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'PIC power supply'
1997\09\04@175729 by ame

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    Hi,

    there is a device from Harris semiconductor which will drop 110 -
    240Vac to 5v 50mA with no transformer.  Effectively this is a
    world-wide autosensing single-chip PSU.  I have one at home, and will
    get the part number if I remember.  In the UK they are available from
    Maplin, not very expensive.

    Andy (#2)

1997\09\05@133524 by ame

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    Hi all,

    I just got this sent to me (thanks Mike), so I didn't have to root
    around my parts box for mine.

    aNDY #2

Author:  "Long, Mike" <spam_OUTMike.LongTakeThisOuTspamalliedsignal.com> at Internet
Date:    9/4/97 15:32

HV-2405E


Mike
----------
Subject: PIC power supply
Date: Thursday, September 04, 1997 3:43PM

    there is a device from Harris semiconductor which will drop 110 -
    240Vac to 5v 50mA with no transformer.  Effectively this is a
    world-wide autosensing single-chip PSU.
    <snip>

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From: "Long, Mike" <@spam@Mike.LongKILLspamspamalliedsignal.com>
To: "KILLspamameKILLspamspamSYNAPTICS.COM" <RemoveMEameTakeThisOuTspamsynaptics.com>
Subject: RE: PIC power supply
Date: Thu, 4 Sep 1997 15:35:00 -0700
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'PIC Power Supply'
1999\07\02@090730 by David Covick
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Any suggestions?

I need to build up a PIC power supply with the following requirements.

12 volts DC in - fixed (not a battery)
7 to 10 volts DC variable output @ approx. 1 amp
5 volts fixed @ 200 mA

Was thinking about LDO types of regulators, and would like the regulators to
be efficient enough not require a heat sink.

Can anyone recommend their favorite part number(s)?

Also, would it be better to run the 5 volt regulator off the variable 7 to
10 volt regulator, or from the 12 volts?

Thanks !!  ( sorry if this is a little off topic? )

David

1999\07\04@100416 by paulb

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David Covick wrote:

> 12 volts DC in - fixed (not a battery)
> 7 to 10 volts DC variable output @ approx. 1 amp
> 5 volts fixed @ 200 mA

> Was thinking about LDO types of regulators, and would like the
> regulators to be efficient enough not require a heat sink.

 A couple of misunderstandings here I think.  You need a LDO regulator
when the input-output differential is less than 2.5 volts.  This *might*
be a touchy point in deriving your 10V from 12V at 1 amp.

 It depends on whether you really want the 10V at 1 amp and whether the
12V is exactly 12V or always more than 12V.  The common LM317 will
*just* deliver 10V at 1A from 12V as long as its temperature is *above*
25¡C (and it's extremely unlikely to be cooler than that, isn't it?).

 If it really is critical, you may need a LDO device.  But then you
talk of "efficiency".  Insofar as this term applies to series
regulators, most LDO types are *less* efficient as they draw more
current through the reference terminal in order to drive the output
device, particularly at (near-)maximum load.

 The term "efficient enough not require a heat sink" really doesn't
make sense.  Series regulators dissipate the difference between input
and output voltage, times current as heat and that's all there is to it.

 A *large* device may to some extent act as its own heatsink but your
7V regulator is going to dissipate 5 watts, and your 5V fixed device,
1.4W.  I'd say the first will need a big heatsink and the second, a
little one.

> Can anyone recommend their favorite part number(s)?

 LM317 for both.

> Also, would it be better to run the 5 volt regulator off the variable
> 7 to 10 volt regulator,

 Definitely not!  Firstly, the variable regulator is already
dissipating the lion's share of power, so why add to that?  Secondly,
you are deliberately subjecting the fixed regulator to a variable input
voltage - why would you want to do that?  Thirdly, you are using the 5V
regulator close to *its* dropout voltage if supplied from 7V.  Finally,
if the variable regulator shuts down, it will take the 5V supply with
it (this may not be a bad thing of course, depending).

> or from the 12 volts?

 Definitely.

 This said, I recently looked into my desktop document scanner and
found it used a common LDO regulator to derive 10V or so from the "12V"
supply, and both 5V regulators ran from that.  The stepper ran from the
10V.  Are you building a scanner perchance?

 Of course, you may ask why I examined the power arrangements in the
scanner?  Well, it overheated of course!  Cooked the electrolytics and
(there's more to the story).  It shouldn't do that twice.  I cut holes
in the casing to clear *and* ventilate the new electrolytics which were
bigger than the originals.
--
 Cheers,
       Paul B.

1999\07\04@105055 by David Covick

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Paul,

Thanks for the input.  You've got me thinking again.  I appreciate the
response, as no one else responded.

The Application is for a 1000 watt digital RF amplifier.

I have a fixed switching power supply that puts out 50 volts @ 25 amps and
12 volts @ 8 amps.

12 volts will be going to a couple of thermoelectric coolers ( attached to
output transformer ).
The 7 to 10 volts adjustable is for the gate drive on the power mosfets
(class-D).
The 5 volts fixed is for the logic.

A long ways away from a scanner.  But, very interesting to hear what they
have done, as well as its failure.  Sounds like you've got it fixed-up
better than their original design.

The reason I wanted efficiency, is I don't want to use a heat sink if
possible.  The circuit board is all surface mount and small.  Also, trying
to keep the height profile low.

