Tips for protecting LED circuits
Time:2024-02-08
Views:222
We all know that LED belongs to voltage sensitive devices. In actual operation, it is limited to a current of 20mA, but often due to various reasons during use, the current increases. If protective measures are not taken at this time, the LED will be damaged if the increased current exceeds a certain time and amplitude. Next, let‘s first understand the basic concepts of LED circuits, the factors causing LED damage, and the protection methods for LED circuits.
1、 Basic concepts of LED circuits
LED (Light Emitting Diode) is a semiconductor that can convert electrical energy into visible light. It changes the principle of the three primary colors of incandescent lamps, tungsten filament and energy-saving lamps, and uses electric field to emit light. According to analysis, the characteristics of LED are very obvious, including long lifespan, high light efficiency, no radiation, and low power consumption. The spectrum of LED is almost entirely concentrated in the visible light frequency band, and its luminous efficiency can reach 80-90%. Comparing LED with ordinary incandescent lamps, spiral energy-saving lamps, and T5 three primary color fluorescent lamps, the results show that the luminous efficiency of ordinary incandescent lamps is 12lm/W, with a lifespan of less than 2000 hours, the luminous efficiency of spiral energy-saving lamps is 60lm/W, with a lifespan of less than 8000 hours, the luminous efficiency of T5 fluorescent lamps is 96lm/W, with a lifespan of about 10000 hours, and the luminous LED with a diameter of 5 millimeters is 20-28lm/W, The lifespan can exceed 100000 hours. Some people also predict that the upper limit of LED lifespan in the future will be infinite.
High power refers to a high luminous efficiency, generally referring to 0.5W, 1W, 3W, 5W or higher. Light intensity and lumen are higher than low power, but they also result in significant heat dissipation. Nowadays, high power applications require a single unit with a larger heat sink. Low power is generally around 0.06W. Plugins and piranhas, etc. Nowadays, LED flashlights are generally used with low power, and the light does not dissipate depending on the angle of LED emission. There are two types: large angle and small angle, small angle does not dissipate, and large angle only disperses.
However, some LEDs may experience an increase in current due to various reasons during use. If protective measures are not taken at this time, the LED will be damaged if the increased current exceeds a certain time and amplitude. So let‘s take a closer look at the specific causes of LED damage.
2、 The main reasons for LED damage are:
2.1. Sudden increase in voltage.
2.2. A local short circuit in the LED power supply circuit caused by a short circuit in a component, printed line, or other wire, causing an increase in voltage in that area.
2.3. LED is damaged due to its own quality, resulting in a short circuit, and its original voltage drop is transferred to other LEDs.
2.4. If the temperature inside is too high, it will deteriorate the characteristics of the LED.
2.5. Water enters the interior, which is conductive.
2.6. Failure to properly prevent static electricity during installation has caused damage to the interior of the LED. Although normal voltage and current values are applied, it is highly likely to cause damage to the LED.
Understood the factors that cause LED damage mentioned above. So, how should I protect the LED circuit?
3、 The methods for protecting LED circuits are as follows:
3.1. Using fuses (tubes) in LED circuits
Due to the fact that fuses are disposable, slow in response, poor in effectiveness, and inconvenient to use, they are not suitable for use in finished LED lights, as LED lights are mainly used in urban lighting and lighting projects. It requires the LED protection circuit to be very strict: it can immediately start the protection when the normal operating current is exceeded, so that the power supply path of the LED is disconnected, and both the LED and the power supply can be protected. After the entire lamp is normal, it can automatically restore power without affecting the operation of the LED. The circuit should not be too complex, the volume should not be too large, and the cost should be lower. So it is difficult to implement using fuses.
3.2. Transient Voltage Suppression Diode (TVS)
Transient voltage suppression diode is an efficient protective device in the form of a diode. When its two poles are subjected to reverse transient high-energy shocks, it can immediately reduce the high resistance between its two poles to low resistance at a speed of 10 to the negative 12th power second for a very short time, absorbing up to several kilowatts of surge power, clamping the voltage between the two poles at a predetermined voltage value, effectively protecting precision components in electronic circuits. Transient voltage suppression diodes have advantages such as fast response time, high transient power, low leakage current, good consistency of breakdown voltage deviation, easy control of clamp voltage, no damage limit, and small size.
However, in practical use, it has been found that it is not easy to find TVS devices that meet the required voltage values. The damage of LED beads is mainly caused by excessive current causing internal overheating of the chip. TVS can only detect overvoltage and cannot detect overcurrent. It is difficult to choose the appropriate voltage protection point, and this type of device cannot be produced and is difficult to use in practice.
3.3. Select self recovery fuse
Self recovery fuse, also known as polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After special processing, conductive particles form a chain like conductive pathway in the polymer. When the normal working current passes through (or the component is at normal ambient temperature), the PTC self recovery fuse is in a low resistance state; When there is abnormal overcurrent passing through the circuit (or when the ambient temperature rises), the heat generated by the high current (or when the ambient temperature rises) causes the polymer to rapidly expand, cutting off the conductive path composed of 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 and the volume returns to normal. The conductive particles then form a conductive path again, and the PTC self recovery fuse returns to its initial low resistance state. In normal working conditions, the heating of the self recovery fuse is very small, but in abnormal working conditions, its heating is very high and the resistance value is very high, which limits the current passing through it and thus plays a protective role.
In specific circuits, you can choose from:
① Shunt protection. Generally, LED lights are divided into many series connected branches. We can add a PTC component in front of each branch for protection. The benefits of this method are high precision and good reliability of protection.
② Overall protection. Add a PTC component in front of all the light beads to protect the entire 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 practical use are still satisfactory.
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