Some years ago, I put together a LM338 based linear voltage regulator PCB design for my electronics projects. I thought I’d publish the EagleCAD PCB design files for this project as they could be useful to other hobbyists. This design is released under the MIT licence, so is free to use.
My LM338 voltage regulator design is based on the Adjustable Regulator with Improved Ripple Rejection example schematic found in figure 27 of the Texas Instruments LM338 datasheet. I’ve taken this design and added some voltage adjustment options, over-current protection and a case.
If you’re not familiar with the LM338 here’s a quick overview from the datasheet:
The LM138 and LM338 devices are adjustable, three-terminal, positive-voltage regulators capable of supplying more than 5 A over an output-voltage range of 1.2 V to 32 V. It requires only two external resistors to set the output voltage. These devices feature a typical line regulation of 0.005% and typical load regulation of 0.1%.
In theory this power supply should be capable of supplying 5A at a range of voltages commonly found in hobbyist digital electronics projects. I’ve been using mine for a few years now without any problems. The resettable fuse goes a long way in protecting the PSU from mishaps when working with breadboard projects. Here is a photo of a completed prototype unit:
A Dangerous Prototypes Sick of Beige 70x43mm acrylic case is included in the design to protect the board (to use the acrylic top plate, laser cutting for the capacitors and controls will be required). Alternatively, custom mounting of the board can be achieved using the M3 mounting holes.
The power LED circuit is driven by a Microchip
CL2N3 IC. I chose this part due to the wide input voltage this PSU can support, and the challenges that brings for driving a power LED. It can be difficult to obtain, but the PSU will operate normally without the LED and
Assembling the LM338 PSU is an easy project to complete which shouldn’t take much more than an hour for a beginner. This project is a great way to get some soldering practice and familiarisation with the PCB manufacturing process if you are new to the electronics hobby.
There are no specific guidelines for assembling this design, but I’d recommend you start with soldering on the smaller parts such as the resistors and work your way up to the largest pieces. This will make moving around the board with your soldering iron easier. Using some sort of clamp or helping hands like shown in the photo below is a good idea too.
If you are using the Sick of Beige case from Dangerous Prototypes, be sure to keep the legs and solder on the underside of the board trimmed down close to the PCB to ensure the acrylic base fits properly.
Should you need more than about 1A out of this circuit, the LM338 must be fitted with an appropriately sized heatsink (not included in the parts list).
As you might expect, using the
DEVTTY.IO linear voltage regulator is pretty straightforward. Input power from a battery or mains adapter can be provided to either the barrel jack or screw terminals. Observe the polarity marked on the PCB by the screw terminals. The LED should illuminate to show the board is operating.
Use the jumper at the bottom left of the board to switch between fixed and adjustable output modes. In variable mode, turn the trimpot to adjust the output. To adjust the voltage in fixed output mode, move the jumper on
J3 to the desired voltage. Fixed output voltages should be adjusted while there is nothing connected to the output.
The board provides four power outputs in the form of three two pin header connectors and a screw terminal. All outputs can be used simultaneously.
The design uses a PTC resettable fuse which will disconnect the output should current exceed 5 amps. Should this occur, allow the board to cool down and it will become operational again.
If you want to make one of these boards for yourself, the EagleCAD (version 7) files required are available on GitHub. A parts list and set of Gerber files are also included within the repository for use with the excellent OSHPark PCB manufacturing service. When uploading the board design to a PCB fab-house, confirm the preview looks the same as the images below:
Get in touch if you make one of these boards for yourself, I’d love to hear how you got on with it and what you’re using yours for.
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