A Digital Optimal Battery Charger with the inbuilt
Fault Detection Property
Abstract— 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.