Reading a 4N35 optocoupler datasheet

[Lucky-Luka]

Hi all
Is there a good samaritan that can help me understand
1)How fast can I drive this optocoupler?
2)Input voltage? Is it 1.2V?
3)Which current and voltage its output can handle? (Less than 50mA and less than 70V? How much less than those values?)
Cheers

[coldfiremc]

If is for switching, 50 usecs is the turn-on turn-off time. This in the kilohertz order. If not, look for capacitance and make a frequency response approximation of it. Gain will decrease considerably beyond the cutoff.

[T3sl4co1l]

You can drive it as fast as you like, it's just an LED.  Use a current limited driver, and expect about 1.2V drop but do not rely on that voltage to be consistent, as it varies inversely with temperature and logarithmically with current.  Hence the current limited driver.

What you get at the output, however, is limited by physics of the phototransistor.  At best, you can use it in photodiode mode, which is good for a few MHz.  This requires a carefully designed amplifier.

As a phototransistor, yes, expect 10s of us for switching speed.  The best case is with almost no voltage swing, which is where they do the test with a 100 ohm load resistor.  With practical values (~kohms), it's very slow, 50 or 100us.

Speed can be improved somewhat by connecting a resistor across the base and emitter pins.  47k to 100k typically.  This destroys CTR at low currents, and still reduces it pretty significantly at full I_f.  But you can get more like 10-20us switching speeds, with typical (say logic level?) voltage swings, this way.

Output current and voltage shall stay within the specified limits, yes.  Power as well, that is, the product of Vce * Ic.  It's not rated for much, so be careful.  In saturated logic applications, this isn't a problem.

Tim