With the maturity of LED technology , LED lighting is used more and more widely, such as LED flashing of mobile phones, LED household lighting, LED headlights and taillights of automobiles. But how to effectively extend the service life of LEDs may not be particularly clear to many people. Our topic today is centered around the impact of over-electric stress (EOS) and how to effectively protect LEDs.
EOS is an abbreviation for Electrical Over Stress, which refers to all excessive electrical stress. EOS impact means that when the current or voltage applied by an electronic component exceeds the maximum design specifications of the component, the component may suffer from performance degradation or even direct damage.
LED devices are susceptible to damage from EOS, which can sometimes cause damage to the device directly, and sometimes failure can occur after a period of EOS. Unstable power output quality, various over-voltage and over-current noises, and inrush currents in hot-swap applications are all factors that can cause EOS failure. This EOS phenomenon is a short-term overload. In a short period of time (typically within one second) the LED is subjected to a spike or spike current that exceeds the design rating of the LED, thereby damaging the LED device.
After a brief introduction to the EOS problem of LEDs, let's take a look at the solution. The protection scheme for protecting the LED from EOS damage is basically to clamp the transient voltage generated by the EOS within the range that the device can withstand. The best protective device to theoretically eliminate this transient voltage is the capacitor, which absorbs the transient voltage very well. However, in practical applications, due to factors such as the high temperature life of the capacitor and the large volume, it is not a good solution.
Therefore, most engineers tend to use TVS voltage regulators for protection when solving this problem. However, when selecting TVS tubes, the maximum power that TVS tubes can withstand must be considered. The transient energy of EOS impact is uncertain. Sex, if you want to fully withstand the transient energy of all EOS impacts, you need to choose expensive high-power TVS tubes, which is often unwilling for product engineers. At that time, if a relatively small power TVS tube is selected due to cost problems, if there is a large energy EOS impact in actual applications, the protection function of the TVS tube may be weakened or even damaged. If the TVS tube is damaged, the subsequent EOS will directly impact the LED, causing damage to the LED. In addition, the accuracy of the clamping voltage of the TVS tube will directly affect the effect of the EOS impact on the subsequent LEDs, because the voltage increase across the LED will immediately appear as the current flowing through the LED increases.
Another solution is to use TE's PolyZen series of components, which can effectively reduce EOS intrusion and improve product reliability. PolyZen products from TE's Circuit Protection Division are stand-alone surface mount devices that integrate a precision Zener diode with selectable Zener voltage (Vz) and a PolySwitch Polymer Positive Temperature Coefficient (PPTC) device. Figure is shown in Figure 1. Designed for use in thin, compact environments where space is at a premium, the PolyZen family uses thermal-protected Zener diodes to help protect electronics from voltage transients, reverse bias, and faulty power supply failures. As shown in Figure 2, a typical application block diagram of Polyzen products, in the fault state, the precision Zener diode can quickly and effectively clamp the voltage and shunt the fault current, while the PolySwitch PPTC component can quickly turn off the excessive current, thus helping Protect Zener diodes and downstream electronic components.
Figure 1 Polyzen product schematic
Figure 2 Typical application of Polyzen products
The typical fault response of PolyZen products is shown in Figure 3. In the illustration, a PolyZen device with 5.6V Zener voltage is selected. Under 24V overvoltage condition (Vin), the system has 10A fault current (Iflt). The precision Zener diode in the PolyZen device can quickly clamp the output voltage (Vout) around 5.6V to protect the load circuit. At the same time, the PPTC in the device can quickly cut off the current and protect the Zener diode and the whole circuit for a long time. .
Figure 3 Typical fault response of Polyzen products
When PolyZende's products are used in LED EOS protection circuits, not only can the EOS transient voltage be clamped below the safe voltage quickly, but also the Zener diode inside the PolyZen device will cause PPTC when the EOS impact energy is large. Action to protect the Zener diode itself and subsequent circuits. Moreover, in some LED lighting systems that cannot be omitted due to malfunction, PPTC is superior to other overcurrent protection devices because PPTC can still illuminate the LED under the protection state without damaging the LED. Moreover, the Zener diode integrated in the PolyZen device has a very high clamping voltage accuracy and can accurately clamp the voltage within a safe range. Therefore, PolyZen devices have more advantages than the EOS protection scheme of TVS tubes.
PolyZen series components are integrated overvoltage and overcurrent protection devices with slim profile and powerful circuit protection to help protect sensitive electronic products from costly products due to overvoltage and overcurrent failures. Rework and warranty issues. The PolyZen family of products provides board designers with convenient overvoltage and overcurrent protection devices that eliminate the need to spend a lot of time integrating and testing inefficient discrete devices and more expensive IC solutions.
Nowadays, the PolyZen series has a rich combination of Zener diode and PPTC for practical application. Its small size, self-contained mounting and versatile protection have become an innovative solution for overcurrent and overvoltage protection applications with significant performance and price advantages, surpassing the use of fuses, Zener diodes and other passive components. Discrete solution.
Displacement sensor, also known as linear sensor, is a linear device belonging to metal induction. The function of the sensor is to convert various measured physical quantities into electricity. In the production process, the measurement of displacement is generally divided into measuring the physical size and mechanical displacement. According to the different forms of the measured variable, the displacement sensor can be divided into two types: analog and digital. The analog type can be divided into two types: physical property type and structural type. Commonly used displacement sensors are mostly analog structures, including potentiometer-type displacement sensors, inductive displacement sensors, self-aligning machines, capacitive displacement sensors, eddy current displacement sensors, Hall-type displacement sensors, etc. An important advantage of the digital displacement sensor is that it is convenient to send the signal directly into the computer system. This kind of sensor is developing rapidly, and its application is increasingly widespread.
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