How to calculate current limiting resistor for optocoupler?

How to calculate current limiting resistor for optocoupler?

I understand that I need a current limiting resistor on the input side of the optocoupler, so here is how I calculated it: From the datasheet, we see that the forward voltage is (typically, @20mA) 1.2V; so subtracting 1.2V from 3.3V leaves us with 2.1V for us to deal with through the resistor. So, by Ohms law 2.1V / .02A = 105 Ohms.

What are the CTR values of an optocoupler?

Each optocoupler type will have a range of CTR values set out in the manufacturer’s datasheet.

How to calculate the CTR of a resistor?

According to the data sheet with If=1mA minimum CTR is 34%. Using series resistor of 1.5k at 3.3V gives If= (3.3-1.2) / 1.5k = 1.4mA. The collector is connected to a 30k pull up resistor.

What is the voltage of an optocoupler gate?

Assuming that a single HCT output is only feeding this optocoupler, a logic 1 voltage of about 4.9V can be presumed. The output current available from a HCT gate to drive the optocoupler input is limited to 4mA, which is quite low for driving an optocoupler.

How many milliamps can an optocoupler handle?

Typical optocouplers can handle input and output currents from a few microamps to tens of milliamps. There are many optocouplers on the market and to find the most appropriate for a particular purpose, vendor’s catalogues and manufacturers datasheets should be studied.

How is Electrical Isolation achieved with an optocoupler?

The spectral response of the LED and the photo-sensitive device are closely matched being separated by a transparent medium such as glass, plastic or air. Since there is no direct electrical connection between the input and output of an optocoupler, electrical isolation up to 10kV is achieved.

Can a microcontroller drive a MOSFET with an optocoupler?

Anything up to about 10 kHz should work OK./ For faster PWM a properly designed driver is required. As far as the MOSFET is concerned, an optocoupler is just a transistor. As far as the microcontroller is concerned, an optocoupler is just an LED.

Do you need a transistor to drive a MOSFET?

So, all you need is a normal transistor-driven MOSFET circuit, and a normal microcontroller-driven LED circuit. Here’s an example of driving a MOSFET with a transistor: So Q2 is the output side of the opto-couper. R2 would be replaced by the input LED side of the opto-coupler and it’s current limiting resistor.

Which is an example of an optocoupler circuit?

There are many different applications for optocoupler circuits, so there are many different design requirements, but a basic design for an optocoupler providing isolation for example between two circuits, simply involves the choice of appropriate resistor values for the two resistors R1 and R2 shown in Fig. 5.2.1.

How does the CTR of an optocoupler vary with age?

Manufacturers will normally quote a range of CTR values for different output phototransistor collector voltages (V C) and different ambient temperatures (T A) The CTR will also vary with the age of the optocoupler, as the efficiency of LEDs decreases with age (over 1000s of operating hours).

Where does the current go in an optocoupler?

You are allowed to run the current from the camera through the transistor side of the optocoupler. Just be sure the polarity is right. Measure the pins for “shutter” and see which one is positive. Positive from the camera goes to pin 4 and the less positive voltage from the camera on pin 3.

What is the voltage of a pc817 optocoupler?

In this case however, a popular PC817 optocoupler from Sharp will use voltages and currents available from HCT logic. Assuming that a single HCT output is only feeding this optocoupler, a logic 1 voltage of about 4.9V can be presumed.

How does the Universal optocoupler TRIAC controller circuit work?

The transistor amplifiers the trigger pulse coming from the optocoupler and the gate current is high enough to trigger the triac in all temperature cases. How does the circuits works? The base of the transistor is driven by the OC. C2 works as capacitive bias resistance to avoid power losses and it also helps avoid DC loading of the supply line.

Can a TRIAC be used as a microcontroller?

I am trying to control home devices using a microcontroller and a TRIAC. For switching, I intend to use an optocoupler and triac-based circuit. The circuit is given below (also plenty are available on the internet, but all are the same).

What kind of circuit is an optocoupler circuit?

FIGURE 2. Basic form and application circuit of a typical optocoupler. Most modern optocoupler devices use a phototransistor as their Rx unit; such a device is known simply as an ‘optocoupler,’ since the input (the LED) and the output (the phototransistor) devices are optically coupled.