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'[PIC]: Need help with a stupid problem'
2002\05\30@132720 by Tal (Zapta)

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face
What is the voltage on the capacitors and what is the current going out to
the circuit ?

WIth this information you can calculate the power dissipated by the
regulators.

 P = Vdrop * I

 Vdrop = Vcap - 9V

I don't think this has to do with the values of the capacitors.

Tal

> {Original Message removed}

2002\05\30@133138 by uter van ooijen & floortje hanneman

picon face
> Attached file as you can see its a small and simple psu.
> this device produce heat to much, it only supply to a opamp about 10-15mA
.
> the regulators are very hot as well the input capacitors. I use large
caps'
> 2200uf each (not 1000uf as in the schematic. could it be the reason for
the
> heating?
> just let me mention that it's a phono pre-amp so I use so large caps.
> furthermore the transformer is 220v-2x18vac

What is the voltage rating of the elco's? For 18 V AC in you would need (at
least) 18 x sqrt(2) x 1.2 = 30.5 Volt.

Wouter van Ooijen
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2002\05\30@140703 by Uri Sabadosh

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What are the input and output voltages on these regulators? You dissipation
is roughly (Vin - Vout) * I(load). I assume dc regulators.

Uri



{Original Message removed}

2002\05\30@142142 by Mark J. Dulcey

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face
Tal Bejerano - AMC wrote:
> Hi 2 All
>
> Attached file as you can see its a small and simple psu.
> this device produce heat to much, it only supply to a opamp about 10-15mA .
> the regulators are very hot as well the input capacitors. I use large caps'
> 2200uf each (not 1000uf as in the schematic. could it be the reason for the
> heating?
> just let me mention that it's a phono pre-amp so I use so large caps.
> furthermore the transformer is 220v-2x18vac

It looks as though you're dropping a lot more voltage in those
regulators than you need to. A 2x12V transformer would probably be a
better choice for those +- 9V outputs.

As someone else already mentioned, you also have to make sure that your
capacitor voltage ratings are suitable.

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2002\05\30@144709 by John Dammeyer

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Sigh!  This sort of issue comes up again and again. Bypass Bypass Bypass
and read the data sheet which says bypass as close as possible to the
leads,  especially if large filter capacitors are used.  Put in a couple
0.01 or 0.1 uF caps right on the leads of the regulators.

And like the rest of the postings on this subject,  I'm assuming you
have used at least 35V capacitors here (1.414* 18V).

For low noise in linear amplifiers there is a better way too.  Use a
7812 and 7912 regulator to create 12V and regulate most of your power
supply to a usable value.  Most of the heat will be dissipated over
these devices.  Then use a second pair of the 7809,7909 regulators to
create your analogue voltages from the +/-12V

And bypass bypass bypass.

John Dammeyer



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www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

2002\05\30@154912 by Rick C.

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face
If you're stuck with that transformer, just use one secondary and ground one
leg. The other leg to the anode and cathode of each diode feeding each
capacitor respecively in a half wave configuration. Since you are not using
much current, you can get away with it. If the cap voltage ratings were
sufficient, the caps are probably getting hot from the natural conduction of
heat from the regulators since you said it was a tight close assembly.
Rick

Tal Bejerano - AMC wrote:

{Quote hidden}

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2002\05\30@163940 by Olin Lathrop

face picon face
> Attached file as you can see its a small and simple psu.
> this device produce heat to much, it only supply to a opamp about 10-15mA
.
> the regulators are very hot as well the input capacitors.

You are trying to make a +- 9V regulated supply.  The transformer
secondaries are too high voltage for this, which will cause unnecessary
heating in the linear regulators.  The unregulated voltages will be 18 *
sqrt(2) = 25V, possibly higher depending on input line voltage and what load
the 18V is specified at.  25 - 9 = 16 volts drop on each regulator.  16V *
15mA = 240mW.  That should cause noticeable heating in a TO-5 package, but
should still be within tolerance.  It should certainly not be "very hot", so
something else is going on.  The capacitors shouldn't be dissipating any
power.  They are either being heated indirectly by the regulators, or
something is very seriously wrong.

Are you sure the capacitors are installed the right way?  If not they will
draw excessive current, get hot, and explode in a minute or so.  I'm serious
about this.  Don't put your face near this circuit if there is a chance the
capacitors are installed backwards.  They are drawn correctly on the
schematic.

Are you sure the load only draws 15mA?  Is that what it's supposed to draw
or what you've actually measured?


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2002\05\30@165250 by Olin Lathrop

face picon face
> If you're stuck with that transformer, just use one secondary and ground
one
> leg. The other leg to the anode and cathode of each diode feeding each
> capacitor respecively in a half wave configuration. Since you are not
using
> much current, you can get away with it. If the cap voltage ratings were
> sufficient, the caps are probably getting hot from the natural conduction
of
> heat from the regulators since you said it was a tight close assembly.

Um Rick, the peak voltage will still be the same.  It will only happen once
every power cycle instead of twice.  Since he's drawing so little current
(supposedly) a half wave rectifier should suffice, but it will produce the
same (actually slightly higher due to one less diode drop) unregulated
voltage.  If you've got the extra transformer secondary, you might as well
use it.


