Electrical – Digital voltage/current controller for DIY bench power supply

constant-currentcurrent-limitingpower supplyvoltage-regulator

I'm trying to design a portable rechargeable bench power supply. I have a 12V sealed lead-acid battery (WP7.2-12) which I can use as the main power source. These batteries are cheap and easy to source, and have reasonable power output specifications.

I would like to be able to digitally control the output voltage and current using a microcontroller.

I'm seeking advice for a voltage/current output controller which would be reasonably easy to interface with a MCU. It needs to be digitally controlled (i.e. serial, SPI, I2C, 8-bit bus, etc), and should be able to provide two modes of operation:

  1. Voltage output with selectable voltage and maximum current
    (0-12V, 0-10A)
  2. Constant current output with selectable current output (0-10A)

(Maybe these features need to be implemented as two separate circuits, using relays to connect the output to one or the other…)

Would an LED driver such as those referenced here be a good route for this type of controller, or would it be best to roll-my-own circuitry for this? Any pointers/tips appreciated.

Obviously there are other components (i.e. overcurrent protection, battery charge controller, deep-discharge prevention, user interface, etc.) that must be implemented as well, but for this question I'm simply seeking a way to control the output voltage/current per the above.

Thanks!

Best Answer

  1. Find a suitable voltage regulator that can supply up to 12 volts at 10 amps and has a feedback (FB) pin that is used for setting the output voltage via a potential divider.
  2. If your input voltage is only 12 volt then use a pre-boost regulator to deliver maybe 15 volts to the regulator described in (1).
  3. If you consider that maybe 11.5 volts is enough at the output then you don't need a pre-regulator if your main regulator has enough grunt and low drop-out to do the job (but you won't quite get 12 volts of course).

Two more things to do and the first revolves around using a digital pot to control the voltage fed back to the FB pin. Alternatively inject a current into the FB node that can "con" the regulator into assuming a diufferent voltage output. Here's the first idea: -

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This was taken from figure 8 in this ADI document.

The second idea is to use this type of injection using a current output DAC: -

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Or like this: -

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And the second thing to do is have a small resistor in series with the output of the regulator (but before the feedback resistors) that can be used to measure load current. You can use a circuit like this that takes the high-side measurement and references it to 0 volts that can be read by an ADC: -

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The above taken from here.

Or you go the whole-hog and get yourself a step-Down controller with Digital Power System Management like the LTC3886: -

enter image description here

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