Current divider mirror
in [Design]
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From: John Larkin on 8 Feb 2010 18:15 On Mon, 8 Feb 2010 15:53:25 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:vf11n5hiervl0ukh1o0qett8gsfut726vk(a)4ax.com... >> The most obvious one is the the charge/discharge currents depend on >> the betas of the upper and lower mirror transistors. That's probably >> why there are two PNPs and three NPNs: they were selected to work. > >Well, the duty cycle ended up fairly close to 50% just picking random 440x's >out of the box. No selection, put it together and it worked. Why, were you >expecting 3 PNP's and 2 NPNs if they were selected? > >Tim Oops, misread the mirror connections. It's not a great mirror setup, but it's not seriously beta dependent. Plenty of other issues, though. John
From: Fred Bartoli on 8 Feb 2010 18:40 Jim Thompson a �crit : > On Mon, 08 Feb 2010 14:23:44 -0800, John Larkin > <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > [snip] >> Putting two or three or seventeen transistors in parallel in a circuit >> like this doesn't scale the mirror ratios, it just sort of half-assed >> averages out the betas. If there is a 2:1 ratio, it's because the NPNs >> have an average beta twice that of the PNPs. >> > [snip] >> >> Next problem? >> >> John > > John Larkin's statement there is SO-DUMBASSED as to warrant special > mention ;-) Keep note of that! > > The only thing that stands out as defective in the schematic is that > the placement of the two 1N914's is wrong to accomplish the desired > up/down current steering. > ??? Not even, but the schmidt trigger has wrong feedback (take it from the other 3904 collector). And the 100p miller cap is not only unnecessary but worsens the PSRR without any benefit. It seems your silicon has one unnecessary pass. -- Thanks, Fred.
From: Jim Thompson on 8 Feb 2010 19:00 On Tue, 09 Feb 2010 00:40:45 +0100, Fred Bartoli <" "> wrote: >Jim Thompson a �crit : >> On Mon, 08 Feb 2010 14:23:44 -0800, John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> [snip] >>> Putting two or three or seventeen transistors in parallel in a circuit >>> like this doesn't scale the mirror ratios, it just sort of half-assed >>> averages out the betas. If there is a 2:1 ratio, it's because the NPNs >>> have an average beta twice that of the PNPs. >>> >> [snip] >>> >>> Next problem? >>> >>> John >> >> John Larkin's statement there is SO-DUMBASSED as to warrant special >> mention ;-) Keep note of that! >> >> The only thing that stands out as defective in the schematic is that >> the placement of the two 1N914's is wrong to accomplish the desired >> up/down current steering. >> > >??? Not even, but the schmidt trigger has wrong feedback (take it from >the other 3904 collector). Yep, the real defect is the Schmitt. Swapping phase still doesn't fix it. I can't figure out what was the intent of whoever designed this. >And the 100p miller cap is not only >unnecessary but worsens the PSRR without any benefit. Have no idea why people spray capacitors around ;-) > >It seems your silicon has one unnecessary pass. My "silicon"? Those GenRad supplies used everything off-the-shelf. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Tim Williams on 8 Feb 2010 19:04 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in message news:5591n51jn35raapv4d7iem769jhtucgo59(a)4ax.com... >>And the 100p miller cap is not only >>unnecessary but worsens the PSRR without any benefit. > > Have no idea why people spray capacitors around ;-) Breadboard, duh ?-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 8 Feb 2010 19:08
"Fred Bartoli" <" "> wrote in message news:4b70a0fd$0$21600$426a74cc(a)news.free.fr... > ??? Not even, but the schmidt trigger has wrong feedback (take it from the > other 3904 collector). Indeed! Then the 4.7k positive feedback is actually positive. That's ONE error. Come on, can't you so-called professionals do better than this? ;-D Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |