Re: op amp output
- From: "frogfot" <frogfot@xxxxxxxxxxx>
- Date: Sat, 16 Apr 2005 16:33:12 +0000 (UTC)
Oobs, sorry for posting same post 5 times.. I'm using mailgate and it
seems to bug.. I've already deleted more than half of them..
Chris wrote:
>First, the schematic transistor TR1 is a current-driven device whose
>gain will be very dependent on temperature. A small change in the
>ambient temperature around Q1 will cause a large change in voltage
>impressed across the 2K load resistor. Bad news if you want to
>maintain a steady setpoint.
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?
>The 7805 is a cheap way to get a good reference voltage for the 50K
>pot, so your reference voltage will be stable when the relay turns off
>and pumps current into the power line.
I was going to use a voltage regulator, while feeding the ralay from
nonregulated current as you've suggested. The circuit will be powered
from a small transformer, so that I don't have to change any batteries
in the final device :P
John Fields wrote:
>I used a MOSFET because the gate doesn't draw any current, so you
>don't have to worry about the comparator output going out of
>saturation when it's sinking the transistor's base current.
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 :)
>If you mean from 25 to 100°C, then I suggest you do something like
>this:
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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