Re: op amp output

Thanks for all replies. I'm pretty sure that all parts are ok and
connected correctly, I've looked it through several times.

John Smith wrote:
>Change the opamp for one which gives rail-to-rail outputs.
>Or create your own rail-to-rail output using transistors.

How stupid of me to forget mention that I used another op, TL082. I've
tested to change to LM358 and it gave almost 0 on low!
Huh, I beginned to use an op instead of transistors for this
application because I thoat this will give simpler circuit.

Ban wrote:
>The whole design on this web page doesn't have
>any hysteresis, which should be there. Just solder a 1Meg resistor
>from pin12 OP to pin4 +IN.
>...
>When the comparator is low, the voltage on pin 12 should be less than
>0.3V with the lowish current draw of the 5k6 pull-up resistor. Thr
>relais is then off. The output should be able to drive the relais
>directly, if the current is less than 25mA.

But is 1M resistor really needed? I thoat it only decreased the
precision.. Now I included it.
The relay coil will drain quite alot. It will control a ~500W boiler.

Chris wrote:
>You're getting pretty close to the full battery voltage when the
>comparator is off, and about 1.3V when on. Again, looking at the
>data***, you can see that the comparator transistor "on" voltage
>starts to rise pretty dramatically when it's trying to sink more than
>about 5mA.

The high/low output doesn't change much if I remove all load from the
op output (if my multimeter isn't counted as a load). But anyway, I'll
use different op amp.

John Fields wrote:
>You don't need Q1 and, assuming that your thermistor has a resistance
>of around 1000 ohms at your setpoint, this should work:

Mine NTC is 10k at 25*C and 500 at 100*C. I don't understand why you've
used an MOSFET (I'm more used to transistors :P ).. and what's the
purpose of Z15V, is it a zener diode?

I was going to use this circuit to control temp in a water-bath at
0-100*C.


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