As LED lighting continues to replace traditional lighting in residential, commercial, and industrial environments, the reliability of the LED power supply has become a key factor in overall product lifetime. While efficiency and cost often receive the most attention, many early failures are actually caused by a less visible issue: inrush current at power‑on.
Inside every LED driver, the moment the AC input is applied is the most stressful electrical event. Large surge currents generated during capacitor charging place heavy stress on rectifiers, electrolytic capacitors, and switching devices. Over time, these repeated surges significantly shorten component life and increase the risk of failure. The MF72 series power NTC thermistors from SHENZHEN HENQYI are designed to address this problem directly by limiting inrush current and protecting the front‑end of LED power supplies.
The Hidden Stress During Startup.
An LED power supply typically includes a rectifier bridge and large bulk capacitors at the input stage. When power is first applied, these capacitors are fully discharged and behave almost like a short circuit. As a result, a very large charging current flows within the first few milliseconds.
In practical systems, this inrush current often reaches 10 to 30 times the normal operating current. For a 100 W LED driver, a rated input current of about 4 A can easily produce a startup surge of 40‑100 A. These repeated surges lead to several long‑term problems. Rectifier bridges and capacitors experience accelerated electrical and thermal aging. Local overheating increases solder joint fatigue and insulation degradation. In large lighting installations, simultaneous startup can also disturb the power grid and cause voltage dips.
Without proper suppression, inrush current becomes one of the main contributors to early LED power supply failure.
How MF72 NTC Thermistors Limit Inrush Current?
The MF72 series uses a simple and reliable operating principle. At room temperature, the thermistor has a relatively high resistance. When power is applied, this resistance limits the initial charging current of the bulk capacitor. As current flows, the thermistor heats up and its resistance drops rapidly. After a short warm‑up period, the residual resistance typically falls below 0.5 Ω, so the thermistor introduces almost no loss during normal operation. This self‑adapting behavior allows the MF72 to provide strong current limiting at startup and low power dissipation during steady‑state operation, without the need for control circuits or relays.
Benefits in LED Power Supply Applications.
Adding an MF72 NTC thermistor at the AC input directly improves several aspects of LED driver reliability.
Extended component lifetime
By limiting the peak surge current, electrical stress on rectifiers and capacitors is significantly reduced. Field experience shows that early failure rates can drop sharply when proper inrush limiting is applied.
Improved safety margin
Lower surge current reduces instantaneous heating, helping prevent solder joint fatigue, insulation damage, and thermal hotspots—especially important in enclosed luminaires and ceiling‑mounted fixtures.
Minimal impact on efficiency
Once warmed up, the MF72 introduces very little additional loss and does not affect steady‑state efficiency or output performance.
Selection Considerations.
Correct selection is essential for effective protection. Engineers typically consider:
- Rated input current of the power supply.
- Bulk capacitor size and charging profile.
- Required cold resistance to limit peak current.
- Maximum steady‑state current capability.
- Disk diameter for surge energy handling.
The MF72 series offers a wide resistance range from 1 Ω to100 Ω and standard disk sizes from 5 mm to 20 mm, covering LED drivers from small residential units to high‑power commercial supplies.
Proven Quality and Support.
SHENZHEN HENQYI has long focused on power NTC thermistors for surge suppression. The MF72 series has passed UL, CQC, and TÜV certifications and is designed for stable operation from ‑40°C to 200°C. Beyond standard products, SHENZHEN HENQYI provides technical selection support to help LED driver manufacturers integrate inrush protection with minimal design changes and predictable long‑term performance.
Inrush current is one of the main hidden causes of LED power supply failure. A properly selected NTC thermistor offers a simple, low‑cost, and highly effective solution. With stable characteristics, compact design, and proven field reliability, the MF72 series helps LED power supplies achieve longer lifetime, higher safety margins, and more consistent operation in modern lighting systems.