CA3140

[Steven Varner]

Howdy,

In Electronotes PCC ENS-76 VCO option 2 (from 
Electronotes #75) the text states:
"Since the CA3140 is not suitable for driving 1k 
loads in our application, we buffer the triangle with 
a 556 before bringing it out. You could use the 556 
as IC-5, omitting IC-7, but the CA3140 is excellent 
as the follower on the capacitor due to its low bias 
current requirements."

Why is the 3140 not suitable for the 1k load? It's 
going to enter an input somewhere with a 100k input 
impedance right?

Also, on MCO-2 (Application note no.67) the Simple 
Triangle-Square Oscillator, a 3140 is recommended for 
the A1 (triangle) op amp.  There is NO 1k impedance 
resistor on the diagram.  If I add one for the output 
here, don't I have the problem mentioned in the VCO 
above?  Can the output just go to the jack with no 
standard impedance?  (The square out has no impedance 
resistors as well, but there should be no problem 
adding a 2:1 divider here).

Steve Varner
svarner at sdcoe.k12.ca.us
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