# Need a little help with my first regulated PSU

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#### jarros

Hey guys! I'm fairly new to diy projects and I'm trying to put together a regulated power supply for my Sonic Impact T-Amp. The amplifier requires a voltage between 12V and 13.8V and requires at least 1.5A. I'm thinking of using 13V even with a current rating of 2-3A to be on the safe side.

I've spent a few hours searching for different regulator schematics, and now I'm comming to the pros (yeah, that's you!) for a little advice. I plan on putting the power supply in the same case as the Sonic Impact amp for simplicity. I would like this power supply to be fairly cheap, under \$30 if possible, and have simple schematics with as few components as possible.

I don't know how to do PCB etching, so this will all be point-to-point wiring.

Any suggestions are welcome! Also, where is a good place to buy components for these sorts of projects? I don't mind ordering online.

Jared

#### AndrewT

Hi,
a single To3 power regulator will do the job. A few resistors and caps to smooth things out. Price well under \$30us.
or hang a power transistor on a 1.5a regulator. See datasheets for circuits.

#### Dark Harroth

To raise a voltage above the normal regulated, this simple circuit can be used:
An externally hosted image should be here but it was not working when we last tested it.

V(out) - desired output voltage; V(reg) - normal regulated voltage (eg. 7812 = 12). R1 value (in Ohms) is calculated using the formula V(reg)/0.025. R2 value is calculated using the formula [V(out)-V(reg)]/0.025.

If you want 13 volts, then the R1 value should be somewhere near 520 Ohms and the R2 value - near 39 Ohms.

But the schematic was taken from an old ELFA factsheet, so I'd at least add a diode between the "in" and "out" terminals of the regulator, so that it would be spike-protected in case of a short-circuit. You should also mount the regulator on a heatsink, as the maximum dissipated power without any heatsink is not more than 2.5-3 Watts (for a TO-3 package).

#### hermanv

Details, details

Depends on where you get the 13V. If from a powerline AC transfomer an allowance of at least +/- 10% is a good idea. Thus 13V would be only 11.8V for low line and 14.3V at high line.

So you would loose your 12 V regulation at low line probably resulting in a lot of hum on the outputs.

Also many 3 terminal regulators need about 1V minimum to work this is called the drop-out voltage. Get a LDO (low drop out) version and/or read the data sheeet carefully.

So say you add 2V to your plan to allow for these problems. Now at high line the power input to the regulator is 16.5V. If you stick to your 3 amp rating suddenly we are talking 14 watts of heat (16.5V-12V) X 3 amps. This isn't that much but if while you are testing, the line voltage happens to be low, far less heat will be generated and you may think you've perfected a design that later melts when the line voltage is high.

#### hermanv

OOPs

I re-read your post you meant 13 V out. My comments are still valid just re-calculate for the input voltage you plan to use.

#### jarros

Thanks for all the replies guys! Sorry I couldn't reply sooner, I've been quite busy the past few days.

hermanv, if I understand you correctly I'll need a higher voltage transformer than my needed output voltage (this is also the trend I noticed through my online searching). However, if I go with a transformer that has a significantly higher voltage (like, say, 20V), the regulator I build will have to throw off that extra heat. Am I good so far?

sklimek, thanks for the suggestion, but I don't think my soldering skills are quite up to the point of soldering on PCB's. That and I need a new soldering iron. The one I have now (an old gun-type 140W Weller) works, but it takes forever to heat up between solders. I'll have to stick to point-to-point soldering for now.

Dark Harroth, I'm slightly confused by your post. When you say "To raise a voltage above the normal regulated," do you mean to use a 12V regulator and modify it so that it regulates at 13V?

Anyone have any recommendations for places to buy these components? Also, does anyone have any specific sugestions for particular components? I did a quick search for "T03 Regulator" but didn't find a whole lot, although it may help if I'm looking to the right stores or etailers.

Again, thanks for helping me out with this project!

Jared

#### richie00boy

If your soldering iron or skills are not up to soldering on a board then chances are that doing it point to point you will have the same problems. You will porbably overheat your components and/or create poor quality joints. Just because something is completely covered in solder doesn't mean it's a good joint.

#### jarros

I shouldn't have any problems with overheating components. I've done quite a bit of point to point soldering in the past, I just have to hold the gun away from the solder point while I hold down the trigger to heat the gun up. It would also be nice to have one with a finer point. I should be able to get by with what I have for now. The iron I have now is similar to this one, but I'd like to pick up a pencil style iron. Will something like this work fine for PCB soldering?

#### richie00boy

That would work. I'd rather have something a little better myself, that's a bit cheap. Maybe \$20 would get you something better, 40W Antex perhaps.

#### sklimek

P2P reg. bd.

Hi Jarros, if you still wanted to do P2P maybe this would help.

Stan

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#### jarros

Re: P2P reg. bd.

sklimek said:
Hi Jarros, if you still wanted to do P2P maybe this would help.

Stan

Thanks for the pic Stan. That looks fairly simple, I should be able to pull it off.

Where's the best place (cheapest) to buy components for these projects?

Jared

#### hermanv

parts availability

Almost all the IC manufacturers now allow you to buy directly from thier web sites. The parts are reasonable but if you only buy one item the shipping cost is disproportionate.

For regulator ICs try ON Semi, Fairchild Semi, Philips, National Semi or just search for three terminal regulator on a search engine.

Digikey and Mouser are two tried and true suppliers that carry lots of stuff. You will need to be pretty sure of what you want before you go to their sites because they offer little general help. The advantage is that resistors , capacitors, heat sinks etc can all be purchased at once so you only pay shipping once. I think both suppliers wave handling fees if your order exceeds \$25.00

Once you buy from them a nice thick catalog will eventually arrive in the mail for the next time you need somthing. Both will get you the stuff as fast as you can afford. I've ordered in the afternoon and had it in my hands the next day before noon but there is a steep premium for this kind of service.

#### jarros

Awesome info guys, I really appreciate the help.

One thing I noticed in digi01's post regarding the regulator was that the trim pot allows the output voltage to be adjusted from 20V to 32V, which is a little high for the range I'm looking at.

I just noticed that in the Class D forums motherone also used digi01's regulator board, but made a few small changes as noted in this post. I'm a little unsure as to where these changes take place in the schematic, so I asked in that thread as well. One change includes using a LM1085 regulator instead of the LM338 that digi uses. Would this enable me to set the regulator to 13V, or should the LM338 be able to do this aswell?

Again, thanks for taking the time to help me out. I feel we're getting pretty close!

Jared

#### sklimek

20 to 32 volts is more an indication of the used transformer for I believe a Gainclone in Digi's thread. Go to National Semi and download LM312 and LM1085 and check their capabilities. After you dial in the correct volts w/ the trim pot replace it w/ a fixed resistor. If Motherone is able to answer you'll be in good hands.

http://www.national.com/

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