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LM324 Voltage Follower problem

D

Devendra

Jan 1, 1970
0
Hello All,

I am having the following circuit...

paste it in notepad to view correctly..

IC=LM324AD +24VDC
|
20VDC 1.22V |\|
o----71.1K--+-----|+\
| | >-+---o Vout (Measures 0.546VDC)
| +-|-/ |
| | |/| |
| | 0V |
30.1K +------+
|
|
|
0V o----------+--------------o

It is a simple voltage follower. But it is not giving the same voltage
at the output.
I am not able to figure out why? May be my IC has gone bad? There are
no gain adjustment resistors, then from where this reduction in voltage
is coming..

Pls help!!
 
B

Ban

Jan 1, 1970
0
Devendra said:
Hello All,

I am having the following circuit...

paste it in notepad to view correctly..

IC=LM324AD +24VDC
|
20VDC 1.22V |\|
o----71.1K--+-----|+\
| | >-+---o Vout (Measures 0.546VDC)
| +-|-/ |
| | |/| |
| | 0V |
30.1K +------+
|
|
|
0V o----------+--------------o

It is a simple voltage follower. But it is not giving the same voltage
at the output.
I am not able to figure out why? May be my IC has gone bad? There are
no gain adjustment resistors, then from where this reduction in
voltage is coming..

Pls help!!

Something is wrong with your connections. There should be also 5.93V on the
non-inverting input with those resistors. Probably you have mixed up the
pins of the IC.
 
E

Eeyore

Jan 1, 1970
0
Devendra said:
Hello All,

I am having the following circuit...


It is a simple voltage follower. But it is not giving the same voltage
at the output.
I am not able to figure out why? May be my IC has gone bad? There are
no gain adjustment resistors, then from where this reduction in voltage
is coming..

The voltage on the non-inverting input does indeed suggest the IC is defective.

Graham
 
C

Chris

Jan 1, 1970
0
Devendra said:
Hello All,

I am having the following circuit...

paste it in notepad to view correctly..

IC=LM324AD +24VDC
|
20VDC 1.22V |\|
o----71.1K--+-----|+\
| | >-+---o Vout (Measures 0.546VDC)
| +-|-/ |
| | |/| |
| | 0V |
30.1K +------+
|
|
|
0V o----------+--------------o

It is a simple voltage follower. But it is not giving the same voltage
at the output.
I am not able to figure out why? May be my IC has gone bad? There are
no gain adjustment resistors, then from where this reduction in voltage
is coming..

Pls help!!

Seconding Graham's motion -- the LM324 is definitely bad.

If your 20V input is coming from another source, you might want to
ensure that there is no voltage input while the LM324 is unpowered.
That's one potential cause of this failure. A simple way to do this is
to place a 1N914 diode from the input to your LM324 power supply.

If there's a possibility that there are transients on the input
voltage, a small (100pF) cap from the junction to GND might also be of
help. The LM324 is slow enough that you won't lose much this way. It
might help to wire the diode and pF cap directly to the power pins.

And as always, if you're tracking all the way down to GND, make sure to
place a load resistor (10K should do) from the op amp output to GND.

Good luck
Chris
 
C

Chris

Jan 1, 1970
0
Ban said:
Something is wrong with your connections. There should be also 5.93V on the
non-inverting input with those resistors. Probably you have mixed up the
pins of the IC.

Yup. Especially power (V+ is pin *4*, GND is pin *11*).

Forgot about that, Most newbies hook up quad op amp power
bass-ackwards and hook up an LM317 like a 78XX at least once. But the
aroma of the magic smoke teaches well.

Cheers
Chris
 
D

Devendra

Jan 1, 1970
0
I have connected +24V to pin no. 4 and Ground to Pin no.11.
I am giving this Vcc +24V, after passing through a diode 1N5408. I have
connected this to protect my circuit from reverse supply connection.

I also have connected a 10V zener across my input voltage, before
giving to the voltage divider.

With the 71K and 30.1K resistor divider, I am getting 1.2V across 30.1K
resistor, even if the voltage applied at 71K resistor is 7.5V (Which
should be almost 2.2V, by voltage divider rule.)

I will try with connecting load at the output of op-amp.

I will let you know the results....

Thanks!
 
P

Phil Allison

Jan 1, 1970
0
"Devendra"<
I have connected +24V to pin no. 4 and Ground to Pin no.11.
I am giving this Vcc +24V, after passing through a diode 1N5408. I have
connected this to protect my circuit from reverse supply connection.

I also have connected a 10V zener across my input voltage, before
giving to the voltage divider.


** Is your input DC positive or negative with respect to 0V ?

The IC cannot accept negative voltage at the inputs without a negative
supply too.




........ Phil
 
E

ehsjr

Jan 1, 1970
0
Devendra said:
Hello All,

I am having the following circuit...

paste it in notepad to view correctly..

IC=LM324AD +24VDC
|
20VDC 1.22V |\|
o----71.1K--+-----|+\
| | >-+---o Vout (Measures 0.546VDC)
| +-|-/ |
| | |/| |
| | 0V |
30.1K +------+
|
|
|
0V o----------+--------------o

It is a simple voltage follower. But it is not giving the same voltage
at the output.
I am not able to figure out why? May be my IC has gone bad? There are
no gain adjustment resistors, then from where this reduction in voltage
is coming..

Pls help!!

Assuming the 20 V supply is separate from the 24V,
did you forget connect the two grounds (20v & 24V)
together?

Ed
 
D

Devendra

Jan 1, 1970
0
Thanks for all your suggestions....

I checked all these things and found my circuit ok.
I just replaced my Op-amp (On-semi) with a New one (Philips) LM324AD
and it started working fine!!

How can I suspect an IC going bad!?

Anyways, my problem got solved....

Thank you all...!
 
J

Jamie

Jan 1, 1970
0
Devendra said:
Thanks for all your suggestions....

I checked all these things and found my circuit ok.
I just replaced my Op-amp (On-semi) with a New one (Philips) LM324AD
and it started working fine!!

How can I suspect an IC going bad!?

Anyways, my problem got solved....

Thank you all...!
A few years ago, I found LM324 to be prone to failure. Must of
been a few bad batches out there. These days, things that I happen
to get in repair that still use this chip in newer packages, seem to
be more reliable now. The old DIP LM324 packages, I use to find
defective in many different products.
 
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