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230V zero crossing detector using optocoupler only and no transformer.

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hanelex

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HI,

I am looking for a circuit/ Ic which can provide a zero crossing output (square wave ideally). The circuit must contain a opto coupler which can be driven WITH A 230V INPUT and give a 5V TTL at the output.


A TRANSFORMER CANNOT be USED.

Please help me asap as i`m fast aproaching my dead line

Regards,
Richard
 

Hey Gentleman!
You can use a linear opto coupler (such as IL300) and then you can use a simple op amp or comparator to obtain an square wave in phase of input. then you will need a differentiator . and then you can use a rectifier for spikes of the out put of the differentiator . ok now your circuit is ready!
Respect
Goldsmith
 

your optocoupler diode had a forward current of 60mA, the typical Vf is 1.25 for 50mA

with 230V RMS the peak will be 230*1.414=325v /1000=32.5mA

So yes you can use it but if you are driving a low current logical input from the opto transistor then there is no need to use that high current.
If you use 1K then the you ween need a resistor about 219v*0.032A= 7W

Alex
 

I found abt this ic HCPL3700 which is a zero crossing detector, but when testing it, the value of resistance given in the datasheet doesn't work, the resistor gets heated up even after using 7w resistor.

Also is there any replacement ic for hcpl3700.
I tried connecting hcpl3700 direct without the resistor, its not working.


Please suggest me a solution as i am in a dilemma.
 

You have to connect a Vcc supply voltage in pin8 and also use a pull up in the output 6 since it uses an open collector.

What resistor value have you used?
You were using the AC inputs right?

After connecting it directly to the mains the input should be damaged from the high current, I would even expect it to blow up !

Alex

---------- Post added at 12:45 ---------- Previous post was at 12:27 ----------

It seems that the resistor is only there to control the threshold and not limit the current so ignore what I said
 

1. I had used 18k (5w) resistors connected to live n neutral & live or neutral, all the possible configurations, but the resistors heated. Also the values mentioned in the datasheet get heated. The formula for calculating rx is also not yielding a proper resistance value. I also used many other values of resistance.(50k-1M)

2. Also i did connect all the connections at the 5V end. I get a brief output when i connect 18k resistor at the input(230v) but the resistor heats up.

3. I found a few line monitoring ic`s but fear the same will occur with them Avago Technologies Isolated Voltage/Current Detector are ideal for voltage sensor applications


4. The ic wen connected directly did not burn up. its still working. wen connected to 18k
 

I found an application note, maybe it helps you


Alex
 

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