Seems like one of those resistors is the sensor? To me it looks like the output is going to try to stay just over 3V but will lag ‘ref out’ up or down if there is any voltage on it. I can’t recall if op amps can sink current or not.
The wife was annoyed that the contractor blew up the new fan hood for the kitchen remodel with a dead short on the output. A Replacement board was 8 weeks out. “Can’t you get out your special catalog and fix it?”. I suppose - hum.. this circuit board is built to drive more than one fan. Let’s take this SCR out and move it over here, solder a new fuse in here… yep - don’t even need to order parts. Mark > On Dec 4, 2018, at 2:43 PM, <[email protected]> <[email protected]> wrote: > > I am reverse engineering a temp control circuit on an electric tankless hot > water heater. > Manufacturer says no user replicable parts inside. Oh yeah? > > It has this as a reference voltage circuit (below) for a comparator to > compare against a thermistor and pot combo. > LM324 > > Odd taking a reference voltage from an input. Have never seen this circuit > before. I think I have drawn it correctly. > The op amp will drive the output to minimize the differences between pins 5&6 > so pin 6 should reflect the voltage of the divider with lower impedance. > > Anyone see why this wouldn’t work? I was sure I had traced it incorrectly, > but I think this really is the circuit. > It seems the values of R10 and R11 are not critical. Or are they? > > > <image[1].png> > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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