I am wanting to build a 24 volt power supply for a project I am working on.
I was wanting to know if anyone would have a schematic for such a power
supply. The power supply needs to be atleast 25 amp. If you can help me
please send me an email to

Thank you,

Craig Clark - N5XNQ
http://home.bellsouth.net/p/PWP-n5xnq

I am wanting to build a 24 volt power supply. The power supply needs to be at
least 25 amp.

Hi Craig, I am sure you know you are trying to build a 625 watt power supply.
As such, a Linear Power Supply will be large, heavy, not to mention expensive.
Unless you have a lot of high volt-amp transformers, 100,000 mfd. Caps as well
as big pass transistors with heat sinks in your junk box, this will be
expensive. If you do have all this stuff, then use any Linear power supply
schematic.
A possibly better soulition would be a Switching Power Supply. These are not
easily built because of the difficulity in obtaining the components. Try
taking a look at Lambda Power Supplies, and look at Ebay selling Lambda stuff
at a good price.


73 Gary N4AST

"Craig" wrote in message
. ..
I am wanting to build a 24 volt power supply for a project I am working on.
I was wanting to know if anyone would have a schematic for such a power
supply. The power supply needs to be atleast 25 amp. If you can help me
please send me an email to

Thank you,

Craig Clark - N5XNQ
http://home.bellsouth.net/p/PWP-n5xnq


Craig -

The ARRL Handbook has featured a "How To" 28 / 24 volt high current power
supply in every ARRL Handbook since 1989 - yes I checked its even in the
2004 version. Mark Wilson, AA2Z built the first one at ARRL labs in 1980s.

Gary makes very good points about linear vs. switching power supplies.

If you wish to build a linear power supply, it is fairly straight forward.
You will need a large transformer than has a secondary in the range of 30 to
36 volts AC at 25 amps.

Heat sink design and size (heat transfer of 625 watts - which is not a small
issue -- think small kitchen cooking appliances)

Some reference sites for building a linear power supply. You can adopt 13.8
VDC designs by remembering that the voltage is double -- and sizing for
current(amperage). The LM723 serves as the "reference voltage" in these
designs. A broken power supply (bad transformer) is a great start - case,
heat sink, etc.

David Metz's theory and building hints
http://www.seits.org/features/pwrsup.htm

KBT DC supplies
http://www.kbt-dc-supplies.com/index.php

Astron schematics (largely 13.8 vdc, but may have a 24 vdc one in listings)
http://www.repeater-builder.com/rbtip/astron-index.html

SWITCH MODE SUPPLIES
http://www.hills2.u-net.com/electron/smps.htm

http://www.geocities.com/CapeCanaveral/Lab/9643/

That should get you started!

Greg, w9gb

"JGBOYLES" wrote in message
...
I am wanting to build a 24 volt power supply. The power supply needs to
be at
least 25 amp.

Hi Craig, I am sure you know you are trying to build a 625 watt power
supply.
As such, a Linear Power Supply will be large, heavy, not to mention
expensive.
Unless you have a lot of high volt-amp transformers, 100,000 mfd. Caps as
well
as big pass transistors with heat sinks in your junk box, this will be
expensive. If you do have all this stuff, then use any Linear power
supply
schematic.
A possibly better soulition would be a Switching Power Supply. These are
not
easily built because of the difficulity in obtaining the components. Try
taking a look at Lambda Power Supplies, and look at Ebay selling Lambda
stuff
at a good price.

73 Gary N4AST

Gary -

Here is what Craig is looking for -- power supply for a ATV solid-state
final amplfier

w9gb
============================
"I am looking for 24 volt dc power supply that can handle a min of 18 amps.
This will be used on the new 200 watt ATV final amp. If you have one your
looking to get rid of please drop me an email with the details.
73's
Craig N5XNQ

There is a 28 volt 10Amp power supply in 2004 ARRL handbook. See
pages 11.36 through 11.39. It should be a simple matter of using a
higher current transformer, rectifier, and additionall 2N3055 pass
transistors for more current, and a minor adjustment of the voltage
adjustment potentiometer to lower the voltage to 24 volts. The
described power supply uses a LM-723 and a LM-317L voltage regulator.
It features current foldback in case the output is shorted.

Eric N7DLV

"Craig" wrote in message ...
I am wanting to build a 24 volt power supply for a project I am working on.
I was wanting to know if anyone would have a schematic for such a power
supply. The power supply needs to be atleast 25 amp. If you can help me
please send me an email to

Thank you,

Craig Clark - N5XNQ
http://home.bellsouth.net/p/PWP-n5xnq

On Sun, 12 Sep 2004 16:54:30 -0500, "Craig"
wrote:

I am wanting to build a 24 volt power supply for a project I am working on.
I was wanting to know if anyone would have a schematic for such a power
supply. The power supply needs to be atleast 25 amp.

