Isolated SEPIC Converter with a novel Voltage Clamp Circuit

In this paper, a novel isolated SEPIC topology is proposed to address the problems associated with conventional isolated SEPIC. A conventional isolated SEPIC uses RCD clamp or an active switch based capacitive clamp circuits to avert the damage of semiconductor devices from inherent voltage spikes induced by the transformer non-idealities. The former method turns impractical when the leakage inductance is significant, also the losses in the resistor in turn lower the efficiency of the system. Whereas the latter method demands additional control circuitry and increases the complexity of control, while occupying more board space and involves additional cost. Proposed topology uses a lossless passive CD (Capacitor-Diode) clamp circuit to minimize excess voltage stress across the switch, while retaining the fundamental features of conventional isolated SEPIC in all operating modes. The energy stored in the clamp capacitor is not dissipated like in the case of a typical RCD clamp proposed in prior arts, instead the clamp capacitor energy is utilized in conjunction with the coupling capacitor of SEPIC converter thereby resulting in a loss less clamp. Furthermore, the efficiency of the converter is increased due to the reduced switching loss, when compared with conventional isolated SEPIC. To validate the analysis, experimental testing is performed for a 34W isolated DCM SEPIC LED driver.