Suppress electrical noise
X capacitors suppress noise between supply conductors. Y capacitors serve the relevant line-to-earth or insulation-crossing position. Identify the noise path before choosing the safety class and capacitance.
Applications
Components for the equipment you build.
From power filtering and surge protection to temperature sensing and DC-link support, explore circuit functions and design considerations by industry.
Component functions
Start with what the circuit needs.
One device may need several of these functions. Choose the component for its circuit position, then check its datasheet against the operating conditions.
Manage voltage transients
Varistors limit transient voltage. Select them by continuous operating voltage, clamping voltage and pulse energy, then coordinate them with the rest of the protection circuit.
Limit start-up current
A power NTC provides resistance when cold to limit charging current at start-up. Its resistance falls as it heats, so the design must also account for a restart before it has cooled.
Measure temperature
A sensing NTC converts temperature into a resistance signal for the control circuit. Measurement accuracy also depends on its resistance–temperature curve, mounting and thermal response.
01 / Application
Industrial
Motor switching, power conversion and long cable runs expose both controls and power stages to electrical noise and transients. Work through the AC input, DC bus and control supply separately to define filtering, surge protection and start-up current limiting.
Typical equipment
- Motor control systems
- Servo drives
- Charging stations
- Industrial automation
Where components fit
AC input filtering
MPK/X1 and MPX/X2 film capacitors serve across-line EMI filters. CY, CD and CE safety ceramic families address common-mode filter positions that match the required safety class.
DC-bus support
MC3D DC-Link film capacitors provide DC filtering and energy buffering in converters such as variable-frequency drives. Check the exact part against actual ripple current and temperature rise.
Surge and start-up protection
MOVs limit transient overvoltage, while power NTCs limit start-up current. The two components address different electrical stresses.
What to check in your design
- Check the supply, earthing scheme, installation position and the equipment’s required X/Y safety class.
- Define bus voltage, ripple spectrum, load cycle and measured hot-spot temperature.
- Validate protection against the actual surge waveform, source impedance and repetition count; test the shortest restart interval.
Explore related series
02 / Application
Automotive
Charging systems and vehicle controls place different demands on insulation, EMI, temperature cycling and transient protection. STE offers safety capacitor and varistor families for automotive electronics. Selection depends on the exact part, its circuit position and the vehicle’s operating conditions.
Typical equipment
- Vehicle driving controls
- Safety and comfort systems
- On-board chargers
- Charging stations and connectors
Where components fit
Charger input filtering
Automotive MPX/X2, MPK/X1 and MPY/Y2 film families address filter positions appropriate to their safety classes. Assess the mains input separately from the vehicle’s DC network.
Common-mode EMI control
Automotive CY and CE safety ceramic capacitors serve the relevant common-mode filter positions. For primary-to-secondary coupling in an isolated converter, establish the required class from the complete insulation diagram.
Transient voltage limiting
Automotive MOVs offer transient protection options for control and power circuits. Evaluate load dump, jump start and inductive pulses against the waveform and duration specified for the project.
What to check in your design
- AEC-Q200 qualified part numbers are available. Confirm the qualification report, covered part numbers and project approval documents.
- Select safety capacitors against the leakage-current budget, creepage, clearance and installation position.
- Check working voltage, transient waveforms, temperature cycling, damp heat and assembly processes, then validate in the equipment.
03 / Application
Home appliances
Motors, heaters and switch-mode supplies share limited board space in household appliances. The input stage needs noise suppression and controlled start-up current; temperature-control circuits need a usable sensing signal. Power and sensing thermistors serve these distinct tasks.
Typical equipment
- Air conditioners
- Refrigerators
- Washing machines
- Ovens
- Small appliances
Where components fit
Mains-input EMI suppression
MPX/X2 film capacitors and appropriately rated safety ceramic capacitors address across-line and common-mode noise respectively. Input MOVs limit transient overvoltage.
