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Old 21st November 2017, 06:37 PM   #11
Fob69 is offline Fob69  France
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I bougth a batch of diods with 0.2, 0.3, 0.4 Vf at 1A on mouser. i should find one ok ...

Thank you for your help

Bernard
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Old 27th November 2017, 05:17 PM   #12
Fob69 is offline Fob69  France
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Hi,

I received my diods and make a test.
The diod that had the lowest drop out (0,21 at 1A), give me a 0,3v drop out at 0,45A ...
I am going to test other diods with a low Vf but given for a higher If, with few hope.

Are the 3,7v Li-on batteries voltage as stable as lifepo4 ?

Other option will be the regulator ...

Do you know if there are other solution for a 0,2V drop out ?

B.

Last edited by Fob69; 27th November 2017 at 05:30 PM.
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Old 27th November 2017, 06:05 PM   #13
miro1360 is offline miro1360  Europe
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did you tried 2-3 diodes in parallel?
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Old 27th November 2017, 07:15 PM   #14
Fob69 is offline Fob69  France
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No ... i can try tomorrow.
Strange behaviour. Why parrallelize them would drop ou voltage more than one ?

I just try a lps + tps7a4700 ldo at 3,1v. The SQ lost is important compare to the lifepo4.

I am waiting for the battery to go around 3,1v and then i will try the lifepo4 parrallel on the tps7a output to compare to the lifepo4 alone and see if voltage is stable.
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Old 27th November 2017, 09:45 PM   #15
miro1360 is offline miro1360  Europe
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when you merge more diodes parallel, than current is divided between them and less current through diode means less voltage drop
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Old 28th November 2017, 05:46 AM   #16
Fob69 is offline Fob69  France
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Ha yes of course.

With the battery after the tps7a, the sound become bad again when the battery voltage goes around the ldo output voltage, and that this one starts to work again.

I don't understand why i can hear a supposed very low noise ldo on this MFC... maybe it is realky low noise but doesn't have tge ability to remove pcb digital noise as lifepo4 battery would do ?

I will do another test : 5v battery supply and then Ldo (and an other test with 3,3v battery + parralel diods).
Do you know wich current do i have to take on the ldo specification to estimate the current loss in the ldo ? (If i put my 5v battery upstream the ldo and that the sq is ok ?

Thank you,

Bernard
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Old 28th November 2017, 12:38 PM   #17
miro1360 is offline miro1360  Europe
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5v battery supply and then Ldo should be good, take current at least 1A, try LM3940 or LM317 (but this one is not LDO)
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Old 28th November 2017, 01:00 PM   #18
Fob69 is offline Fob69  France
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Quote:
Originally Posted by miro1360 View Post
5v battery supply and then Ldo should be good, take current at least 1A, try LM3940 or LM317 (but this one is not LDO)
I had lowest sound quality with the lps + tps7a so i have a doubt. It can be :
Because i have common mode noise that comes from ac that goes to my mfc/player/dac.
Because i have noise that goes throught the ldo. When a ldo is given for very low noise, isn't suppose to filter this normal mode current noise ?
Because lifepo4 acts as a denoiser on whole pcb/ground plane because of its very low impedance.

If it is the last option ldo after battery will give a not so good result.
Other problem is i risk to get a lost of battery charge due to the heat.

I am going to test...

B.
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Old 28th November 2017, 01:24 PM   #19
mchambin is offline mchambin  France
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Quote:
Originally Posted by Fob69 View Post
I bougth a batch of diods with 0.2, 0.3, 0.4 Vf at 1A on mouser. i should find one ok ...

Thank you for your help

Bernard
As far as I know, Ge is 0.3, Si is 0.7, Shotsky 0.4
I am curious about 0.2
__________________
Transistor junction temperature is not transistor case temperature.
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Old 28th November 2017, 03:02 PM   #20
miro1360 is offline miro1360  Europe
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first try more diodes in parallel, if datasheet is right, than low current leads to lower temperature and lower voltage drop ... more diodes parallel == less current through one diode
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