Integrated GaN AC-DC Charger with VCC Self-bias and Peak Power Capability

Inhalt:
The demand for smaller, lighter, higher efficiency AC-DC USB power delivery (PD) chargers is always a challenge for power supply design engineers. Below 100W, quasi resonant (QR) flyback is still the dominating topology, with gallium nitride (GaN) technology, engineers can push the power density and efficiency higher. In order to provide bias power for the primary controller, it requires an auxiliary winding on the transformer and rectifying and filtering circuitry. To make things worse, the USB PD charger output voltage has a wide range. For example, USB PD Standard Power Range (SPR) covers output voltage ranges from 5V to 20V, and the latest USB PD Extended Power Range (EPR) allows the output voltage to go as high as 48V. Since the auxiliary voltage is proportional to the output voltage, this will increase the bias voltage range on primary controller, which require extra circuitry and degrade effi-ciency. In this article, we will introduce a self-biased flyback converter solution to address these design challenges, also this converter provides peak power capability by incorporating continuous conduction mode (CCM) operation which can significantly reduce transformer size.