Building an isolated power supply sounds like something for advanced makers. Yet, the flyback converter is one of the most elegant circuits in power electronics: compact, efficient, and capable of delivering a safely isolated output voltage with relatively few components.
What is a flyback converter?
A flyback converter is a type of switching power supply where energy is temporarily stored in a transformer. A switch turns the primary side on and off. During the on-phase, the transformer stores energy. During the off-phase, it releases that energy to the secondary side — and that is the exact moment when galvanic isolation occurs.
What is a flyback converter used for?
- Phone adapters and USB chargers
- Power supplies for industrial electronics
- Auxiliary power supplies in larger systems
- DIY project power supplies where isolation is required
The TNY180: a complete system in a single IC
The TNY180 from Power Integrations integrates the switch, the controlled oscillator, and multiple protection functions into a single component.
| Feature | Value |
|---|---|
| Integrated MOSFET | Yes — no external power transistor required |
| Overcurrent and short-circuit protection | Built-in, automatic recovery |
| Thermal protection | Built-in |
| Output power | Up to approx. 5–8 W |
Safety when working with mains voltage
A flyback converter operates directly on rectified mains voltage on the primary side — approximately 325 V DC in Europe. This safety point is non-negotiable.
- Use certified components. Use X2 capacitors on the mains voltage side.
- Respect safety clearances on the PCB. A minimum creepage distance applies between the primary and secondary traces.
- Never measure the primary side with an ordinary multimeter while the circuit is live.
- Discharge capacitors before measuring or soldering.
Getting started: what do you need at a minimum?
To design a basic flyback converter with the TNY180, you need the following core components:
- An input rectifier (diode bridge and buffer capacitor) to convert 230 V AC to DC
- The TNY180 IC to drive the primary side
- A flyback transformer tailored to your desired output parameters
- A fast output diode (Schottky) for efficient rectification on the secondary side
- An output filter (low-ESR capacitor) to smooth out the ripples
- A feedback loop via an optocoupler and voltage reference (such as a TL431) to regulate the output voltage safely across the isolation barrier
Power Integrations provides a free design software tool (PI Expert) that calculates the exact values for the transformer and surrounding components for the TNY series. This eliminates guesswork and ensures you build an efficient and safe circuit.
