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The idea of little nano-generator chips inside all sorts of products for harvesting small amounts of energy to operate low power circuits is very appealing.
TI has announced a new highly efficient boost charger IC for nano power energy harvesting that is able to harvest energy in the microwatts to milliwatts range.
TI says that when the new IC is used in a solar panel powering a handheld device operating in indoor light conditions the new boost charger can increase the usable energy harvest by 30 to 70% compared to a linear regulator. This is a particularly important technology for sensors in things like security systems and other uses that only need tiny bits of power to operate. The IC can harvest energy from a variety of sources including solar, thermoelectric, electromagnetic, and vibration. That allows the size of the solar panel to be reduced making the products cheaper to produce and more compact.
This paper presents an efficient AC-DC power converter that avoids the bridge rectifier stage and directly converts low AC voltage to a required high dc output voltage. Being able to harvest that power from solar energy or vibration makes the sensors much easier to install. The circuit is a unique integration of boost and buck-boost converter to condition the positive and negative half portions of the input AC voltage, respectively.
The topology uses only a single inductor and capacitor to reduce the size of the converter. This topology provides an efficiency of 71% and is designed with the purpose of minimizing the size, weight and power losses. The idea thatenergy can be harvested from the ambient environment and a device can operate without a battery is very attractive for low power electronic applications.
Since electro- magnetic micro generators have higher energy density, they are being considered in this paper.The electromagnetic micro generators are mass-spring damper based arrangement (as shown in Fig. 1) in which the ambient mechanical energy is converted to electrical energy by electromagnetic coupling [6]. The output voltage of this micro generator is of AC type, whereas the electronic loads require DC voltage.
Hence, the micro generator output has to be pro- cessed by a suitable power converter before providing to the electronic loads.Fig.

1 Schematic diagram of electromagnetic micro generatorThe block diagram for the low voltage energy harvesting is shown in Fig. The ambient vibration in the form of mechan- ical energy is converted to electrical energy by the MEMS transducer. During thepositive half cycle of the input AC voltage, S1 is turned ONand D1 is reverse biased and hence, the circuitry operates in the boost mode. During the negative half cycle, the buck-boost mode starts by turning ON S2 and reverse biasing D2.Fig. 4 Bridgeless boost rectifier for energy harvestingThe section 2 describes the various operating modes of the converter and section 3 discuss on design procedures and guidelines. The boost converter is the common power conditioning interface due to its simple structure, voltage step-up capability, and high efficiency.
The buck-boost converter has ability to step up the input voltage with a reverse polarity; hence, it is an appropriate candidate to condition the negative voltage cycle.
Besides, the boost and buck-boost converter topologies could share the same induc- tor and capacitor to meet the miniature size and weight re- quirements. Here, the actual voltage is being compared with the reference voltage, and the error signal is then given to another comparator which compares the control voltage with a saw- tooth voltage waveform. Closed-loop control Scheme for the proposed Converter2.3 Modes of OperationThere are six operation modes for the bridgeless boost con- verter as shown in Fig.
Modes I-III is for the circuit opera- tion in the positive half cycle, whereas, modes III-VI are for the circuit operation during the negative half cycle. During the positive half cycle, S1is turned ON and D1 is reverse biased while S2 is turned ON and D2 is reverse biased during the negative half cycle. Both the diodes are reverse biased and load is powered by the energy stored in the output filter capacitor, C.
This avoids the reverse recovery losses of the diode and load is again powered by the energy stored in the capacitor. The converter would return to Mode IV as soon as S1 is turned ON, if the input voltage is still negative.Fig. 7 shows the waveforms of the proposed boost rectifi- er in the boost and buck-boost operation modes.Fig.

Due to the DCM operation, the input current sensor can be eliminated and switching loss can be reduced.
Since the circuit size can be reduced and the efficiency can be enhanced, DCM operation is more suitable than the continu- ous conduction mode (CCM) operation.3 PSIM SIMULATION MODELThe proposed direct AC to DC converter circuit with boost and buck-boost converter is simulated using PSIM. Here, the actual voltage is compared with the reference voltage (3.3V) and the error signal is given to a PI controller. Then, a hysteresis control is given by using a saturation block which limits the PI controller output (control voltage) to remain within certain limits. The control voltage is again compared with a saw tooth waveform from the signal generator so that gate pulses are being given to the boost and buck-boost con- verter switches according to the detection of positive and neg- ative peaks, respectively. For closed loop operation the PSIM model of boost- buck-boost converters created as in Fig.
It can be seen that the inductor is operated during the entire half cycle, which is during both positive and negative half cycle of the input voltage.Fig. Ross, a€?Design and fabrication of a new vibration based electromechanical power generator,a€? Sens. Parsa, a€?Energy harvesting and efficient power generation from human activities,a€? in Proc.
Holmes, a€?Converter circuit design, semiconductor device selec- tion and analysis of parasitics for Micropower electrostatic genera- tors,a€? IEEE Trans.
Holmes, a€?Ar- chitecture for vibration-driven Micropower generators, a€?Microelec- tromech. 2004[9] Rohan Dayal, Suman Dwari, Leila Parsa,a€?A New Design for Vibra- tion-Based Electromagnetic Energy Harvesting Systems Using Coil Inductance of Microgeneratora€?, IEEE Transactions on Industry Ap- plications.

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