I'd use one of those small inexpensive inverters which put out 120vac
and then use a conventional transformer/rectifier system. You can pick
up the inverter at any truck stop.

============================
Those 'inexpensive inverters' might need some attention in respect of
the 'hash' they create , possibly causing interference in the receiver.

Frank

ORIGINAL MESSAGE:

On Mon, 26 Dec 2005 21:11:35 -0800, Highland Ham
wrote:

Those 'inexpensive inverters' might need some attention in respect of
the 'hash' they create , possibly causing interference in the receiver.

Frank

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

True for any kind of inverter.

73, Bill W6WRT

I need to generate 6v DC and 90v DC from a 12v DC automotive electrical
system [to power an RT-70A/GRC surplus military radio]. I need about 250 mA
at +6 volts and about 75 mA at +90 volts. [ I was thinking about using the
guts from an old battery back up but it would be a bit of a kluge.] Are
there any 90 volt regulators in the 78xx series? How do I get the voltage
up to where I can get something that I can get the 90 volts from. Getting
the 6 volts doesn't seem to be a problem. A 7806 off the battery should
work for that unless any of you can see a problem doing that. [ Maybe the
common common would be a problem. Right now I'm running it off of an HP6299A
and an HP6236B with commons jumpered. I'd like to be able to go portable
with it. ]



90V @70ma is only 6.3W and a step-up of no more than 90/12=7.5. This
would be something like a 24VAC center-tapped transformer turned
backwards with a multivibrator drive of the secondary at 50-60Hz and the
usual primary is rectified and capacitor filtered to produce the 90V.
Since the reflected current is only about 1/2A, you can then feedback
the rectified HV to drive an error amp that regulates the center tap
down to 9V or so.

On Tue, 27 Dec 2005 02:02:15 GMT, "James F. Mayer"
wrote:

I need to generate 6v DC and 90v DC from a 12v DC automotive electrical
system to power an RT-70A/GRC surplus military radio. I need about 250 mA
at +6 volts and about 75 mA at +90 volts. I was thinking about using the
guts from an old battery back up but it would be a bit of a kluge. Are
there any 90 volt regulators in the 78xx series? How do I get the voltage
up to where I can get something that I can get the 90 volts from. Getting
the 6 volts doesn't seem to be a problem. A 7806 off the battery should
work for that unless any of you can see a problem doing that. Maybe the
common common would be a problem. Right now I'm running it off of an HP6299A
and an HP6236B with commons jumpered. I'd like to be able to go portable
with it.



Hello James,
Speaking as a cheapskate ham/hobbyist, how
about salvaging parts from a computer power supply.
Find a dud power supply for free at computer
shops/dumpsters/rubbish tips/roadside etc.
Salvage the TL494 integrated circuit that can
be found in many computer power supplies.

You could build a 90 Volt power supply as
Ray Robinson has down here
http://www.shlrc.mq.edu.au/~robinson...verter_4W.html

Here is a link to the TL494 Data sheet
http://focus.ti.com/lit/ds/symlink/tl494.pdf

This link tells you how to use the TL494 IC
http://focus.ti.com/lit/an/slva001d/slva001d.pdf

Use another TL494 in a buck converter for your
12 Volts to 6Volts power supply module.
Look at the bottom of this page for more info.
http://focus.ti.com/docs/prod/folders/print/tl494.html
Your 7806 is probably a better idea, saves a lot
of messing about.
Or
you could use the guts of a mobile phone
car charger. The charger that fits into the
cigarette lighter in a motor car.
You can find them in pawn shops for a dollar
or two. Dud ones even cheaper. Usually
just a broken connection from rough handling.
http://www.onsemi.com/pub/Collateral/MC34063A-D.PDF
Look at page 7 Figure 10 Step down converter.

In the few car phone chargers that I opened,
the IC was a MC34063 and the schematic was
very similar to that shown in figure 10
Just change R1 or R2 slightly so that you
get 6 Volts out.
You may have to check/change the value of
resistor Rsc to be closer to that shown in figure 10
You might even get away with not changing the
inductor. Try it and see if the original inductor
works well enough for you.

A ton of reading, bits and pieces for free
or dirt cheap.
What a great hobby, this is James, eh!

