build a simple 5v power supply for digital circuit

[Spehro Pefhany]

"Spehro Pefhany"
"Phil Allison"



** Completely different matter.

Remaining within context is a real trial for you.

My context (in this thread)is hobby-level power supply circuits.
Switching zeners rather than resistors is not an unreasonable
approach, but we're still left with the spiking-during-switching
issue.

** The Poptronics abortion runs at circa 11mA.

5 / 470 = ???

Right, okay, bad memory, more like a 2:1 difference.

......... Phil

Best regards,
Spehro Pefhany

 

[Eeyore]

Another potential problem with the original circuit is that the output
voltage will spike as high as Vin - 1.xV during the switch transitions
unless it's a shorting type rotary switch.

If it was done the sensible way by adding resistors in parallel that problem
could at least be minimised.

Graham

 

[Jamie]

Jim Thompson a écrit :
///

Hello
nobody mentioned it but the schematic is faulty!
Negative output should not be connected to the "mass" leg of the
regulator. Else, output voltage cannot be different from 5V - other
effects neglected
pom

Yes, it was mentioned, you're just a little late

 

[PinkFloyd43]

I came across this universal psu design while searching for 5V
psu info ...
is there a problem with the universal psu schematic (page 2)
shown in the following document ?
more specifically with the selectable voltage part of the
schematic

http://www.qsl.net/lu3mgp/electronica/UniversalPowerSupply.pdf


also
i am trying to understand how that PSU can produce higher voltage
than 5V while using a 7805 5V regulator and no path for the
bridge rectifier (+) voltage to bypass the 5V regulator ?

thanks for any help
robb

Everyone seems to agree the schematic is a POS, any links to
what more than one person believes to be a decent 5V PS?

 

[Jamie]

(images on a.b.s.e)

i built and experimenting with the 5v DC psu

The images do not show a filter cap after the bridge and
before the 7805. Add a large cap (4700uF shown) across
the brideg output:

--------
| +|-----+------in[7805]out---
| Bridge | | + |
| | [4700uF] |
| | | |
| -|-----+-----------+

You know, that's a good catch. Power supplies to many of us
are like car's. We assume to much..

You get in your car to drive it, you shouldn't have to
question if you have an engine in it! You just naturally assume
that. But then again, that analogy maybe flawed if you live in a
shady neighborhood

 

[Jamie]

Everyone seems to agree the schematic is a POS, any links to
what more than one person believes to be a decent 5V PS?

In my opinion, you would be better off with fixed post regulators of
every voltage you need all branching off from the same bridge and filter
cap..

If you want a variable out, you can create one from one of the higher
voltage fixed post regulators with 2 Resistors and a pot.

Some Links.

http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html
http://www.paia.com/KRUKits/K4/K4.pdf
http://www.aaroncake.net/circuits/supply6.asp
http://members.tripod.com/michaelgellis/power2.html
http://www.educypedia.be/electronics/circuitssupplies.htm

 

[Phil Allison]

"Phil Allison"

"Fred Abse"

** The following section has just been added to this popular audio design
site to debunk the notion posted by Fred Abse.

http://sound.westhost.com/power-supplies.htm#myth



....... Phil