Power Electronics

ICs Make Isolated Converters As Simple as Bucks

Linear Technology’s new family of dc-dc converters offer the performance and simplicity of a buck regulator for the design of isolated power supplies. These primary- and secondary-side ICs introduce multiphase operation for current sharing and paralleling of two circuits to achieve higher output current. Other advantages include self-starting capability (which eliminates the need for an extra transformer winding), no-optocoupler design, fast transient response and synchronous rectification for efficiency up to 94%.

The chipset supports standard output voltages such as 5 V, 12 V, 28 V and 52 V as well as low voltages down to 0.6 V. Furthermore, the chips allow the use of inexpensive and off-the-shelf magnetics and discrete components. An example of an application is an isolated power supply with 36-V to 72-V VIN range and 3.3-V VOUT at 30 A or 1.2-V VOUT at 100 A.

The primary-side controllers, the LTC3705 and LTC3725 are forward drivers. The LTC3705 is a dual switch driver and the LTC3725 is the simpler version with single-switch operation. The secondary-side ICs, the LTC3706 and LTC3726, are current mode synchronous rectifiers with a self-starting architecture.

The LTC3706 is suitable for multiphase operation whereas the LTC3726 is ideal for single-phase operation. The 1000-piece price per unit for the LTC3705, LTC3706, LTC3725 and LTC3726 are $2.63, $3.88, $2.56 and $3.19, respectively.

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