primitive circuit - where is my mistake?

A

anonymous

Guest
I was putting together some bits for a power supply. Ive been away from
electronics for too long and am trying to get back in the swing.

At this point here is what I have:


+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)----- (nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There is no
load on it. Where is my mistake?
 
Okies. I tried flipping the vr as I can't really tell from the drawings
which is the "front". It didn't change the heating problem and Im only
getting 2V when measured from Vout to gnd. Flipping it gives the same result
either way.

"John Popelish" <jpopelish@rica.net> wrote in message
news:4164855C.9774C53C@rica.net...
anonymous wrote:

I was putting together some bits for a power supply. Ive been away from
electronics for too long and am trying to get back in the swing.

At this point here is what I have:

+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)-----
(nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There is
no
load on it. Where is my mistake?

First, go back to the data sheet and make sure you have the pins
correctly connected.
http://www.national.com/ds/LM/LM340.pdf

The 7805 is not guaranteed to be stable unless there is a small
capacitor between input and ground, and very close to the regulator.
At least .22 uf ceramic or low inductance film is recommended. A .1
uf cap output to ground is also recommended, though they claim it is
stable without it. The output voltage regulation is only specified
for load current greater than 5 milliamps, so you might connect a 1k
resistor output to ground to provide this minimum load, till you have
the design verified and ready ot connect to some other load.
--
John Popelish
Click to expand...
 
"anonymous" <anonymous@catfarm.com> wrote in message
news:ao29d.213633$3l3.91076@attbi_s03...

+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)-----
(nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There
is
no
load on it. Where is my mistake?

Okies. I tried flipping the vr as I can't really tell from the drawings
which is the "front". It didn't change the heating problem and Im only
getting 2V when measured from Vout to gnd. Flipping it gives the same
result
either way.
Click to expand...
The 3 terminal regulators are a hardy bunch but they are NOT indestructible!
Spend some time studying the package and its pin layout. Take note of
John's
instructions regarding the caps and note that you are loosing 9 volts across
the
regulator IF it were to work correctly. That will generate lots of heat and
will
require a heat sink of sufficient size to cool the part. It is possible
that your
part went into thermal shutdown mode. Try applying not less than 11 volts
to
the input of the regulator.
 
"anonymous" <anonymous@catfarm.com> wrote:

I was putting together some bits for a power supply. Ive been away from
electronics for too long and am trying to get back in the swing.

At this point here is what I have:


+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)----- (nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There is no
load on it. Where is my mistake?
Click to expand...
Whether or not it's the cause of the overheating I don't know (I'd
have suspected incorrect pin connections), but you are supplying the
7809 with only about 1.8V !

Swap the LED and R.

BTW, that's an odd value for R? How did you arrive at it?

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> schreef in bericht
news:r5t9m05los8bcmfvlc28s1naa5quj801j5@4ax.com...
"anonymous" <anonymous@catfarm.com> wrote:

I was putting together some bits for a power supply. Ive been away from
electronics for too long and am trying to get back in the swing.

At this point here is what I have:


+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)----- (nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There is
no
load on it. Where is my mistake?


Whether or not it's the cause of the overheating I don't know (I'd
have suspected incorrect pin connections), but you are supplying the
7809 with only about 1.8V !

Swap the LED and R.

BTW, that's an odd value for R? How did you arrive at it?

--
Terry Pinnell
Hobbyist, West Sussex, UK
Click to expand...
Aye Terry,

You must have been very sleepy (or I must be now). Or, as I see now, you
supposed to be the "schematic" in fixed font. As far as I can see it is
not. So no need to swap R and LED. They are simply in series. As for the
resistor, suppose they LED to need 2.4V. So you have (18-2.4)/770=20mA
current through the LED. (Or, the other way around 15,6/20=780Ohm.) You and
I should decide to take an 820Ohm resistor.

As for a 7809 becoming hot without load, it cannot be but defective. Maybe
it has been flipped. One way to destroy an otherwise rugged 78xx regulator.

petrus bitbyter.


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.771 / Virus Database: 518 - Release Date: 28-9-2004
 
"petrus bitbyter" <p.kralt@reducespamforchello.nl> wrote:


Aye Terry,

You must have been very sleepy (or I must be now). Or, as I see now, you
supposed to be the "schematic" in fixed font. As far as I can see it is
not. So no need to swap R and LED. They are simply in series. As for the
resistor, suppose they LED to need 2.4V. So you have (18-2.4)/770=20mA
current through the LED. (Or, the other way around 15,6/20=780Ohm.) You and
I should decide to take an 820Ohm resistor.

