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EMC Reference Designs

You will find here proven EMC Reference Designs for PCBs and wirings. These designs passed EMC tests and are free for you to copy. However, there is no guarantee for a passed EMC test by just copying a design. EMC immunity and emissions depend also on many factors like PCB layout, chassis, electronic circuits close by, cabling layout, cable length, PCB grounding, cable shield grounding, etc.


In case you would like to share your reference designs here as well, please write us:

  1. DC Power Supply Input [industrial]

  2. CAN Interface [industrial]

  3. Wideband Analog Input Buffer (30 MHz) [industrial]

  4. Motor, Encoder and PWM [commercial]

DC Power Input

DC Power Supply Input [industrial]

  • ESD (±8kV contact discharge): 33nF/1kV capacitors as close as possible to input connector.

  • Burst (±4kV): 33nF/1kV capacitors, TVS diode ST BZW50-33B.

  • Surge to earth (±4kV): VDR Vdc=68V Vclamp=140V, Gas Discharge Tube (GDT) 2035-09-SM 90V/10kA.

  • Surge between power lines 24V/0V (±4kV): TVS diode ST BZW50-33B (peak pulse power 5000 W).

  • Common mode emission: Common mode choke, 33nF to shield/earth.

  • Differential mode emission: Supply ripple filtering (C5, L1, C6).

  • Cable shield: Lay cable shield to earth/case for high-frequency signals. For low-frequency signals: prevent ground loops current through cable shield.


CAN Interface [industrial]

  • ESD (±8kV contact discharge), burst (±2kV): TVS diode Würth 824022 as close as possible to the CAN input connector.

  • Emission: common mode choke Würth 744230251.

  • Cable shield: lay cable shield to earth/case for high-frequency signals. For low-frequency signals: prevent ground loops current through cable shield.

EMI CAN industrial interface
CAN Interface

Wideband Analog Input Buffer [industrial]


  • Radiated immunity / emission (10V/m, 80MHz...1GHz): ferrite bead Würth 742792093 as close as possible to the analog input connector, together with the 3.3pF capacitor.

  • ESD (±8kV contact discharge): schottky diode BAV99W and 1uF capacitor as close as possible to input connector.

EMI analog input buffer filter
Wideband Input Buffer

Motor, Encoder and PWM [commercial]


  • Radiated Emission (CISPR 11 / EN 55011, class B): General concept = place EMC filter close to source of emission. This means: close to motor driver (H-bridge), PWM driver and encoder logic. PWM / motor power lines: do not place filter capacitors along the way from driver to motor. This would lead to unnecessary current flows (current spikes) which leads to emission.

  • Bulk capacitors: Bulk capacitors are placed close to the H-bridge transistors (e.g. FETs) to stabilize the power supply. Typically these bulk capacitors have values from μF to mF to F (depending on the size of the motor).

  • Filter capacitors: Place filter capacitors as close as possible to every connector. These capacitors have typically values from pF to nF. Do not place capacitors in the differential power lines of motors (MOTOR+, MOTOR-), this may lead to unbalanced common mode current (radiated emission).

EMI concept for motor, encoder, PWM
Motor, Encoder, PWM
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