On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote:

If you want to keep it to a couple transistors they would be expensive.
You are better off using either more NTE-180 or more mj2955, but I would
cut the voltage down to around 18 volts instead of 24 volts as this
higher voltage leads to more heat for the transistors. Rob

How come no one's yet recommeded that great old PSU war-horse, the
2N3055? Six of them on a decent heat sink and you're sorted!

--

"Windows [n.], A thirty-two bit extension and GUI shell to a sixteen bit patch
to an eight bit operating system originally coded for a four bit
microprocessor and produced by a two bit company."

Paul Burridge wrote:
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote:


If you want to keep it to a couple transistors they would be expensive.
You are better off using either more NTE-180 or more mj2955, but I would
cut the voltage down to around 18 volts instead of 24 volts as this
higher voltage leads to more heat for the transistors. Rob


How come no one's yet recommeded that great old PSU war-horse, the
2N3055? Six of them on a decent heat sink and you're sorted!

2N3055 are great, but 2N3771 are better! Rob

Paul Burridge wrote:
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote:


If you want to keep it to a couple transistors they would be expensive.
You are better off using either more NTE-180 or more mj2955, but I would
cut the voltage down to around 18 volts instead of 24 volts as this
higher voltage leads to more heat for the transistors. Rob


How come no one's yet recommeded that great old PSU war-horse, the
2N3055? Six of them on a decent heat sink and you're sorted!

2N3055 are great, but 2N3771 are better! Rob

the trasformer is in the KW range.....
it's a big nasty beast.


--
http://www.qsl.net/sv1hao
"clarke" wrote in message
...
Hi, check this link and see what you need to do,
one or two pass trans. will not do the job for you,
easier to use 6-10 pass trans to share the load.

http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm

Is your transformer able to supply necessary power to this supply ?

regards,
clarke


Deos wrote:

Hi everyone I have made a power supply for my rigs

The schematic is the typical regulator with power transistor wrapped
around
it for the extra juice.

I need 40 amps continues ..

I tried 4 mj2955 which are rather nice for foot warming in the winter .

I also tried nte-180 which are very good. is there anything better at a
logical price

I would like to keep the number of transistors down to 1 or 2.

Can someone advise my on what to use for power?

--
http://www.qsl.net/sv1hao

the trasformer is in the KW range.....
it's a big nasty beast.


--
http://www.qsl.net/sv1hao
"clarke" wrote in message
...
Hi, check this link and see what you need to do,
one or two pass trans. will not do the job for you,
easier to use 6-10 pass trans to share the load.

http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm

Is your transformer able to supply necessary power to this supply ?

regards,
clarke


Deos wrote:

Hi everyone I have made a power supply for my rigs

The schematic is the typical regulator with power transistor wrapped
around
it for the extra juice.

I need 40 amps continues ..

I tried 4 mj2955 which are rather nice for foot warming in the winter .

I also tried nte-180 which are very good. is there anything better at a
logical price

I would like to keep the number of transistors down to 1 or 2.

Can someone advise my on what to use for power?

--
http://www.qsl.net/sv1hao

dont have any idea how to work with mosfet
any links in the right direction?


--
http://www.qsl.net/sv1hao
"Frank Dinger" wrote in message
...
Hi everyone I have made a power supply for my rigs

The schematic is the typical regulator with power transistor wrapped
around
it for the extra juice.

I need 40 amps continues ..



I tried 4 mj2955 which are rather nice for foot warming in the winter .

I also tried nte-180 which are very good. is there anything better at a
logical price

I would like to keep the number of transistors down to 1 or 2.

Can someone advise my on what to use for power?
========
Assuming that so far you have only considered bi-polar transistors
,perhaps
it would be beneficial to look into the application of Power MOSFETs. In
the
'on' state they have a very low resistance ,hence at high currents they
dissipate less heat .
Consequently you would need smaller heat sinks.

Frank GM0CSZ / KN6WH

dont have any idea how to work with mosfet
any links in the right direction?


--
http://www.qsl.net/sv1hao
"Frank Dinger" wrote in message
...
Hi everyone I have made a power supply for my rigs

The schematic is the typical regulator with power transistor wrapped
around
it for the extra juice.

I need 40 amps continues ..



I tried 4 mj2955 which are rather nice for foot warming in the winter .

I also tried nte-180 which are very good. is there anything better at a
logical price

I would like to keep the number of transistors down to 1 or 2.

