When you apply a pulse the the transformer the (magnetizing) current will increase according to the formula V= L di/dt or di = V/L dt Where V is the applied pulse voltage and dt is the pulse width.

Yes, the saturation current is that which saturates the magnetic core material. It should be listed in the transformer specifications.
Thanks!

Then,,,should I only care about inductance of the primary side only although the inductance of the secondary is also listed in the datasheet? I guess secondary current is not affecting magnetization of the core.

#### crutschow

Joined Mar 14, 2008
29,796
A transformer has one main mutual inductance (not counting leakage inductance).
This mutual inductance is related between the primary and secondary by the square of the turn's ratio.
So, as far as magnetizing current is concerned, you only need the primary inductance.
And any secondary current, caused by the primary voltage, is normal primary and secondary transformer current, and is not part of the magnetizing current.