From: Tilmann Reh
Subject: Re: Improving Rise/Fall times on Opto
Date: Fri, 06 Dec 2002 09:47:35 +0100
Organization: Autometer GmbH
NNTP-Posting-Date: 6 Dec 2002 08:46:40 GMT
X-Mailer: Mozilla 4.78 [de] (Windows NT 5.0; U)
> Dear Group, could anyone suggest an effective ciruit that will vastly
> imrpove the rise and fall times on the output of a 4N35 or equv
> curently I am using a 68K from base to emitter in the output transistor. The
> output transistor is connected as emiitter-follower to prevent the circuit
> from inverting the input.
> Is there a way of improving the sharpness of the pulse?
Not much, probably.
Rise and fall times (as well as delays) are rather large with
those simply couplers.
If you increase the base-emitter resistor, it will turn on faster
but turn off really slooooow. Otherwise, if you decrease it, it
will be hard to turn on at all.
You might consider using a faster device, i.e. PC900 or H11L1,
or even much faster: 6N137. However, all those receiver-IC types
require a separate 5V supply for the receiver...
Dipl.-Ing. Tilmann Reh
Autometer GmbH Siegen - Elektronik nach Maß.
In a world without walls and fences, who needs Windows and Gates ?