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LM311 V-F

HI,

I am currently using a LM311 as a V-F. I have it set for 150mV/Hz with the following components.

Rt = 200K Ct = 100nF Rs = 13.8K Cl = 1uF Rl = 100K

For testing I have used some components that I have had laying around and I am finding that the output is greatly effected by temperature. The resistors are surface mount metal film but I have used an XR7 for Ct and a Tantalum for Cl. The datasheet recommends NP0 or C0G series for Ct and I have found one with 30ppm/C in an SMT package ok but it also says I should use a Mylar Cap for Cl. I have had a bit of a look around and the only 1uF Mylar caps I can find are huge and not available in SMT. Can anyone recommend a good choice for Cl? I was also wondering if Cl had to be 1uF, I am guessing it does but the datasheet isn't very clear, maybe I could use a smaller value?

Best regards.

AJ

Reply to
AJ
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The rate is determined by the ratio of the two capacitors, so they GOTTA be very stable.

The actual capacitor values are not critical, it's only their ratio that is important.

Just dont go much below say 500pf as then stray capacitances may become significant.

So you could scale down the values by a factor of 100 easily. Maybe even 1000 if there isnt much stray capacitance.

Reply to
Ancient_Hacker

Mylar SMT capacitors are not available, because polyester cannot survive the high temperatures required for the SMD process.

Here's one series that goes up to 1uF in SMT, with somewhat different characteristics because of the different dielectric:

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And some nice 5mm lead pitch through-hole stacked-film caps (molded case and dipped, respectively):

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Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

If you're going that small, wouldn't that put it into a range where you could use NP0s or C0Gs for both? Would they track better?

Thanks, Rich

Reply to
Rich Grise

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