Making a power suply

[Someone Electro]

I orderd a free catalog at Conrad (they sell electronic stuf) and the chepsest variable power suply i found was for 52$ but it cod suply only 1,5 A. So i decided to make my own power suply.

I alderdy have an transformer wich can suply 10 A at 20 V (200W is plenty of juce)

Then i have to buy and refinder,cap,regulator,voltmeter

I sherced the catelog forund all components at a resenoble price to make an +7A,0-20V power suply at 40-50$
But it came to an halt at the regulators:
- 3 A regulator at 6$ (LM350 T)
- 10 A regulator at 50 $ (LT 1038 CK)

PROBLEM!!!: :x :cry:
Is it posible to wire 3 regulators togeter (9 ampers sunds rely good)it wod save 29 $.If it is how. (I dot want to burn them )

hmm... 9A 0-20V Shortcircuit and overheting prtotected homeade power suply cod be made at 40 $.So i wod save 120$ (comecial ones like this cost 160$!!! :shock: :shock: :shock: )

 

[stevez]

Do you really need to go to zero volts? Datasheets show some of the traditional linear regulators at 1.25 volts min. One idea from my references - use an LM317 or LM338 with wrap around power transistor(s) such as 2N3055. I do not have enough experience to comment on how well it will regulate as compared to alternatives. LM317s can be had for $1 or less and 2N3055s for $1 to $2 each. Note that the LM338 is supposed to handle 5 amps by itself.

Other designs that I've seen use LM723 to drive pass transistors - again the 2N3055 shows up in many designs.

Watch out for dissapation of the 2N3055. While it's max current is substantial you need to look at the current and votage drop across the whole range if you expect to be able to deliver 7amps across the desired range.

All of the above is linear and relatively old stuff however it would seem that the devices have many low cost equivalents. Supporting components can be salvaged easily. There are some fairly economical switching regulators. In the end the lowest cost approach may depend on parts that you can obtain from salvage. The linear regulators described above require large filter capacitors which are easy for me to obtain but maybe not for you.

 

[Someone Electro]

I ment to ask if you can wire 3 regulators togeter to take more curent.

I ment whith the 0 the minimal voltege of the regulator (If i wanted 0V i wod thurn the switch off :lol: )

If i conetced it as shown in the picture these 3 regulators cod the max. curent be extended

 

[k7elp60]

I recently built an adjustable powersupply using the LT1083 adjustable regulator. It's spec's specify 7.5 A maximum. What I found was the power dissipation was a problem. I have discovered that most 3 terminal regulators like the LT1083, and LM338 that have internal power dissipation limiting do not work well as wide range adjustable power supplies. As the internal circuitry will see a input/output differential and with the internal current limiting it will shut down before it should, even with a extremely large heat sink.
The best I have found is to use a 723 and external pass transistors. The 723 has a couple of pins for current limiting. I have used resistors in parallel connected to these pins to get the resistance low enough for I current limiting. I have even used up to 10 or eleven 0.68 ohm resistors in parallel. 0.68 ohms is for 1 amp. Rule of thumb R=0.68/I limit.
If using bipolar transistors like 2N3055 in parallel, they need equalizing resistors in the emitter leads.
Another thing to consider is the current rating of the transformer. With brute force filtering(rectifier directly to the filter capacitor) one can only expect to get capacity X about .6 to prevent overheating, this is because of the charge current of the capacitors may be multiple times the current rating of the transformer.

 

[chemelec]

3 PARALLEL LM350's NOT WORK Properly.

Additionally Maybe not even one.
You Don't say What the Output Voltage of your Transfomer is?

First, At 9 Amps, You better have some Very Large Filter Caps to reduce ripple.

Second, These Devices are Rated at a Specific Amperage, Like 3 Amps for the LM350, BUT they are Also Rated for a Maximum Wattage. If the Wattage EXCEEDS its Limit, It will NOT HANDLE THE RATED AMPERAGE.

Third, You Better have some VERY GOOD HEATSINKS, no matter which way you do this. Or they WILL BURN UP.

Don't know where you got a price of $6.00 each, That is Awfully High Priced. I buy them for Under $3.00 each Canadian. (About $2.25 US)

Here is the Proper way to Increase Current of either the 317 or 350.[/quote]

 

[Someone Electro]

My transformer gives out 20V and i found an heatsink big for CPUs.

They also have a LT1083CP wich can take 7,5 A but it costs 27$.I gues 7,5 A is enugh

Cnorad is the bigest suplyer in our tiny country (who wod pay the shipment form other countrys).

 

[chemelec]

It May be Big for CPU's, But Not likely good enough for this Application.
Maybe with a Fan.

According to my Data Book, The LT1083 is a Fixed Voltage Regulator. Either 5 or 12 volts. Not Adjustable.

Also it has a Maximum Input of 20 Volts. When you Rectify your transformer, You WILL EXCEED THAT.

I think you need a Much Better Understanding of What you are attempting.

Take care.........Gary

 

[Someone Electro]

I found an heat sink that has 2 °C/W (Its specialy made for amps and power suplys)

Here is an datashet for the LT1083

**broken link removed**

It can handle 20 V (30V is max.) and there is a shematic how to wire two togeter.
Im planig a fan too.

I made an shematic.

 

[k7elp60]

It should work fine for currents up to and a little over 1 amp of load current. For output currents greater than that depending on the voltage you may have the ripple valley's in the output. The rule of thumb for filter capacitors is 3000uf of filtering per amp of load current.

 

[Someone Electro]

I simulated it and the 4 400 uF cap cod stand up to 3A at 20V. So i will use an 10 000 uF cap (It did well in the simulation). Il use the higher curents to run big motors (over 3A) and smal ones to run circuits (up to 1A)so i neen stable power up to 1A (I dont care if the motors are a bit loud)