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transformer peak current values

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Zak28

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Many SMPS and specialty transformers have peak current ratings.

Is it generally bad practice to run it within 100mA of the peak current rating?

Or even perhaps they can be safely run with even a bit more than its peak current rating.
 

not a good idea to go beyond ratings
the margin i like depends on the max expected current.
20% if I can get it.

you choose your margin based on training and experience.
 
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    Zak28

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Hi,

What do you think?
* If a transformer rated with 100A ... runs with additional 100mA... will it cause a problem? (0.1% overcurrent)
* If a transformer rated with 10mA ... runs with additional 100mA... will it cause a problem? (1000% overcurrent)

Klaus
 
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KlausST said:
Hi,

What do you think?
* If a transformer rated with 100A ... runs with additional 100mA... will it cause a problem? (0.1% overcurrent)
* If a transformer rated with 10mA ... runs with additional 100mA... will it cause a problem? (1000% overcurrent)

Klaus
Click to expand...

Is a 10a peak transformer likely to be damaged with 9.89-9.90amps peak?

Im sure brand name matters too but damage doesn't seem to be the issue rather the issue seems to be the inductance changes beyond the rated peak current as stated in the datasheet.

wwfeldman said:
not a good idea to go beyond ratings
the margin i like depends on the max expected current.
20% if I can get it.

you choose your margin based on training and experience.
Click to expand...
There is no mention of any current safety margins anywhere in the datasheet.
 

Hi,

So you have a damaged transformer?

What is damaged? How?

****
Damage often is caused by overtemperature.
Temperature rise is a function of power dissipation.
Ohmic power dissipation is caused by RMS current (not average current).

Especially at SMPS transformers the average current may differ a lot from RMS current.

Let's imagine a square wave current 0A/10A with a duty cycle of 10%
* average current is 1A
* RMS current is 3.16A.

3.16A causes 10 times the power dissipation compared to 1A = 10 times the temperature rise.

*******
Frequency may also cause increased power dissipation in the wires
Proximity effect, skin effect...

Klaus
 
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KlausST said:
Hi,

So you have a damaged transformer?

What is damaged? How?

****
Damage often is caused by overtemperature.
Temperature rise is a function of power dissipation.
Ohmic power dissipation is caused by RMS current (not average current).

Especially at SMPS transformers the average current may differ a lot from RMS current.

Let's imagine a square wave current 0A/10A with a duty cycle of 10%
* average current is 1A
* RMS current is 3.16A.

3.16A causes 10 times the power dissipation compared to 1A = 10 times the temperature rise.

*******
Frequency may also cause increased power dissipation in the wires
Proximity effect, skin effect...

Klaus
Click to expand...

Im not inquiring about damaged parts this was to prevent damage to rather expensive transformers.

It does seem when they claim 10amps peak they mean just that and beyond it inductance varies out of bounds causing the transformer to be of no use at current range which exceeds specification. The particular transformer is a specialty transformer which goes along with a DC converter IC the transformer is made for the frequency the IC uses.
 

Hi,

Every transformer has da datasheet.
--> post it here.

And any good transformer manufacturer provides additional information about transformer operation and so on.

***
SMPS transformers (as well as SMPS inductors) should have at least two current ratings.
1) RMS current (or DC current ) limit for thermal considerations
2) peak current limit for inductance / saturation considerations.
Often there are charts in the datasheet where you see the I - L behaviour.

You say "peak current where the inductance begins to drop" (the second one).
Operation beyond this rating will not harm the transformer (as long as you are within RMS specification)...it rather may harm your electronics.
Some cores have relatively hard saturation, where the inductance quickly drops when beyond the current limit. This means the current will rise very fast. You need a fast overcurrent protection not to drive into excessively high currents.
Other cores - often by the use of air gap - will saturate more softly.

Klaus
 

KlausST said:
Hi,

Every transformer has da datasheet.
--> post it here.

And any good transformer manufacturer provides additional information about transformer operation and so on.

***
SMPS transformers (as well as SMPS inductors) should have at least two current ratings.
1) RMS current (or DC current ) limit for thermal considerations
2) peak current limit for inductance / saturation considerations.
Often there are charts in the datasheet where you see the I - L behaviour.

