HCPL-3700 circuit Please

[rizzy_dascal]

Hi,

I have a HCPL-3700 optocoupler and I need to interface with a pic chip, basically I want to tell the chip when 230 volts is present.

I have been told that although the optocoupler has ac or dc input it is best to first convert ac to dc ?

Thanks in advance
Rizzy

 

[sreekanthr.ele]

if you ae going to give AC signal connect between 1 and 4
for dc connect between 2 and 3

form 8th pin connect a pull up to 6th pin max 10k

and you will the output as per truth table

 

[rizzy_dascal]

Hi sreekanthr.ele

Can I put 230 volts ac straight into the chip ?

Should there be a fuse ?

Thanks
Rizzy

 

[jayanth.devarayanadurga]

HCPL 3700 datasheet https://www.fairchildsemi.com/ds/HC/HCPL3700.pdf

It is clear in datasheet that you can give AC or DC input to this opto-insolator. Pins 2 and 3 is input DC volts and pins 1 and 4 is for AC volts input. pin 8 is Vcc and its max absolute rating is -0.5 V to +20 V but recommended voltage is +2 V to +18 V. If you are interfacing it with MCU which works at 5 V then give +5 V for Vcc pin of opto. Pin 7 has no connection. Pin 5 is Ground. Pin 6 is Vo i.e., Voltage output pin whose range is -0.5 V to +20 V and it should give an output of 0V to 5V if you need to interface this pin with MCU. The opto has inverted output i.e., if input is high Vo is low and if input is low Vo is high. A 0.1 uF capacitor should be connected between pins 8 and 5. It is mentioned that Vin ie.n pins 2 and 3 (dc V input) max rating is -0.5 V. I don't know if it is correct or not. It is not mentioned in the datasheet whether 230 V AC/DC can be given to AC/DC input.

See this datasheet

You have to choose a proper value od Rx.

 

[rizzy_dascal]

Hi,

I simply want to tell my pic chip that a pump motor is running and has 230 volts at it.

I have a HCPL-3700 chip optocoupler

I have a pic 16f877A microcontroller

I don't understand the datasheet which is why I am asking for professional help on the matter.

I simply need to know how to connect the 230 volts side of the HCPL-3700 ie can I connect 230 v ac straight to the chip or do I have to drop it somehow ?

If somebody could post a simple diagram I would be most grateful

Thanks In Advance
Rizzy

 

[jayanth.devarayanadurga]

I think you have to drop it. The AC/DC Vin range is not mentioned in the datasheet. Search for your opto's interface circuits.

See these links
https://www.edaboard.com/threads/230864/

 

[rizzy_dascal]

Hi Jayanth,

Yes this is what I am talking about, I just need a circuit to drop the voltage to an acceptable level for input, I think the Zero crossing circuit is wrong for me though.

Thanks
Rizzy

 

[elecbaba]

See page 5 of the document.

 

[rizzy_dascal]

Thank you Elecbaba,

But I am only a beginner and I can't quite get my head around that graph, it looks as though I need a capacitor and a couple of resistors on the ac side but I am not quite sure how to work it for 230 volts..

Thanks
Rizzy

EDIT:

I have just had another look at the graph, would it be 100k ohms for 250 volts AC so about 90k ohms for 230 volts then divided by 2
and that is the value for each side ?

 

[elecbaba]

You can try with this circuit.

 

[rizzy_dascal]

Hi Elecbaba,

Thank you for taking the time to post the diagram it was very kind of you, it looks like I was on the right track with the graph

Thanks Again
Rizzy

 

[FvM]

You can try with this circuit

As calculated in the application note, the filter capacitor raises the threshold to about 300 VAC (RMS) with 100k external resistance, means the optocpupler will never switch with 230 VAC. The resistors should be reduced to about 30k/0.5W each.

 

[rizzy_dascal]

Hi FVM,

Thank you for the warning, tricky little things to calculate really...

cheers
Rizzy