inductor voltage

[dr.power]

Hello guys,

I have got a question about the Inductors. I would like to calculate and then measure the peak voltage that a given inductor can reach when connected to an alternating voltage. I am familiar with this formula:
Vl= L dI/dt
But do not know how to calculate and then measure the peak/Maximum of the inductor voltage.
The inductor which I have got has an inductance of say 70uH, the frequency is 40kHz once and 400kHz once again. The input alternating voltage is 40V.
Is the above given parameters enough to calculate the maximum expected voltage across the inductor?

Thanks

 

[WTP Pepper]

di/dt will depend on the load and the series resistance of the inductor. Post a schematic of your setup.

 

[Roff]

Hello guys,

I have got a question about the Inductors. I would like to calculate and then measure the peak voltage that a given inductor can reach when connected to an alternating voltage. I am familiar with this formula:
Vl= L dI/dt
But do not know how to calculate and then measure the peak/Maximum of the inductor voltage.
The inductor which I have got has an inductance of say 70uH, the frequency is 40kHz once and 400kHz once again. The input alternating voltage is 40V.
Is the above given parameters enough to calculate the maximum expected voltage across the inductor?

Thanks

I think you need to restate your question.
If you apply 40V, then 40V is what you have. The current will vary with frequency and voltage.

 

[Grossel]

Hi.

It's not that easy, I'm afraid. Each inductor will have both a resistive and capacitive component in addition to the inductive component. Those factors (especially the capacitive) will have a huge influence of the peak voltage.

An inductor will also have an upper voltage limit, where any higher voltage will cause arcing and thus reduce the voltage.

 

[Ratchit]

Dr. Power,

I have got a question about the Inductors.

That is what we are here for. Only we work with inductors, not Inductors.

I would like to calculate and then measure the peak voltage that a given inductor can reach when connected to an alternating voltage. I am familiar with this formula:
Vl= L dI/dt

That formula won't do you much good in this case.

But do not know how to calculate and then measure the peak/Maximum of the inductor voltage.

You don't have to do so. Remember this, an inductor driven by a voltage will produce a back voltage that will not exceed the driving voltage. This back voltage will limit the current even if the inductor did not have any resistance.

You essentially have a inductor in series with a resistor. The inductive reactance of the inductor is 17.59 ohms for 40 kHz and ten times that amount for 400 kHz. Assume an inductor resistance of 1 ohm. It is easily seen that the inductive reactance is so much greater in this circuit, that just about all the 40 volts will be across the inductor. So the inductor will have a maximum of 40 volts across it when the sinusoidal wave peaks.

Ratch

 

[Roff]

Hi.

It's not that easy, I'm afraid. Each inductor will have both a resistive and capacitive component in addition to the inductive component. Those factors (especially the capacitive) will have a huge influence of the peak voltage.

An inductor will also have an upper voltage limit, where any higher voltage will cause arcing and thus reduce the voltage.

I wasn't making any assumptions about what the OP really meant. He said he was going to connect an alternating voltage to an inductor. There was no mention of resistors, switches, etc. That's why I suggested he rephrase the question. You other guys apparently know what he meant.
Carry on.

 

[dr.power]

Hi guys and thanks for all inputs,

Actually I have seen some circuits iwhich include a piezo transducer as the speaker use an inductor in series with the piezo and the driver. for instance I have seen a very small Alarm used the said setup I mentioned, It could generate a VERY load annoying alarm just by two samll 1.5V batteries as power supply. It means that the inductor there was sucseccfully able to incarse the volatge of the setup to say more than 10 times or so at 1 to 2KHz, So I want to use this setup on my piezo's at 40kHz and at higher frequncies, But do not know how to find the maximum expected voltage of the inductor when connected to the driver and to the piezo so that do not harm to the piezo load. There should be a way/method to calculate and the measure it.

Thanks

 

[MrAl]

Hi,

It's actually easy to calculate in theory but in real life it could be very hard to do because we dont konw all the intrinsic values inherent in the inductor and piezo. However, this should be very easy to measure by using an AC voltage meter or equivalent and adjust the frequency for max peak across the piezo. The AC meter (or equivalent) has to be able to respond adequately at the required frequencies.

 

[Roff]

Do you have a part number for the piezo transducer? A link to the datasheet would be even better.