You say "peak current where the inductance begins to drop" (the second one).
Operation beyond this rating will not harm the transformer (as long as you are within RMS specification)...it rather may harm your electronics.
Some cores have relatively hard saturation, where the inductance quickly drops when beyond the current limit. This means the current will rise very fast. You need a fast overcurrent protection not to drive into excessively high currents.
Other cores - often by the use of air gap - will saturate more softly.

Klaus
Click to expand...

This is 20a peak rated GA3459-BL https://www.mouser.com/datasheet/2/597/ga3459-463457.pdf but also specialized for a similar LT IC as the 10a peak
transormer is
DA2034-AL https://www.mouser.com/datasheet/2/597/da2032-463371.pdf
and its made by the same manufacturer.

Notice its absent of any charts this isn't likely due to bad manufacturer rather specialized parts but still no mention of saturation or RMS or other objects.
 

You need to consider the context. In my view, the said Ipk specification is a design corner parameter rather than an absolute maximum. If you run the transformer in the specified operation points, you'll touch the Ipk value. It's a 90% inductance point, exceeding Ipk a little bit will hardly burn the transformer, but you should monitor the transformer temperature in your actual design in any case. There are other factors like cooling and ambient temperature that have more effect on the transformer temperature than a few percent of peak current.
 
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FvM said:
You need to consider the context. In my view, the said Ipk specification is a design corner parameter rather than an absolute maximum. If you run the transformer in the specified operation points, you'll touch the Ipk value. It's a 90% inductance point, exceeding Ipk a little bit will hardly burn the transformer, but you should monitor the transformer temperature in your actual design in any case. There are other factors like cooling and ambient temperature that have more effect on the transformer temperature than a few percent of peak current.
Click to expand...

Cooling should be as simple using broad traces since most of the terminals are tied together.

Im not sure if its permissible to glue small aluminum heatsinks to them since they might interfere with residual magnetism. The datasheets are lacking much information.

But its unlikely the transformer will detach from its traces from severe and prolonged magnetorestriction in which case it should be evident with other indicators that such thing is likely to occur.
 
Last edited:

wwfeldman said:
not a good idea to go beyond ratings
the margin i like depends on the max expected current.
20% if I can get it.

you choose your margin based on training and experience.
Click to expand...

imho, the world works like this:
somebody makes a widget, specifies how to use it, presumably, they built it a little better than they spec-ed it, and sells it.

somebody buys it, reads the data sheet, uses it and sells a framis using the widget.
depending on one's training and experience, you apply your own margin, so that you "guarantee" you stay within the specs on the data sheet.

the goal is to "guarantee" that the framis will work well, which requires the widget work well. therefore, one adds margin

data sheets do not specify margin. it is something you add to ensure your device works
 

Coilcraft responds just per the same basis which I claimed earlier that being its an issue of meandering inductance past the peak current rating.
Hello, this is in regards to Coilcraft product#DA2034-ALD and it is rated for 10A peak and there isn't any mention of current safety margins. Does this mean its fine to run the DA2034-ALD at currents of 9.40-9.90amps?
Click to expand...

Hi Zak,

The 10 A rating is the peak primary current that will cause the inductance to drop by 10%.

Below 10 A peak current, the inductance will not drop as much, above it inductance will drop more.

Note that this is a peak (instantaneous) rating and not a maximum or rms current rating. DA2034-AL was designed for charging applications using the LT3750/LT3751 capacitor charger controller. A continuous current rating has not been established for this transformer.

You are welcome to some free evaluation samples. Just click on the part number on this web page to request samples: https://www.coilcraft.com/da2032.cfm

Best Regards,

Chris
Click to expand...

FvM was correct in the transformer not being harmed by the ~10A peak. Still the datasheet could have depicted graphs with varying inductance with peak current along with some more objects.
 
Last edited:

Calculated according to the output power of the switching power supply and the pulse width modulation rate and the primary voltage. Generally speaking, it can only be an estimate. General value
Transformer input power = P out / 70%
 

Still the datasheet could have depicted graphs with varying inductance with peak current along with some more objects.
Click to expand...
I agree it could. Other datasheets have it. However, even without an explicit specification, you canL just apply a typical L versus I curve of similar components.
 

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