Optocoupler driver IC for isolated power supplies improves transient response

20 October 2004 Power Electronics / Power Management

Linear Technology has introduced an optocoupler driver for isolated power supplies that need tight regulation, fast transient response and overshoot protection.

The LT4430, housed in a small

6-pin SOT-23 package, includes a precision low voltage reference (0,6 V, ±0,75%), a high-bandwidth (9 MHz) error amplifier, an inverting optocoupler driver and an overshoot control circuit.

The device simplifies loop frequency compensation as the error amplifier's high bandwidth minimises phase shift and ground-referenced optocoupler drive eliminates the secondary feedback path present with existing optocoupler drivers, says Linear. The LT4430 has a wide input supply range from 3 V to 20 V and the short-circuit protected optocoupler driver can supply up to 10 mA. The device has applications in 48 V input isolated DC/DC converters, industrial control systems, automotive and heavy equipment power supplies.

The optocoupler driver IC has a unique overshoot control circuit that provides independent control of startup and short-circuit recovery characteristics without compromising loop bandwidth and resultant transient response. Existing optocoupler drivers often require sub-optimum small-signal frequency compensation to control both large-signal dynamic and output overshoot at startup, says the company, which degrades the power supply's overall performance. The LT4430's reference stability and error amplifier's 80 dB open loop DC gain help ensure tight DC regulation over all input line and output load conditions.

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