Hello I am in the current process of designing a pitch generator I am going to use for my end of the year physics project and in need of some help. A few components that I am utilizing require a dual polarity power supply, +15 and -15 volts, my question is: Can I use two regulators, the +15v putting out a maximum of 1A and another -15v putting out a maximum of 100mA? The dual polarity components will theoretically draw a total of 68.35mA from each power supply so I don't think it would be a problem but because of current differences I am not sure. The ground will be established between them, like center tap if you will. A few more components (Leds, have to make it look good) will draw from the +15v regulator through resistors. How much of a voltage/current do you think I will need to power the circuit? I know that the voltage input has to be above the regulators, like 18v, but I'm not sure about the current input. Can 1A work or will I have to go up to 1.5A? This is a side question if anyone can answer: The output of my circuit will be either a sine wave or a square wave. Do I have to match speaker impedence or can I feed it directly to a speaker with maybe a 386 audio amp in between? Thank you very much!
Dual regulators is fine, but what math are you using to justify one requiring 1A while the other only requires 100ma? I take it there is going to be a *lot* more stuff running off of the +15v line? The other question is what dual polarity components? If you can provide mfg/part#/specs we can see how this works a bit better and can let you know if there is anything out of the ordinary that might be of interest. I would suggest, using either Diodes or another regulator for the other voltages. Only because resistors change with current and temperature. Unless you go through the process of calculating the exact draw currents of every device attached to the resistor network, it can easily become a very unreliable method of voltage conversion (especially if the load is an amplifier which constantly varies it's input draw). Most regulators that are going to provide you with +15v are going to require something in the minimum range of 24v to operate. You have to take into consideration the total wattage requirements, and find an appropriate regulator. +15 @ 1A and -15 @ 100ma is going to require 15.15 watts minimum, depending on what other components you are driving from this, will increase the wattage accordingly. You will need a regulator that can handle whatever wattage requirements you may have. Considering your need for varying voltage levels, you may want to look at a switching power supply instead of just a bunch of regulators. That will offer you the best overall source of power/current for your system. You could build the switching system yourself if you like, but with the number of PS mfgs out there, it would be a lot easier just to buy one. Speaker impedance determines current draw necessary from the amplifier. Since impedance varies with frequence and mechanics, it all depends on what you plan on feeding. You can feed a speaker with *anything*. The problem *really* becomes, what do you want to hear? If you are feeding a set of headphones, a 386 audio amp will probably work just fine. However, something larger (like stereo speakers) would require something a bit beefier than a 386. If you're working with something like a little peizo speaker, or small 1-2" dome speaker, you might be fine with the 386 also. I would *never* recommend drawing off of the direct circuit. With any speaker you have back EMF you have to worry about. The amplifier is going to be able to handle this back EMF (with that as part of the design), however your output circuit might not, and you could fry something as a result. In addition, it is unlikely your circuit is going to be able to handle the current requirements necessary to move that speaker.
If I understand you right, you want to use 2 15v wallmart transformers? Or an actual regulator? With the walmarts, if they aren't grounded (floating voltage), then connect them in series, and use the joint between them as 0 and te other sides as -15 and 15. I think negitive voltage regulators don't make negitive voltage, just limit it.
I think he means components requiring a split supply rail - e.g. op-amp etc. Depending on the capacitor you use and the current draw, the input voltage can be as little as 17V
Before you go off on a tangent, look closely at his post and he quotes that he is going to be running much more off of this regulator than just an op-amp. While the 7815 can handle over 1A using 18v's, it is by no means as stable as providing a higher voltage to the 7815. In addition, if he's going to be running this off of some Wal-wart, he'd be better off using a 24v wart than an 18v wart as the regulation on those warts are pretty lousy. As he draws more current, that 18v wart is going to go under, and he's probably going to run out of steam on his op-amp. Better to play it safe and run a little higher.
The only components that are going to be running off both the +15v and -15v are the the pitch generator IC itself, 8038, and probably an op-amp. The rest of the components such as the 386 audio amp and the LEDs for indication of notes/octaves and so on run off the +15v. The components that need dual polarity is the 8038 frequency generator IC and op-amp. I could wire the lines before input to be "like" dual polarity and utilize only one regulator but this is also a learning exerience for me so I'm willing to try something new. Thank you for telling me this, I will probably utilize a 5v @ 100mA regulator from the +15v after feed in from a pi-filter for the indicator LEDs with of course a resistor so the swing won't be too dilated. I'm planning to build this project in a hand-sized clear plastic box used to hold things like small screws and pins. I think I will be able to construct it that small, the box is 3.5"x2"x1". The transformer, rectification, and some filtering will be in the wallplug itself while the main circuit will be in the component box. I plan to have either headphone output or line output selectable since I will be the one using it. Which leads me to another problem, what governs line-out? The voltage maximum and current maximum? Thanks for telling me, I'll have to find a circuit that will isolate that from the main body of the circuitry. An actual regulator. Thank you for answering.
You can probably get away with running a few LM7815's just fine then. I would still make sure you input is either a *very* stable 18v or higher. Since it seems you are going to use a wal-wart, then I would *definately* suggest configuring it for 24v operation, just to make sure. There *are* multi-output regulators out there, but it might be difficult finding one that fits your needs exactly. It sounds like the switching PS is out as you probably won't fit it in the case (that or it would need to be external). The problem with Line Level outputs is they are generally designed by using a -10dbu to +30dbu designation with an Impedance of 10kOhms. I belive this works out to something like 2v P-P, but I cannot remember what the current requirement turns out to be. The amp should be able to handle that for you, as it will just heat up the 386 a tad when operating. Since you aren't going to be probably driving this other than with a set of headphones, it'll probably be minimal. Your line-level output wouldn't really even need to worry about it, since back-emf isn't a problem, only with speakers.
Thank you so much kt3946, I'll put you down as a big help on my physics project. I'll probably have this done either late next week or two weeks from now, pics for all, circuit diagram, and theory of operation will be included.
