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USB Power Isolator

For some applications, a galvanically isolated power supply is required to avoid ground loops or short circuits, or simply for mutual protection. The USB Power Isolator offers the possibility of a simple isolation (2.5kV) of the 5V rail of a USB power adapter with an unregulated output and a maximum continuous current of 1A. The USB Power Isolator isolates the power rail only, for full isolation including data lines take a look at the ADuM3160 USB Isolator.

Working Principle
Using its powerful Timer/Counter D (TCD), the ATtiny212/412 controls a center-tapped transformer utilizing the push-pull topology by providing complementary output signals with intermediate dead times (break-before-make time) to drive the two ground-referenced N-channel MOSFETs connected to the transformer’s outer taps and alternately turn them on and off. The implemented switching frequency of 400kHz is specially tailored to the Würth Elektronik 750315371 transformer, but other frequencies and features like spread spectrum clocking can be implemented in software if required.

There are actually special ICs to drive push-pull transformers, in the case of the WE750315371 this is for example the SN6505B. However, the small ATtinys are significantly cheaper and can easily imitate the tasks of these ICs.”

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