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Old 22nd September 2012, 05:26 PM   #441
EssB is offline EssB  United Kingdom
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OK, I'll try it in LTSpice and see what I get. Gotta go out for a couple hours, back later.
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Old 22nd September 2012, 07:17 PM   #442
davada is offline davada  Canada
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Quote:
Originally Posted by dirkwright View Post
Ah! so that's what I do.

Ok, tried that. I got a really ugly looking oscillation. I ran it for both 10 and 20 seconds. Sump'in ain't right.
With my oscillator sims I run them for minutes.

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Old 22nd September 2012, 08:33 PM   #443
EssB is offline EssB  United Kingdom
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Ok it runs in LTSpice. Injecting 50 cycles of 1KHz at 1uA into pin 6 of IC2b gets it running within 1 second at 10V p-p. After 2 secs the AGC starts to get the level down to about 4V p-p after 5 secs.

It starts up more smoothly if you can skip the initial DC operating point solve at the start. That will allow C2 to charge up normally allowing the AGC loop to start up as designed

I used this Phillips PMBF4391 model
.MODEL PMBF4391 NJF(VTO=-8.0337E+000 BETA=1.56450E-003
+ LAMBDA=1.00000E-002 RD=8.25115E-001 RS=8.25115E-001
+ IS=6.54620E-016 CGS=8.25000E-012 CGD=1.32500E-011
+ PB=7.72344E-001 FC=5.00000E-001)
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Old 23rd September 2012, 01:16 AM   #444
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Quote:
Originally Posted by EssB View Post
Ok it runs in LTSpice. Injecting 50 cycles of 1KHz at 1uA into pin 6 of IC2b gets it running within 1 second at 10V p-p. After 2 secs the AGC starts to get the level down to about 4V p-p after 5 secs.

It starts up more smoothly if you can skip the initial DC operating point solve at the start. That will allow C2 to charge up normally allowing the AGC loop to start up as designed

I used this Phillips PMBF4391 model
.MODEL PMBF4391 NJF(VTO=-8.0337E+000 BETA=1.56450E-003
+ LAMBDA=1.00000E-002 RD=8.25115E-001 RS=8.25115E-001
+ IS=6.54620E-016 CGS=8.25000E-012 CGD=1.32500E-011
+ PB=7.72344E-001 FC=5.00000E-001)
Thanks! I will get to this tomorrow hopefully.
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Old 23rd September 2012, 01:02 PM   #445
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I used your model, but I still can't get it to work. I think I just don't know enough about using my software.
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Old 23rd September 2012, 04:07 PM   #446
davada is offline davada  Canada
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Originally Posted by dirkwright View Post
I used your model, but I still can't get it to work. I think I just don't know enough about using my software.
It wouln't hurt to download LTspice and try it. It's free.

I have used a single 1us 10V pulse though a 1 Meg resistor somewhere into the input of the multiplier just to get them going.

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Last edited by davada; 23rd September 2012 at 04:13 PM.
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Old 23rd September 2012, 05:08 PM   #447
EssB is offline EssB  United Kingdom
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Originally Posted by davada View Post
I have used a single 1us 10V pulse though a 1 Meg resistor somewhere into the input of the multiplier just to get them going.
Yes, they don't need much. In fact, this one will start by itself if the initial DC operating point solve is skipped. With other designs, I've found that forcing them with a few cycles at their operating frequency and at the right level gets them started and stabilised quicker. This one seems less responsive to such treatment.
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Old 23rd September 2012, 05:44 PM   #448
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So, I have some good news anyway. I lashed up a LME49720 in a mixed feedback arrangement with a Jensen 112-LCF output transformer (not their best output transformer by far) and got this result. I think it's pretty good. On the bench, bandwidth was really great. It's running on 2x9V batteries.
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File Type: jpg mixed feedback LME7920.JPG (158.3 KB, 196 views)
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Old 23rd September 2012, 06:18 PM   #449
davada is offline davada  Canada
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Quote:
Originally Posted by dirkwright View Post
So, I have some good news anyway. I lashed up a LME49720 in a mixed feedback arrangement with a Jensen 112-LCF output transformer (not their best output transformer by far) and got this result. I think it's pretty good. On the bench, bandwidth was really great. It's running on 2x9V batteries.
Are you using the feedback technique in there app note?

It look like it needs some trimming.

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Old 23rd September 2012, 06:23 PM   #450
davada is offline davada  Canada
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Quote:
Originally Posted by EssB View Post
Yes, they don't need much. In fact, this one will start by itself if the initial DC operating point solve is skipped. With other designs, I've found that forcing them with a few cycles at their operating frequency and at the right level gets them started and stabilised quicker. This one seems less responsive to such treatment.

I wonder if the right kind-amount of stimulus other than feeding the signal back could be done. Kind of like flicking a tuning fork.

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