Regards,
John Crighton
Sydney

ORIGINAL MESSAGE:

On Tue, 27 Dec 2005 05:58:18 GMT, (John Crighton)
wrote:


Hello James,
Speaking as a cheapskate ham/hobbyist, how
about salvaging parts from a computer power supply.
Find a dud power supply for free at computer
shops/dumpsters/rubbish tips/roadside etc.
Salvage the TL494 integrated circuit that can
be found in many computer power supplies.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Excellent info, John. Thanks!!

73, Bill W6WRT

On Tue, 27 Dec 2005 05:58:18 GMT in sci.electronics.design,
(John Crighton) wrote,
This link tells you how to use the TL494 IC
http://focus.ti.com/lit/an/slva001d/slva001d.pdf

So why is the guy from TI showing NTE transistors for the power
switching? Nothing in the TIP line good enough?

"David Harmon" wrote in message
...
On Tue, 27 Dec 2005 05:58:18 GMT in sci.electronics.design,
(John Crighton) wrote,
This link tells you how to use the TL494 IC
http://focus.ti.com/lit/an/slva001d/slva001d.pdf

So why is the guy from TI showing NTE transistors for the power
switching? Nothing in the TIP line good enough?



Probably good enough for his measly 32 volts. I need to modify that
circuit to work on outputs of 90 volts and 6 volts.

Buy a DC-DC converter that includes other protection
features (ie overvoltage and overcurrent protection) and
outputs known parameters (ie ripple voltage). I doubt you
will find a single DC-DC converter for both voltages. But a
small converter for each voltage should work. Many sources
including this one that just arrived on my desk -
www.astrodyne.com .

BTW, power from automotive systems should also worry about
load dump. Technically load dump can be a transient as much
as 270 volts on a 12 volt system. In reality, such events may
only be 50 volts or less. Transients that would not damage
other automotive electronics already designed for this rare
and so destructive event.

That is a problem with some regulators such as 78xx series.
Maximum voltage is typically not sufficient for automotive
purposes - would require additional protection.

"James F. Mayer" wrote:
Probably good enough for his measly 32 volts. I need to
modify that circuit to work on outputs of 90 volts and 6 volts.

On Wed, 28 Dec 2005 02:20:02 -0500, w_tom wrote:

On Wed, 28 Dec 2005 02:20:02 -0500, w_tom top-posted:
....
BTW, power from automotive systems should also worry about
load dump. Technically load dump can be a transient as much
as 270 volts on a 12 volt system. In reality, such events may
only be 50 volts or less. Transients that would not damage
other automotive electronics already designed for this rare
and so destructive event.

That is a problem with some regulators such as 78xx series.
Maximum voltage is typically not sufficient for automotive
purposes - would require additional protection.

This is what transzorbs
http://www.vishay.com/docs/88301/15ke.pdf
and hash chokes are for.

I'm not affiliated with Vishay, formerly General Semiconductor,
just a satisfied customer. I've used them to protect circuits
against the transients caused by a 5 KV arc in an ion gun. :-)

Cheers!
Rich



"James F. Mayer" wrote:
Probably good enough for his measly 32 volts. I need to
modify that circuit to work on outputs of 90 volts and 6 volts.

On Tue, 27 Dec 2005 02:02:15 GMT, "James F. Mayer"
wrote:

I need to generate 6v DC and 90v DC from a 12v DC automotive electrical
system to power an RT-70A/GRC surplus military radio. I need about 250 mA
at +6 volts and about 75 mA at +90 volts. I was thinking about using the
guts from an old battery back up but it would be a bit of a kluge. Are
there any 90 volt regulators in the 78xx series? How do I get the voltage
up to where I can get something that I can get the 90 volts from. Getting
the 6 volts doesn't seem to be a problem. A 7806 off the battery should
work for that unless any of you can see a problem doing that. Maybe the
common common would be a problem. Right now I'm running it off of an HP6299A
and an HP6236B with commons jumpered. I'd like to be able to go portable
with it.


Hello again James,
I just came across this site while looking
for something else.

http://web.telia.com/~u85920178/use/tubepsu.htm
Look at the the 6V AC from 12 V DC. Nifty!

Here is another
http://www.i4at.org/lib2/inverter.htm
You want DC out so you will have to fit a bridge rectifier
and filter capacitors to the output of the transformer
just like Harry Lythall's circuit above.

Regards,
John Crighton
Sydney