A power supply, comprising a controller comprising a first switch coupled between a first node and a second node, a first resistor coupled between the second node and a third node, a second resistor coupled between the first node and a fourth node, a capacitor coupled between the fourth node and a fifth node, an amplifier coupled at a first input to the fourth node, at a second input to the third node, and at an output to the fifth node, and a comparator coupled at a first input to the fifth node and at a second input to the third node.