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2002\05\30@175548 by Tal Bejerano - AMC

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Olin

About the caps' I found that I use 16v instead of using 35v.
the transformer is what I have in my junk box, you know those who are packet
in plastic case the deliver about 40mA. I will buy 12vx2 tomorrow and check
again.
about the consumption: I didn't measure it but data say "6mA" it's a LM4558.
other problem I have is "hum" look like main 50hz. I feel handicapped with
out a scope but I try to reduces it in many ways. it's really a bad project
for cause this IC is very sensitive.


Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

2002\05\30@182242 by Jinx

face picon face
> About the caps' I found that I use 16v instead of using 35v

I'm surprised they've lasted this long at 25V

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2002\05\30@184012 by Olin Lathrop

face picon face
> About the caps' I found that I use 16v instead of using 35v.
> the transformer is what I have in my junk box, you know those who are
packet
> in plastic case the deliver about 40mA. I will buy 12vx2 tomorrow and
check
> again.
> about the consumption: I didn't measure it but data say "6mA" it's a
LM4558.

Does that include the load?  Probably not.

> other problem I have is "hum" look like main 50hz.

If your caps were getting warm, then they were drawing current, which would
aggrevate the hum.  I wouldn't chase that until the caps are right and the
voltages look reasonable with no load.  Then connect a known load, like a
resistor, and see how much the supply droops and if anything gets hot.


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2002\05\30@195828 by Brian Aase

picon face
It's very common for hum to sneak into simple analog circuits
from not-so-obvious places.  Here are a couple of things to
look for:

1. The layout of your actual power supply wiring.  Make
absolutely sure that you create a central "magic point" at
which the transformer center-tap wire and the two 1000uF
electrolytic capacitors all join together.  Then run a bus from
exactly this point out to the regulators, and the to rest of your
circuit.  This forces all the very nasty charging currents to keep
to themselves, rather than coupling into your amplifier.

2. You mention that you're using a 4558 opamp.  In no way
should this be a "sensitive" part, it's very tame and well-behaved.
Again, local power supply bypassing is critical.  Be sure there's
something like a 0.1uF cap from each of the opamp's power
terminals to the nearest circuit ground point, and that these
caps are physically very near the opamp.  Without these, your
circuit may very well have a high-frequency parasitic oscillation,
and -- surprise -- the resulting common-mode conduction in
the opamp's output stage can draw an unexpectedly large
(but still not fatal) current and things will overheat.  Audible hum
is a common manifestation of such an oscillation, because the
opamp is operating in a sort-of unintended mode and its
power supply rejection suffers.

BTW, there's nothing at all "stupid" about the problems you're
experiencing.  We've all been there.  These oh-so-simple circuits
can misbehave in an astounding number of ways, you just have to
keep at it till you've learned the right tricks. ;-)


----- Original Message -----
From: "Tal Bejerano - AMC" <KILLspamkooterKILLspamspamZAHAV.NET.IL>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Thursday, May 30, 2002 3:45 PM
Subject: Re: [PIC]: Need help with a stupid problem


> Olin
>
> About the caps' I found that I use 16v instead of using 35v.
> the transformer is what I have in my junk box, you know those who are
packet
> in plastic case the deliver about 40mA. I will buy 12vx2 tomorrow and
check
> again.
> about the consumption: I didn't measure it but data say "6mA" it's a
LM4558.
> other problem I have is "hum" look like main 50hz. I feel handicapped with
> out a scope but I try to reduces it in many ways. it's really a bad
project
> for cause this IC is very sensitive.
>
>
> Regards
>
> Tal Bejerano
> AMC - ISRAEL
>
>
> {Original Message removed}

2002\05\30@212138 by Bob Ammerman

picon face
You toasted your caps. You'll need new ones even at 12Vx2 transformer: I'd
recommend at least 20V preferably 25V.

Bob Ammerman


----- Original Message -----
From: "Tal Bejerano - AMC" <spamBeGonekooterspamBeGonespamZAHAV.NET.IL>
To: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Sent: Thursday, May 30, 2002 6:45 PM
Subject: Re: [PIC]: Need help with a stupid problem


> Olin
>
> About the caps' I found that I use 16v instead of using 35v.
> the transformer is what I have in my junk box, you know those who are
packet
> in plastic case the deliver about 40mA. I will buy 12vx2 tomorrow and
check
> again.
> about the consumption: I didn't measure it but data say "6mA" it's a
LM4558.
> other problem I have is "hum" look like main 50hz. I feel handicapped with
> out a scope but I try to reduces it in many ways. it's really a bad
project
> for cause this IC is very sensitive.
>
>
> Regards
>
> Tal Bejerano
> AMC - ISRAEL
>
>
> {Original Message removed}

2002\05\31@024451 by Tal Bejerano - AMC

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face
Brian

You are right! i let the autoroute to deside the routing process and forgot
the a rule that a very good engineer told me ones: "never let autorute do
your power circuits" i attach the result autoroute from eagle as example i
think you'll get my point.
look like i need to do it manualy.

Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

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