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what does this circuit suggest??

sid2286

Aug 24, 2011
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I'm trying to understand this circuit and its working...it looks like it a multi-vibrator but cannot get a proper pulse at the output! :( please suggest something....
 

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duke37

Jan 9, 2011
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It looks like as if it could be a multivibrator to me also, what I see as a first look.

The 2N2222 has a negative supply on its collector.
I do not fully understand the op-amp circuit - that will take some thought. It is not the usual mixture of positive and negative feedback.
The loop C3, D2, R5 does nothing.
D1 is connected to ground, so where is the output?
 

davenn

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Sep 5, 2009
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where did this cct come from? do you have a link to it. Or is it something you made up.?
I really cant see how it could operate, as Duke37 said there stuff in there that doesnt do anything. and other parts wired incorrectly

cheers
Dave
 

sid2286

Aug 24, 2011
102
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Aug 24, 2011
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thanks for your feedback!

I was going through a circuit i found for loop indicator!

loop indicator: is a device wherein, the input is 4-20mA current and indicator corresponds to 0-process value for 4mA and 100 for 20mA on LCD display. and further the current is given to some external load like PLC or simply grounded.

Now, the entire circuit works on a current source(i.e 4-20mA), no external voltage is applied.
As i was checking the voltages the voltage at the output ahead of diode was -1.8V. which is amazing coz thats like the heart of everything. i tried giving external -1.8v to the circuit and it works ok.

Now i want to generate a -ve 1.8v using a current source and opamps. how do i do it?

Regards,
Sid
 
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