Part 3 of the Open Hardware lab power supply design. This time the prototype build on a breadboard and some basic measurements, checks, and playing around.
Eight years old and still relevant. Absolutely awesome. Havn't seen anything like this anywhere else; not only talking through the circuit but walking through the whole design process with a master. Priceless.
Wow, Dave. It's really special to see this latest series of vids. Comparing where you started to where your at now, I can discern no less determination, charisma and honesty than that first vid... but without the distraction of that day job, well, what your doing here is really meaningful and helpful. As a father, I'm certain that Sagan will be proud of what your helping people everywhere learn to do (both in terms of EE, but more also generally: how to help other people and make ends meet too)
It's wonderful to see that you're doing so much work every day. This really is an example of "how it should be done". This will be the quality I'll start to want from everyone who even desires to make any tutorials about subject x :D Without people like you Dave, TH-cam wouldn't have any quality videos. Keep these coming :)
Wow - a must have Video not only for all electronics and digital oscilloscope beginners. Wonderful !!!!!!! What is so fantastic in this series ist that you not only say what is but also what one might think but in fact not is. Sometimes i think you just read my mind. Fantastic !
Dave, great stuff, as usual. You are the EE equivalent to khan academy. Very well set up, good explanations, give reasons why/why not, etc. You're a wonderful teacher, keep it up.
This series of videos has been well planned out and very informative. Thank you for posting these. I really do appreciate the effort you put into your videos. When you get around to doing the video for the final project I would hope that you also include some information on "the traps for young players" when designing the layout of the PCB. I will be looking forward to more of these educational videos from you. Thanks
I only wish that there was someone with your knowledge and personality in the electronics repair indusry. I am familiar with Jestine from Malasia and Dave from Oregon, but apart from that no one seems to come near your standard. For a newbie like me 70% of this great video soared over my head.
EEVblog I am learning so much from your channel please dont pay the haters any mind , keep on doing your thing . We need to design a circuit to slowly electrocute the haters ..
Tnx for beautiful TubeYou Psu-construction video-series. ..Big appreciation for 'all' your video-making and qualitative electronic lectures Dave. Also nice atmosphere with those crickets sounding now&then :) ..No such sounds here up north. (br, from norway to australia)
@Wilfredkazoks The light is not the same from all angles, so it constantly has to be changed, and my camera has a problem where it automatically jumps back out of manual exposure mode to auto after returning from playback mode. I do try and put it on manual exposure when possible, I forgot this time with the paper, sorry.
@superdau You didn't miss anything, the fact that it was available led me to use it, and it was helpful to show show the issue with identical comparator inputs. You can certainly use another transistor, and that's a more accurate way to do it.
17:20 To make the LED indicator for the "current limiting" mode work correctly, you can use comparator to monitor the voltage at pin 7 (input voltage to the transistor) (to compare it against about 0.6V - this voltage can be derived with voltage divider from the 2.5V reference).
Hey Dave, Im Loving this "Lab Power Supply" series more then any other. I have considered building it myself, and I came to the conclusion that the amperage and voltage that you have based this series on is a too low. If it was ~20A and ~35V, I would have built it by now. You are working with such a low voltage and amperage design that I just cant bother with taking the design to that stage. I wrote a WHOLE LOT! of massively positive things, but apparently I have a limit to how much i can write.
i've had a little play around with an old school bench supply, used the original Xformer but gutted the late 60's era regulating circuits. i have managed to get reasonable results using a series pass transistor and the "jellybean" quad opamps. not current limited but i do have a constant current mode with preset current limits and voltages using the radio buttons and rotary switches the old supply had, 0 to near 15 volts with reasonable regulation and less than 2 amps
thanks Dave for the detailed tutorial but im still left with one question i would like to build this same thing but have it be capable of 30v 10amp i know i need a different current resistor and transistors to handle the output current but im concerned about the op amp, will it be ok with 30-35v input?? thanks!
@Microman171 The LT3080 is designed to be stable. If you roll your own, you have worry about stability over a wide range of loads. May or may not be a problem for you, but something to watch out and test for.
@horfittunge Thanks. Interesting in that it's not even supposed to be a tutorial, it's just me breadboarding a design and doing a few tests and yapping on while doing it :->
One power-up test I'd be curious about is with the output voltage set to under 0.7V.. just because of that knee in the other power ups it makes me wonder if it can regulate down below 0.7v while it comes on. Learned lots though :)
@EEVblog Limited by the reference. Up the unregulated rail to 12V and change the opamp gain to 3 and you will get 6V out, just change the one resistor from 22k to 27K will probably do it.
