The main reason for the failure or necrosis of white LED lights.
White LED lamp bead belongs to voltage sensitive device, in the practical work is 20 ma current limit, but often due to increase in the use of a variety of reasons caused by the current, if do not take protective measures, the increase of current exceeds a certain amount of time and amplitude after LED lamp bead will be damaged.
The main reasons for the damage of LED lamp beads include:
A sudden increase in the supply voltage.
A short circuit of a component or printed line or other conductor in a line that leads to a local short circuit of the LED lamp, which increases the voltage in the area.
The original voltage drop is passed on to other LED lamp beads.
The temperature in the lamp is too high, which makes the characteristic of LED lamp bead bad.
The interior of the lamp is in water, and the water is conductive.
At the time of assembly, there is no anti-static work, so that the inside of the LED lamp bead has been damaged by static electricity.
Although it is normal voltage and current value, it is very easy to damage the LED lamp bead.
So, how can I protect the LED lamp bead circuit?
1. Fuse (tube) in protective circuit
Due to the fuse is a one-off, and slow response, poor effect, use of trouble, so the fuse is not suitable for LED lighting products, because leds are now mainly in the city of light engineering and lighting engineering.
It requires very demanding: LED lamp bead protection circuit in can start immediately beyond normal use current protection, let the LED power supply channel is disconnected, the LED and the power can be protected, and automatically restore power after the whole lamp is normal, does not affect the LED work.
The circuit should not be too complicated and not too large, and the cost will be low.
So it's very difficult to implement a fuse.
2. Use of transient voltage suppression diode (TVS)
Transient voltage suppression diode is a kind of diode - type efficient protective device.
When it's poles reverse transient high-energy shock, at 10 to the minus 12 power seconds the speed of a very short time, make yourself between the poles of reduced to low resistance, high resistance to immediately absorb up to several kilowatts of surge power, voltage clamping between the poles in a predetermined voltage value, effectively protect the precision components in the electronic circuit.
Transient voltage suppression diode has a fast response time, the transient power, low leakage current, breakdown voltage deviation good consistency, clamping voltage control more easily and without damage to the limit, small volume, etc.
However, it is not easy to find TVS devices that meet the required voltage value in actual use.
The damage to LED beads is mainly caused by the overheating of the current ambassador chip.
TVS can only detect overvoltage and cannot detect current.
It is difficult to master the appropriate voltage protection point, which is difficult to produce and is difficult to use in practice.
3. Select self-recovery fuse.
The self-restoring fuse is also known as the high polymer positive temperature thermistor PTC, which is composed of polymer and conductive particles.
After special processing, the conductive particles form a chain conductive path in the polymer.
When the normal working current is passed (or the component is in normal ambient temperature), PTC self-restoring fuse is in a low resistance state;
When the circuit has the abnormal through the current through the environment (or temperature), large current the heat generated by the environment (or temperature) make polymer rapid expansion, is cutting off the conductive particles form conductive pathways, PTC self recovery fuse in high impedance state;
When the circuit through the current (overtemperature condition) disappears, polymer cooling, return to normal size, the conductive particles constitute a conductive path, again PTC self recovery fuse and the initial state of low resistance.
In normal working condition, the heating of the safe tube is very small. In abnormal working condition, it has a high temperature resistance, which limits the current through it and thus ACTS as a protective effect.
In the specific circuit, you can choose:
The protection of the road.
The general LED light is divided into a number of chain branches.
We can add a PTC component in front of each branch for protection.
The benefits of this approach are high precision and good reliability.
Add a PTC component to the front of all the beads to protect the entire lamp.
The advantage of this approach is simplicity, not volume.
For civilian products, the results of this protection are satisfactory in practice.