DIY Small Bench Power Supply

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Introduction: DIY Small Bench Power Supply

About: Always loved electronics. I like to reuse parts or componets and I Love to be part of the Instructable community.

This is a small bench power supply that I made some time ago, and because I was very busy I couldn't do the instructable for it. I do apologise for taking so long, I hope it was worth the wait :).

After making my Mini Adjustable Power Supply I was very happy with it, but I was missing a more accurate control of the voltage and current. So I decided to make this slightly bigger (but still small) bench power supply.

The heart of the unit is basically the same as on the other power supply. It is based on the LM2596S. This IC can handle up to 3A with a good heat sink. I would use it only for 2A to be on the safe side.

There is a video of the unit working on the last step of this instructable.

Enough talking about it... let's make it...

Step 1: Materials and Tools

Here is a list of materials and tools I used for this project. Many of them can be replaced with other components that you may have already, but I would definitely use an aluminium enclosure, as I used it as a heat-sink as well. I have tried to find the cheapest components, but double check that the price has not changed, you may find it cheaper somewhere else.

MATERIALS

-Aluminium Enclosure (link)

-DC-DC Bulk Converter (LM2596S) (link)

-6 Pin Headers (link)

-10k Multi turn Potentiometer x2 (link)

-Potentiometer knobs(link)

-Volt, Amp Metter (link)

-Heat sink paste.

-Toggle Switch(link)

-Rocker Switch(link)

-Nail Polish.

-Nail Polish remover or Acetone.

-Power Panel Mount Connector (link) Check the power supply connector to get an appropriate connector.

-Banana sockets (link) (You may get cheaper ones, but I like the ones on the link because they are smaller)

-Banana test leads (You may have already one, I won't put a link as it may be worth getting a decent one)

OPTIONAL

The rest of the components are only necessary if you want to have LEDs to let you know if you limiting the current or the voltage, and to let you know if the output is set to on.

-attiny85 (link)

-2x Generic PNP transistors

-500R resistor x4 (or a close one)

-10k resistor x2

-100nf ceramic capacitor x2

-5V regulator L7805CV

-Heat-sink for the voltage regulator

-3mm Red LED x2

-5mm Two Colours LED and Panel mount for it.

-Etching Solution (Ferric Chloride) It is also used for PCB etching.

-Two containers for using the etching solution. One should fit inside the other and the inner one has to be big enough so the aluminium enclosure fits inside. (See step 2 for photos). They also need to be heat resistant.

TOOLS

-Dremel

-Cutting disk

-Drill and various drill bits

-Heat glue gun

-Solder and soldering iron

For the optional upgrade of warning LED's you will also need:

Household iron

Laser Printer

Step 2: Design and Etching the Enclosure

After taking measurements of the enclosure and all the components, I designed the layout of the front of the unit with Photoshop. I added the file so you can modify it to your needs. If you are designing it in another enclosure, just make sure you take into account what's inside the enclosure and fitting points.

Print the design on photo paper and with a good quality laser printer.

Place the front of the aluminium enclosure on top of the photo paper, printed side facing the aluminium. Use the iron to heat as evenly as you can the other side while applying pressure. Do this for about two minutes, or when you see the back looking like the one on the photo.

Wait for it to cool down, and peel the paper off. If everything when well your design will be left on the enclosure.

Inspect the printed area to see bright spots, and paint them with nail polish. Anything that is not covered will be etched.

Use tape to protect the rest of the front of the enclosure so you don't damage it with the etching solution.

Put some hot water in the bigger container and place the other one inside.

WARNING!! Wear gloves and eye protection when handling the etching solution. Use the solution only in a well ventilated area. The etching solution will stain yourself as well as pretty much everything it touches, and it will damage anything metal, especially be careful with the sink if is the metal type, when washing the enclosure.

Pour some of the etching solution in the smaller container and leave for a few minutes to warm up. Place the front of the box in there. Agitate for about two minutes and a half. (Time will depend on the temperature of the etching solution).

Once it has been etched, wash with cold water. I use some etchant neutraliser to stop the etchant reaction, but it is not necessary if you keep applying cold water for some time. Apply nail polish and let it dry. Carefully remove the excess to leave nail polish only on the etched area. This may take a few attempts, but I didn't want to sand the aluminium

Step 3: Drilling and Fixing Components

I always cover the enclosures with decorators tape to protect it while drilling and cutting it. It also helps the marking procedure as it is a lot easier to mark on the tape than on the aluminium.

I measured all the components during the design process, so it was a matter of just drilling and cutting where the marks were. Just make sure your components will fit before this step.

I placed all the components on the aluminium where they will stay so I could access everything to solder the cables.

Step 4: Heat-sink for the DC-DC Converter

I decided to use an aluminium enclosure so I could use it also as a heat-sink. I cut a small piece of aluminium and after applying heat paste, I glued it to the back of the regulator. Then I applied heat paste on the back of the enclosure and hot glued the regulator to the back.

Step 5: Schematic and Diagrams

These schematics are self explanatory. The first one is without the LEDs, the second has the option of LEDs for the output and to let you know if you are limiting the voltage or the current.

The colours on the voltage and current meter may change on your model, so please check your wiring with the meter provider.

Here you can see the schematic bigger.

Step 6: LEDs On/Off and Limiting Warning (Optional)

For the CC/CV LEDs I used the dremel to sand a bit of the top of the LED to avoid it being too bright on that area. I drilled an opening on the top of the meter and placed both of the LEDs inside as per photo.

