Opto coupler

Hello,

I just finish building a small circuit utilizing an opto coupler, the
mct6.
I use an LM331to translate voltage to frequency, that works, but when
I add the optocoupler in , it do not keep the frequency intact. I mean
it has huge rise and slow time. Basiclaly If I use a pic chip to count
the frequency it is basically tell me its high all the time. Is there
an opto coupler that can react faster ? or this is it. I am trying to
make a voltage checker circuit using two different grounds.

thanks
ken

 

What is the frequency? Here is the respond time
ons Symbol Min Typ** Max Units

SWITCHING TIMES

(RL = 100 ??, IC = 2 mA, VCC = 10 V) ton 2.4 ?s

Non-Saturated Turn-on Time

Non-Saturated Turn-off Time (RL = 100 ??, IC = 2 mA, VCC = 10 V) toff 2.4 ?s

 

Hi, Ken. Try an H11L1 -- it has a data rate of 1MHz and digital open
collector output. It'll work fine at LM331 frequencies (f(max) <
100KHz) and can be driven directly by the LM331 output -- the opto-LED
only requires 2mA to change the logic state on the other side
(although you should drive it with 4 or 5mA to be safe).

Be sure to remember the pullup resistor (10K should be fine) from OUT
to Vcc on the PIC side.

Cheers
Chris