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I need guidance on designing a Variable DC power supply with the following characteristics:

  • Microcontroller controlled
  • DC output ~ 1V - 30V
  • Current handling: ~5 amperes
  • Power handling: ~50 watts

I am an electrical engineer but I don't really design power supplies.

I plan to commercialize a product however I am currently just breadboarding and getting a feel for what works.

Can anyone point me to how get started quickly?

I've tried working out a concept already: microcontroller --> potentiometer --> Switching voltage regulator (the voltage regulator receives voltage from a bench top power supply. I don't really know how to design things that tap directly off mains power yet)

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    \$\begingroup\$ Have you watched the series of videos that Dave from the EEVBlog made: youtube.com/watch?v=CIGjActDeoM&list=PLBF35875F73B5C9B5 ? That should introduce you to (lab) power supply design. I don't really design power supplies. and Can anyone point me to how get started quickly? if you want to do this "quickly" then you might want to simplify things, a rushed/ quick design is rarely a good design. Especially your I plan to commercialize a product means you have to get it right. Or are you aiming to dissapointed your customers? \$\endgroup\$ – Bimpelrekkie Apr 18 at 15:37
  • \$\begingroup\$ @Bimpelrekkie, your youtube recommendation is very good. As usual I gave Dave 5 stars.Me ok booomer built a 2N3055 NPN BJT based serial PSU when studying my rusty EE diploma last century. I still remember vividly the great joy when I completed the project and showed it around to my friends. \$\endgroup\$ – tlfong01 Apr 19 at 1:48
  • \$\begingroup\$ But I am too lazy to DIY any PSU now. As Dave used to say, many electronics hobbyists are now shifting to system integration, instead of components integration*. So I am ordering an assembled PSU (the shop also sells DIY kit for hackers, though). If you wish to know more details (PSU with USB and WiFi control!) Please see my comments to @bobflux below. \$\endgroup\$ – tlfong01 Apr 19 at 2:56
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    \$\begingroup\$ Why are you re-inventing the wheel? What does this product offer that existing supplies on the market don't? What about displays? Which countries do you plan to sell it in? How will you fund prototyping and EMC testing? And so on... \$\endgroup\$ – Lundin Apr 20 at 13:58
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    \$\begingroup\$ @Norberto_M7 Okay but you still need a plan for standards compliance and EMC testing, based on the market you plan to sell it to. \$\endgroup\$ – Lundin Apr 28 at 6:39
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If you want a cheap power supply that will do that, get a Korad KD3005P.

If you want to design it, first you need to decide on specs like:

  • Voltage, current, power (that's done)

  • Output ripple voltage in voltage mode, and current ripple in current limit mode

This is important if you use a switching converter, you'll want to know how much switching noise remains in the output.

  • Accuracy of voltage setting, also readback if it supports it, and same for current if it supports it.

  • What kind of load impedance it should be stable with (capacitance, ESR, etc)

  • If it is like a bench power supply with settable current limit, speed of switching from voltage to current mode and back.

This one is tricky. If you set the voltage to 30V and the current to 20mA, then connect a 5mm LED on the output, the output capacitors will be charged to 30V. If the capacitors are large, the LED will blow before the current limit circuit even notices. So the capacitors have to be tiny. But the current limit circuit also has to be fast enough.

microcontroller --> potentiometer --> Switching voltage regulator

It would be cheaper and more efficient to control the output voltage of a mains-powered switching supply. But this then becomes a SMPS design problem.

If you use a constant voltage SMPS and a switching converter, then you nee a switcher that will support the whole voltage range. Make sure to check the maximum ON-time of the FETs, because it's never 100% for a design that uses NMOS, so if you want 30V on the output you'll need a few extra volts on the input.

If you replace the feedback divider with a digital potentiometer, loop gain will change depending on potentiometer setting. So you'll need to have an AC feedback path through a series RC that doesn't go through the pot, and a DC path that goes through the pot. Also output voltage won't go below the internal voltage reference. And, if the digipot is a 5V device, then it won't work with more than 5V signals, which could severely limit your output voltage range.

