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How to build a cheap 3A regulated power supply

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This is a design for a cheap high current power supply, with a small parts list.


  • Voltage: 1.25-20V
  • Max Current: ~3A
    • varies depending on output voltage. Max current is larger than 2A and smaller than 4.5A, if proper transformer is used.
  • Internal current limit
  • Internal short circuit protection
  • Internal temperature compensation
  • Good Line regulation, load regulation, and ripple rejection


  • It does not go to zero, the lowest voltage is 1.25V
  • Current limit is different at different voltages.
    • At low voltages the IC limits the current. See Fig. 1
    • At high voltages the transformer limits the current, by saturating



  • 1 - LM350 - 3 Amp adjustable Regulator
    • List of compatible replacements: LM150, LM150K, LM350, LM350A, LM350K
  • 1 - Bridge Rectifier
    • I used a RBV-1506 7.5A Bridge Rectifier, because i had one. You can use any Bridge Rectifier greater than 4.5A
    • List of compatible bridge rectifiers:
    • Or you can make one using 4 rectifiers rated greater than 3A
  • 2 - 1N4002 rectifier diode
    • List of compatible replacements: 1N4003, 1N4004
  • Capacitors
    • 2 - 1μF ceramic capacitor
    • 1 - 2200μF electrolytic capacitor
    • 1 - 1000μF electrolytic capacitor
  • Resistors
    • 1 - 220kΩ (optional with neon lamp, not needed if lamp has an internal resistor)
    • 1 - 220Ω
    • 1 - 2.5kΩ potentiometer
  • Large heat sink for the LM350 IC
  • Heat sink compound
  • Neon lamp
    • This is optional. Used to indicate power on. If lamp has an internal resistor you do not need R1
  • SPST switch
    • Most single-pole single-throw (SPST) switches will work. Needs to handle 1A and 120V or greater
  • Transformer
    • 120V to 20V RMS
    • 50W recommended, if your get lower your current limit will be lower at higher voltages, due to transformer saturation

Components listEdit

  • R1: 220kΩ (optional with neon lamp, not needed if lamp has an internal resistor)
  • R2: 220Ω
  • R3: 2.5kΩ potentiometer
  • C1: 2200μF capacitor
  • C2: 1μF ceramic capacitor
  • C3: 10μF capacitor (optional)
  • C4: 1μF ceramic capacitor
  • C5: 1000μF capacitor
  • D1: 1N4002 rectifying diode (optional, protection)
  • D2: 1N4002 rectifying diode (optional, required if using C3)
  • T1: 1:6 transformer 50W
  • S1: SPST switch
  • NL1: neon lamp (optional)
  • U1: full-wave rectifier bridge
  • U2: LM350 voltage regulator
  • Large heat sink
  • Box




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