1. Three Common Y Capacitor Connection Methods

Y capacitors are safety-certified capacitors mainly used for common-mode noise suppression while ensuring electrical isolation and user safety. Proper connection and selection are critical for EMC performance and safety compliance.

(1) AC Input Side: L→PE and N→PE (Most Common Configuration)

Connection:

• One Y capacitor connects from Line (L) to Protective Earth (PE)

• One Y capacitor connects from Neutral (N) to Protective Earth (PE)

Function:

This configuration provides a high-frequency noise path to earth, effectively reducing:

• Common-mode interference

• High-frequency EMI noise generated by switching power supplies

It is widely used in:

• Power adapters

• LED drivers

• Industrial power supplies

• Home appliances

  
  

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(2) Primary Ground (Hot Ground) → Secondary Ground (Cold Ground) in Isolated Power Supplies

Connection:

The Y capacitor is connected between:

Primary-side ground and secondary-side ground

This is a common configuration in isolated switching power supplies.

Recommended capacitor:

Y1 Safety Capacitor

Reason:

• Provides reinforced insulation

• Withstands higher isolation requirements

• Improves safety margin

Using paired Y capacitors can further improve EMI performance and system balance.

(3) Primary High Voltage Side (L/N) → Secondary Ground (Cold Ground)

Connection:

• L connects to secondary GND through one Y capacitor

• N connects to secondary GND through another Y capacitor

Function:

This helps reduce common-mode noise caused by parasitic capacitance coupling between:

• Primary winding

• Secondary winding

It is commonly applied in:

• High-frequency switching power supplies

• PD fast chargers

• Compact adapters

2. Schematic Symbol and Physical Appearance

Schematic Symbol:

Y capacitors are usually marked as:

• CY

• Y1

• Y2

They use the standard capacitor symbol with safety classification identification.

Physical Appearance:

Typical Hawtry Y capacitors feature:

• Blue disc ceramic structure

• Safety class marking: Y1/Y2

• Hawtry certification markings

• Safety approvals including:

• CQC

• VDE

• UL

• ENEC

3. Key Safety Design Requirements

(1) Safety Class Selection

Y1 capacitors are generally used for reinforced insulation applications and provide higher safety margins.

(2) Capacitance Selection

Typical Y capacitor capacitance range:

1nF ~ 4.7nF

The capacitance should not be unnecessarily increased because excessive capacitance may cause:

• Higher leakage current

• Safety compliance issues

• Increased standby power consumption

(3) Paired Connection Design

For AC input applications:

• L → PE uses one Y capacitor

• N → PE uses one Y capacitor

Benefits:

• Balanced leakage current

• Improved EMI filtering performance

• Better system stability

(4) PCB Layout Requirements

Recommended PCB layout:

• Keep connection traces short

• Use wider traces where possible

• Minimize loop area

• Place capacitors close to the input noise source

• Maintain required creepage and clearance distances

Proper PCB layout is essential for both:

• EMC performance

• Safety compliance

  
  

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4. Typical Y Capacitor Application in PD Fast Chargers (Without X2 Capacitor)

Modern compact PD fast chargers often remove the X2 capacitor due to limited PCB space and efficiency requirements.

A typical solution:

Input Side:

• CY1: L → PE

• CY2: N → PE

Transformer Side:

• CY3: Primary ground → Secondary ground (Y1 class)

Combined with:

• Frequency modulation technology

• Common-mode choke

• Additional differential-mode filtering

The design can achieve improved EMC performance even without an X2 capacitor.

Conclusion

Hawtry Y Safety Capacitors provide reliable solutions for:

• EMI suppression

• Isolation protection

• High-frequency noise filtering

Correct selection of:

• Safety class (Y1/Y2)

• Capacitance value

• Connection method

• PCB layout

is essential to achieve both EMC compliance and electrical safety.

With international certifications including UL, VDE, ENEC, and CQC, Hawtry Y capacitors are widely used in:

• Power adapters

• PD fast chargers

• LED drivers

• Industrial power supplies

• Smart appliances