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Old 6th November 2006, 09:52 AM   #11
Pafi is offline Pafi  Hungary
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Baldin!

BTW:

Quote:
The + input of the Comperator, is connected to a voltage divider
I see reverse connection on your pic!

Quote:
the output is 10,4 V
On pin7? Connected to Q13?
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Old 6th November 2006, 10:13 AM   #12
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Bit late in the day..... What Powerbecker/Heinz drew....

Same idea, mine is more stupid though...

DNA
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Old 6th November 2006, 10:14 AM   #13
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Oooops no picture....

DNA
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Old 6th November 2006, 07:11 PM   #14
Baldin is offline Baldin  Denmark
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powerbecker:
Thanks .... that cleared it up
Think I'll try that first, as it will be easiest to implemtent on the current PCB


Pafi
The circuit is "right" ... the divider is conected to - and not + as I wrote!
Yes the output is high = 10,4V on pin 7 which is connected to the base of the following Q13.

Otherwise like your approach .... will try that on the next D thing .... didn't think of the pre-bias, and thought I couldn't trip a BJT directly from the current sensing resistor.
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Old 6th November 2006, 07:48 PM   #15
Pafi is offline Pafi  Hungary
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Quote:
The circuit is "right" ... the divider is conected to - and not + as I wrote!
OK, but then what is the problem? When "+" is positiver then "-", then high output is normal...

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Yes the output is high = 10,4V on pin 7 which is connected to the base of the following Q13.
...except in this case. 10,4V on a good B-E diode is impossible.
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Old 6th November 2006, 08:56 PM   #16
Baldin is offline Baldin  Denmark
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The 10,4V is measured with Q13 dismounted.

Don't know where the basis resistor for Q13 went! (as the LM319 is an open collector output, Q13 will be biased through R57 (2k2) and will still work, though it was not intended to be designed this way..... think I will increase R57 to 10k to lower the basis current in Q13!!

Problem is that when plus is tied to ground (or no current is running in the sense resistor), then minus is higher (set by the divider), but the output is high (10,4 V)

Now that I'm digging a bit, I have found the simulations .... and find that these are using a TL072 as comparator .... and that it includes a bias resistor for Q13 ...... think I have been a little to fast here

The only reason I'm using the LM319 in this place is because I had one half free, as the other half is used in the oscillator
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Old 7th November 2006, 05:49 PM   #17
Pafi is offline Pafi  Hungary
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Problem is that when plus is tied to ground (or no current is running in the sense resistor), then minus is higher (set by the divider), but the output is high (10,4 V)
Oops, you are right.
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