power supply circuit

[ehsjr]

F Murtz wrote:

F Murtz wrote:

I would like to make an adjustable power supply using a transformer
with a 24v 5a single wound secondary I would like the voltage to be
adjustable from lowest to highest possible given transformer I would
like to have regulated current

There is another possibility I also have a larger transformer with two
32v 4.7a secondaries If anyone has a schematic for an adjustable power
supply with adjustable current regulation making the most of the
transformer specs I would be eternally grateful



Thanks to every one for their help on power supply design from spec
sheets etc but I was hoping for an already designed circuit

In a reply in another neswgroup someone recommended that you
look in the ARRL handbook; it was also suggested that you look
at an Astron power supply schematic at repeater-builder.com
http://www.repeater-builder.com/astron/pdfs/seits-astron-article.pdf
Both sources give you what you want - a schematic of an
already designed circuit. You can modify the designs as
necessary to suit your needs.

Ed

 

[MooseFET]

On Jun 10, 11:21 pm, Bill Bowden <wrongaddr...@att.net> wrote:

On Jun 9, 5:42 am, F Murtz <hagg...@hotmail.com> wrote:

I would like to make an adjustable power supply using a transformer with
a 24v 5a single wound secondary I would like the voltage to be
adjustable from lowest to highest possible given transformer I would
like to have regulated current

There is another possibility I also have a larger transformer with two
32v 4.7a secondaries If anyone has a schematic for an adjustable power
supply with adjustable current regulation making the most of the
transformer specs I would be eternally grateful

Look up the LM338 three terminal regulator. It's rated at 5 amps and
35 volts from output to input.

But certainly not at the same time:

http://www.national.com/mpf/LM/LM338.html

All you need is a couple resistors or a
pot to set the output voltage. Use a 10 amp bridge rectifier to
convert the transformer secondary AC to DC and a 20,000uF, or
thereabouts filter cap. Connect the capacitor to the (+) input of the
regulator and ground and adjust the resistors for the desired output
votage. The regulator also has current limiting, but not sure what it
is. You can get 1.2 volts to maybe 24 volts DC out, but you need a
large heat sink when the output is set low and drawing 5 amps.

Go read the datasheet before you believe this last bit.

Earlier, I posted the simple math that suggests that you want about 10
TO-220 packaged transistors to get that much power.


Here's a bit of ascii art for a way to share the power around:

NPN R4
----------------- ----/\/\----
! Q2 \ /e !
! --- !
! R2 PNP ! R3 !
+-/\/\--- -------+-----/\/\----+
! e\ / Q1 !
! --- U1 !
! R1 ! ------- !
--+--\/\/---+-----! LM317 !----+---+---
------- !
! !
+-/\/\---
!
\
/
\
!
GND

The capacitors have been left out because I am too lazy to do them.

When U1 draws current R1 develops a voltage due to Ohms law. Once
Q1's e-b draw is overcome, R2 sets how much voltage is needed on R1
per mA flowing in Q1.

R3 and R4 repeat the trick. If you set the resistor values correctly,
you can spread the full load power over the three devices.

To get 10 or so devices, the Q2 R4 circuit becomes several transistors
each with its own emitter resistor.

-Bill

 

[JosephKK]

On Wed, 11 Jun 2008 03:07:12 GMT, "-=Spudley=-" <-=Spudley=-@work.com>
wrote:

"F Murtz" <haggisz@hotmail.com> wrote in message
news:484F3906.4080401@hotmail.com...
Phil Allison wrote:
"F Murtz" <haggisz@hotmail.com

**Beware - cross-posting Hotmail wanker on the loose....


Thanks to every one for their help on power supply design from spec
sheets etc but I was hoping for an already designed circuit


** Do you still expect to get visits from the " tooth fairy " ???




..... Phil


Phil very sorry if cross posting is illegal but I thought different people
used different ngs other wise there would be only one and I thought I
would reach a greater audience.
If the only way to obtain a circuit for a power supply is to get a degree
in everything I suppose I should instead of asking on news groups.

Your first clue and News Groups life lesson is to ignore Phil and his
obsessive compulsive disorder driven, vitriol. (Killfile him, and your NG
life will be so much more pleasureable)

Much agreed, I do as well.

 

[Phil Allison]

"JosephKrautKunthead "

Much agreed, I do as well.

** Fuck off - you PITA brain dead troll.




..... Phil

 

[MooseFET]

On Jun 10, 4:26 pm, rebel <m...@privacy.net> wrote:

On Tue, 10 Jun 2008 06:36:46 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 9, 6:32 pm, rebel <m...@privacy.net> wrote:
On Mon, 9 Jun 2008 07:55:58 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 9, 5:42 am, F Murtz <hagg...@hotmail.com> wrote:
I would like to make an adjustable power supply using a transformer with
a 24v 5a single wound secondary I would like the voltage to be
adjustable from lowest to highest possible given transformer I would
like to have regulated current

There is another possibility I also have a larger transformer with two
32v 4.7a secondaries If anyone has a schematic for an adjustable power
supply with adjustable current regulation making the most of the
transformer specs I would be eternally grateful

How much current do you want?