Dave, great tutorial. I was wondering if you would consider doing a short video showing how the PWM would replace the pots for the limit control voltages. Obviously PWM from the duty adjust on a signal generator. But then I was hoping you could show someone how to do the same thing with a simple opamp 4 bit DAC (r*2^n opamp adder) that is controlled by DIP switches or a shift register. Just to show what you can do for controls if someone wasn't using a PWM for the reference voltage.
@randomgarfield @LeonValkenborg Yes, there are countless high current/high voltage linear and switchmode PSU's on the market, and they are cheap as chips. I'm doing something different, which will become clearer with time...
The bounce at the beginning is due to the output current sink turning on. Nothing due to the LT part, just the dropout and fast turn on of that old current sink.
My first reaction on the current limiting mode LED: If you're using the spare OP-amp, why not compare the output of OP-amp 1b with a constant 0.4 V or so. Then you'll have an exact sensing without any fine tuned voltage divider (the 0.4 V voltage only need to be roughly in the ballpark).
Question: For the CC limit LED. Could you not attach it to the positive rail via the 1k resistor and to the iset output (node 7) before the transistor? My logic is that it doesn't turn on until the transistor is turned on. Would that work? Or, is it going to be a problem in the lower mA range?
Just built it up. The LED turns on exactly when activated, "but" it is a gradual increase in voltage so the LED starts off dim and then increasingly gets brighter until it reaches 2 volts. Where as mirroring the opamp, the LED switches on instantly, albeit a smidge early. Once again, Dave is king...
Just stopped at 15:55 - why what would be against connecting opamp 2b to the output of 1b, thus as soon as the current limiter kicks in and there's > .65V on pin 7, we would have a clean indication the limiter is active, and just need to amplify that? Also of course, a simple npn transistor would also do that for us
Having a strange issue where my differential amplifier is giving output values with about a gain of 6. No idea why all the resistors are the same and I'm using the tlc272.
Why did you use a second opamp for the limit LED (except for the fact that it comes free with one of the packages already in the design ;) ). Couldn't you just hook another transistor to the output of 1b to drive a LED against V+? The output of 1b seemed to jump to at least 1V as soon as current limit mode kicks in. If it's the part count I would not have hooked up the second opamp in parallel, but have it compare the output of 1b to lets say 0,5V. What did I miss?
@LeonValkenborg Dave already stated he has no interest in high voltage and high current PSUs. Seriously though how often do you require more than 12V and an amp when you're breadboarding something. However his design does scale (although expensive). If you want 20A, just use 18 LT3080s. :) They'll also go up to 30V without issue too, but you'd be really silly to scale it that large.
@aseglkj Stability across a wide range of loads is a major consideration with a roll-your-own solution. See a previous video I have done on exactly this solution. It is not a horrible design, I deliberately traded off extra cost for development simplicity and guaranteed stability.
@randomgarfield for higher current its better to use a switch mode design as you wont need a truck sized heatsink, further more you can control both voltage and current in the same stage if you use a micro or a dedicated ic.
I have some thoughts about current limiting transistor. What can you say about the voltage on the base, when it's turning into the current limiting mode (opening transistor). From your video it is seen like a jump from not limiting, to limiting. Isn't it smooth? Because the volgate on the transistor base is quite slowly rising... Can you comment this?
shoot, thats pretty low noise, the one i rolled myself using spare parts, an LM324 and external series pass transistors does about 50 odd mV of noise, i didnt have my own Oscope but i used a PC based scope, it seemed to measure 50 - 100 mV above/below 0 (AC coupled), pretty horrible compared to the 3080 but not bad considering i cobbled it together
LT3080 is $31 in the little package, The bigger packages are $116 and $91. LT stuff is completely exorbitant. It's lazy to pay through the nose for a part to do all the work for you.
alright i might have a go with this supply, i wont have the regulator or the opamps, (i have got 324's though) i might want to find a site that gives free samples or similar for some of the parts and i can probably scrounge some of the passives
@laharl2k I wasn't being serious about scaling this up. Although you can make very large linear supplies that don't require huge heatsinks if low voltage output isn't a requirement.
