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Old 19th July 2005, 07:17 AM   #1
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Unhappy Jung problems

I built a jung super regulator according to the schematic given at http://tangentsoft.net/elec/opamp-linreg.html . When I plug it in, the LED goes green for a second and then turns off. I also get about 9 volts higher at output than I am supposed to be getting (LED is off). I'm using a 890/1.13k combo for R1 and R2, respectively, to get a little above 12V output. What could be going wrong? Thanks!
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Old 19th July 2005, 07:26 AM   #2
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Check all wireing, all diodes & el. caps orientation for start.
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Old 19th July 2005, 09:00 AM   #3
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What's your input voltage? Are you sure about it? You say you expect 12V, but with R1=890, R2=1.13k, you design for Vout = 15.6V. You should have at least 18VDC at the input. Is that right?

If not, the opamp will increase its output voltage in an attempt to get to 15.6V, and the collector of Q2 rises until its Q-B junction starts to reverse conduct, and the voltage across R4 goes up until there is no more voltage (or even reverse voltage) across the LED, it goes off.

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Old 19th July 2005, 02:30 PM   #4
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My input voltage is at least 20V off-load. I'm using a PCB mount Amveco toroidal transformer (two 7v windings in series) with a bridge rectifier. On load it should give a little higher than 18V.

Also, when you use the equation R8 = R9*(Vout-Vref) / Vref , and substitute 890 for R8, 1130 for R9, and 6.0 for Vref; you get 12.33V for Vout.

Thanks for the help, can you guys think of anythig else that could be wrong? Seems like the voltage isn't being regulated as the output is about the same as the input voltge.
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Old 19th July 2005, 04:54 PM   #5
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Quote:
Originally posted by rhymeswthorange


Also, when you use the equation R8 = R9*(Vout-Vref) / Vref , and substitute 890 for R8, 1130 for R9, and 6.0 for Vref; you get 12.33V for Vout.

The LM329DZ as VRef will yield 6.9V, not 6.0V --

While it isn't a problem here, Jung pointed out in the TAA 2000 issue -- that there are occasionally dud LM329's so make sure that it is actually working.

PS -- Jan wrote one of the original series (1995) articles.
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Old 19th July 2005, 05:05 PM   #6
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Yeah, I meant 6.9 (calculation yields 12.33 with 6.9). Alright, I'll check it out. Thanks!
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Old 19th July 2005, 08:27 PM   #7
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Could a failed opamp cause this? The one I ordered was a surface mount type (SOIC-8), and after some effort I eventually got single strands of wire from my stranded hookup wire soldered to each contact. I wonder if in the process of doing this, I damaged the amp. The soldering iron wasn't held to the leads for very long (didn't need to be), but how sensitive are these chips to heat? Could, say, a second of soldering undo the chip? I also wiped some excess flux away with some alcohol (and let it dry before it was fired up). Would a failed opamp cause this type of behavior?

P.S. I have yet to check the other suggestions - have to get home first
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Old 20th July 2005, 05:14 AM   #8
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Well, now i supplied the regulator with a 460 ohm load. The LED stays on, and the voltage aross the load is 18V. When I put a 250 ohm load on it, the voltage across is 15.2. Is this supposed to be happening?


... at least the lights are on...
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Old 21st July 2005, 04:49 AM   #9
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Anyone have any ideas?

Thanks in advance!
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Old 21st July 2005, 11:39 AM   #10
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what's the voltage on pin6 of the AD825?, did you use a 1n5235 zener diode or a 1n4148 from the opamp to the collector of Q3?
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