TIDT278 April   2022

 

  1.   Description
  2.   Features
  3.   Applications
  4. 1Test Prerequisites
    1. 1.1 Voltage and Current Requirements
    2. 1.2 Considerations
    3. 1.3 Dimensions
  5. 2Testing and Results
    1. 2.1 Efficiency Graphs
    2. 2.2 Loss
    3. 2.3 Load Regulation
      1. 2.3.1 5-V Output Voltage
      2. 2.3.2 3.3-V Output Voltage
      3. 2.3.3 12-V Output Voltage
    4. 2.4 Line Regulation
      1. 2.4.1 5-V Outputs
      2. 2.4.2 3.3-V Output Voltage
      3. 2.4.3 12-V Output Voltage
      4. 2.4.4 Efficiency and Loss in Dependance of Input Voltage
    5. 2.5 Cross Regulation Light Load and Full Load
      1. 2.5.1 Bias Current 1 mA
      2. 2.5.2 Bias Current 5 mA
    6. 2.6 Thermal Images
    7. 2.7 Bode Plots
  6. 3Waveforms
    1. 3.1 Switching
      1. 3.1.1 Q1 Drain to GND
      2. 3.1.2 Q1 Gate to GND
      3. 3.1.3 D1 Anode to 12 VOUT
    2. 3.2 Input Voltage Ripple
    3. 3.3 Output Voltage Ripple
      1. 3.3.1 5-V Output Voltage (Primary)
      2. 3.3.2 5-V Output Voltage (Secondary)
      3. 3.3.3 3.3-V Output Voltage
      4. 3.3.4 12-V Output Voltage

Description

This tiny 4-W flyback converter with additional three isolated output windings generates four outputs in total. With a windings ratio of 1:1 in between the primary and auxiliary winding, the conventional RCD snubber could be replaced by an AC flying capacitor providing better efficiency and lower EMI, but this requires the lowest leakage inductance.

The input is in the automotive range of 7 V up to 42-V surge, three outputs are post-regulated by LDO to improve line and load regulation and power supply ripple rejection (PSRR).

A differential input filter has been added to attenuate conducted emissions, and a Schottky rectifier acts as reverse-polarity protection.

As for all multi-output primary-side regulated approaches using general purpose controllers no load at the auxiliary windings is a limitation for cross regulation.