Then I came up with a (quite complex) idea which might work
I prefer to go with 3 fixed independent flyback or forward converters, each followed by a buck converter.
Then I came up with a (quite complex) idea which might work: Let's take one power supply of 30V / 3A and three adjustable buck-regulators, one for each output channel. The buck-regulators will provide adjustable power supply to three power op amps driven by good quality 30kHz sine wave. Each power op amp will drive a 1:1 transformer driving a rectifier, filtering capacitors and the linear post-regulator. There will be required some opto-isolated feedback from the output back to the buck-regulators. Using the 30kHz sine wave will keep filtering capacitor size small and less bulky. This design is a mix of switching preregulator and linear regulator, and the 30kHz transformers are used for isolation and noise filtering.
How does this sound to you - other than this is a bit complex solution for a quite simple problem. However, this solution is quite flexible and scalable, and it will keep the size and generated heat down . Do you think that this solution would be able to provide low noise output, or do you think that buck-regulators might still emit too much switching noise to the secondary side of the 30kHz transformer so that the 100uV design target is difficult to achieve?
Then I came up with a (quite complex) idea which might work: Let's take one power supply of 30V / 3A and three adjustable buck-regulators, one for each output channel. The buck-regulators will provide adjustable power supply to three power op amps driven by good quality 30kHz sine wave. Each power op amp will drive a 1:1 transformer driving a rectifier, filtering capacitors and the linear post-regulator. There will be required some opto-isolated feedback from the output back to the buck-regulators. Using the 30kHz sine wave will keep filtering capacitor size small and less bulky. This design is a mix of switching preregulator and linear regulator, and the 30kHz transformers are used for isolation and noise filtering.
How does this sound to you - other than this is a bit complex solution for a quite simple problem. However, this solution is quite flexible and scalable, and it will keep the size and generated heat down . Do you think that this solution would be able to provide low noise output, or do you think that buck-regulators might still emit too much switching noise to the secondary side of the 30kHz transformer so that the 100uV design target is difficult to achieve?Linear already did very similar things some 27 years ago
http://cds.linear.com/docs/en/application-note/an29f.pdf
Funny how they have an answer to almost any analog problems ever existed. I see 30uV noise figures on page 5. I'm sure somehow you can adopt design to work in the 21 century.
Then I came up with a (quite complex) idea which might work: Let's take one power supply of 30V / 3A and three adjustable buck-regulators, one for each output channel. The buck-regulators will provide adjustable power supply to three power op amps driven by good quality 30kHz sine wave. Each power op amp will drive a 1:1 transformer driving a rectifier, filtering capacitors and the linear post-regulator. There will be required some opto-isolated feedback from the output back to the buck-regulators. Using the 30kHz sine wave will keep filtering capacitor size small and less bulky. This design is a mix of switching preregulator and linear regulator, and the 30kHz transformers are used for isolation and noise filtering.
How does this sound to you - other than this is a bit complex solution for a quite simple problem. However, this solution is quite flexible and scalable, and it will keep the size and generated heat down . Do you think that this solution would be able to provide low noise output, or do you think that buck-regulators might still emit too much switching noise to the secondary side of the 30kHz transformer so that the 100uV design target is difficult to achieve?Linear already did very similar things some 27 years ago
http://cds.linear.com/docs/en/application-note/an29f.pdf
Funny how they have an answer to almost any analog problems ever existed. I see 30uV noise figures on page 5. I'm sure somehow you can adopt design to work in the 21 century.
Indeed. I have read this great application note and the original idea of using the sine wave came from the design "Ultralow Noise 5V to ±15V Converter" - the 30uV output noise is something to go for. However, I wanted to be able the adjust the secondary voltage in order to reduce the heat in the linear post regulator, thus the idea of using power op amps and variable supply voltage for the op amps = tracking pre-regulator. However, the application note states that the efficiency is only 30%.
Where exactly do you need this high current and low noise? I'm asking, because when I need a low noise power supply, the only way to do it is to have it onboard with the precision circuits. I mean it is kinda pointless to have a low noise circuit, and then connect it to it's PSU with 1 meter cable and create a bad PSR(R) with the cable. Even it is 4 wire PSU, you still have loop compensation and other problems. An onboard good old LM317 or a 78xx creates a power supply which is usually much better than any remote PSU.
Hi Albert22,
Sorry, bad link
This is the good one, sorry no English version... Google is your Friend
http://www.circuitsonline.net/forum/view/110029/11/voeding
Kind regarts,
Blackdog
Hi Circuiteromalaguito,
Tomorrow i wil awnser your questions, now iam tired :-)
Kind regarts,
Blackdog
PS
Schematic editor: http://www.abacom-online.de/uk/html/splan.html
Hi Circuiteromalaguito,
Tomorrow i wil awnser your questions, now iam tired :-)
Kind regarts,
Blackdog
PS
Schematic editor: http://www.abacom-online.de/uk/html/splan.html
How about just amplifying a voltage reference? Is it going to be noisier than all the complicated contraption?
Hi,
Sorry for the delay...
1e
LT1021, you can use different 5V references, i do not know were you live, here in the netherlands i can buy what i want from many suppliers.
It is also posible to use a different reference like the LT1027-5V, LT1236-5V, TI REF5050 or an LTC6655-5V.
I have a lot of LT1021 on stock fore a project, but the LT1027 its even better in some specs.
A LT1021 here in the Netherlands cost about 8-Euro, a LT1027 about 12-Euro.
2e
BOM Costs...
I do not know, i dit not make a calculation...
3e
Relais
Yes its more than one relais, but i wil not use a relay's, it wil use a Powerfet preregulator like the schematic on de Circuitsonline website.
4e
I use two transformers or maybe one, it is bettet to use a toroid and lay some extra turns arround the toroid so u don't need T3.
T3 can be a verry smal transformer, about 2 Watt's, maybe it's easter just tho buy the transformer than put extra turns on the big one.
5e
Would you provide the schematic in some interoperable form? I'm still very slow drawing schematics
I do not understand this question, sorry...
Kind regarts,
Blackdog