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CISPR 15: Electrical Lighting and Similar Equipment — Radio Disturbance Limits
Emission limits and measurement methods for lighting equipment EMC
1. Standard Scope and Key Concepts
CISPR 15 specifies limits and measurement methods for radio-frequency disturbances produced by electrical lighting and similar equipment operating in the frequency range 150 kHz to 30 MHz (conducted) and 30 MHz to 300 MHz (radiated). The standard covers all types of lighting equipment including LED lamps and modules, fluorescent lamps with electronic ballasts, compact fluorescent lamps (CFL), incandescent lamps with dimmers, discharge lamps, and UV/infrared radiation equipment for non-medical purposes.
A distinctive feature of CISPR 15 is its historical treatment of lighting equipment as predominantly capacitive-load devices, which influences the measurement setup and impedance stabilization requirements. The standard also includes specific provisions for self-ballasted LED lamps, recognizing the rapid growth of solid-state lighting and its unique EMC challenges related to switch-mode LED drivers operating at high frequencies.
The most significant change in recent editions of CISPR 15 has been the extension of radiated emission requirements up to 300 MHz (previously 30 MHz limit), driven by the proliferation of high-frequency switching LED drivers whose harmonics extend well beyond the traditional AM radio band.
2. Emission Limits
CISPR 15 defines conducted and radiated emission limits that vary by frequency and equipment type. The standard also specifies limits for the disturbance voltage at the mains terminals (conducted) and the radiated electromagnetic field from the lighting equipment.
| Frequency Range | Conducted Limits (dBµV) QP | Conducted Limits (dBµV) AV | Notes |
|---|---|---|---|
| 150 – 500 kHz | 66 – 56 (decreasing) | 56 – 46 (decreasing) | Mains terminals |
| 500 kHz – 5 MHz | 56 | 46 | Mains terminals |
| 5 – 30 MHz | 60 | 50 | Mains terminals |
| 30 – 100 MHz (radiated) | 40 – 47 dBµV/m at 10 m | — | Radiated field |
| 100 – 300 MHz (radiated) | 47 – 54 dBµV/m at 10 m | — | Radiated field |
Special limits apply to lighting equipment with dimming functionality, as the dimmer switching action generates additional emissions. For phase-cut dimmers (TRIAC-based), the abrupt current switching generates significant harmonic content extending into the MHz range. The standard also specifies limits for the weighted disturbance power (disturbance voltage at the lamp terminals) for certain luminaire types.
LED lamps with integrated TRIAC dimmer compatibility face a fundamental EMC conflict: the dimmer requires a minimum holding current to operate correctly, but the LED driver’s input stage (typically a bridge rectifier with capacitive smoothing) draws current only near the AC voltage peaks, which can cause dimmer misfiring and generate unpredictable emission patterns. Additional resistive or capacitive bleed networks are needed, which must be carefully designed to avoid excessive power loss.
3. Engineering Design Insights for Lighting EMC
For switch-mode LED drivers, the primary emission source is the switching transistor (MOSFET or integrated switch) operating typically at 50–200 kHz for isolated flyback topologies, or up to 1 MHz for resonant LLC converters. The fast voltage transitions (dv/dt) across the switching node couple through the transformer interwinding capacitance to the AC mains, creating common-mode emissions. Key mitigation techniques include: a primary-side snubber circuit (RCD) across the transformer primary to dampen ringing at switch turn-off; a Y-capacitor (1000–4700 pF) from the secondary DC output to the primary-side ground to provide a low-impedance return path for common-mode currents; and a ferrite bead on the gate drive trace to control the switching speed.
Input filtering for LED drivers requires both common-mode (CM) and differential-mode (DM) filtering. A typical CM choke for a 10–50 W LED driver is in the range of 10–30 mH with a saturation current rating 1.5× the peak input current. The DM filter typically consists of an X-capacitor (0.1–0.47 µF) combined with a small DM choke (100–470 µH). The physical layout of the filter components on the PCB is critical — the CM choke should be positioned such that the AC input traces do not couple noise past the filter through parasitic capacitance.
For linear fluorescent ballasts operating at 20–50 kHz, the primary concern is the harmonics of the switching frequency appearing on the mains. While the fundamental is within CISPR 15 limits, the 3rd and 5th harmonics (60–250 kHz) can be problematic. An LC filter resonant at the switching frequency with a notch characteristic can effectively suppress these harmonics.
A carefully designed resonant LLC LED driver topology inherently produces lower EMI than a hard-switched flyback converter. The sinusoidal switching transitions of the LLC converter reduce dv/dt and di/dt, resulting in 10–20 dB lower conducted emissions. The trade-off is increased component count and design complexity, but for >50 W applications, the EMI benefit often justifies the additional cost.
4. Frequently Asked Questions
Q: Do incandescent lamps without dimmers need CISPR 15 testing?
A: Simple incandescent lamps (resistive load) generate negligible electromagnetic disturbance and are generally exempted from testing. However, incandescent lamps with any form of dimmer, or those incorporating electronic components, fall within the scope of CISPR 15.
A: Simple incandescent lamps (resistive load) generate negligible electromagnetic disturbance and are generally exempted from testing. However, incandescent lamps with any form of dimmer, or those incorporating electronic components, fall within the scope of CISPR 15.
Q: Are solar-powered garden lights with LED emitters covered by CISPR 15?
A: Yes, LED-based lighting equipment is covered regardless of the power source. However, during battery-only operation (disconnected from solar panel and any charging circuit), the conducted emission limits via mains are not applicable, though radiated limits still apply.
A: Yes, LED-based lighting equipment is covered regardless of the power source. However, during battery-only operation (disconnected from solar panel and any charging circuit), the conducted emission limits via mains are not applicable, though radiated limits still apply.
Q: What is the relationship between CISPR 15 and energy efficiency regulations?
A: CISPR 15 requirements are independent of energy efficiency. However, the EMC filter components (particularly the CM choke) introduce power losses that can reduce overall driver efficiency by 1–3%. Engineers must balance EMC compliance against efficiency targets — this is particularly challenging for high-power (>100 W) LED drivers where filter losses become significant.
A: CISPR 15 requirements are independent of energy efficiency. However, the EMC filter components (particularly the CM choke) introduce power losses that can reduce overall driver efficiency by 1–3%. Engineers must balance EMC compliance against efficiency targets — this is particularly challenging for high-power (>100 W) LED drivers where filter losses become significant.
