Low cost var. out PSU with laptop adapter

A common ground PSU with 2 to 17V variable or 5V linear output using a laptop power adapter and an external multimeter

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I have made a common ground PSU with 2 to 17V variable or 5V linear output using a laptop power adapter and an external multimeter. Initially I had planned making a 2ch PSU but needed to build one with only one potentiometer on hand. I included a switch to a LM7805 linear regulator due to common use of this voltage. A overall isolating switch was also used.

Phase 1 - Single channel 2-17V or 5V, single adapter PSU


Using two LM317 variable regulators and two (1K and 5K) potentiometers for fine and coarse control for each IC, I have designed and am in the process of building a low cost variable output PSU. I discovered that the panel meters and power source make up the majority of the device price and as a student decided to work around this problem.

I found that laptop adapters could supply the DC voltage I required and banana plugs at relevant points would allow the use of a multimeter instead of a panel meter.

Phase 1

Using a LM317 and LM7805, along with a 10k potentiometer, a single channel common ground PSU was made with a laptop power adapter. Banana plug outputs allowed ease of connection and measurement.

  • 1 × LM317 Power Management ICs / Linear Voltage Regulators and LDOs
  • 1 × LM7805 Power Management ICs / Linear Voltage Regulators and LDOs
  • 2 × Female banana plug Panel mount female banana plug ports
  • 1 × Plastic enclosure
  • 1 × 1 uF Capacitor

View all 10 components

  • Complete for now

    J3TTBlack8802/09/2015 at 18:47 0 comments

    I am not sure if I will always feel this way (I probably won't) but I haven't needed to improve my device. I mostly work with simple motors and microcontrollers which find my single output device perfectly appropriate. Accordingly I'm going to close off this project for now. If anyone is particularly interested in the final product, I will make sure to complete it, after finding the right enclosure (my current delay).

  • Phase 1 Complete

    J3TTBlack8801/11/2015 at 00:41 0 comments

    As described above, I needed a PSU for another project and only had one potentiometer. I added a 7805 for it's common use but now have an elegant little PSU with 2-17V variable and 5V linear output.

  • Undergraduate unemployment

    J3TTBlack8808/02/2014 at 21:13 0 comments

    I am still waiting for a little flush capital to buy the components for this. I have finished my studies but find myself in a bit of limbo due to my obiligation to start working for Eskom (our local power utility) next year, no one will hire a recent graduate for only a few months it seems. But I am going to buy the components this week probably, for anyone still interested in the results :-)

  • First stage complete

    J3TTBlack8806/25/2014 at 09:12 0 comments

    I have most of the components except the potentiometers and housing (I have multiple old laptop adapters luckily) and am just looking for time and these components to somplete the project.

View all 4 project logs

  • 1
    Step 1

    The LM317 output voltage (between a minimum of 1.25V and maximum of 44V) is determined by the resistors (R1 and R2) in the Oregano circuit diagram, with the equation below.

    \color{White} \large V_o=1.25(1+R_2/R_1) +100\times10^{-6} (R_2)-V_{D}

    \color{White} \large V_D=Diode_{ } voltage

    NOTE: Remember to include your diode voltage in your calulations.

    NOTE2: Fine and coarse voltage control could theoretically be achieved with a 1k and a 5k linear potentiometer.

  • 2
    Step 2

    Arrange the components, according to the circuit diagram, on the protoboard to be used and solder it up.

  • 3
    Step 3

    You will now need to prepare your housing. I had duffed a previous project so had this housing available but a Dremmel makes light work of it but the exact arrangement depends on your components, I was fortunate enough to have quite a small 10k potentiometer.

View all 6 instructions

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