How to protect the LED lamp bead circuit
1. Fuse (tube) is used in the protection circuit
Since the fuse is one-time, slow in response, poor in effect, and troublesome to use, the fuse is not suitable for use in finished LED lights, because LED lights are now mainly used in urban glory projects and lighting projects. It requires the LED lamp bead protection circuit to be very strict: when the current exceeds the normal use current, the protection can be started immediately, so that the power supply path of the LED is disconnected, so that both the LED and the power supply can be protected, and the whole lamp can be automatically restored after normal use. Power supply, 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 lower. Therefore, it is very difficult to use the fuse method.
2. Use transient voltage suppression diodes (TVS for short)
TVS diodes are high performance protection devices in the form of diodes. When its two poles are impacted by reverse transient high energy, it can immediately reduce the high resistance between its two poles to low resistance at a speed of 10 to the minus 12 second power in a very short time, absorbing 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. TVS diodes have the advantages of fast response time, large transient power, low leakage current, good consistency of breakdown voltage deviation, easier control of 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 beads is mainly caused by the overheating of the inside of the chip due to excessive current. TVS can only detect overvoltage but not overcurrent. To choose the appropriate voltage protection point is difficult to grasp, this kind of device cannot be produced and it is difficult to use in practice.
3. Select the resettable fuse
The resettable fuse, also known as the polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After special processing, the conductive particles form chain-like conductive paths 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 high 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, and the PTC self-recovery fuse is in a high resistance state; when the overcurrent (overtemperature state) in the circuit disappears, the polymer cools and the volume recovers Normally, the conductive particles re-form the conductive path, and the PTC resettable fuse is in the initial low resistance state. In the normal working state, the heat generation of the self-recovery fuse is very small. In the abnormal working state, its heat generation is very high, and its resistance value is very large, which limits the current passing through it, thus playing a protective role. In a specific circuit, you can choose:
a Shunt protection. Generally, LED lights are divided into many series branches. We can add a PTC component in front of each branch for protection. The advantage of this method is high accuracy and good reliability of protection.
b Overall protection. Add a PTC component in front of all light beads to protect the whole 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 satisfactory.
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