• EEVblog #224 – Lab Power Supply Design – Part 3

    Part 3 of the lab power supply design. This time the prototype build on a breadboard and some basic measurements, checks, and playing around.

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      • http://lidi.uw.hu/index.php Lidi

        So far looks nice. Please check the power turn off performance too.

      • Henrik Jensen

        I do not like you over current detection circuit for the led, why not let the opamp sense on the output of the over current opamp, just set the threshold at 0.3 volt, then the led will always turn on exactly when the over current limit is activated.

      • Markus

        Hi Dave, this is an excellent topic and you present it well, a real pleasure to watch !

        I also like your basic design, very universal and mod-friendly.

        One question concerning driving the current limit LED: I would have added a second transistor to the output of OP-amp 1b, sort of in parallel to the transistor conveying the current limitation to the LT3080. I think this would avoid the complication of adding a second OP-amp in parallel and have the slightly out of sync.


        • http://www.eevblog.com EEVblog

          Yes, that is a more accurate method. It was handy to show the pitfall of opamp input errors though.

          • Markus

            That’s a good excuse !

      • http://none Allan


        You have set a new video standard for teaching circuit design. Very cool.

        Yes, I liked seeing the RC time behavior in the “set” pin circuit path.

        I think you should take a couple of matched NPN transistors and make a current mirror. Use it to make a constant-current source driving a high-power LED. Then compare its output with that of your CCCV lab. PSU prototype’s current with supply-voltage fluctuations.

      • Bill

        Very nice. Please continue through to a finished product. Very much would like to see the board layout.


      • RJSC

        So, there went the “go down to 0V spec”.
        Is there a negative version of the LT3080, so that we could build a dual power supply?
        Of course we can build two separate (floating) supplies and connect the ground of one to the positive of the other, but then you couldn’t control both with the same micro-controller.

        • http://www.eevblog.com EEVblog

          No, the output can still go down to 0V, you just need a load.

      • Steve

        One concern I have is that the capacitor on the adjust pin cannot be discharged very fast. What happens to the output current when you switch in a higher current load?

        I expect the current to rise above the limit and then ramp down as the capacitor gets discharged.

      • http://load-8-1.blogspot.com/ Thomas

        Hi Dave.

        I’ve been planning to build a lab power supply for some time, and your design seems great. My electronics skills are quite limited though, so I have a couple of questions:

        What is the input voltage limit of the circuit, 16V?
        My plan was to use a 19.5V laptop PSU as the power source. Do you know any suitable replacements for the AD620 and TLC2272 that handles 20 volts or more?

        I live in Norway, and the LT3080 is not that easy to get a hold of. Haven’t found it on eBay and DigiKey charges a lot for shipping. Can you think of any good alternative to the LT3080?

        By the way: Your blog is great! Keep up the good work.

        • http://www.eevblog.com EEVblog

          Search for “high side current monitor”. There are many they go to high voltages. The LT3080 can easily handle the voltage. You can use an LM317 is you like the 1.25V offset, or can drive it negative.

      • Sebastian


        I like watching your videos – its tough to get bored.

        Would like to see heatsink temperature measurement for low output voltage at maximum load. Expect it to be “a little” higher than you’ve got at maximum output voltage.

      • Luke

        I like where the design is going. Truly, I think that there is an opportunity here for something special that companies like Agilent refuse to make: An all in one, digitally controlled power supply, load and multi-meter with a data logger. Especially if the whole thing could be controlled via a pc without some bloated software app like they always make. Would be ideal for a lot of automated testing applications and clean up a lot of test equipment clutter on my bench.

        This could be a fusion of many eevblog topics, uCurrent, Multi-meter concept, digital load, digital power supply to name a few.

        Keep to blogs coming, BTW when will the fully moved in office be revealed?

        • http://www.eevblog.com EEVblog

          It’s still in the hands of the lawyers and banks… Supposed to be settled before xmas though.

          • Luke

            Agilent’s product portfolio or the office?

            Just kidding, best of luck with the office.

      • AS

        The 20mV minimum output is what you should get sinking 10uA into 2kOhms. I don’t really know a good way for you to get real zero-output without a negative rail to sink the 10uA into.

        • Luke

          A 10 uA negative rail wouldn’t be so bad to create with a 7660 charge pump.

      • Tooms

        Anyone know where to buy the LT3080 as private person in the EU zone ?

        • Exile

          You, can buy it from http://www.elfa.se, but not cheapest one and the don’t have the to220 packet. or you buy LT3083 it should work and it handle 3A.

          • Tooms

            just looked at the page and they request an login before order and you can only get login as an firm.

      • Exile

        No, just press “Continue without logging in” button.

        • Tooms

          Yes i see that and when click the “Continue without logging in” then on the next page it tells me that i can not place the order before login, so that is no go

          • Exile

            Weird, works fine for me…

      • Timothy Hobbs

        what are the most important specs for the op amp if i choose another one for a higher voltage

        • Exile

          It can handle out and in port rail to rail, otherwise it will not go to “zero”…

      • John C

        Anyone else notice how often Dave says “bang”?

      • http://laboratory-glasswares.blogspot.com//www.blogger.com/rearrange?blogID=1616373348466254871&widgetType=Profile&widgetId=Profile1&action=editWidget&sectionId=sidebar-right-1 weblink

        You could certainly see your enthusiasm within the work you write. The sector hopes for even more passionate writers such as you who are not afraid to say how they believe. Always follow your heart.

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