Constant power limiter: a linear approximation

There sometimes arises the need to limit a power converter´s output power rather than just current. This paper shows a circuit that uses a linear approximation to obtain constant power limiting. It is inexpensive and easy to implement. For this circuit, two different cases of constant power limiting are presented and analyzed. The paper starts with discussion and examples as to why constant power limiting is needed. The equations of the two characteristics are derived. It is shown that the constant power limiter provides 20-30% more available power for a given input power limit than a constant current limiter. A circuit implementation is shown along with test data. The paper concludes with a summary of the design procedure