Electromagnetic compatibility of lighting equipment
The EU decision to finally abolish incandescent lamps by 2012, the progress in the luminescent power of light emitting diodes (LED) and the further development of low-pressure and high-pressure discharge lamps are all leading to a sharp increase of electronic modules in lighting technology.
Common mode chokes for lighting
CE marking and conformity declaration
In the implementation of the EMC directive, a harmonisation of standards for lighting technology also ensured that there is a uniform evaluation of EMC in the European community zone. Lamps and lamp accessories may only be marketed in the EU if the manufacturer or its agent conﬁrms this evaluation by an appropriate conformity declaration. Special standards apply with respect to EMC (electromagnetic compatibility) and interference, and diﬀer in certain points from the standards for households and industry.
The standard applies to all lighting equipment and its accessories. Excep-tions apply to equipment operating in ISM (industrial, scientiﬁc, medical) frequency bands, to lighting technology in aircraft and airports and to other speciﬁcally exempted equipment. The limit values for conducted and radiated interference emission for all other lighting equipment are set forth there.
Figure 1 - Limit values with non-suppressed harmonics of a fixed-frequency switching regulator
Conducted noise emission
he following limits apply to the mains connection:
A quasi-peak (QP) of 110 dBμV is permissible between 9 kHz and 50 kHz. From 50kHz to 150kHz, the limit value runs linearly to the logarithm of frequency from 90 to 80dBμV. The limits for QP and average (AV) from 150 kHz and up comply with the generic standard EN 61000-6-3: Emission standard for residential, commercial and light-industrial environments.
Since the electronics and the illuminant do not always form a unit, and interferences can therefore also be emitted through the cable to the lighting means, limit values are also speciﬁed for lamp connections. They are QP (AV) 80 (70) dBμV from 150 to 500 kHz and QP (AV) 74 (64) dBμV from 0.5 to 30 MHz. A setup and test with a load emulation of the illuminant are likewise described. Limit values are deﬁned for control inputs, if the electronics have them.
Radiated interference emissions
A QP limit value of 30 dB (μV/m) for ﬁeld-based noise emission applies between 30 MHz and 230 MHz, and a value of 37 dB applies from 230 to 300 MHz, with a measuring distance of 10m.
This standard describes the permissible harmonic current emissions for devices with an input current of up to 16 A per phase. Lighting equipment and accessories are assigned to class C.
Up to an eﬀective input power of 25 W, the moderate limit values that can be achieved without a correction of the power factor apply to lighting equip-ment for discharge lamps (Table 1). For all other lighting equipment (e.g. LED lamps, ignition and starting devices), no limit vales for harmonics are prescri-bed up to 25 W.
Alternatively to the limit values of the table 1, it is also sufficient if the third-order harmonic current does not exceed 86% of the fundamental oscillation current and the fifth-order harmonic current does not exceed 61%, if the current flow lasts at least from 60° to 90° and the peak value is reached before or at 65°.
The following limits apply to devices with an effective input power of >25 W:
Table 2: * Lambda ist the power factor of the circuit
The standard permits the use of several operating devices with <25 W in a lamp with the limit values for <25 W.
This standard describes the limit values for voltage ﬂuctuations and ﬂicker in low-voltage supply systems up to 16 A per phase. No limit values apply to lamps. Lighting ﬁxtures with incandescent lamps up to 1000 W rated power and lighting ﬁxtures with discharge lamps up to 600 W rated power need not be tested.
The interference immunity requirements for devices for generic lighting purposes are established here. The reader is referred to the relevant generic standards EN 61000-4-x for tests such as electrostatic discharge, HF-EM ﬁeld, LF-EM ﬁeld, burst, surge and voltage dips; the intensity of the tests as well as the criteria for the various types of lighting devices (e.g. starter units, discharge lamps, emergency lighting) are set individually.
EMC filters in lighting technology
The objective of the noise-elimination measure is avoid propagation of the interference currents generated in the electronics. Conducted interference is primarily emitted via the mains line and the line to the illuminant. For lighting devices with lager power, the use of IEC power entry modules or single-phase EMC ﬁlters on the mains side is possible.
