DIY_UEGO updates

[rr]

Richard Wakeling wrote:

> Hi Bob,
>
>     Are you saying that because the emitter of Q1 is now +4V instead of +2.5V
> D12 & D13 are no longer required and R17 & R15 need to be changed? Sorry just
> wanted to be clear about this.
>

No & yes, respectively. Q1 and the R15-17 resistors form a voltage divider
for the + input of the op-amp. Change the voltage at the top, and the voltage in
the middle changes.

>     Could you explain what Q1 is doing in that section of the circuit. I am sure
> others would like to know how that part of the circuit works. There was some
> talk that it should have been a NPN not the PNP as shown in the circuit.

Here is a cut from one of Chad's emails (1/18/01):


> :To fix the Q1 issue,
> :What may need to be done is a 33k resistor from Q3 base to U5A out.  I have this in
> :Proto #1 but is very rough.  The circuit may need a diode to give a small voltage
> :drop.
> :
> : like this: Q5 base -> 33K resistor -> U5A output.  Remove R32 and possibly D12 and
> :13.
> :
> :The purpose of Q1 ( which is wired correctly) is to yank the "Vs Cold" comparison from
> :0.47 volts to 1.12 volts ( when warm).  The idea is to kill ion current IF it gets
> :cold.  A warm Vs Cell will NOT output 1.2 volts.    Q1 doesn't need to be turned OFF,
> :it is by default.  It gets TURNED ON by the op amp going LOW.
> :
> :The same op-amp is used to kill the ion current.  It does this by shorting the FET
> :gate to ground through Q5.  Q5 should be ON when U5A is outputting a HIGH.
> :
>

BobR.


>     What we need is some one to take account of all these mods so there is no
> unnecessary questions to what is the latest correct mods required.
> Thanks Bob.
>
> Cheers Richard
>
> rr wrote:
>
> >
> > Re-visiting the Q1 circuit. Once the voltage supplies were
> > changed from +-2.5v to +-4v, along with D12 & D13 going away.
> > The resistors R17 & R15 need to be changed:
> >
> > Use a 93.1k for R17.
> > Use a 24.0k for R15.
> >
> > R16 stays at 180K.
> >
> > BobR.
> >
> > ----------------------------------------------------------------------------

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