LearnTronics
Simple Boost Converter
Recipe #38 — simple boost converter
Inductive flyback can be controlled rather than merely suppressed. A boost converter deliberately stores energy in an inductor and then redirects that energy into an output capacitor at a voltage higher than the input.
State 1 — switch ON: current through L1 rises and magnetic energy is stored. D1 is usually reverse-biased because the switch node is low.
State 2 — switch OFF: L1 tries to keep current flowing, raises the switch-node voltage, forward-biases D1, and sends energy into COUT and the load.
State 2 — switch OFF: L1 tries to keep current flowing, raises the switch-node voltage, forward-biases D1, and sends energy into COUT and the load.
Ideal continuous-conduction relation: VOUT ≈ VIN / (1 − D)
Why output can exceed input
The source voltage and the inductor's turn-off voltage act in the same direction during the energy-transfer interval. The diode steers that energy to the output capacitor rather than letting it return through the switch.
The real circuit needs control and limits
A useful converter needs a switching device, oscillator/controller, current limiting, suitable diode, inductor current rating, capacitor ESR rating, feedback regulation, and careful layout. The ideal duty-cycle formula does not include losses or discontinuous conduction.