LED light bead damage caused by the main reasons are:
A sudden rise in ① supply voltage.
A short circuit of a component or printed line or other conductor in a ② line that forms the local short-circuit of the LED light Bead supply path, which increases the voltage of the place.
③ A LED light bead because of its own quality causes damage and thus form a short-circuit, its original voltage drop on the transfer to other LED light beads.
The temperature in the ④ luminaire is too high to make the characteristic of the LED light bead become bad.
⑤ lamp inside the water, water is conductive.
⑥ in the assembly time did not do anti-static work, so that the interior of the LED lamp bead has been damaged by static electricity. Although the application of normal voltage and current value, it is very easy to cause the damage of LED lamp bead.
So, how do I carry out the protection of LED light bead circuit?
1. The protection circuit uses the fuse (tube)
Because the fuse is one-time, and slow reaction, poor effect, use trouble, so the fuse is not suitable for the LED lamp finished products, because the LED lights are now mainly in the city's Guangcai project and lighting project. It requires LED lamp bead protection circuit to be very harsh: in excess of the normal use of current can immediately start protection, so that led power supply access is disconnected, so that led and power can be protected, the entire lamp after normal and can automatically restore power, does not affect led work. The circuit can not be too complex volume can not be too large, the cost is lower. So it is very difficult to implement it in a way that fuses.
2. Use transient voltage suppressor diodes (TVs for short)
The transient voltage suppressor diode is a diode-type high-performance protection device. When the two poles are subjected to a reverse transient high energy impact, they can be 10 minus 12 seconds in a very short time, so that their bipolar impedance immediately reduced to low resistance, absorbing up to thousands of watts of surge power, the voltage between the two poles in a predetermined voltage value, effectively protect the electronic circuit in the precision components. The transient voltage suppressor diode has the advantages of fast response time, large transient power, low leakage current, good consistency of breakdown voltage deviation, easy control of clamping voltage, no damage limit and small volume.
However, it is difficult to find a TVs device that satisfies the required voltage value in practical use. LED light bead damage is mainly due to electric current over the ambassador's internal overheating caused by the chip. TVS can only detect overvoltage and not detect current. To choose the right voltage protection point is difficult to grasp, this device can not be produced and can hardly be used in practice.
3. Select Self Recovery fuse
Self-recovery fuse is also known as polymer positive temperature thermistor PTC, which is composed of polymers and conductive particles. After special processing, conductive particles form a chain-like conductive pathway in the polymer. When the normal operating current is passed (or the component is in the normal ambient temperature), the PTC Self recovery fuse is in a low resistance state, and when an abnormal overcurrent is passed (or ambient temperature rises) in the circuit, the heat generated by the high current (or ambient temperature rise) causes the polymer to swell rapidly, cutting off the conductive pathway formed by the conductive particles, The PTC self recovery fuse is in a high impedance state; when the overcurrent (over-temperature state) of the circuit disappears, the polymer cools and the volume returns to normal, in which the conductive particles again form the conductive pathway, and the PTC Self recovery fuse assumes the initial low resistance state. In the normal working state self-recovery of the tube fever is very small, in the abnormal working state of its high temperature resistance is very large, but also limited through its current, thus playing a protective role. In the specific circuit, you can choose:
① shunt protection. The general LED lamp is divided into many threaded branches. We can add a PTC component to the front of each slip to protect it separately. The benefits of this approach are high accuracy and good protection.
② overall protection. Add a PTC component to the front of all light beads to protect the whole lamp. The benefits of this approach are simple, not taking up volume. For civilian products, the results of this protection in practical use are satisfactory.