Inverting Buck-Boost Converter Calculator
Design an inverting buck-boost converter by calculating duty cycle and inductance from voltage, switching frequency, and ripple current. Free DC-DC design tool.
About This Calculator
About the Inverting Buck-Boost Converter Calculator
This Inverting Buck-Boost Converter Calculator helps electronics engineers, students, and hobbyists design and analyze DC-DC converters with inverted topology. An inverting buck-boost converter is a switching power supply that produces a negative output voltage from a positive input voltage, with the ability to step up (boost) or step down (buck) the voltage magnitude depending on the duty cycle. Enter the input voltage, desired output voltage, switching frequency, and maximum ripple current to instantly compute the duty cycle and required inductance.
The inverting buck-boost converter operates by storing energy in an inductor when the switch is on and releasing it to the output when the switch is off, with the output polarity inverted relative to the input. The duty cycle is calculated as D = Vout / (Vin + Vout), where the voltages are taken as absolute values. The inductance is then determined using L = (D × Vin) / (fsw × Iripple). A duty cycle below 50% indicates buck mode (output magnitude less than input), while above 50% indicates boost mode (output magnitude greater than input).
Key design considerations include selecting the appropriate switching frequency to balance inductor size and switching losses, choosing the ripple current as a percentage of the average inductor current (typically 20-40%), and verifying that the inductor saturation current rating exceeds the peak current. The results assume continuous conduction mode (CCM) with ideal components.
Who Uses This Calculator
Power electronics engineers designing negative voltage rails for operational amplifiers, audio equipment, and industrial sensors use inverting buck-boost converter calculations daily. Hobbyists building portable electronics projects benefit from quick parameter estimation. Students learning power electronics can verify their theoretical calculations.
Frequently Asked Questions
What is an inverting buck-boost converter?
An inverting buck-boost converter is a DC-DC power converter that produces a negative output voltage from a positive input voltage. It can step up or step down the voltage magnitude while inverting the polarity. The output voltage is determined by the duty cycle: Vout = D/(1-D) × Vin. It uses an inductor, switching transistor, diode, and capacitors to store and transfer energy efficiently.
How do you calculate the duty cycle of an inverting buck-boost converter?
The duty cycle of an inverting buck-boost converter is calculated as D = Vout / (Vin + Vout), where Vin is the input voltage and Vout is the absolute value of the output voltage. For example, with an 18V input and 12V output, the duty cycle is 12/30 = 0.4 or 40%. The converter operates in buck mode when D is less than 0.5 and in boost mode when D is greater than 0.5.
How is the inductance calculated for an inverting buck-boost converter?
The inductance for an inverting buck-boost converter is calculated as L = (D / (fsw × Iripple)) × Vin, where D is the duty cycle, fsw is the switching frequency, Iripple is the maximum ripple current, and Vin is the input voltage. For example, with D = 0.4, fsw = 200 kHz, Iripple = 200 mA, and Vin = 18 V, the inductance is 180 µH.
What is the difference between inverting and non-inverting buck-boost converters?
The main difference is the output voltage polarity. An inverting buck-boost converter changes the polarity of the output voltage (positive input becomes negative output), while non-inverting designs like SEPIC or Ćuk converters maintain the same polarity. Both can step up or step down voltage, but the inverting topology is simpler and uses fewer components for applications requiring a negative voltage rail.
What are common applications of inverting buck-boost converters?
Inverting buck-boost converters are commonly used in applications that require a negative voltage rail from a positive supply, such as operational amplifier circuits, audio amplifiers, LCD bias supplies, automotive electronics, battery-powered devices, and industrial sensor systems. They are also used in power supply designs where ground-referenced negative voltages are needed.
What are the advantages and disadvantages of buck-boost converters?
Advantages of buck-boost converters include high efficiency, compact size, ability to both step up and step down voltage, and support for inverting output polarity. Disadvantages include generation of electromagnetic interference (EMI), complex duty cycle control, lower efficiency during extreme duty cycles, and higher output voltage ripple compared to dedicated buck or boost converters.
How do you choose the switching frequency for an inverting buck-boost converter?
Choosing the switching frequency involves a trade-off between component size and efficiency. Higher frequencies (500 kHz to 2 MHz) allow smaller inductors and capacitors but increase switching losses. Lower frequencies (50 to 200 kHz) reduce switching losses but require larger magnetic components. Typical designs use 100 to 500 kHz for a good balance between size and efficiency.