Ideas for a new circuit

Tony Clark clark at andrews.edu
Mon May 25 17:56:46 CEST 1998


>    Then I would feed this into a precision full-wave rectifier so that 
>
> [Luke:] Guys, Anyone know of any circuits for a PRECISION full wave
> rectifier ? The old 4 diode bridge has that 0.7v drop problem.
> 
> any ideas?

   Sure.  Take a look at the saw-to-tri converter on the Archive:

http://aupe.phys.andrews.edu/diy_archive/schematics/misc/saw2tri.gif

   The left half of the circuit, first op-amp and 3 schottky diodes make 
up the precision rectifier.  The circuit, however, has a strange quirk.  
Some people had mentioned to me about the slight offset of the rectifier 
around 0V.  In the circuit as shown, it does exhibit a small 0.2V 
offset.  That is, the rectifier turns on at 0.2V.  However, the circuit 
will turn on exactly at 0V if you increase the amount of current the 
circuit pulls.
   I had originally done the circuit using half of a TL084, with all four 
op-amps working simultaneously.  With the increased current consumption, 
the circuit worked fine.  But when I moved it to a TL082, it had the 
offset.
   The solution is to replace the 10K resistors with 1.0K resistors.  
Once that happened, it happily worked again.

   Hope that helps.  :)

   Tony

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I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu     | aupe.phys.andrews.edu/diy_archive
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