Variable Lab Bench Power Supply.

Bench power supplies are boxes that you plug into the wall, and provide an adjustable range of DC voltage on their output terminals. They usually have some knobs and a meter of some sort on them to help dial in the correct voltage. Some also have current limiting to help when troubleshooting or testing a new project. (Keeping the current limited to just above what the device needs can help prevent shorts from damaging components).

This is a fully adjustable bench power supply with Constant Voltage(CV) and Constant Current(CC) adjustments. To use, turn on the supply with the leads disconnected. Make sure the Current knob is not all the way down. Adjust the voltage knob to get the desired VDC on the display. Plug in your device. If the bottom CC light is on, that means it's in current limiting, and it's backing down the voltage to limit the current.

Specifications:
Output: Adjustable 1.3V to 19.5V

Max Adjustable current: 4.5 A

Short circuit protection: Yes (limit current 8A)

Overtemperature protection: (automatically shut off the output after overtemperature).

Input reverse polarity protection: No

Step 1: Materials :

Here is a list of materials I used for this project:

1 x XL4015 DC-DC STEP DOWN ADJUSTABLE MODULE

1 x VOLMETER AMMETER DISPLAY

1 x POWER SUPPLY 19.5V 4.55A (LAPTOP CHARGER)

2 x 10KΩ POTENTIOMETER

1 x LM7805 VOLTAGE REGULATOR

2 x KNOBS

1 x 4mm BANANA JACKS (RED + BLACK)

1 x4mm BANANA SOCKETS OR BINDING POST (RED + BLACK)

1 x SPDT SWITCH

1 x AC SPDT SWITCH

1 x USB FEMALE PORT

1 x CLOVERLEAF SOCKET OR 3-PIN SOCKET ( I SCRAPED FROM LAPTOP CHARGER)

WIRES

CABLE ZIP TIES

SOME 3D CARBON FIBRE VIYNL WRAPS

SCREWS

Step 2: ModifIcation in the DC-DC Converter.

Remove the small two of potentiometer which are on the DC-DC module, and replace with two rotary potentiometer with ribbon cables.

One is for CC and the other one for CV.

Step 3: POWER SUPPLY:

For the power supply I have used an old LAPTOP CHARGER.

Remove the SMPS from the charger case. This SMPS is rated at 19.5v 4.55A total of 90W. Which is enough for this project. I also removed the cloverleaf jack from the charger itself.

Step 4: Schematic and Diagrams:

Refer to the diagram to connect all of parts together.

SAFETY FIRST:

MAKE SURE YOU GROUND THE SMPS.

I forget ground in the scematic.

POSITIVE FROM SMPS TO IN+ OF CONVERTER AND RED WIRE OF VOLTMETER AMMETER DISPLAY. GROUND TO IN- OF CONVERTER AND BLACK WIRE OF VOLTMETER AMMETER DISPLAY.

YELLOW WIRE FROM VOLTMETER AMMETER TO OUT+ FROM CONVETER.

CONVERTER OUT- TO THICK BLACK WIRE OF THE DISPLAY.

THICK RED WIRE OF DISPLAY TO GROUND TERMINAL OF BINDING POST.

AGAIN OUT+ OF CONVERTER THROUGH A SPDT SWITCH TO POSTIVE TERMINAL OF BINDING POST AND INPUT OF LM7805 VOLTAGE CONVERTER FOR REGULATED+5V OUPUT THROUGH USB.

REMEMBER;

Voltmeter connects parallel and Ammeter in series.

The output connection wire should have a sufficient diameter to carry the desired current.

use heat shrink tubing for the connections and good amount of hot glue to lock things on place.

Step 5: Enclosure:

I have used a wooden box for this project with dimensions of 190mm x 60mm x 90mm (l x b x h).

For the front panel, first i marked the outline an by using simple tools like drill and hand saw.

6mm hole for the potentiometers and binding posts.

3mm holes for leds.

4mm hole for spdt switch.

Used BLACK MATTE PAINT for the body.

And last VINYL WRAPPED THE FRONT PANEL.

This is diy project, so.... its upto you how you design the enclosure. ;)

Do this as You comfort.

Step 6: Assemble Everything Into One Piece.

I LABEL" V " AND " A " ON THE FRONT PANEL USING NAIL PAINT.

Step 7: TESTING!

FOR THE REGULATED +5V OUTPUT FROM USB SET VOLTAGE TO ABOVE 5.2V.

FOR VARIABLE OUTPUT, OFF THE OUTPUT SWITCH, SET THE DESIRED VOLTAGE USING THE KNOB AND THEN SWITCH ON THE OUTPUT SWITCH.

