In this article, we continue our discussion on the importance of grounding when installing LED lighting equipment. Part 1 of this three-part series focuses on the ground plane of the printed circuit board (PCB) used in the LED driver. We’ll touch on the importance of the relationship between power quality in the facility electrical and grounding system and the LED driver’s PCB ground plane in Part 2. Part 3 of this series will explain how strategic power quality monitoring can identify disturbances that can cause premature failure of digital-based LED drivers.
Early generation electronic ballasts for fluorescent, HID, and even early LED drivers required PCB ground planes to provide zero-voltage reference planes and stabilize analog circuits for their power supplies and what little external dimming control was included in the design. With early power supply circuits being analog, simple analog circuit ground planes were included in the PCB designs.
In an analog circuit world, we know that electrical disturbances — of which most originate from inside customer facilities — can impact the performance of analog circuits and cause them to fail prematurely. Examples include voltage surges (combination and ring wave) and other voltage transients. Older facilities used (and some still do) little or no non-linear loads (NLLs). However, analog power supply failures were typically associated with surges and transients that have high magnitudes like those generated by lightning and other electrical events. Electrical events that produce voltage surges and transients with high enough magnitude to damage analog circuits can also be generated in customer facilities and still occur with little, no, or improperly installed surge protective devices (SPDs). Using the right SPDs at the right locations connected to the facility power system in the proper way provides suitable absorption of surge and transient energy in facilities where most, if not all, of the equipment uses analog power supplies.
As facilities began to upgrade their production processes and equipment, NLLs with switching power supplies began to show up. Upgrades started with the power equipment like analog electronic lighting (mostly fluorescent) and variable-frequency drives (VFDs) of low horsepower. Here, disturbances (including surges and transients) occurred on the power conductors, and the effects were felt on ground conductors caused by operating these loads in facilities but at levels that analog-based power supplies could tolerate. If the new loads didn’t contain manufacturing defects (and included proper on-PCB-board surge protection), their immunity to disturbances occurring in customer facilities was good enough to manage the risks associated with product malfunctions and early failures.
Today, it’s a different story. Customers have been installing higher power NLLs like VFDs rated up to hundreds of horsepower. Not surprisingly, the same electrical infrastructure in these facilities is being used to power and ground these larger NLLs and to power and ground newer more sophisticated electronic equipment like advanced production control systems and dimmable/programmable LED drivers. Sophisticated electronic equipment like digital-based LED drivers require higher-performance PCB ground planes capable of managing internal noise and disturbance currents on the PCB. Larger NLLs are also using higher power electronic switching circuits with higher switching frequencies. This is a necessity to minimize power losses and the size and weight of the power electronic systems. Lower losses mean higher efficiency. Moreover, more advanced controls have been integrated into these NLLs to provide better control of their mechanical loads. All of these improvements increase the risks of facility-generated disturbances and noise currents impacting the performance of LED drivers, especially if the drivers don’t employ a high-performance ground plane in their designs.
Advancements in LED driver designs have given us not only LED arrays that can be controlled using various on-board and off-board control techniques, but also LED drivers that are programmable to better match their output to the LED arrays. LED drivers can provide color tunable light outputs. These features require a sophisticated circuit design, as well as a high-performance ground plane, as a part of the LED driver PCB. While power supply control to improve power factor correction (PFC) and harmonic current control has also improved, the design of the DC side of the drivers has also improved, but is completely different, given the number of digital components and circuitry required to provide these new LED lighting functions.
Today’s LED drivers have become much more digital than analog. More surface-mount devices (SMDs) are being used for passive and active (analog and digital) components. These component size reductions are necessary if all of this functionality is to be squeezed into the shrinking LED driver form factors. On top of this, higher power drivers continue to be designed. This means the manufacturer is squeezing more power into smaller electronic compartments. All of these improvements, however, require high-performance PCB ground planes.
With the large number of LED drivers on the market and any one lighting/driver manufacturer producing multiple designs, the types of PCB designs and ground plane designs used in drivers are many. With respect to the ground planes designed into driver PCBs, the questions are: “What types of ground plane designs are being used in all of these drivers? Are the ground planes suitable for managing the disturbances that occur inside the driver circuits?”
Proper management of internal disturbances and noise must be accomplished before the design can be made to handle the electrical power disturbances and noise generated inside the customer’s facility. Then, the more important question becomes: “Are the ground planes that must support the analog and digital components and circuits inside the driver capable of sustaining acceptable driver functionality when the facility power and ground system throws all of its ugly power and ground disturbances at the LED luminaire?” Why is this question so important?
The Figure is a simplified example of an LED driver design where the AC-to-DC PFC-based electronic switching power supply is included in the left dashed box. The DC-to-DC electronic switching power supply is included in the right dashed box. The number and complexity of digital integrated circuits (ICs) used in LED driver designs is growing, owing to the need for ground planes that can provide circuit stability and proper power quality immunity to facility-generated disturbances and noise.
Failure to design the right type of ground plane for both the AC-to-DC and DC-to-DC parts of the driver not only increases the risk of design malfunctions but also decreases the immunity of the driver to electrical power quality disturbances (see Photo). Many articles have been written on ground plane design, but one should be careful to implement the correct ground plane design rules in digital-based LED drivers. Part 2 of this series will address the compatibility between the facility power and ground performance (i.e., its power quality) and the performance of the digital-based LED driver.
Keebler is a senior power quality engineer and power systems consultant at Electrotek Concepts, Inc. in Knoxville, Tenn. He can be reached at [email protected].