Another option is to inject a DC offset into the feedback node, for example by connecting the "GND" end of the feedback divider to the output of a DAC. Say the switcher has an internal 1V2 reference, and you set the feedback divider so you get 30V on the output. If you shift the "GND" end of the feedback divider to +1.2V, then you get 0V output, so with a 3.3V or 5V DAC and a resistor divider, you can set your output voltage easily. It can also go below the internal reference voltage.

Note that there already are tons of cheap products that do this.

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  • \$\begingroup\$ I am glad to read your last line on cheap digital control PSU. Me poor electronics hobbyist has be using LM2596 based PSU modules all these years. So the time has come for me to upgrade to all digital PSU. Thanks again for opening my ok-boomer eyes. \$\endgroup\$ – tlfong01 Apr 19 at 1:51
  • \$\begingroup\$ Your AliEx catalog is a long list of gems in the AliBaba cave's PSU corner. Now I have too much money left over from my abandoned overseas holiday trips, but nothing to do for another coming boringly long lock down week. So I have already ordered a new PSU toy to kill time. My new toy is a digitally controlled (USB and WiFi) adjustable PSU (R...W), for only US$50, affordable for poor hobbyist like me. I am hoping the toy by SfEx to arrive in 2 days, as usual. In the meaning time I will watch EEvblog Dave's video in PSU design :). Many thanks again for you great tip. Cheers. \$\endgroup\$ – tlfong01 Apr 19 at 3:20
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    \$\begingroup\$ I really recommend Korad KD3005P, it's a linear power supply so it doesn't have switching noise in the output, which is nice for analog work. It's cheap.And it has an isolated USB port which is basically a USB-serial chip, so you can control it with the PC, read back the current, etc. \$\endgroup\$ – bobflux Apr 19 at 10:56
  • \$\begingroup\$ KD3005P sounds interesting. I also need a no-switching-noise PSU for my MOSFET/Tunnel Diode I-V curve plotting project: (1) MOSFET I-V Curve Plotting: electronics.stackexchange.com/questions/552237/…, By the way, I am now reading a TaoBao shop's catalog on PSU: Koprad KD3005D/P Adjustable and Programmable DC Regulating Power Supply - TaoBao: item.taobao.com/…, Do you have any general comments on their whole range of PSU? (Click the thumb images for details) \$\endgroup\$ – tlfong01 Apr 19 at 14:03
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    \$\begingroup\$ I only own 3005P so no comment on the others. I got two single channel supplies because it was same total price as the bigger 2 channel power supply, but if one breaks down, at least I still have one working lol. The PC interface works well, if you buy one, ask me for the python code. You can update voltage or current about 10 times per second, so you could use it as a (slow) curve tracer. But your MOSFET will heat up faster than that, so measurement would be wrong. \$\endgroup\$ – bobflux Apr 19 at 14:18
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Some steps that you will need to do: Set micro-controller PWM (arduino) to 62500Hz frequency and learn how to change the duty cycle of that PWM wave, connect output of PWM to low pass filter so you get almost DC out and feed that voltage/current into MOSFET or BJT (NPN), you will also need two buttons to control the PWM duty cycle.

You will need an transformer of about 34-36V to get 30V, i do not know any easy available voltage sources with more that 24V (laptop chargers etc), and you better start learning with 12V for start, you will burn a lot of your stuff with higher voltages or even harm your self.

So start with 12V and use BJT transistors then when you get it working you can scale it up latter if needed.

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Question

How to get started quickly to commercialize a product as specified below?

  1. PSU

  2. Voltage output: 1V ~ 30V

  3. Current: ~ 5A

  4. Power: ~ 50W

  5. MCU controlled


Answer

  1. For startup newbies wishing to manufacture products in "The World's Factory", I would recommend to start with MIT Innovation Node Hong Kong.

  2. For practice, I would recommend to start with Riden RD6006-W or Korad KD3005P. You can google for other similar models to suit your particular user requirement.

  3. Warning: 90% of new startups fail.


References

(1) MIT Innovation Node Hong Kong (News 2015)

(2) MIT Innovation Node Hong Kong (Home page 2021)

(3) What Percentage of Startups Fail? (67+ Stats for 2020) - Review 42, 2021feb25


/ to continue, ...

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