THANK YOU!

Comments

[AroAro]

This project or something like that happens very often.
I have already responded to other projects - it works better!
For good projects, the voltage can be set much more accurately by a second potentiometer. - Simply connect a second resistor (about 5 - 10% of the voltage regulator) in series with the voltage regulator.

In good projects, the voltage can be reduced to 0 volts.
This is easy with 2 power diodes between output converter and output jack. A switch that bypasses the diodes when you need the full voltage. A load resistor from the output to the input ground of the converter, which is off when the diodes are bypassed. Output mass would affect the current regulation.

19 volts output voltage are very little. It should be 24 volts at the output.

A 7805 is outdated. Today you get for the same money a small board with a switching regulator.

[RobS23]

I've been considering this but have yet to see an example with a clear wiring pic

[AroAro]

It can be done even better.
My current variant.
R1 R2 reduce the output voltage, otherwise there is no regulation at maximum voltage.
An offset of approx. 3 volts is added via R3 and LED1.
US1 works as a low-resistance output.
US2 divides the voltage, since US1 can carry a maximum of 30 volts.
US1 can be replaced by an NPN transistor with a very high current gain.
R8 voltage coarse and R9 voltage fine

[RobS23]

Nice! You should really post the a guide to the full project for people to see!

[AroAro]

This is actually quite simple. You only have to increase the output voltage by about 2-3 volts and give this increased output voltage via the adjustment potentiometer on the FB input.
This is done via R3 and a white LED.
The C parallel to the LED improves dynamic behavior.
The Mosfet takes the voltage from high resistance.
R8 and R9 then divide the output voltage so that the FB input
receives a voltage that he can compare for the control.
The solution is in principle for all switching regulator IC.
All possible combinations of potentiometer and fixed resistor between FB and ground are used on the circuit board. Therefore you may have to adapt the resistors to the circuit.
Problem 1: the IRLML6346 can only handle a maximum of 30 V. Therefore the voltage was divided by US2.
It is also possible to replace it with a mosfet with a higher voltage or an NPN - Darlington transistor with a higher current gain and voltage.
Probklem2: We actually need a voltage that is at least 5 volts higher than the output voltage. There must be a constant flow of a small current from the supply voltage via R3 and the LED to the output.
That could be a big hassle.
Therefore we first divide the output voltage down to approx. 3/4 before we increase it by approx. 2-3 V.
This also ensures that more current can flow from the output to ground than via the LED.
I hope Google did a reasonable job of translating as English is not my language.

[MarcoT68]

Hi AroAro, please can you explain better the first point? Perhaps with a schematic diagram. Otherwise we can change the 10 k pot with 5 k pot. Tks

[İsmailM41]

Ampermetren's black wires are not connected to the different tutorials, why? Same thing?

[Maggie Shah]

Maybe you are talking about the voltmeter. The Ammeter Voltmeter Display has 2-black wires. One is for the Ammeter and the second one is for the Voltmeter. The voltmeter connects in parallel to the given supply, apparently in some case the Voltmeter is grounded. And lastly the Ammeter connects in series, means that the current flows through the Ammeter and complete the current loop.
If you've further queries, let me know.

[SteveSi]

The thin black wire on the VA meter should not be connected. It will prevent the current limit pot from working because it shorts out the shunt in the DC-DC board. If you check resistance from thin black wire to thick black wire of VA meter you will see 0 Ohms! if you look at the instructions for the VA meter - you only connect the thin black wire if powering from an isolated supply such as a battery.

[Patas_de_Urso]

Good evening, I'll start doing this project, first and foremost congratulations for the good work, I have a doubt about the connection of the led?

If the bottom CC light is on, that means it's in current limiting, and it's backing down the voltage to limit the current??

[İsmailM41]

Ampermetren's black wires are not connected to the different tutorials, why? Same thing?

[Maggie Shah]

Thank you. it looks like this on working bench

[RahulY45]

Wow. Great job. Its really compact fir small benches

[RahulY45]

Nice and compact built.

[cbaladeh]

Well done, where the LEDs are connected?

Thanks

[Maggie Shah]

I've removed the onboard led on the converter and inplace of them I've attached the 3mm led which are in front of the panel

[cbaladeh]

Thank you, I was not sure of that. GGGGreat job

[Surajit Majumdar]

Nice built:) voted for u

[Maggie Shah]

I Appreciate ?

[TheDman22554]

The Type of Step down converter is different in the supply list than the one used in the build tutorial. This could just be because i'm a little bit of an electronics noob, but i really need a variable power supply and want to build this. Awesome build otherwise!