The energy conversion device (10) includes a power module (14), a unit (16) for cooling the power module (14), and a sealed enclosure (12) housing the power module (14) and at least part of the cooling unit (16). The cooling unit (16) includes a cooling circuit (18), in which a coolant circulates, a first heat exchanger (20) with the power module (14), through which the coolant passes, and at least one pump (24) making the coolant circulate in the circuit (18). The cooling circuit (18) includes a pressure regulating branch (26), extending between an outlet and an inlet of the driving pump (24), the regulating branch (26) including a pressure regulating valve (28), normally closed, capable of opening when the pressure difference between the outlet and the inlet of the driving pump (24) exceeds a predetermined threshold.