First, let's talk about what is the LED driver? It can convert the power supply to a specific voltage and current to drive the LED light-emitting voltage converter. Usually, the input of the LED driving power supply includes high-voltage power frequency AC (ie, mains), low-voltage DC, high-voltage DC, low-voltage high-frequency AC. (such as the output of an electronic transformer). The output of the LED driver is mostly a constant current source that changes the voltage as the LED's forward voltage drop changes.
The core components of the LED power supply include a switch controller, an inductor, a switching component (MOSfet), a feedback resistor, an input filter component, an output filter component, and the like. According to different occasions, there must be input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.
Classified by drive
(1) Constant current type
The output current of the constant current driving circuit is constant, and the DC voltage of the output varies within a certain range according to the magnitude of the load resistance. The load resistance is small, the output voltage is low, the load resistance is larger, and the output voltage is also The higher;
The constant current circuit is not afraid of load short circuit, but it is forbidden to completely open the load;
The constant current driving circuit drives the LED, which is ideal, but relatively high in price;
Attention should be paid to the maximum withstand current and voltage values used, which limits the number of LEDs used.
(2) Voltage regulator
When the parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, and the output current changes as the load increases or decreases;
The voltage regulator circuit is not afraid of the load open circuit, but it is forbidden to completely short the load;
Driving the LED with a voltage-stabilized driving circuit, each string needs to be added with a suitable resistor to make each string of LEDs display brightness average;
The brightness is affected by the rectified voltage changes.
LED drive power features
(1) High reliability
Especially like the driving power supply of LED street lamps, it is installed at high altitude, the maintenance is inconvenient, and the maintenance cost is also large.
(2) High efficiency
LEDs are energy-saving products, and the efficiency of driving power supplies is high. It is very important to dissipate heat from the power supply installed in the fixture. The power source has high efficiency, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LEDs.
(3) High power factor
The power factor is the grid's load requirements. Generally, household appliances below 70 watts have no mandatory indicators. Although the power factor of a single power consumer with low power has little effect on the power grid, the amount of lighting used at night is large, and the similar load is too concentrated, which will cause serious pollution to the power grid. For 30 watts to 40 watts of LED driver power, it is said that in the near future, there may be certain indicators for power factors.
(4) Driving method
There are two types of traffic: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. In this way, the combination is flexible, and all the LED faults do not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, which is the driving mode adopted by “Zhongke Huibao”. LEDs are operated in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and it is necessary to solve a certain LED failure without affecting the operation of other LEDs. These two forms coexist for a while. Multi-channel constant current output power supply mode will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.
(5) Surge protection
The ability of LEDs to withstand surges is relatively poor, especially against reverse voltage capability. It is also important to strengthen protection in this area. Some LED lights are installed outdoors, such as LED street lights. Due to the start of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause LED damage. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have a certain lack of surge protection, and as the power supply and lamps are frequently replaced, the LED drive power supply should have the ability to suppress the intrusion of surges and protect the LED from damage.
(6) Protection function
In addition to the conventional protection function, the power supply preferably increases the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; it must meet the requirements of safety regulations and electromagnetic compatibility.
Advantages and disadvantages of overall constant current and path-by-channel constant current operation
Compared with the overall constant current, the constant current is more disadvantageous and the cost is higher. But it can really protect the LED and extend the life of the LED, so the constant current is the future trend.