[Diy_efi] DIY-WBO2 circuit improvement suggestion

[Perry Harrington]

So I downloaded the GIFs and printed them for the DIY-WB today.  Now I understand
the whole voltage issue.

With a little work the heater circuit could be redesigned to work at lower voltages.
Since what the real issue is total power dissipation in the heater, a higher current
at lower voltage would probably acheive the same results.

It seems the analog portion is the problem WRT dropouts and low voltage.

For this I propose a simple solution: A capacitor charge pump.

Maxim makes a couple of suitable devices which they sell for generating 12v programming
voltages for flash.  The parts are MAX662A, MAX734, and MAX732.  They generate
30ma, 120ma, and 200ma respectively.

If you redesign the +-4v regulator circuit to use the 662, it would permit operation
off a supply down to 4.75v.  I'd recommend putting a low dropout +5v regulator
in front of the pump and just regulate the input, then you could regulate the 12v
output to 8v with a low dropout (LM2936) regulator.

The 662 part should be suitable, as the power supply uses the 324 in voltage follower
mode for the gnd tap.  Since the output of this device can only sink 25ma or so, the
30ma supply should work.

--Perry

-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/		 

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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