save my optocoupler 4N25

vinodquilon

Member

• Jun 9, 2010

• #1

Pls find the attachment of a self-explanatory telephone ring detection circuit.

The problem is that my 4N25 is not secure.
'After' four or five times of operation, it destroyed itself.
Then I replaced it with another, but same fate.

I think the protection circuit of 4N25 has no better immunity against high ring volt.

Any suggestions to rectify my problem ?

 

Attachments

• ring_detection.pdf

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bychon

New Member

• Jun 9, 2010

• #2

The limiting devices should keep the current through the opto LED down to 3 ma and the LED will only support 2 or 3 volts, so voltage should not be a problem. I suggest that a part of the limiting circuit has failed. For instance, if voltage is eating the opto, then diode D2 must have failed.

 

Boncuk

New Member

• Jun 10, 2010

• #3

Hi vinodquilon,

it is most unlikely the telephone ring signal will exceed 60V.

Here is 0-crossing unit connected to mains via a bridge rectifier and a current limiting resistor directly to the diode of the 4N25.

I haven't experienced a damage optocoupler till now.

Use an 18K/1W current limiting resistor to fit your needs for the ring signal. The resistor has to dissipate ~375mW.

Boncuk

 

Attachments

• 
  0-DETECT-SCH.gif

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I

indulis

New Member

• Jun 10, 2010

• #4

Telephone ringing circuits

 

bychon

New Member

• Jun 10, 2010

• #5

To sumarize Boncuk's post, ring voltages are commony over 100 volts.

 

Boncuk

New Member

• Jun 10, 2010

• #6

bychon said:

To sumarize Boncuk's post, ring voltages are commony over 100 volts.

Click to expand...

Oops, forgot to mention that 60V apply to the ring signal in Germany pretty precisely for remote impedance check

However "over 100 volts" could also be 1,000V - so the info is a bit vague.

The 4N25 works reliably from 5 to 40mA LED forward current with sufficient CTR.

One private hint: There is no reason to haste, causing two typos within one line.
(summarize, commonly)

Regards

Boncuk

 

bychon

New Member

• Jun 10, 2010

• #7

Atually, there were 3 mistakes. The post about ring voltages was by indulis, and thanks for the spell check. I haven't found another spell checker on this site.

 

M

MrAl

Well-Known Member

Most Helpful Member

• Jun 11, 2010

• #8

Hi,

This guy posted same question and schematic on another site and never came back.
I would suggest checking the wiring very carefully, then a base resistor of maybe 1 megohm from base to emitter.

 

vinodquilon

Member

• Jun 11, 2010

• #9

Sorry for late replay.

Replay...

Thanks for all.

I set-up the same circuit again on a separate bread board with all new components except 4N25.
The circuit was fine for the first few checks, again the problem arises. That is I cannot get +5V
at pin4. This seems to be the problem is not with opto.

CI tantalum, electrolytic is not avail.

I cannot measure AC voltage across R1 with ordinary multimeter as intermittently occurring ring volts. I don't have any oscilloscopes.

R1 10K 0.5W

Deliberately I avoided isolation transformer as it only for electrical protection.

 

vinodquilon

Member

• Jun 11, 2010

• #10

Hi Boncuk,

When I set-up 0-DETECT-SCH, I got constant VCC continuously at pin 4 when Ringing occurs. But I would like it to be of on-off pulses. ON pulse indicates the presence of Ring volt.

 

Last edited: Jun 11, 2010

vinodquilon

Member

• Jun 11, 2010

• #11

Hey bychon,
[The limiting devices should keep the current through the opto LED down to 3 ma and the LED will only support 2 or 3 volts, so voltage should not be a problem. I suggest that a part of the limiting circuit has failed. For instance, if voltage is eating the opto, then diode D2 must have failed. ]

How can I improve the current capability of D2 ?

 

bychon

New Member

• Jun 11, 2010

• #12

Replace it with a 1n4007 or an ECG125

But why increase the current ability of a diode that only has to survive .003 amps?

 

Last edited: Jun 11, 2010

vinodquilon

Member

• Jun 11, 2010

• #13

bychon said:

Replace it with a 1n4007 or an ECG125

But why increase the current ability of a diode that only has to survive .003 amps?

Click to expand...

But no improvements.

 

vinodquilon

Member

• Jun 11, 2010

• #14

I have checked opto using multimeter in diode mode and its LED section outputs
1257
for transistor section
6 to 5 outputs 715
6 to 4 outputs 726

I have checked zener also and outputs 850.

 

bychon

New Member

• Jun 11, 2010

• #15

Judging from post #10, "I get constant Vcc at pin 4 continuously when ringing occurs" and post #14, volts supported at 1 ma (missing all the decimal points) the circuit is working.

What is your next goal?

 

vinodquilon

Member

• Jun 11, 2010

• #16

bychon said:

Judging from post #10, "I get constant Vcc at pin 4 continuously when ringing occurs" and post #14, volts supported at 1 ma (missing all the decimal points) the circuit is working.

What is your next goal?

Click to expand...

I have checked opto by completely disconnecting from the main circuit.

 

C

colin55

Well-Known Member

• Jun 11, 2010

• #17

The way to test the circuit is this:
Connect everything up and leave the input to the optocoupler open.

With a 12v supply and 1k resistor plus 10 pot, reduce the resistance to the LED and see when the voltage on the emitter starts to rise. I would put a 100u in place of 1u to see this effect.

The problem is this: The optocoupler needs more current to illuminate the LED to turn the transistor on sufficiently to charge the 1u.

I always put the ring voltage through a bridge as you don't know the polarity of the phone line. Some phone lines actually change polarity!

I have done the same thing with an 8 pin PIC and a few components. It is much better to time the rings rather than count them. I would also join 5 6 7 outputs to get a more-reliable result.

 

Last edited: Jun 11, 2010

Boncuk

New Member

• Jun 12, 2010

• #18

vinodquilon said:

Hi Boncuk,

When I set-up 0-DETECT-SCH, I got constant VCC continuously at pin 4 when Ringing occurs. But I would like it to be of on-off pulses. ON pulse indicates the presence of Ring volt.

Click to expand...

Did you also use the Schmitt-Trigger as posted? I use it for extra short pulses to compensate mains frequency variations to fire a 40A triac timely.

Boncuk

 

vinodquilon

Member

• Jun 12, 2010

• #19

It was the problem with Telephone jack as I cannot measure ring volts at the time of ringing.
Now all problems cleared.

Thanks everyone for their patience support.

Now we can close this subject.

 

M

mneary

New Member

• Jun 13, 2010

• #20

CI tantalum, electrolytic is not avail.

Click to expand...

That is your problem. Assuming that you mean C1 instead of CI, it should not be tantalum or electrolytic. It should be a film capacitor rated at 150V or more.