From other postings it appears that you need a power supply for an ATV
transmitter (repeater?), one should note that ATV transmitters are
usually operated at nearly constant duty (and FM ATV transmitters
additionally at constant load), while typically amateurs transmitters
are operated at (much) less than 50 % duty cycle. I the ATV power
supply, the temperature balance will be reached during each operation
cycle and in the interest of reliable operation, this temperature
should be as low as possible.

Thus, when looking for various designs in the amateur literature,
select one with rated capacity well above the transmitter requirement.
Use larger heat sinks than specified or use a fan. Some
overtemperature protection is also needed, especially if a fan is used
and it fails.

The 24 V 10 A design in the ARRL Handbook is a good starting point. It
uses four 2N3055 series pass transistors, thus 2.5 A/transistor. Even
at full load, the average voltage drop across the transistor could be
8 V, so each individual series pass transistor (and heatsink) is
required to dissipate 20 W. These are quite reasonable figures for the
2N3055.

Upgrading this to 25A should require a larger transformer, capacitor
and rectifier. Ten series pass transistors with larger heatsinks
should keep the individual transistor loading at the same level.The
short circuit measurement resistor value should be reduced.

The worst case current gain for the 2N3055 is specified as 20 @ 4A, so
the total base current for the ten 2N3055 would be well below 1.25 A,
which the single 2N3055 driver could well handle and still assuming
hfe=20, the uA723 would have to supply 63 mA, well within
specifications, however, the power dissipation might be a problem.

Those are worst case specifications for these transistors at larger
currents, but looking at the Motorola 2N3055 transistor, the typical
hfe=50 at 2.5 A at room temperatures or above, thus the total base
current for the ten 2N3055 would be 500 mA and at that current the
single driver 2N3055 will have a hfe 100 at or above room
temperatures, thus the uA723 would have to supply 5 mA and there would
not be any power dissipation issues.

Of cause, when using typical values (instead of worst case values) to
build a one-off project, one should verify by measurement that the
typical values apply. This is specially important when "no-name"
components are used.

Using larger storage capacitors than specified will reduce the voltage
drop during each cycle, thus a slightly lower secondary voltage can be
used, which drops the total power dissipation.

Paul OH3LWR

"Paul Keinanen" wrote in message
...
On Sun, 12 Sep 2004 16:54:30 -0500, "Craig"
wrote:

I am wanting to build a 24 volt power supply for a project I am working
on.
I was wanting to know if anyone would have a schematic for such a power
supply. The power supply needs to be atleast 25 amp.

From other postings it appears that you need a power supply for an ATV
transmitter (repeater?), one should note that ATV transmitters are
usually operated at nearly constant duty (and FM ATV transmitters
additionally at constant load), while typically amateurs transmitters
are operated at (much) less than 50 % duty cycle. I the ATV power
supply, the temperature balance will be reached during each operation
cycle and in the interest of reliable operation, this temperature
should be as low as possible.

Thus, when looking for various designs in the amateur literature,
select one with rated capacity well above the transmitter requirement.
Use larger heat sinks than specified or use a fan. Some
overtemperature protection is also needed, especially if a fan is used
and it fails.

The 24 V 10 A design in the ARRL Handbook is a good starting point. It
uses four 2N3055 series pass transistors, thus 2.5 A/transistor. Even
at full load, the average voltage drop across the transistor could be
8 V, so each individual series pass transistor (and heatsink) is
required to dissipate 20 W. These are quite reasonable figures for the
2N3055.

Upgrading this to 25A should require a larger transformer, capacitor
and rectifier. Ten series pass transistors with larger heatsinks
should keep the individual transistor loading at the same level.The
short circuit measurement resistor value should be reduced.

The worst case current gain for the 2N3055 is specified as 20 @ 4A, so
the total base current for the ten 2N3055 would be well below 1.25 A,
which the single 2N3055 driver could well handle and still assuming
hfe=20, the uA723 would have to supply 63 mA, well within
specifications, however, the power dissipation might be a problem.

Those are worst case specifications for these transistors at larger
currents, but looking at the Motorola 2N3055 transistor, the typical
hfe=50 at 2.5 A at room temperatures or above, thus the total base
current for the ten 2N3055 would be 500 mA and at that current the
single driver 2N3055 will have a hfe 100 at or above room
temperatures, thus the uA723 would have to supply 5 mA and there would
not be any power dissipation issues.

Of cause, when using typical values (instead of worst case values) to
build a one-off project, one should verify by measurement that the
typical values apply. This is specially important when "no-name"
components are used.

Using larger storage capacitors than specified will reduce the voltage
drop during each cycle, thus a slightly lower secondary voltage can be
used, which drops the total power dissipation.

