Summary of Flyback Switch Mode Power Supply Circuit
This flyback SMPS boosts about 20V to ~40V (adjustable via feedback resistors) using an off-the-shelf CoilCraft transformer and an LM3479 controller operated at ~500 kHz (R1 = 39k). The regulator VCC is driven from a separate +5V supply allowing VPIN to be a wide range. The design includes a non-dissipative snubber on the MOSFET drain to limit voltage spikes. Calculators allow feedback or transformer changes. Daycounter offers contract electronics design services.
Parts used in the Flyback SMPS:
- LM3479 controller IC
- CoilCraft off-the-shelf transformer
- MOSFET (drain with snubber)
- Non-dissipative snubber components
- Feedback resistors
- Components to generate +5V regulator supply
- R1 timing resistor (e.g., 39K)
This is a flyback SMPS that will boost voltage a voltage of around 20V to 40V, or more if you change the feedback resistors. It uses an off the shelf transformer from CoilCraft. The LM3479 is a nice controller because it’s frequency of operation can be set by changing R1. At 39K it runs at about 500KHz.
One innovation of the circuit is that the regulator is driven with +5V, a smaller voltage than VPIN. Separating the regulator voltage supply from the supply driving the coil allows VPIN to be nearly any value. Of course you need to have the 5V generated else where.
The circuit also has a non-dissipative snubber circuit on the drain of the MOSFET, to limit the voltage spikes when the transistor turns off.
See our calculators to make modifications to the feedback circuit, or use a different transformer.
Do you need help with an electronics design? Daycounter provides contract electronics design services. Contact us to give you a quote on your electronics design project.
For more detail: Flyback Switch Mode Power Supply Circuit
- What input and output voltages does this flyback SMPS support?
The circuit boosts around 20V to about 40V, and output can be increased by changing the feedback resistors. - Which transformer is used in the project?
An off-the-shelf transformer from CoilCraft is used. - What controller IC does the design use?
The design uses the LM3479 controller IC. - How is the switching frequency set?
The operating frequency is set by R1; at 39K it runs at about 500 kHz. - How is the regulator supply handled?
The regulator is driven from a separate +5V supply independent of VPIN, allowing VPIN to be nearly any value. - Does the circuit include protection for MOSFET voltage spikes?
Yes, it includes a non-dissipative snubber on the MOSFET drain to limit voltage spikes when the transistor turns off. - Can I change the feedback or transformer?
Yes, calculators are provided to modify the feedback circuit or to use a different transformer. - Is design help available for custom electronics?
Daycounter provides contract electronics design services and can be contacted for a quote.