For the On/Off LED I used some heat shrink, but some tape will do.

Here is the code for the Attiny85, It is very simple, and I'm sure there are ways to do the same without a microcontroller, but I have a few of then around and I love to use them.

#include

#include

int LED = 1; //LED for CC
int LED2=2; //LED for VC
int Signal=0;
int SignalYN;

void setup() {

pinMode(LED, OUTPUT);

pinMode(LED2,OUTPUT);

pinMode(Signal,INPUT);

}

void loop() {

SignalYN=digitalRead(Signal);

if (SignalYN==HIGH){ // Limiting the Current
digitalWrite(LED,HIGH);
digitalWrite(LED2,LOW);
}else {
digitalWrite(LED2,HIGH); //Limiting the Voltage
digitalWrite(LED,LOW);
}

}

Step 7: Testing

Here is a video of a test of the power supply. I hope you enjoy this instructable. I will be happy to answer any questions or help you out to build your own.

Microcontroller Contest

Second Prize in the
Microcontroller Contest

10 People Made This Project!

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148 Discussions

Hye newton. Can u show me how to make the load using LED , as u make to test on the power supply. It is 50 W load is it. Do you have the schematics. ?

nice and cool!

Hi newtonn2,

Great instructable. I plan to use the
original the original CC/CV led output by replacing the original smd led
with a panel mountable one. What do you think, is there any reason why
shouldn't it work?

Hi i browsing ebay for laptop chargers and all over 3amp mine is 3.2 is it ok or too much?

1 reply

Please help, I know this is an old project but I'm just about ready to start building this and need a couple of questions answered to a few things that don't add up or look right to me. On the optional components list I see 2 10K resistors, I'm not seeing them at all on the schematic? Also I see 5 500K resistors on the schematic and not 4 like the components list? I'm a complete NOOB at this and wondering if I'm not reading the print right or if it is mislabeled somewhere, or some revisions didn't get documented or changed? Does anyone have a drawing of this ALL laid out on a perfboard?

1 reply

Mine isn't as pretty as all of yours, but I love it, and more importantly when I teach kids robotics it comes in SO HANDY! This is great, I will make a few more so that all the kids can use them when needed. This is my favorite instructable! Thank you.

-Jim

Photo-2016-04-12-22-22-33_2158.JPGPhoto-2016-04-12-22-22-39_2159.JPGPhoto-2016-04-12-22-22-18_2156.JPGPhoto-2016-04-12-22-22-27_2157.JPG
2 replies

what enclosure do you use?

Hi,

Can anyone suggest equivalent for BC327? I am unable to find them in my country.

Thanks

Awnish

1 reply

Hi,

Regarding PNP transistor, any general perpose small transistor is OK.

In our country, 2SA1015s(PNP) or 2SC1815s(NPN) are easy to get.

I'd like to paste substitute list below.

https://groups.google.com/forum/#!topic/aus.electronics/_aXrv4hJ6ko

or google it by 2sa1015 substitute.

But I mentioned before, I recommend you to use NPN circuit substitution

for lower threshold.

regards,

can you use a substitute for the attiny85

Very nice instructable and interesting idea to built just a box with DC-DC converter :) You can connect almost every kind of power source (i.e. LiPo) to it which is awesome!

And this is why I think that "step-up/step-down" module will be more useful. I'm building power supply based on this module:
http://www.aliexpress.com/item/Boost-Buck-Voltage-...

how do you program the tiny85 with your code and i have a single potentimeter dc board and will that work for this project

This is probably an unreasonable question, but is there a reference for resistance values for set voltages. I'm wondering if a rotary switch with appropriate resistors on each output could be used to give the power supply a few static voltage settings (i.e. 5v, 6v, 9v, 12v, 18v, 24v).

Thanks in advance!

Hi. I am following your projects for a while and i am very pleased for the quality and completeness of your work. For this one i have a couple of questions.

1. Why you haven't used the onboard leds for CV and CC as in your other project and used an Attiny instead?

2. What is the purpose of the dual led ( i guess it changes color when there is power to the output but i am not sure)

3. Should i use a 3A fuse to the output to protect the LM2596 or it has internal protection?

Thank you for the excellent job.

2 replies


Hi there, Thank you very much.

1) I used the Attiny because the other LED's dim a bit and it was not as accurate. I thing there is only one LED for whenever you limit the current, but I wanted to have to LED's like a standard power supply.

2) Yes! It changes color when the output is on.

3) I'm not sure if there is a protection on the LM2596, but it is always a good idea.

I hope you can have it working soon. Please share some pictures once you'r done.

Hi again. I have programmed the attiny and on the breadboard works as it should. But on the actual circuit it is stuck on showing CV (constant voltage even if the led on the lm2596 board gets on. I have checked the voltage and pin 5 on attiny gets 3.1+ volts when the led is on. Also while i was measuring with the multimeter the voltage on pin 5 the leds CC and CV from pins 6 and 7 of attiny toggle. If i manage to turn CC on then when the led on lm2596 turns off the attiny gets that we are in CV and lights the correct led. But it never again lights the CC led. I have tried using a pull down resistor of 10K between pins 5 and ground on attiny with no luck. Also i have measured the VCC on attiny and it is 4.95V. Do you have an idea why this is happening? Thank you in advance.