What provides the centrifugal force for planets orbiting a star?

Perhaps you are thinking of the centrifugal force as something that prevents the planet from falling into the star? There is only centrifugal force in the orbiting frame of the planet. In this frame, the planet is not accelerating, so you a need centrifugal force to balance the centripetal force. It is perfectly valid to consider the star as your reference frame, but then there is no centrifugal force at all, and the planet is accelerating towards the star.