Electronics > Projects, Designs, and Technical Stuff

0.13x vs 1.0x gain op amp regulated power supply - fail

<< < (8/8)

xavier60:

--- Quote from: HendriXML on February 17, 2019, 05:19:34 pm ---
--- Quote from: xavier60 on February 14, 2019, 02:51:31 pm ---Also, the op-amps won't have to be powered at the full input voltage.
The balanced amplifier would need to have near perfect CMRR to prevent input voltage variations affecting regulation voltage.

--- End quote ---
When I was done experimenting, I thought why not see wether this circuit can operate on an adapter. The adapter is about 9V and I added 2 smoothing capacitors of 2200uF.
The result was that the output became very “noisy” with loads, I don’t think there’s even a repetition going on.

So as an experiment and a way to check out idea’s it did a good job. But as a proper supply I would call it a fail.

As a battery voltage dropper its probably ok, I will have to check that. But I think its going to be recycled  :-+

Could you give an advise on an op amp which can regulate well on about 5-7 V, without being to sensitive to variations? Would be nice if it is THT and can be bought on AliExpress. But I wonder if it’s not the time get stuff elsewhere.

--- End quote ---
I went through the same process a while back, trying my own ideas and failing because I didn't know enough to understand the challenges involved.
I settled on the well known floating type topology and successfully completed a  bench supply project
Although the performance is good, I found debugging to be awkward, having to take measurements with respect to the positive output terminal.
The LM358 is more than good enough for experimenting. It operates from 3 to 36 volts. One important op-amp parameter to be aware of is the input common-mode range. It includes ground voltage for the LM358 which can be very useful in certain applications.
You will lean a lot from data PDFs.

Are you just experimenting or intending to construct something?
 

HendriXML:

--- Quote from: xavier60 on February 17, 2019, 10:42:24 pm ---Are you just experimenting or intending to construct something?

--- End quote ---
Just experimenting yet, at least until I got some “model” of how the components really work. On the way it is nice to end up with something that works, at which you can look back at. I already have a fume extracter for instance which I’m happy about. It’s starts when the you take the iron out of the stand, and it keeps blowing for a while after you put it back. This gives the smoke time to travel through a ventilation hose ending outside. In practice I don’t use the hose, but its much better than nothing. It has also dimmable LED’s (variable current).  :-+ Even used diffusion sheet to have less reflection on those tinned area’s.
I was making some boxed modules with logic gates, LED output, switches and stuff for my son (9) to play with. But he’s not really attracked to it. I think as a toy it needs to look more simple with only the printed symbols, ins and outputs. The prototypes are with lot of transistors, no ic’s.
For safety I want it battery powered, so if the circuit drops the voltage in a stable way I might use it. But I may also drop the whole idea. He plays this game Scrap Mechanic where he can do “virtually” much more cool stuff. And I don’t see any reason why playing with the boxes I (would) made would be more fun. Times have changed.

HendriXML:
About the circuit: the next time I will use a larger perf board. Also first deciding which components might be swapped and use pinheaders for them. Using dupont female connecters to make those components swappable or directly solder them on the pins.

On breadboard's I've got mixed feelings. If you've got cheap resistors they are a bit loose (I bend them, doubling the thickness) adding components on heatsinks is also somewhat complicated.

HendriXML:

--- Quote from: HendriXML on February 17, 2019, 05:19:34 pm ---The result was that the output became very “noisy” with loads, I don’t think there’s even a repetition going on.

--- End quote ---

I replaced the Mosfet, and indeed the strange noise went away. The circuit was somewhat stable using an adapter, but had a 100 hz ripple. Possibly the op amp needs a stable powersource. The used op amp is also not very suited for the usage, but I had it laying around.

Using a C1 capacitor: 10 nF made the circuit oscillate. 4.4 nF was OK, but did not enhance the performance.
So I won’t post any more graphs.

Working with header pins and dupont connectors worked fine. Having a wire with one dupont connecteron it makes it much easer to place header pins and keep them steady while soldering. The wire can for instance go down in another hole adding some pull to the pin.

HendriXML:
Some conclusions that I draw from this adventure:

* A programmable power supply can be used to automate characterization
* Excel can make good graphs, giving the possibility to combine more traces and or do more complex math between them
* Using XML as a data format worked nice and fast. No asking for headers, data types etc. if you supply a XML schema.
* Maxima can be used to make graphs as well, can be saved as PNG or SVG, but doesn’t need Visio for that. It has less options to change the appearance.
* Maxima can be used to fit curves, having some idea of what function it should match with is important.
* The website zunzun.com can do curve fitting also, and has a lot of possibilities and also gives a function
* When using low gain error amplification it is important to not let the gate capacitance disturb the short feedback loop. However this also means sacrificing in gate drive speed.
* In a low current situation the Mosfet as a high Rsd resistance. Voltage drops are huge with only a small change in current. Because of the gate capacitance changing to a low resistance state takes some few 100ns of time. A end capacitor can slow down the voltage drop a bit, giving the circuit more time to adapt.
* The first stage gain needed to adapt is low, it even works with 0.13x gain, but no real advantages where found doing this. Except it was more stable without a endcap. However this situation was unusable.
* Even powermosfets can easily be zapped.
* Better to choose a large perf board, keeping space for modifications
* Using headers and dupont connectors to add swappable components works
* Don’t underestimate the usability of BJT’s
* A lm358 is a good and affordable op amp to experiment with
* There’s a difference in having a working concept and a working product. Both should be celebrated!  :popcorn:

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod