Under the background of the current global energy shortage worries, saving energy is an important issue we will face in the future. In the field of lighting, the application of LED light-emitting products is attracting the attention of the world. It must be the trend of future development, and the 21st century will enter the era of new lighting sources represented by LED.
On the primary side of a power supply circuit, a typical solution to transient inrush currents is a metal oxide variable resistor (MOV). These devices clamp the input inrush current to a level that allows the power components to remain unaffected and operate normally. The main criteria for selecting MOVs include operating voltage, energy handling performance and peak pulse current performance.
The operating voltage of an MOV is the voltage level at which the MOV can function properly without breaking down (becoming conductive). This voltage is usually the first parameter to decide, and it's simple. To specify the operating voltage, the line voltage of the equipment is increased by 20% to allow the voltage of the power system to increase. The purpose of this is to ensure that the MOV reacts to transient events in the system and not to temporary conditions. As shown in Figure 1.
Integrated Devices Help Reduce Component Count
Under normal operating conditions, the AC line voltage applied to the MOV will not exceed the maximum AC root mean square voltage (VAC RMS) rating of the device, and it is assumed that as long as the transient energy does not exceed the maximum rating of the MOV, short-term transient The state event can then be clamped to a suitable voltage level. However, persistent abnormal overvoltage/limited current conditions such as loss of neutral can cause the MOV to enter a thermal runaway state.
MOVs are usually protected from overheating by placing a thermal cut-off (TCO) device in series with the MOV. Typical line voltage transient protection schemes can also incorporate an overcurrent protection element (such as a fuse) to protect the system from damage caused by overcurrent overloads exceeding a predetermined level.
Overcurrent Conditions and Thermal Runaway
Tyco Electronics' AC 2Pro. device integrates a polymer positive temperature coefficient (PPTC) element and an MOV element into a thermal protection device to provide resettable functionality during overcurrent or overvoltage conditions. This approach to integrating devices helps manufacturers meet industry requirements such as IEC61000-4-5 and IEC60950.
Unprotected standard MOV components are typically limited to 275VAC RMS for a common input voltage range. Under neutral loss conditions, they can have negative results from overheating, even if a fuse or mains resistor has been used upstream in the circuit.
The PPTC element in the AC 2Pro device helps prevent thermal runaway, keeping the varistor surface temperature below 150°C and preventing the device from reaching unsafe temperatures caused by overvoltage transients.
working principle
While the AC line voltage applied to an MOV will typically not exceed the device's maximum continuous operating voltage rating, it is possible for overvoltage transients to occur that exceed these limits. The 2Pro device integrates PPTC technology with MOVs to improve overcurrent and thermal protection when the MOVs are exposed to continuous overvoltage conditions for a long time.
In the event of an overvoltage transient, such as the loss of neutral event shown in Figure 2, the PPTC element in the 2Pro device heats up, trips, and enters a high impedance state, helping to reduce the risk of MOV device failure.
Benwei Lighting is an LED Tube, LED flood light, LED Panel Light, LED High Bay, LED manufacturer with 12 years of experience. If you want to purchase a high-quality LED flood light or have a more in-depth understanding of the application of LED flood lights, please contact send us inquiry， our web: https://www.benweilight.com/.
