Here's an updated copy...
And I didn't add the specifications ( wanted to make sure it is drawn correctly ) on the components yet.

nite

PS I will catch up on your last post on the front on the morning

 

1.5A is the maximum current. If you need more, you need to add an external pass transistor. The datasheet usually has examples.

If you're going to be doing low power work, you can get a wall wart; you can use AC, DC, or unregulated DC. With AC, you need a rectifier + filter cap; with unregulated DC, you need a filter cap, with regulated DC, you feed directly into the LM317 input; possibly with a cap.

I'll see if I can find a link for the National Semiconductor Voltage Regulator Handbook. It gives information regarding rectification, filtering, and transformer secondary requirements.

 

I think someone has already worked out all the parameters ( Tony Van Roon )...
http://www.sentex.ca/~mec1995/circ/VarReg1/VarReg1.html

The Voltage Regulator's Handbook...
http://www.smcelectronics.com/DOWNLOADS/1980-VOLTREG.PDF

cheers

 

I think someone has already worked out all the parameters ( Tony Van Roon )...
http://www.sentex.ca/~mec1995/circ/VarReg1/VarReg1.html

That circuit, minus the rectifier/filter, is in most LM317 datasheets. That article is decent and has the seemingly customary bits of misinformation. But everyone already knows they can't believe everything they find on the WEB...

Let me know if you want help with adding current limiting. The only one I've seen in an LM317 datasheet was low side for a battery charger; I don't care for low side limiting because it creates a "floating" ground.

If you study the LM317 schematic, you'll see a good way to implement component protection. Most voltage regulators have built-in thermal and over current protection; but that doesn't mean they can't be damaged...

 

After thinking about it...
I would like to try the wall wart version of the power supply.
Looking at AC/DC adapters which adapter should I get ( regulated if they have it )
there's a lot of them...

http://www.digikey.com/product-sear...=0&page=1&quantity=0&ptm=0&fid=0&pageSize=500

what would be the input voltage and wattage
they come in female plugs ( which makes it easily portable or changeable )

I guess the part that is confusing me is...
whether its a transformer or a wall wart--------> one buys a 37 volt (secondary output on transformer / or DC regulated wall wart ).

I understand the mains input...but I don't understand the output...
i.e. one buys a ac transformer with the primary ( 120 volt ac ) and...? secondary of 37 volt...?
12 volts ac ( center tap is 12 with two 6 volts )
24 volts ac ( center tap is 24 with two 12 volts )
or 40 ac volt secondary ( and 2 volts ...)

and I guess the question also applies to the wall wart...


cheers

 

Let me know if you want help with adding current limiting. The only one I've seen in an LM317 datasheet was low side for a battery charger; I don't care for low side limiting because it creates a "floating" ground.

Yes
I would like to see how that works...

 

If it were me, I'd check out Goodwill or a surplus store to get a wall wart. At Goodwill they're typically $3-4.

what would be the input voltage and wattage

I assume you meant output voltage... That depends on what voltage you want from your power supply. The output voltage needs to be 2-3 volts higher than the highest voltage you want and it's current rating should be 2X the max current you want.

they come in female plugs

There are half a dozen or so standard plug sizes; I prefer 2.1mm.

i.e. one buys a ac transformer with the primary ( 120 volt ac ) and...? secondary of 37 volt...?
12 volts ac ( center tap is 12 with two 6 volts )
24 volts ac ( center tap is 24 with two 12 volts )
or 40 ac volt secondary ( and 2 volts ...)

and I guess the question also applies to the wall wart...

Transformers with a center tapped output are generally used for making complementary supplies (e.g. +15V and -15V) or wired in parallel to increase output current.

For your application I'd recommend a DC wall wart. If it doesn't say the output is regulated, assume it's unregulated; meaning the output voltage will actually be 1.414X higher.[/QUOTE]

 

The wall wart that I found:
input 120 VAC 60 Hz 25 watt / output 25.5 VAC 650 mA class 2 transformer
I have to check it out to make sure its working ( it was connected to my sprinkler system )
I would like to go with it because of the things I have to do to make it regulated...

All the best

 

The sprinkler supply is usually for the 24vac solenoids, this will be 35vdc when rectified.
Max.

 

The wall wart that I found:
input 120 VAC 60 Hz 25 watt / output 25.5 VAC 650 mA class 2 transformer

If you use this for making a 12V supply, 2/3 of your power is going to be dissipated in the regulator. But for tinkering, power efficiency probably isn't a concern...

