A High speed digital Subsystem requires three voltages $$V_{1} , V_{2}$$ and $$V_{3}$$ with 1 : 2 : 1 power 3 ratings respectively. The power supply is designed with the distribute power conversion scheme as shown in the following figure. What is the overall power conversion efficiency?

$$\frac{4 \times \eta_{1} \times \eta_{2} \times \eta_{3}}{\eta_{2} \eta_{3}+2 \times \eta_{3}+\eta_{2}}$$

$$\frac{\eta_{1} \times \eta_{2} \times \eta_{3}}{\eta_{2} \eta_{3}+2 \times \eta_{3}+\eta_{2}}$$

$$\frac{4 \times \eta_{1} \times \eta_{2} \times \eta_{3}}{\eta_{2} \eta_{3}+ \times \eta_{2}+\eta_{3}}$$

$$\frac{2 \times \eta_{1} \times \eta_{2} \times \eta_{3}}{\eta_{2} \eta_{3}+ \times \eta_{2}+\eta_{3}}$$