The fuse (tube) is used in the protection circuit. Because the fuse is one-off, has a slow response speed, poor effect, and troublesome use, the fuse is not suitable for use in the finished LED lamp, because the LED lamp is mainly used in the city's glorious engineering and lighting. Chemical engineering. It requires the LED lamp bead protection circuit to be very harsh: the protection can be activated immediately when the normal use current is exceeded, so that the power supply path of the LED is disconnected, so that the LED and the power supply can be protected, and it can automatically restore after the entire lamp is normal. Power supply does not affect the operation of the LED. The circuit cannot be too complicated, not too big, and the cost is low. Therefore, it is very difficult to implement using a fuse.
Use Transient Voltage Suppression Diode (TVS for short).Transient Voltage Suppression Diode is a high-efficiency protection device in the form of a diode. When its two poles are subjected to a reverse transient high-energy impact, it can immediately reduce the high resistance between its poles to a low resistance at a speed of 10 minus 12 seconds in a very short time, and absorb up to several kilowatts of surge power.
The voltage between the two poles is clamped to a predetermined voltage value, which effectively protects the precision components in the electronic circuit. Transient voltage suppression diodes have the advantages of fast response time, large transient power, low leakage current, good uniformity of breakdown voltage deviation, easier control of the clamping voltage, no damage limit, and small size.
However, it is not easy to find TVS devices that meet the required voltage value in actual use. The damage of the LED light bead is mainly caused by the overheating of the chip. TVS can only detect overvoltage but not overcurrent. It is difficult to choose a suitable voltage protection point, and this kind of device cannot be produced and it is difficult to use in practice.
Choose self-recovery fuse self-recovery fuse, also known as polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After special processing, the conductive particles form a chain-like conductive path in the polymer. When the normal working 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 resettable fuse is in a high-resistance state; when the overcurrent (over-temperature state) in the circuit disappears, the polymer cools and the volume recovers Normally, the conductive particles re-constitute the conductive path, and the PTC resettable fuse is in the initial low resistance state.
In the normal working state, the self-recovery fuse has very little heat, and in the abnormal working state, its heat is very high and the resistance value is very large, which limits the current passing through it, thereby playing a protective role. In the specific circuit, you can choose:
①Shunt protection. Generally, LED lights are divided into many branches connected in series. We can add a PTC component in front of each branch for protection. The advantage of this method is high accuracy and good protection reliability.
②Overall protection. Add a PTC component in front of all the light beads to protect the entire lamp. The advantage of this method is that it is simple and does not take up volume. For civilian products, the results of this protection in actual use are still satisfactory.
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