Power supplies having a single isolation device for feedback and fault detection

A method of detecting fault conditions in an isolated power supply including a controller, a transformer having a primary winding and a secondary winding, at least one power switch coupled to the primary winding of the transformer, an output terminal coupled to the secondary winding, a feedback circuit coupled to the output terminal, a fault detection circuit coupled between the output terminal and the feedback circuit, and a single isolation device coupled between the feedback circuit and the controller, the method comprising:

• transmitting a feedback signal to the controller via the single isolation device, the feedback signal defined by comparing a sensed output voltage at the output terminal to a voltage reference;
• controlling switching operation of the power switch based on the feedback signal received at the controller;
• modifying the feedback signal transmitted to the controller via the single isolation device when the sensed output voltage exceeds a fault reference;
• and
• detecting a fault condition when a slew rate of the feedback signal exceeds a fault threshold slew rate value.

A method of initiating a soft start of an isolated power supply including a controller, a transformer having a primary winding and a secondary winding, at least one power switch coupled to the primary winding of the transformer, an input terminal, an output terminal coupled to the secondary winding, a feedback circuit coupled to the output terminal, and at least one isolation device coupled between the feedback circuit and the controller to provide a feedback signal to the controller, the method comprising:

• initializing an accumulator value when an input voltage is detected at the input terminal of the power supply;
• periodically comparing the accumulator value to an error value of the feedback signal;
• when the accumulator value is less than the error value of the feedback signal, controlling operation of the power switch based on the accumulator value and incrementing the accumulator value each operating cycle;
• and
• when the error value of the feedback signal is less than the accumulator value, controlling operation of the power switch based on the error value of the feedback signal.