Explore how Jaron’s integrated MOV, X2 capacitor, and NTC thermistor network improves surge protection, EMI filtering, and inrush current suppression for AC/DC power supplies.
In AC/DC converter design, the input stage must withstand surge voltages and inrush current peaks.
Surges from lightning or grid switching can exceed 2kV, while inrush current during power-up can be 5–10 times the nominal current.
Proper protection is essential to prevent component stress and extend power supply lifetime.
A well-coordinated combination of MOV, X2, and NTC provides a robust first line of defense for AC/DC input protection — suppressing surges, filtering differential noise, and limiting inrush current simultaneously.
① MOV Varistor: Clamps high-voltage surges within nanoseconds. The JARON 10D471K absorbs up to 120J and ensures residual voltage below 900V under 2kV surge.
② X2 Safety Capacitor: Suppresses differential-mode noise and stabilizes input voltage.
The X2-MKP series meets IEC 60384-14 standards and withstands repetitive surge stress.
③ NTC Thermistor: Limits inrush current during startup, then self-heats and reduces resistance for normal operation.
JARON MF72 series ensures inrush limitation while maintaining low steady-state losses.
AC Input ── MOV ──┬── Bridge ── DC Bus
│
X2
│
NTC ──► Load
This topology allows MOV to absorb surges, X2 to filter differential noise, and NTC to limit inrush current, ensuring stable startup and EMI compliance.
Test conditions:
Input voltage: AC 230V ±10%
Surge test: IEC 61000-4-5 ±2kV
Power-on surge current test: 25°C cold start
|
Test Project |
No protection |
Three-in-one solution |
Improvement range |
|
Surge residual pressure |
980V |
540V |
↓45% |
|
Peak current |
48A |
8.5A |
↓82% |
|
EMI interference |
Passing the limit +5dB |
Reduced to -12dB |
Improvement of 17dB |
With the integrated MOV+X2+NTC solution, residual surge voltage dropped by 45%, inrush current by 82%, and EMI noise improved by 17dB, ensuring compliance with IEC and UL standards.
|
Devices |
Suggested location |
Layout Description |
|
MOV |
AC input terminal |
Closely attached to the fuse, the shortest circuit absorbs surges. |
|
X2 capacitors |
Between L and N |
By placing it close to the rectifier bridge, a low-impedance filtering path is formed. |
|
NTC |
Connected in series with L line |
Avoid placing it near heat sources and ensure adequate space for heat dissipation. |
Layout recommendation: place MOVs close to the fuse, X2 near the rectifier bridge, and NTC in the live line with sufficient thermal spacing.
|
Standard Number |
Summary |
Corresponding devices |
|
IEC 61000-4-5 |
Surge immunity test |
MOV varistor |
|
IEC 60384-14 |
Safety capacitor requirements |
X2 capacitors |
|
UL 1434 |
Thermistor safety test |
NTC thermistor |
All components comply with IEC, UL, and environmental directives, ensuring compatibility with international markets.
This protection solution can be widely applied to:
Switching power supplies (SMPS);
Industrial control power supplies;
Charging stations and inverters;
White goods (washing machines, induction cookers, power tools);
LED drivers and lighting systems.
JARON's integrated MOV + X2 + NTC input protection solution, through system matching and layout optimization, achieves:
45% reduction in surge residual voltage;
Over 80% suppression of power-on surges;
17dB improvement in EMI suppression performance;
Meets IEC 61000-4-5 and CISPR 22 standards.
MOV+X2+NTC | AC/DC Protection Design | Surge Suppression | Power Input Filter
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