Custom Made Voltage Regulator - Page 1
Forum section: electronics / beginners

author: cabledude
author_rank: Newbie
timestamp: February 01, 2022, 04:25:17 pm
content: Hello all,New visitor here, not an EE, just have a DIY project I’d like help with.I believe the best way to describe the project is as a voltage regulator. The objective is to try to contain a variable voltage input within a more narrow range as output. I believe he input voltage will range from .1-1 volts and the desired output range is .7-.9 volts. I do not know the current, although I might be able to measure that soon. Ideally, I believe the output would follow the wave pattern of the input, only be limited to the .7-.9v range.I’ve done some research on how to possibly do this, but I’m coming in as a complete novice. I didn’t even know about Ohm’s Law. The initial approach was to build a circuit using a resistor and capacitor, so I purchased some breadboards and an assortment of resistors and capacitors. Over time I learned that I was basically building a low pass frequency filter. This was interesting and fun, but as I understand it, my need is not to control frequency, but amplitude.It dawned on me that I was needing to build a voltage regulator, so I looked into regulator circuit design. This was above my head, at least for the moment, but I also found a wide range of readily available “voltage regulator” assemblies that I could simply purchase, so I wondered if instead of building a solution from components, I could buy one.And here I am at EEVblog forum.I think ideally, the solution would be “passive” and not require a power supply, but that is not a requirement.I suppose the narrow question would be whether there is a readily available item that accomplishes the task - something on Amazon or the like. If so, I’ll simply buy it and wire it in. However, if this project will require fabrication, I would look for advice as far as how to build the circuit, or if that is beyond the reasonable scope of a novice experiment, how to find someone to help me.Thank you.

author: Ian.M
author_rank: Super Contributor
timestamp: February 01, 2022, 04:49:38 pm
content: Voltage regulators almost invariably work on continuous DC, so if you want to 'follow' the 'wave pattern' of the input signal you almost certainly *DON'T* want a voltage regulator.Taking a wild assed guess: Is the input an audio signal? If so you *MAY* want some sort of limiter or compandor or AGC circuit.However lets take a step back and try and avoidthe XY problemthat I think you are probably presenting us with.What's the 'big picture' overview of your project? What are you trying to do overall and what constraints exist, (and how hard are the constraints on a 1-5 scale from 'nice to meet if affordable' to 'carved in stone by your preferred deity')?

author: Manul
author_rank: Super Contributor
timestamp: February 01, 2022, 10:59:36 pm
content: Quote from: cabledude on February 01, 2022, 04:25:17 pmBased on your given data, yes, it can be done with only resistors and a voltage supply. Although devil is in details. For example, how accurate it should be, input impedance, output impedance. To make it work under varying external conditions you might need output or input buffers (that might be an op amp).I totally agree with Ian.M, you should give more information, at least tell what is the source of input voltage and what will be connected to the output.

author: rpiloverbd
author_rank: Regular Contributor
timestamp: February 02, 2022, 12:18:06 pm
content: I think you can do it by making a voltage divider circuit with one fixed and one variable resistor.

author: Ian.M
author_rank: Super Contributor
timestamp: February 02, 2022, 12:29:27 pm
content: Quote from: rpiloverbd on February 02, 2022, 12:18:06 pm Does your Visualization of the Cosmic All, which must of course include the O.P.s application, also show how a resistive "voltage divider circuit" can amplify 0.1V in to 0.7V out?

author: devinatkin
author_rank: Contributor
timestamp: February 03, 2022, 04:12:42 pm
content: What is your end goal with it. Cause yeah, it sounds like it can be accomplished with a big capacitor. Is this thing a signal or a power source. If you're just interested in smoothing a power source then whack a large capacitor on there. Get high enough capacitance and yeah it should get nice and smooth. If it's a signal, then whacking an op amp with with a low pass filter will give you the best results (Going completely passive is an option, but if you don't know anything about the supply a simple op-amp circuit will give you much higher input impedance and make it less likely that something gets mucked up.

author: cabledude
author_rank: Newbie
timestamp: February 14, 2022, 01:47:59 pm
content: Thank you all for the responses.I agree that the "voltage regulator" was not the right way for me to think about this. How about more along the lines of a voltage "adjuster?" For example, if the midpoint of the voltage wave is .5v and the amplitude is 1v such that the wave modulates between 0 and 1 across .5 as the x-axis, what if I wanted an adjustable way to reduce the amplitude. A good way to describe it might be a volume knob, where 0% on the volume knob resulted in a flat voltage of .5v and 100% resulted in the original voltage wave varying between 0-1v.Thanks.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 14, 2022, 03:08:59 pm
content: A small incandescent light bulb (eg a fairylight) in a voltage divider will act as a compressor- choosing R1 and the Amp gain will be tricky. It won't be very accurate or temperature stable though.A clue about your application will help us help you. What is the purpose of this range redcution?

