I am trying to build up my own regulated power supply, as a way of getting confident with simple electronics and actual hand labour. I am an electrical engineering student, so this is why I am interested in the subject.

I started designing a power supply some weeks ago, following multiple datasheet components and the internet tutorials. This is what I've got for now:


I'd like to know from someone with enough experience, if the schematics are correct? Also, is there a simple way of adding a current regulator branch to the already done circuit, that is rather simple? (I've seen some online, but they use lots of active components and they do not seem to be worth investing time at the moment).

Finally, does anyone who is familiar with Proteus know why, when trying to simulate, it gives timesteps errors? Thanks!


After reading the suggestions so far, I decided to switch to a simpler 1A output. This is the result:

updated schematic

The input is 28V AC 1A. Are my potentiometers well placed? (I added resistors in parallel to achieve around 4.5k Ohms).

  • 1
    \$\begingroup\$ what is the purpose of RV3? \$\endgroup\$
    – jsotola
    Commented Nov 27, 2019 at 0:50
  • \$\begingroup\$ Fine tuning, saw many people online putting 2 pots in series. Is it okay? \$\endgroup\$ Commented Nov 27, 2019 at 1:10
  • \$\begingroup\$ you can put in as many as you like ... it is the overall resistance that is important ... pay attention to the values that people are using though ... i would think that the "fine tuning" pot would be different from the main one \$\endgroup\$
    – jsotola
    Commented Nov 27, 2019 at 1:15
  • 1
    \$\begingroup\$ The wiper of RV1 is connected wrong if you want RV3 to be useful for fine tuning. \$\endgroup\$
    – The Photon
    Commented Nov 27, 2019 at 1:19
  • 1
    \$\begingroup\$ @jsotola, the schematic shows different values for RV1 and RV3. Both of them are way out of line in comparison with R1. \$\endgroup\$
    – The Photon
    Commented Nov 27, 2019 at 1:20

1 Answer 1


The pots are far too high value and are connected wrong (wiper should be connected to element end on each individually).

R1 is okay, sets resistor chain current at about 6.2mA (the chip needs a load of 5mA to regulate).

Maximum total resistance should be (Max output voltage- 1.2V)/0.0062 so for (say) 20V maximum output, total max resistance should be about 3K. 2K + 500 ohms could be used, and then R1 dropped to increase the current for the desired maximum output voltage. Pots are not available in such a wide range of values of resistance as resistors, usually you can get 100\$\Omega\$, 200\$\Omega\$, 500\$\Omega\$, 1K\$\Omega\$, 2K\$\Omega\$, 5K\$\Omega\$, etc.

As you have not defined input voltage, output voltage range or current, we can't really say that the capacitor values are wrong but the 1000uF smoothing capacitor is a very poor match for a 5A regulator. You need to calculate the ripple voltage requirement and the required ripple current rating. Chances are you'll need a much higher value of capacitance, and you'll have to define the voltage rating carefully to accommodate the peaks of the waveform, and the case where the mains is a bit on the high side of nominal. For 2Vp-p ripple at 50Hz mains, your output current would be limited to less than 200mA.

C3 could certainly be larger (or paralleled with an electrolytic capacitor) to decrease the output impedance, and C2 could be larger as well.

R2 might be on the low side, depending on the input voltage. A modern LED requires only 1mA or so to be quite bright.

If you are really intending on getting multiple amperes out of this, the thermal design will be important. Assuming (say) a 28V nominal input and 3V 4A output, the power dissipation would be about 100W, a non-trivial amount of heat to dispose of, requiring something of the order of a CPU cooler.


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