Been doing a lot of data sheet looking since my post, and I am looking at
the Linear Technology LT1086.  This regulator is like the LM317, only is
much more efficient by somehow taking a lot of the wasted power and dumping
it back into the load....so they say :)

I think this is going off topic....the PIC monitors the heat sink
temperature as well as the amp input frequency and can shut down the amp.
also, it provides for a pulse mode operation.

Thanks,

David - WA6LBX



{Original Message removed}

1999\07\04@170818 by l.allen

picon face
{Quote hidden}

My particular favourite is the DC-DC switching step down converter
MAX649. Its output can be variable, its very efficient at 90%,
components run cool, typ 2 Amp output and the inductor is small and
off the shelf!
The 5volt 200mA can be  a MAX639, needs no external
mosfet. Sure they are switching regs but at 300kHz its not that hard
to clean up even for sensitive ADC use.
Efficiency is not effected much by Vin (must be 4<Vin<16.5)
Check it out a http://www.maxim-ic.com

Note... there is an obsession with LDO regs these days but their use
is very limited, the low drop out is suitable for battery operation
where the power source is stable and the emphasis is low current
operation, low quiesent current and squeezing every last usable
volt out of the battery. The trade off is.. the ripple rejection on
an LDO sucks. It still wastes Vin-Vout x I as heat.

If you need an LDO then I recommend a MAX883.

Lance
Lance Allen
Uni of Auckland
New Zealand


'PIC power supply'
2000\04\13@072928 by jugger nut
picon face
Hi!


To the PICLISTer..


Im designing a simple 15 minutes timer but when i turn it on the 7SEGMENT
displays 18 but sometimes it will display 15. I look at the PIC  code will
its okey then i try it with  the Mplab debugger and watch the registers and
memory values well its also okey as i debug it. I try to turn on, off ,
on..until it display 15. In that case i suspect the power supply transient.

Help me..somebody who are expert in power supply designing please help me?


juggernut





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2000\04\13@075710 by chiptech

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Check with a different display. Could be a faulty one.

When you see 15 on the display, check the voltage at the I/O pins of the PIC.

Pailoor

jugger nut wrote:

{Quote hidden}

2000\04\13@104923 by M. Adam Davis

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I ran into a similar problem with my 6-digit LED counter.  The LEDs require so
much current, that sometimes the power will sag enough to reset or halt the uC
when you change the display.

Fix this by putting a .1uF 6v cap directly across the pic VDD and VSS pins, as
close as you can get to the PIC.  The further away it'll be, the less effective
it'll be.  When breadboarding I generally take a cap with 1" leads, and place in
in the board straddling the chip.

When the LEDs draw too much current that the power sags, the capacitor will keep
the processor running.

Another thing to check is the make sure you don't have the watchdog enabled
(unless you use clrwdt frequently).

-Adam

jugger nut wrote:
{Quote hidden}

2000\04\13@184707 by Tony Nixon

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jugger nut wrote:
>
> Hi!
>
> To the PICLISTer..
>
> Im designing a simple 15 minutes timer but when i turn it on the 7SEGMENT
> displays 18 but sometimes it will display 15. I look at the PIC  code will
> its okey then i try it with  the Mplab debugger and watch the registers and
> memory values well its also okey as i debug it. I try to turn on, off ,
> on..until it display 15. In that case i suspect the power supply transient.
>
> Help me..somebody who are expert in power supply designing please help me?
>
> juggernut
>
> _______________________________________________________
> Get 100% FREE Internet Access powered by Excite
> Visit http://freelane.excite.com/freeisp

Make sure all your used RAM registers are initialized properly.

Sometimes it helps to have a short time delay routine after initializing
the ports to give them time to stabilize after power up. This probably
doesn't matter unless you are relying on pins set as inputs.

--
Best regards

Tony

http://www.picnpoke.com
spamBeGonesalesspamBeGonespampicnpoke.com

2000\04\14@085522 by jugger nut

picon face
Hi Adam ,

Greetings from the Island of Cebu Philippines!

Thanks for the know and experiences about PIC to me.

rgds;

juggernut



On Thu, 13 Apr 2000 10:47:00 -0400, pic microcontroller discussion list
wrote:

>  I ran into a similar problem with my 6-digit LED counter.  The LEDs
require so
>  much current, that sometimes the power will sag enough to reset or halt
the uC
>  when you change the display.
>
>  Fix this by putting a .1uF 6v cap directly across the pic VDD and VSS
pins, as
>  close as you can get to the PIC.  The further away it'll be, the less
effective
>  it'll be.  When breadboarding I generally take a cap with 1" leads, and
place in
>  in the board straddling the chip.
>
>  When the LEDs draw too much current that the power sags, the capacitor
will keep
>  the processor running.
>
>  Another thing to check is the make sure you don't have the watchdog
enabled
{Quote hidden}

7SEGMENT
>  > displays 18 but sometimes it will display 15. I look at the PIC  code
will
>  > its okey then i try it with  the Mplab debugger and watch the registers
and
>  > memory values well its also okey as i debug it. I try to turn on, off ,
>  > on..until it display 15. In that case i suspect the power supply
transient.
>  >
>  > Help me..somebody who are expert in power supply designing please help
me?
{Quote hidden}

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