According to the analysis of the specific application of the LED display module, in the LED display module, the worst temperature characteristic is the electrolytic capacitor. At present, ordinary electrolytic capacitors have a nominal value of minus 40 degrees. At temperatures of minus 40 degrees or lower, the characteristics of electrolytic capacitors can become poor or even completely fail. This is because at a temperature of minus 40 degrees or lower, the viscosity of the electrolytic solution of the electrolytic capacitor becomes large and even a crystallization phenomenon occurs. Electric iron
Under normal circumstances, the voltage on the LED module is 5V. Under the action of the OE signal switch, the power supply voltage will fluctuate, and the highest value is about 5.37V. For LED modules without electrolytic capacitors, under the control of the OE signal, high glitches appear on the power supply, with the highest voltage reaching 10.8V or higher. This voltage has greatly exceeded the normal voltage allowed by the IC power supply. The current working voltage of the logic part driven by the constant current source is 5V. It is required that no glitches greater than 7V appear on the power supply. High-voltage glitches can cause breakdown of MOS devices in the internal logic portion of the IC, resulting in IC failure.
For the problem of capacitor failure, the following measures can solve the problem.
1. For particularly cold areas, the module uses or installs -55 degrees low temperature electrolytic capacitors, so when the temperature is minus 40-45 degrees (check meteorological data, in some parts of northeast China in recent years, the lowest temperature is -40 to -45 degrees), the capacitor can still work normally. In addition, tantalum capacitors have very good low temperature characteristics. For display screens in cold climates, 1-2 tantalum capacitors can be added to the LED module to ensure good filtering characteristics at low temperatures. Electric iron
2. Install temperature control device and air conditioner or heating device in the display. The temperature control system ensures that the display cannot be turned on under ultra-low temperature conditions. In cold winter weather, before the display is turned on, use an air-conditioning system or heating device to heat the interior of the display for a period of time (1-2 hours), so that the temperature in the display is above minus 25 degrees, and then turn on Display power.
3. Add a Transient Voltage Suppressor (TVS for short) to the unit module PCB or power terminal. TVS is a high-performance protection device in the form of a diode. When the module fails in the ultra-low temperature capacitor, the TVS diode can absorb high-voltage glitches to avoid damage to the board components. The clamping voltage of the TVS diode can be selected around 7.0V.
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