Ideal boost equations in continuous conduction mode (CCM). During switch ON (time $DT$) the inductor sees $V_i$ and its current ramps up with slope $V_i/L$; during OFF ($(1-D)T$) it delivers current to the output through the diode, falling with slope $-(V_o-V_i)/L$. In steady state the rise equals the fall, which yields $V_o=V_i/(1-D)$. The ripple $\Delta I_L$ shrinks as $L$ and $f_s$ increase. The ideal model ignores losses, so real designs must verify diode/synchronous-rectifier losses, inductor saturation, control stability, and switch ratings.
What is a boost converter
A boost (step-up) converter is a switching power supply that produces an output DC voltage $V_o$ higher than its input $V_i$. It uses four elements — an inductor, a switch (MOSFET), a diode, and an output capacitor. Rapidly switching the MOSFET stores energy in the inductor and "pumps" it to the output. Ideally the output depends only on the duty ratio $D$: $V_o=V_i/(1-D)$. For example $D=0.5$ doubles the voltage and $D=0.8$ multiplies it fivefold. This simulator animates the switching action itself, showing the inductor current ramping up and down as a triangular wave while it lifts the output voltage in real time.
How to read it
In the circuit, during the ON phase (green) current flows into and charges the inductor; during OFF (yellow) the path through the diode delivers it to the output.
The current waveform shows the triangular ripple ΔIL. It grows with higher D and shrinks with larger L or fs.
The Vout–D curve marks the current operating point and makes the sharp non-linear rise near D→1 obvious at a glance.
Learn Boost Converter Duty Cycle by dialogue
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When reading Boost Converter Duty Cycle, where should I look first? Moving Input voltage Vin changes both the plots and the result cards.
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Start with Ideal output voltage, but do not treat the number as the whole answer. Use Boost duty curve to confirm the assumed state, then read Inductor current for the distribution or trend. The duty curve rises sharply as D approaches one.
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I can see why Input voltage Vin changes Ideal output voltage. How should I judge the influence of Duty ratio D?
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Move Duty ratio D in small steps and watch Inductor ripple current. That reveals which term is controlling the result. The ideal boost equation ignores losses. Real design must check diode or synchronous losses, inductor saturation, control stability, and switch ratings. A single operating point is not enough; sweep the realistic scatter range.
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What is Device stress for? It feels like the ordinary curve already tells the story.
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Device stress is for finding boundaries where the condition becomes risky or margin collapses quickly. The current view checks whether inductor ripple is excessive. In Early component sizing for DC-DC boost converters, the important question is often what happens after a small change, not only the nominal value.
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So if Ideal output voltage is within the target, can I accept the condition?
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Treat this as a first-pass review. It helps with Estimating inductor saturation current and ripple and Checking risky high-duty operation, but final decisions still need standards, measured data, detailed analysis, and vendor limits. The stress view shows how boost ratio raises device voltage rating.
Physics model and key equations
The relations follow from volt-second balance in continuous conduction mode (CCM). During ON time $DT$ the inductor sees $V_i$ and its current rises by $\Delta I_L = V_i D/(L f_s)$. During OFF time $(1-D)T$ it sees $-(V_o-V_i)$ and falls by the same amount. In steady state the net change is zero, so $V_i D = (V_o-V_i)(1-D)$, which rearranges to:
The average inductor current equals the input current and is $1/(1-D)$ times the output current — which is why device current stress climbs steeply at high boost. The CCM/DCM boundary is where $\Delta I_L/2 = I_{L,\text{avg}}$; below it the converter enters discontinuous conduction mode (DCM).
Real-world applications
Early component sizing for DC-DC boost converters (inductor, switch, diode selection).
LED drivers, solar MPPT, automotive 48 V step-up, battery boost stages.
Estimating inductor saturation current and ripple; checking risky high-duty operation.
Common misconceptions and pitfalls
Pushing D toward 1 does not give unlimited boost. In a real circuit losses cap the gain and efficiency drops sharply.
Ripple is not "smaller is always better" — it trades off against inductor and capacitor volume. A typical target is ΔIL ≈ 30–40% of output current.
At light load the converter enters DCM and $V_o=V_i/(1-D)$ no longer holds. Checking the CCM margin is essential.
Related engineering fields
Power electronics, magnetic component design, control theory (current/voltage mode), EMC and thermal design.
For further study
Extends to synchronous boost, interleaved boost, the averaged model and small-signal transfer function (right-half-plane zero), and peak-current-mode control.
FAQ
Start with Ideal output voltage and Inductor ripple current. Then use Boost duty curve to confirm the assumed state and Inductor current to read distribution or bias. The duty curve rises sharply as D approaches one
Move Input voltage Vin alone, then move Duty ratio D by a comparable amount and compare the change in Ideal output voltage. Device stress shows combinations where margin or performance changes quickly.
Use it for Early component sizing for DC-DC boost converters. Instead of trusting a single point, widen the input range and check whether Ideal output voltage keeps enough margin before moving to detailed analysis.
The ideal boost equation ignores losses. Real design must check diode or synchronous losses, inductor saturation, control stability, and switch ratings. Final decisions still require standards, measured data, detailed analysis, and vendor limits.
How to Use
Enter input voltage (6–48 V typical for automotive/industrial boost stages) in the Vin field.
Set duty cycle as a decimal (0.3–0.8 range; 0.5 = 50% switch-on time).
Input inductance in microhenries (10–100 µH common for 100 kHz converters).
Specify switching frequency in kilohertz (50–500 kHz depending on semiconductor and core losses).
Read ideal output voltage, inductor ripple current, switch voltage stress, and CCM margin instantly.
Worked Example
A 24 V input boost converter with L=47 µH, fsw=100 kHz, and D=0.6 delivers: Vout = 24 / (1 − 0.6) = 60 V. Inductor ripple ΔI = (24 × 0.6) / (47 × 10⁻⁶ × 100 × 10³) = 3.06 A peak-to-peak. Switch voltage stress Vswitch = Vout = 60 V. Minimum inductor current I_min = (Vout − Vin) / L × t_off; typical CCM margin 15–25% indicates stable continuous conduction mode.
Practical Notes
Higher duty cycles (D > 0.7) require careful PCB layout and low-loss inductors to manage increased ripple and core saturation in boost applications (telecom 48 V rails, industrial 400 V).
Ripple current scales inversely with L and fsw; doubling frequency halves ripple for same core volume.
Switch voltage stress (FET or diode) must exceed Vout by 20% minimum derating; use SiC or GaN for high-frequency (>300 kHz) designs to reduce losses.
Verify CCM margin >10% to avoid discontinuous mode; below this, output regulation degrades with load variations.