Opto coupler

Feb 17, 2007 2 Replies
L

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



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X

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

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C

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

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