It is nice (personally i would not use LM's but that's me) Whole OP-amp for current limit LED?! Just hook up LED in series with base of current limiting BJT, lower series base resistor, and add one resistor between base and emiter of current limiting BJT and voila. I've found i like 100microamps trough 5mm clear hi eff red led just fine, more then 3 mA is too bright for me, so choosing right resistors you can get it to work nice!
pls recommend,,, no change constant 5v,, no matter what load does,,,, while i control from 1 to 80 ma ,,, in this case,,, constant 5v,,, current limit not affecting voltage,,,
your output voltage does not seem to stay stable as you increase the amount of current drawn. it drops from 3.145v to 3.114v. should the output voltage not be monitored by a voltage devider and used to control the pass device?
I have a question. What if we exchange the LT3080 for a TIP122 and modify the voltage control loop like this: - the 1k that went to adjust goes to base - the 12k that also went to adjust goes to emiter (and emiter becomes the regulator output) - collector goes to VCC No other circuit changes. Would it still work? In my mind it seems like it should? Of course we are left with no thermal protection. But voltage and current adjust should work, right? The question is based on a problem with availability of LT3080 for me (or rather it's price is not friendly and in comparison I can fry TIP122's all day long).
Harald Sangvik Well, I do believe you are fundamentally wrong. The way I proposed to connect the transistor was a emitter follower, with a modification to the control loop. The regulator in it self also has some kind of transistor that is the pass element. Idea was to scrap the expensive part and exchange it for a cheap one. Reread my previous post. And if you can't understand it - try simulating it.
You would need to pay more attention to regulation, where a regulator will do everything for you. I will design this circuit using a LM338 and a NE555 negative voltage rail for going down to 0 volts. Should be good for 15V 3A using a laptop brick as a power supply
Just finished building it. Yes, it has current limit. Had to do some dicking around with the current limit cicruit. Had to drive both the current limit opamp and sinking the control pin to negative, otherwise it would current limit at 1.25 volts. It goes all the way down to 0 with a 300 ohm resistor attached. Haven't received the lm334 yet. Everything is made using jellybean parts, LM338, LM358 and NE555. Except for the voltage reference. Used a REF02 5v reference for that. I have also added an arduino Nano for reading the voltage and current, and maybe logging, wireless etc. To get the negative 1,25 volts, i fed the 5v reference into the inverting input of an opamp, and a 6,8k resistor to the pot. I have also ordered an AD620, to see if i can get even more accuracy out of it
Eight years old and still relevant. Absolutely awesome. Havn't seen anything like this anywhere else; not only talking through the circuit but walking through the whole design process with a master. Priceless.
love these videos. Thanks
Thanks for the awesome video !
Love the automatic subtitles generation (6:40) : "1 milliamp current source" -> "1,000,000 carrot sauce" :D
i got "1 milliamp car sauce"
Excellent series so far. Love how it evolved from "tap, tap, tap-tap!" to "bang! bang! BANG!" Awesome energy you have.
Wow, Dave. It's really special to see this latest series of vids. Comparing where you started to where your at now, I can discern no less determination, charisma and honesty than that first vid... but without the distraction of that day job, well, what your doing here is really meaningful and helpful. As a father, I'm certain that Sagan will be proud of what your helping people everywhere learn to do (both in terms of EE, but more also generally: how to help other people and make ends meet too)
@SuperEvilbug Yes, this will hopefully become a kit. The final design I have in mind will be more than what you see here, and rather novel I think.
It's wonderful to see that you're doing so much work every day. This really is an example of "how it should be done". This will be the quality I'll start to want from everyone who even desires to make any tutorials about subject x :D
Without people like you Dave, TH-cam wouldn't have any quality videos. Keep these coming :)
Wow, this must seriously be the best tutorial I've ever watched. Super great job Dave!
Wow - a must have Video not only for all electronics and digital oscilloscope beginners. Wonderful !!!!!!! What is so fantastic in this series ist that you not only say what is but also what one might think but in fact not is. Sometimes i think you just read my mind. Fantastic !
Dave, great stuff, as usual. You are the EE equivalent to khan academy. Very well set up, good explanations, give reasons why/why not, etc. You're a wonderful teacher, keep it up.
This series of videos has been well planned out and very informative. Thank you for posting these. I really do appreciate the effort you put into your videos. When you get around to doing the video for the final project I would hope that you also include some information on "the traps for young players" when designing the layout of the PCB. I will be looking forward to more of these educational videos from you. Thanks
I only wish that there was someone with your knowledge and personality in the electronics repair indusry. I am familiar with Jestine from Malasia and Dave from Oregon, but apart from that no one seems to come near your standard. For a newbie like me 70% of this great video soared over my head.
