In this paper, an isolated high step-up single switch DC-DC converter for renewable energy source is proposed. In the proposed converter high step-up voltage is obtained by single power switching technique that operates low duty cycle with isolated transformer inductors and switched capacitors and power diodes. The disadvantage of conventional converters is that it has high duty ratio and high voltage stress on power devices with less efficiency. The proposed converter eliminates the switching losses and recycles the leakage energy which includes reverse recovery energy of the power diode by using passive clamp circuit. To achieve high output voltage gain, the isolated transformer primary terminal and secondary terminal are connected in series during switching operation. PSIM software has been used for simulation. Simulation circuit is analyzed at 40Vdc/400Vdc, 200 W and this operation is validated by implementing in the hardware model at 12Vdc/120Vdc, 60 W. © 2014 Production and hosting by Elsevier B.V.