I am trying to bring up a circuit using a quad op-amp - LM324

I can't fathom it.

I have enough supply rails.

I am within common mode specs - about -3v from supply rails.

But two op amps at least are simply NOT WORKING.

I have 0.4v more on the +Ve input to the -ve, and yet the output is
about at +1,5v from negative supply..

I have voltage going to the chip. Pin 4, with pin going anti clockwise
viewed from the top, from the notch and the dot...pin 11 to negative..

I've replaced the chip. Same crap.

Come up with whatever stupidity I must have done, because for the life
of me I can't see it..

"The Natural Philosopher" wrote in message
...
I am trying to bring up a circuit using a quad op-amp - LM324

I can't fathom it.

I have enough supply rails.

I am within common mode specs - about -3v from supply rails.

But two op amps at least are simply NOT WORKING.

I have 0.4v more on the +Ve input to the -ve, and yet the output is about
at +1,5v from negative supply..

I have voltage going to the chip. Pin 4, with pin going anti clockwise
viewed from the top, from the notch and the dot...pin 11 to negative..

I've replaced the chip. Same crap.

Come up with whatever stupidity I must have done, because for the life of
me I can't see it..
I've no info on the LN324, however have you tied the input to zero via
,,,say 10K R and have you got NFB say 100K R (gain of 10) or are you using
it in open loop??
Don

Donwill wrote:
"The Natural Philosopher" wrote in message
...
I am trying to bring up a circuit using a quad op-amp - LM324

I can't fathom it.

I have enough supply rails.

I am within common mode specs - about -3v from supply rails.

But two op amps at least are simply NOT WORKING.

I have 0.4v more on the +Ve input to the -ve, and yet the output is about
at +1,5v from negative supply..

I have voltage going to the chip. Pin 4, with pin going anti clockwise
viewed from the top, from the notch and the dot...pin 11 to negative..

I've replaced the chip. Same crap.

Come up with whatever stupidity I must have done, because for the life of
me I can't see it..
I've no info on the LN324, however have you tied the input to zero via
,,,say 10K R and have you got NFB say 100K R (gain of 10) or are you using
it in open loop??
Don


Oh, its all properly in a circuit with various gains.

The point is that the chip itself is showing nonsense on the pins. IF
the +ve input is higher than the -ve it should drive towards the
positive rail. It isn't. Nothing is holding the output down..there's a
2k2 resistor to it and thats it.

All I can think of is I have it in the wrong way round, but I've
quadruple checked the data sheet, and definitely pin 4, the positive
rail, is 4 anti-clockwise from the notch, looking on top.

I have 0.4v more on the +Ve input to the -ve, and yet the output is about
at +1,5v from negative supply..

Check the pin out. The LM324 is weird and has the +,- and out in strange
places.

The + inputs are next to the power supply pins. Next out are the - inputs.
In the corners are the outputs.

Christian.

The Natural Philosopher wrote:

Oh, its all properly in a circuit with various gains.

Full circuit on Web please, so we can see exactly what you're doing.
Circuit construction? - rat's nest lash-up, Veroboard or similar, or a
pukka PCB? Does the actual circuit you've built agree with the circuit
diagram you've drawn? Shorts and opens on PCB tracks are not unknown.
Any unused devices in the package? - if so, how wired?

The point is that the chip itself is showing nonsense on the pins. IF
the +ve input is higher than the -ve it should drive towards the
positive rail. It isn't. Nothing is holding the output down..there's a
2k2 resistor to it and thats it.

'324s are easy, and usually trouble-free. Is anything oscillating? -
have you had a 'scope on it? What's the supply voltage between the
rails? Is the supply current being drawn normal (around 700 uA per
amplifier plus o/p load current), or excessive?

All I can think of is I have it in the wrong way round, but I've
quadruple checked the data sheet, and definitely pin 4, the positive
rail, is 4 anti-clockwise from the notch, looking on top.

Yep, that's right.

--
Andy

The + inputs are next to the power supply pins. Next out are the - inputs.
In the corners are the outputs.

Note that this is different to most packages, where the -,+ and out are in a
fixed order, with the amps "pointing" in one direction. This would easily
explain why two appear to work and two do not.

Christian.

The Natural Philosopher wrote:
I am trying to bring up a circuit using a quad op-amp - LM324

I can't fathom it.

I have enough supply rails.

I am within common mode specs - about -3v from supply rails.

But two op amps at least are simply NOT WORKING.

I have 0.4v more on the +Ve input to the -ve, and yet the output is
about at +1,5v from negative supply..

I have voltage going to the chip. Pin 4, with pin going anti clockwise
viewed from the top, from the notch and the dot...pin 11 to negative..

I've replaced the chip. Same crap.

Come up with whatever stupidity I must have done, because for the life
of me I can't see it..

When you have eliminated the impossible...

Even if both chips are now faulty, probability suggests that they
died in the same way. Pull the chip and check that the circuit board
corresponds to the diagram, that the output resistor is K and not ohms,
etc.