When the nerds finally take over the earth, truly thou shalt be crowned as their king......
HAHAHAHAHAHHAHAHAHAHAHAHAHHA, sure thing!
EEVblog I am learning so much from your channel please dont pay the haters any mind , keep on doing your thing . We need to design a circuit to slowly electrocute the haters ..
It's good to use regular diode in series with zener diode, to minimize the voltage-temperature changes
Beauty!
I've really enjoyed following this process.
Thanks.
Tnx for beautiful TubeYou Psu-construction video-series.
..Big appreciation for 'all' your video-making and qualitative electronic lectures Dave.
Also nice atmosphere with those crickets sounding now&then :) ..No such sounds here up north.
(br, from norway to australia)
what a fucking great vid series!!!! thanks for the course, dave. you're awesome!
Really interesting to see the startup transient on the digital scope. You weren't able to see that on the old analog scopes!
Wow, that DaveCad-XL is impressive!
@Wilfredkazoks The light is not the same from all angles, so it constantly has to be changed, and my camera has a problem where it automatically jumps back out of manual exposure mode to auto after returning from playback mode. I do try and put it on manual exposure when possible, I forgot this time with the paper, sorry.
These videos are amazing . thanks to you .
I am learning a lot. Thank you....keep it up!
I've been binge watching these and my brain is turned to mush but it's soooooo cool
I love the LT3080 - great component with some surprising features. I use it a lot.
@superdau You didn't miss anything, the fact that it was available led me to use it, and it was helpful to show show the issue with identical comparator inputs. You can certainly use another transistor, and that's a more accurate way to do it.
17:20
To make the LED indicator for the "current limiting" mode work correctly, you can use comparator to monitor the voltage at pin 7 (input voltage to the transistor) (to compare it against about 0.6V - this voltage can be derived with voltage divider from the 2.5V reference).
Love the vids...
Did anyone count how many times he says bang? Lol
Or 'I like it!'? I really love the videos.
@EEVblog In either case, I love it!
Keep it up.
Bang! Jk - Excellent vid Dave!!!
Hey Dave,
Im Loving this "Lab Power Supply" series more then any other.
I have considered building it myself, and I came to the conclusion that the amperage and voltage that you have based this series on is a too low.
If it was ~20A and ~35V, I would have built it by now.
You are working with such a low voltage and amperage design that I just cant bother with taking the design to that stage.
I wrote a WHOLE LOT! of massively positive things, but apparently I have a limit to how much i can write.
Amazing Video, Merry Christmas Dave!!! (in Advance)
Nice work yet again, Dave. I'm reading data sheets in your voice now. 8)
Hi Dave!
The design videos are great! Definitely keep them coming!
What's next? pcb and case design? panel meters?
38:50 Can't remember if this series was before or after the videos about scope input microphonics, but that screen tap was a great unstaged example.
i've had a little play around with an old school bench supply, used the original Xformer but gutted the late 60's era regulating circuits. i have managed to get reasonable results using a series pass transistor and the "jellybean" quad opamps. not current limited but i do have a constant current mode with preset current limits and voltages using the radio buttons and rotary switches the old supply had, 0 to near 15 volts with reasonable regulation and less than 2 amps
thanks Dave for the detailed tutorial but im still left with one question
i would like to build this same thing but have it be capable of 30v 10amp
i know i need a different current resistor and transistors to handle the output current but
im concerned about the op amp, will it be ok with 30-35v input??
thanks!
Thanks Dave
I have a new drinking game: you have to drink every time Dave says BANG!
should have joined me on the other parts with the whiteboard and tapping
@ZitroOgu You can, yes, but only if you have the package that has the pin separate. Keeping lowest common denominator here. Forgot to mention that.
with the added uc this design would be great hardware for a diy single cell lipo charger :)
I subscribed .... I love your channel
@Microman171 The LT3080 is designed to be stable. If you roll your own, you have worry about stability over a wide range of loads. May or may not be a problem for you, but something to watch out and test for.
@horfittunge Thanks. Interesting in that it's not even supposed to be a tutorial, it's just me breadboarding a design and doing a few tests and yapping on while doing it :->
Bad man, you made me longing for a decent oscilloscope now!
@Th3Su8 My videos are almost never "planned out", these ones included. They kinda "just happen" :->
Is there a Dave-CAD download for this or shall I just do a screen-grab?
