Power Supply

[windozeuser]

hello fellow friends I have a problem...

I want to build a 16 volt DC regulated power supply

I have a 35 volt AC Transformer @ 3A

I was wondering what Do I need to get it down to regulated 16V DC @ 3A

Rectifier?

Voltage Regulator IC?

Cap?

THank you!

I Well Be Building this with my new ColdHeat Soldering Iron !

 

[Edmond]

This is not a lucky thing. If you use a linear stabiliser, the power loss will be too high. Look: the rectified voltage UDC=35*SQR2=35*1,41=49,5V. The difference voltage (49,5-16=33,5V) will fall down on the through transistor. The power loss: P=33,5V*3A=101W. So you must use a high power transistor with a fan cooler. The friendly solution is a switching power supply, or an other transformer with a lower output voltage (ex.: 16V AC).

 

[windozeuser]

Thanks for your Reply!

How about a 20 VOlt Ac Transformer @ 3A ?

Also What Size Cap (uF) you think I need on the output andwhat kind of voltage regulator that will output the whole 3A at a regulated 16V DC

The Rectifier I have can handle up to 120 V AC @ 45 A

Do you think I would need a fan on the regulator? or just a big a$$ Heatsink

 

[jrz126]

repeating edmund's calc, gives you 36.85W as heat, which is still kinda high. Could you get it down 15V?

for the heatsink, is size of the supply a factor? With a fan on the heatsink, it will remove the heat quicker therefore you can use a smaller one.

Oh yeah, whereabouts in PA are you?

 

[Russlk]

If your transformer had a center tap on the secondary, it would be just right, but if it has only two leads on the secondary, better get another transformer.

 

[windozeuser]

Thanks for your replies!

First -- I live In western PA around Butler County
Good to see fellow People on the board from PA


Second-- I want to see of this is possible --

I am building this Power supply for a IBM Thinkpad 380Z Laptop

The power Requirements are 16V @ 2.54A (3A)

Can anyone Draw a simple Schematic or a parts lists so I can buy from Jameco


Please post your comments if the laptop could be safely ran on this type on power supply

with just a Transformer,rectifer,Voltage regulator, and Cap

Thanks

Btw Please design one that would be safe on the laptop

Hope Im not being troublesome Thanks!

 

[Juglenaut]

1N6275A
Zener transient voltage Suppressor

Nominal breakdown voltage 15 volts

 

[k7elp60]

Thanks for your replies!

First -- I live In western PA around Butler County
Good to see fellow People on the board from PA


Second-- I want to see of this is possible --

I am building this Power supply for a IBM Thinkpad 380Z Laptop

The power Requirements are 16V @ 2.54A (3A)

Can anyone Draw a simple Schematic or a parts lists so I can buy from Jameco


Please post your comments if the laptop could be safely ran on this type on power supply

with just a Transformer,rectifer,Voltage regulator, and Cap

Thanks

Btw Please design one that would be safe on the laptop

Hope Im not being troublesome Thanks!

Have designed and built many powersupplies I will design and post a schematic with parts list from Jameco, as soon as I can. I'll leave up to you for the enclosure, but I will suggest an enclosure for you.

 

[windozeuser]

THANKS k7elp60! for your big help your the kind of people that this forum is filled with. Thanks for the Freindly Fast and Great Electronics Forum

 

[jrz126]

Thanks for your replies!
First -- I live In western PA around Butler County
Good to see fellow People on the board from PA

Wow, I'm up in Erie. I think you are the closest person to me on this board. We're practically neighbors :lol:

 

[k7elp60]

16 Volt Power Supply

Here is a schematic for you. You can use the 20Volt transformer and the existing bridge rectifer that you have.
I wanted to use the 35 volt transformer and a switching regulator, but Jameco didnot list some of the parts necessary for that design in there current catalogue.

This design is a linear regulator. Their catalogue lists two versions of the LM338, I like the LM338K version as it matches the holes already drilled in the heatsink and it is easier to mount the associated parts for the regulator. When using the specified heatsink, I usually drill an additional hole close to the fins and mount a soulder lug on the same side as the pins of the LM338. I use this solder lug as a tie point for the ground end of R2 and C3. Then run a wire from the solder lug to the negative side of C1 & C2. (It is best to mount R1,R2 and C3 very close to U1)
This is the parts list, all items are Jameco part numbers.
C1,C2 4700uF 35V axial electrolytic, 199401CX
C3 4.7uF 25V tantalum 94043CX
R1 120 ohm 1/4 W 5%, 30082CX
R2 2.2k ohm 1/4 W 5%, 30314CX
U1 LM338K, 23835CX
U1 is mounted on a heatsink,number 16512CX and mounted with a mounting kit, number 34139CX.

The rule of thumb for linear power supply filters is 3000uF/Amp of load current. Generally when the load current matches the current rating of the transformer the DC voltage across the filter = the rms of the transformer.
Don't be surprized if the transformer runs quite warm, as the peak charging current for the filter capacitors exceeds the rating of the transformer.
The output voltage may be slightly different than the 16V, but this is due to component variations. If you want to replace R2 with a 1.5K resistor and a 1K pot inseries you will be able to adjust the voltage to the exact voltage you want.
Cheers

 

[windozeuser]

Thank you k7elp60 Very Much!!!!

Thanks for the schematic and the tips and being a great board member