Non-Isolated and Isolated LED Drivers for Sports Lighting Application

LED lighting industry has been evolving for tens of years and there are always questions about “isolated and non-isolated” , which one is better? In the past, this kind of debate only existed in the low and mid power designs but nowadays, the question goes on to high power applications like sports lighting and harbor lighting.

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My answer is that we can only say that which one is more suitable for certain applications or luminaire designs. Both of them have the reasons to be utilized in the market. And this article provides some ideas for luminaire designers on how to choose between the two kinds of LED drivers.

The difference between non-isolated and isolated LED driver

This figure below shows the details about the two structures. The key difference is about the isolation transformer which insulate the output from the high AC input voltage.

And the table below shows more about the electrical differences.

Isolated dimming and isolated LED drivers

Both concepts can be easily mixed together when we are talking about “Isolated” since this word can be used for describing both dimming or LED driver itself. They are totally different concepts. Isolated dimming means that the dimming interface like DALI, 0-10V or PWM signals are insulated from input, output or physical earth. So no matter the LED driver output is safe or not, at least the dimming controllers which are connected directly to the luminaires are safe. And that is the reason isolated dimming should be employed by users. According to IEC-1, all the luminaires no matter non-isolated LED drivers are used or not, the dimming interface or circuitry has to be isolated separately. The electric strength level of input, output, case and dimming interface is shown as below table.

How to choose and design with non-isolated LED drivers.

It is not easy to find a right non-isolated LED driver for high power design, the following has to be considered carefully:

a.Efficiency and thermal. Non-isolated LED drivers have the advantage efficiency compared with conventional isolated LED drivers. But it does not mean efficiency is not important. Better efficiency means lower power loss and less heat generation thus the LED LED driver can have longer life and higher reliability with better thermal situation. Checking the case temperature at Tc point is mandatory for a good luminaire design.

b.Dimming performance. Using a lower cost LED driver does not mean we have to sacrifice performance. Smooth dimming with either 0-10V or DALI or DMX control compatibility is important for stadium lights, especially the fast dimming response.

c.Find the right input voltage range for different countries.

d.Try to use the high LED voltage to achieve the best efficiency.  

e.Utilize the LED board with higher insulation. 3kV insulation voltage is suggested.

f.Do adequate insulation for the whole luminaire to make sure that all the points that can be touched by human body are safe and able to pass insulation test.

In commercial and industrial LED lighting, drivers historically were isolated using transformers to step-down voltage, however there is increasing use of non-isolated drivers.

Understanding Isolated Drivers

An isolated driver is an electrical device that employs a transformer to step down high voltage to a lower one, which is then rectified into DC output. The term “isolated” stems from the fact that the primary coil (high voltage) and secondary coil (low AC voltage output) of the transformer are not directly connected.

Non-Isolated Drivers Explained

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A non-isolated driver directly connects the load terminal to the input terminal without using a transformer for voltage reduction. This type of driver introduces high AC voltage directly to the load terminal.

Key Differences

Safety Considerations

Isolated drivers are generally considered safer due to the separation between high-voltage input and low-voltage work area, reducing the risk of electric shock. Non-isolated drivers, however, transmit high voltage directly to the working area terminal, presenting some higher risk of electric shock.

Safety measures for non-isolated drivers:

1. Proper connection of Class I grounding with the power supply system
2. Greater voltage protection of aluminum substrates (up to 3 KV)

Efficacy

Non-isolated drivers generally offer higher efficiency, leading to better luminaire efficacy compared to isolated drivers.

Luminaire Lifetime

Isolated drivers provide better protection against power surges and spikes, which can extend the life of LED components. The electrical isolation helps prevent high voltage from directly reaching the LED board, reducing the risk of damage.

Cost

Isolated drivers typically cost more due to their more complex AC/DC flyback circuit structure, which allows for multiple outputs. Non-isolated drivers use simpler DC/DC boost or step-down buck circuits, resulting in lower costs. Therefore, non-isolated drivers can lower luminaire first costs, as well as lower operating cost, due to their higher efficacy. Potentially longer isolated driver lifetime can also potentially impact costs. Overall, there are some complex cost trade-offs, with non-isolated drivers better for first costs and energy costs, but isolated drivers potentially better for luminaire lifetime.

Market Trends and Manufacturer Practices

The market has increasingly accepted non-isolated drivers as production technology has matured. Some manufacturers offer both isolated and non-isolated driver solutions in their product lines. Some manufacturers also provide customization options, allowing customers to request isolated drivers or non-isolated ones, based on specific requirements.

When choosing between isolated and non-isolated LED drivers, consider the trade-offs between safety, efficiency, lifetime, and lifecycle costs. While isolated drivers offer enhanced safety and better protect luminaire lifetime, non-isolated drivers provide lower costs and higher efficiency. The choice ultimately depends on the specific application and safety requirements of the lighting project.

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