Power Electronics

Flyback Transformers for LT3799, LT3799-1 and LT3798 Designs

Wurth Electronics Midcom Inc. introduces a series of transformers specifically designed to work with Linear Technology's LT3799, LT3799-1 and LT3798 Isolated No Opto-Coupler Flyback Controllers with Active PFC designs.

The transformers from Wurth Electronics Midcom developed for Linear Technology's LT3799, LT3799-1 and LT3798 utilize different modes of flyback operation, catering to power levels ranging from 4W to 100W+. The transformers are designed using a special winding technique to produce a very low leakage inductance, less than one percent, which maximize the power factor and efficiency of the Linear Technology drivers. The designs comply with various UL, EN and IEC safety standards and satisfy reinforced insulation requirements. High dielectric (Hipot) withstanding requirement of up to 4.5KVac is achieved by these flyback designs.

The LT3799 is an isolated flyback controller with power factor correction specifically designed for driving LEDs. The controller operates using critical conduction mode allowing the use of a small transformer. Using a novel current sensing scheme, the controller is able to deliver a well regulated current to the secondary side without using an opto-coupler. A strong gate driver is included to drive an external high voltage MOSFET. Utilizing an onboard multiplier, the LT3799 typically achieves power factors of 0.97. The FAULT pin provides notification of open and short LED conditions. The LT3799-1 offers improved line regulation over the LT3799, but is not designed for use with a TRIAC dimmer.

The LT3798 is a constant-voltage/constant-current isolated flyback controller that combines active power factor correction (PFC) with no opto-coupler required for output voltage feedback into a single-stage converter. A LT3798 based design can achieve a power factor of greater than 0.97 by actively modulating the input current, allowing compliance with most Harmonic Current Emission requirements. It is well suited for a wide variety of off-line applications. The input range can be scaled up or down, depending mainly on the choice of external components. Efficiencies higher than 86% can be achieved with output power levels up to 100W. In addition, the LT3798 can easily be designed into high DC input applications.

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