A novel lossless digital inductor current sensing technique based control implementation for switching DC/DC converter

Current sensing techniques are widely used for over current protection and current mode control of switching DC-DC converters for loop control. The major drawback with the conventional current sensing technique is that the accurate tuning of the low pass filter time constant with the inductor and its dc resistance (DCR) is required. However, this can hardly be guaranteed as the tuning depends on the tolerance of the components and the operating conditions. Moreover, the conventional solutions are not so trivial and they either require customized integrated circuit or additional computation power. To overcome these problems of the conventional current sensing techniques, a single analog comparator based lossless digital current sensing technique is proposed and implemented for loop control of an isolated full bridge buck converter in this paper. In the proposed lossless digital current sensing technique, the status of a 1-bit high frequency switch node voltage (V_sw) is recreated by using one simple analog comparator and subsequently converted into n-bit signal in the field programmable gate array (FPGA) based digital domain. This n-bit information about the V_sw is filtered/integrated in FPGA to give the information about the inductor current. This predicted inductor current information is used for implementation of the loop control of full bridge buck converter. The proposed concept gives a simple solution as it avoids the use of one extra analog to digital conversion (ADC) IC and thereby avoiding its design and implementation complexity. The steady state and dynamic analysis is carried out. Analysis, simulation, and experimental results are presented in the paper to verify the properties of the proposed algorithm.