Today's multi-input energy harvesters need to accommodate different energies, such as sub-1mu W from radio frequency (RF), tens of mu W from thermal energy generators (TEG), and hundreds of muW from photovoltaic (PV). The generic harvesting controller in  cannot be used for ultra-low energy sources due to the increased quiescent current (I Q). Although an ultra-low energy source can be obtained by the Battery-TEG Pile-up Buck (BTPB) supply  (top left of Fig. 30.2.1), the increased peak inductor current causes a larger input source voltage ripple, Delta VSRC. If VBAT=1.2V and VSRC=0.5V from TEG, then Delta VSRC will increase to 28.8mV (equal to 11.5% of VOC/2, where VOC is the open circuit voltage), as shown in the middle of Fig. 30.2.1, thereby increasing power loss and degrading maximum power point tracking (MPPT) efficiency. Also, energy cannot be harvested in  when VStextRC is negative due to the bipolar TEG. A bulky transformer is used in  to obtain a bipolar VStextRC, and yet, resulting in a low power density that is not suitable for Internet of Things (loT) applications.