Contrast and Analysis of Isolated and Non-isolated Power Supply

1. Isolated power supply

An isolated power supply uses magnetic components such as transformer to electrical connect the input power and output power, which are independent from each other even there is output short-circuit. The output voltage can be adjusted through the transformer.

2. Non isolated power supply

A non-isolated power supply uses no transformer to directly connect the input terminal and output terminal. Voltage reduction is done through BUCK circuit to set down the voltage and make a constant-current control. So that the most distinct advantages of non-isolated power supply are low cost, simplistic and high performance. However, there is electric shock hazard if touch it when the light is full loaded, and so lead to safety risk.

3. Contrast of isolated and non-isolated driver

Theoretically speaking, in the electronic circuit, the less electronic components, the more reliable it is. But why is non-isolated power supply is less reliable than the isolated power supply? The reason is that non-isolated circuit is very sensitive but poorly restraining to power surge.

As for isolated power supply, power is input into transformer first and to LED load next. But part of the input power is loaded into the LED in the non-isolated circuit. So that isolated circuit can well restrain to power surge and less damage than that in the non-isolated circuit. And this is why most people require isolated power supply in the market.

Non-isolated driver are more effective than isolated ones, and also with lower cost. Isolated driver are always difficult in making high efficiency and cannot do well with the high temperature, and is with a high cost.

4. Power surge damage to LED drivers

Damage in non-isolated driver is resulted from the power surge of the AC power, a high voltage but strong power even up to 3000V in a short time, which may occur under thunder and lighting, will go straight to the output terminal in the BUCK circuit and damage the constant current detector ring, even damage the LED chip, therefore make a 300V shoot-through and burn down the light fitting.

80% of LED drivers are broken down in using, and other mini-size switching power as well. All of them are damaged by the power surge. LED driver is broken because LED is very sensitive to such power surge because of its loading character.

However, power surge problem not only occurs in non-isolated drivers, but also the isolated driver as well. There are many isolated drivers, such as the outdoor street lamp power supply, will be broken down in a short time of using because of the power surge. As the developing of new technology, non-isolated power supply is mature and stable. If the structure is well designed, it can be a safe power supply as isolated ones.

5. Different application on isolated and non-isolated driver

Here comes some reference in using LED driver, it is concluded by years of experience.

• For the high power LED driver, isolated driver is safer, a non-isolated driver may risk overweight concern.
• For the low power LED driver, it should be decided according to particular case. To use non-isolated driver, two points should be concerned: a) cost permitted, b) heat available.
• Suitable application places for non-isolated driver: a) indoor lighting, stable power supply and less influence by power surge. b) High voltage and small current, efficiency and cost cannot benefit from non-isolated driver in the low voltage and high current. c) Stable voltage.

6. One Percent’s Non-isolated Power Supply

One Percent has been focus on non-isolated driver, and lots of experiment and testes are made to check the availability of such non-isolated driver with our LED Downlights.

As the following chart of data shows, with the same downlight and LED chip, non-isolated driver is at least 5% more efficient than the isolated one. So that non-isolated driver is more enery efficient.

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