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.
Two PCB implementations are available. The first outputs unregulated 5V via a female USB socket and can be easily plugged in between the USB power adapter and the consumer. The second can be used as a split power supply with +5V and -5V.
|4.5 - 5.5V
|4.7 - 5.5V
|Output Voltage Ripple