Isolated versus Non-isolated Drivers for LEDs|
Article - March 17, 2016 By LarsonElectronics.com
Isolated vs Non-isolated Drivers for LEDs
Light emitting diodes (LEDs) are being developed to become more efficient and cost effective for industrial sectors. One of the ways manufacturers are contributing to this trend is through performance-enhancing designs. In particular, drivers are being optimized to improve the lifespan and reliability of LED fixtures.
Read on to understand the difference between isolated and non-isolated LED drivers.
Isolated LED Drivers
The circuit structure of an LED light with an isolated driver typically incorporates a flyback converter topology. This provides protection against fluctuating electrical currents via an isolating transformer. In this configuration, the LED driver’s output voltages may reach DC30-42V. This suggests that the parts are applicable for LEDs that use high power circuits above 15-20 watts, including outdoor fixtures. The transformer is also flexible, allowing individuals to step up or step up/down the voltage’s output using a variety of methods.
Isolated LED drivers refer to the positioning of the driver, away from the AC line of the fixture. Manufacturers may incorporate an isolated driver in their design to make room for cooling and shade features. From a safety perspective, this type of configuration is safer for consumers because it greatly reduces the possibility of electrical shock (individuals can touch the LED lamps, even during operation). By comparison, luminaries that are equipped with non-isolated drivers require insulation to prevent electrical shock.
From a cost perspective, lights that rely on isolated drivers are more expensive, because more parts are used in the design. When it comes to electrical efficiency rates, luminaries that support isolated power supplies are only around 88 percent efficient. Its non-isolated counterparts can reach up to 90 percent electrical efficiency, but are also considered to be less stable.
Non-isolated LED Drivers
LEDs with non-isolated drivers support buck or buck-boost topologies without an isolating transformer. The driver, which is not shielded from the AC power source, makes use of inductors as the averaging element. Non-isolated power supply output voltages range between AC30-84V, making it ideal for LEDs with high voltage, low current (15 watts and lower) requirements, such as indoor retrofit lamps. Meeting safety requirements set forth by various regulators, including UL and CE, are more difficult with non-isolated drivers. When using this type of driver, manufacturers must meet UL 8750 regulations for LED Equipment for Use in Lighting Products (Section 8.5.2, 126.96.36.199 and 188.8.131.52).
Issues with non-isolated configurations arise when LED components are mounted on a heat sink for thermal dissipation. For such cases, the heat sink, in its exposed nature, needs to be insulated from the AC input voltage. It is important to consider that insulation negatively affects a heat sink’s thermal conductivity properties, because it is not in direct contact with the parts that radiate high levels of heat. Additionally, if the heat sink is not grounded electrically, it can generate electromagnetic interference (EMI).
As mentioned earlier, a major drawback with non-isolated drivers is instability. Furthermore, the risk of electrical shock during handling is greater for operators, and the components are highly sensitive to electrical surges. Because of this, the LED chip is more prone to damage. To protect the units, manufacturers utilize voltage dependent resistors in the circuit’s design. The component is designed to interrupt electrical surges by responding to changes in the electrical current. Incorporating non-isolated drivers into LED fixtures can drive costs down, due to the straightforward configuration of the circuitry.