The difference between isolated and non isolated LED power supplies

Isolation power supply uses a transformer to reduce 220V voltage to a lower voltage, and then rectifies it into DC power output for use. Because the main coil of the transformer bears a voltage of 220V, and the secondary coil only bears the output low AC voltage, and the main and secondary coils are not directly connected, it is called an isolated power supply. The conversion process of a transformer is electrical magnetic electrical, and it is not connected to the ground, so there is no risk of electric shock.

Non isolated power supply is a type of power supply that uses 220V to directly input into electronic circuits, and outputs voltage through electronic components. The input and output are directly connected through electronic components, so it is called a non isolated power supply; On the surface, the difference between the two is whether there is a transformer or not. The non isolated design of LED is limited to double insulated products, such as substitute products for light bulbs, where the LED and the entire product are integrated and sealed in non-conductive plastic, so there is no risk of electric shock to the end user. Secondary products are all isolated and relatively expensive in price. Non isolated circuits involve the input power being directly applied to the LED load through voltage regulation, which poses a risk of electric shock.

But as a complete LED lighting fixture product, the parts of the product surface that users can come into contact with must be isolated to prevent electric shock. From the perspective of the entire product system, isolation is inevitable, and the only difference is the location where isolation is set.

As a product that ensures safe use for end users, we will definitely consider the reliability of insulation and isolation.

In terms of performance, the advantages of isolated power supplies are: they do not pose a threat to the human body, perform well in a wide voltage range, and non isolated ones are now very mature. The voltage range is slightly worse than isolated ones, ranging from 110V to 300V, while isolated power supplies can achieve 60-300V. The high and low currents are very uniform. Isolation type drive; Safe but inefficient, non isolated drivers have higher efficiency. The choice between isolated and non isolated drivers should be based on actual usage requirements.

In terms of constant current accuracy, the isolated type can achieve within ± 5%, while the non isolated type is difficult to achieve.

Non isolated circuits are highly sensitive to surges and have poor suppression capabilities. Lightning surge, this voltage is an instantaneous high voltage, up to several thousand volts, with a short time and extremely strong energy. When this voltage enters the power supply, it will be instantly transmitted to the output of the non isolated BUCK circuit, damaging the constant current detection loop or further damaging the chip, causing a 300V straight through and burning out the entire lamp tube. In fact, it refers to non isolated power supplies. When shipped in bulk, the repair rate is higher than that of isolated LED driver power supplies, mostly due to explosion damage. The probability of isolated power sources exploding is much smaller, with non isolated ones generally around 2% to 3%.

Many power grids have unstable voltage and isolation, and the phenomenon is that chips, MOSFETs, and constant current loops are all burnt out, but isolation is relatively less.

The cost of electronic products is not only the design and production cost, but also includes the maintenance cost for large-scale products. In terms of the structure of LED power supply circuits, the current isolation schemes are mostly AC/DC flyback circuit schemes, which are relatively complex and costly. The non isolated type basically uses DC/DC boost or buck circuits, which are relatively simpler and therefore have relatively lower costs.

Non isolated systems typically achieve an efficiency of over 90% and have a higher power factor due to the reduced energy loss of transformers. The energy efficiency of isolation is generally 88%, depending on the power, so the isolated power supply also generates a relatively large amount of heat.

Non isolated power supplies have advantages in efficiency and cost compared to isolated power supplies. Isolating power sources is not easy to achieve high efficiency, and if not handled properly, it generates a lot of heat and incurs high costs, especially for LED fluorescent lamps with built-in tubes. But for non isolated power supplies, due to their poor ability to suppress lightning surge voltage, they will encounter many damages when shipped in large quantities.

Compared to isolated power supplies, non isolated power supplies mainly reduce the number of transformers and design the architecture with minimal materials to achieve the same product functionality, so non isolated power supplies have a significant cost advantage. This is probably the reason why non isolated power supplies are very popular in China.