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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.
Which is the best optocoupler for a computer?
The problem is lessened by ensuring that the external circuit is fully isolated from the computer and an optocoupler such as the PC817 is a cheap and effective (assuming no major user errors) solution.
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.
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.
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.
When do I need to replace my optocoupler?
In color TV, display and other switching power supply maintenance, if the optocoupler is damage, it must be replaced by linear optocoupler. The commonly used 4-pin linear optocouplers: PC817A, PC111, TLP521 and so on.
What should the current Ic of the optocoupler be?
In the case of the TTL output at the input of the optocoupler, the current should remain IOL ≤ 16 mA. The CTR value of 50 % results in the maximum output current IC for the optocoupler of 8 mA.
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 happens when current stops flowing through an optocoupler?
When current stops flowing through the LED, the photosensitive device also stops conducting and turns off. All of this switching happens through a void of glass, plastic, or air with no electrical parts between the LED or photosensitive device. It’s all about the light.
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).