A LED turn-light consists of the following:
– an array of thirteen LEDs, supplied by 40 V and dissipating 12 W power
– an electronic circuit (driver) supplied with 12 V DC containing a DC/DC converter in the boost topology, driven at a frequency of 350 kHz
– a wire harness connecting the LEDs to the driver.
Our analysis will be focused only on the driver circuit which is made on a Printed Circuit Board and is protected by a metallic cover as shown in Figure 1.
In the top part of the PCB, the EMC input filter, constituted by an inductor and two capacitors, is implemented. Since its role consists in limiting the product’s conducted noise levels, its design must be carefully checked. The aim is to demonstrate that the use of simulation software can be extremely helpful to engineers for the most critical choices.
The LED driver board is composed of four layers that have been described in simulation software. In order to reduce the number of mesh elements (and also the solving time), each layer has been “slightly” cleaned-up in the context for CAD defeaturing. The metallic cover is also modeled (see Figure 2)
Once the 3D geometry has been described, the electronic components achieving the DC/DC conversion function and the EMC input filter are introduced in the project. All the passive components (resistors, inductors and capacitors) have been modelled by their equivalent high-frequency circuit (with their parasitic elements) obtained by measurements with a Vector Network Analyser.
The active components of the boost converter (MOSFET and diode) are described with two equivalent Differential-Mode (DM) current sources whose values (obtained by measurement) represent the current flowing through the MOSFET and the diode, as shown in Figure 3. The common-mode noise sources are represented using voltage sources for predicting high-frequency conducted noises.
The first goal of our study is to estimate the conduced noises on the power-supply line (+12 V and GND) and their comparison to the measured values in the frequency band between 100 kHz and 100 MHz. The objective is to highlight the importance of taking into account the parasitic effects of conductors and components in such analysis
The simulation software dedicated to electrical interconnections modeling for EMC & power electronics applications – InCa3D allows to create an accurate simulation model of the device.
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