author: tooki
author_rank: Super Contributor
timestamp: February 14, 2022, 04:35:54 pm
content: Quote from: cabledude on February 14, 2022, 01:47:59 pmPeople aren’t asking for an analogy. They’re asking for what your concrete application is.

author: donlisms
author_rank: Frequent Contributor
timestamp: February 16, 2022, 01:02:07 am
content: If I understand what you're asking for, you want to change the range of the voltage, and the offset of it. This a linear transformation; i.e., you can accomplish it by multiplying the input by a certain coefficient, and then adding a constant offset. The math is "out = input * A + offset." That's a fairly simple thing to accomplish with an opamp; it's kinda what they do. It's how it would normally be done in a circuit design.The basic challenge with doing it passively is turning 0.1 volt into 0.7 volts. Making more volts is not a passive operation; it's active. So somehow, somewhere, you're going to need circuit elements that are able to introduce additional voltage. Capacitors can only sorta do that, in limited ways (usually involving diodes), and I think in your application, it's difficult to see how to make the thing happen. Resistors definitely can't add voltage by themselves. Control voltage (and current) coming from somewhere else, yes... but not adding any.You want to change an input range of 0.9 volts into a range of 0.2 volts; that's a gain of (output/input) 0.2/0.9, which is 0.222. That's the gain of your amplifier.Once that gain is applied, an input of 0.1 volts becomes 22.2mV, but you want 700mV. So now you need the offset, which is the difference between what you want and what you have: 678mV. So you need a non-inverting amplifier with a gain of 0.222 and an offset of 678mV. If you put in a DC voltage, it would transform it as you describe. If you were to put in an AC voltage, a signal of some kind, possibly even audio... it would transform it as you describe.If you were to study opamps (which I would suggest is a Good Thing because it seems like you like to learn things) this should end up being pretty easy. It's unlikely you'd find anything like this off-the-shelf, because not many other people in the universe needs an amplifier configured exactly like this!

author: SmallCog
author_rank: Frequent Contributor
timestamp: February 16, 2022, 02:09:51 am
content: Definitely read up on op amps, fascinating little things everyone with a passing interest should learn aboutAlso have a read of basic amplifier theory (eg this, but there's litterally thousands of websites)https://www.tutorialspoint.com/amplifiers/amplifier_basic.htmIt sounds like you want to play with gain (size of the waveform) as well as offsetsRead up on the function of a coupling capacitor, basically this will let you get your waveform without it's DC bias (the dc voltage its wobbling around) and after you've fiddled with the gain of the signal, your circuit can always add a suitable DC offset back onto it.

author: m3vuv
author_rank: Super Contributor
timestamp: February 16, 2022, 08:21:15 am
content: seems like his reluctance to answer what he wants to use it for means worthless answers without gazing into a crystal ball!!

author: Terry Bites
author_rank: Super Contributor
timestamp: February 16, 2022, 09:34:07 am
content: Maybe we should get as stoned as he is so we can tune in to the vibe??

author: Terry Bites
author_rank: Super Contributor
timestamp: February 18, 2022, 02:09:00 am
content: Easy. Create a ciruit with the transfer function of y = 0.2222x + 0.6778 Slope and ofsett with analog computer and excel. If you're a propper head case try y = 0.0869ln(x) + 0.9

author: xavier60
author_rank: Super Contributor
timestamp: February 18, 2022, 03:51:44 am
content: Quote from: cabledude on February 14, 2022, 01:47:59 pmThis will do that. It's like the way some tone controls work. In this case the capacitor would be made large enough to better filter the signal.

author: fourfathom
author_rank: Super Contributor
timestamp: February 18, 2022, 04:07:41 am
content: I agree, we really ought to have a description of the application.But, if the goal is to translate an input voltage between 0.1V and 1.0V to an output voltage between 0.7V and 0.9V. this can be done with two resistors and a positive voltage (see attached)

author: bdunham7
author_rank: Super Contributor
timestamp: February 18, 2022, 04:15:47 am
content: Do the input and output have to share a common ground? If not, you can maybe do it passively with a resistive divider and a voltage source. But without knowing the impedance of the source and load, which determines how much current is involved, we're all just stabbing in the dark. If you need it buffered (load impedance is much lower than the input, so you need current gain) then this is just a textbook op-amp exercise.