Fully Programmable Modular Bench Power Supply -- Part 13

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gerrysweeney.co...
I need to make various changes to the physical construction driven by the screw-up of the star earthing topology on the first PCB layout, I need to layout another board revision. I cover the various design changes and perform some basic power, DC condition and regulator response tests, I identify and resolve some issues and re-select better performing op-amps as an alternative to the LT1013, I have selected the OPA2277U part, and I have also tweaked the power supply implementation for the drive circuitry to reflect the fact that the newly specified op-amp is not a single-supply rated part.

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27 сен 2024

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Комментарии : 19

@gerrysweeney 11 лет назад

It could be, the LT1013 is 113db typical, the OPA2277 is 140db typical so its definitely better. When I was measuring it there was definitely current flowing which was developing a voltage across the resistor which was being amplified. Putting the Op-amp in with lower input bias current resolved that problem to a point beyond which the error was material for the design.

@gerrysweeney 11 лет назад

Thanks for the feedback. Gerry

@elboa8 11 лет назад

Nice video(s). I never thought of reducing the voltage like that.Good tip.

@GapRecordingsNamibia 2 года назад

Hi Gerry, Very late to these videos of yours and don't know if you'll answer, But, worth a try, I've tried to look and understand how you are switching the output on and off via software. I would think that somehow the 2N7002 is being used and then "Biasing" the bases of the TIP147's to positive? Would be nice to have some insight into how you are doing this. Also, does the output remain off while everything is being switched on? ie From a cold start? Thank you for your time and effort, and way ahead of it's time.

@SebastianScholle 4 года назад

Your PC interface is amazing. I'd really like to understand how you got them to communicate. Serial right? How does the App get the data from the board?

@nlhans1990 11 лет назад

Could the current measurement offset (the 3mA error with no load) also be caused by poor common-mode rejection (CMR/CMRR)? If that's 60dB (worst-case, depends on resistor accuracy), it means the amp will output 1/1000th of the common input voltage. 5V input voltage means 5mV output offset. Maybe an instrumentation amplifier or current sense yields better results.

@gerrysweeney 11 лет назад

Only started using video on part 8. Part 1 through 7 are on my blog at gerrysweeney(dot)com - see the link above

@DanFrederiksen 11 лет назад

Switchmode backend would get rid of that primitive expensive transformer lump.

@gerrysweeney 11 лет назад

Yeah it would, and if I knew how to design one I would probably give it a go. I have been thinking about de-coupling the bulk caps and rectifier from the module to make it a DC regulator, that way I can use primitive transformer or switch mode. Gerry

@DanFrederiksen 11 лет назад

Gerry Sweeney I think that socalled offline switching regulator chips can do all the heavy lifting including maybe reference circuits in the specsheets. You can browse them on digikey. Maybe it can be done relatively easily.

@gerrysweeney 11 лет назад

Dan, I was recently playing with a boost/buck regulator chip from Linear, I built the example circuit in the data sheet and it was hopeless - probably something I was doing and I have not given up just yet. I guess the point I am making is actually switching regulators are hard. Single chip Buck or Boost regulators are simple enough but to make a swicth mode, probably flyback topology to deliver 250W in an efficient and reliable way is not a trivial task - as much as I would love to try I don't have access to someone with enough experience I could draw on to shortcut the what looks like a very long and painful learning curve. :)

@gerrysweeney 11 лет назад

I use DipTrace

@ChipGuy 11 лет назад

What happend to part 1-7 ???

@SebastianScholle 4 года назад

No videos were made for those parts. You'll need to visit his blog.

@nlhans1990 11 лет назад

Those CMMR are from the op-amp itself, but typically a difference amplifier circuit overrules (has worser figures). Take a look at Intersil's appnote 1298. I overlooked one fact though and that is you're measuring low-side. So CMMR isn't as much an issue as it would be high-side. My bad :) Anyway, nice blog and video series!

@gerrysweeney 11 лет назад

No worries, thanks for the commons.