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'[OT] 300V Switcher'
2000\01\19@162725 by Donald L Burdette

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I'm trying to figure out how to build a 300VDC power supply that will be
powered from a battery, nominally 3V, 6V, or 9V (customer wishes to have
one board that can be stuffed for 3 different versions).

I only need about 3-5 mA at 300V, and I wouldn't have much of a problem
with this except for one thing - the board with components needs to fit
in an area 1.1" (28mm)  wide and 0.2" (5mm) high!  He's being generous
and allowing me to make it several inches long.

This design isn't too bad until you run the numbers and realize that the
duty cycle on a standard boost circuit would be 97-99%, and most
controllers won't go higher than 85-90%.  If I try to use a flyback
transformer, the inductance of the secondary has to be 7-10 mH, which is
quite high.

I've thought about trying to see how laptop display backlight conrtollers
work, but I don't know where to look.

Anyone got any ideas?

BTW, this is not completely OT since the micro on this board is a 16F873.

Thanks.

Don

2000\01\19@163722 by Craig Lee

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Check out the infamous Sam's circuits at http://www.repairfaq.org.  I've
seen just such a circuit to produce a 300V supply from a penlight cell.

However it does use a hand-wound transformer to give you this.

While on this topic, I'm looking for a 6000 VAC supply that I can vary
from HZ to KHZ.  It can run of 120VAC.

Yet another PIC project...

Craig

> {Original Message removed}

2000\01\19@164758 by Terry A. Steen

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Perhaps you can step up with a switcher to power an oscillator. Drive a
step up transformer with the oscillator and rectify the output (or add a
voltage doubler?). Sounds a bit over done, but I did make a 120VAC source
like that one time... It was part of a course, I doubt it is the best 'real
world' way to do it.

Terry

At 04:23 PM 1/19/2000 -0500, you wrote:
{Quote hidden}

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2000\01\19@180308 by Lee Jones

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> I'm trying to figure out how to build a 300VDC power supply that
> will be powered from a battery, nominally 3V, 6V, or 9V (customer
> wishes to have one board that can be stuffed for 3 different versions).

The voltages you mention suggest multiples of 1.5V cells,
i.e. alkaline batteries.

> I only need about 3-5 mA at 300V, and I wouldn't have much of a
> problem with this except for one thing - the board with components
> needs to fit in an area 1.1" (28mm)  wide and 0.2" (5mm) high!  He's
> being generous and allowing me to make it several inches long.

That's 0.9 to 1.5 watts.  At 3 volts, current required (0.3 to 0.5
amps) exceeds the rated delivery of even an alkaline D cell.  At
the higher voltages, a cell might be able to handle the current flow
but battery life could be unacceptable.

What kind of batteries are you planning on using?

Are you sure you need that much current at 300 VDC?

                                               Lee Jones

2000\01\19@181758 by William Chops Westfield

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   That's 0.9 to 1.5 watts.  At 3 volts, current required (0.3 to 0.5
   amps) exceeds the rated delivery of even an alkaline D cell.

Really?  My AA-powered flashlight draws about .2A, and MANY applications
draw momentary power far in excess of .5A...

BillW

2000\01\19@190223 by Lee Jones

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>> That's 0.9 to 1.5 watts.  At 3 volts, current required (0.3 to 0.5
>> amps) exceeds the rated delivery of even an alkaline D cell.

> Really?  My AA-powered flashlight draws about .2A, and MANY applications
> draw momentary power far in excess of .5A...

I was, possibly incorrectly, assuming that the power was required
continuously.  My current capability was based on the "rated drain"
column in the Panasonic Alkaline Batteries section of the Digi-Key
catalog (number Q001, page 515).  Size D is listed as 320 mA; all
other sizes have lower rated drain figures.

