Isolated dc/dc converter, feedback circuit thereof, power supply device, power supply adaptor, and electronic device using the same

A feedback circuit disposed at a secondary side of an isolated DC/DC converter, wherein the DC/DC converter includes:

• a transformer having a primary winding and a secondary winding;
• a switching transistor connected to the primary winding of the transformer;
• a rectification element connected to the secondary winding of the transformer;
• a photo coupler;
• a primary side controller which is connected to an output side of the photo coupler and is configured to switch the switching transistor in response to a feedback signal from the photo coupler;
• and
• the feedback circuit configured to drive the photo coupler,
• the feedback circuit comprising:
• an input terminal which receives a voltage detection signal corresponding to an output voltage of the DC/DC converter;
• an output terminal connected to an input side of the photo coupler;
• a ground terminal;
• a shunt regulator configured to amplify an error between the voltage detection signal and its target voltage and draw a first current corresponding to the error from the input side of the photo coupler via the output terminal;
• and
• a protection circuit configured to draw a second current from the input side of the photo coupler via the output terminal when an abnormality of the secondary side of the DC/DC converter is detected, and
• wherein the feedback circuit is packaged in a single module.