[sdiy] expo with no tempco & no heater?

[James Patchell]

The circuit works...but there are some major if-buts....

1. The loop created by Q3 and IC3 can latch up...under certain 
circumstances...it may take a bit of work to solve this...

2. There is no way to control the exp current out with a control voltage 
and be temperature compensated...in the circuit, as drawn... the VPAT is 
used to set the voltage across a pot...you can also use the VPAT as a 
reference input on a multiplying DAC or as an input on a multiplier...it is 
possible to use the same type of circuit I did in the one Scott Bernardi 
and I designed, however, our circuit...which does the same thing...does not 
suffer from the latch up problem this one has.

         For those who never saw the No-Tempco expo circuit we came up 
with...take a look at:
http://www.oldcrows.net/~patchell/synthmodulesII/200-1007.pdf

At 10:49 PM 4/27/2005 +1000, Paul Perry wrote:
>Exponential converter with no tempco, and no heater?
>
>http://www.edn.com/article/CA178103.html
>
>Presume this has been posted before, but I missed it..
>I saw it when trying (so far unsuccessfully) to find an
>EDN design for a quad op amp circuit that enables you
>to match a transistor pair via a scope.
>
>paul perry Melb Australia

         -Jim
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http://www.oldcrows.net/~patchell

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