Magnetically Isolated Digital Coupling Circuit Solves Gate Drive and Communications Dilemmas

by Andrew Ferencz, Ferencz Consulting, Southborough, Mass., How2Power Today, Mar 30 2012

Focus:
Power engineers often need digital isolation for a variety of reasons including controlling switches on the other side of an isolation barrier, driving high-side switches, passing communication signals, and using digital methods to encode analog signals such as a PWM signal. Packaged solutions exist include optical, magnetic and even capacitive isolators, but each solution has some tradeoffs. This article describes a simple digital isolation circuit consisting of a tiny toroidal pulse transformer, two transistors, and a few passives. It achieves safety isolation by using triple-insulated wire and appropriate spacing between the terminals. Though comparable to a gate-drive transformer, the transformer developed for this circuit is simpler, smaller, and lower in cost. Operation of this circuit and keys to implementing it are explained. This circuit’s advantages versus other isolator types are discussed.

What you’ll learn:

• How to build a small, low-cost digital isolation circuit for passing gate-drive and communications signals like RS-232 and I2C

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