Getting Started with PSU Designer II: Tips for Power Supply DesignDesigning reliable power supplies requires the right tools and a clear workflow. PSU Designer II is a specialized application aimed at simplifying power-supply design — from selecting topology and components to simulating performance and preparing PCB layouts. This article walks through the essentials for beginners and intermediate users: setting up a project, choosing topologies, component selection, simulation best practices, thermal and EMI considerations, PCB layout tips, and verification steps before manufacturing.
What is PSU Designer II?
PSU Designer II is a focused design environment for switching and linear power supplies. It integrates topology selection, component databases, circuit simulation, and manufacturing-ready outputs. The tool accelerates iteration by automating many calculations (like control-loop compensation and magnetic design) and giving quick visual feedback on performance metrics such as efficiency, ripple, transient response, and thermal limits.
1. Project setup and initial choices
Starting a new design in PSU Designer II is about defining the problem precisely.
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Define the specifications:
- Input voltage range (min, max)
- Output voltage(s) and current(s)
- Efficiency targets
- Regulation and ripple requirements
- Load types (constant, pulsed, dynamic)
- Size, cost, and thermal constraints
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Choose the right topology:
- For single-output, low-voltage, high-current: buck converters.
- For step-up needs: boost converters.
- For multiple isolated outputs: flyback or forward converters.
- For high power, isolated rails: full-bridge or half-bridge.
- Linear regulators (LDOs) for noise-sensitive, low-dropout needs.
PSU Designer II usually provides templates for common topologies — use them as starting points, then adjust parameters.
2. Sizing power components
Accurate component sizing prevents surprises later.
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MOSFETs and switches:
- Prioritize on-resistance (RDS(on)) and gate charge (Qg) trade-off — low RDS(on) reduces conduction losses but often increases gate charge and switching losses.
- Check SOA and thermal resistance (RθJA). Use MOSFETs with adequate voltage margin (typically 20–40% above maximum input).
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Inductors:
- Use the tool’s inductor calculator. Key inputs: ripple current (% of full load), switching frequency, and core material.
- Watch for saturation current (Isat) — choose Isat > peak inductor current.
- Consider DCR for conduction loss estimation.
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Output capacitors:
- Account for ESR and capacitance vs. voltage and temperature. Low-ESR electrolytics or ceramics (with proper bulk capacitance) reduce ripple.
- For high ripple current, check capacitor ripple-current rating and thermal behavior.
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Diodes:
- For synchronous designs, MOSFET body diodes often suffice. For non-synchronous or high-voltage use, choose fast-recovery or Schottky diodes.
- Check reverse-recovery characteristics at the switching speed.
PSU Designer II’s component database and loss calculators help compare parts quickly.
3. Control loop and compensation
Stable regulation is essential.
- Select a control architecture the tool supports (voltage-mode, current-mode, peak-current, hysteretic, etc.).
- Use the loop analysis module to derive the plant transfer function. PSU Designer II can propose compensation networks (type II/III) based on phase margin and crossover frequency targets.
- Typical targets:
- Phase margin: 45–60°
- Gain crossover: around one-fifth to one-tenth of switching frequency for voltage-mode designs
- Verify with step-load simulations (load transients) and adjust compensation to meet overshoot and settling-time specs.
4. Simulation best practices
Simulations reveal issues before hardware.
- Start with idealized parts to validate topology and control concept, then replace with real component models (SPICE, vendor models).
- Run DC sweep, transient, and small-signal analyses:
- Transient: check startup behavior, load-step response, and short-circuit behavior.
- Thermal: simulate losses distributed in MOSFETs, diodes, inductors, and resistors.
- EMI-related: simulate switching edges and node voltages to estimate conducted emissions risk.
- Perform corner-case simulations: input undervoltage/overvoltage, cold-start, hot-swap, extreme load steps.
PSU Designer II lets you batch-run simulations with parameter sweeps (frequency, load, temperature) to explore robustness.
5. Thermal, mechanical, and EMI considerations
Real-world reliability depends on thermal and EMI control.
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Thermal:
- Map losses to PCB/parts and estimate junction temperatures using RθJA/RθJA values. Aim to keep junction temps well below maximum rated (commonly Tj < 125–150°C).
- Consider heatsinking, copper pours, and airflow in the design constraints within PSU Designer II.
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EMI:
- Fast switching edges raise EMI; manage by adjusting gate resistances, snubbers, or slowing edges only as needed.
- Use input/output LC filters for conducted emissions; simulate filter interaction with the converter to prevent instability.
- Ensure proper return paths and minimize loop areas for high di/dt currents.
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Mechanical:
- Plan component placement for heat sources and ensure creepage/clearance for high-voltage isolation (flybacks, mains designs).
6. PCB layout tips specific to power supplies
Layout is as important as circuit selection.
- Minimize high-current loop area: place input caps close to the switching device and path to the inductor.
- Separate power and signal grounds; use a single-point or controlled star connection for sensitive ground references (feedback, sense resistors).
- Place sense resistors and feedback components close to the controller IC to reduce noise pickup.
- Use wide copper pours and multiple vias for current paths and thermal relief.
- Keep switching nodes (hot nodes) away from sensitive traces and analog circuitry.
- Route high-speed traces with consistent impedance where needed and avoid 90° bends in current-carrying traces.
- For isolated designs, provide creepage and clearance; route primary and secondary grounds carefully and place transformers to minimize coupling of stray fields.
PSU Designer II often integrates layout rules and can export step files or PCB netlists for ECAD tools — use these to enforce mechanical and spacing requirements.
7. Test plan and verification before manufacture
A structured test plan prevents field failures.
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Create a test checklist:
- Power-up and no-load behavior
- Regulation under nominal load
- Load-step and recovery tests
- Efficiency across load range
- Thermal imaging under full load
- Short-circuit protection and hiccup-mode tests
- EMI pre-compliance checks (conducted and radiated)
- Burn-in tests for early-life failures
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Prototype iterations:
- Start with a bench prototype on a plated prototype PCB. Use scope probes at designated test points.
- Instrument with thermocouples and current probes. PSU Designer II’s reports can guide which nodes to monitor.
8. Common pitfalls and quick fixes
- Excessive EMI: add RC snubbers, slow MOSFET edges slightly, or add common-mode chokes.
- Instability: revisit compensation values, reduce parasitic impedances, add feedforward or modify crossover frequency.
- Overheating: improve copper, add airflow/heatsinks, or choose lower-loss components.
- High ripple: increase output capacitance, lower ESR, or adjust inductor ripple target.
9. Leveraging PSU Designer II effectively
- Use templates and examples as starting points, not final designs.
- Keep the component database updated with vendor models; PSU Designer II’s accuracy depends on correct models.
- Automate parameter sweeps early in the design process to find robust operating regions.
- Document design decisions within the project (reasons for topology, component trade-offs, and test results).
Conclusion
PSU Designer II speeds up power-supply development by combining topology templates, component libraries, simulation, and layout guidance. Success comes from precise specification, careful component selection, proper loop compensation, disciplined layout, and thorough testing. Use the tool to iterate quickly, validate across corner cases, and ensure thermal and EMI performance before committing to production.
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