Posts posted by Niksun
Ack! Yes, you are correct. If you draw a horizontal line which starts at the right end of R3 and goes right, that will be the regulated Vout. PSU Ground can also be extended to the right for the regulated ground.
In terms of R3: can you not simply set your voltage, short the output of the PSU, then adjust the current limit with R3? Perhaps another (safer) way is to add a normally open 3A push-button switch in series with a 30 ohm, 10W resistor across the regulated Vout and ground and use that to short the output of the PSU when the switch is closed, then adjust the current limit. Perhaps I can refer you to a web site, but I'm not sure the rules on this forum (some do not like to have people posting URLs).
Thanks for all your help, by the way.
Oh, and possibly I can do this better with just a FET and a potentiometer to limit the current, but I'm not exactly sure how to do this yet.
I keep getting stuck on the current limiting rheostat. No matter how I do it, it's going to potentially dissipate a lot of power. I tried placing a 0.833 ohm resistor in series, but that still could mean 0.85W between both if the rheostat is set at 1 ohm. Sure, a 100W 100 ohm rheostat would then work, but again, those are fairly expensive. Plus, this may also limit my upper current limit to less than the 1.5A the LM317 can provide.
So, after some quick research, I have another idea. Since I want to include both a voltmeter and an ammeter, perhaps a slightly different design can be beneficial. In my last schematic, I included analog meters. This new design incorporates digital meters and limits the current without using an LM317. Essentially, I remove the current limiter (which includes the LM317 and the 500 ohm rheostat). My digital meters are powered via a 9V battery and do not share the PSU ground.
What do you folks think? Will it work?
OK, so here's what I have so far. I have added an analog voltmeter and ammeter. I've also updated the notes (primarily for my newbie self) :P
I figure I should have the heat managed with properly heatsinked LM317s. Also, I should have the full 1.5A available so long as I stay within the 15V Vin/Vout difference.
I have to find some power rheostat which can handle 1.57W at its 1ohm setting. I was able to find such an item, but it was very expensive ($30 or so). I don't really want to spend that much, so I'll try to find a better way to limit the current... maybe.
If anyone has any more suggestions, please post them. Thanks!
A tiny portion of its resistance track will dissipate 1.9W, get extremely hot and maybe burn. Therefore R1 must be a wire-wound rheostat rated to carry 1.5A at low resistance setting. I hope you can find one.
I think I found something that may work. I couldn't find a data sheet on it though. It's a 20 ohm wire-wound linear taper potentiometer rated at 2-4W. The part description:
"Nice quality screwdriver adjust full size 20 ohm 2-4Watt potentiometer by Clarostat features 3/8" panel mount bushing. Enclosed case wirewound potentiometer is marked A43-20ohm. Comes in factory box with panel mounting nut. Linear taper."
I know it's only 20 ohms, but at this point I don't think I mind having a 62.5mA minimum current limiter.
I also found a 50 ohm (or even 1kOhm or 2kOhm) wire-wound 5W potentiometer.
OK, so if I understand the LM317 (I decided to switch to the LM317) data sheet correctly, so long as the Vin/Vout difference is within 15V, then I should 1) be able to get 1.5A out of the LM317 (so long as I have a Vin/Vout difference of at least 3V or so), and 2) have manageable heat so long as I use a decent heatsink.
I'm thinking of supplying the current limiting LM317 with [email protected], which should supply the voltage regulating LM317 with a minimum of 15V (up to 3V is used by the current limiting LM317). Since the minimum Vout is 1.25V, then my Vin/Vout difference here is 13.75V which is fine. I figure I can get a maximum of about 12V (forget the diodes I mentioned previously to allow for an output of 0V). I figure I'll replace R3 with a 5k potentiometer.
For higher voltages, I figure I'll just supply my variable PSU with [email protected] Again, that will probably supply the voltage regulating LM317 with 27V which will give me an output maximum of about 24V. In order to ensure that I do not go below 12V (which would generate a Vin/Vout difference of 15V), I can replace R3 with a 1.8k resistor in series with the 2.5k potentiometer. If the pot's resistance is 0 ohms, then the 1.8k resistor ensures that my minimum Vout is about 12V.
Does this make sense?
Another issue is that I wish the 1.8k resistor to only be used if I am using the 30V supply. I think I'll put a switch to select which AC adapter I use, but without using another switch to select the resistor, how can I make sure that the 1.8k is included in the circuit if the 30V adapter is selected?