The voltage regulator handbook you have has examples for rectifying and filtering. At that voltage and current, diode selection isn't critical. The formula for filter cap will probably give you a huge cap, but you can reduce that if you won't be operating the regulator near 30V.

With a 650mA AC source, you'll be able to get around 500mA before you start stressing the wall wart. That formula is in the handbook too.

 

Yes
I would like to see how that works...

Do you want the supply to shutdown or just current limit?

 

I have seen 48 volts from digikey for 22.00
271-2704-ND / AC/DC WALL MOUNT ADAPTER 48V 30W ( they don't have one at 40 volts )

There's another: NEW Motorola Well Regulated Power Supply 48V DC 16W 350ma .35A Amp 100-250VAC IN
on Amazon

but the current isn't one amp

 

Do you want the supply to shutdown or just current limit?

No I wouldn't want the supply to shut down...

so basically I probably should look for 14 or 15 DC regulated adapter that goes to the max of LM317 current...
And go from the lowest voltage of the LM317 to 12 DC with current adjust to the max of LM317 current abilities...
I don't think I'm going to find a 40 VDC 1.5 amp adapter... at this point.

cheers
PS I guess if I want to use the LM317 to its fullest I'd have to find a transformer with a 40 volt secondary

 

The sprinkler supply is usually for the 24vac solenoids, this will be 35vdc when rectified.
Max.

So where do you find a wall wart that uses everything that the LM317 provides...

 

PS I guess if I want to use the LM317 to its fullest I'd have to find a transformer with a 40 volt secondary

40v secondary = 56vdc.
ebay is a good source of W.W.'s.
Max.

 

No I wouldn't want the supply to shut down...

The Nat Semi LM317 datasheet has a example of constant voltage/current.

so basically I probably should look for 14 or 15 DC regulated adapter that goes to the max of LM317 current...

That would give you less waste heat in the regulator if you're going to be operating it in the 9-12V range. I'd use 3V for the drop out voltage if you're going to cut it that close.

I don't think I'm going to find a 40 VDC 1.5 amp adapter...

A 24VAC adapter will get you pretty close and they're readily available at 1A. If you want higher current, transformers will offer more variety.

 

A 24VAC adapter will get you pretty close and they're readily available at 1A. If you want higher current, transformers will offer more variety.

Dennis,
Digikey has them ( and that's probably where I'll get the parts ). If 1 amp is all the LM317 has... that's fine. Negative or positive center...?
I would like to do a transformer but not right now... I have 5 NTEs' version of the LM317 on order...I would like to be able to plug the wall wart into the " box " and plug my RS vintage Analog Multimeter into it. But a panel variable 0 - 1 amp ammeter with a switch for 10 amp with a shunt across it...

 

40v secondary = 56vdc.
ebay is a good source of W.W.'s.

Max
sometimes you can get great finds on ebay...but you have to be careful...sometimes you get clowns. I remember something I bought from ebay and the person stated it was this and it turned up to be " that " . the seller wanted to charge me a fee for returning the " that stuff "... I called up my credit card company and stated not to pay for it ( and had the proof that I sent it back ). Just recently I got a batch of breadboards that were misprinted... and I got store credit ( but I told the credit card company not to pay for it - I haven't resolved it yet )....

btw... I settled on the 24 volts dc ( regulated I think ) with 1 amp

 

Dennis,
Digikey has them ( and that's probably where I'll get the parts ). If 1 amp is all the LM317 has... that's fine. Negative or positive center...?

Center positive is more common in the US.

I have 5 NTEs' version of the LM317 on order...

Wish you would have mentioned that before. NTE is nothing but overpriced. You should be able to get LM317 for $0.50 or so from many sources.

I would like to be able to plug the wall wart into the " box " and plug my RS vintage Analog Multimeter into it. But a panel variable 0 - 1 amp ammeter with a switch for 10 amp with a shunt across it...

I'd discourage the use of an ammeter unless you really need to measure current directly. They will disturb the circuit they're used in. Even for voltage measurements, an analog meter can put a significant load on whatever you're trying to measure. I think the best my RCA analog meter could manage was 50 Kohms/volt; vs 1M+ for digital meters, for volts measurements.

 

Wish you would have mentioned that before. NTE is nothing but overpriced. You should be able to get LM317 for $0.50 or so from many sources.

really...
I had better results with NTE parts than I did with digikey... maybe I went for the too cheap versions on digikey...
But I should get the parts pretty soon... actually I had problems with 4017s and the 4081 s... I only bought 5 555 s and I had to buy more from NTE...
Go figure...

All the Best

PS I am in and out for the last couple of days... My wife is in the hospital and I have a cast on my foot to be remove today ( freedom at last )