Summary of experience: Summary of the experience of three protection methods for LED circuits

Although LED technology is the mainstream in today's market, there are still many problems in LED technology that have not been overcome, and the lifespan of LEDs, as well as energy conservation and price issues, have always been a topic of intense discussion. In this process, the LED circuit protection circuit is very important, so let's not talk about it first. Let's first discuss the experience summary of the three protection methods of the LED circuit:

1. Protect the LED circuit with a fuse (tube)

Since the fuse is disposable and the reaction speed is slow, the effect is poor, and the use is troublesome, the fuse is not suitable for use in the finished LED lamp, because the LED lamp is now mainly in the glory engineering and lighting engineering of the city. It requires the LED protection circuit to be very demanding: the protection can be started immediately when the current is exceeded, the LED power supply path is disconnected, the LED and the power supply can be protected, and the power can be automatically restored after the entire lamp is normal. Does not affect the LED work. The circuit should not be too complicated, the volume should not be too large, and the cost should be low. Therefore, it is very difficult to implement the fuse.

2. Use transient voltage suppression diode (TVS for short)

The transient voltage suppression diode is a high efficiency protection device in the form of a diode. When its two poles are subjected to reverse transient high energy impact, the high resistance between the two poles can be immediately reduced to low resistance at a very short time of 10 minus 12 power seconds, absorbing up to several kilowatts of surge power. The voltage clamp between the two poles is at a predetermined voltage value, which effectively protects the precision components in the electronic circuit. The transient voltage suppression diode has the advantages of fast response time, large transient power, low leakage current, good uniformity of breakdown voltage, easy control of clamp voltage, no damage limit, and small volume.
However, in actual use, it has been found that it is not easy to find a TVS device that satisfies the required voltage value. The damage of the LED light source is mainly caused by overheating inside the chip due to excessive current. TVS can only detect overvoltages and cannot detect overcurrents. It is difficult to master the proper voltage protection point, and the device cannot be produced and is difficult to use in practice.

3. Select self-recovery fuse

The self-recovering fuse is also called a polymer polymer positive temperature thermistor PTC, and is composed of a polymer and conductive particles. After special processing, the conductive particles form a chain-like conductive path in the polymer. When the normal operating current passes (or the component is at normal ambient temperature), the PTC resettable fuse is in a low-resistance state; when there is an abnormal overcurrent in the circuit (or the ambient temperature rises), the large current (or the ambient temperature rises) The generated heat causes the polymer to expand rapidly, which cuts off the conductive path formed by the conductive particles. The PTC self-recovery fuse is in a high-resistance state; when the overcurrent (over-temperature state) disappears in the circuit, the polymer cools and the volume recovers. Normal, in which the conductive particles reconstitute the conductive path, the PTC self-recovery fuse is in an initial low resistance state. In the normal working state, the self-recovery fuse has little heat, and in the abnormal working state, its heat is very high, which limits the current passing through it, thereby protecting. In the specific circuit, you can choose:

1 branch protection. The general LED light is divided into a number of serial branches. We can add a PTC component in front of each branch to protect them separately. The benefits of this approach are high accuracy and good reliability of protection.

2 overall protection. A PTC element is added in front of all the beads to protect the entire lamp. The benefit of this approach is simple and does not account for size. For civilian products, the result of this protection in actual use is still satisfactory.

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