High-Frequency Switching Power Supply Principles: Differences Between High-Frequency Transformers and Pulse Transformers

I. Fundamental Differences

1. High-frequency transformer: Power transformer operating above medium frequency (10kHz).

2. Pulse transformer: Wide-bandwidth transformer.

II. Application Differences

1. High-frequency transformer:

• Main application: High-frequency switching power transformers in switching power supplies

• Secondary application: High-frequency inverter power transformers in inverter power supplies and welding machines

2. Pulse transformer:

• Radar and conversion technology

• Matching load resistance to transmission line characteristic impedance

• Step-up/down of pulse voltage

• Pulse polarity reversal

• Isolation between primary and secondary circuits

• Phase relationship acquisition via multiple secondary windings

III. Operational Principles

1. High-frequency transformer:

• Must minimize leakage inductance and distributed capacitance during design

• Reason: Transmits high-frequency pulse square waves where parasitics cause:
  • Surge currents
  • Voltage spikes
  • Top oscillation (ringing)
  • Increased losses

2. Pulse transformer:

• Converts sine-wave input to narrow-pulse output using core's magnetic saturation

High-Frequency Transformer
Power transformer operating >10kHz. Primarily used as:

• Switching power transformers in switching power supplies

• Inverter power transformers in inverter supplies/welding machines
  Frequency classifications:
  10kHz-50kHz, 50kHz-100kHz, 100kHz-500kHz, 500kHz-1MHz, >10MHz

Pulse Transformer
Wide-bandwidth transformer. For communication applications:

• Nonlinear distortion is critical performance indicator

• Must operate at core's initial permeability

• Requires larger size even for low-power units (e.g. input transformers)
  Key design focuses:

• Frequency response optimization

• Loss reduction