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Hi,
In order for me or anyone to help with this, i need to ask a few questions.
1. What is the min and max current level you need to work with?
Minimum AC current =125mA
Maximum AC current = 2.5A
beyond these two limits i turn off the current carrying appliance/device.
2. I take it this is AC current?
Yes 230v AC
3. What kind of basic accuracy are you after?
Not very accurate.As i said earlier that i just need two limits beyond which is fault condition.But i guess the lower limit will define the accuracy.
4. What kind of time response to an overcurrent do you need?
Not very responsive.Maybe 500ms is good enough or even 1 second.
Actually most current transformers will run you that much or more and will not respond to DC.Thats a lot of cost.
This system will be manufactured in good quantity and current protection was just another feature thrown in at the last moment.
Also Allegro doesnt seem to have good support in my part of world.
I would really wind a Current Transformer myself in a really small form factor and that would be it!!!
I dont understand why you wont approve of a CT?
Since I dont require response and accuracy as much.
Thanks again
The hall effect sensors are technically another IC but they are low power, do not require any line side power supply, and replace the input amplifier and filtering that you would need with other solutions.
Hello
There is a footprint limitation for this.I have already validated it with a ct but the space problem has got me shifted to the hall sensor..So pls help me with this
thanks & regards
Hi,
I also thought that you said you were using a 3.3v source voltage?
Your schematic shows a 5v source, so which is correct?
I ask this because more improvements could be made to my circuit if you
instead use a 5v source.
I have two voltages 3.3v is for the MCU and 5v is for the ACS712.So the 5v could be used for the opamp as well.
Ok, i see your circuit puts out 2.5v for zero AC input. Is this what
you really want? You do loose some ADC range that way.
Also, you can not use an LM358 like that with a 2.5 amp signal because it
will saturate near the peak, leading to a large error in the measurement.
The gain has to be reduced or use another op amp and possibly still
lower the gain a bit.
The value that ACS712 puts out at its VIOUT for zero i/p current is 2.5v.Subsequent currents will be higher or lower than this reference voltage at
185mv/A.So i am just removing this shift.And if 5v as Vcc is used then i dont think saturation will occur
If you make the circuit ac coupled you get rid of any dc offset drift.
The one like you did?.but remember that the o/p from ACS712 is NOT AC or if put in right words,just moves around +2.5v..so still AC coupling will help?
What is the purpose of the diode on the output of the opamp?
What is the purpose of the diode on the output of the opamp?
it is a peak detector.
Are you having other specific issues right now?
There are lots as i am continuing this thread.I am attaching a current approach which i am using now (as "tl431incl.png") and the proposed approach (as "with tps61222.PNG") with the boost converter.
As for your 3.3V being unstable, it's probably from the 5V boost converter. Do you have a fairly large cap on the output of the 3.3V regulator? Boosting to 5V is going to cause a fairly large current ripple on the 3.3V line, ~30-40% ripple as a quick guesstimate. I may have missed something, but why not regulate to 5V, then a second regulator at 3.3V?
In the schematic you can see a ACST4 Triac which has to be fired only in this peculiar way.
Now if i use the LNK304 to generate the +5v first(actually its -5v ,i have only reversed the GND reference) then the Triac will always be fired,since the Neutral=+Vcc=+5v and the gate is at +3.3v ,MCU o/p pin for triac off condition...(you have to visualise a bit here)..so it is imperative that the Triac COMMON terminal and the GATE terminal share a common rail or to be precise;voltage levels, which you can see in the first schematic.I am using a 2.5v reference at the Vss terminal so effectively Vdd-Vss~2.6v (since Vcc=5.1v)..Now i have two grounds in my circuit .one with 5v and the other with 2.6v.This schem is not working for the ADC reading as it should.So i proposed another one using the boost converter so that both grounds are at same potential and i generate 3.3v first so that the Triac can be fired flawlessly.Now the ACS712 needs 5v so i am left with no other way to power that up unless i use a boost converter ic.The opamp too is a proposed idea and yet to be implemented once my printed boards for the TPS61222 arrive.(they are so tiny that almost impossible to solder on a general purpose board)
I have made some boards for the TPS61222 3v to 5v boost converter which are not yet here.So i m yet to check the consequences of that.
Furthermore i found this project which has an exact objective which i have (at least with the ACS712 and the ADC) but since there is not much on the codes there to understand how he has done it.
Is expecting more help from you wrong?
Please get back if you can
Thanks and regards
Can you share your adc codes with me for the ACS712 readings?..atleast i can get some idea what you are doing..or else some kickstart in that direction too will help!