How to use the ultra-bright white LED to transform the electric bicycle lamp, the lamp must be powered by constant current, so that the brightness of the lamp does not change with the battery voltage. The selection of the led lamp should be white light LED should be selected for the concentrating type.
Most electric bicycles use incandescent light bulbs as the light source for the lights. Since the battery voltage varies greatly, the bulb is often undervoltage. The dim light greatly reduces the safety of night riding. Transform the circuit of electric lights with super bright white LEDs.
Because the maximum voltage of 36V battery can reach more than 45V. The maximum voltage of 48V battery can reach more than 60V. Therefore, the lamp must be powered by a constant current, so that the brightness of the lamp does not change with the battery voltage, and the LED is not burned by excessive current. Figure l connects the LM317 to a constant current source of 60 mA to power the LED. The operating voltage of the white LED is approximately 3.1V to 3.5V. Therefore, the electric vehicle of the 36V battery can be connected in series with 9 to 10 LEDs. The four groups connected in series are connected in parallel, and each LED has an operating current of about 15 mA. In the figure, the LEDs connected in series are connected in parallel with each of the four re-use wires to prevent the influence of the brightness of the lamp when the LED is damaged. Thus, when one LED is damaged, the three LEDs connected in parallel are increased to 20 mA, and the others are still 15 mA, which does not affect the brightness of the lamp. White LEDs should be concentrating. Although the battery voltage can be as high as 60V, it exceeds the maximum input voltage of the LM317. However, since the LED in series has a voltage drop of 30 to 40V, the voltage difference of the LM317 does not exceed 20V, and its maximum power consumption is only 1.2 watts, without the heat sink.
If the LM317 cannot be found, a high-power triode can also be used to form a constant current source. The circuit is shown on the right. The LED1 can be red-emitting, and the forward voltage drop is about 1.8 to 1.9V. The B of the triode is preferably greater than 100 if B is too small. The resistance R can be appropriately reduced to ensure a constant current of 60 mA.
Remove the original headlight bulb. According to the size of the lamp, the input voltage of this power supply is 15V. The output is 5V, 4A. Because the input and output voltage difference is 10V. Power transistors consume up to 40W. Therefore, the heat dissipation design was carefully carried out. The radiator uses the aluminum radiator shown on the right. Its thermal resistance is 0.75 ° C / W. When the transistor and the insulating sheet are modified with high-brightness LEDs, the electric bicycle lamp block printing plate is modified, and the LED and related circuits are installed, fixed in the lamp, and the power cord is connected. The reflective bowl of the original lamp can retain the best retention. The lamp power does not exceed 3W. However, the luminous flux is more than 100 lumens, which is a true long-life energy-saving lamp.
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