Optocoupler puzzle

R

Randy Day

Guest
I dug an old 4N35 out of the junk box, and
wired it up two ways (below).

I put ~150us pulses on pin 2, and expected
to see something similar at the output. What
I get is a scope waveform that slowly ramps
to about 2v over the 150us, before ramping
back to rest in about 20us.

I tried changing the 1k to 500ohm, and the
10k to 1k, but it still showed a ramp.

What the heck am I seeing, and why?

+5v +5v
| |
.-. .-.
| |1k | |10k
| | | |
'-' '-'
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----+-- out
| |
--|3 4|-----|
| | |
'-------' gnd

+5v +5v
| |
.-. |
| |1k |
| | |
'-' |
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----|
| |
--|3 4|----+-- out
| | .-.
'-------' | |10k
| |
'-'
|gnd
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)
 
Randy Day wrote:
I dug an old 4N35 out of the junk box, and
wired it up two ways (below).

I put ~150us pulses on pin 2, and expected
to see something similar at the output. What
I get is a scope waveform that slowly ramps
to about 2v over the 150us, before ramping
back to rest in about 20us.

I tried changing the 1k to 500ohm, and the
10k to 1k, but it still showed a ramp.

What the heck am I seeing, and why?

+5v +5v
| |
.-. .-.
| |1k | |10k
| | | |
'-' '-'
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----+-- out
| |
--|3 4|-----|
| | |
'-------' gnd

+5v +5v
| |
.-. |
| |1k |
| | |
'-' |
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----|
| |
--|3 4|----+-- out
| | .-.
'-------' | |10k
| |
'-'
|gnd
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)
Click to expand...
Try this:
Ground pins 2 and 4. Input to pin 1 through your resistor,
and output from pin 5, with 100 ohms from pin 5 to +5V.

Ed
 
In article <MPG.23854834f1e92fcc98968c@shawnews.ss.shawcable.net>,
randy.day@shaw.cax says...
I dug an old 4N35 out of the junk box, and
wired it up two ways (below).

I put ~150us pulses on pin 2, and expected
to see something similar at the output. What
I get is a scope waveform that slowly ramps
to about 2v over the 150us, before ramping
back to rest in about 20us.

I tried changing the 1k to 500ohm, and the
10k to 1k, but it still showed a ramp.

Change the 10K to a 47K (or a 100K) and see what happens.
Click to expand...

What the heck am I seeing, and why?

+5v +5v
| |
.-. .-.
| |1k | |10k
| | | |
'-' '-'
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----+-- out
| |
--|3 4|-----|
| | |
'-------' gnd

+5v +5v
| |
.-. |
| |1k |
| | |
'-' |
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----|
| |
--|3 4|----+-- out
| | .-.
'-------' | |10k
| |
'-'
|gnd
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)
Click to expand...
 
In article <DnPSk.1094$mi4.721@nwrddc02.gnilink.net>,
ehsjr@NOSPAMverizon.net says...
Randy Day wrote:
I dug an old 4N35 out of the junk box, and
wired it up two ways (below).

I put ~150us pulses on pin 2, and expected
to see something similar at the output. What
I get is a scope waveform that slowly ramps
to about 2v over the 150us, before ramping
back to rest in about 20us.

I tried changing the 1k to 500ohm, and the
10k to 1k, but it still showed a ramp.

What the heck am I seeing, and why?

+5v +5v
| |
.-. .-.
| |1k | |10k
| | | |
'-' '-'
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----+-- out
| |
--|3 4|-----|
| | |
'-------' gnd

+5v +5v
| |
.-. |
| |1k |
| | |
'-' |
| .-------. |
|--|1 6|-- |
| | |
in --|2 5|----|
| |
--|3 4|----+-- out
| | .-.
'-------' | |10k
| |
'-'
|gnd
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)

Try this:
Ground pins 2 and 4. Input to pin 1 through your resistor,
and output from pin 5, with 100 ohms from pin 5 to +5V.
Click to expand...
Tried your suggestion, and it helped a bit.
What really made a difference was lowering
the 1k to 200 ohms.

Remind me not to use the 4N35 for any
low-power projects. ;)

Thanks, Ed.
 
On 2008-11-13, Randy Day <randy.day@shaw.cax> wrote:

Tried your suggestion, and it helped a bit.
What really made a difference was lowering
the 1k to 200 ohms.
Click to expand...
yeah I can see (with 20/20 hindsight) that it would.
did you think to check the datasheet?

Remind me not to use the 4N35 for any
low-power projects. ;)
Click to expand...
that's what the datasheet is for
 
On Wed, 12 Nov 2008 20:08:55 -0600, Randy Day <randy.day@shaw.cax> wrote:

:I dug an old 4N35 out of the junk box, and
:wired it up two ways (below).
:
:I put ~150us pulses on pin 2, and expected
:to see something similar at the output. What
:I get is a scope waveform that slowly ramps
:to about 2v over the 150us, before ramping
:back to rest in about 20us.
:
:I tried changing the 1k to 500ohm, and the
:10k to 1k, but it still showed a ramp.
:
:What the heck am I seeing, and why?
:
: +5v +5v
: | |
: .-. .-.
: | |1k | |10k
: | | | |
: '-' '-'
: | .-------. |
: |--|1 6|-- |
: | | |
: in --|2 5|----+-- out
: | |
: --|3 4|-----|
: | | |
: '-------' gnd
:
: +5v +5v
: | |
: .-. |
: | |1k |
: | | |
: '-' |
: | .-------. |
: |--|1 6|-- |
: | | |
: in --|2 5|----|
: | |
: --|3 4|----+-- out
: | | .-.
: '-------' | |10k
: | |
: '-'
: |gnd
:(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
:chat.de)


First, try reading the data sheet.
http://www.datasheetcatalog.org/datasheet2/1/03tgz200g5x4946jka7isojyj5wy.pdf
 
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