Core Optimizer
Overview
The Core Optimizer™ is a dedicated tool designed to help you find the most suitable core for your application. You can select and compare many different core shapes and materials simultaneously, allowing you to intuitively find a trade-off between core losses and volume that meets your target specification. We encourage you to make your design process more efficient and take full advantage of this tool.
There are two sections to this tool:
-
Ve vs. N turns
-
Core Losses vs. N turns
The best section to use will depend upon your goal, see below.
Ve vs. N turns
The main goal of this section is to allow you to quickly compare core shapes, sizes, and materials to find the most suitable core solution for your application.
To provide the tool with some context about your higher-level goals you must first specify either your target Bpeak Limit (mT) or your total Core Loss Target (W). The quality of your inputs here will have a significant impact on the tool’s outcome, so please take your time to read the specific sections below giving you extended guidance on choosing these inputs.
Once you have set a target value, the next step is to prime the optimizer with relevant core parameters:
-
Core Shape Family
-
Core Material
-
Number of Stacks (if relevant)
Once you have provided this information, you may click ‘PLOT SELECTED CORES’ and this will populate the graph with a set of results. You can experiment with different combinations and simultaneously plot up to ten different results.
If you wish, you can click on the legend to hide/unhide plots from view. The “DELETE” button will remove the last plot added to the Optimizer.
The two axes for the graph shown in this section, as in the title, are Number of Turns (X) and Effective Core Volume (Y). The Optimizer will strive to maintain your limit provided and show you a range of results for each scenario created.
In this example we selected a Flux Density limit of 120mT, and we can see that as the turn count increases the effective volume of the cores can be decreased, hence showing a range of discrete core sizes within the same family. We have also compared several different core families with the same material.
To make the most of this tool, it’s important that you can effectively translate the results provided. Once you click on a point in the graph, important information about that point will appear on the right-hand side, as shown below.
Note that the Core Optimizer™ tool focuses on delivering you optimal results for your core, but this may not necessarily lead to optimal results in your winding strategy, so here are some useful pointers below.
-
As the turns increase and the effective volume of the core decreases, the current density in your windings will increase, making it harder to achieve a feasible winding strategy. The further you travel along the x-axis, the more challenges you will face in your winding stage.
-
Keep an eye on your inductance, the tool will try its best to maintain your high-level goals set above, this may mean that the inductance strays from the parameter you set as a target in the waveform page.
If you have decided upon an appropriate core for your application and you want to move to the next stage, simply click on the point you like and hit “APPLY” in the results window. This will move your choice to the core configuration page for further fine tuning.
Core Losses vs. N turns
The goal of this section is to provide insight, at a specific core level, about the relationship between turns and core losses. In a similar way to the last section, you will create your initial conditions to prime the optimizer tool. The difference now is that you can only set the Bpeak Limit as a target, and you must choose a specific discrete core size.
The greatest core losses will be seen with the lowest turns, and this will coincide with the Bpeak Limit you set. As the turn count increases, in the results box on the right you will see the inductance increase whilst the core gap remains null.
Once your target inductance is reached, the optimizer will begin appropriately gapping your core options to maintain the target. Naturally, as you increase the turns the flux density will continue to decrease and thus the core losses. When selecting your core, be mindful of the gap and the effects that may have (due to its fringing field) on the winding losses, and once again bear in mind your turns count and current densities.
How to Pick an Appropriate Bpeak Limit
Your choice of Bpeak Limit will depend on the material you are going to choose, both in terms of understanding the relationship between this value and the overall core losses, and how this is impacted by the frequency you are operating at.
