Inverting Buck-Boost Converter Calculator
Design and analyse an inverting buck-boost converter: enter the input voltage, duty cycle, load current, switching frequency and inductance to get the output voltage (always inverted), average and peak inductor currents, current ripple, and conduction mode.
V
%
A
kHz
µH
Inverted polarity: output is negative when input is positive
- 1
Duty cycle fraction
D = 40% ÷ 100 = 0.4 - 2
Complement (1 − D)
1 − 0.4 = 0.6 - 3
Numerator Vin × D
12 × 0.4 = 4.8 - 4
Output voltage
Vout = −(4.8) ÷ 0.6 = -8Output polarity is inverted relative to the input voltage.
How does this calculator work?
Vout = −Vin × D / (1 − D) — the inverting buck-boost produces a negative output voltage. At D < 50% the magnitude is below Vin (buck region), at D > 50% above Vin (boost region). The inductor ripple ΔIL = Vin × D / (L × f) determines whether the converter stays in CCM (continuous) or enters DCM. All figures assume ideal lossless components.
Formula
How this is calculated
The inverting buck-boost converter is a single-switch topology that produces a DC output with polarity opposite to its input. When the switch is on for fraction D of each switching period T = 1/f, the inductor is connected across Vin and its current ramps up, storing energy. When the switch turns off for the remaining fraction (1 − D), the inductor reverses its voltage polarity and drives current into the output capacitor and load — but now current flows in the direction that makes the output terminal negative with respect to ground. The ideal steady-state output is Vout = −Vin × D / (1 − D): at D < 50% the magnitude is smaller than Vin (buck-like), at D > 50% it is larger (boost-like).
The inductor ripple current ΔIL = Vin × D / (L × f) determines how much the instantaneous inductor current swings around its average. The average inductor current equals Iout / (1 − D) for a lossless converter. If the minimum instantaneous current (IL_avg − ΔIL/2) stays above zero, the converter operates in Continuous Conduction Mode (CCM), which this calculator assumes for the output voltage formula. If it drops to zero before the next switching cycle, it enters Discontinuous Conduction Mode (DCM), where the voltage conversion ratio becomes load-dependent and the formula above no longer applies accurately.
All figures assume 100% efficiency (no switch or inductor losses). Real converters typically achieve 85–95%. Use the input/output power figures as a starting point for loss budgeting. Component values (inductance, capacitance, MOSFET ratings) should be verified against manufacturer datasheets for the target switching frequency and thermal constraints.
Frequently asked questions
The topology grounds the inductor differently from a standard boost converter. During the off phase, the inductor drives current through the output diode in a direction that makes the output terminal sit below ground, producing a negative voltage. This is the defining characteristic of the inverting buck-boost.
In Continuous Conduction Mode (CCM), the inductor current never reaches zero during the off phase. In Discontinuous Conduction Mode (DCM), it does, and the converter then idles until the next on pulse. The output voltage formula Vout = −Vin × D/(1−D) is only valid in CCM; in DCM the ratio depends on load current too.
A larger inductance reduces ripple current (smaller ΔIL), ensuring CCM at lighter loads and lowering peak currents on the switch and diode. A common starting point is to allow 20–30% peak-to-peak ripple relative to the average inductor current. Rearrange ΔIL = Vin × D / (L × f) for L to find the minimum inductance for your target ripple.
Also known as
TG we-Calculate Editorial Team. (2026). Inverting Buck-Boost Converter Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/inverting-buck-boost-converter
TG we-Calculate Editorial Team. "Inverting Buck-Boost Converter Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/inverting-buck-boost-converter.
TG we-Calculate Editorial Team, "Inverting Buck-Boost Converter Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/inverting-buck-boost-converter
@misc{wecalculate_inverting_buck_boost_converter, title = {Inverting Buck-Boost Converter Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/inverting-buck-boost-converter}}, year = {2026}, note = {TG we-Calculate} }
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