Luminous Diode Resistance Cold Knowledge

Do I have to add resistance? What will happen without resistance without the voltage? Yes, the light -emitting diode must be added with resistance to use. The light emitting diode cannot be directly in a certain voltage. The flow resistance must be limited. Otherwise. Why can't the light emitting diode directly connect to the voltage glow diodes that cannot be directly connected to both ends of the voltage is mainly caused by two reasons: 1) the positive voltage drop is inconsistent; 2) the current changes are large. The reason below. The positive pressure drop of the light -emitting diode is different. When working normally, the light emitting diode will have a positive pressure drop VF. The VF is not a certain value, but a scope. Taking the red light emitting diode as an example, the range of VF is (1.7-2.2) V, and each time The consistency of the characteristics of the light diode is not good, and it is slightly different, so it is difficult to find a voltage that is suitable for all diode. 2. The correct way to light emitting diode. The light emitting diode generally has two driving methods. The first method is to connect with the current -limited resistance string in the voltage; the second method is to use the constant current source to drive. Constant voltage driver. In order to prevent the current from being too large, the light -emitting diode is burned out, and the light -emitting diode and a current -limiting resistance need to be stream. The value of the resistance is concluded by the following formulas: R = (V-Vf)/i. Among them, VF is the forward voltage of the emitting diode, and i is the current that I want to flow. Taking the red light emitting diode as an example, the range of the front voltage drop VF is (1.7-2.2) V and the working current is 2-25mA. If you bring it into the formula. This driving method is generally used in the case where the number of LEDs is small. If it is used as a power indicator and alarm indicator light circuit, if the number of driving diode is large, you can consider using the constant current source driver. Hengliu source is widely used in the home lighting industry. Since all LEDs are connected in series, as long as one LED is damaged, all LEDs are not bright. 3. Comparison of two driving methods, the current limiting resistance method, is mostly used in the case where the number of LED lamp beads is relatively small. The advantage is that the circuit is simple, and the disadvantage is that the positive pressure reduction of the light emitting diode is inconsistent, so the brightness of multiple use is different. The driving method of Hengliu source can ensure that the brightness of each emitting diode is basically the same, but the damage of individual LED lamp beads will affect the operation of all LED lamp beads. Summarize the light emitting diodes cannot be used directly in the power supply.