The best solution to protect LED circuits

White light LEDs are voltage-sensitive devices. In actual operation, the upper limit of the current is 20mA. However, the current often increases due to various reasons during use. If no protective measures are taken, the LED will be damaged after the increased current exceeds a certain time and amplitude.

The main reasons for LED damage are:

1.Sudden increase of supply voltage.

2. A short circuit of a component, printed line or other wire in the circuit forms a local short circuit in the LED power supply path, which increases the voltage in this place.

3. If an LED is damaged due to its own quality reasons and forms a short circuit, its original voltage drop will be transferred to other LEDs .

4. The temperature inside the lamp is too high, causing the characteristics of the LED to deteriorate.

5. Water has entered the lamp, and water is conductive.

6. The LED was not properly protected from static electricity during assembly, causing the inside of the LED to be damaged by static electricity.

Normal voltage and current values ​​can easily cause damage to the LED.

So, how can I protect the LED circuit ? Here are some tips:

1. Use fuses (tubes) in the protection circuit

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 immediately activated, 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 suppressor diodes (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 two poles to a low resistance in a very short time of 10-12 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 diode has 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 lamps is mainly caused by overheating of 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 down and the volume returns to normal, in which the conductive particles re-constitute the conductive path, and the PTC resettable fuse is in the initial low resistance state.

In normal working state, the heat generated by the self-resetting fuse is very small. In abnormal working state, its heat is very high and its resistance is very large, which limits the current passing through it, thus playing a protective role. In the specific circuit, you can choose:

1. Branch 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.