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VK6JY > TECH 18.11.05 14:44l 50 Lines 1825 Bytes #999 (0) @ WW
BID : 5607-VK6JY
Read: GUEST DL1LCA OE7FMI
Subj: Re: Frustrating Opamp
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0ACC<DB0GOS<DB0OVN<ON0LGE<ON0DXC<ON0RET<
DB0RES<ON0AR<VE2PAK<N1UAN<ZL2BAU<VK6HGR<VK6BBR<VK6ZRT<VK6JY
Sent: 051118/1228Z @:VK6JY.#ALY.#WA.AUS.OC #:5607 [Albany] wFBB7 $:5607-VK6JY
From: VK6JY@VK6JY.#ALY.#WA.AUS.OC
To : TECH@WW
Hi all
Adding to the thoughts from Ralph, VK2ZRG on the 741 case..
It sounds as if Andrew, ZL4AJS is trying the 741 on a single supply rail.
Then the sensor signal is badly close to the ground (-) rail. If that is
mandatory, you will have to add a central bias to the sensor to match it
to the other input, somewhere near the half-rail potential. (R3 & R4)
Single Rail:
----+---+-----------+---------------------- (+12)
| | |
R3 R1 |
Sensor | | .---------.
,-----------------|+ |
S | | : 741 |---------> Out
`------+ +------|- |
| | `---------'
R4 R2 |
| | |
----+---+-----------+---------------------- (Gnd)
Split Rails:
Junction of R1 & R2 very close to Gnd and making say
R2 variable will allow coarse set point adjustments.
If these were both 100k ohms a small pot between them
of about 5 or 10 k would provide much finer control.
--------+-----------+---------------------- (+9v)
| |
R1 |
Sensor | .---------.
,--------- | -----|+ |
S | : 741 |---------> Out
`------. +------|- |
Ground | | `---------'
--- R2 |
| |
--------+-----------+---------------------- (-9v)
The inputs of the (square) Op-Amp are now nowhere near the rail/s.
Regards from John VK6JY @ VK6JY.#ALY.#WA.AUS.OC
Albany WA FBB 7.00i 18-Nov-2005 20:20 WAST
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