Controlled power-up
PP and PS power NTCs limit the inrush current that charges input storage capacitors. Account for self-heating, steady-state current and the appliance’s restart pattern.
Temperature sensing and control
MF51, MF52 and CWF sensing families provide resistance signals for temperature control. Match the sensor construction and mounting to the air, surface or medium being measured.
What to check in your design
- Distinguish EMI filtering from capacitive-dropper duty; similar packaging does not make the duties interchangeable.
- Review the temperature range, humidity, condensation exposure and terminal insulation.
- Validate sensor tolerance, response time, thermal contact and the control algorithm together.
04 / Application
Power supplies & AI servers
From compact chargers to AI server power supplies, power conversion brings EMI, insulation and thermal design together. Input filtering, isolation coupling, resonant conversion and inrush limiting each call for components suited to the waveform, temperature and safety requirements.
Typical equipment
- AI server power supplies
- Chargers and adapters
- PC power supplies
- Energy-storage power supplies
- Industrial power supplies
Where components fit
Input filtering and isolation coupling
X-class film capacitors address across-line noise. Y-class ceramic capacitors serve the relevant common-mode and primary-to-secondary coupling positions. SMD-X1Y1 provides a surface-mount option.
Resonant conversion and DC filtering
Polypropylene film families serve the applicable pulse and resonant circuits, while MC3D addresses DC-link filtering. Choose the family from the waveform, current and thermal conditions.
Start-up and surge control
Power NTCs limit storage-capacitor charging current; MOVs limit input voltage transients. Compact layouts still need sufficient thermal margin and coordinated protection.
What to check in your design
- Define circuit position, topology, waveform and frequency before reviewing ratings and losses.
- Check total Y-capacitor leakage, insulation distances, and the soldering and moisture-handling requirements of SMD parts.
- Verify temperature rise and protection during cold start, hot restart, full load and the intended ambient conditions.
05 / Application
Communications
Communication equipment needs continuous power with controlled supply noise and external transients. Start STE capacitor, thermistor and varistor selection at the power and isolation circuits. Protection on high-speed data lines needs a separate signal-integrity assessment.
Typical equipment
- ADSL modems
- Optical modems
- ISDN equipment
- Network equipment
- PBX systems
Where components fit
Adapter and isolated-supply filtering
Safety film and ceramic capacitors suppress EMI in the equipment’s power supply. Select Y-capacitor values together with the leakage-current budget and insulation requirements.
Power-input transient management
Varistors can protect suitable power-entry points against transients. Their suitability depends on the installation point, voltage range and pulse conditions.
Compact assembly and temperature sensing
SMD safety capacitors offer a packaging option for height-constrained power boards. Sensing NTCs provide signals for equipment temperature monitoring.
What to check in your design
- Separate AC input, DC supply and signal ports; do not transfer a power-protection design directly to a high-speed signal line.
- Assess common-mode current using the cabinet or terminal’s grounding and insulation scheme.
- Check temperature rise in continuous operation, ventilation and residual stored energy during servicing.
06 / Application
Renewable energy
Photovoltaic and storage converters face DC-bus ripple, power cycling and changing environmental conditions over long service periods. Design the DC link, AC-side filter and surge protection for their respective operating conditions, including damp heat and condensation where exposed.
Typical equipment
- Transformers
- Power converters
- Photovoltaic modules and systems
- Energy storage
Where components fit
DC-link filtering
MC3D film capacitors provide DC filtering and energy buffering in converters and solar inverters. Review ripple current, hot-spot temperature and the intended service life.
AC-side EMI suppression
X- and Y-class safety capacitors suppress noise at the appropriate AC filter positions. THB film families are an option to review for damp-heat exposure, using the test conditions of the relevant datasheet.
Coordinated surge protection
MOVs contribute to transient voltage limiting and must coordinate with upstream protection, fusing and thermal-failure handling. A single MOV does not replace a system-level lightning-protection design.
What to check in your design
- Provide maximum DC-bus voltage, ripple spectrum, load cycle and cooling conditions.
