You need to set up the voltage divider such that taking into account all tolerances, the voltage at PGFB is above 309 mV when the output has settled. 150 kohm and 3 kohm would therefore not work, 150 kohm and 3.3 kohm should work when you use accurate resistors, 150 kohm and 3.9 kohm should work when the resistors are not that accurate. With 150 kohm and 3.9 kohm, it would typically fast charge up to 300 mV * (150 kohm + 3.9 kohm)/3.9 kohm ~= 11.8385 V and then settle slowly from there.
Thank you.
No, I was planning on keeping it simple, a single center tapped secondary of 24VAC (30*1.33=39Vrms), a single bridge rectifier, 2 CRC filter (1 for the negative rail to the lt3094) like this :
https://electroschematics.com/wp-content/uploads/2010/12/12-VOLT-DUAL-POWER-SUPPLY.jpgOr maybe should I use 2 bridge rectifiers like this :
https://www.diyaudio.com/archive/bl...1498953002-dual-bridge-rectifier-pcb-dbrb.png
Having 2 bridge rectifiers is the superior method, probably less ripple ?
I did not plan on adding pre regulators, Do you recommend pre regulator ? the load will be pretty light a dual opamp in a single package.
Last edited:
You need something like 15.8 V to keep the regulator out of dropout and the maximum recommended input voltage for the LT3045 is 20 V. With +/- 10 % mains voltage tolerance and with the ripple voltage that you will get, I don't see how you can keep it in such a narrow range without some preregulator. You could for example use a run-of-the-mill 18 V LDO to protect the LT3045 against too high input voltages. It doesn't matter when the 18 V LDO goes into dropout at low mains voltages, just as long as the momentary input voltage of the LT3045 stays well above 15.8 V.
Thank you, so it will be better. Will it also lower the noise a bit ?
What is the best pre regulator I can use before the 3042. Do you know if there is a schematic on this post or else where ?
I am a bit affraid of the pcb design tho now with all these parts but tha is how you learn.
Hey I want to thank you a lot for your help guys, I really appreciate everything you do.
I use 1% 25ppm, Thank you. I will buy a tantalum it is cheaper at higher voltage rating. Thank you for the help.
An LM2941 could be used as an 18 V preregulator. The maximum input voltage is then 26 V, the minimum to keep the LT3045 out of dropout would be about 16.8 V. See https://www.ti.com/lit/ds/symlink/lm2941c.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&DCM=yes&ref_url=https://br.mouser.com/&distId=26 You can probably get the voltage in the 16.8 V to 26 V range with a 15 V transformer, rectifier and capacitor.
Last edited:
Thank you. I kind of understood about the 1.5v for lower noise and the 0.26v for the dropout, means 16.76v min. Thank you so much for you care.
Can I ask you if it will be good enough as a preregulator ? I can buy more expensive parts as I am only building it for myself.
I dont really care about the cost of the preregulator, but I dont want to pay too much if it will not bring any improvement. My main concern is to not add noise, or even better, lower it even more with a preregulator.
I you had to choose the best pre regulator (best for the task, not the best on the market) which one you would choose ?
Can I ask you if it will be good enough as a preregulator ? I can buy more expensive parts as I am only building it for myself.
I dont really care about the cost of the preregulator, but I dont want to pay too much if it will not bring any improvement. My main concern is to not add noise, or even better, lower it even more with a preregulator.
I you had to choose the best pre regulator (best for the task, not the best on the market) which one you would choose ?
Hi, was going to order the LM2941 (it is fine LDO thank you for the recommendation) but for the negative rail I would like to avoid the lm2991, from a simple research on diyaudio it seems it is a very bad regulator, it is noisy and its psrr is sub par from what I read it's noise is also in the 200 to 450uV in real life it seems :
https://www.diyaudio.com/community/threads/simple-linear-crcrc-psu.353363/page-2#post-6304334
see this also :
Is there another combo I can use ? LT3080 maybe and its negative equivalent (but it 6euros vs 2.5euros for the lm2941).
Thank you.
https://www.diyaudio.com/community/threads/simple-linear-crcrc-psu.353363/page-2#post-6304334
see this also :
Is there another combo I can use ? LT3080 maybe and its negative equivalent (but it 6euros vs 2.5euros for the lm2941).
Thank you.
The LT3094 that you want to use for the negative rail has a noise of 0.8 uV RMS from 10 Hz to 100 kHz and a PSRR of more than 75 dB. That means that as long as the noise of the preregulator is well below 4.5 mV RMS, it won't dominate the noise at the LT3094 output, so 450 uV should do fine.
Thank you guys for your help. So it will work fine with an lm2941/2991 combo.
And sorry for still asking after all your recommendations, but i am really passionate about this.
But is there any ldo preregulator with fixed noise independant of vout (and is the lt3080 one) and better psrr as an upgrade ?
And sorry for still asking after all your recommendations, but i am really passionate about this.
But is there any ldo preregulator with fixed noise independant of vout (and is the lt3080 one) and better psrr as an upgrade ?