One power-up test I'd be curious about is with the output voltage set to under 0.7V.. just because of that knee in the other power ups it makes me wonder if it can regulate down below 0.7v while it comes on. Learned lots though :)
@EEVblog Limited by the reference. Up the unregulated rail to 12V and change the opamp gain to 3 and you will get 6V out, just change the one resistor from 22k to 27K will probably do it.
Dave, great tutorial. I was wondering if you would consider doing a short video showing how the PWM would replace the pots for the limit control voltages. Obviously PWM from the duty adjust on a signal generator.
But then I was hoping you could show someone how to do the same thing with a simple opamp 4 bit DAC (r*2^n opamp adder) that is controlled by DIP switches or a shift register. Just to show what you can do for controls if someone wasn't using a PWM for the reference voltage.
Boom! And there it is!
@randomgarfield @LeonValkenborg Yes, there are countless high current/high voltage linear and switchmode PSU's on the market, and they are cheap as chips. I'm doing something different, which will become clearer with time...
awesome
Dave must be popular at work, saying bang all the time while he's working on stuff lol
Bang! subscribed.
Could make a parody of this video just with the amount of "bangs" that were said haha. But I really do love the videos. Only poking some fun.
@xng14 Yep, I have a nice, and I think kinda novel build coming up, will be a while though...
The bounce at the beginning is due to the output current sink turning on. Nothing due to the LT part, just the dropout and fast turn on of that old current sink.
@electrodacus Yeah. I thought it was a good example of how it can hide things, so quickly shot a separate video.
My first reaction on the current limiting mode LED: If you're using the spare OP-amp, why not compare the output of OP-amp 1b with a constant 0.4 V or so. Then you'll have an exact sensing without any fine tuned voltage divider (the 0.4 V voltage only need to be roughly in the ballpark).
Question: For the CC limit LED. Could you not attach it to the positive rail via the 1k resistor and to the iset output (node 7) before the transistor? My logic is that it doesn't turn on until the transistor is turned on. Would that work? Or, is it going to be a problem in the lower mA range?
Just built it up. The LED turns on exactly when activated, "but" it is a gradual increase in voltage so the LED starts off dim and then increasingly gets brighter until it reaches 2 volts. Where as mirroring the opamp, the LED switches on instantly, albeit a smidge early. Once again, Dave is king...
Can you use a reversed biased LED as a voltage reference (given it will be shielded from light)? I have some junk hong kong cheapies.
Dave I love your blog & will to "like" it. I am dying to get some of your T-shirts! Please, where do u get them?!?!
Just stopped at 15:55 - why what would be against connecting opamp 2b to the output of 1b, thus as soon as the current limiter kicks in and there's > .65V on pin 7, we would have a clean indication the limiter is active, and just need to amplify that? Also of course, a simple npn transistor would also do that for us
and BANG!
Having a strange issue where my differential amplifier is giving output values with about a gain of 6. No idea why all the resistors are the same and I'm using the tlc272.
Why did you use a second opamp for the limit LED (except for the fact that it comes free with one of the packages already in the design ;) ). Couldn't you just hook another transistor to the output of 1b to drive a LED against V+? The output of 1b seemed to jump to at least 1V as soon as current limit mode kicks in. If it's the part count I would not have hooked up the second opamp in parallel, but have it compare the output of 1b to lets say 0,5V.
What did I miss?
Would like to use Arduino parts. Maybe a Arduino Nano board?
@LeonValkenborg Dave already stated he has no interest in high voltage and high current PSUs. Seriously though how often do you require more than 12V and an amp when you're breadboarding something. However his design does scale (although expensive). If you want 20A, just use 18 LT3080s. :) They'll also go up to 30V without issue too, but you'd be really silly to scale it that large.
What type of capacitors are those in red and blue? Thanks
@aseglkj Stability across a wide range of loads is a major consideration with a roll-your-own solution. See a previous video I have done on exactly this solution.
It is not a horrible design, I deliberately traded off extra cost for development simplicity and guaranteed stability.
@randomgarfield for higher current its better to use a switch mode design as you wont need a truck sized heatsink, further more you can control both voltage and current in the same stage if you use a micro or a dedicated ic.
