For designers who need cost-effective yet high-efficiency power supply designs, flyback transformers are the most popular choice and can typically supply up to 120 Watts. Providing circuit isolation, the potential for multiple outputs, and the possibility for both positive and negative output voltages in switched-mode power supplies.
They are constructed by winding the primary around a ferrite rod and the secondary around the primary. This minimizes leakage inductance of the primary. This is then housed in a ferrite frame that closes the magnetic field.
How the Flyback Transformer Works
Flyback transformers are based on buck-boost topology. Here, the transformer provides isolation and, where needed, voltage transformation by the turns ratio. The Coilcraft Flyback Transformers use MOSFET.
A typical flyback circuit. Image Credit: Coilcraft.
Using the appropriate duty cycle, the Coilcraft Flyback Transformers open and close the MOSFET switch to achieve the required output voltage. Typically, this duty cycle does not exceed 0.5. Several combinations of duty cycles and turn ratios can be used to achieve the necessary output voltage.
Types of Coilcraft Flyback Transformers
Coilcraft has a range of off-the-shelf transformers that are made to be easily deployable. While available in lots of different power levels, they operate well in applications with power levels other than what the transformer is labeled; nominal frequency and circuit reference are only given as a guide.
Some of the flyback transformers that Coilcraft has to offer include:
Wide input voltage (4.5 – 1,000 Vdc)
Telecom input (36 – 72 Vdc and 36 – 57 Vdc)
Telecom extended input (10 – 72 Vdc)
2 – 36 Vdc Input
400 Vdc Input
AC line input
Capacitor charging transformers
All in all, there are well over 100 different models available that cater to different applications or are designed to work with different manufacturers’ products.
The JA4635-AL and KA4823-CL flyback transformers, for example, are designed for Microchip Technology’s Grid-Connected Solar Microinverter, with the latter flyback transformer, the KA4823-CL, purpose-built for 220 Vac applications with higher SRF and efficiency.
Other iterations of the flyback transformer include the FA2706-BL for ST’s PM8800 PoE Device Controller, the A0009-AL for TI’s LM5000 High Voltage Switch Mode Regulator, and 2 – 36 Vdc input.
Coilcraft, Inc., founded in 1945, is a world leader in the design and manufacture of magnetic components for a wide range of applications, including signal generation, telecommunications, and consumer electronics.
While the company primarily manufactures off-the-shelf products, they also provide a bespoke design service to meet customers' specific requirements.