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Are you really fine with IC voltage regulators ?
Are you really fine with IC voltage regulators ?
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Old 17th September 2020, 10:27 AM   #231
jan.didden is offline jan.didden  Europe
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way (50...60mhz output transistors as unfortunately 80-90 MHZ- output transistors

Allow me to split some hairs. It is MHz. Mega = 10^6; m = 10^-3.
Herz is a person's name so must be capitalized. ;-)

Jan
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Old 17th September 2020, 11:00 AM   #232
dreamth is online now dreamth  Romania
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ok
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Old 17th September 2020, 12:26 PM   #233
dreamth is online now dreamth  Romania
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By the way...he nakamichi dragon, zxl1000, cr4,zx 9,bx300, lx3,lx5, dr, etc...regulator is esentially a collector output too , i's just that it's not obvious...
Are you really fine with IC voltage regulators ?
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Old 17th September 2020, 02:43 PM   #234
Ketje is offline Ketje  Belgium
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Regulator with emitter out,
drop-out voltage must be high enough to allow for a controlable base current
no start-up problem
Collector out,
very low drop-out possible
look out for start-up problem.
Mona
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Old 17th September 2020, 02:45 PM   #235
jan.didden is offline jan.didden  Europe
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Yes, most of the latest very-low-dropout regulators have a collector output. Sometimes dropouts down to 200mV or even less. This is very important in for instance CPU power supplies that have to deliver 0.8V at several 10's of amps.

Jan
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Old 17th September 2020, 03:44 PM   #236
MarcelvdG is offline MarcelvdG  Netherlands
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Those are usually multiphase buck converters, so switched mode regulators rather than series regulators.
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Old 17th September 2020, 04:11 PM   #237
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by jan.didden View Post
I remember a very old article (probably in ETI at the time) from Stan Curtis, similar discussion for a power amp. One with a common emitter output stage, with the output collectors being the output, and the other with common collector stage, the emitters being the output.

Open loop, you see quite a difference in output impedance, IIRC the collector outputs were 60 ohms, the emitter outputs were a few ohms only. But when you close the feedback loop the differences become so small that it's almost impossible to measure. This is exactly what happens in these regulators.

So, yes, I agree to your reasoning, but at the end of the line the differences are so inconsequential that other considerations may dictate which configuration to prefer. Engineering being the art of picking the best compromise ;-)

Jan
I remember an article in the Journal of the Audio Engineering Society from Edward M. Cherry and a lot of other people about the same subject. The main text gave the impression that there was hardly any difference between common collector and common emitter, not even for the stability, but they were actually overstating their case a bit.

When you read the article carefully including the appendices, it turned out that the common emitter version required an extra left half plane zero (lead compensation) to get the same stability as the common collector version. When there was no possibility to realize such a zero or no possibility to realize it without messing up something else, the common collector version was in fact more stable.

I don't remember if they even considered the right half plane zero due to the base-collector capacitance in a common emitter stage that you don't get with a common collector stage, it could be that they neglected that.

I also remember an article from Rudy Eschauzier and Johan H. Huijsing (if I'm not mistaken) about making a common collector stage with grounded emitter. When you drive a transistor from a differential stage and connect the differential stage to the base and the collector while the load is (for AC) between the collector and emitter, you have made a common collector stage, no matter what terminal is connected to ground (if any). Apparently they didn't realize they had found a creative way to make a common collector stage, as the title of the article was something with multipath right half plane zero removal.

Last edited by MarcelvdG; 17th September 2020 at 04:24 PM.
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Old 17th September 2020, 04:22 PM   #238
Mark Johnson is offline Mark Johnson  United States
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Are you really fine with IC voltage regulators ?
A couple of applications engineers from TI wrote some very nice articles and app notes about instability of low dropout voltage regulators (using the "common emitter" topology). See attachments.

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Old 17th September 2020, 09:28 PM   #239
mchambin is offline mchambin  France
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Extremely interesting articles. I am presently messing with a regulator topology that is stubbornly sensitive to the output capacitor ESR.
I hope I will understand this dreadful ESR range of stability.
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Old Today, 10:23 AM   #240
dreamth is online now dreamth  Romania
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You might find useful this statemnt on ESP site .I often saw LDO's using very high output capacitors who's esr nor esl factors are really low , but you can control them in a real circuit with a little bit of holistic thinking.Sometimes a 10 000uf capacitor works great with an LDO, but at the same time if you are using an LDO with a high Vin-Vout margin everything is safe with almost every capacitor output .
LDO Regulators

Two years ago a i had a small project with a school that asked me to make a small instalation that would show students how you can charge a smartphone using a bike and a dynamo.As it was for students it had to be very descriptive with lots of lights(vu-meters, voltage and current display at all times. I made two types of regulators for the usb carger: one was a 0.5v drop regular LDO chip, the other was a buck boost converter and actually one of the most efficient on the market. Due to the very low output of the bike dynamo it prooved that the series regulator LDO had the same efficiency as the switching circuit, but to make sure that both the LDO and the switching charger would get me the best efficiency all the time no matter how hard the kids were pedalling, i chose a trick shown by a guy whose post you have below. Since then i always try using voltage multipliers in my low power circuits as they also show better filtering right from the start . For a static instalation that you don't need to move pedaling the sealed lead battery regulator was the real deal
Attached Images
File Type: png esp.png (82.8 KB, 22 views)
File Type: png esp1.png (97.9 KB, 21 views)
File Type: png dynamoregulator.png (53.4 KB, 21 views)

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