Optically Isolated Amps Make Efficient Isolated Power Supplies


IXYS announced new low voltage optically isolated error amplifiers with an input voltage range of 1.6V to 10V, each having an integrated programmable precision shunt reference. The devices have a combination of features making them optimal for use in isolated AC-to-DC power supplies and DC-to-DC converters.

A unique feature of the device is that the error amplifier and shunt reference can operate down to 1.6V, the industry’s lowest level, enabling higher efficiency, isolated low voltage power supply designs. The LIA135 and LIA136 offer a 1.299V internal precision voltage reference with a very low 0.5 per cent tolerance for improved power supply accuracy.

Optically isolated error amplifiers are important integrated devices for secondary to primary side feedback in AC-to-DC power supplies and DC-to-DC converters. These optical devices save board space and replace bulky transformer secondary feedback circuits. The LIA135 and LIA136 combination of features are optimal for use in isolated power supply design as the bias current for the shunt regulators does not pass through the LED. This eliminates bias-related optical current, providing the user with the industry’s largest dynamic range (1000:1).


The optocoupler portions of the LIA135 and LIA136 comprise of infrared LEDs that are optically coupled to NPN phototransistors. The optocouplers’ current transfer ratios are between 500 per cent and 2000 per cent. The LIA136 offers enhanced performance characteristics and an extended operational temperature range to 110 deg C.

Available in DIP and surface mount (SMT) packages, the devices are UL and CSA Certified.

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