Inverting Buck-Boost Converter Calculator
Calculate duty cycle and inductance for inverting buck-boost DC-DC converters
Converter Parameters
DC input voltage to the converter
Desired DC output voltage (inverted polarity)
MOSFET switching frequency
Maximum inductor current ripple
Calculation Results
Duty Cycle Formula: D = Vout / (Vin + Vout)
Inductance Formula: L = D × Vin / (fsw × Iripple)
Output Polarity: Inverted relative to input voltage
Converter Analysis
Example Calculation
Buck-Boost Converter Design
Input Voltage: Vin = 18V
Output Voltage: Vout = -12V
Switching Frequency: fsw = 200kHz
Ripple Current: Iripple = 200mA
Step-by-Step Calculation
D = |Vout| / (|Vin| + |Vout|) = 12 / (18 + 12) = 0.4 = 40%
L = D × Vin / (fsw × Iripple) = 0.4 × 18 / (200×10³ × 0.2) = 180μH
Result: D = 40% (Buck Mode), L = 180μH
Converter Components
MOSFET Switch
Controls power transfer
Switching transistor Q1
Inductor
Energy storage element
L1 - calculated value
Freewheeling Diode
Current flow control
D1 - rectifier diode
Capacitors
Input/output filtering
Cin & Cout
Design Tips
Output voltage polarity is inverted
Can step up or step down voltage
Higher efficiency than linear regulators
Consider EMI and control complexity
Understanding Inverting Buck-Boost Converters
What is an Inverting Buck-Boost Converter?
An inverting buck-boost converter is a DC-DC power converter that can either step up (boost) or step down (buck) the input voltage while inverting its polarity. Unlike non-inverting converters, the output voltage has opposite polarity to the input.
Key Characteristics
- •Inverted output voltage polarity
- •Can step up or step down voltage
- •Single inductor energy storage
- •Continuous or discontinuous conduction
Key Formulas
D = |Vout| / (|Vin| + |Vout|)
L = D × Vin / (fsw × Iripple)
- D: Duty cycle (0 to 1)
- Vin, Vout: Input and output voltages
- L: Inductance (H)
- fsw: Switching frequency (Hz)
- Iripple: Maximum ripple current (A)
Note: Buck mode (D < 0.5), Boost mode (D > 0.5)
Applications
- •Negative Voltage Generation: Creating negative rails from positive input
- •Dual Polarity Supplies: Bipolar power supply systems
- •Battery Powered Systems: Wide input voltage range applications
- •Automotive Electronics: Variable battery voltage systems
Advantages vs Disadvantages
Advantages:
- • High efficiency (80-95%)
- • Compact design
- • Wide voltage conversion range
- • Inverted output capability
Disadvantages:
- • EMI generation
- • Complex control circuits
- • Discontinuous input current
- • Lower efficiency at extreme duty cycles