- Assess humidity, condensation, altitude and actual insulation distances; a single test does not establish equipment service life.
- Plan precharge, discharge and fault isolation, then verify surge coordination at system level.
07 / Application
Safety & monitoring
Monitoring and alarm equipment depends on its auxiliary power supply and control circuits. Address supply noise, switching transients and start-up current separately, with component selection supporting the equipment’s continuity and fault-response requirements.
Typical equipment
- Security monitoring systems
- Fire-alarm systems
- Smart-grid equipment
Where components fit
Auxiliary-supply filtering
MPX/X2 and the appropriate Y-class safety capacitors address across-line and common-mode noise in auxiliary supplies, helping manage noise that reaches control circuits.
Input transient protection
MOVs limit transient voltage at suitable input points. Cable length, the installation environment and upstream protection affect the stress reaching the component.
Supply start-up management
Power NTCs can limit charging inrush in suitable supplies. Systems with backup power or repeated switching need validation of restart temperature and recovery time.
What to check in your design
- Define the installation location, cable lengths and external supply conditions.
- Verify disconnection, recovery or alarm behavior after a fault; component approval does not replace system functional validation.
- Include backup-supply transfer, continuous-operation temperature rise and the maintenance cycle in testing.
08 / Application
LED lighting
Lighting supplies must control EMI while handling switching, input surges and heat inside the luminaire. Outdoor and horticultural installations can add moisture exposure and long operating periods, so component selection needs to reflect the actual fixture environment.
Typical equipment
- LED lighting
- Industrial lighting controls
- Landscape lighting
- Horticultural lighting
Where components fit
Driver-input filtering
X-class film and the appropriate Y-class ceramic capacitors serve the differential- and common-mode filters in LED drivers. SMD safety families offer an option for compact layouts.
Surge and inrush management
MOVs limit input voltage transients and power NTCs limit charging current at start-up. Frequent switching requires checking the current-limiting behavior of a still-hot NTC.
Capacitors for damp-heat exposure
THB film families provide an option for damp-heat exposure. Check the exact part against applied voltage, temperature, humidity and the equipment’s service-life requirements.
What to check in your design
- Establish the supply environment and surge-test conditions before coordinating protection components.
- Measure component temperature rise inside the enclosed luminaire and check the shortest switching interval.
- For capacitive-dropper circuits, define isolation boundaries, discharge paths and part suitability for that duty.
09 / Application
Medical equipment
Auxiliary supplies, controls and high-voltage power stages in medical equipment have different insulation and noise constraints. STE component selection starts with these electrical functions. Equipment safety and patient-related protection must be established in the complete device design.
Typical equipment
- Oxygen concentrators
- X-ray and CT systems
- MRI equipment
Where components fit
Auxiliary-supply EMI suppression
Safety ceramic and film capacitors serve suitable power-supply filter positions. For line-to-earth or isolation-crossing locations, work back from the equipment’s leakage-current and insulation requirements.
High-voltage power circuits
HV/SV ceramic families offer capacitors for high-voltage bypass, coupling and DC supplies. SV capacitors can serve suitable X-ray power-supply circuits. Selection requires the actual voltage waveform and electric-field environment.
Temperature sensing
Sensing NTCs provide resistance signals for supply and equipment temperature monitoring. For body-temperature measurement, review NTC families intended for electronic thermometers and validate the complete measurement system separately.
What to check in your design
- Define the component’s insulation domain, accessible parts and allowable leakage current.
- For high-voltage use, review continuous voltage, pulses, frequency, derating and mounting insulation.
- Validate electrical safety and EMC against the equipment standard; a component safety approval is not a medical-device approval.
Application support
Contact an application engineer Tell us about your circuit.
Share the circuit position, operating voltage and waveform, temperature, space constraints and approval requirements. STE engineers can help you review series options, datasheets and samples.
Use the exact part’s datasheet for final selection and validate it in your application.