Why does an optocoupler have a high saturation voltage?

Why does an optocoupler have a high saturation voltage?

You could also place the transistor on the high side with a resistor between emitter and output ground, so when the input goes high the output at the emitter is high too. But beware, most common optos have a high saturation voltage because of the limited base drive, sometimes in the order of 1 Volt!

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 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.

Can a optocoupler supply power to a transformer?

As you may have guessed, optos cannot do something that transformers can – supply power. While a transformer can power isolated circuitry, with current technology we cannot efficiently transfer power though light.

How does an optocoupler work like a relay?

They basically act like regular relays but use light to trigger the hot side TRIAC, which consumes a lot less current than a relay coil. One disadvantage is that semiconductor devices tend to fail shorted, while electromechanical relays fail open.

Is the opto output the same as the input?

Of course, logic output (and matching speeds) optos are available, but require a separate power supply for the output side. The nice thing about the opto output is that since it is completely galvanically isolated from the input side, it can float at any voltage – or in other words, it acts like a floating ‘switch’, though not a very good one.

How does a linear optocoupler in a circuit work?

The linear optocoupler works by adding the control voltage to the input end of the optocoupler. At the output end, a voltage is produced proportionally to further control the next stage of the circuit. The linear optocoupler consists of a light-emitting diode and a photistor.

How does an optocoupler work with a base lead?

Optocoupler with phototransistor base lead. A capacitor is connected between base and emitter of the phototransistor. This acts in effect like a low pass filter, adding some smoothing to the input signal, and bypassing sharp spikes. It does reduce signal sensitivity and introduce a delay, though.