Stability analysis of a constant off-time peak-current mode LED driver

A constant off-time peak-current-mode LED driver circuit provides not only accurate LED current control, but also relatively high power conversion efficiency, and is simple in circuitry. However, there is a feedback instability problem associated with the control scheme in practical circuits. A stability analysis concludes that the sample-and-hold device used in the control circuit causes this instability problem. A “slope compensation” scheme is proposed to alleviate this problem. Circuit simulation and experimental results validated the proposed scheme.