Experience summary of three methods to protect LED circuits

1. Use fuses (tubes) to protect LED circuits

Since fuses are disposable, slow to react, poor in effect, and inconvenient to use, fuses are not suitable for LED lamps, because LED lamps are now mainly used in urban lighting projects. It requires the LED protection circuit to be very demanding: when the normal current is exceeded, the protection can be activated 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 power supply can be automatically restored after the entire lamp is normal, without affecting the operation of the LED. The circuit cannot be too complicated, the volume cannot be too large, and the cost must be low. Therefore, it is difficult to implement using fuses.

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

Transient voltage suppression diode is a high-performance 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 two poles to a low resistance at a very short speed of 10 to the negative 12th power of seconds, absorb up to several kilowatts of surge power, and clamp the voltage between the two poles at a predetermined voltage value, effectively protecting the precision components in the electronic circuit. Transient voltage suppression diodes have the advantages of fast response time, high transient power, low leakage current, good consistency of breakdown voltage deviation, easier to control clamping voltage, no damage limit, and small size.

However, in actual use, it is not easy to find TVS devices that meet the required voltage value. The damage of LED light beads is mainly caused by overheating inside the chip due to excessive current. TVS can only detect overvoltage but not overcurrent. It is difficult to choose the appropriate voltage protection point, so such devices cannot be produced and are difficult to use in practice.

3. Choose a resettable fuse

The resettable fuse is also called a polymer positive temperature thermistor (PTC), which is composed of polymers and conductive particles. After special processing, the conductive particles form a chain-like conductive path in the polymer. When the normal working current passes through (or the component is at normal ambient temperature), the PTC resettable fuse is in a low resistance state; when an abnormal overcurrent passes through the circuit (or the ambient temperature rises), the heat generated by the large current (or the ambient temperature rises) causes the polymer to expand rapidly, thus cutting off the conductive path formed by the conductive particles, and the PTC resettable fuse is in a high resistance state; when the overcurrent (overtemperature state) in the circuit disappears, the polymer cools and the volume returns to normal, in which the conductive particles re-constitute the conductive path, and the PTC resettable fuse returns to the initial low resistance state. In normal working conditions, the resettable fuse generates very little heat, but in abnormal working conditions, it generates a high heat and has a large resistance, which limits the current passing through it, thereby playing a protective role. In a specific circuit, you can choose:

①Branch 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 protection reliability.

② Overall protection. Add a PTC element in front of all light beads to protect the entire lamp. The advantage of this method is that it is simple and does not take up space. For civilian products, the results of this protection in actual use are satisfactory.