DIY_UEGO

Chad Clendening clendenc at execpc.com
Fri Jan 19 05:08:38 GMT 2001


This Q1 looks a little funny.   After looking at it a while, I would have to agree it
won't work as it should.

Proto # II was made from this schematic.  I have the Q3 mistake noted here, actual
values used, but I made no mention of changes to the Q1 area.  This may have been a
last minute find - I don't know.    I added 2 resistors and 2 diodes to the bases of
Q2 and 3 to bias them both slightly ON ( class AB).

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.

I should be having another circuit built in the next few weeks.  One of my techs will
build it and I am sure I will have a few corrections to deal with.  They rarely make
mistakes so I have only myself to yell at,

--" you built it like I told you, you should know better!!!"

 So far, I have build my 2 protos and some errors simply get looked over due to
knowledge of the circuit.


Chad


> Date: Wed, 17 Jan 2001 10:17:52 -0600
> From: Robert R Ducker <bducker at txdirect.net>
> Subject: Re: diy uego
>
>      Bruce, I hope things are going well for you.
>      Here's some more UEGO stuff. Something I forgot to mention last time,
> there's an error in the controller schematic that doesn't seem to have been
> posted before. Q1 is shown reversed emitter-collector and should be NPN
> rather than PNP. So it should be a 2N3904, used as a follower with the
> collector tied to +V. This turns the ion kill stuff into a mess otherwise.
> If this has already been posted about, my apoligies, I couldn't find it.
> I also talked about pots R1 and R2 last time, should have called them R19
> and R20.
>
> Bob D
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