Inverting Buck-Boost Converter Calculator

Calculate duty cycle, voltage gain, currents, inductance, capacitance, ripple, and semiconductor stresses from converter design inputs. Inverting Buck-Boost Converter Calculator supports engineers, students, and electronics designers developing continuous-conduction power supplies.

Highlights

  • Calculate the duty cycle and voltage gain for inverting buck-boost converters.
  • Determine input and output currents, power requirements, and converter efficiency effects.
  • Size the required inductor and output capacitor based on ripple targets.
  • Estimate inductor, switch, and diode peak and RMS currents.
  • Verify continuous-conduction operation and assess key semiconductor stresses.

Table of Contents

  1. How Inverting Buck-Boost Converter Calculator Works?
  2. Practical Use Cases
  3. Accuracy and Limitations
  4. Quick Examples
  5. Frequently Asked Questions (FAQs)
  6. Cite This Calculator

How Inverting Buck-Boost Converter Calculator Works?

An inverting buck-boost converter produces an output with polarity opposite to the input. This calculator uses the ideal continuous-conduction-mode (CCM) relationships to estimate the duty cycle, voltage gain, currents, inductance, capacitance, and semiconductor stresses from the input voltage, output-voltage magnitude, output power, efficiency, switching frequency, and ripple targets.

The required duty cycle is determined by the desired output-voltage magnitude relative to the input voltage:

D=VoVin+Vo

Here, D is the switch duty cycle and Vo is the output-voltage magnitude. The output polarity is negative, so the actual output voltage is:

Vout=−Vo

The voltage-gain output reports the magnitude ratio:

|G|=VoVin=D1−D

Load current and input requirements follow from power balance and the specified efficiency. Efficiency is represented as a decimal fraction, η:

Iout=PoutVo,Pin=Poutη,Iin=PinVin

In CCM, the average inductor current is related to the output current by:

IL,avg=Iout1−D

The selected ripple percentage determines the peak-to-peak inductor ripple. The calculator then estimates the current limits and required inductance:

ΔIL=IL,avg×r100,Lmin=VinDfΔIL
IL,peak=IL,avg+ΔIL2,IL,min=IL,avg−ΔIL2

The output-ripple target gives the allowable ripple voltage and the minimum output capacitance:

ΔVo=Vo×rv100,Cmin=IoutDfΔVo

For the switch and diode stress estimates, the peak current is taken as the peak inductor current. The RMS estimates use the triangular-ripple approximation:

IL,rms=I2L,avg+ΔI2L12
Iswitch,rms=DIL,rms,Idiode,rms=1−DIL,rms

Calculated quantityBasis
Duty cycleInverting buck-boost voltage relationship
Output and input currentPower, voltage, and efficiency
Inductor valuesSpecified current ripple and switching frequency
Output capacitorSpecified output-voltage ripple
Switch and diode stressesPeak and RMS triangular-current estimates

Practical Use Cases

Power-supply engineers can use the calculator to select an initial duty cycle, inductor, output capacitor, and semiconductor current ratings for a negative-output rail, such as generating a regulated negative supply from a positive source.

Embedded-system designers can estimate the input current and output ripple when powering operational amplifiers, sensor interfaces, analog-to-digital converters, or communication circuits that require a negative voltage rail.

Electronics students can compare the effects of output-voltage magnitude, switching frequency, efficiency, and ripple targets on duty cycle, average inductor current, peak current, and component sizing.

Battery-powered product designers can estimate the required supply current and inductor stress when creating compact inverting converters for portable instrumentation, audio circuits, or mixed-signal electronics.

Hardware prototyping teams can use the peak and RMS current estimates as an early screening tool for choosing an inductor, switch, diode, and capacitor before detailed thermal, transient, and electromagnetic-interference testing.

Accuracy and Limitations

The calculator provides first-order steady-state estimates for an ideal inverting buck-boost converter operating in continuous conduction with triangular inductor ripple. It does not include diode forward voltage, switch voltage drop, inductor winding resistance, capacitor ESR and ESL, switching transition losses, leakage effects, control-loop response, transient load behavior, thermal derating, or electromagnetic-interference constraints. The calculated minimum inductance and capacitance should therefore be treated as design starting points, and the computed minimum inductor current should be checked to confirm CCM under the actual minimum-input-voltage and maximum-load conditions.

Quick Examples

Example #1: 12 V to -24 V Supply

Design a moderate-power inverting buck-boost converter for generating a negative 24 V rail from a 12 V input.

Example #2: 5 V to -12 V Sensor Rail

Size a compact converter for producing a low-power negative supply rail for analog sensors and signal-conditioning circuits.

Example #3: 48 V to -15 V Industrial Converter

Evaluate a higher-input-voltage converter for supplying a regulated negative rail in an industrial control system.

Frequently Asked Questions

An inverting buck-boost converter reverses the output polarity relative to the input. The output voltage magnitude may be higher or lower than the input depending on the operating duty cycle.

Continuous-conduction mode means the inductor current remains above zero throughout each switching cycle. It generally provides smoother current and is common in higher-power converter designs.

Increasing switching frequency typically reduces the inductance and capacitance needed for a given ripple specification. However, higher frequency can increase switching losses, electromagnetic interference, and thermal stress.

Select an inductor with a saturation-current rating above the peak inductor current and an RMS-current rating suitable for thermal operation. Additional margin is recommended for tolerances and transient conditions.

The switch and diode should be rated above the maximum voltage they may experience, including the input voltage, output voltage magnitude, and switching transients. Voltage and current derating help improve reliability.

Cite This Calculator