[Diy_efi] DIY-WBO2 circuit improvement suggestion

[bcroe at juno.com]

Perry, 

The problem is getting nearly 1.5 amps to the heater at 
10 volts, with current limiting.  When you have that, it is  
easy to steal .025 amp at 8 volts for the amplifiers.  A 
0.12 amp charge pump won't do it.

How do you plan to get the heater to work at lower voltage 
and higher current?

Bruce Roe

On Thu, 13 Jun 2002 17:30:45 -0700 Perry Harrington 
<pedward at apsoft.com> writes:

> 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

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