DIY Digital Lab Power Supply: Part 3 - Ec-Projects
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- čas přidán 4. 09. 2024
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Hey Mads,
I'm liking this "development style" of series, you don't see this too often by youtubers. Being educational, I'd be curious to see even more testpoints being put on the scope, like outputs of opamps etc. I also like your practical introductions to complicated topics, just like you did here with frequency domain.
What made me comment is that, looking at the circuit, I think I'm seeing a more evident feedback (than the regulator loops themselves) that can cause stability problems: the way the current control is hooked up. Let's say we're voltage regulating, and current regulation is just kicking in. This drives the Base of the PowerTransistor lower, but in turn, the voltage regulator is going to be trying to compensate that. Depending on the exact gains of each part, the opamp might go all the way up to saturation, or you're not able to make the current go lower, or it'll just be unstable, probably on the edge of being current limiting, or at the extreme ends.
What I'm proposing is to have one single opamp controlling the Transistor (the one called Voltage regulator opamp so far), and to manipulate either of its inputs by the current sensing circuitry, as if it would be measuring too high of a voltage, or as if we were turning the reference voltage down, to make it drive the voltage down as needed.
Looking forward to watching next episodes.
Thanks for your comment :)
I think you are right. We might end up doing something like that. I was playing around with the same idea a few days ago and it seems to give a much better "transient response" when operating in CC mode.
I.E. if you set a current limit of 1 A and then change the resistance of the load.
This power supply designing series was really good. why did not you continue?
this is much better explained than Dave's power supply design on EEVBlog, thanks much for doing this!
I'm really enjoying this power supply series. Just one question - when will we see Part 4?
2:05 First of all, Great video series!!!
I know this comment is almost a decade late, but I don't get why you were saying that you could still source current in the voltage regulation section if the current regulation section was turned all the way down or off??? Shouldn't there be no current to supply to the voltage regulation section to source the current? I know that the op amp passes current to the transistor but if there is no current being supplied to the collector of the transistor it shouldn't pass current beyond what the op amp can provide(10-100mA). Just a thought.
It seems like you might be in the analysis paralysis phase of the project, Dont worry I find myself there too on a lot of my projects. 😁
When will Part 4 of this series be published? I'm following along, building my own supply. I like your videos. Thumbs up, and looking forward to Part 4.....
maybe the oscillation comes from the comparator after the differential amplifier. Because it is an open loop with out feedback it creates that oscillation because if the voltage of the differential is bigger than the Vset then the op amp drives it's output low, and a fraction later you get 0 out of the differential then the Vset is bigger than the voltage of the differential and the output of the comparator again gets high and this oscillation continues
Maybe I am not right but this is how I think it, with all the respect :)
Did you consider using a MOSFET for the voltage regulation rather than a transistor? Since no current is drawn from the gate, that would solve your problem with the base current showing up in the output in a much more straightforward way, I think.
I'm enjoying this video series: it's interesting to follow along with the development cycle. Thanks.
Don't forget the gate capacitance of the MOSFET. I'd go as far as to say that MOSFETs like to oscillate even more. I think this approach with manipulating the two gain paths to be more asymmetric works much better.
A unity opamp should suffice to eliminate that, no? I have long considered using a LT1970 for a power supply. Mostly as the stuff I do only need a few milliamps, but also the datasheet has a circuit to drive a mosfet for higher current. In fact I would just like to see a nice DIY 12V 500mA (maybe 1A if possible) precision supply.
Hello...all time hand made good .
Keep the work mate!
I was just wondering if you would finish the now 3 part power supply from a year ago. 30 volt ,,, 3 amp,, Thank you for reading
why are you persistent on using high side current sensing and live with the base current error? You should measure the current on the low side as that eliminates base current error. Furthermore your high side diff amp will have significant errors if you build it your self with off the shelf resistors. On the low side sense your diff amp will reduce to a simple non inverting (of even unity gain) amp meaning you can use cheap opamp and less errors!
good project!
let him build it, once he tests it we will see whats wrong with it. He will have some oscillations for sure but it can be fixed. Also it will be a good learning experience for him and for his viewers. Also i can tell that his over current protection wont work
Base current error in the first test, or in the last? Think I got rid of that. You are right about the low side regulation, but wouldn't that complicate the voltage regulation instead. Without thinking too much about it, I think that would require a differential measurement then.
It is supposed to be for beginners to follow. Basically how to make the two circuits and experience the problems which one may face by putting them together. That's why we take one incremental step at a time. :)
What about using PNP pass transistor?
Yes, that would solve both the base current issue and simplify things. Most supplies I've seen use a PNP (or P-mosfet) as the pass element.
Still, I haven't designed a supply like this, so my comment is definitely coming from the cheap seats. :) I'm enjoying this, so I subscribed!
@@setSCEtoAUX pnp will be not reliable for linear power supply
I'm curious how it can be solved to have a limited "constant current" mode as well. If I understand correctly, here current limit cause the output voltage to be dropped to zero. However sometimes it's also useful to only drop the output voltage to a level where the current is about at the selected limit. For example to figure the forward voltage out for a LED or such, with limiting its current to 10mA for example. Surely it creates under-voltage situation which is not what you want in some situations, so maybe it should be made optionally? I'm not so much familiar with power supply designs so I am not sure if my question has too much sense though :)
You can learn from inplix scripts how to make it yourself.
your audio is not left-right balanced. makes it very hard to watch the video
I thought it was going to be digital ...... Or is digital is still in 1970 ish ........