Power supply from single tap transformer

[be80be]

I been playing with this idea it don't look to bad on the scope with big caps the transformer is not a really big one 350mA but i don't need much just playing with some op amps. Should I add a 10 ohm 5 watt resistor to limit inrush current.

 

[chemelec]

Should be OK as is.

 

[AnalogKid]

One of the capacitors is reverse-connected. Also, just checking, this circuit has been around since the 20's.

ak

 

[be80be]

I flipped it one times to many I know it's been around a long time kind of like me but. I didn't say I invented it I'm just playing with it I had the caps right I draw it on Linux and it only let me save in .ps so converted that to a png and it looked bad so I cleaned it up in paint and flipped the ( the wrong way you couldn't see what they where looked like two pipes ||.

But that's not what I ask I ask if I need a inrush resistor. Don't think I do because the supply output is maybe 350mA and I'm not needing but maybe 50 mA tops

 

[chemelec]

One of the capacitors is reverse-connected. Also, just checking, this circuit has been around since the 20's.

ak

The Caps are Connected Correct for Both a Positive and Negative Output.

No you Don't Need an Inrush Resistor.

 

[be80be]

Now to figure a regulator out of parts I have I need to lower it down to 5+ volt 5- for a 10 volt duel supply I hope I can find a lm79 adjustable to match a lm317.

 

[AnalogKid]

The Caps are Connected Correct for Both a Positive and Negative Output.

They are now, but not when it was first posted.

ak

 

[AnalogKid]

Now to figure a regulator out of parts I have I need to lower it down to 5+ volt 5- for a 10 volt duel supply I hope I can find a lm79 adjustable to match a lm317.

As I recall, the 79xx, like the 78xx, are fixed output regulators. (Note, I haven't checked recently to see if an adjustable flavor has been added to the product line by any of the many manufacturers.) You can turn one into an adjustable regulator by adding something between the ground pin and GND. Note that the ground pin current varies with output current, so a simple resistor will decrease regulation performance. By the time you add a complete feedback system to get things back to decent regulation, you're basically using the 79xx as a pass transistor with a really high "saturation" voltage.

ak

 

[audioguru]

Your rectifiers are simply half-wave that produces double the amount of ripple as full-wave. It will be OK with huger filter capacitors.

 

[be80be]

The caps are fine I said I forgot to flip them when fixed my drawing. I ask about inrush not caps I should of put my glasses on. Lol.

 

[chemelec]

For +5 & -5 Volts, Just use a 78L05 and 79L05 Regulator.
Put an Additional Filter Cap after Each Regulator.
(Just a 10uF would be Suitable value for these.)

 

[be80be]

Got find a lm7905 but I'm thinking while I'm play with it I'll try to make my own regulators just to learn something.

 

[crutschow]

Got find a lm7905 but I'm thinking while I'm play with it I'll try to make my own regulators just to learn something.

You'll probably learn that it's much easier to buy the IC's.

 

[be80be]

You'll probably learn that it's much easier to buy the IC's.

Your right I about burnt my finger lol playing with it last nigh. There's a circuit in a appnote that shows using a 7805 to get negative output it don't work if you use it with
two 5 volts sides.

 

[chemelec]

If the Postage Cost wasn't so HIGH (Going to you from Canada), I would send you one for Free.

 

[be80be]

Ill use some battery's till I can figure enough stuff to order from china heck it only $2.85 but the wait is killer. I been waiting 3 weeks on some stuff now. ESP2866e.
I told a kid I'd send him a pickit2 clone I did it cost a little over $20 to send it to Russia and they sent it back to times cause it was marked wrong. I had to tell what it was. Bunch of red tape.

 

[Nigel Goodwin]

Ill use some battery's till I can figure enough stuff to order from china heck it only $2.85 but the wait is killer. I been waiting 3 weeks on some stuff now. ESP2866e.

The trick to China is ordering more than you need, and before you need it

I've got various versions of ESP2866e's in stock, for when I 'might' need them

 

[Tony Stewart]

To prevent dropout and efficiency loss, choose an LDO with <0.5V dropout rather than >2V
Ripple is a factor of N * RC where 1% is 5RC and Cap ripple current Peak/Average load will be 1/% ripple V
So 10% V ripple means p-p ripple current is 10x Avg load while Caps are rated for Irms current.
Some NTC thermistors drop in resistance 40:1 up to rated current. cheaper than power resistors. This reduces inrush current significantly on caps.
**broken link removed**
This one starts at 200 Ohms and drops to 5 Ohms at 85'C with 500mA load so you might expect 10 Ohms.

 

[be80be]

The trick to China is ordering more than you need, and before you need it

I've got various versions of ESP2866e's in stock, for when I 'might' need them

I thought there's only one esp2866-12E I have the esp2688 -12 so i'm good there LOL just no - 5 regulators lol. And then when I order I always get cared away and get gunk I don't need