It only needs a single rail. Attach the bare chip to nine or so volts
with all outputs taken to inverting inputs, non-inverting to half-rail.
If the outputs aren't within a few mV of the NI inputs then the chip
is NBG, if it is OK then there is definitely a map-is-not-the-territory
type problem, and if both chips are dead this is even more likely.

I am assuming you're using a scope and the beast isn't oscillating?

The message
from The Natural Philosopher contains these words:

But two op amps at least are simply NOT WORKING.

Are they oscillating like mad? That can sometimes happen and without a
scope you'd not spot it.

--
Skipweasel
Pay no attention to that man behind the curtain.

"The Natural Philosopher" wrote in message
...
I am trying to bring up a circuit using a quad op-amp - LM324

I can't fathom it.

I have enough supply rails.

I am within common mode specs - about -3v from supply rails.

But two op amps at least are simply NOT WORKING.

I have 0.4v more on the +Ve input to the -ve, and yet the output is about
at +1,5v from negative supply..

I have voltage going to the chip. Pin 4, with pin going anti clockwise
viewed from the top, from the notch and the dot...pin 11 to negative..

I've replaced the chip. Same crap.

Come up with whatever stupidity I must have done, because for the life of
me I can't see it..

Have a read of
http://focus.ti.com/docs/apps/catalo...tName=slod006b

are you useing the opamps as opamps or as comparators? Some opamps don't
like large differntial input voltages and suffer phase reversal..

Circut on the web please...

"The Natural Philosopher" wrote in message
...
I am trying to bring up a circuit using a quad op-amp - LM324

I can't fathom it.

I have enough supply rails.

I am within common mode specs - about -3v from supply rails.

But two op amps at least are simply NOT WORKING.

I have 0.4v more on the +Ve input to the -ve, and yet the output is about
at +1,5v from negative supply..

I have voltage going to the chip. Pin 4, with pin going anti clockwise
viewed from the top, from the notch and the dot...pin 11 to negative..

I've replaced the chip. Same crap.

Come up with whatever stupidity I must have done, because for the life of
me I can't see it..

As others have said, check for oscillation - unloaded op-amps can pick up
crap and fly into oscillation, terminate the outputs of the unused op-amps.

Andy.

Andy Wade wrote:
The Natural Philosopher wrote:

Oh, its all properly in a circuit with various gains.

Full circuit on Web please, so we can see exactly what you're doing.
Circuit construction? - rat's nest lash-up, Veroboard or similar, or a
pukka PCB? Does the actual circuit you've built agree with the circuit
diagram you've drawn? Shorts and opens on PCB tracks are not unknown.
Any unused devices in the package? - if so, how wired?

The point is that the chip itself is showing nonsense on the pins. IF
the +ve input is higher than the -ve it should drive towards the
positive rail. It isn't. Nothing is holding the output down..there's a
2k2 resistor to it and thats it.

'324s are easy, and usually trouble-free. Is anything oscillating? -
have you had a 'scope on it? What's the supply voltage between the
rails? Is the supply current being drawn normal (around 700 uA per
amplifier plus o/p load current), or excessive?

It was oscillating...bugger. I only WANT DC response..and I gave away my
scope years ago,.

Will have to pop over to a mates next week.


All I can think of is I have it in the wrong way round, but I've
quadruple checked the data sheet, and definitely pin 4, the positive
rail, is 4 anti-clockwise from the notch, looking on top.

Yep, that's right.

Yep. It was hooting away madly. Its quasi stable now to the point where
its beginning to do what it should, but readings are affected by leads
moving around, which suggests its still unstable.

Guy King wrote:
The message
from The Natural Philosopher contains these words:

But two op amps at least are simply NOT WORKING.

Are they oscillating like mad? That can sometimes happen and without a
scope you'd not spot it.

Yup.

It was.

Circuit severely modified now, and sort of half works. Needs a scope now
tho.

On Fri, 10 Nov 2006 20:09:18 +0000, The Natural Philosopher
wrote:


'324s are easy, and usually trouble-free. Is anything oscillating? -
have you had a 'scope on it? What's the supply voltage between the
rails? Is the supply current being drawn normal (around 700 uA per
amplifier plus o/p load current), or excessive?

It was oscillating...bugger. I only WANT DC response..and I gave away my
scope years ago,.


Try an 0.01 uf cap down to ground from the amp outputs. It's quick and
dirty.

If it works try a smaller cap ( 'till it doesn't :-) )

[...]

Yep. It was hooting away madly. Its quasi stable now to the point where
its beginning to do what it should, but readings are affected by leads
moving around, which suggests its still unstable.

DG

In article ,
The Natural Philosopher wrote:
Are they oscillating like mad? That can sometimes happen and without a
scope you'd not spot it.

Yup.

It was.

Circuit severely modified now, and sort of half works.

