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op amp output

Wouldn't that 2 op circuit have the same ambient temp dependance?

I was thinking to go as simple as possible, while keeping the precision. Though if this circuit will make no temp drift during the operation, it would be preferred above "1 op circuit". Seems like I'm going to use a dual op anyway.

By the way, in that corrected circuit you've posted, should the 1N914 be connected to +5V too instead of unregulated Vcc? Oh, and what is the purpose of those two diodes?

I was go>I used a MOSFET because the gate doesn't draw any current, so you

Got it, though if I understood the graphs for LM358 (op that Chris suggested) correctly, at +10 mA the output should be at maximum 0,2 V. And that current should be more than enough for my "coil driver". Lol, the reason I try to avoid MOSFETs is because they don't like me.. First time I bought 2 of them, they died before I could test them.. (I heard they're very sensitive to static electricity..) And besides, I get most of my transys from my dead tv, there's no MOSFETs for some reason :)

Yp, exactly, I just wanned it to have somewhat wider "regulation window" or how to call it..

Heh, now I really don't know which circuit to use.. :P What would be the main differences in this circuit and that 2 op circuit that Chris posted? Soz, I'm not that much into electronics to see the difference :P

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Reply to
frogfot
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Alrighty, I decided to use my old thermostat circuit with some minor modifications (added 0,1 uF filtering caps).. Here's it in mspaint:

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Note, the motor is just a stirrer for the heat-bath.

One question remains, is it ok to feed the relay from regulated 5V? It eats only 81 mA and I will have a 100 uF cap on the 5V supply.

I used to have the relay connected this way.. but since I didn't use the circuit much, I dunno how it will feel on the long run..

Thanks

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Reply to
frogfot

R2, the feedback resistor does not have a value, the cathode bar is missing from the relay shunt diode. You might add a small cap across the motor and sure, you can run your relay from the regulated supply, you can also run it from the regulator input.

Reply to
Lord Garth

Nice.

I was thinking to set R2 to 1M and R1 will depend on the NTC resistor.

Huh?

But wouldn't that 1000uF cap be enough?

Thanks alot

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Reply to
frogfot

The diode across the relay showed up without the bar on the cathode end. Your diode symbols in the bridge are fine.

A small cap will bypass high frequency noise.

Reply to
Lord Garth

The LM358 and LM324 get close to gnd , but the output Z goes up to

10k ohms when output goes dn to about .6 vdc . 555 timer was

similar "Z" . LM393 comparator is same . As it gets to gnd it

has higher Z .

Op amps can't do low Z .

Op amps have poor feq response and poor settling time unless

they are modern FET input types . LF357M is a 20 mhz op amp

but has poor offset ( Vos) over temp . as do the TL082 and family

.

expect Vos to double every 11 C !!

Old LM301 or LM308 (?) can beat this Vos over temp by orders of

magnitude !!

There are expensive Vos chips that take out the Vos ....

I use MPSA42 or a cheap diode ( 1N4004 ) for sensing temp' .

I used a diode and then years later put a LM34DZ temp sensing

chip next to it and they tracked same !!

Reply to
Paul Jones

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