3A Variable Bench PSU with Color Display

I am playing with electronics since I was a child and made numerous circuits. But still now, I didn’t made any power supply unit for general purpose use. So tired of making PSU for each circuit, I decided to make a stable Bench PSU for general purpose use with some enhanced features. I decided to made the core power supply analog controlled and extra features digitally controlled.
So that’s why I choose LM350 linear regulator chip as the heart because 3A is sufficient for day to day use.
For the digital part, the functionalities I choose are listed below:
1.Digital readout of Voltage.
2.Digital readout of current.
3.Digital readout of LM350 temperature.
4.Smart Fan controlled cooling for LM350.
All the mentioned criteria’s were full filled by ATMEGA8 so it was finalized for this circuit.
3A Variable Bench PSU with Color Display
The ADC I choose is ADS1115 which is 16 bit ADC.I will discuss about it later.
Now for current measuring, I used ACS714/5A breakout board which does it job pretty good.
LM35 is used as the conventional temperature sensor and it also does it job perfectly.Atmega8 senses temp and controls the fan according to it.
Now last but not the lease…the Display!!!Generally we see 16×2/20×4/128×64 monochrome type of display in this type of power supply. But I thought something different and used really cheap 128×64 SPI color display. It generally uses ili9341 as it’s controller and is pretty popular as display driver. It is SPI controlled. But you need 5v to 3.3v level shifter to run this type of display which are available at the market and are pretty cheap.
Now comes the software part. Coding the software took me a lot of time. I put enough comments at the end of each line by which anyone cans easily understand the functions. I modularized the code so debugging is very easy. I used winavr and C to write the code.
So now it’s time to get into the next step to see what are need to run this circuit.

Step 1: Parts Required

Parts are listed below and i have mentioned the sites to get the difficult parts online.

1) ATMEGA8 x 1

2) ADS1115 breakout board x 1(You can find it here. Or you can also see at official Ad fruit website here).

3) ACS714 breakout board x 1(You can find it here. Or you can find it at Polulu official website here).

4) ILI9341 SPI 2.2″ color display x 1(You can find it here. Or you can find it at official Ad fruit’s website here).

5) 5v to 3.3v level shifter x 2(You can find it here or at here).

6) LM350 x 1

7) 5k 10 turn pot x 1(to get precise voltage division at output)/Normal 5k pot

8) 7805 x 2.

9) 7812 x 1

10) LM1117(5v to 3.3v supply IC). x 1

11) IRF540 x 1

12) IRLB8748 / IRL540 logic level mosfet/Last option, if you couldn’t found them, try with IRFZ44(this should also work but i didn’t tried that myself) x 1

13) 18V zener diode(1/2w preferable). x 1


120 Ohm,10k x 3,18k,5k preset.

15) Capacitors:

100NF/104PF x 7

102PF x 1

22PF x 2

10uF/63v x 5

22uF/25v x 1

4700uF/63v x 1

220uF/35v x 1

16) 8 Mhz xtal x 1

17) Diode:

1N4148 x 1

1N4007 x 2

6A4 / 6 amp diode x 4/Bridge rectifier-KBL04.

18) *12-0-12/4 amp CT type transformer(I used this transformer from scrap without using center tap. You can use any other transformer. But keep one thing in mind that the Max input/output differential of LM350 is 35v to 37v)

in mind that the Max voltage differential between).

19)*Heat sink(For LM350 , IRF540 , 7805)

20) *12v Cooling Fan(see the heat dissipation part)

21) *CPU SMPS cabinet.(I used a faulty SMPS cabinet. You can use whatever you want).

22) Banana Jack + Socket – 1 pair(BLACK+RED).
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