Now a power management architecture for energy harvesting will be discussed. Outside of the IC is the AC or DC energy harvesting source, the storage device to buffer the load, and the load itself, which could be a CPU, wireless transceiver or sensor. An all-purpose power management IC should be able to accept inputs from a variety of harvester sources, possibly concurrently, and combine the available power. A common consideration is vibration and solar. AC inputs must undergo some transformation in order to charge the storage device. The common approach here is to use a bridge rectifier, however, more advanced techniques are also possible. The green boxes in the diagram show that the interface to the harvester must be controlled and optimized to ensure maximum power extraction from the source. Thermal sources require an impedance match. Solar sources require operation at the maximum power point, which can be accomplished by regulating the load on the interface. Once the power is efficiently extracted and conditioned from the source, it is used to charge the storage element. In some architectures, the charger becomes an integral part of the design of the optimal harvester interface. The cold start unit is used when the storage device is not useable. It is powered from the harvester itself and it converts some of this power to charge the storage device. The storage device may require some management. In the case of a battery, it may require protection from temperature, over voltage, or under voltage. Some indication of the storage capacity will be useful information for the system processor to use so that it can adjust the load. Finally, one or a number of efficient power supply outputs are necessary to power the load.