LED lighting over-current protection device applications

LED has the characteristics of low power consumption, long life, environmental protection and other distinctive features. After penetrating from the small-size backlight application field to the large-size panel backlight, it has now further expanded into the general lighting application field and is currently in the landscape, architecture, commerce, automotive, The rapid development of mobile lighting and other fields.

Faced with many applications of LED lighting, there are various driving solutions because the market does not form a unified specification, but it never changes, and from the point of view of overcurrent protection, it is based on the input current of the lamp body. It can be divided into two basic types: DC input and grid AC input. The main difference between the two types is whether the drive power supply has AC to DC modules. Of course, there are many low-cost solutions such as resistors, capacitors, and bucks on the market. There is no module for EMI rectification and constant-current driving. However, since the requirements for the selection of the primary-side fuses are the same as those shown in Figure 2, they are included in the second type.

There are three main purposes for LED lighting over-current protection:

First, for the purpose of protecting personal and property safety, protection devices are often added for this purpose in applications where the power input voltage is relatively high.

Second, the subsystem is isolated from the external system. If the external system is unstable, it will affect the security of the subsystem. On the other hand, the internal device of the subsystem is damaged, such as the short-circuit failure mode of the parallel device, or the internal cause of external factors. The safe insulation level is destroyed, causing the internal circuit to be shorted to ground. If no fuse action is cut off from the external system and no effective measures are taken in time, the external system's insurance system will be activated, which will cause interruption of the entire power supply system. This will indirectly cause unexpected losses in important places such as hospitals, and may even cause casualties. Therefore, it is sometimes necessary to add two fuses at the input of the power supply.

Third, protect important and precious electronic components or devices. For LED lighting fixtures, the cost of LED lamp beads accounts for most of the cost of the entire lamp. In non-isolated power-driven or non-constant-current driven circuits, the necessary overcurrent protection of the driven output is required.

Because the power input architecture is different, there are major differences in the selection of overcurrent protection devices.

1, for the DC input type of DCin fuse selection, need special attention to the fuse temperature reduction factor parameters, because the high power LED heat is relatively large, the temperature inside the led lamp cup is relatively high, if you choose the temperature reduction comparison Larger fuses will select the larger current specification. Under the same operating current, the protection capability of the fuses with large current specifications will be relatively reduced; in addition, the location of DCin will use capacitance filtering as the back end will produce relatively large Start pulse current, so choose the fuse in this area need to pay attention to strictly consider the conditions of the pulse, otherwise the error option can easily cause the fuse to be turned on impulse pulse phenomenon, it is difficult to pass many times of the switch machine experiment and inrush current test, recommended in this use resistance Strong pulse capability.

2. For the fuse selection of the drive output, while paying attention to the fuse temperature reduction factor, it is also necessary to consider the fuse's fuse speed index. Since the current fluctuation is not large here, if the circuit is abnormal or the components fail, it is necessary to Quickly cut off the circuit to protect the LED string at the back end. In this position, it is recommended to select the fuse with quick cut type and temperature reduction.

The above two kinds of occasions generally have more SMD low-voltage fuses on the market to choose from, such as AEM Technology's SolidMatrix® technology fuses, sizes from 0402 to 1206, current specifications from 0.5 to 30A, fast break, fast break, High-pulse, slow-cut, and many different series, different specifications, and different characteristics of the product for your engineers to use.

3, and ACin location for AC input LED lighting, especially LED bulbs need to consider the size of the fuse, but also need to consider the fuse voltage value. However, currently available fuses capable of withstanding a wide range of AC voltages are generally relatively large. Few fuses with small-sized fuses can withstand voltages up to 250VAC. For this application dilemma, AEM Technologies has introduced the AirMatrixTM AF2 series of chip fuses. Only 6.1mm*2.5mm*2.2mm, petite but able to withstand 250VAC voltage, but also has the advantages of high consistency, low internal resistance, high pulse resistance, etc., will bring you a new application experience for our engineers and friends.

Some engineers and friends think that fuses can protect the fuses from being used when the positive and negative electrodes and the zero line are disconnected from the overcurrent. Here, we share our experiences with our engineers and friends. The fuse needs to have a potential difference with the ground. The fuse used on the ground can also cut off the circuit. However, after the cutoff, there is still a potential difference between the entire lighting appliance and the earth. Once the internal device occurs, Short circuit will cause circuit hazard. Therefore, in countries where some sockets can be plugged in, such as Germany or China, from a safety point of view, it is necessary to consider adding fuses to LNs of some LED lighting fixtures that can be reversed.