Do not belive everything on the net.CTR are important to calculate with. Look at the 4N27, 10% up to what I have seen as max, 600%.The solution with the zeners are not optimal when the input signal varies 20 volts (60-80)I have read earlier in this tread why the design was made like this.Was it nessecery to let voltage in the span 0-50 volts be absolutly off.With only a resistor, 0-10 volts can be off and over 60 on.Pelle
With voltages varying so much, I am having problems choosing the components. Either they use too much power, or the resistors do not suit to all cases.Please could you suggest another method ? Anyone else?
One more question: how many 75V inputs are there that you wish to monitor?
I think I'd probably use a comparator with high value resistors.
6) At first I wanted to use zener diode to make a clear distinction between voltages under around 50Vdc and over it. The reason was that it should be around 75, so anything lower than 50Vdc does not make sense. However, I wouldnt mind if it can detect a range like under 50Vdc (logic 0) over 50Vdc (logic 1)
If its much more easier, I dont mind if the circuit will be activated as soon as there is any voltage on the positive.