An energy storage device, consisting of interface power terminals, rechargeable current source, first half-bridge, second half-bridge, inductor with an inductor's current sensor and control unit, while each half-bridge has a control input, positive terminal, negative terminal and toggle terminal, designed to connect to either the positive or negative terminal depending on the signal at the control input, the first half-bridge is connected in parallel to the rechargeable current source by positive and negative terminals, the negative terminal of the first half-bridge is connected to the negative terminal of the second half-bridge, the toggle terminal of the first half-bridge is connected to the toggle terminal of the second half-bridge by the inductor, the positive and negative terminals of the second half-bridge are the interface power terminals, differing by having the control unit has a reference input and contains first Schmitt trigger, whose output is connected to the control input of the first half-bridge, second Schmitt trigger, whose output is connected to the control input of the second half-bridge and summation circuit, whose output is connected to the inputs of the first and second Schmitt triggers, the first input of the summation circuit is connected to the output of the inductor's current sensor, and the second input of the summation circuit is the reference input of the control unit.