Thanks in advance.
Got a question.
I am working on a 0-28V, 0-3A power supply using several LM350 linear regulators. I'm including necessary capacitors to minimize ripple and ringing and implementing short circuit protection via some standard rectifier diodes. I'm wondering if the following schematic makes sense. D2 and D3 drop the reference 1.25V out of the regulator to allow for a minimum Vout of 0V. R3 allows a variable Vout up to ~28V with a 32VDC source (which is nothing more than a transformer and rectifier bridge). D1 and D4 offer short circuit protection.
1. Should D1 and D4 be of the 1N5401 type as well (3A maximum as opposed to 1A maximum 1N4002s)?
2. Do I need any kind of load resistor after D3 (or maybe it has to be east of D4, or even east of C3)?
3. Do I need any kind of minimal resistor before R1?
4. What will happen if, for instance, I set R1 to near 0 resistance? There should be a maximum of 3A coming out of the regulator no matter what R1's resistance is, right? This is in relation to question 3. The problem with placing a minimal resistor in series with R1 is that, even at 1 Ohm, it would cap the maximum at 1.25A. I'd need something rated at ~0.4 Ohms to get a maximum of 3A.
5. Should D1 really be 2 diodes (i.e. sould D1 end to the left of the LM350 on the right, and then should I place another diode just east of R1)? I don't think so because I can't imagine any current flowing from the LM350 on the right's input to the LM350 on the left's output (i.e. a short circuit).
6. D2 and D3 on average drop about 1.4V together. The reference voltage is 1.25V, and since the diodes are in place, they effectively drop the reference voltage to 0V (no negative voltage is possible due to the diodes, right?)
7. In terms of a transformer, does anyone know what kind I should get? I want about 32VDC as input to the regulator. I read that 32VAC will be rectified to something greater than 32VDC, but I'm not sure.
Thanks a bunch!! I'm just starting out and learning.
Oh, and I know that both LM350s will have to be properly heatsinked. Anyone know how hot they can get with this circuit?
Noted. I am trying out a circuit now to charge them to see if it will even work. In any event, does anyone have some sort of current schematic for the 0-30V, 0-5A PS? Thanks.
Gah!! I apologize; I made a mistake. I meant 0-30V and 0-5A. Wow, the "5" key is awfully close to the "3" key, eh? :P
As an aside, I've been investigating recharging regular, old alkaline batteries (I know, most think this is not a good thing) with this PS. In any event, I figure that capping the current at ~65mA and setting the voltage to the appropriate value for the cell I wish to charge, it may just work. What do you think?
OK, so does anyone have a "latest" schematic for this puppy (the 0-50V, 0-5A)? Also, some of us are still learning and may need more specifics in terms of what parts to heatsink and what parts to get, so perhaps a list of parts would be nice. Thanks a bunch and keep up the great work!
I am a beginner in actually "messing" around with electronic circuits but have been around them for a while and am very comfortable tinkering around. For example, I've been working with FPGAs for several years, albeit mostly on the software side of things. I have also made a robot which wanders around avoiding obstacles via infrared.
In any event, I am very interested in building the power supply as it is in its current state (0-30VDC, 0-5A, I believe). I am interested in having a voltmeter and ammeter in place (will build it in a case and have these on the front of the case), and am interested in having a dual power supply. Now, does anyone have the "final" schematic for this thing (including the voltmeter, ammeter, and dual power supply requirements), perhaps also a "detailed" parts list (i.e. a volt rating for all the capacitors, heatsink requirements, fan requirements, etc). Even better would be like a parts list from mouser or something in order to ease the ordering process. I know, this may be asking too much, but I figure why not ask. You folks are really helpful from what I've been reading, and this seems to be a very cool place to wander around!
I have been reading a whole bunch about this stuff lately and seem to be moving from the software side to hardware. I have messed around with simple circuits (built a battery charger to recharge store-bought alkalines at ~65mA, a MIRT, also one of those rotating persistence of vision LED thingies, etc). I would very much like to build this power supply. Any suggestions for a beginner?
Thanks for your help.
Making a [email protected] Power Supply using linear regulators (LM350)
in Electronic Projects Design/Ideas
OK, so if it were up to you, would you go with my double LM317 design with the high watt rheostat to limit the current? I'm not sure the best way to go about placing a potentiometer there to vary the current limit (due to the potentially large amount of power dissipated by the pot), but I do know that I want to have a ~15mA to 1.5A variable current limiter.