The EEVBlog drinking game. Dave says "Bang", take a swig. You'll be drunk in the first 10 minutes and in hospital before the end of the video. :)
I have some thoughts about current limiting transistor. What can you say about the voltage on the base, when it's turning into the current limiting mode (opening transistor). From your video it is seen like a jump from not limiting, to limiting. Isn't it smooth? Because the volgate on the transistor base is quite slowly rising... Can you comment this?
shoot, thats pretty low noise, the one i rolled myself using spare parts, an LM324 and external series pass transistors does about 50 odd mV of noise, i didnt have my own Oscope but i used a PC based scope, it seemed to measure 50 - 100 mV above/below 0 (AC coupled), pretty horrible compared to the 3080 but not bad considering i cobbled it together
LT3080 is $31 in the little package, The bigger packages are $116 and $91. LT stuff is completely exorbitant. It's lazy to pay through the nose for a part to do all the work for you.
@EEVblog does it have a flux capacitor by chance? :)
@Dysl3xicDog Not yet, patience!
alright i might have a go with this supply, i wont have the regulator or the opamps, (i have got 324's though) i might want to find a site that gives free samples or similar for some of the parts and i can probably scrounge some of the passives
@laharl2k I wasn't being serious about scaling this up. Although you can make very large linear supplies that don't require huge heatsinks if low voltage output isn't a requirement.
It is nice (personally i would not use LM's but that's me)
Whole OP-amp for current limit LED?!
Just hook up LED in series with base of current limiting BJT, lower series base resistor, and add one resistor between base and emiter of current limiting BJT and voila.
I've found i like 100microamps trough 5mm clear hi eff red led just fine, more then 3 mA is too bright for me, so choosing right resistors you can get it to work nice!
Dave do you have a BOM and a official schematic to work from?
@EEVblog lab power supplies as well ;)
i'd like to combine power supply and charger for all kinds of accumulators
You should connect the unused op amps properly.
pls recommend,,, no change constant 5v,, no matter what load does,,,, while i control from 1 to 80 ma ,,, in this case,,, constant 5v,,, current limit not affecting voltage,,,
Is that really an 11500€ oscilloscope? :O
Do you often draw schematics on paper? :)
your output voltage does not seem to stay stable as you increase the amount of current drawn. it drops from 3.145v to 3.114v. should the output voltage not be monitored by a voltage devider and used to control the pass device?
@Afrotechmods : Bangg !
bang!
What about making a power supply with digital thumbnail switches? I have some mini-lever digital switches from Digitran Company, Pasadena California.
@1710WL get it right! it's 1.21 jigawatts. ;) hehehe
lets put the 22 micro F in and bag the noise is gone.
reminds me of bam! the dirt is gone
how can I get the maximum output voltage up to 30V?
and... Bang!
;)
@turbochargedbrick it's davecad!
I have a question.
What if we exchange the LT3080 for a TIP122 and modify the voltage control loop like this:
- the 1k that went to adjust goes to base
- the 12k that also went to adjust goes to emiter (and emiter becomes the regulator output)
- collector goes to VCC
No other circuit changes.
Would it still work? In my mind it seems like it should? Of course we are left with no thermal protection. But voltage and current adjust should work, right?
The question is based on a problem with availability of LT3080 for me (or rather it's price is not friendly and in comparison I can fry TIP122's all day long).
The TIP122 is a transistor, not a voltage regulator. It doesn't operate like the LT3080
Harald Sangvik Well, I do believe you are fundamentally wrong. The way I proposed to connect the transistor was a emitter follower, with a modification to the control loop. The regulator in it self also has some kind of transistor that is the pass element.
Idea was to scrap the expensive part and exchange it for a cheap one.
Reread my previous post. And if you can't understand it - try simulating it.
You would need to pay more attention to regulation, where a regulator will do everything for you.
I will design this circuit using a LM338 and a NE555 negative voltage rail for going down to 0 volts.
Should be good for 15V 3A using a laptop brick as a power supply
Harald Sangvik Nice hack idea. But no current limit?
Just finished building it.
Yes, it has current limit. Had to do some dicking around with the current limit cicruit.
Had to drive both the current limit opamp and sinking the control pin to negative, otherwise it would current limit at 1.25 volts.
It goes all the way down to 0 with a 300 ohm resistor attached. Haven't received the lm334 yet.
Everything is made using jellybean parts, LM338, LM358 and NE555. Except for the voltage reference. Used a REF02 5v reference for that.
I have also added an arduino Nano for reading the voltage and current, and maybe logging, wireless etc.
To get the negative 1,25 volts, i fed the 5v reference into the inverting input of an opamp, and a 6,8k resistor to the pot.
I have also ordered an AD620, to see if i can get even more accuracy out of it
"BANG"
The original spec was for 6V but now we seem to be maxing at 5.5V... :/
вау, круто