The invention discloses a
transformer primary side series connection LLC and output parallel connection BUCK two-stage converter which comprises two high-frequency isolation transformers, wherein primary sides of the two high-frequency isolation transformers are connected in series and then connected into an LLC resonant network; the other end of the LLC resonant network is connected into a
bridge circuit; secondary sides of the two high-frequency isolation transformers are sequentially connected with rectifying circuits and BUCK circuits; and output ends of the two BUCK circuits are staggered and connected in parallel. The converter can achieve
zero voltage switch-on of switching tubes on the primary sides of the high-frequency transformers, and zero
current switch-off of rectifying tubes on the secondary sides of the high-frequency transformers, so that the efficiency and the
power density of the
LLC converter are improved; and equal primary side
voltage of two primary side series connection high-frequency transformers of a preceding-stage converter can be achieved based on control of the same duty ratio of the two BUCK circuits which are staggered and connected in parallel, so that the two high-frequency transformers share equallyinput power,
magnetism equilibrium distribution of the high-frequency transformers is achieved, the reliability of the converter is improved, and the cost is lowered.