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This paper presents a new capacitor charger for energy-harnessing applications such as energy transfer from a low-power battery to a load capacitor. The proposed structure uses a switching technique for step-by-step charging of the load capacitor. It comprises a control section, output stage metal-oxide-semiconductor field-effect transistors, and an external inductor. In order to improve the circuit efficiency under different power transfer scenarios, the switching capacitor charger operates at the boundary of continuous conduction mode and discontinuous conduction mode. Two blocks of peak current controller and zero current detector have been employed in a feedback loop to control the inductor current, which resulted in conduction power dissipation reduction. Also, the circuit with switching at low frequencies significantly reduces the switching loss. The performance of the proposed circuit is demonstrated using theoretical elaborations. In addition, the proposed structure is evaluated and simulated in a 0.18μm standard complementary metal-oxide semiconductor technology. Based on the obtained results, the efficiency of the presented circuit at 15.62mW input power is 96%, and the charging time is about 0.54ms, which is suitable for low-power applications. [ABSTRACT FROM AUTHOR]

There are cases in energy supply applications with low-power batteries, where the power required by the load is larger than the supply maximum deliverable power. Using a capacitor to create a high instantaneous power for the load was investigated as a useful solution. To increase the charging efficiency, a stepwise method for charging the capacitor was employed. This paper presents a new pulsed power supply approach in which the charging process is resumed after high instantaneous power delivery. Through this, the loss of residual energy in the capacitor was decreased and load turn-on speed and energy efficiency were significantly improved. The proposed structure consists of a buck converter that charges the capacitor using inductor current. A pulse frequency modulation (PFM) technique was used to generate the necessary signals for the buck converter switches, which resulted in controlling the inductor current. The proposed circuit was designed and simulated in a 0.18 μ m CMOS technology. It was shown that the designed CMOS circuit could reach a peak energy efficiency of 93.2% with a sleep period of 1.05 ms when the load consumes 7.06 μ J of energy. [ABSTRACT FROM AUTHOR]

In energy harnessing applications there are instances where energy should be transferred from a low-power, low-leakage backup battery to a temporary power delivery output capacitor. The high power delivery feature of the storage capacitor usually comes at the price of higher leakage current and thus it cannot replace the long-term energy storage backup battery. This paper presents a CMOS capacitor charger circuit which connects a long term low power battery to a short-burst high power delivery capacitor. The proposed circuit uses a switching output stage with an external inductor to reduce the dissipation during the capacitor charge-up cycle. A sigma-delta modulation approach is used to control the power switches. Under low power transfer scenarios which perform transfer in a longer duration, the proposed approach shows better performance compared with previously presented techniques. It is shown that under different transfer durations the control section only consumes 970nWs. The efficiency of the proposed circuit is more than 90% for average input powers in the 0.7 mW to 2 mW range. [ABSTRACT FROM AUTHOR]