Yet Another Bench Supply

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Design of bench supply modules for digitally controlled voltage and current output.

Making use of SMPS supply from mains voltage, a switched buck regulator to minimise losses in the final linear regulator section.

Up to 36v input, 3A per module.

This project started as an incentive to gain a better understanding of power supplies and analogue design, whilst furnishing me with a reliable and hopefully accurate bench power supply. That and wanting to design it myself, rather than purchase an ebay special.

The design consists of;

  1. Switched mode section that converts 20V to 36V down to 3V above the required output. Makes use of a unity gain opamp with integral resistors to make a voltage follower that feeds back to the switch mode regulator.
  2. Linear section that converts the remaining 3V difference to the required output voltage and also provides programmable current limiting. [Ref.]
  3. Control section of the linear regulator
  4. Analogue components for the ATMega MCU, namely precision voltage reference and ADC for setting the current limit and output voltage of the supply
  5. Digital section consisting of MCU with programming interface, LCD display and controller/switches for user interface.
  6. Power supply for the control circuitry, 5, +12, -12 volt output for three bench supply units.

This project is still under development and as of this time is entirely theoretical, I've not done any testing or implementation.

Bench supply-A5.TSC

TINA model - linear section voltage and current control

tsc - 49.14 kB - 11/15/2016 at 21:57



TINA model - voltage follower for controlling switched mode voltage output

tsc - 7.38 kB - 11/15/2016 at 21:57


Adobe Portable Document Format - 69.27 kB - 11/15/2016 at 21:56



circuit diagram

Adobe Portable Document Format - 64.95 kB - 11/15/2016 at 21:56


Adobe Portable Document Format - 29.91 kB - 11/15/2016 at 21:56


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  • Design considerations - updates

    David Brown11/15/2016 at 21:55 0 comments

    I've been reading up on a few more details of power supply and analogue design, chiefly grounding considerations; for things like ground differential, controlling where the current flows, whilst keeping it away from areas that could be sensitive to it, but minimising the resistance.

    So I have been tweaking the supply board so that there are effectively four ground areas. One for the switched mode mode section, one for the linear section, one for the analogue control circuits (Op Amps one side, with precision voltage source, ATMega analogue supply and the control DAC ) and finally one for the digital section. These can be identified on the plot of the current layout, circuit posted in files section.

    There has also been some work on the power supply for the bench supply, which requires +12V, -12V & +5V. I had looked at using a charge pump arrangement to give the -12V but when evaluating the current requirement it was not up to the job. So I have gone with a design from Texas Instruments for a 100mA -12V circuit using their TPS5401 part. [Ref.]

    Having switched to this it then made sense to use this as the basis for the +12V 500mA and +5V 500mA sections. When looking for the data sheet [Ref.] I discovered that Ti now have a pretty good online design tool; WEBBENCH Designer. Using this allowed me to quickly put together the circuits for the other two sections (the negative voltage version is not supported by WEBBENCH). The resulting design is below, circuit in the files section, still under consideration.

    I've made use of the cascaded startup that switches on the 5V section first and then the +12V and lastly the -12V. The board is designed to run three of the bench supply units at a time.

  • Design itterations

    David Brown10/06/2016 at 01:04 0 comments

    I've been playing with the design some more, and moved the large capacitor off the board. The linear control section was then relaid and separate grounds introduced for the analogue, digital and power sections.

    Finally I've added a voltage difference section that maintains a constant 3v higher output of the switched section compared to the linear section using a difference amplifier than can be run off the max 36v input voltage.

    The BOM cost is higher than expected, but the aim is for something that will last a few decades, board size is ~100x40mm.

  • First-pass design

    David Brown09/30/2016 at 03:10 0 comments

    As mentioned in the heading, this is a positive section bench power supply based on Kerry Wong's supply. I've made some changes to suit 3A current and reduced the voltage control to match a 2.048V DAC and precision external reference for the ATMega328p which will handle control and display on I2C 16x2 LCD.

    The +12V, -12V, +5V supply will be off the board and shared between up to three modules, I've yet to design this.

    I've posted up TINA-TI simulation model of the linear section and the corresponding schematic for the module. Any comments welcomed.

    OSH render of the rev A2 design

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