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Optimization

Circuit Optimization Strategies

This page covers practical strategies for optimizing your VIC circuit design using the calculator. Learn how to achieve specific goals like maximizing Q, hitting a target frequency, or optimizing voltage magnification.

Optimization Goals

Different applications may prioritize different characteristics:

Goal Optimize For Trade-offs
Maximum Voltage High Q, matched resonance Narrower bandwidth, critical tuning
Stable Operation Moderate Q, wide bandwidth Lower peak voltage
Frequency Flexibility Lower Q, broader response Reduced magnification
Energy Efficiency Minimize losses (DCR, Rsol) May require larger components

Strategy 1: Maximizing Q Factor

Q determines voltage magnification and selectivity. To maximize Q:

Reduce Choke DCR:

  • Use larger wire gauge (lower AWG number)
  • Use copper instead of aluminum
  • Minimize wire length (fewer turns with higher-μ core)
  • Consider Litz wire for high frequencies

Reduce Solution Resistance:

  • Increase water conductivity slightly (add small amount of electrolyte)
  • Increase electrode area
  • Decrease electrode gap (but watch capacitance change)
  • Ensure good electrode contact

Increase L or Decrease C:

  • Higher L/C ratio raises Z₀ = √(L/C)
  • Q = Z₀/R, so higher Z₀ means higher Q
  • Must maintain same f₀ = 1/(2π√LC)

Q Factor Relationships:

Q = 2πf₀L/R = Z₀/R = √(L/C)/R

To double Q: halve R, or quadruple L (while quartering C to maintain f₀)

Strategy 2: Hitting Target Frequency

When you need a specific resonant frequency:

Approach A: Fixed L, Adjust C

  1. Design or select choke for desired L
  2. Calculate required C: C = 1/(4π²f₀²L)
  3. If Cwfc ≠ required C:
    • Add parallel capacitor if Cwfc is too low
    • Modify electrode geometry if adjustment is large

Approach B: Fixed C, Adjust L

  1. Measure or calculate WFC capacitance
  2. Calculate required L: L = 1/(4π²f₀²C)
  3. Design choke for that inductance

Approach C: Adjust Both

  1. Start with practical component ranges
  2. Use calculator to explore L/C combinations
  3. Choose combination that also optimizes Q

Fine-Tuning Frequency

Adjustment Effect on f₀ Typical Range
Add parallel capacitor Decreases f₀ 1-50 nF typical
Adjust core gap (if gapped) Changes L → changes f₀ ±20% L adjustment
Add/remove turns Changes L significantly L ∝ N²
Change water level Changes C → changes f₀ Proportional to area

Strategy 3: Matching Primary to Secondary

For maximum energy transfer, align primary and secondary resonances:

Exact Match (f₀pri = f₀sec):

  • Maximum voltage transfer at resonance
  • Narrow combined response
  • Requires precise tuning

Slight Offset (5-10% difference):

  • Broader frequency response
  • More tolerant of drift
  • Slightly reduced peak transfer

Calculator Approach:

  1. Design secondary (L2 + WFC) first—this is usually more constrained
  2. Calculate secondary f₀
  3. Select C1 to tune primary to match: C1 = 1/(4π²f₀²L1)
  4. Verify with simulation

Strategy 4: Optimizing for Available Components

When working with existing components:

Step 1: Characterize What You Have

  • Measure L of available chokes
  • Measure C of your WFC
  • Note DCR values

Step 2: Calculate Natural Resonance

f₀ = 1/(2π√LC)

This is where your circuit wants to resonate.

Step 3: Evaluate Performance

  • Is f₀ in your driver's range?
  • Is Q acceptable at this frequency?
  • Are there SRF issues?

Step 4: Adjust as Needed

  • Add tuning capacitor if f₀ is too high
  • Consider different choke if f₀ is way off
  • Accept the natural f₀ if performance is good

Sensitivity Analysis

Understanding how sensitive your design is to variations:

Parameter Change Effect on f₀ Effect on Q
L +10% f₀ -5% Q +5%
C +10% f₀ -5% Q -5%
R +10% No change Q -10%
Temperature +10°C f₀ +2% (due to εr drop) Q +5% (Rsol drops)

Common Optimization Mistakes

❌ Chasing Extreme Q

Very high Q makes the circuit sensitive to drift and hard to tune. Q of 50-100 is often more practical than Q > 200.

❌ Ignoring SRF

A design that works on paper fails if operating frequency is too close to SRF. Always check this!

❌ Forgetting Water Resistance

Solution resistance often dominates losses. Pure distilled water has higher resistance than you might expect.

❌ Not Accounting for Parasitics

Real circuits have stray inductance and capacitance. Leave margin for these effects.

❌ Over-constraining the Design

If you fix too many parameters, you may have no degrees of freedom for optimization.

Optimization Checklist

  1. ☐ Define your primary optimization goal
  2. ☐ Identify fixed constraints (available components, frequency range)
  3. ☐ Calculate baseline performance
  4. ☐ Identify largest loss contributor (DCR vs Rsol)
  5. ☐ Make targeted improvements to dominant loss
  6. ☐ Verify SRF is >3× operating frequency
  7. ☐ Check that primary/secondary are reasonably matched
  8. ☐ Run simulation to verify improvements
  9. ☐ Consider sensitivity to variations
  10. ☐ Document final design parameters

Remember: Optimization is iterative. The calculator makes it easy to try variations quickly. Don't expect to find the optimal design on the first try—explore the design space!

Next: Interpreting Calculation Results →

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