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13.8V 45A High-Current Power Supply Using 7812 and TIP26C

This high-current DC power supply provides a regulated 13.8V output at up to 45A. It uses a 18V-0-18V transformer, a 7812 voltage regulator for voltage reference, and five TIP26C power transistors in parallel to handle high current. A large 45,000µF filter capacitor ensures smooth and stable DC output.

Power Supply Requirements

  • Input: 220V/110V AC mains stepped down by a 18V-0-18V transformer.
  • Output: Regulated 13.8V DC at 45A.
  • High-capacity filter: 45,000µF electrolytic capacitor to reduce ripple under full load.
  • Heatsinking required for TIP26C transistors and 7812 regulator.

Key Components

  • 7812 Voltage Regulator: Provides a stable 12V reference for the control circuit.
  • TIP26C Power Transistors (x5): Operate in parallel as pass devices to deliver high current to the load.
  • 18V-0-18V Transformer: Steps down mains AC to approximately 36V AC center-tapped for rectification.
  • Bridge Rectifier: Converts AC from the transformer to unregulated DC.
  • Filter Capacitor 45,000µF: Smooths the DC voltage and minimizes ripple at high current.
  • Resistors: Set the biasing and current sharing among TIP26C transistors.

Circuit Operation

  • The transformer steps down 220V AC mains to 18-0-18V AC, providing center-tapped AC for full-wave rectification.
  • The bridge rectifier converts AC to unregulated DC voltage.
  • The 7812 regulator provides a stable 12V reference for controlling the TIP26C transistors.
  • The five TIP26C transistors in parallel act as pass elements, sharing the load to provide up to 45A to the output.
  • The 45,000µF filter capacitor smooths the DC voltage, keeping ripple low even under high current draw.
  • Output voltage is regulated at approximately 13.8V, suitable for battery charging or other high-current DC applications.

Key Features

  • High-current output: 13.8V at 45A
  • Stable voltage regulation using 7812 reference and TIP26C pass transistors
  • Large filter capacitor (45,000µF) ensures low ripple
  • Transformer-based design for isolation and step-down from mains
  • Suitable for charging large lead-acid batteries or powering high-current DC loads
  • Current sharing among multiple TIP26C transistors ensures reliability

Construction Notes

  • Mount all TIP26C transistors and the 7812 regulator on large heatsinks with thermal paste to prevent overheating.
  • Ensure proper current sharing among TIP26C transistors using emitter resistors.
  • Use thick wires or copper busbars for high-current output connections to minimize voltage drops and heating.
  • Check the bridge rectifier and filter capacitor voltage/current ratings for safety under full load.
  • Test the power supply gradually under increasing load before connecting batteries or sensitive devices.
  • Include fuses or circuit breakers for overload and short-circuit protection.

Power Supply 13 volts 45 amperes