# Energy Management Integrated Circuit for Multi-Source Energy Harvesters in WBAN Applications
## 4 Circuit Block Designs
### Algorithm for the Control Method  
A digital control block generates an enabling signal for the comparators, and a control signal for the path switches based on the output of the comparators. The initial signal enables operation of the comparators, and they are only enabled when there is need to monitor the state of the harvested energy. Periodically enabled comparators detect the amount of energy harvested and inform the state to the digital control block. Based on the state of the harvested energy, the digital control block generates control signals whether to turn on the switch or not. The turn on signal ensures the harvested power is provided to a load.  
Figure 6: Low power analog blocks: (**a**) analog path switches; (**b**) comparators; and (**c**) oscillator.  
Figure 7 shows a flowchart for the process of the proposed algorithm of the digital control block. When different magnitude of energy is harvested in multiple and multi-type energy harvesters at the same time, the harvested energy should be supplied to a load effectively. To achieve this goal, a novel power managing algorithm is necessary. When n multi-source energy harvesters start to harvest, i is initialized to '1'. Here, i is defined as one value among 1, 2,..., n. The harvested energy starts to charge the temporary storage capacitor, Ci. The statei of the ith energy harvester is initialized to a low state. According to the statei, the load to which the harvested energy will be supplied is determined. With low statei, the sequence of low-power path proceeds, and with high statei, the sequence of high-power path proceeds. The algorithms for the low-power -and high-power paths are completely separate, and do not share connecting time. Therefore, in combining energy from multi-source harvesters, the harvesters on the low-power path share time among themselves, and the harvesters on the high-power path allocate time to themselves in parallel with the harvesters in the low-power path.  
In the low-power path process, if the voltage of Ci is higher than the threshold voltage, Vth, the energy stored in Ci is connected to a low load during \(\Delta\)t. Then the voltage of Ci begins to decrease, and at the same time, the other storage capacitors except Ci continue being charged from each energy harvester. After \(\Delta\)t, i is changed to i + 1, and the voltage of Ci + 1 is checked. If the voltage of Ci + 1 is lower than the threshold voltage, Ci maintains the connection with a low load. After connecting Ci to a low load, the statei changes to high state. At the next stage, Ci proceeds the high-power path sequence. If i is equal to n, i is initialized to 1, and the process returns to checking state process.  
In the high-power path process with a high state, the voltage of Ci is monitored. When the voltage of Ci is higher than the threshold voltage, Vth, the energy stored in Ci is connected to a high load during \(\Delta\)t. After \(\Delta\)t, i is changed to i + 1, and the voltage of Ci + 1 in high state is checked. If the voltage of Ci + 1 is lower than the threshold voltage, Ci maintains the connection with a high load. If the voltage of Ci begins to decrease, the connection Ci with a high load is disconnected, and the state  
Figure 7: Flowchart for the process of the proposed algorithm.  
of Ci is changed to low state. If not, the state of Ci is maintained in a high state. The other process is the same as with the low-power path process.  
By adopting this novel algorithm, all of the attached energy harvesters have the same chance to supply energy to a load, and the harvested energy is distributed to a load efficiently. According to the magnitude of harvested energy in each harvester, an optimal load is selected to prevent the harvested energy from being wasted. This process is compatible with a wide range of input energy.