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Old 8th October 2012, 12:12 AM   #1571
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Originally Posted by fas42 View Post
To keep the ball rolling, here's a quickie knock up of the schematic from #1568 for those who are averse to fiddling with the versions already posted. Appears to be OK, haven't checked everything, I'm sure people will point to any problems ...

The PSRR looks much, much better of course. One thing though, can't push the output standing current up to 8mA easily for some reason ...

Frank

Fiddle around with R10 vand R11, make them a little bigger and then do the trim. There certainly are values that get the desired currents.
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Old 8th October 2012, 12:38 AM   #1572
EUVL is offline EUVL  Europe
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> EUVL - I consider that there is enough here to burn a prototype.%

Noted.
Am busy the next week or so, so it will take a while.


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Last edited by EUVL; 8th October 2012 at 01:03 AM.
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Old 8th October 2012, 12:56 AM   #1573
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Originally Posted by scott wurcer View Post
Fiddle around with R10 vand R11, make them a little bigger and then do the trim. There certainly are values that get the desired currents.
Yes, simple adjustment of R10=R11= 30R will do it. Then values of R18 from 540 to 640R depending on the BJTs get it there.

Which would you suggest as the best way for trimming the DC operating point?

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Old 8th October 2012, 12:15 PM   #1574
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Are transistors Q15 and Q16 thermally coupled to the output transistors Q11 and Q14? Should R18 be a ten turn? Is it gona be tweaky if not a ten turn? Thanks, Ray
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Old 8th October 2012, 12:29 PM   #1575
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Should there be anti latch up diodes on the input(1n6263)??? Thanks, Ray
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Old 8th October 2012, 03:12 PM   #1576
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Should there be anti latch up diodes on the input(1n6263)??? Thanks, Ray
I would use ordinary diodes, plenty of SMT duals out there like BAV99/199 for instance. I use the 99's for normal clamp use and the 199 has <200fA typical leakage if needed.

Here's a plot of the trim, looks like a 2k pot would be better once the small resistors are picked. Depending on the devices I would pick R10 and 11 to max the bias out at 10ma or so then the trim always goes down to the desired value. You could also just select R10 and 11 to get around the right value the absolute Vbe's won't vary that much.

Checked over supply and temp should be no problems with simple thermal contact between the four output devices.
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Old 8th October 2012, 09:00 PM   #1577
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Here's a JFET JE990 with up to date parts. The J305 is a place holder since I did not have models for the depletion mode MOSFET's. These devices would also do a nice PA front end. I can't offer much help since this is LTSPICE, but it looks like a nice project.

Thanks to Pete Basel for entering the original.
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Old 8th October 2012, 10:23 PM   #1578
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Originally Posted by scott wurcer View Post
Here's a JFET JE990 with up to date parts. The J305 is a place holder since I did not have models for the depletion mode MOSFET's. These devices would also do a nice PA front end. I can't offer much help since this is LTSPICE, but it looks like a nice project.

Thanks to Pete Basel for entering the original.
Hi Scot,
Thank you.
What depletion mode MOSFET's would suit here?
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Old 8th October 2012, 11:26 PM   #1579
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Hi Scot,
Thank you.
What depletion mode MOSFET's would suit here?
The C. P. Clare devices like the CPC3730 are very attractive. There are 4 makers now with promising devices and it seems there are enough conventional applications that they will remain available.

The J111 will work too.

EDIT - Just a note we are enjoined from installing LTSPICE on computers owned by our company, this is perfectly within reason since they are paying the bills.
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Old 9th October 2012, 05:50 AM   #1580
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Scott I assume you meant the 2nd definition re: LTspice?

tr.v. en·joined, en·join·ing, en·joins
1. To direct or impose with authority and emphasis.
2. To prohibit or forbid.

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