Buck Converter Using 3842
Introduction to Buck converterA Buck converter is a switch mode DC to DC electronic converter in which the output voltage will be transformed to level less than the input voltage. It is also called as step down converter. The name step down converter comes from the fact that analogous to step down transformer the input voltage is stepped down to a level less than the input voltage. By law of conservation of energy the input power has to be equal to output power (assuming no losses in the circuit).Input power (P in) = output power (P out)Since V in V out in a buck converter, it follows then that the output current will be greater than the input current.
Uc3843 Buck Converter
Therefore in buck converterV in V out and I in I in. As the duty cycle increases the output voltage increases and output current decreases. Discontinuous conduction modeAs mentioned before the converter when operated in discontinuous mode the inductor drains its stored energy completely before completion of switching cycle. The current and voltage wave forms of buck converter in discontinuous mode is shown in the figure belowThe inductor in discontinuous mode drains all the current which it piled up in charging interval of same switching cycle.
Uc3842 Buck Converter Design
The current through the inductor is given as= (1/L).area under the curve of voltage v/s time. Hence from the wave forms shown in the figureV out.δ.T s = (V in-V o).D.T sV out/V in =D/ (D+ δ)and the ratio of output to input current from law of conservation of energy is I out/I in =(D+ δ)/D. Applications of Boost converter. Buck converters are used in self-regulating power supplies. They are used as low-loss current sources to drive LED arrays(solid state lighting applications).
Used as interface between battery and components in Notebooks. Buck converters are used as Point-of-load (POL) converters in servers. Buck converters are used in advanced telecom and datacom systems.