With the maturity of high-power LED technology , the drive design of high-power LEDs is particularly important. According to the characteristics of high-power LED devices, if the driving current is too large or the operating temperature is too high, beyond the tolerance of the LED components, the LED devices are easily damaged. Therefore, a constant current, constant temperature control, and reliable, comprehensive protection LED drive system is required.
1. Features of high power LED drive control technology
According to the characteristics of LED driver power supply and grid power usage rules, the following aspects must be considered in designing and selecting LED driver power supply:
(1) The driving power of the LED street light should not be installed at a high altitude, which will bring inconvenience to the maintenance work, and the maintenance cost is large, so it is necessary to select a high-performance driving power source.
(2) High-power LEDs are energy-saving products, and the requirements for the driving power supply are also high. The efficiency of LED illumination decreases as the LED temperature increases, so the heat dissipation inside the LED is extremely important for the normal operation of the LED. The performance of the power supply is high, the power loss is small, and the heat generated inside the LED is small, which delays the temperature rise of the lamp or the display. It has a positive effect on reducing the light decay of LEDs.
(3) At present, there are two main ways of LED driving. One is that the constant voltage power supply supplies a plurality of constant current power supplies, and each constant current power supply separately supplies power to the LEDs of the respective circuits. This method is extremely flexible, such as an LED appears. Failure will not affect the normal operation of other LEDs but the cost is higher. The other is for direct constant current supply. The LEDs operate in series or in parallel, and the cost is slightly lower, but the flexibility is poor. Multi-channel constant current power supply mode has great advantages in performance and cost, and is the focus of development.
(4) The anti-surge capability of LED is poor, especially the ability to resist reverse voltage. Some LED displays or street lights are installed outdoors. Due to the lightning sensor and the grid load, various surges will occur in the grid system, which will have a bad effect on the LEDs. Therefore, the driving power of the LED needs to have the ability to suppress surge intrusion to ensure that the LED is not damaged.
(5) When the lamp is installed outdoors, the structure of the power supply should be moisture-proof and waterproof, and the outer casing should also be wear-resistant.
(6) In addition to the conventional protection of the power supply, it is preferable to increase the negative feedback of the LED temperature to prevent the LED temperature from being too high and affecting the stability of the light output.
2. High-power LED drive control system faces challenges
When the precision constant current power supply design has reached the stable output of the power supply, the power supply stability is a necessary condition for the light source to stabilize. Under the premise of the power supply stability, the current output by the light source may fluctuate during a long period of work. In order to obtain a stable current and improve the light stability of the LED, the output current is regulated by the magnitude of the voltage by controlling the peripheral voltage of the constant current power supply. The circuit design of the control part of the LED drive system is tightly wrapped around the single-chip microcomputer. Combined with the keyboard and LED digital display, the voltage sampled from the A/D is appropriately adjusted by the feedback and input voltage, and then D/A Analog voltage to input voltage.
Combined with the development of high-power LEDs at home and abroad, LED drive systems mainly face the following challenges:
(1) The life of the drive circuit needs to be improved, especially the life of key components such as capacitors will have a direct impact on the life of the power supply.
(2) LED drivers should move toward higher conversion efficiency, because the power of the unoutputted light is dissipated as heat, and the low conversion efficiency will have a bad effect on the energy saving effect of the LED.
(3) The LED is efficiently dimmed by a large dimming ratio, and the color characteristics are also ensured at low brightness and high brightness.
(4) Reducing its cost. Nowadays, in low-power applications, the cost of constant-current driving power supply is close to 35%, which is basically the cost of light source, which hinders the promotion of LED in the market to some extent.
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