Regulated Power Supply on the Cheap




Introduction: Regulated Power Supply on the Cheap

About: Thank you all for following me.

The regulated power supply is must to have device for each electronics freak.

In this instructable I will show you how to construct such kind of device on the cheap (less than $10)

Step 1: The Core of the Device ...

The most expensive part for a regulated power supply is the input AC/DC converter ( in most cases having quite heavy, expensive and difficult to have transformer, rectifier and filtering electrolytic capacitors). In this design this part is replaced by the recycled from defected printer SMPS (switched mode power supply).

The old and nonfunctional printers are big treasures - they contain a lot of stuff, which can be reused: motors, metallic parts, buttons, LED's, connectors...etc. For our design we need to take away the power supply block of the printer. Usually the whole block is designed as separate module, even in its own case, with contact interface to the other printer electronics. On the picture you can see two SMPS blocks used in "Canon" and "HP" inkjet printers.

I would strongly recommend, before using such block, to check its functionality. Normally on the bottom side of the device can be found a table of all produced by it voltages and the maximum load current for each voltage. The tables of both presented SMPS blocks are shown on the pictures. The existence of these voltages must be checked. You should have in mind, that some of the SMPS devices does not start without load. To measure the voltages, at least one voltage output shall be loaded wit some resistor or light bulb.

The best case, when making the regulated power supply should be if you can assemble the whole device inside the case of the SMPS block. For that reason the block must be open without any damages and it must have enough place for the additional parts. In my case both of the devices was not satisfying these requirements. Additional case was needed.

Step 2: My Choice

Comparing both tables of the produced voltages, I have decided to use the "HP" SMPS (the black one), because it was able to deliver more power, and two voltages (14.4V and 30V) were enough for me on this stage.

Step 3: The Cable Interface

The selected SMPS had to be connected with the regulating circuitry, placed in separate case in the appropriate and easy to use way. Originally it had 3-pin header connector, shown on the picture. I could not find such connector to use it from the other side. I decided to replace it with more comfortable and reliable avionic metallic 3-pin connector ($1.5 at ebay). If you have more voltages to use, you have to buy connectors with more pins.

I have carefully removed the original connector and have mounted the avionic one. To keep the cables collected, I have used a piece of heat shrinkable tube.

Step 4: The DC/DC Converter

For the voltage regulator I have used a LM2596 stepdown DC/DC converter module ($2 on ebay). It is able to produce output voltage from 1.23 V to the value of the applied at its input voltage. I have decided to supply it with the 30V output of the SMPS block, what would give a regulated voltage range from 1.23 V to ~ 30 V. To have easy manual control over the output voltage, I have unsoldered the blue trimmer potentiometer and replaced it with 10 KOhm potentiometer with knob ($1 on ebay). For the shown here module, only two wires are enough for this connection. On the LM2596 module two of the potentiometer terminals are shorted together. I have shorted also these two terminals on the potentiometer (the middle and one of the external ones). The wires connecting the board and the potentiometer shall be kept as short as possible.

Step 5: LED Display

To control autonomously the regulated voltage, I have decided to use a LED Voltmeter (0 V-30 V) ($2 on ebay) .

Step 6: Output Terminals

I have decided to have two output voltages:

1. First : regulated - 1.23 V-~30 V, produced by the LM2596 module

2. Second : fixed 14.5 V - directly from the output of the SMPS block.

For this purpose I needed 3 output connectors. I decided to use banana jacks. I had 3 available ($1.8 on ebay) - unfortunately two black and one red. One black of them became the GND connector. The other two (red and black) I have dismounted and swapped their parts. In this way each of them had a red part, in distinction to the fully black ground one.

Step 7: The Case

All these parts had to be assembled in a small plastic case (local store - $2). Using a "Dremel" tool, I did a openings and holes for the LED voltmeter, the avionic connector, the potentiometer and the banana jacks.

Step 8: The Schematic

On this picture is presented the schematic of the regulated power supply.

In short: The LED voltmeter is supplied by the 14.5 V and senses the regulated voltage at the output of the LM2596 module. In this way the LED voltmeter shows also the presence of both voltages: if 14.5 V does not exist, it will not work, if the regulated is missing, it will show "0". The regulated power supply is connected to the middle output terminal. The 14.V voltage appears at the right output terminal. The 30 V voltage delivered by the SMPS module is applied to the input of the LM2596 module.

Step 9: Assembling Phases....

In the bottom can be seen the LED voltmeter and the mounted banana and avionic jacks. I have used some hot glue to make the construction stronger.

Step 10: Mounting of the DC/DC Converter

The LM2596 board was fixed by two bolts and nuts on the bottom of the box.

Step 11: Remaining Parts

According Murphy : after assembling of each apparatus, always remain spare parts :-)

Step 12: In Action...

The fully assembled regulated power supply - small and nice.

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    7 years ago on Introduction

    Hello! I first want to start off by saying, this is a great Instructable. Clear pictures, descriptions and all. I'm fairly new to the electrical world, and I have a couple of questions. My main use for this power supply would be for testing car bulbs, 12v LED's and the like. Would I be able to use your power supply for that? From reading this, it seems that I can just dial the potentiometer back to about 12.4V and it would work. Am I correct in thinking this?

    Also, you did two output voltages, one for the regulated and one for the 14.5V from the block itself. Was the 14.5V done specifically for the LED display, or would it also work if I connected a ground and then connected to the 14.5V output? Sorry for the hassle and thank you for your time!


    Reply 7 years ago on Introduction

    Hi Jseverson1,

    First of all you have to be aware of the following: your power supply unit must be able to deliver the all needed power required from your LED's. That means: it must have not only 12V output voltage, but I must be able to source the required current. If you try to require more current that needed few things could happen: the voltage on the output will drop to unpredictable value; some overcurrent and overtemperature protection of the module can trigger and to switch off the output or you can burn out the device. The module , which I used can deliver 2A. You can find some able to source 3A (ebay) - but they require additional heat sink. This give you respectively power 24 and 36 W. May be this will be enough for your bulbs.
    The AC/DC converter taken from the printer (or other device) must be able to deliver a little much power than these 24 or 36W to compensate the conversion loses. Normally on the device you can see labels, where the output voltage and maximum current generated by the device is written. You can calculate the power which can be delivered by this voltage output simply multiplying both values. You must be careful with the units used : A, mA....If the resulting value is 5-10% higher then the power consumed by your bulb the whole system will work.
    You are right : you can simply tune the output voltage by the trimmer potentiometer to the needed value and leave it - it will stay stable. You do not need even the LED display - you can use external multimeter and after fixing the voltage to disconnect it. With the time some voltage drift could happen, but it will be small.
    In my implementation the AC/DC converter had two outputs and I has only one DC/DC module. I could put such module on both channels, but I decided to put it on the 30V output. In this way the voltage generated by the DC/DC module could be set by the potentiometer somewhere between 1.23V (the min) and 29V(max). The output voltage is always lower then the input voltage for the buck converters. The 14.5 voltage can be also used for supplying of other devices it is always fixed. Both supplies share the same ground. This makes the whole power supply unit more flexible - you have a fixed and regulated supply, which can be used separately.
    Some AC/DC printer converters have even more outputs - you can use them as fixed or to put buck or even boost converters and to generate different regulated voltages. You can use also a computer PSU what has directly 12V output.


    Reply 7 years ago on Introduction

    Thank's.Done with my handy :-).