Often happens with this sort of op-amp. Stick a 510 ohm resistor in the
supply with a 47 µF between + connection and ground - both as close to the
op-amp as possible.

Needs a scope now tho.

Essential bit of kit. Dunno what I'll do when my 'ol Tek 465B bites the
dirt. It's one piece of test gear that doesn't seem to have come down in
price for decent stuff.

--
*Laugh alone and the world thinks you're an idiot.

Dave Plowman London SW
To e-mail, change noise into sound.

Derek Geldard wrote:
On Fri, 10 Nov 2006 20:09:18 +0000, The Natural Philosopher
wrote:

'324s are easy, and usually trouble-free. Is anything oscillating? -
have you had a 'scope on it? What's the supply voltage between the
rails? Is the supply current being drawn normal (around 700 uA per
amplifier plus o/p load current), or excessive?

It was oscillating...bugger. I only WANT DC response..and I gave away my
scope years ago,.


Try an 0.01 uf cap down to ground from the amp outputs. It's quick and
dirty.

If it works try a smaller cap ( 'till it doesn't :-) )

This is not recommended. Introducing an RC delay in the closed loop is
how oscillators are designed. Also loading opamps with C is a famous
cause of oscillation. It might work in this case, but it wont get you a
stable circuit. It also increases supply i draw.

324s only do around 6kHz rail to rail swing, but they go much higher
with smaller excursions.

Check out National semiconducors application notes series, they have
tons of great stuff on opamps, and its all online free.

324s are known for trouble, as theyre minimum cost corner-cutting
opamps, prone to crossover distortion, interaction between channels,
and latchup if you go near the rails. But oscillation is not a
particular problem with them, theyre just too slow to do a lot with rf.
Any rf trouble will at least be low amplitude.

Nearly forgot, with their slow speed, a free PC software scope should
be adequte for working with them.


NT

In article ,
The Natural Philosopher wrote:

Yep. It was hooting away madly. Its quasi stable now to the point
where its beginning to do what it should, but readings are
affected by leads moving around, which suggests its still
unstable.

ASCII art below. View with a fixed font such
as courier new.
Cf
+----||----+ Vout/Vin = 1 + Rf/Rs.
| Rf |
+---/\/\---+
| __ |
+--|- \|+V | Rout
| |324---+---/\/\-----+--Vout
Vin--------|+_/| 20-40ohms |
| | |
\ | ===Cstray
Rs/ | |
\ | |
| | |
0v------+------+----------------+--0v

Always have a capacitor Cf across the feedback
resistor to roll off the frequency response, even
just 100pF or so.

Most opamps are sensitive to a capacitive load,
even the Cstray of output cabling. So isolate
the output pin from the Cstray with a low-value
resistor, Rout, close to the output pin.

Have a power supply decoupling capacitor near
the package of course.

+---------+
| __ |
+--|- \ |
|324--+
+--|+_/
|
0v------+--

Wire any unused sections as above so that they
are safe and don't flap about.

--
Tony Williams.

Derek Geldard wrote:
On Fri, 10 Nov 2006 20:09:18 +0000, The Natural Philosopher
wrote:


'324s are easy, and usually trouble-free. Is anything oscillating? -
have you had a 'scope on it? What's the supply voltage between the
rails? Is the supply current being drawn normal (around 700 uA per
amplifier plus o/p load current), or excessive?
It was oscillating...bugger. I only WANT DC response..and I gave away my
scope years ago,.


Try an 0.01 uf cap down to ground from the amp outputs. It's quick and
dirty.


Ahah. Thats an option I hadn't tried.Ta m8.


If it works try a smaller cap ( 'till it doesn't :-) )

[...]

Yep. It was hooting away madly. Its quasi stable now to the point where
its beginning to do what it should, but readings are affected by leads
moving around, which suggests its still unstable.

DG

In message , The Natural
Philosopher writes
Guy King wrote:
The message
from The Natural Philosopher contains these words:

But two op amps at least are simply NOT WORKING.
Are they oscillating like mad? That can sometimes happen and without

scope you'd not spot it.

Yup.

It was.

Circuit severely modified now, and sort of half works. Needs a scope
now tho.
Where do you live? Could maybe lend one to you?
--
Clint Sharp

Clint Sharp wrote:
In message , The Natural
Philosopher writes
Guy King wrote:
The message
from The Natural Philosopher contains these words:

But two op amps at least are simply NOT WORKING.
Are they oscillating like mad? That can sometimes happen and without
scope you'd not spot it.

Yup.

It was.

Circuit severely modified now, and sort of half works. Needs a scope
now tho.
Where do you live? Could maybe lend one to you?
Near Newmarket, Suffolk.

In message , The Natural
Philosopher writes
Circuit severely modified now, and sort of half works. Needs a scope
now tho.
Where do you live? Could maybe lend one to you?
Near Newmarket, Suffolk.
Ah, bit too far then. Manchester.
--
Clint Sharp