Detect 10V…To.. 260V AC/DC with HCPL-3700?

Hi thanks for your idea. what I am not clear about is where the 220k resistor is placed

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I have a 12VDC refrigerator that I can either plug into AC outlet or use a 12VDC barrel connector in the side. Two different power sources. The 12VDC barrel connector never sees 230vAC so it is not a problem.

The OP has never clearly stated what kind of situation would cause a single point to see 10vDc and 230vAC. I cannot imagine what kind of a weird solution we might be solving - I think we need to hear the core problem and offer better solutions.




The idea is simple to be able to activate one or more digital inputs with a voltage of 12 to 250 ac / dc. to be able to activate it as desired.

For example, we may have a case in which we have 24vdc maneuvers and we will activate with 24vdc but in others we may only have 110vac and we can activate them in the same way without installing additional transformers.

frangimeno said:

Hi thanks for your idea. what I am not clear about is where the 220k resistor is placed

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After R2 & R5, across the AC input to the bridge rectifier.
It's to discharge or bypass any capacitive pickup; the optoisolator may switch with less than 50uA through the LED.

Note that you will have to modify the 4N25 parameters for it to work in simulation - the TLP627 has a CTR of 1000, while the 4N25 is rated around 50 - 80? if I remember correctly.

Edit - And R3 MUST be 10K for it to work over the range I worked out.

You might be able to use a hall sensor like an ACS712. Works for both ac/dc current. If you need to know voltage, you could do some math in the arduino to figure it out..

A few years ago I needed a similar circuit that the OP is asking for to detect Zero RPM on a 90V DC motor (The motor acting as a generator in free spin).... Anyway a variation the current regulator circuit posted in #8 driving an Opto-Isolator as the LOAD worked great. What you need to consider is that most off the shelf transistors (used in the current regulator) have an upper limit of 50V or so.... so you need to select transistors that can handle your input voltage or cascade (cascode) the current limiter. Even though I was only using 90V, I found some transistors that would handle 250V and I tested the current regulator circuit up to about 200V and down to about 10V with a variac transformer.

Well, the circuit you propose works but it needs very bulky resistors. Thank you very much for your interest to all.

I am going to opt for the microchip circuit. It is a small chip and it is not expensive and the external components do not take up much.

For those who can serve you these are the values of R1:
10k - 3.3V
18K - 5V
52k - 12V

CN1- 10 ... 400V AC / DC
CN2 - DC OUT

* Schematic and values of microchip reference components.

That does not provide isolation - it will pass high voltages to the output.
If you do not need isolation, you can use eg. 1M resistors direct from the test inputs to a couple of MCU pins...

ps. The ratings of the resistors for my circuit are pretty much the same as for the HCPL-3700 circuit you started with??

In the VCC output I will put an optocoupler.

Hello friends, in case someone is of use to you, after the tests with the LR8 the conclusion is that it goes perfect, from 9VDC / VAC to 260VDC / VAC.
I have configured the LR8 so that it takes 3V and I have put an opto to the FOD852300 output that has a ctr of 1000% with a resistance in the 1k led, the consumption is 0.002 mA/ Iinput 240VCA. and the temperature of the LR8 less than 15 degrees centigrade .

The truth is that microchip does not disappoint, it makes good products.


Greetings and thanks.