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Adjustable 1 to 32V, 5A DC Power Supply Using LM338

This adjustable DC power supply provides 1 to 32V output at up to 5A current using the LM338 voltage regulator. Voltage adjustment is achieved with a 5K multi-turn potentiometer, allowing precise control. The circuit is designed for robust operation with proper heatsinking and protection.

Power Supply Requirements

  • Use a 50-100W transformer as the main power source.
  • The AC voltage from the transformer should be less than 25V AC to the rectifier.
  • Diodes rated 10-15A are required for the rectifier bridge to handle full load current.
  • Use external power supplies for sensitive loads like LCD panels to avoid voltage ripple.

Key Components

  • LM338 Voltage Regulator: Adjustable 5A linear regulator for stable DC output.
  • 5K Multi-turn Potentiometer: Allows precise adjustment of output voltage from 1V to 32V.
  • Heatsink with Thermal Paste: Ensures LM338 stays cool under high load.
  • Rectifier Diodes (10-15A): Convert AC from transformer to DC for the regulator.
  • Filter Capacitors: Smooth the DC output for low ripple.
  • Optional Output Capacitors: Improve transient response for sensitive loads.

Circuit Operation

  • The transformer steps down mains AC voltage to below 25V AC.
  • Diodes form a bridge rectifier, converting AC to unregulated DC.
  • Filter capacitors smooth the rectified voltage before feeding the LM338 regulator.
  • The LM338 provides adjustable output voltage set via the 5K multi-turn potentiometer.
  • At full load, proper heatsinking with thermal paste prevents overheating and maintains regulator stability.
  • External sensitive loads, like LCD panels, should receive power from dedicated regulated sources to avoid noise or voltage fluctuations.

Key Features

  • Adjustable output from 1V to 32V DC
  • Maximum current up to 5A
  • High-precision voltage adjustment with 5K multi-turn potentiometer
  • Robust design with 10-15A diodes and adequate transformer rating (50–100W)
  • Thermal protection with heatsink and thermal paste
  • Suitable for powering a wide range of electronics and small devices

Construction Notes

  • Mount the LM338 securely on a heatsink using thermal paste to ensure proper heat transfer.
  • Verify diode ratings and orientation to handle maximum current safely.
  • Use short, thick wires for high-current connections to reduce voltage drops.
  • Check transformer AC voltage under load; it must remain below 25V AC to the regulator input.
  • For sensitive devices like LCD panels, use a separate low-ripple regulated supply to avoid interference.
  • Test the voltage range and current limit with a dummy load before connecting critical equipment.

Power supply 1-32 V 5A