4-W discontinuous conduction mode primary-side regulated flyback reference design


Design files


This tiny 4-W flyback converter with additional three isolated-output windings generates four total outputs. By windings ratio 1:1 in between primary and auxiliary winding, the conventional RCD snubber can be replaced by an AC flying capacitor providing better efficiency and lower EMI This requires the lowest leakage inductance. The input automotive range is 7-V to 42-V surge. Three outputs are post regulated by an 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.

  • Three isolated outputs at 12 V, 5 V and 3.3 V and one single non-isolated output at 5 V
  • Both 5-V and 3.3-V outputs are post regulated for the lowest possible noise
  • Differential-input filter to prevent from reflected ripple
  • Temperature rise less than +35 K at full load
  • A table for all 16 load combinations with light load and full load is provided
Output voltage options PMP30921.1 PMP30921.2 PMP30921.3 PMP30921.4
Vin (Min) (V) 7 7 7 7
Vin (Max) (V) 27 27 27 27
Vout (Nom) (V) 5 12 5 3.3
Iout (Max) (A) .05 .17 .05 .3
Output Power (W) .25 2.04 .25 .99
Isolated/Non-Isolated Non-Isolated Isolated Isolated Isolated
Input Type DC DC DC DC
Topology Flyback- DCM Flyback- DCM Flyback- DCM Flyback- DCM
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A fully assembled board has been developed for testing and performance validation only, and is not available for sale.

Design files & products

Design files

Download ready-to-use system files to speed your design process.

TIDT278.PDF (2762 K)

Test results for the reference design, including efficiency graphs, test prerequisites and more


Detailed schematic diagram for design layout and components


Complete listing of design components, reference designators, and manufacturers/part numbers


Detailed overview of design layout for component placement


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TIDCG68.ZIP (123 K)

Design file that contains information on physical board layer of design PCB


PCB layer plot file used for generating PCB design layout


Includes TI products in the design and potential alternatives.

Boost controllers (external switch)

LM51551-Q12.2-MHz wide VIN, 1.5-A MOSFET driver, non-synchronous boost controller, hiccup mode protection

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TPS745-Q1Automotive 500-mA, low-IQ, high-PSRR, low-dropout (LDO) voltage regulator with power good

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TPS763-Q1Automotive 150-mA, 10-V, low-dropout voltage regulator with enable

Data sheet: PDF | HTML

Technical documentation

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Type Title Date
Test report 4-W Discontinuous Conduction Mode Primary Side Regulated Flyback Ref. Design PDF | HTML Apr. 28, 2022

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