# primary inductance

Discussion in 'General Electronics Chat' started by cryosar, Nov 9, 2009.

1. ### cryosar Thread Starter Active Member

Apr 2, 2009
40
0
Hi,
Am designing a SMPS. I have got the transformer from the vendor. now i have to verify the value of primary inductance of the transformer. the switching frequency of SMPS is 66kHz. I have LCR meter which can measure the frequency of 1kHz and 100 Hz. If i measure in 1Khz am getting the required primary inductance value. can anyone tel me what am measuring is correct or not?

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
I guess you are asking if you can trust the primary inductance value you measure at 1kHz to be near to what it will actually be at 66kHz.

It will probably be a reasonable estimate of the basic primary inductance but the parasitic components and losses experienced at 66kHz won't be evident in the 1kHz measurement.

I guess you could attempt to measure the primary inductance at 66kHz if you had a signal generator with sufficient (variable) output and a dual channel oscilloscope. You'd need some means of measuring the (magnetizing) current - such as a (preferably low inductance) calibrated current shunt. Not sure how informative this would be anyway, other than ensuring nothing really strange happens at 66KHz. Something strange happening is unlikely if the transformer was designed for operation in that frequency range.

3. ### cryosar Thread Starter Active Member

Apr 2, 2009
40
0
Now there is transformer saturation problem for me. though i increased the turns in the primary & secondary as per turns ratio by maintaining the same pri inductance am not able to solve it. can anybody tel me how to solve this?

4. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
512
Drive it with a square wave from a power driver at the correct frequency and use a scope/current probe to look at the di/dt rate through the primary. Since you know the driving voltage you are applying, that gives you the inductance directly.

You could build up a simple switcher that switches at about 50kHz and use the primary of the transformer as the inductor and use a scope to look at the di/dt. Leave the transformer secondary open.

5. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
You probably need to provide some more information - particularly about the circuit where you are (presumably) having problems with the design.

Do you have details of the core magnetic parameters and physical dimensions, etc.

6. ### cryosar Thread Starter Active Member

Apr 2, 2009
40
0
i have attached my ckt have a look

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