555 EFI again...

[Clare Snyder]

Chris Morriss wrote:
> 
> In message <35A14466.3AD1CF47 at brokersys.com>, Walter Petermann
> <corsaro at brokersys.com> writes
> >Frederic Breitwieser wrote:
> >>
> >> >I'm finished with the circuit and am working on the power supply.
> >>
> >> I would love a copy :)
> >>
> >
> >Here it is:
> >
> >http://brokersys.com/~corsaro/wiring_diagrams/555fe.htm
> >
> >let me know what you think.
> >
> > Walter
> I'm writing this before looking at this website, so perhaps this design
> is OK.  The point I want to make is that the core of a simple EFI is the
> voltage to pulse-width stage.  If you use a 555 and simply alter the
> threshold level you won't get a linear v to PW relationship.  A normal
> 555 monostable uses an R-C network for the timing.  The voltage across
> the capacitor rises in an exponential fashion, whereas we require that
> the voltage rises in a linear ramp.  This can be acheived by using a
> constant current source to charge the cap.  Voltage across the cap will
> vary according to dv/dt = i/C.
> 
> With this technique the desired pulse width can be set by altering the
> threshold voltage, or by keeping a fixed threshold and making the
> current source into a voltage controlled one.  This can be done by the
> conventional op-amp and transistor VCCS, (ground referenced) with a
> current mirror used to provide the current from the V+ rail.
> --
> Chris Morriss
How do we implement this - modification to the referenced circuit?
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