As for a 7809 becoming hot without load, it cannot be but defective. Maybe
it has been flipped. One way to destroy an otherwise rugged 78xx regulator.

Thanks petrus, you're right - I mistakenly read it like this:
Click to expand...

http://www.terrypin.dial.pipex.com/Images/7809Query.PDF

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
"anonymous" <anonymous@catfarm.com> wrote in message
news:ao29d.213633$3l3.91076@attbi_s03...
Okies. I tried flipping the vr as I can't really tell from the drawings
which is the "front". It didn't change the heating problem and Im only
getting 2V when measured from Vout to gnd. Flipping it gives the same
result
either way.
Click to expand...
In that case I sugest it was the wrong way round to start with and was fried
pretty quickly. if it wasnt it certainly is now !
instability might be a problem but i would be surprised if it cuases a hi
curent through the gnd pin wich is the only place to go in order for it to
heat up.

Best bet is to find a better drawing to look at, and get a new regulator.

Colin =^.^=
 
"anonymous" <anonymous@catfarm.com> wrote in message
news:myb9d.349134$Fg5.88185@attbi_s53...
Ive tried 2 different 7809s now with the same result. Why am I only seeing
2V from gnd to Vout?

Ill add the extra caps and put a small load on it and see what happens.
Click to expand...

Perhaps the problem is too much input V? How about if I put an 11V (or
similar) zener in front of the voltage regulators? (the final circuit will
have 4 vrs).
 
"anonymous" <anonymous@catfarm.com> schreef in bericht
news:ESb9d.83937$He1.22203@attbi_s01...
"anonymous" <anonymous@catfarm.com> wrote in message
news:myb9d.349134$Fg5.88185@attbi_s53...
Ive tried 2 different 7809s now with the same result. Why am I only
seeing 2V from gnd to Vout?

Ill add the extra caps and put a small load on it and see what happens.




Perhaps the problem is too much input V? How about if I put an 11V (or
similar) zener in front of the voltage regulators? (the final circuit will
have 4 vrs).
Click to expand...
Get a datasheet of that regulator, so you can read for yourself what max.
Vin is allowed. If you have an 18V input *and* a 220nF decoupling capacitor
on the input *and* another 100nF on the output *and* a load of let's say
1k/1W on the output *and* have connected your 7809 correctly *and* measuring
only 2V on the output *then* either your voltmeter or your 7809 is gone. An
78xx regulator that becomes hot without significant load it is defective
anyway.

petrus bitbyter


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.771 / Virus Database: 518 - Release Date: 28-9-2004
 
On Thu, 07 Oct 2004 13:43:40 -0700, Peter Bennett
<peterbb@nowhere.invalid> wrote:

On Thu, 07 Oct 2004 10:10:46 -0500, John Fields
jfields@austininstruments.com> wrote:


Dunno, but to consolidate some other replies, try this:

_____
| O |
|_____|
| |
FRONT VIEW OF 7809 -->| |
|_____|
| | |
IN-->| | |<--OUT
| | |
+18V>-----+-------+-------+----+ | +--+------+--->+9OUT
| | | | | |
[820R] |+ | | | |
| [1000ľF] [0.1ľF] | [0.1ľF] [1K]
[LED] | | | | |
|K | | | | |
GND>------+-------+-------+------+----+------+--->GND

Solder the capacitors into the circuit as close to the 7809 as
possible.

The OP said he couldn't tell which side was front.

The front is the side the lettering is on, and the metal tab is flush
with the back of the plastic part of the package.
Click to expand...
---
If you look at the rear of the TO-220 package you won't see the
dividing line between the plastic part of the package and the tab.

However, if you look at the front of the package you will, and I've
shown the dividing line, above. With that as a reference, the OP
should be able to hook it up as shown.

--
John Fields
 
"anonymous" <anonymous@catfarm.com> wrote in message
news:myb9d.349134$Fg5.88185@attbi_s53...
Ive tried 2 different 7809s now with the same result. Why am I only seeing
2V from gnd to Vout?
Click to expand...
Are you certain that you have a 7809 regulator ? Could it be that you have
a
component with a date code from February1978? (9th week of 1978)
 
"Peter Bennett" <peterbb@nowhere.invalid> schreef in bericht
news:0iabm0lhe4i9ceq8grhtb16vm5usikt540@4ax.com...
On Thu, 07 Oct 2004 10:10:46 -0500, John Fields
jfields@austininstruments.com> wrote:


Dunno, but to consolidate some other replies, try this:

_____
| O |
|_____|
| |
FRONT VIEW OF 7809 -->| |
|_____|
| | |
IN-->| | |<--OUT
| | |
+18V>-----+-------+-------+----+ | +--+------+--->+9OUT
| | | | | |
[820R] |+ | | | |
| [1000ľF] [0.1ľF] | [0.1ľF] [1K]
[LED] | | | | |
|K | | | | |
GND>------+-------+-------+------+----+------+--->GND

Solder the capacitors into the circuit as close to the 7809 as
possible.

