The causes of EMC interference can be of various kinds. Therefore, standard filters are not always the simplest and best solution. SCHURTER now offers an “Evaluation Board” with which an almost ideal filter for the specific incident can be built within a short time in an iterative process.
Every developer of an electrical or electronic device is faced with the same problem: in the end, the device must comply with international EMC guidelines regarding emissions and immunity. In the age of the substitution of mechanical and mechatronic systems by purely electrical ones, EMC is becoming increasingly important.
Origin
EMC problems, often of an unpredictable nature, mostly arise in the power section. Like most electronic assemblies, the power section is also increasingly being mounted on printed circuit boards with discrete components. Due to the high integration of components to achieve a compact design, thermal problems can arise due to high currents on the printed circuit board. The resulting EMC interference can affect adjacent components due to the lack of spatial separation. Therefore, a compact filter directly on the PCB with discrete components is often the best solution. And a current compensated choke with capacitors is the most efficient measure in EMC
Suppression.
Nothing goes without measurements
First of all: Nothing goes without measurements. The ones who can carry out EMC measurements themselves according to EN 55011 should take a closer look at the DKIH Evaluation Boards. Variants of the boards are available for 1-phase and 3-phase systems. These evaluation boards are suitable for systems up to 50 ampères.
Filter Design
An EMC filter should bring the emissions below the limits specified for the application. Most product standards require measurements in the range from 150 kHz to 30 MHz conducted and 30 to 1000 MHz radiated. Line filters are often required to ensure EMC-compliant operation. Classical LC filters consist of a combination of interference protection capacitors and a choke. The choke is typically designed as a currentcompensated choke with two opposing windings and the same number of turns. This compensates the magnetic fields, which means that the normal operating current does not see any inductance. A diagram of a typical 1-phase filter can be seen below. With a current compensated choke and two X capacitors between L and N and two Y capacitors to ground. This circuit is very effective with low power dissipation, but provides good noise attenuation over a wide frequency range.
Measurement at the real interferer
The universal design allows the construction of a classic LC filter circuit. Two X capacitors of various sizes can be installed before and after the choke and a total of four Y capacitors. Leakage resistors are provided to protect against electric shock. The connection is made via two 6.3 x 0.8 mm tabs, a 4 mm hole or direct soldering of the cables to the large-surface pads. It is recommended to make the earth connection as flat as possible using copper tape or wide copper strands. The effect of the Y capacitors is considerably influenced by the connection
If no previous measurements or simulations have been made, it is usually not known whether we are dealing with a high asymmetrical (L/N to PE) or symmetrical (L to N) interference. It is always advisable to make a measurement first without filter components on the device. It must be ensured that the maximum interference level is found. This is decisive for EMC conformity.
Step 1
Measurement without filter components, conducted 150 kHz – 30 MHz
Step 2
Configuration of the Evaluation Board DKIH1-EVB with choke 0.8 mH (10 A ferrite) and capacities of 2 x 470 nF and 4 x 2.2 nF
Step 3
Configuration of the evaluation board DKIH1-EVB with choke 0.8mH (10 A ferrite) and larger X capacitors of 2 x 1.0 µF and 4 x 2.2
Step 4
Configuration of the evaluation board DKIH1-EVB with nanocrystalline choke 6.9 mH (10 A NK), capacitors remain at 2 x 1 µF and 4 x 2.2 nF
Step 5
Configuration of the Evaluation Board DKIH1-EVB 6.9 mH (10 A NK), X capacitors increased to 2 x 2.2 µF, Y capacitors remain at 4 x 2.2 nF EMC Products • Very good suppression thanks to larger X capacitors. • Circuit can still be cost- and spaceoptimized.
Step 6
Configuration of the evaluation board DKIH1-EVB with ferrite choke 0.8 mH (10 A ferrite), capacitors remain the same at 2 x 2.2 µF, 4 x 2.2 nF
Step 6 Configuration of the evaluation board DKIH1-EVB with ferrite choke 0.8 mH (10 A ferrite), capacitors remain the same at 2 x 2.2 µF, 4 x 2.2 nF
Read more: Link application note The ideal filter in just 6 steps
