Non-isolated power supplies are better used in the low-cost lighting market

As an important part of LED lighting fixtures, the driving power supply is moving to the extremes of the trend. One is the mid-to-high-end external drive with various control functions, and the other is the linear solution that meets the low-cost market. Under this trend, "non-isolated" power supplies have become the first choice for some application companies with their relatively low price and high efficiency. Some even boldly predict that " LED bulbs will use non-isolated power supplies in 2015" .

Compared with the isolated power supply, the non-isolated power supply is designed to eliminate the isolation transformer, so that the entire drive power supply is reduced in size, and no voltage conversion is required during operation, so that the non-isolated power supply can theoretically achieve higher efficiency than the isolated power supply. .

In fact, whether using isolated or non-isolated power supplies, LED lighting products must ensure absolute safety, and the difference between the two is that the former design the insulation part on the power supply, while the latter pass the isolation idea to the light fixture. The outer shell part.

"non-isolated" is cheaper

“Non-isolated” in the drive power supply means that there is a direct connection between the load end and the input end of the circuit. There is no isolation transformer. The architecture is designed with the least amount of materials to achieve the same product function, so the cost will follow. decline. It is understood that the cost of a non-isolated power supply is at least 10% lower than that of an isolated power supply, and the difference depends on the power. In the domestic lighting market where prices dominate, this is the main reason for the popularity of non-isolated power supplies.

In addition, the efficiency of the non-isolated power supply is higher. “Because there is a high-voltage to low-voltage process in the middle of the isolation product, its efficiency is theoretically not as non-isolated.” Non-isolation is less energy-efficient due to less transformation, and efficiency is generally It is over 91% and has a higher power factor. The isolation is generally about 88% energy efficiency, depending on the power.

Also because of the existence of the isolation transformer, the isolated power supply generates more heat during operation. In LED lamps with limited space and difficult heat dissipation, the use of non-isolated power supplies has a greater advantage.

In the domestic LED lighting market, the bulb lamp is one of the most demanding markets in the current market. It has been analyzed by industry insiders that the most suitable way for bulbs is due to the large difference between the grid voltage rectification and the output load voltage. It is driven by a flyback isolation buck. However, the isolation circuit has a complicated structure, many devices, high cost, low efficiency, and is not suitable for mass production, and the non-isolated circuit has a relatively simple circuit, uses few devices, has small volume, low cost, and high efficiency. With the market's demand for cost and efficiency, non-isolated circuits are on the stage in the field of low-power LED driving. Some even said that in 2015, bulb power will be completely isolated by non-isolation.

In this regard, Li Chengyu, head of sales department of Guangdong Kegu Power Co., Ltd. believes that because the value of LED bulbs is not too high, the use of non-isolated power supplies is a further cost reduction requirement, while the products with the most non-isolated power supplies are integrated. The only reason for downlights with non-isolated power supplies is the cost advantage.

Insulated housing becomes an important line of defense

Although the non-isolated power supply is cheap, its security has always been a concern for everyone. Since the non-isolated circuit is directly added to the LED load after the input power is applied through the buck-boost, there is a hidden danger of electric shock when the human body is in direct contact. Insulation is achieved by the outer casing of the LED luminaire. A single non-isolated power supply is definitely not in compliance with safety regulations. For finished lamps, only the places that the human body can touch are insulated to meet the standards. The non-isolated power supply actually transfers the idea of ​​isolation to the outside of the luminaire. "To ensure the overall safety of the luminaire, it is necessary to do the isolation measures through the lamp housing, which will add a little cost."

The development of insulating materials has also brought more possibilities to the application of non-isolated power supplies. "In the past, many lamps were directly exposed to metal structures. Now, the concept of plastic-clad aluminum is very simple. ”

Recently, the matching solutions for glass tubes and non-isolated power supplies have become hot topics in the industry. Due to the insulation characteristics, uniform heat dissipation and good light transmission of the glass tube itself, the cost is much lower than that of the plastic tube and the aluminum alloy tube. The combination with the non-isolated power source once again reduces the cost of the LED tube . However, the problem of glass cracking and splashing makes the glass tube unable to pass the UL-approved drop test, and the solution remains to be perfected.

The use of non-isolated power supplies in general lighting is in compliance with safety standards, and has been tested by a number of standards, provided that the power supply manufacturers and application manufacturers fully communicate to ensure the absolute safety of the lamp housing. "Do not use non-isolated power supplies. Enterprises have a relationship, for example, a customer base of a power supply manufacturer is a bulb, then this power plant will produce more non-isolated power; even if it is a panel light, just communicate with the lamp factory, do something wrong. Isolation is also achievable, and some customers are already choosing this method. We are the power supply manufacturer, we must let the lamp factory understand this non-isolation to protect the product safety, must cooperate with the power supply and the lamp factory. To solve this problem."

Indoor lighting is more suitable

Non-isolated power supply can be applied to any occasion, provided that external protection measures are in place. "The key is to ensure that the safety of the whole set of lamps can be done well. For example, the bulbs mentioned above, including panel lights and ceiling lamps, can be used for non-isolation. Do, it is no problem to do the insulation protection of the luminaire. However, in terms of stability, the non-isolated power supply is not as good as the isolated power supply. This short board directly leads to the non-isolated power supply not suitable for some occasions. The use of a non-isolated power supply is more likely to cause damage to the LED source than with a luminaire that uses an isolated power supply.

It is understood that non-isolated circuits are very sensitive to surges and have poor suppression. When the grid voltage is unstable, such as lightning strikes, the voltage across the AC line rises instantaneously, even up to 3000V. Although the time is short, the energy is extremely high. When a large load is disconnected, the non-isolated circuit is instantaneously transmitted to the output, destroying the constant current detection loop, or further damaging the chip, thereby damaging the entire lighting device. Although the same problem exists in the isolated power supply, the isolated power supply is lower than the non-isolated power supply in terms of the probability of damage.

Secondly, the non-isolated power supply has LED parameters, which are generally suitable for high voltage and low current applications.

In home lighting, or indoor lighting scenes with a small number of lamps, because of the good electrical environment, the impact of the surge is small, combined with the insulation shell, the use of non-isolated power has a greater cost advantage. In outdoor high-power lighting, the power supply working environment is more severe, the probability of lightning surge is greater, and relying entirely on the lamp housing insulation will greatly increase the cost of the entire lamp. In this case, the significance of applying non-isolated power is not Big.

From the perspective of the entire lighting fixture product, isolation is inevitable. The difference between the two power supply schemes is that the location of the isolation setup is different, and the specific solution is determined by the design requirements, product positioning and specific application scenarios of the fixture.