Paul OH3LWR


Craig -

Paul and Eric and provided a good background on how to adopt the ARRL
design.
You can substitute the 2N3771 transistor for the common 2N3055 pass
transistor (this is what Astron has done on many of their latest models).

Greg
w9gb

On Mon, 13 Sep 2004 12:36:04 GMT, "G.Beat"
wrote:

Paul and Eric and provided a good background on how to adopt the ARRL
design.
You can substitute the 2N3771 transistor for the common 2N3055 pass
transistor (this is what Astron has done on many of their latest models).

This suggestion makes sense for low voltage (5-12 V) high current
power supplies, since the worst case current gain (15) has been
specified for Ic=15 A and in general, the typical current gains are
better at very large currents than with 2N3055. Also the Vbe and
Vce(sat) voltages are lower at similar collector currents, thus, the
capacitor voltage can be slightly lower. From the current handling
point of view, the number of devices could be reduced. However, the
power dissipation would have to be checked, although the junction to
case thermal resistance is smaller, this does not help the heatsink
very much.

However, the ARRL 24 V supply uses only 2.5 A/transistor, so the
current gain and Vbe and Vce(sat) are not really an issue, but the
power dissipation issues are much worse on 24 V than on 12 V. The
power dissipation may still require that ten 2N3771 are used, which
are usually a bit more expensive than ten 2N2055 transistors :-).

Please note that the maximum Vce for 2N3771 is only 40 V and since the
capacitor voltage can exceed 40 V and in case of a short circuit, the
emitter is close to 0 V, the Vce could be exceeded. At least use the
2N3772 for the 24 V supply, since the maximum Vce is 60 V. The 2N3055
is also specified for Vce=60 V.

Paul OH3LWR

On Mon, 13 Sep 2004 23:10:03 +0300, Paul Keinanen
wrote:

On Mon, 13 Sep 2004 12:36:04 GMT, "G.Beat"
wrote:

Paul and Eric and provided a good background on how to adopt the ARRL
design.
You can substitute the 2N3771 transistor for the common 2N3055 pass
transistor (this is what Astron has done on many of their latest models).

This suggestion makes sense for low voltage (5-12 V) high current
power supplies, since the worst case current gain (15) has been
specified for Ic=15 A and in general, the typical current gains are
better at very large currents than with 2N3055. Also the Vbe and
Vce(sat) voltages are lower at similar collector currents, thus, the
capacitor voltage can be slightly lower. From the current handling
point of view, the number of devices could be reduced. However, the
power dissipation would have to be checked, although the junction to
case thermal resistance is smaller, this does not help the heatsink
very much.

However, the ARRL 24 V supply uses only 2.5 A/transistor, so the
current gain and Vbe and Vce(sat) are not really an issue, but the
power dissipation issues are much worse on 24 V than on 12 V. The
power dissipation may still require that ten 2N3771 are used, which
are usually a bit more expensive than ten 2N2055 transistors :-).

Please note that the maximum Vce for 2N3771 is only 40 V and since the
capacitor voltage can exceed 40 V and in case of a short circuit, the
emitter is close to 0 V, the Vce could be exceeded. At least use the
2N3772 for the 24 V supply, since the maximum Vce is 60 V. The 2N3055
is also specified for Vce=60 V.

Paul OH3LWR

I suppose it is to be used for a linear amplifier, and then it is a
not a good idea to use stabilized voltage. It might have been needed
for 14V, although Atlas 210-X was operated without - with a varying
voltage between 11-16V, but is not the same problem for 24V.
With maximum voltage of +32V the output may drop down towards 24V, and
no problem at all - apart from setting a limit for the power input

73
Jan-Martin
LA8AK
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

"Paul Keinanen" wrote in message
...
On Mon, 13 Sep 2004 12:36:04 GMT, "G.Beat"
wrote:

Paul and Eric and provided a good background on how to adopt the ARRL
design.
You can substitute the 2N3771 transistor for the common 2N3055 pass
transistor (this is what Astron has done on many of their latest models).

This suggestion makes sense for low voltage (5-12 V) high current
power supplies, since the worst case current gain (15) has been
specified for Ic=15 A and in general, the typical current gains are
better at very large currents than with 2N3055. Also the Vbe and
Vce(sat) voltages are lower at similar collector currents, thus, the
capacitor voltage can be slightly lower.

[snip]

Please note that the maximum Vce for 2N3771 is only 40 V and since the
capacitor voltage can exceed 40 V and in case of a short circuit, the
emitter is close to 0 V, the Vce could be exceeded. At least use the
2N3772 for the 24 V supply, since the maximum Vce is 60 V. The 2N3055
is also specified for Vce=60 V.

Paul OH3LWR

Yes, I also have the 2N3772 in my parts replacement bin - and have used as
replacements for shorted 2N3055 pass transistors.

w9gb