Lets just assume you make DC from the AC and then regulate down.

Doing a couple of figures for making 4A into lets say zero volts:

24V * sqrt(2) = 34V

34V * 4A = 136W

The the regulator circuit needs to get rid of 136W.

Minor points - the transformer isn't rated to deliver 136W, and that 34V is
unloaded peak.

When working out the power in the regulator, it is best to assume that
the peak voltage is what you get. The rated voltage on the
transformer is for a normal line voltage. In the high line case, you
can get a little more.

I appreciate that, but my original comments stand. There is no valid reason to
state "the regulator circuit needs to get rid of 136W" when the transformer is
not rated to deliver that power.

You seem to have a poor understand of what the rating of a transformer
means.

 

[rebel]

On Sat, 14 Jun 2008 07:48:55 -0700 (PDT), MooseFET <kensmith@rahul.net> wrote:

On Jun 10, 4:26 pm, rebel <m...@privacy.net> wrote:
On Tue, 10 Jun 2008 06:36:46 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 9, 6:32 pm, rebel <m...@privacy.net> wrote:
On Mon, 9 Jun 2008 07:55:58 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 9, 5:42 am, F Murtz <hagg...@hotmail.com> wrote:
I would like to make an adjustable power supply using a transformer with
a 24v 5a single wound secondary I would like the voltage to be
adjustable from lowest to highest possible given transformer I would
like to have regulated current

There is another possibility I also have a larger transformer with two
32v 4.7a secondaries If anyone has a schematic for an adjustable power
supply with adjustable current regulation making the most of the
transformer specs I would be eternally grateful

How much current do you want?

Lets just assume you make DC from the AC and then regulate down.

Doing a couple of figures for making 4A into lets say zero volts:

24V * sqrt(2) = 34V

34V * 4A = 136W

The the regulator circuit needs to get rid of 136W.

Minor points - the transformer isn't rated to deliver 136W, and that 34V is
unloaded peak.

When working out the power in the regulator, it is best to assume that
the peak voltage is what you get. The rated voltage on the
transformer is for a normal line voltage. In the high line case, you
can get a little more.

I appreciate that, but my original comments stand. There is no valid reason to
state "the regulator circuit needs to get rid of 136W" when the transformer is
not rated to deliver that power.

You seem to have a poor understand of what the rating of a transformer
means.

On the contrary. A 24V 5A secondary is rated for 120VA. Your education
suggests something different? Please inform us all as to YOUR transformer
theory.

 

[MooseFET]

On Jun 14, 9:29 pm, rebel <m...@privacy.net> wrote:

On Sat, 14 Jun 2008 07:48:55 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 10, 4:26 pm, rebel <m...@privacy.net> wrote:
On Tue, 10 Jun 2008 06:36:46 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 9, 6:32 pm, rebel <m...@privacy.net> wrote:
On Mon, 9 Jun 2008 07:55:58 -0700 (PDT), MooseFET <kensm...@rahul.net> wrote:
On Jun 9, 5:42 am, F Murtz <hagg...@hotmail.com> wrote:
I would like to make an adjustable power supply using a transformer with
a 24v 5a single wound secondary I would like the voltage to be
adjustable from lowest to highest possible given transformer I would
like to have regulated current

There is another possibility I also have a larger transformer with two
32v 4.7a secondaries If anyone has a schematic for an adjustable power
supply with adjustable current regulation making the most of the
transformer specs I would be eternally grateful

How much current do you want?

Lets just assume you make DC from the AC and then regulate down.

Doing a couple of figures for making 4A into lets say zero volts:

24V * sqrt(2) = 34V

34V * 4A = 136W

The the regulator circuit needs to get rid of 136W.

Minor points - the transformer isn't rated to deliver 136W, and that 34V is
unloaded peak.

When working out the power in the regulator, it is best to assume that
the peak voltage is what you get. The rated voltage on the
transformer is for a normal line voltage. In the high line case, you
can get a little more.

I appreciate that, but my original comments stand. There is no valid reason to
state "the regulator circuit needs to get rid of 136W" when the transformer is
not rated to deliver that power.

You seem to have a poor understand of what the rating of a transformer
means.

On the contrary. A 24V 5A secondary is rated for 120VA. Your education
suggests something different? Please inform us all as to YOUR transformer
theory.

Yes that is the *rating* in VA and yes that works out to 120/1.5=80W
of power from the rectifier. It however is far below the limit of
what you can actually get out of the transformer. It is what the
maker says the transformer can do forever on a normal line voltage and
usually with an air temperature of some 50C. The transformer does not
contain any significant current limiting. The output impedance is
fairly low. The heat sinking on the regulator needs to be designed to
withstand the high line case with a short circuit on the output. This
is a lot more than the rated power of the transformer.

If the OP goes with less than the amount of heat sinking I suggested,
I predict he will be replacing the transistors very early in the power
supplies life.