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Inverting Buck-Boost Converter

Generates negative output voltage from positive input. Duty cycle D = |Vout|/(Vin + |Vout|). Essential for dual-rail supplies, op-amps, and audio amplifiers. Operates in CCM or DCM.

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D = |Vout|/(Vin + |Vout|) for duty cycle Output voltage magnitude is negative Inductor sees Vin + |Vout| during switch off CCM requires L > L_crit

Key quantities
D = |Vout|/(Vin+|Vout|)
Duty Cycle
Key relation
Pout = |Vout| ร— Iout
Output Power
Key relation
ฮ”IL = Vinร—D/(fร—L)
Inductor Ripple
Key relation
V = Vin + |Vout|
Switch Stress
Key relation

Ready to run the numbers?

Why: Inverting buck-boost provides negative rails from single positive supply. Used in op-amp circuits, audio amplifiers, and systems requiring negative bias. CCM/DCM boundary affects component sizing.

How: Switch duty cycle controls output magnitude. Inductor stores energy during on-time, transfers to output during off-time. Critical inductance ensures CCM operation.

D = |Vout|/(Vin + |Vout|) for duty cycleOutput voltage magnitude is negative
Sources:IEEE Power Electronics SocietyTexas Instruments Power Design

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Design Buck-BoostEnter input/output voltage and current

Input Parameters

โš ๏ธInput voltage must be a positive number
Input voltage must be a positive number

For educational and informational purposes only. Verify with a qualified professional.

๐Ÿ”ฌ Physics Facts

โšก

Duty cycle D = |Vout|/(Vin + |Vout|) for inverting buck-boost

โ€” Power Electronics

๐Ÿ“Š

Output power Pout = |Vout| ร— Iout; efficiency typically 80-95%

โ€” Converter Design

๐Ÿ”‹

Inductor ripple ฮ”IL = Vin ร— D / (f ร— L) in CCM

โ€” Inductor Selection

๐Ÿ“

Switch stress: V = Vin + |Vout|, must handle full voltage

โ€” Component Rating

What is an Inverting Buck-Boost Converter?

An inverting buck-boost converter (also known as a negative buck-boost converter) is a DC-DC power converter that generates a negative output voltage from a positive input voltage. Unlike standard buck or boost converters, this topology produces an output voltage that is inverted in polarity relative to the input, making it essential for applications requiring negative voltage rails such as op-amp power supplies, audio amplifiers, and signal processing circuits.

Polarity Inversion

Inverting buck-boost converters produce negative output voltage from positive input, enabling dual-rail power supplies.

Key Feature:

Vout = -|Vout| (negative)

Switching Operation

Uses a switch and diode to alternately charge the inductor from input and discharge to output capacitor, creating inverted polarity.

Operation:

  • Switch ON: Inductor charges
  • Switch OFF: Energy inverted to output

Common Applications

Used in op-amp power supplies, audio amplifiers, signal processing, test equipment, and dual-rail systems.

Examples:

  • Negative rail generators
  • Audio amplifier supplies
  • Op-amp dual rails

How Does an Inverting Buck-Boost Converter Work?

Inverting buck-boost converters operate by rapidly switching a power MOSFET on and off, controlling energy flow through an inductor. During switch ON-time, the inductor charges from the input. During switch OFF-time, the inductor discharges through a diode to the output capacitor, creating a negative output voltage. The duty cycle determines the output voltage magnitude according to |Vout| = Vin ร— D/(1-D).

๐Ÿ”ฌ Operating Principles

Switch ON (Ton)

  1. 1MOSFET turns ON, connecting input to inductor
  2. 2Current through inductor increases linearly
  3. 3Energy stored in inductor magnetic field
  4. 4Output capacitor supplies load current

Switch OFF (Toff)

  • MOSFET turns OFF, disconnecting input
  • Inductor current flows through diode to output
  • Polarity inversion creates negative output
  • Output capacitor charges with inverted polarity

When to Use an Inverting Buck-Boost Converter

Inverting buck-boost converters are essential when you need to generate negative voltage rails from positive supplies. They're ideal for dual-rail power supplies, op-amp circuits, audio amplifiers, and any application requiring negative bias voltages.

Dual-Rail Power Supplies

Essential for op-amp circuits, audio amplifiers, and analog signal processing requiring both positive and negative rails.

Benefits:

  • ยฑ12V, ยฑ15V rails
  • Symmetrical supplies
  • Op-amp compatibility

Audio Amplifiers

Power audio amplifiers require negative supply rails for proper biasing and signal swing capabilities.

Applications:

  • Power amplifiers
  • Preamplifiers
  • Headphone amps

Test Equipment

Laboratory instruments, oscilloscopes, and measurement equipment often require negative bias supplies.

Benefits:

  • Precision biasing
  • Signal processing
  • RF circuits

Inverting Buck-Boost Converter Calculation Formulas

Understanding inverting buck-boost converter formulas is essential for power electronics design. These formulas relate duty cycle, inductor and capacitor values, ripple, and efficiency for negative voltage generation.

๐Ÿ“Š Core Inverting Buck-Boost Formulas

Duty Cycle (D)

D=fracโˆฃVoutโˆฃVin+โˆฃVoutโˆฃD = \\frac{|V_{out}|}{V_{in} + |V_{out}|}

Duty cycle determines the output voltage magnitude. It's the ratio of switch ON-time to the total switching period.

