hello,
i want to measure a voltage of 700 v max and feed it to the ADC of microcontroller so , i want to isolate the circuit with a linear optocoupler.
i want to use LIA120 but i can't understand how to design the circuit?
if any one help me to design that one or recommend another type of linear optocoupler which he had used before

thanks in advance

 

You might find the HCPL-7840 isolation amp is easier to use - http://www.avagotech.com/cs/Satelli...hcpl-7840&selectedDocumentTypes=1206560579586

 

thanks beenthere,
but the input diffrential voltage is very small about 200 mV to guarantee linearity.
do u think it'll be accurate to measure 700 volt. and it malny designed for sensing current
thanks again for your reply

 

Presumably you've also considered a Hall Effect voltage transducer. Simple & robust - but may not meet your economic constraints, if any.

 

Another technique for achieveing opto-isolation is to use a Voltage-to-Frequency converter the output of which you pass through an opto-isolator. The output of the opto-isolator can then be fed to a Frequency-to-Voltage converter to recover a facsimile of the original DC signal.

hgmjr

 

thanks t_n_k
do u recommend me certain model ?
thanks hgmjr
does Voltage-to-Frequency deal with the harmonics of the signal and also can i isolate ac using it ?

 

t?
thanks hgmjr
does Voltage-to-Frequency deal with the harmonics of the signal and also can i isolate ac using it ?

What frequency components do you expect to encounter in the 700 volt AC signal?

Yes opto-isolation is achievable. The V-to-F feeds a corresponding F-to-V. These two stages are separated by an opto-isolator. It is the opto-isolator that provides the isolation.

Of course to accomplish full isolation, the v-to-f stage will need its own independent power source.

hgmjr

 

An observation.....

700V ....High voltage.........where are we?
do you know the OP?

 

Greetings shoka,

Can you provide us with more details about what you are trying to accomplish with this measurement scheme? 700Vac is a very high voltage to be working around.

hgmjr

 

i have an induction generator which is driven by motor emulated wind turbine , the voltage out of the the generator is rectifier ans then inverted to give 380v, 50 Hz as the induction generator works with variable speed (means variable voltage and variable frequency) i need the linear optocoupler for isolation purposes

 

You are trying to pass 380v through an opto?

It will be a VERY VERY large custom made opto. (house size)

Why use optical isolation? How about a transformer?

 

Hello,

You could also take a look at an isolation amplifier.
These have an input of ± 10 Volts so a 1:100 attenuator will give you a ± 1000 Volts range.

Bertus

 

thanks t_n_k
do u recommend me certain model ?

Try Google with the search term "700V voltage transducer" and you'll get a few hits.

 

Perhaps the easiest and the safest way to deal with the 700Vac source is to use a stepdown transformer. A 100:1 stepdown would get you in the ballpark and then all you would need is a resistor voltage divider to get you the rest of the way to your target voltage.

hgmjr

 

plz any one tell me how to design a circuit for hcnr200 linear optocoupler ??

thanks in adance

 

plz any one tell me how to design a circuit for hcnr200 linear optocoupler ??

thanks in adance

Thats not enough information.

Do you want a circuit for a hcnr200 linear opto that handles 700 volts?

Here is the datasheet, it has many circuits using the hcnr200:
http://www.datasheetcatalog.org/datasheet/hp/HCNR200.pdf

READ the datasheet to be sure you are using the opto within its operational specs.