11/29/2023 0 Comments Optoisolator circuit![]() If you want to use a capacitor to further reduce the power consumption, then I suggest a 0.022uF capacitor and a series resistor of at least 10K. So I would use two 100K 0.25W series resistors. You can express CTR as a percentage, like 50, or a single number, like 0.5. Using a base resistor in the manner shown below provides a feedback loop, which can then be used to modulate when the phototransistor reaches saturation. Typical isolating optocoupler applications include low-voltage to high-voltage (or vice versa) signal coupling, interfacing of a computer’s output signals to external electronic circuitry or electric motors, etc., and interfacing of ground-referenced low-voltage circuitry to floating high-voltage circuitry driven directly from the main’s AC powe. Ideally, CTR (IC/IF) is the ratio of the phototransistors output collector current (IC) to the LEDs forward current (IF). In a simple 2-terminal phototransistor circuit, the base resistor (RB) is omitted from the circuit model and the connection is left open. So far, I came up with the following circuit: R15+R21 limit the forward current to 14mA12V and 30mA24V. The simplest approach to define the efficiency of an Opto-coupling is to cite its output-to-input current transfer ratio (CTR). There should be some protection against reverse polarization, transient over-voltage and permanent over voltage (up to 40V) to some degree. 1mA is enough provided you don't use too low a value of pullup resistor on the other side of the opto coupler. I have to provide some isolated inputs that accept 12-24V. It isn't necessary to run the opto coupler anywhere near 10mA of current. Here is the drawing of an optocoupler : Transmitter. ![]() If the LED power source is not able to provide all the required current at the square wave frequency then the LED output will lag, and at some frequency not deliver enough light for the photo transistor.So if you can put the scope input across. As the LED takes currents from 2 to 30mA, the control voltage can generally be between 4V and 30VDC. Also, any transients on the mains will result in current surges through the opto coupler. It sort of sounds like a power availability issue more than a opto-coupler problem. When you switch the 240V mains on and the capacitor charges, you will get a 300mA surge through the opto coupler if the mains voltage happens to be near the peak part of the cycle. The 1K resistor suggested in that thread is IMO far too low a value. This universal triac controller circuit with optocoupler solves the problem that triacs have when functioning at low temperatures (triac needs higher gate current) by adding a transistor at the output of the optocoupler circuit. To avoid having to use a high wattage resistor I have connected a capacitor and resistor in series as outlined in the thread How to detect power failure? - Project Guidance - Arduino Forum using the reactance of the capacitor to drop the voltage across the input of the PS2505.
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