4N35: I burnt it up, I think...

Well, Im not stupid, but I sure feel like it right now.

Using 5vdc (source is from 7805), I apply +5 through a 1k resistor and then to pin 1, and pin 2 is GND.

The opto got hot, and didnt work. Hot enough you cant touch it. I took the power off, re-examined my schematic, my connections and the solder joints. Took out the 4N35, and replaced it, I figured I burnt it up. The second one had a short life too.

For the love of money, using a 4N35 cant be rocket science!

My target application is Pic(axe) chips where a leg will go LL +5, I want to use the opto to do simple low voltage, low current switching.

Thanks for any help- I only have 18 left and would like to get something working before I deplete my stock! HA HA!

Andrew

RogerTango said:

Well, Im not stupid, but I sure feel like it right now.

Using 5vdc (source is from 7805), I apply +5 through a 1k resistor and then to pin 1, and pin 2 is GND.

The opto got hot, and didnt work. Hot enough you cant touch it. I took the power off, re-examined my schematic, my connections and the solder joints. Took out the 4N35, and replaced it, I figured I burnt it up. The second one had a short life too.

For the love of money, using a 4N35 cant be rocket science!

My target application is Pic(axe) chips where a leg will go LL +5, I want to use the opto to do simple low voltage, low current switching.


Thanks for any help- I only have 18 left and would like to get something working before I deplete my stock! HA HA!

Andrew

Click to expand...

Well the input to the isolator doesn't sound wrong (data sheet even shows running at 10ma Vs your 5ma, 1000 ohms) Perhaps the problem is on the output side of the isolator? Can you post a pic of the circuit?

PS: I've got several Picaxe chips and modules around here, love them. However Arduino is my current favorite if you ever want to dip your toes into C programming, it's not as scary as it might seem....

You ask, so I post, however it is as simple as I described.

**broken link removed**


**broken link removed**


Its been over 20 years since I worked with optos so I am learning from scratch again.

Thanks for the help-
Andrew

Let me ask this, I am reading other post and a bit confused, nevermind the headache I got trying to understand the (or any) datasheet:

How much voltage is supposed to be applied between pin 1 and 2?

With 2x 470k ohm resisters in series, my 5v dropped to 3.5v. But that took two 470k's to do it! I need to brush back up on ohm's & Kerchef's laws.

Andrew

I think I am seeing 1.5v max LED voltage from the datasheet. Am I right?

Andrew

RogerTango said:

Let me ask this, I am reading other post and a bit confused, nevermind the headache I got trying to understand the (or any) datasheet:

With 2x 470k ohm resisters in series, my 5v dropped to 3.5v. But that took two 470k's to do it! I need to brush back up on ohm's & Kerchef's laws.

Andrew

Click to expand...

"How much voltage is supposed to be applied between pin 1 and 2?"

You don't provide a fixed voltage, you supply a fixed current, just like if you were powering a LED which is what a optoisolator uses inside for it's emitter. Data sheet shows 10ma recommended, so 5vdc source minus 1.18 internal opto diode drop = 3.82 V divided by .01 amps = 382 ohm resistor. 470 ohms should work fine. Make sure your +5vdc indeed measures +5.

Can't be certain, but take another look at the solder side of Pin 1 .... is there possibly a small solder trace between Pin 1 and the ground pin? ... Difficult to tell for sure from the photo ... you might clean up all the solder surrounding the pins, and examine with a magnifier .... just to be sure.

Lefty: Well, as you can anticipate by my sig line, I was confused, now Im more confused! HA HA! According to what you are saying, I am thinking you need to know the amount of current (amps) that is flowing? The wallwart is 12v 1a, I assume there is still the 1a current after the 7805's 5v output. Or am I not seeing the forest for the trees?

Ill drop a new opto on and apply power with a 470ohm and see what happens. I wish I understood more about what I am doing, that is the most frustrating part of my projects!

88: The traces are good, I looked at it under a 10x loupe. That was one of the things I was thinking about before I posted, a dead short. Thanks for posting.

Thank you all very much for your assistance,
Andrew

There's not much you can do wrong with this indeed...
You got the right voltage: 5V after the 7805?
You didn't solder for half a minute each solder point? Don't think so, because they look okay...

Okayyyy- Maybe I didnt put the 1k in series on the first two optos I sent to Davey Jone's Locker, but Its working this time. New opto on the board and a 1k resistor in series, opto works fine as measured with ohm meter across pins 4 and 5 with power applied and removed. So now I need to make a new protoboard with a 1k on it.

I am building several different prototype boards all based around the family of Picaxe chips, I have an 08M and 14M already on PCB, a 5v regulated board, a gang of 4 LEDs with 330ohm board (to light LED directly from leg of Picaxe), a MOSFET board, and this optoisolator board will be finished soon.

I hope yet to build a temp sensor board and a switch board (analog feedback to IC). There are other proto boards I want to build also, as needs dictate.

With the family of proto boards, I can quickly wire up projects for development, once everything is working (I hope) lay it out on PCB and yield a finished product.

Thanks!
Andrew

"Maybe I didnt put the 1k in series on the first two optos I sent to Davey Jone's Locker"

That is most likely the case But don't despair, I always found I learned a lot more from my screw-ups then from my successes.

And don't even get me started about my starter wife

Lefty