LED street lamp design constant current module selection strategy

We know that all LEDs must be powered by a constant current source, but at present, many solar street light manufacturers are mostly looking for a suitable constant current module after the LED module has been designed. As everyone knows, this design method will encounter problems, at least making this design not the best. There may also be a need to redesign the LED modules. I often receive phone calls from customers, how much power can your constant current drive module bring? This kind of question is practically unanswerable. Because how much power the constant current module can bring is related to many factors. From the perspective of the constant current module itself, it is mainly related to the heat dissipation requirements and heat dissipation conditions, and of course, it is also related to the current driving capability of the driver chip. However, even if these have been determined, for example, the constant current module SLM2842 has been selected, then its driving ability seems to be completely determined! actually not! Although its limit driving capability can be known, such as its maximum switching current, its maximum input current, its maximum input voltage and maximum output voltage, etc. However, the driving power of a constant current module is not only related to its heat dissipation capacity, but also related to its working efficiency. And its work efficiency is related to many external factors, especially user usage. Therefore, the requirements and characteristics of the constant current source should be considered when designing or selecting LED modules. one. LED connection structure When designing and selecting LED modules, some requirements related to constant current modules and others need to be considered. 1. The number of LEDs connected in series should be less than 10, because as LED lamps, there is a safety requirement. According to the EU IEC61347-2-13 (5/2006) standard, for LED modules powered by DC or AC power, it is required that the voltage in the LED lamps should not exceed the maximum safety extra low voltage (SELV), that is, its working output voltage ≤ 25Vrms ( 35.3Vdc), so the total number of LEDs in series should not exceed 10. 2. As a solar street light, LED modules are usually used for the convenience of repair and replacement. Each module is usually designed to be rectangular, and the constant current module is also designed in it. It is recommended that the power of each module be less than 30W. In this way, a street light of about 100W uses 3-4 LED modules, while a 150W LED street light uses 5-6 LED modules. Then high power can use 7-8 modules. 3. In each LED module, a 1W LED is usually used, and its connection mode is series-parallel mode. If the LED has a protection diode, it can be connected in series first and then in parallel. If there is no protection diode, then it must be connected in parallel first and then in series, so as not to damage one string and not light up. 4. To use several series and several parallels, it is necessary to further understand the performance and characteristics of the constant current module. two. The performance and characteristics of constant current module Ordinary regulated power supply is that the output voltage does not change when the load changes. The constant current module is a power supply that keeps the output current constant when the input voltage changes. Before using it, you must understand its various characteristics. 1. Current setting: Generally, the output current of the constant current module can be adjusted in a wide range according to the user's requirements, as long as the output current setting resistance is simply changed. 2. Type: There are three types of constant current modules: boost type, buck type and buck-boost type. Which one to choose is entirely determined by the relationship between the required input voltage and output voltage. However, from the viewpoint of obtaining the maximum efficiency, the step-down type should be selected. The buck type is the input voltage is relatively high. Therefore, the input current is relatively small, so the loss caused by copper loss is relatively small, and the step-down constant current module usually has higher efficiency. Therefore, the number of LEDs connected in series in the load must be minimized so that a step-down constant current driver module can be used. 3. The relationship between input voltage and output voltage Whether it is a boost type or a buck type constant current module, the closer the boost ratio or the step-down ratio is to 1, the higher the efficiency. Of course, it cannot be equal to 1, and 2-3V must be set aside for the constant current module to consume. And this is completely determined by the whole lamp design of the street lamp. Therefore, this factor must be considered in the overall design of the street lamp to select the number of LEDs connected in series with the power supply voltage and the load. Instead of designing it, it requires how much efficiency the constant current module must provide. 4. Dimming capability: constant current modules usually have dimming capability, and this dimming capability does not simply adjust its output current, but uses a dimming method called pulse width modulation (PWM), which uses Due to the rapid switching ability of LED and the visual residue of human eyes, the apparent brightness has changed. Thereby, the change of the chromatogram caused by adjusting the current is avoided. This dimming capability is very important in the design of solar street lights, because using this capability allows the brightness of the street lights to change according to traffic flow, thereby further achieving the purpose of energy saving.