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Old 5th June 2012, 02:08 PM   #41
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by andrea_mori View Post
The project is op-amp based, so I investigated if there was reason to build a discrete operational amplifier, but finally I concluded that it is better to use a monolithic OA, such as AD797, AD825, OPA627, OPA132 or so.
Have you read Jung's article dated 2000? The AD825 is the preferred OPA for voltage reference in its regulators.

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Originally Posted by analog_sa View Post
I have little doubt that at least the requirements for analogue circuit regulators are very different from those meant to power digital circuits.
I agree 100%.

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Originally Posted by andrea_mori View Post
I agree with you that different circuits requires different power supplies.
Btw if you had an ideal supply you could use it either for analogue than digital circuits. Obviously ideal supply does not exists and I have no claim to build it.
It can be done but it would be a waste of money.
I prefer to have several independent PSU than to connect several lines to a SOTA one.
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Old 5th June 2012, 03:18 PM   #42
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Originally Posted by Telstar View Post
Have you read Jung's article dated 2000? The AD825 is the preferred OPA for voltage reference in its regulators.
I have read Jung's article, but I'm designing a series regulator operating in a different mode. As you can see in the schematics I do not use the opamp to modulate a current source like in Jung Super Regulator, rather the pass transistor is modulated directly from opamp error signal.
BTW I choose LT1028 that has superior performance than AD825, IMHO. LT1028 shows impressive electrical characteristics:
input noise voltage: 1nV/sqrt(Hz)
PSSR: 133 dB
GBW: 75 MHz
Only slew rate is lower than AD825, but don't forget that a shunt regulator follows the series regulator in my design, so I think relatively slowly opamp such LT1028 (11V/us) do not affect the final regulation because shunt section improves transient response.
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Old 5th June 2012, 03:30 PM   #43
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Originally Posted by qusp View Post
hmm, so the opa637 is for higher voltage versions yes? its really not very happy with low gain in my experience it needs to be 3-4x or above, certainly not unity
Maybe there's another way to implement OPA350 in any case, low and high voltage, let opamp operate always at low voltage like in the attached schematic.
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File Type: jpg HG-SHUNT_REGULATION_4V.JPG (32.5 KB, 402 views)
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Old 5th June 2012, 03:46 PM   #44
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by andrea_mori View Post
I have read Jung's article, but I'm designing a series regulator operating in a different mode. As you can see in the schematics I do not use the opamp to modulate a current source like in Jung Super Regulator, rather the pass transistor is modulated directly from opamp error signal.
BTW I choose LT1028 that has superior performance than AD825, IMHO. LT1028 shows impressive electrical characteristics:
input noise voltage: 1nV/sqrt(Hz)
PSSR: 133 dB
GBW: 75 MHz
Only slew rate is lower than AD825, but don't forget that a shunt regulator follows the series regulator in my design, so I think relatively slowly opamp such LT1028 (11V/us) do not affect the final regulation because shunt section improves transient response.
I hadnt seen the schematics when I posted. Your circuit looks good and does not seem over-expensive for a high quality digital PSU. Glad you ditched the inductors I'm looking forward to the PCB.

BTW, are the diodes schottky?
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Old 5th June 2012, 04:22 PM   #45
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Originally Posted by Telstar View Post
I hadnt seen the schematics when I posted. Your circuit looks good and does not seem over-expensive for a high quality digital PSU. Glad you ditched the inductors I'm looking forward to the PCB.

BTW, are the diodes schottky?
Diodes are FRED epitaxial with 35 ns trr.
BTW you can use shottky like SB3100, MBR3100 or so.
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Old 7th June 2012, 03:16 PM   #46
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Default Question

In order to use OPA350 also in regulator that output a voltage greater than 5.5V we have to reduce its power supply voltage to 4/5V.
After some simulations I found two way as in the attacched schematics: first simply with 3 red LEDs, the second more complex with TL431.
I would like to know which one you favor, or if you have any other suggestion.

Thanks all
Andrea
Attached Images
File Type: jpg HG-SHUNT_REGULATION_4V_LED.JPG (34.8 KB, 367 views)
File Type: jpg HG-SHUNT_REGULATION_4V.JPG (34.1 KB, 361 views)
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Old 7th June 2012, 06:17 PM   #47
dtproff is offline dtproff  United States
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Quote:
Originally Posted by andrea_mori View Post
In order to use OPA350 also in regulator that output a voltage greater than 5.5V we have to reduce its power supply voltage to 4/5V.
After some simulations I found two way as in the attacched schematics: first simply with 3 red LEDs, the second more complex with TL431.
I would like to know which one you favor, or if you have any other suggestion.

Thanks all
Andrea
TL431 for the thermal stability of its bandgap reference.

Tony
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Old 8th June 2012, 07:16 PM   #48
AndrewT is offline AndrewT  Scotland
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Gootee,
looks like they have not read your two posts. They are still worried about the opamps.
Good decoupling at the load will reduce the slew rate of the step response on the supply rails and that reduces the need for ultra high speed opamps. They don't seem to see the connection.
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Old 8th June 2012, 08:43 PM   #49
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Quote:
Originally Posted by andrea_mori View Post
In order to use OPA350 also in regulator that output a voltage greater than 5.5V we have to reduce its power supply voltage to 4/5V.
After some simulations I found two way as in the attacched schematics: first simply with 3 red LEDs, the second more complex with TL431.
I would like to know which one you favor, or if you have any other suggestion.

Thanks all
Andrea
I would not use such a simple emitter follower. I would use a 3-pin 5V regulator for the opamp supply: more accurate, lower impedance, better rejection. With an electrolytic on its output.

jan didden
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Old 8th June 2012, 08:55 PM   #50
dtproff is offline dtproff  United States
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Originally Posted by janneman View Post
I would not use such a simple emitter follower. I would use a 3-pin 5V regulator for the opamp supply: more accurate, lower impedance, better rejection. With an electrolytic on its output.

jan didden
So I have to ask... You are already using a part that has 90dB CMRR, how much quieter do you need to be?

This isn't a slam, I'm just curious.

Tony
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