Many power system designers will have faced the choice of two unattractive options when required to provide two or more outputs from a single ac-dc flyback converter circuit. The easiest option is to add additional windings to the secondary side of the transformer: but with a feedback circuit on only the main output, the other outputs are unregulated.
As an alternative, a dc-dc converter can be connected to the main output rail to provide a secondary regulated output. But now the circuit performs two-stage conversion rather than single-stage, resulting in substantially lower conversion efficiency. What’s more, the addition of the dc-dc converter adds to bill-of-materials cost and increases the circuit’s board footprint.
So this is why the options for creating a multi-output ac-dc converter have been fairly described as unattractive.
No longer however: with the introduction of the Power Integrations InnoMux™-2 ac-dc converter IC, power system designers can produce two or three outputs from a single-stage flyback conversion circuit, with regulation on all outputs of better than ±3%, and total conversion efficiency higher than 90%. It’s suitable for power supplies which are rated for loads up to 100 W.
The operation of the InnoMux-2 converter takes advantage of some clever innovations by Power Integrations which enable two or three independent feedback circuits to direct energy through the transformer separately to each power rail. As with the first-generation InnoMux converter IC, the secondary feedback signal is transferred via the unique FluxLink technology to the primary side, eliminating the need for an expensive optocoupler in the flyback converter.
Now, by using InnoMux-2, designers can implement accurately regulated multi-output ac-dc power supplies with a single converter IC, greatly reducing component count while increasing efficiency by as much as 10% compared to two-stage conversion architectures. Efficiency is aided by the ICs’ 750 V PowiGaN™ gallium-nitride transistors, zero-voltage switching (without an active clamp) and synchronous rectification.
Flexible output options include up to three independently regulated voltage outputs, or two voltage outputs and a constant current output, which may be used for instance for driving backlight LEDs for a display, or for high-speed battery charging. This capability makes the InnoMux-2 ideal for products including TVs, monitors, appliances, networking equipment, home and building automation, LED emergency lighting, and industrial power supplies.
Designers can start working with the InnoMux-2 now by evaluating reference designs created by Power Integrations – a 52 W power supply for a TV (DER-714), a 23 W power supply for a monitor (DER-715), or a 62 W industrial or appliance power supply with three voltage outputs (DER-716).
Or contact a Future Electronics Power Specialist Engineer for more information about how to integrate the InnoMux-2 converter in your multi-output flyback converter design.