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Buck-Boost Converter Calculator

Design Buck-Boost Converter (step-up/down) DC-DC converters for power electronics applications

Enter Design Parameters

Buck-Boost Converter Circuit

Buck-Boost Converter Circuit

Input Voltage (V_in):

Output Voltage (V_out):

Output Power (P_out) [W]:

Inductor Ripple (%):

Switching Frequency (Hz):

Enter all parameters and click Calculate

Buck-Boost Key Equations:
Duty Cycle: D = |V_out| / (|V_out| + V_in)
Output Current: I_out = P_out / |V_out|
Inductor Ripple: ΔI_L = (Ripple %) × I_in
Inductor Value: L = (V_in × D) / (ΔI_L × f_sw)
Capacitor Value: C = ΔI_L / (8 × f_sw × ΔV_out)
Load Resistor: R = |V_out| / I_out

Buck-Boost Converter Examples

Example 1: Step-Up (24V to -48V)

Given: V_in=24V, V_out=-48V, P_out=240W, Ripple=20%, f_sw=50kHz

Duty Cycle: D = 48/(48+24) = 0.6667 (66.67%)
Output Current: I_out = 240/48 = 5A
Input Current: I_in = (240/24) = 10A
Inductor Ripple: ΔI_L = 0.2×10 = 2A
Inductor: L = (24×0.6667)/(2×50000) = 160μH
Capacitor: C ≈ 6.25μF (ΔV_out = 4.8V)
Load Resistor: R = 48/5 = 9.6Ω

Example 2: Step-Down (36V to -12V)

Given: V_in=36V, V_out=-12V, P_out=60W, Ripple=15%, f_sw=100kHz

Duty Cycle: D = 12/(12+36) = 0.25 (25%)
Output Current: I_out = 60/12 = 5A
Input Current: I_in = 60/36 = 1.67A
Inductor Ripple: ΔI_L = 0.15×1.67 = 0.25A
Inductor: L = (36×0.25)/(0.25×100000) = 360μH
Capacitor: C ≈ 0.78μF (ΔV_out = 1.2V)
Load Resistor: R = 12/5 = 2.4Ω

Example 3: High Power Conversion (48V to -72V)

Given: V_in=48V, V_out=-72V, P_out=500W, Ripple=10%, f_sw=75kHz

Duty Cycle: D = 72/(72+48) = 0.6 (60%)
Output Current: I_out = 500/72 = 6.94A
Input Current: I_in = 500/48 = 10.42A
Inductor Ripple: ΔI_L = 0.1×10.42 = 1.04A
Inductor: L = (48×0.6)/(1.04×75000) = 369μH
Capacitor: C ≈ 1.73μF (ΔV_out = 7.2V)
Load Resistor: R = 72/6.94 = 10.37Ω