Shown on this slide is a secondary side control block diagram. In order to power a controller on the secondary side, it is necessary to create a bias supply that is isolated from one ground to another ground. The LM25037 is shown as the controller on the secondary side. This is just one example of a secondary side controller, and one of the TI digital controllers would be another example. Basically, this controller is regulating on the secondary side ground, and it needs bias power. Ideally, that bias power would come from a small and inexpensive device. Historically, it has been a bit of a challenge to create that supply.