Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Optocouplers in series

Status
Not open for further replies.

fernandomierhicks

Newbie level 4
Joined
Jun 13, 2011
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,336
Hi:

I am working on a high voltage application where current optocouplers do not meet the desired isolation voltage.

If I use a pair of optocouplers, the output of one connected to the input of the other (taking into account, minimum current requirements of input stage, and using a floating supply source for the different circuits at different voltages), would this effectively double the isolation voltage?

Thanks

Fernando
 

kak111

Advanced Member level 4
Joined
Mar 30, 2011
Messages
1,366
Helped
933
Reputation
1,868
Reaction score
907
Trophy points
1,413
Location
Finland
Activity points
10,942
If we examine DC case only high voltage divides 50&50
but with higher frequencies and voltage spikes with high dV/dt
there is 3 meaningful capacitances. ( Inductive parts too, not drawn )
Consisted of wire to wire and wire to groud effects.
If values C1 and C2 are not equal , voltages over isolators are not equal too.
then there is supply to ground capacitance C3.
I drew only capacitances , but inductive effect between wires and parts
make same thing to happen.

View attachment DoubleOptoCoupling.pdf


I suggest to use some HV-isolator type
or optocable between devices

I remember that cheap 4N25 has 7.5kV versions.

and then
for ex. OPI1268S
• 20KV Isolation
• 30 KV/uS dv/dt immunity
• 2 Mbit/s transfer rate

http://www.optekinc.com/datasheets/OPI1268S.pdf

KAK
 

fernandomierhicks

Newbie level 4
Joined
Jun 13, 2011
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,336
Sorry, I think I used the term optocoupler wrong, what I want to do is measure small currents at high voltages. So I am using a isolation amplifier, that works on the same principle as the optocoupler.

If thereare no high voltage spikes, and it will be constant DC, would there be any problem using the optocouplers in series?
 

kak111

Advanced Member level 4
Joined
Mar 30, 2011
Messages
1,366
Helped
933
Reputation
1,868
Reaction score
907
Trophy points
1,413
Location
Finland
Activity points
10,942
Need some info for system, for clarifying it for myself.

What is the highest voltage in measured circuit. (DC or AC frequency = ??? )
What is the max. / min. measured current value.
What is the needed accuracy.

I presume measuring principle is shunt resistor.



Regards KAK
 

fernandomierhicks

Newbie level 4
Joined
Jun 13, 2011
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,336
its 2500 Volts Dc currents in the micro and nano amperes range, accuracy, as best as possible, possibly in the microamperes scale. I found a isolation amplifier capable of isolating 2500V (AD210BN) I will give it a try and post the results...
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top