Buck Converter Calculator
Design buck (step-down) DC-DC converters. Calculate inductor, capacitor values, and component ratings.
Calculator
How to Use This Calculator
This buck converter calculator helps you design step-down DC-DC power supplies by calculating the key component values for your specific requirements.
- Select a Common IC — Or enter your own input/output specifications
- Set Voltage and Current — Define input voltage, output voltage, and load current
- Choose Switching Frequency — Higher frequency = smaller components, but more losses
- Set Ripple Requirements — 30% inductor ripple and 50mV output ripple are typical
- Adjust Efficiency — Use 85% as starting point, adjust based on IC datasheet
- Click Calculate — Get component values and design recommendations
Buck Converter Theory
A buck converter is a DC-DC switching regulator that steps down voltage while stepping up current. It's more efficient than linear regulators because it switches rather than dissipating excess power as heat.
Basic Operation
- Switch ON: Current flows through inductor, storing energy
- Switch OFF: Inductor releases stored energy through diode
- Output Filter: Capacitor smooths the output voltage
Key Equations
Continuous vs Discontinuous Mode
This calculator designs for Continuous Conduction Mode (CCM), where inductor current never reaches zero. CCM provides better efficiency and easier control. The 30% ripple current target ensures CCM down to ~15% load.
Component Selection
Inductor Selection
| Parameter | Requirement | Why |
|---|---|---|
| Inductance | Calculated value ±20% | Controls ripple current |
| Saturation Current | > Peak current × 1.2 | Prevents core saturation |
| DC Resistance (DCR) | As low as possible | Reduces I²R losses |
| Core Material | Ferrite or powdered iron | Low core losses at frequency |
Output Capacitor Selection
| Type | ESR | Best For |
|---|---|---|
| MLCC (Ceramic) | Very Low (<10mΩ) | High frequency, low ripple |
| Polymer | Low (10-50mΩ) | Balance of cost and performance |
| Electrolytic | Higher (50-200mΩ) | Bulk capacitance, cost-sensitive |
Input Capacitor
The input capacitor handles high-frequency ripple current and must have low ESR. Use ceramic capacitors close to the IC. The calculator provides minimum capacitance; add more for margin.
Design Tips
Layout Best Practices
- Keep the switch node small to reduce EMI
- Place input capacitor close to VIN and GND pins
- Use wide traces for power paths (input, output, ground)
- Keep feedback resistors away from noisy switch node
- Use a ground plane on bottom layer
Frequency Selection
| 100-300 kHz | Larger inductor/caps, higher efficiency, lower EMI |
| 300-1000 kHz | Good balance of size and efficiency |
| >1 MHz | Smallest components, requires careful layout |
Efficiency Considerations
- Light Load: Efficiency drops due to switching losses
- Heavy Load: I²R losses in inductor and MOSFETs dominate
- High Vin/Vout Ratio: Diode losses increase (consider sync rectifier)
- High Frequency: Switching losses increase
Common Mistakes to Avoid
- Using inductors with saturation current too close to peak current
- Ignoring ceramic capacitor derating (X5R/X7R lose capacitance with voltage)
- Poor layout causing excessive EMI or instability
- Not accounting for efficiency when sizing input current
Frequently Asked Questions
Why is my calculated inductor value different from the datasheet?
IC datasheets often recommend specific inductors tested with that IC. Their values may differ due to different ripple current assumptions, optimized efficiency points, or specific operating conditions. Use the datasheet value as a reference but verify it meets your ripple requirements.
Can I use a larger inductor than calculated?
Yes, a larger inductor reduces ripple current and improves efficiency at heavy loads. However, it increases size, cost, and may slow down transient response. It also reduces efficiency at light loads.
What's the minimum load for CCM operation?
With 30% ripple current, CCM is maintained down to about 15% of rated load. Below that, the converter enters DCM (Discontinuous Conduction Mode). Many modern ICs handle both modes automatically.
How do I reduce output ripple further?
Add more output capacitance (especially low-ESR ceramic), use an LC post-filter, or increase switching frequency. Note that ceramic capacitor ESR dominates ripple at high frequencies.
Should I use synchronous or asynchronous rectification?
Synchronous (MOSFET instead of diode) is more efficient, especially at high output currents and low Vout. Asynchronous (diode) is simpler and cheaper, suitable for light loads or cost-sensitive designs.
Verify Your Component Selections
After calculating your component values, use Schemalyzer to verify your schematic design. Our AI-powered analysis catches common errors and suggests improvements.
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