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Flyback controller needs no optoisolator

Posted: 13 Jan 2006 ?? ?Print Version ?Bookmark and Share

Keywords:LT3825? DC/DC controller? Linear Technology? flyback? optoisolator?

Linear Technology Corp. introduced a new synchronous flyback DC/DC controller with precision regulation and high efficiency for 10W to 60W or up to 12A output isolated power supplies. The LT3825 is a current mode controller that regulates the output voltage based on sensing secondary voltage via a transformer winding. This allows for tight output regulation without the use of an optoisolator, explained the company.

Synchronous rectification increases conversion efficiency and improve output cross regulation in multiple output power supplies. For example, the LT3825 is used to convert an input supply of 36V to 72V to an isolated output of 3.3V at 12A with up to 90 percent efficiency and 0.009 percent regulation. Applications include isolated power supplies in telecom, medical, industrial and instrumentation systems.

The LT3825 has a feedback amplifier that eliminates the need for an optoisolator by sampling a transformer winding voltage during flyback period and using this voltage to precisely regulate the output voltage. This alleviates the designer from spending time trimming the power supply. The elimination of the optoisolater is said to improve the output transient response. A programmable primary gate delay function eliminates multiple discrete components from the circuit and optimizes MOSFET switching time and transformer selection. To further simplify the design, the LT3825 allows its switching frequency to be adjusted from 50kHz to 250kHz with a capacitor. The IC can also be synchronized to an external oscillator.

The LT3825 is rated for operation from -40C to 125C and is offered in a thermally enhanced 16-lead TSSOP. For 1,000-piece orders, price is set at $3.10 each.

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Related Datasheets
Part Number Description Category
? LT3825 Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range ICs, Interface



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