LM13700 VCO Design help

Thread Starter

MachineHum

Joined Nov 3, 2014
74
Hey guys/girls,

I'm designing a VCO using TI's LM13700 (Datasheet below)
http://www.ti.com/lit/ds/symlink/lm13700.pdf

On page 19 there is a pretty good looking schematic. Working the math is no issues, but all the formulas are using Ic and Ia, and to get these I need to know the voltage at the two points I've marked below. Obviously I can't assume their high impedance inputs because that would make the current zero.

Selection_001.png

If anyone has an answer that would be very helpful, bonus points for resources to learn about TC amps.

Thanks

MH
 

AlbertHall

Joined Jun 4, 2014
12,073
From the data sheet, page 11:
Next, set IBIAS. The Bias Input pins (pins 1 or 16), are 2 diode drops above the negative supply, and therefore
VBIAS = 2(VBE) + V- , which for this application is -13.6 V. To set IBIAS to 1ma when VC = 15 V requires a 28.6-kΩ;
30-kΩ is a standard value and is used for this application. The gain will be linear with the applied voltage.
 
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