Dual Output Isolated Flyback Design: 5V @ 0.2A, 12V @ 2.1A w/2 addl out 3.3V @ 0.5A, 5V @ 0.5A


Design files


This design utilizes the LM5020 Current Mode PWM Controller configured in a dual output Flyback converter.  This isolated design operates at 300 kHz and uses a custom transformer to convert the input voltage, via flyback action, to an output voltage level of 12V at 2.1A, as well as produce an isolated 5V@0.2A rail.  The relative low output power of this design, and the fact that Vcc is not required to power additional IC’s, allows the primary bias winding to be connected to Vin.  The LM5020 has a minimum input voltage of 13V so a start-up bias circuit was added to apply an external voltage to Vcc until the input voltage reached the proper threshold level.

With total potential output power less than 30W, a custom EFD20 core was chosen for this design.  Because of the input voltage range, a CCM to DCM transition tradeoff was made to minimize losses associated with DCM operation.   Radiated EMI requirements necessitated the use of snubbers and other filtering elements to minimize high energy signals from interfering with adjacent circuitry.

 The 12V rail also fed a 5V@0.5A rail, as well as an optional 3.3V@0.5A rail.  The secondary side feedback components are selected appropriately to ensure the voltage regulation remains solid and that proper gain and phase margins are maintained for stable operation and quick transient response.

InputsOutput #1Output #2Output #3Output #4
  • Internal Start-up Bias Regulator
  • Error Amplifier
  • Precision Voltage Reference
  • Programmable Softstart
  • A Peak Gate Driver
  • Maximum Duty Cycle Limiting (80% for LM5020-1 or 50% for LM5020-2)
  • Programmable Line Under Voltage Lockout (UVLO) with Adjustable Hysteresis
  • Cycle-by-Cycle Over-Current Protection
  • Slope Compensation (LM5020-1)
  • Programmable Oscillator Frequency with Synchronization Capability
  • Current Sense Leading Edge Blanking
  • Thermal Shutdown Protection
??image.gallery.download_en_US?? View video with transcript Video

A fully assembled board has been developed for testing and performance validation only, and is not available for sale.

Design files & products


Includes TI products in the design and potential alternatives.

AC/DC & DC/DC controllers (external FET)

LM502013-100V Wide Vin, Current Mode PWM Boost, Flyback, Sepic Controller

Data sheet: PDF
AC/DC & DC/DC converters (integrated FET)

LM27363V to 18V Input, 0.75A Step-Down Converter with Light Load Efficiency

Data sheet: PDF | HTML

Technical documentation

= Top documentation selected by TI
No results found. Please clear your search and try again.
View all 1
Type Title Date
* User guide Dual Output Isolated Flyback Design:User Guide Jan. 27, 2012

Support & training

TI E2E™ forums with technical support from TI engineers

View all forum topics

Content is provided "as is" by TI and community contributors and does not constitute TI specifications. See terms of use.

If you have questions about quality, packaging or ordering TI products, see TI support. ​​​​​​​​