Boost Converter
Calculate duty cycle, inductor value, and output capacitance for any DC-DC step-up (boost) converter — free, instant, and accurate.
Results update live and use industry-standard boost converter design equations.
What Is a Boost Converter?
A boost converter (also called a step-up converter) is a type of DC-DC switching power supply that produces an output voltage higher than its input voltage. Unlike a linear regulator, which can only step voltage down and wastes the difference as heat, a boost converter steps voltage up efficiently — often above 90% efficiency — by switching current through an inductor at high frequency.
A boost converter is built from four core components:
- Inductor (L) — stores energy from the input source
- Switch (MOSFET) — controlled by a PWM signal to charge/discharge the inductor
- Diode (or synchronous MOSFET) — routes stored energy to the output
- Output Capacitor (C) — smooths the output voltage and supplies the load when the switch is closed
How a Boost Converter Works
A boost converter operates in two alternating states, controlled by the switch's duty cycle:
- Switch closed (on-time): Current ramps up through the inductor, storing energy in its magnetic field. The diode blocks reverse current, so the output capacitor alone supplies the load.
- Switch open (off-time): The inductor's stored energy is released, and — because inductors resist sudden current changes — its voltage adds on top of the input voltage. This combined voltage charges the output capacitor and supplies the load through the diode.
Because the inductor's collapsing field is what "boosts" the voltage, output voltage rises as duty cycle increases — up to the physical limits of the components. This step-up in voltage always comes with a proportional step-down in output current relative to input current, since power in ≈ power out (minus efficiency losses).
Boost Converter Design Formulas
Use the calculator above for instant results, or calculate by hand using the equations below.
1. Duty Cycle (D)
D = 1 − (Vin / Vout) × Efficiency
Ideal (100% efficient) case:
D = 1 − (Vin / Vout)
The duty cycle tells you what fraction of each switching cycle the MOSFET spends "on." As the required boost ratio (Vout/Vin) increases, duty cycle increases toward 1 (100%). Real-world converters use the efficiency-adjusted formula since conduction and switching losses mean the switch must stay on slightly longer than the ideal case predicts to hit the target output voltage.
2. Inductor Selection (L)
L = (Vin × (Vout − Vin)) / (ΔIL × fsw × Vout)
Inductance is chosen to keep ripple current (ΔIL) at roughly 30–40% of the average input current. Too small an inductor causes excessive ripple, core saturation risk, and higher peak currents through the switch and diode. Too large an inductor is bulkier, costlier, and slows the converter's transient response.
3. Output Capacitor Selection (C)
Cmin = (Iout × D) / (fsw × ΔVout)
Unlike buck converters, boost converters are discontinuous at the output — during the switch's on-time, the diode is reverse-biased and the output capacitor alone must supply the entire load current. This makes output capacitor sizing more critical in boost topologies than in buck topologies. Undersizing C leads to excessive output voltage ripple (ΔVout); low-ESR ceramic or polymer capacitors are typically required to meet ripple targets at higher output currents.
Practical Applications of Boost Converters
- LED Drivers — Boosting 3V from a AA/AAA battery to 30V+ to drive a series string of LEDs efficiently, without the current losses of a resistor-based design.
- USB Power Banks — Boosting a 3.7V Li-Ion/Li-Po cell up to the regulated 5.0V required by the USB output spec.
- Solar / Energy Harvesting — Boosting the low, variable output of a small solar panel or piezoelectric harvester up to a usable charging voltage (often paired with MPPT control).
- Automotive & Battery Systems — Boosting a partially-discharged 12V lead-acid or battery-pack voltage back up to a stable 12–14V rail for accessories.
- Nixie Tube & Display Drivers — Generating 170–180V from a 12V supply to power vintage gas-discharge (Nixie) displays.
- White LED Backlighting — Common in portable electronics where a single Li-Ion cell must drive an LCD backlight requiring a higher forward voltage.
Frequently Asked Questions
Can a boost converter step down voltage?
No. A standard boost converter's topology requires Vout to stay higher than Vin. If Vin exceeds Vout, current flows uncontrollably through the inductor and diode straight to the load — with no switching control to limit it — which can damage downstream components. If your application needs to both step up and step down depending on conditions (e.g., a battery voltage that sags below your target output), you need a buck-boost converter, not a standard boost.
Why is my boost converter getting hot?
Heat is almost always concentrated in the MOSFET or diode, since these carry the full switched current. The most common cause is an excessive duty cycle: if your design requires D > 80% (i.e., a Vout/Vin ratio above roughly 4:1 or 5:1), the switch conducts for most of each cycle, driving up conduction losses. As a rule of thumb, keep the boost ratio under 4:1 for a single stage — for higher ratios, consider a two-stage boost or a transformer-based (flyback) topology instead.
What is the Right Half Plane Zero (RHPZ)?
The Right Half Plane Zero is a control-loop stability quirk unique to boost (and buck-boost) converters operating in continuous conduction mode. When the controller suddenly increases duty cycle to demand more output power, output current actually dips before rising — the opposite of what a normal control loop expects. This inverted response limits how aggressively you can compensate the feedback loop, which is why boost converters generally need a lower control bandwidth and more careful PID/Type III compensation design than buck converters.
What duty cycle range is realistic for a boost converter?
Most practical single-stage boost designs stay between roughly 10% and 80% duty cycle. Below ~10%, the boost ratio is so small a boost topology may not be worth the added complexity over other options. Above ~80%, efficiency drops sharply and component stress rises — at that point, a two-stage boost, a coupled-inductor (SEPIC) design, or a flyback converter is usually a better fit.
How do I choose a switching frequency for a boost converter?
Higher switching frequencies allow smaller inductors and capacitors (smaller, cheaper boards) but increase switching losses and EMI. Lower frequencies improve efficiency but need larger, bulkier magnetics. Most integrated boost controllers/converters run between 300 kHz and 2 MHz; check your specific converter IC's datasheet for its recommended range before finalizing L and C values.
Does inductor ripple current affect efficiency?
Yes. Higher ripple current (a smaller inductor) increases RMS current through the inductor, MOSFET, and diode, which raises I²R conduction losses and can push the inductor toward core saturation. Lower ripple (a larger inductor) improves efficiency and reduces EMI but adds size, cost, and slows transient response. The commonly used 30–40% ripple target is a practical middle ground between these tradeoffs.