White LED is a voltage sensitive device with a current limit of 20mA in actual operation. However, due to various reasons, the current often increases during use. If no protective measures are taken, the increased current will be damaged after a specified time and amplitude.

The main reasons for LED damage are:

(1) Sudden increase in power supply voltage;

(2) A partial LED power circuit short circuit is formed due to a short circuit of a certain component, printed line or other wire in the circuit, causing the voltage in that area to rise;

(3) One LED forms a short circuit due to its own quality damage, and its original voltage drop is transferred to other LEDs;

(4) Excessive temperature inside the lamp leads to deterioration of LED characteristics;

(5) Fill the lamp with water and conduct electricity;

(6) Failure to properly prevent static electricity during assembly resulted in damage to the interior of the LED due to static electricity.

Although normal voltage and current values are used, it is also easy to cause damage to the LED.

Can suitable circuit protection components be selected for LED circuit protection? Here are some suggestions:

1. Use fuses (tubes) in the protection circuit

Because fuses are disposable, slow to react, ineffective, and difficult to use, fuses are not suitable for LED light products, as LED lights are mainly used in urban gloss and lighting projects. It requires a very strict protection circuit: exceeding the current can immediately start the normal use of protection, causing the power supply path to disconnect, resulting in the protection of the power supply. When the entire lamp is normal, the power supply can be automatically restored without affecting the operation. The circuit should not be too complex or too large, and the cost should be low. So it's difficult to use fuses.

2. Use transient voltage suppression diodes (TVS)

Transient voltage suppression diode is a high-performance diode protection device. When its two poles are subjected to reverse transient impact, it can immediately reduce the high resistance between the two poles to low resistance at a speed of 10-12 seconds, absorb surge power of up to several kilowatts, and clamp the voltage between the two poles within a predetermined voltage value, protecting precision components in electronic circuits. Transient voltage suppression diodes have the advantages of fast response time, high transient power, small leakage current, good consistency of breakdown voltage deviation, convenient breakdown voltage control, no damage, and small size.

However, in practical use, it is not easy to find TVS devices that meet the required voltage values. The damage to LED lights is mainly caused by overheating inside the current ambassador chip. TVS can only detect overvoltage and cannot detect overcurrent. It is difficult to choose a suitable voltage protection point, so the device cannot be manufactured and is difficult to use in practice.

3. Choose a self recovering fuse

Self recovery fuse, also known as polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After processing, conductive particles form conductive pathway chains in the polymer. When subjected to normal operating current (or when the component is at normal ambient temperature), the PTC self recovery fuse has low resistance.

When abnormal overcurrent (or environmental temperature rise) occurs in the circuit, the heat generated by high current (or environmental temperature rise) causes the polymer to rapidly expand, while cutting 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) in the circuit disappears, the polymer cools down, the volume returns to normal, the conductive particles reconstruct the conductive path, and the PTC self recovery fuse returns to the initial low resistance state.

Article source: Jiangmen PCB Customizationhttp://www.yonghongpcb.com/