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Inverting Buck-Boost Converter Calculator

Use the inverting buck-boost converter calculator to find your circuit's duty cycle and inductance.

Clear
Duty cycle29.412%D = V_out ÷ (V_out + V_in) — the ideal continuous-conduction value, before switch and diode drops
Conversion ratio0.4167×stepping down
Switching period4 µs
On time1.1765 µs
Off time2.8235 µs
Output power10 W
Input power11.1111 Wat 90% efficiency
Input current925.9259 mALESS than the output current — a buck trades voltage for current, which is why it is not a linear regulator
Power dissipated1.1111 Was heat in the switch, diode and inductor
Inductor ripple current175.219 mA8.76% of the output current — 20 to 40% is the usual design target
Peak inductor current2.0876 Awhat the inductor and switch must actually be rated for — sizing on the average current undersizes them
Minimum current for continuous conduction87.6095 mAyou are in continuous conduction, so the duty-cycle formula above is valid
Inductance for 30% ripple13.7255 µH
At twice the switching frequencyhalf the rippleripple is inversely proportional to both frequency and inductance, which is the trade that sets converter size — faster switching allows a smaller inductor but costs switching losses

The formula

buck D = V_out/V_in; boost D = 1 − V_in/V_out

Each topology has its own relation

A buck converter's duty cycle is simply the voltage ratio; a boost converter's is one minus the inverse ratio. They are not interchangeable — applying the buck formula to a step-up conversion gives a duty cycle above 1, which is why this page refuses the combination rather than returning a meaningless number.

All these relations assume continuous conduction and ideal components. A real converter needs a somewhat larger duty cycle, because the switch and diode each drop a few tenths of a volt and the inductor has resistance. Below a critical load the inductor current reaches zero each cycle, the converter enters discontinuous mode, and the duty cycle stops following the simple formula altogether — which is why the minimum continuous-conduction current is reported.

The peak inductor current, not the average, is what sizes the inductor and the switch. With 40% ripple the peak is 20% above the output current, and a component chosen on the average figure will saturate.

Ripple is inversely proportional to both frequency and inductance, which sets the central trade in converter design: switching faster allows a physically smaller inductor, at the cost of switching losses that rise with frequency.