DC-DC power converters employ switched-mode circuitry to change dc voltages and currents with efficiencies approaching 100%. Basic converter circuits can reduce the voltage (buck converter), increase the voltage (boost converter) or both (buck-boost, Cuk, and SEPIC converters).
Transformer-isolated circuits include the bridge, forward, and flyback converters.Loss mechanisms include conduction loss arising from resistances or forward voltage drops of the power components, and switching loss generated during the transistor and diode switching transitions.
Synchronous rectifiers can be employed to reduce the significant conduction loss caused by diode forward voltage drops in low-voltage applications.
The discontinuous conduction mode may arise when the inductor current is sufficiently small, which causes the output voltage to be strongly load-dependent.
Voltage-mode control employs pulse-width modulation to regulate the converter output voltage or other quantities through variation of the transistor duty cycle.
Another popular technique is current-mode control, in which a circuit causes the peak transistor current to follow a control reference signal.Averaging methods are commonly employed to model the dynamics and efficiency of dc-dc power converters.
The state-space averaging method leads to an equivalent circuit model that predicts the converter small-signal transfer functions. The circuit averaging technique is easily applied to simulate the converter transfer functions, in both continuous and discontinuous conduction modes, using computer programs such as SPICE.