[Diy_efi] need schematic critique

[Dave Harvey]

J,
To expand on Mark's comments, I suggest that you connect the output of 
the LM339 to the base of an NPN transistor and drive the relay with the 
transistor. Connect a 2.2K resistor from the LM339 output to +8V. 
Connect the transistor emitter to ground. Connect the relay between the 
collector and +12V (use a 12V relay). A 2N2222A can handle up to 50mA 
for the relay coil. The LM339 output will now only swing 0.6V, so reduce 
R3 to 10K or so. With this configuration, the relay is energized when #1 
 > #2. If you want the opposite polarity, then swap the 2 pots and 
adjust the feedback resistor (R3) value to get the desired hysteresis. 
You might want to bypass Pin 4  to ground with 0.1uF to filter any noise 
pickup. Is the 47K pot located near the LM339? Also the flyback diode 
should connect across the relay coil. When a relay (or any inductor) is 
denergized, the voltage across the winding reverses.

V = L * di/dt

Feel free to contact me off-list if you like.

-- Dave

Mark Bowers & Family wrote:

>Needs work....
>
>- LM339 does not have drive output capable of sinking enough current for a
>relay drive, and it's an open collector output device so can only sink
>current, not drive current into the relay..
>- So you need a driver stage after the LM339, and possibly an inversion of
>the logic.
>
>Didn't look at the ref schematic yet. You can write me at mbalntel at cfw.com
>
>Mark Bowers
>
>
>----- Original Message -----
From: Toyota Supra <turbosupramk3 at hotmail.com>
>To: <diy_efi at diy-efi.org>
>Sent: Sunday, February 16, 2003 6:50 PM
>Subject: [Diy_efi] need schematic critique
>
>
>  
>
>>hi all,
>>
>>i need a schematic critique on the schematic housed below, it is in .jpg
>>format or .psd
>>
>>http://68.7.7.84:8080/schematics/
>>
>>i have included the psd in case someone wanted to edit it to something
>>better
>>
>>specifics on it are as follows :
>>
>>variable resistor input, ranging from 0 to 3.5vDC
>>circuit is to kill signal to normally open relay at 3.2vDC
>>i would like approximately a tenth of a volt of hysteresis
>>
>>
>>below is a link that i would like to use to control the reference voltage
>>for pin 4 of the LM339 chip, will it work?
>>
>>http://www.mitedu.freeserve.co.uk/Circuits/Power/lm317.htm
>>
>>
>>thanks to all that look at this
>>
>>-j
>>
>>
>>_________________________________________________________________
>>Tired of spam? Get advanced junk mail protection with MSN 8.
>>http://join.msn.com/?page=features/junkmail
>>
>>
>>_______________________________________________
>>Diy_efi mailing list
>>Diy_efi at diy-efi.org
>>http://www.diy-efi.org/mailman/listinfo/diy_efi
>>
>>    
>>
>
>
>_______________________________________________
>Diy_efi mailing list
>Diy_efi at diy-efi.org
>http://www.diy-efi.org/mailman/listinfo/diy_efi
>
>  
>



_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi