Here is the circuit diagram of a 30V/3A adjustable regulator using the LM723 IC from the National Semiconductors. LM723 is an integrated series regulator whose output voltage can be adjusted between 2V and 37V. The IC by itself can deliver an output current of 150mA and the maximum input voltage to the IC is 40V.
Here 3A output current is attained by adding a pass transistor (Q1) to the ICs output. The pass transistor used here is a Darlington transistor MJ3001. The internal reference voltage of the IC is 7.15V and it is available at pin6. POT R1 can be used to adjust the output voltage.
Circuit diagram.


  • Assemble the circuit on a good quality PCB.
  • T1 can be a 230V primary, 25V secondary, 5A step down transformer.
  • Q1 must be fitted on a proper heat sink.
  • Output voltage can be adjusted by using the POT R1.



  1. hi setharaman please replay to the comment below

    • seetharaman

      Pin no 2 & 3 are for current sensesense, it is correct.

  2. hi setharaman,are you sure that we can vary current in the circuit that you have suggested in the link,because i doubt the correctness of pin connections

  3. hi setharaman how can i vary the current in this power supply,is it posible

    • bananaman

      Anybody got a 30V 2A fix?

      I guess it will be a couple of components to change?

      Any help would be appreciated.

  4. is it okay if i replace MJ3001 with TIP142?
    MJ3001 is hard to find in my country, including the substitute like BDX65, BDW83, or 2N6058
    it is also darlington, how do you say about it?

  5. admin

    all other resistors can be 1/4 watt.

    6A6 is a 6 ampere diode

  6. With the exception of R5, can the rest of the resistors be of a low power rating, say 1/4 W?

    What is the designation of the 6A6 for the diodes? Are these regular 1n400x diodes?