he white LED is a voltage-sensitive device. In actual operation, the current is 20 mA. However, the current may increase due to various reasons in use. If no protection is taken, this increased current will increase the current. The LED will be damaged after a certain amount of time and time.
The main causes of LED damage are:
1 Sudden increase in supply voltage.
2 Short-circuit of a component or printed wire or other wire in the circuit creates a local short circuit in the LED power supply path, which increases the voltage at this location.
3 An LED is short-circuited because of its own quality, and its original voltage drop is passed on to other LEDs.
4 The temperature inside the lamp is too high, which deteriorates the characteristics of the LED.
5 Into the water inside the lamp, the water is conductive.
6 Anti-static work was not done during assembly, causing the interior of the LED to be damaged by static electricity. Although the normal voltage and current values are applied, it is extremely easy to cause LED damage.
So how do I protect the LED circuit?
1. Use fuses (tubes) in the protection circuit
Because the fuse is one-time, and the reaction speed is slow, the effect is poor, and the use is troublesome, so the fuse is not suitable for use in the LED lamp product, because the LED lamp is mainly in the glorious engineering and lighting project in the city. It requires the LED protection circuit to be very demanding: it can immediately start protection when the normal use current is exceeded, so that the LED power supply path is disconnected, so that both the LED and the power supply can be protected, and after the entire lamp is normal, the power can be automatically restored. Does not affect the LED work. The circuit can not be too complex, the volume can not be too big, the cost is even lower. Therefore, the use of fuses is difficult to achieve.
2. Use Transient Voltage Suppression Diode (TVS)
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 shocks, they can reduce the high resistance between their two poles to low resistance and absorb up to several kilowatts of surge power at a speed of 10 seconds and minus 12 seconds. 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 consistency of breakdown voltage deviation, easier control of clamping voltage, no damage limit, and small size.
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 beads is mainly caused by the overheating of the current inside the ambassador chip. TVS can only detect overvoltage and cannot detect overcurrent. To select the appropriate voltage protection point is difficult to grasp, this device can not be produced it is difficult to use in practice.
3. Select the resettable fuse
The self-healing fuse is also called a polymer positive temperature thermistor PTC and is composed of a polymer and conductive particles. After special processing, the conductive particles constitute 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-impedance state; when there is an abnormal overcurrent in the circuit (or the ambient temperature rises), the large current (or ambient temperature rises) The heat generated rapidly expands the polymer, which cuts off the conductive path formed by the conductive particles. The PTC resettable fuse is in a high-impedance state. When the over-current (over-temperature state) in the circuit disappears, the polymer cools down and the volume recovers. Normal, in which the conductive particles reconstitute the conductive path, the PTC resettable fuse is again in an initial low-resistance state. In the normal working state, the self-recovery fuse has very little heat. In an abnormal working state, its heat is very high and the resistance value is very large, thus limiting the current passing through it, thereby playing a protective role. In the specific circuit, you can choose:
1 shunt protection. The general LED lamp is divided into many serial branches. We can add a PTC component in front of each branch to protect them. The benefits of this approach are high accuracy and good protection.
2 overall protection. A PTC module is attached to the front of all the beads to protect the entire lamp. The benefits of this approach are simple and do not occupy volume. For civilian products, the results of such protection in actual use are still satisfactory.
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