Output Voltage Magnitude (|Vout|)

โˆฃVoutโˆฃ=VintimesfracD1โˆ’D|V_{out}| = V_{in} \\times \\frac{D}{1-D}

Output voltage magnitude equals input voltage multiplied by duty cycle divided by (1-D). The actual output is negative: Vout = -|Vout|.

Inductor Current Ripple (ฮ”IL)

DeltaIL=fracVintimesDfL\\Delta I_L = \\frac{V_{in} \\times D}{fL}

Inductor current ripple depends on input voltage, duty cycle, switching frequency, and inductance. Lower ripple requires larger inductance.

Output Voltage Ripple (ฮ”Vout)

DeltaVout=fracDeltaILtimesDfC+DeltaILtimesESR\\Delta V_{out} = \\frac{\\Delta I_L \\times D}{fC} + \\Delta I_L \\times ESR

Output voltage ripple has two components: capacitive ripple (from capacitor charging/discharging) and ESR ripple (from capacitor equivalent series resistance).

Critical Inductance (Lcrit)

Lcrit=fracVintimesD2Ioutf(1โˆ’D)L_{crit} = \\frac{V_{in} \\times D}{2I_{out}f(1-D)}

Minimum inductance required for continuous conduction mode (CCM). Below this value, the converter operates in discontinuous mode (DCM).

Efficiency (ฮท)

eta=fracPoutPin=fracPoutPout+Ploss\\eta = \\frac{P_{out}}{P_{in}} = \\frac{P_{out}}{P_{out} + P_{loss}}

Efficiency is the ratio of output power to input power. Losses include switch, diode, inductor, and capacitor losses.

Frequently Asked Questions (FAQ)

What is the difference between an inverting buck-boost and a standard buck-boost converter?

An inverting buck-boost converter produces a negative output voltage from a positive input, while a standard buck-boost maintains the same polarity. The inverting topology is essential for dual-rail power supplies where both positive and negative voltages are needed, such as in op-amp circuits and audio amplifiers.

How do I choose the right switching frequency for my inverting buck-boost converter?

Higher switching frequencies (200-500 kHz) allow smaller inductors and capacitors but increase switching losses. Lower frequencies (50-100 kHz) improve efficiency but require larger components. Choose based on your size constraints, efficiency requirements, and cost considerations. Most applications use 100-300 kHz as a good compromise.

What causes voltage ripple in an inverting buck-boost converter?

Voltage ripple has two main components: capacitive ripple from the output capacitor charging/discharging (proportional to inductor current ripple and duty cycle), and ESR ripple from the capacitor's equivalent series resistance. To minimize ripple, use larger capacitance, lower ESR capacitors, higher switching frequency, or larger inductance to reduce current ripple.

When should I use CCM vs DCM operation mode?

Continuous Conduction Mode (CCM) is preferred for higher power applications (>1W) as it provides lower peak currents, better efficiency, and smaller output ripple. Discontinuous Conduction Mode (DCM) is suitable for low-power applications (<0.5W) where smaller inductors are acceptable and load current is light. CCM requires larger inductance but offers better performance.

How do I calculate component stress for switch and diode selection?

The switch (MOSFET) must handle voltage stress equal to Vin + |Vout| and peak current equal to peak inductor current. The diode must handle the same voltage stress and average current equal to output current. Always select components with at least 20% margin above calculated stress values for reliability and safety.

What safety considerations are important for high-voltage inverting buck-boost converters?

For outputs above 48V (HIGH VOLTAGE), ensure proper isolation, use safety-rated capacitors, implement overvoltage protection, and follow electrical safety standards. High-voltage designs require careful PCB layout with adequate creepage and clearance distances. Consider using isolated gate drivers and protection circuits to prevent hazards.

Can I use an inverting buck-boost converter for battery-powered applications?

Yes, inverting buck-boost converters are excellent for battery-powered applications requiring negative rails. They can operate efficiently from battery voltages (3-12V) to generate negative supplies for op-amps and audio circuits. Choose components optimized for low quiescent current and high efficiency at light loads to maximize battery life.

Official Data Sources

This calculator uses verified data from authoritative sources in power electronics and electrical engineering:

IEEE Power Electronics Society

Professional power electronics standards and publications

Last Updated: 2026-02-01

Power Electronics Handbook - Rashid

Authoritative power electronics reference

Last Updated: 2025-01-01

Texas Instruments Power Design Resources

Power converter design tools and application notes

Last Updated: 2026-02-01

Analog Devices Power Management

Power management ICs and design resources

Last Updated: 2026-02-01

โš ๏ธ Disclaimer

This calculator is provided for educational and design assistance purposes only. Results are based on ideal component models and theoretical calculations. Actual performance may vary due to:

  • Component tolerances and manufacturing variations
  • Parasitic effects (PCB trace resistance, inductance, capacitance)
  • Temperature effects on component values
  • Non-ideal switching behavior and losses
  • EMI/EMC considerations and layout effects

For production designs: Always verify calculations with SPICE simulations, prototype testing, and consult component manufacturer datasheets. High-voltage designs (>48V) require additional safety considerations and compliance with electrical safety standards. This tool does not replace professional engineering judgment or safety analysis.

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