Figure 3: Current-compensated toroldal core chokes from Schaffner for 0.3 to 10 A.
The integration of the ﬁlters on the circuit board using current-compensated chokes is advisable for lower powers. The RN series makes the construction of EMC ﬁlters with high power density possible due to the use of toroidal cores, and has high saturation resistance as well as outstanding thermal behavior.
RN chokes are less sensitive to electromagnetic coupling than other designs because of the closed toroidal core and the compact design of the magnetic circuit.
Mains ﬁlter design for lighting technology
Figure 4: Typical arrangement of a main filter
The mode of operation of the individual components will be brieﬂy explai-ned with reference to a typical mains ﬁlter. The parasitic capacitances of the interference source to earth are one propagation path for interference. The heat sink is a typical example of this for power electronics. The noise currents ﬂow via the parasitic capacitor to ground and back to the interference source via the mains lines or other lines. This noise is called common-mode or asymmetric interference.
To avoid propagation via the mains line, the load-side Y-capacitors in the ﬁlter form a noise sink. At the same time, the impedance of the mains line is increased by a current-compensated choke. For low power, small parasitic capacitance to earth or high requirements for leakage currents as in medical technology, noise elimination with Y-capacitors can also be left out.
The second path for propagating noise is diﬀerential mode or symmetrical interference. The typical source for this is the voltage ripple caused by the switching process and impedances of parallel components such as capaci-tors and the circuit path to their terminals.
These interferences would mainly propagate via the connected mains conductors P and N to mains.
The load-side x-capacitor Cx-2) is an interference sink for these noise currents. With a load-side inductor (PFC choke or DC reacror) the x-capacitor forms a ﬁrst low-pass ﬁlter and symmetrises the noise level on the two mains lines. The stray inductance of the current-compensated choke, together with mains-side capacitor Cx-1, forms another low-pass ﬁlter to suppress the propagation of symmetrical interference to mains.
Figure 5: Network emulation with impedance curve
In general a structure as shown in Figure 4 is suﬃcient. The requirement for damping can be found by measuring the module without interference suppression with the network emulation
As shown in Figure 1, the harmonics of the switching process can exceed the permissible limit values from EN 55015. The selection of the switching frequency determines the third, ﬁfth, through n-th harmonics. EN 55105 allows 110 dBuV as the limit up to 50 kHz, and after that the limit value runs linearly to the logarithm of frequency from 90 to 80 dBμV. It is therefore advisable to keep the switching frequency below 50 kHz.
For example, if 48 kHz is selected as the switching frequency in consideration of the bandwidth of the quasipeak measurement, no interference below this frequency will be caused by the switching process. Thus a value of 110 dBμV applies to the ﬁrst harmonic, and then 81 dBμV for the third harmonic at 144 kHz.
If measurement of the non interference-suppressed module containing the load-side x-capacitor shows that limit values have been exceeded, an appro-priate preselection can be made based on the damping curves of the RN choke (see Figure 6).
Figure 6: Damping curves of the Schaffner RN143 series
The rated value for the choke current must be measured for the lowest possible mains voltage and the largest load case and the highest permissible temperature under full load. By matching the resonant frequency to the spectrum of the switching processes, it is possible to damp the third harmo-nic at 144 kHz by about 70 dB with an RN143-05-02, if that is necessary. The decisive factor is ultimately the measurement with the network emulator, however.
Current-compensated chokes for the load and control terminals
In addition to their use as mains ﬁlters, current-compensated chokes can also be used for noise suppression of the load terminal. For ballasts with an ignition voltage, this level must match the rated voltage of the choke.
For control terminals, RN chokes can not only help suppress the propagation of interference but can also improve interference immunity in order to meet the criteria of the interference immunity tests "Fast transients" (EN 61000-4-4) and "Surge voltages/surge currents" (EN 61000-4-5).
RN chockes - proven quality
The UL-tested RN chokes can be used from 40°C to +125°C, have an MTBF of 4 million h and meet the requirements for RoHS and REACH. RN chokes are available from stock anywhere through a world-wide distribution and sales network.