A digital optimal battery charger with the inbuilt fault detection property

This paper presents a digital optimal battery charger that has an inherent characteristics of detecting the fault (main switch failure, i.e., TOP FET failure of the converter) within one switching cycle. The charger consists of synchronous buck converter and a novel carrier generation (synthetic ripple) based digital feedback clamped hysteretic modulator. The proposed charger charges the battery with the constant current for less battery state of charge (SOC) and charges it with the constant voltage when the battery SOC reaches near 100%. The charger facilitates smooth and stable transition from constant current (CC) mode to constant voltage (CV) mode without the need of extra switch or control loop. The novel feedback clamped digital hysteretic modulator used in the charger generates carrier to the hysteretic comparator in the field programmable gate array (FPGA) based digital domain by generating piece-wise linear synthetic ripple using sensed converter voltages (switch node voltage and the output voltage), without the need of direct inductor current sensing and adding the output voltage to it. The regulation loop is clamped and hence the charger remains in the feedback controlled during the whole charging cycle. Experimental and simulation results verify the operation of the proposed charging system on 20 W prototype. The performance of the charger is verified on a 6 V-4.5 Ah lead acid battery as well.