Commercially available voltage regulator IC’s can deliver up to 1A output current. For example 78xx series regulators are available in different voltage ratings, but in any case the current should not exceed 1A.

The transistor Q1 (2N 29055) used here has 5A current capacity. The resistor R1 is used to keep the current through regulator IC below 300mA. When the current through R1 increases the base current of Q1 (2N 29055) also increases &the load required load current flows through this transistor. By this way a current greater than the capacity of the regulator IC can be delivered to the load. The C1 is used to filter the ripples off the rectifier output.

Circuit diagram with Parts list.



  1. Assemble the circuit on good quality PCB.
  2. T1 can be  a 230V primary,15V/1A secondary , step down  transformer.
  3. If 1 A bridge is not available,make one using four 1N 4007 diodes.
  4. The series regulator IC should be selected according to the desired output voltage.
  • IC 7805 for 05V
  • IC 7806 for 06V
  • IC 7809 for 09V
  • IC 7812 for 12V


  1. hi can i get simple schematic diagram of switched mode power supply

  2. willywilly

    the Q1 is mj29055???????????????????
    is it mj 2955 or 2n 3055 ????????????


  3. Seetharaman

    Great idea for increasing the current capability of 3 pin regulators. Kindly mount the series pass transistor and the 3 pin regulator ic on the same heat sink ofcourse with suitable insulating washers, to avail the built in thermal protection of the 3pin IC

  4. The diagram for your regulated power expander circuit is wrong.

    The bridge rectifier D1 is drawn the wrong way round. Rotate it 90 degrees clockwise and it’ll work.

    Regards, Dave.

    • Mistake from my part.
      I have corrected it.

      Thanks for pointing out.

  5. Dear Sir,
    Regulator for a model airplane.
    1) The input voltage will be 7.4 to 11.3 volt using a Lipo or Nicad, Or Lifi battery.
    2) Output should be exactly 5 volt.
    3) Max current draw will be 5 amps/7 amps.

    Please let me know if i can use a redunct power suppy for inputs, that is connect two Inputs of 7.4 volt and output 6 volt.

    Your expert inputs/ideas will be appreciated.

    With Regards
    Rajesh N