In an isolated LED driver the Input (AC side) & Output (LED side) are separated by power transformer which provides galvanic isolation. Isolated power supply transform the 110/220V AC voltage to the lower voltage by means of an isolation transformer. The primary and secondary coils of transformer are not electrical connected by a wire, track etc. This topology can pass high voltage test. The advantage of this transformer is that any disturbance on primary side of the circuit is not directly passed onto output side. So, the output (LED’s) gets some degree of protection against transients and surges occurring on the primary side.
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The disadvantages of this configuration is higher cost. Also, the transformer leads to a few points loss of efficiency.
It is suitable for indoor lighting such as living room, bedroom, some lighting corridor. One also has an option of making these lights smart by using mobile apps which can remotely turn on/off or dim. Further sensors can be used to detect presence/absence of a person and lights can be switched off for additional power savings.
In a non-isolated LED driver, there is no power transformer. Non-isolated refers that output terminal and the input terminal are directly electrical connected.
The lack of transformer isolation in non-isolated circuitry, means that the LEDs are more susceptible to damage by surge coming from the AC mains as a result of load switching transients or disturbance on primary side.
Consequently, surge protection components are needed on both the AC and DC sides to provide adequate surge immunity effectively.
Non-isolated LED driver is higher on power efficiency than isolated LED driver due to the fact that transformer losses are avoided.
Conclusively, isolated or non-isolated LED driver have their own advantages and disadvantages. Based on the functional and safety requirements one should decide the topology to be used. Pyrotech provides both types of solution to meet customer needs.
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.
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.
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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.
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.
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.
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