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What kind of resistor does an optocoupler use?
The optocoupler infrared LED is driven at about 4mA via a 1kΩ resistor from IC1 output. As the CTR of the PC817 is around 115% the phototransistor can supply about 9mA as the supply to the phototransistor output is now taken from the 12V motor supply. This is more than the 5mA minimum required to drive the 2N3904 into saturation.
How is the optocoupler connected to the TTL?
Here, the optocoupler LED and current-limiting resistor R1 are connected between the 5V positive supply rail and the output-driving terminal of the TTL device (rather than between the TTL output and ground), because TTL outputs can usually sink a fairly high current (typically 16mA) but can source only a very low current (typically 400µA).
How to calculate optocoupler efficiency in a circuit?
The most convenient way of specifying optocoupling efficiency is to quote the output-to-input current transfer ratio (CTR) of the device, i.e., the ratio of the output collector current (I C) of the phototransistor, to the forward current (I F) of the LED. Thus, CTR = I C /I F.
How is an optocoupler used in the design process?
The start of the design process is to specify the input and output conditions the optocoupler is to link. Typical optocouplers can handle input and output currents from a few microamps to tens of milliamps.
Can a optocoupler be used with an Arduino?
I’m trying to input 12v into Ardunio Digital inputs. But since Arduino digital input max voltage is 5v, I would like to use an optocoupler as a switch for 12v input into 5v from Arduino itself. So I have got P621 Opto, But I’ little concerned about the opto handle 12V??
What kind of current does an opto coupler need?
As the current available from typical computer input/output ports may only be a few µA, as computer port lines are usually designed to drive some type of logic input, the input to this motor drive circuit is via a HCT Schmitt inverter gate, which only requires an input current of 1µA, with the 12V 40mA motor being driven by a 2N3904 transistor.
What is the purpose of an optocoupler interface?
The main purpose of an optocoupler interface is to completely isolate the input circuit from the output circuit, which normally means there will be two completely separate power supplies, one for the input circuit and one for the output.
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.
What are the characteristics of an optocoupler schematic?
The first variant above indicates a bidirectional input and phototransistor output optocoupler schematic featuring a couple of back-to-back connected gallium-arsenide IRED’s for coupling input AC signals, and also to safeguard against reverse polarity input. Commonly this variant may exhibit a minimum CTR of 20%.
How does an optocoupler limit the gate voltage?
You can limit the gate voltage by having a resistor in series with the optocoupler’s transistor. If the transistor to ground is 4k7 you can pick 10k for this. If the optocoupler’s LED is on the transistor will conduct and make the gate high, switching the MOSFET on.
Why do you need an optocoupler to drive a microcontroller?
The optocoupler’s isolation gives you the advantage that you can place its output transistor anywhere you like, independent of the microcontroller’s supply voltage. Driving the opto-coupler means driving its LED. If the microcontroller can’t drive it directly you’ll need a small transistor for that.