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Calculate switching duty cycle (D), critical boundary inductance (Lcrit), peak inductor ripple current (ΔIL), and continuous conduction mode (CCM) for DC-DC boost converters.
Frequently Asked Questions
What is the relationship between duty cycle and output voltage in a boost converter?
In an ideal DC-DC boost converter operating in Continuous Conduction Mode (CCM), output voltage is given by Vout = Vin / (1 - D), where D is the switching duty cycle. For example, a 50% duty cycle (D = 0.5) doubles the input voltage.
What is Continuous Conduction Mode (CCM) vs Discontinuous Conduction Mode (DCM)?
In CCM, inductor current never falls to zero during a switching cycle, resulting in lower peak currents, smaller output ripple, and easier loop stability. In DCM, inductor current drops to zero before the next cycle starts, typically occurring at very light loads.
Why is the inductor ripple current target typically set between 20% and 40%?
A ripple ratio below 20% requires an unnecessarily bulky and expensive inductor. A ripple ratio above 40% increases AC core losses, RMS switch currents, and output ripple voltage.
Why must inductor saturation current (Isat) exceed peak inductor current?
If inductor current exceeds Isat, the magnetic core saturates, its inductance plummets to near zero, and rapid current runaway destroys the switching MOSFET.