Equivalent Circuit Construction of Common Mode Choke Coils (Practice)
Table of Contents
- Obtain resistance and stray capacitance that become iron loss
- Leakage inductance frequency characteristics
- DC Resistance of Wiring
- Consideration of Common Mode Impedance
- How to configure the coupling coefficient k
- Completion of equivalent circuit of LDFL002302LS-V0E
- Actual measurement and simulation comparison
- Equivalent Circuit Model Verification Summary
Here, we follow the construction procedures indicated in Equivalent Circuit Construction for Common Mode Choke Coils (Theory). (Sample used: Part number LDFL002302LS-V0E)
1. Obtain resistance and stray capacitance that become iron loss
As shown in the figure below, connect both ends of the primary and secondary windings together, then connect to an impedance analyzer and measure the impedance.
Find C, R, Lo indicated in STEP 1 of Equivalent Circuit Construction for Common Mode Choke Coils (Theory).
| C |
R
|
Lo | |
| Measured value | 4.2pF | 5.8kΩ | 15mH |
| Circuit input value | *2.1pF (1/2 times) | *11.6kΩ (2 times) | 15mH |
*: Calculation for distributing the measured value to the primary and secondary coils
2. Leakage inductance frequency characteristics
As shown below, short the winding on one side (secondary side), connect the winding on the primary side to the impedance analyzer, and measure the leakage inductance value Lℓeak.
| Lℓeak | |
| Measured value | Ls=11μH |
| Leakage inductance | *5.5μH (1/2 times) |
*: Calculation for distributing the measured value to the primary and secondary coils
3. DC Resistance of Wiring
With the secondary side open, use a mΩ meter to measure the D.C.R. portion for both ends of the primary coil.
| DCR | |
| Measured value | 60mΩ |
| Circuit input value | *30mΩ (1/2 times) |
*: Calculation for distributing to both ends of the coil
4. Consideration of Common Mode Impedance
Due to the presence of resistance that becomes iron loss, winding capacitance, and leakage inductance, the frequency characteristics of the impedance shown below allow the dominant component to be inferred based on frequency.
5. How to configure the coupling coefficient k
From the leakage inductance Lℓeak, the coupling coefficient k is shown by the following formula in STEP 2 of Equivalent Circuit Construction for Common Mode Choke Coils (Theory).- Ls
- : Inductance measured from the primary coil when the secondary coil is shorted
- Lo
- : Inductance for one circuit (including leakage inductance)
The coupling coefficient k is the most important parameter for understanding the characteristics of common mode choke coils.
6. Completion of equivalent circuit of LDFL002302LS-V0E
We created an equivalent circuit based on the actual frequency characteristics of LDFL002302LS-V0E. (Based on Equivalent Circuit Construction for Common Mode Choke Coils (Theory))
| Each component | Circuit | Numerical value (input values) |
| stray capacitance | C | 2.1pF |
| iron loss (Loss of magnetic material) | R | 11.6kΩ |
| Self-inductance | Lo | 15.0mH |
| coupling coefficient | k | 0.9996333 |
| copper loss (Loss of wire) | DCR | 30mΩ |
| Dummy resistance | Rd | 1GΩ |
7. Actual measurement and simulation comparison
Comparing the simulation in the above equivalent circuit model and the measured common mode impedance, as shown below, the results are almost identical.
8. Equivalent Circuit Model Verification Summary
When constructing a common mode choke coil equivalent circuit, it is possible to construct a practical circuit model by accurately obtaining the presence of resistance, winding capacitance, and leakage inductance, which are core losses, and their numerical values.If you have any questions or inquiries that do not apply to the above, please contact us at the following address.