The OP said he couldn't tell which side was front.
Click to expand...

That's one of the reasons he needed a datasheet.

petrus bitbyter


The front is the side the lettering is on, and the metal tab is flush
with the back of the plastic part of the package.


--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs:
http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq
Click to expand...



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.771 / Virus Database: 518 - Release Date: 28-9-2004
 
anonymous wrote:
I was putting together some bits for a power supply. Ive been away from
electronics for too long and am trying to get back in the swing.

At this point here is what I have:

+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)----- (nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There is no
load on it. Where is my mistake?
Click to expand...
First, go back to the data sheet and make sure you have the pins
correctly connected.
http://www.national.com/ds/LM/LM340.pdf

The 7805 is not guaranteed to be stable unless there is a small
capacitor between input and ground, and very close to the regulator.
At least .22 uf ceramic or low inductance film is recommended. A .1
uf cap output to ground is also recommended, though they claim it is
stable without it. The output voltage regulation is only specified
for load current greater than 5 milliamps, so you might connect a 1k
resistor output to ground to provide this minimum load, till you have
the design verified and ready ot connect to some other load.
--
John Popelish
 
Ive tried 2 different 7809s now with the same result. Why am I only seeing
2V from gnd to Vout?

Ill add the extra caps and put a small load on it and see what happens.

Okies. I tried flipping the vr as I can't really tell from the drawings
which is the "front". It didn't change the heating problem and Im only
getting 2V when measured from Vout to gnd. Flipping it gives the same
result
either way.


The 3 terminal regulators are a hardy bunch but they are NOT
indestructible!
Spend some time studying the package and its pin layout. Take note of
John's
instructions regarding the caps and note that you are loosing 9 volts
across
the
regulator IF it were to work correctly. That will generate lots of heat
and
will
require a heat sink of sufficient size to cool the part. It is possible
that your
part went into thermal shutdown mode. Try applying not less than 11 volts
to
the input of the regulator.
Click to expand...
 
On Wed, 06 Oct 2004 23:31:34 GMT, "anonymous" <anonymous@catfarm.com>
wrote:

I was putting together some bits for a power supply. Ive been away from
electronics for too long and am trying to get back in the swing.

At this point here is what I have:


+18V---770 ohm resistor --- led -- ground
|
----------4700 uF electrolytic ----- ground
|
---------- (Vin)7809 voltage regulator (Vout)----- (nothing)
|
-------ground

when powered up the led lights but the vr gets v hot v quickly. There is no
load on it. Where is my mistake?
Click to expand...
---
Dunno, but to consolidate some other replies, try this:

_____
| O |
|_____|
| |
FRONT VIEW OF 7809 -->| |
|_____|
| | |
IN-->| | |<--OUT
| | |
+18V>-----+-------+-------+----+ | +--+------+--->+9OUT
| | | | | |
[820R] |+ | | | |
| [1000ľF] [0.1ľF] | [0.1ľF] [1K]
[LED] | | | | |
|K | | | | |
GND>------+-------+-------+------+----+------+--->GND

Solder the capacitors into the circuit as close to the 7809 as
possible.


--
John Fields
 
On Thu, 07 Oct 2004 10:10:46 -0500, John Fields
<jfields@austininstruments.com> wrote:


Dunno, but to consolidate some other replies, try this:

_____
| O |
|_____|
| |
FRONT VIEW OF 7809 -->| |
|_____|
| | |
IN-->| | |<--OUT
| | |
+18V>-----+-------+-------+----+ | +--+------+--->+9OUT
| | | | | |
[820R] |+ | | | |
| [1000ľF] [0.1ľF] | [0.1ľF] [1K]
[LED] | | | | |
|K | | | | |
GND>------+-------+-------+------+----+------+--->GND

Solder the capacitors into the circuit as close to the 7809 as
possible.
Click to expand...
The OP said he couldn't tell which side was front.

The front is the side the lettering is on, and the metal tab is flush
with the back of the plastic part of the package.











--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top