The number one rule is to ensure that the core isn’t going to saturate under the operating conditions you have. You can find this information in the material datasheets online, below we have provided a table showing the saturation levels of some of our popular materials. Remember that maximum saturation current decreases with temperature, so you will need to be appropriately conservative with your design.
|
Material |
Bsat @ 25 oC (mT) |
Bsat @ 100 oC (mT) |
|
3C90 |
470 |
380 |
|
3C91 |
470 |
370 |
|
3C92 |
540 |
460 |
|
3C92A |
570 |
480 |
|
3C94 |
470 |
380 |
|
3C95 |
530 |
410 |
|
3C95A |
550 |
430 |
|
3C95F |
550 |
430 |
|
3C96 |
500 |
440 |
|
3C97 |
550 |
430 |
|
3C98 |
530 |
440 |
|
3C99 |
500 |
450 |
|
3F4 |
410 |
350 |
|
3F36 |
520 |
420 |
|
3F46 |
520 |
430 |
|
N27 |
500 |
410 |
|
N41 |
490 |
390 |
|
N49 |
490 |
400 |
|
N51 |
480 |
380 |
|
N72 |
480 |
370 |
|
N87 |
490 |
390 |
|
N88 |
500 |
400 |
|
N92 |
500 |
440 |
|
N95 |
525 |
410 |
|
N97 |
510 |
410 |
|
PC47 |
530 |
420 |
|
PC200 |
485 |
410 |
The values in the table above are maximum values as a guideline. If you are designing for an application with predominantly DC currents and small AC currents, then you may successfully design with greater Flux Densities closer to these values. In these cases, it is useful to operate with high Flux Density to improve the Power Density of your design.
However, if you are operating with a higher ratio of AC current, such as most transformer applications and AC inductors, you must be mindful that higher operating frequencies will incur greater core losses, so you should operate at with an appropriately lower flux density.
We don’t have a rule of thumb for this, but we recommend you start with a high value and let the Optimizer provide you with a good range of options to analyse. The proof will be in the final core losses and the temperature rise you see in the full design. Alternatively, if you are more interested in the final core losses as a target, follow our guidance below as a starting point.
How to Pick an Appropriate Core Loss Target
This can be quite a subjective value, but the aim here is to give you a little guidance and a starting point. As a rule of thumb, your magnetic can be expected to account for up to 1/6th of your converter’s total losses.
If you have in mind an efficiency for your converter then that’s great, you have a starting point. From our observations through experimentation and online literature, a guiding target for your converter efficiency may be derived from the graph below.
Where:
Total Converter Efficiency, Total Transformer Efficiency, Percentage of Transformer losses to total converter.
From here you can calculate a starting point for your magnetic loss:
Magnetic Loss = (Input Power * (1- Total Converter Efficiency)) * Percentage of Transformer losses to total converter
Input Power is the amount you specified on the Waveform Page and in the graph above, the x-axis.
From here you have a choice to make about the ratio of core to copper losses, this can be highly dependent on your application, topology, and your overall design priorities.
If you are unsure, start with a 50/50 split. You can always quickly adapt to different scenarios once you get more familiar with the tool and your design.
So, to get an initial Core Loss Target value take your Magnetic Loss calculated above and divide it by 2.
What Core Material Should I Pick?
Manufacturers often give recommendations on the frequency ranges of their materials. These recommendations will consider the relationship between frequency and core losses.
For guidance, please see the table below with some recommendations. Remember, these are not definitive as the proof is always in the outcome, we are supplying you with this information as a little help to kickstart your Core Optimizer™ experience.
|
Material |
Fmin (kHz) |
Fmax (kHz) |
|
3C90 |
10 |
200 |
|
3C91 |
10 |
300 |
|
3C92 |
10 |
200 |
|
3C92A |
10 |
200 |
|
3C94 |
10 |
300 |
|
3C95 |
100 |
500 |
|
3C95A |
100 |
500 |
|
3C95F |
200 |
500 |
|
3C96 |
200 |
400 |
|
3C97 |
100 |
500 |
|
3C98 |
200 |
400 |
|
3C99 |
10 |
300 |
|
3F4 |
1000 |
2000 |
|
3F36 |
500 |
1000 |
|
3F46 |
1000 |
3000 |
|
N27 |
25 |
150 |
|
N41 |
25 |
150 |
|
N49 |
300 |
1000 |
|
N51 |
25 |
150 |
|
N72 |
25 |
300 |
|
N87 |
25 |
500 |
|
N88 |
25 |
500 |
|
N92 |
25 |
500 |
|
N95 |
25 |
500 |
|
N97 |
25 |
500 |
|
PC47 |
25 |
500 |
|
PC200 |
700 |
4000 |