                                               Lee Jones

2000\01\19@195836 by Donald L Burdette

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On Wed, 19 Jan 2000 15:01:36 -0800 Lee Jones <.....leeKILLspamspam@spam@frumble.claremont.edu>
writes:

>That's 0.9 to 1.5 watts.  At 3 volts, current required (0.3 to 0.5
>amps) exceeds the rated delivery of even an alkaline D cell.  At
>the higher voltages, a cell might be able to handle the current flow
>but battery life could be unacceptable.

I don't know what battery specs you are looking at, but I just checked
the duracell web site, and the performance curves for AA cells are
plotted out to 1 watt EACH.  The discharge curve for D cells is plotted
for loads up to 2 amps, but of course <G> no curves are available in
watts.


2 AA cells can put out 1W for 2 hours, terminating at 1.0V.  2 D cells
could do it for 18 hours or so.
This load will be intermittant and only a few seconds at a time, so that
kind of lifetime is acceptable.

>Are you sure you need that much current at 300 VDC?
No.  It might be higher.  Worst case it could be 7 mA, but I'm hoping to
keep it to 3 or less.  Unless the customer decides to expand the thing
again...

Really, what I want is 100-110VAC sine wave at 700-900 Hz, 10 mArms to
drive an EL panel.  I've been thinking to build a DC-DC to get 300 VDC,
then use a class D (switching) amp to generate the sine wave.  I'm hoping
that since the EL is mostly capacitive, and the switching amp is way more
efficient than a linear, the load on the 300V will be no more than 3mA.
But since I've yet to build any of this, I have no idea what the real
efficiencies will be.

And before you ask, my customer insists it must be sine wave.  I know it
would be much easier to go with some kind of filtered square wave, but he
won't hear of it.

Any ideas welcome.


Don

2000\01\19@205934 by Wagner Lipnharski

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a) Customers have ideas, requirements, and more important they have
money.
b) We can produce solutions and invoices.

It is our job, as technicians, to understand what the customer needs and
give them the best possible solution. Not always the proposed solution
is what the customer was expecting, but for sure it could be more
"technically correct".

Linear Technologies book "Linear Applications Handbook, VOL III - 1997",
application note 66, starting on page 58, there are some pretty circuits
to generate power to EL lamps, using LT1301 and LT1303. They work from 2
to 6V at input, with 100µA to 2mA output and so on.  The output curves
are NOT senoidal, it is a kind of sqare wave with some ramps, probably
caused by the EL capacitance.  The LT1303 use a 1:15 transformer, 400Hz,
output AC is generated from the step-up DC, working somehow like a poor
push-pull style.

It is an interesting subject to read. If you have no access to this
book, drop me directly an email, I will scan the pages and post at my
website for download, but Linear people is nice and they post a PDF file
of this AN66:

(1.5MB - 5 min download at 48kbps):
http://www.linear-tech.com/pdf/an66f.pdf

Everything is there, it worths the download time.

Note to remember: If a customer asks a perfect square wave at his
stepper motor power drive output, you tell him that it is there, you can
even swere it is that way, but never show him the waveform at the
oscilloscope.  He will be happy, the circuit will works for years, and
the bottom line here is "Need To Know".  What good it will be to the
humanity to know that the earth planet is getting close to the sun at a
rate of 15 miles per year? and that the earth rotation is reducing day
by day and in some place in the future it will stop (relative to the
sun) as the moon did already (relative to the earth)...?  If the EL
works pretty nice with a square wave, looking hard, very hard at the
scope your customer can ending up seeing a sinewave, believe me.

Wagner.


Donald L Burdette wrote:
{Quote hidden}

2000\01\20@065042 by paulb

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Wagner Lipnharski wrote:

> Note to remember: If a customer asks a perfect square wave at his
> stepper motor power drive output, you tell him that it is there, you
> can even swear it is that way, but never show him the waveform at the
> oscilloscope.  He will be happy, the circuit will works for years, and
> the bottom line here is "Need To Know".

> If the EL works pretty nice with a square wave, looking hard, very
> hard at the scope your customer can ending up seeing a sinewave,
> believe me.

 Wagner, you are, as always, a gem! ;-)  What more could I say?
--
 Cheers,
       Paul B.

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