Redesigned the expo converter

Mon, Apr 11, 2011

As seen in the previous post, the following formula determines the cutoff frequency of the typical LM13700 lowpass filter design:

The only variable part in this formula is the Iabc part, the incoming current from the expo converter. The cutoff frequency of the JUNO106 filter varies between 5Hz and 50000Hz (from the manual). To achieve this, Iabc low and Iabc high must differ a factor of 10000. I redesigned the expo converter as following:

Resulting in the following:

The current @ 5Hz is now 100nA and the current @50kHz is 1mA which differ a factor 10000. Nice!