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Case analysis and solutions for conduction failure caused by the use of Class II drivers in Class I LED lighting fixtures
Author.
LCS
Source:
Post time:
2026-01-04
In recent years, when testing LED lighting fixtures according to the EN 55015 standard, we often encounter situations where the conducted emission from the power port exceeds the limit requirements. After disassembly analysis, it was found that the LED driver (purchased Class II driver) of this type of lamp is usually tightly installed on the back of the metal lamp bead support plate. The driver itself is not equipped with a grounding terminal, but due to the need for PE (protective grounding) protection for the metal casing of the lamp, a three core wire (including PE wire) is led out from the lamp. This design may result in electromagnetic interference inside the driver being unable to effectively dissipate through the grounding path, thereby affecting the conducted emission performance.
The data exceeding the standard is as follows: the overall peak and average waveforms of the exceeding radiation are relatively high, and the reading point can only read 1db;
Analysis of the reasons for exceeding the standard:
1、 Prioritize investigating the LED driver to determine if the entire light is not functioning properly due to the LED driver; Through communication with the driver manufacturer, whether this driver has passed authoritative certifications such as TUV, CCC, FCC, and provided EMC reports. The laboratory conducted retesting confirmation, measuring the conducted radiation of LED drivers separately with lamp loads. The test results are as follows:
The confirmation results indicate that the overall light exceeding the standard is not caused by the LED driver, but by the driver itself having a margin of 10db.
2、 Based on the laboratory staff's years of testing experience and analysis of test data, the problem may lie in the compatibility between Class II drivers and Class I lighting fixtures. This may be the essence of the problem. We attempted to disconnect the grounding wire of the support board for testing and found that the test waveform did not deviate significantly from the individually tested LED driver, with sufficient margin to confirm the problem.
3、 Based on the theoretical analysis of EMI, the maximum probability is the equivalent distributed capacitance formed by the LED driver body and the metal shell, which ultimately forms an equivalent near-field coupling circuit, namely the LED driver metal support plate PE line LISN and the metal reference ground plane of the shielding chamber, forming an equivalent common mode interference circuit, thereby affecting the voltage flowing through both ends of the LISN 50 Ω impedance.
4、 Based on the above analysis, effective solutions without replacing the driver can be roughly divided into two types:
Reduce the distributed capacitance and drive the LED away from the metal support plate;
Add filtering between L&N and PE to reduce the disturbance voltage at both ends of L N;
5、 Attempt method a, fix the LED driver and the metal support plate with a 1cm high insulating gasket, so that the bottom of the LED driver is 1cm horizontally away from the metal support plate. The experimental results are qualified.
6、 Try method b, add a filtering circuit between the AC input lines, and use a common mode inductor to cross the ground through a Y capacitor, as shown in the figure below. After retesting, the margin is nearly 20db.
Summary:
1. When purchasing drivers for LED lamps, priority should be given to the anti electric shock level of the entire lamp, and blind matching is not allowed, otherwise there is a high probability of compatibility issues, resulting in ineffective conduction and emission.
2. This problem is not only caused by LED drivers, but also by sensors, controllers, etc.
3. Method B involves adding a filtering circuit, which may be questioned in safety certification unless a certified finished filter is used. However, most of the internal circuits of the finished filter are not as effective as self-made filtering circuits, and purchasing finished filters invisibly increases production costs. For example, in this case, if the customer's manufacturing process cannot elevate the LED driver and does not accept method B, then this case is basically unsolvable.
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