Can someone advise my on what to use for power?
========
Assuming that so far you have only considered bi-polar transistors
,perhaps
it would be beneficial to look into the application of Power MOSFETs. In
the
'on' state they have a very low resistance ,hence at high currents they
dissipate less heat .
Consequently you would need smaller heat sinks.

Frank GM0CSZ / KN6WH

On Mon, 20 Oct 2003 20:28:06 GMT, Jim Higgins
wrote:

The basic design demonstrates a generally acceptable approach to
designing a power suppy, but some of the components chosen just
don't seem up to meeting the design criteria of 24 volts in, 12
volts out at 30 amps.

Such designs are simply brain dead.

If you need +12 V at 30 A and you are using NPN series pass
transistors, you should use about 13 V at the end of the capacitor
discharge cycle. This should be doable with far less than 24 V
capacitor nominal voltage.

Assuming the capacitor voltage drops from say 17 V to 13 V during each
half cycle, the power dissipation in the series pass transistors will
be ((17+13)/2 V)-12 V) x 30 A or 90 W, so this is doable with 3-6
transistors.

However, the required base voltage varies between 14 and 18 V, so a
separate power supply is required, either with a separate secondary
winding or by using some kind of voltage doubling, but this needs to
supply only 2-4 A.

The other alternative is to use PNP series pass transistors on the +12
V side, in which case a high, separate voltage is not needed.

Paul OH3LWR

On Mon, 20 Oct 2003 20:28:06 GMT, Jim Higgins
wrote:

The basic design demonstrates a generally acceptable approach to
designing a power suppy, but some of the components chosen just
don't seem up to meeting the design criteria of 24 volts in, 12
volts out at 30 amps.

Such designs are simply brain dead.

If you need +12 V at 30 A and you are using NPN series pass
transistors, you should use about 13 V at the end of the capacitor
discharge cycle. This should be doable with far less than 24 V
capacitor nominal voltage.

Assuming the capacitor voltage drops from say 17 V to 13 V during each
half cycle, the power dissipation in the series pass transistors will
be ((17+13)/2 V)-12 V) x 30 A or 90 W, so this is doable with 3-6
transistors.

However, the required base voltage varies between 14 and 18 V, so a
separate power supply is required, either with a separate secondary
winding or by using some kind of voltage doubling, but this needs to
supply only 2-4 A.

The other alternative is to use PNP series pass transistors on the +12
V side, in which case a high, separate voltage is not needed.

Paul OH3LWR

Assuming that so far you have only considered bi-polar transistors perhaps
it would be beneficial to look into the application of Power MOSFETs. In the
'on' state they have a very low resistance ,hence at high currents they
dissipate less heat .

Consequently you would need smaller heat sinks.

dont have any idea how to work with mosfet

In this particular application - pass transistors in a linear
regulator - I don't see that MOSFETs would have any particular
advantage.

It's true that modern power MOSFETs have a very low series resistance
when switched "fully on". This allows for low losses, and relatively
low heat dissipation, if they're used in an application where "fully
on, or fully off" is suitable. "Hard" power switching, or pulse-
width-modulated drive applications such as a switching regulator or a
DC motor-speed controller are good places for MOSFETs (or IGBTs).

However, a linear regulator isn't this sort of application. In these
regulators, you aren't driving the pass transistor "hard on" -
because, if you did, the regulator would simply pass the full input
voltage to its output and wouldn't regulate at all! Instead, you're
switching the transistor on only partway, so that it's passing only
the amount of current needed to "pull up" the outputs to the
regulation voltage.

The rest of the voltage (input minus output) is going to appear across
the pass transistor (and possibly one or two other components in
series with it, such as ballast resistors) and will be dissipated as
heat. This will be true regardless of whether the regulating element
is a MOSFET, bipolar transistor, or whatever. If you're sucking 30
amperes, and dropping 10 volts between input and output, your pass
elements will be dissipating 300 watts.

The only ways I know of to reduce the heat dissipation are to either
lower your input voltage (but not enough to cause the circuit to drop
out of regulation), or move to a lower-loss architecture such as a
buck-mode switching regulator. The latter can be quite efficient
(often 90% or better), but you have to work REALLY HARD to build one
which won't emit enough radiated and conducted RF switching noise to
totally yngvi up your HF reception.

I agree with the other posters, who suggest that it's probably
preferable to use a sufficient number of simple, easy-to-buy
pass transistors (2N3055 being the classic example). Use enough
so that you can use 'em well within conservative ratings - don't
go anywhere near the edge of the "safe operating area" - and
ballast them so that they share current properly.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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