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Old 29th November 2017, 09:30 AM   #31
Fob69 is offline Fob69  France
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Quote:
Originally Posted by mchambin View Post
You can use LM337 for a ultra low noise supply.
There is no need for huge caps or sophisticated add ons.
Cascading two LM337 will give zero ripple.
Why this one would give me a better result than the other ultra low noise regulator ? (That for me at this time are far from my lifepo4)

A ldo does nothing for comon mode noise if connected to AC, rigth ?

How can i calculate the loss of curent with a ldo ? It is important if i use a battery upstream for AC isolation ...

B.
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Old 29th November 2017, 07:41 PM   #32
Fob69 is offline Fob69  France
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I suppose power lost with ldo = Vdo x Iout ?? (130ma in my config, not so bad).
Thinking about it i am going to test : large 6,4v lifepo4 >> tps7a4700, 3,3v >> A123 lifepo4 3,3V>> diods >> 3, 05v

I should have :
- the Ac decoupling
- stable voltage
- the very low noise
- the very low ouput impedance (that will be better with the lifepo4 A123 at 3,3v than 3,1 so why the diod). I need 3,1v ouput for my MFC.

...

Last edited by Fob69; 29th November 2017 at 07:48 PM.
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Old 2nd December 2017, 06:09 AM   #33
gentlevoice is offline gentlevoice  Denmark
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Battery DC converter
Hi ... maybe you already found out yourself but

Quote:
I suppose power lost with ldo = Vdo x Iout ?? (130ma in my config, not so bad).
if what you mean is that the power dissipated in the ldo is the voltage across the ldo x the current through the ldo then that is correct.

Cheers,

Jesper
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Old 2nd December 2017, 08:25 AM   #34
Fob69 is offline Fob69  France
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Quote:
Originally Posted by gentlevoice View Post
Hi ... maybe you already found out yourself but
if what you mean is that the power dissipated in the ldo is the voltage across the ldo x the current through the ldo then that is correct.
yes, if what you mean by "the current through the ldo" is the current lost by the ldo, not the output ldo current (?)

I did test this morning 6,4v lifepo4>>tps7a>>3,3v lifepo4. Sounds great.
This evening with quiet environment if will test without ldo / without 3,3v lifepo4 to see if i hear differences.

B.
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Old 2nd December 2017, 08:57 AM   #35
JPS64 is online now JPS64  Germany
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Battery DC converter
How is deep discharge managed?
Are the LiFePO4 protected?
Don't forget, they go low to 2V!

JP
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Old 2nd December 2017, 09:19 AM   #36
Fob69 is offline Fob69  France
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Quote:
Originally Posted by JPS64 View Post
How is deep discharge managed?
Are the LiFePO4 protected?
Don't forget, they go low to 2V!

JP
On the 6,4 one there is a under voltage protection.
On the 3,3v A123 there is not, but my device auto switch off at <3v. You are right there my be input leak on the device when it is off and the 3,3v switched on. I will check it.
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Old 2nd December 2017, 01:51 PM   #37
Fob69 is offline Fob69  France
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After new tests : The voltage is stable (i had thermal shutdown with the TPS7A and put a larger heatsink).
With 3,1V ldo output (so the lifepo4 used as a buffer is on low charge), i can hear the TPS7A.
I set the TPS7A to 3,3V and put two low drop out diods in parrallel after the 3,3V lifepo4, so i get the 3,1V output but the battery is in high load. -> I don't hear the tps7A any more, it is like if it was not there.

An interresting thread on the sugbect : Noise measurements for LiFePo4 and supercapacitors?

Is there a way to manage the risk of full discharge of my lifepo4 3,3v buffer in case i forget to switch off ?

B.
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Old 2nd December 2017, 02:02 PM   #38
Fob69 is offline Fob69  France
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Old 6th December 2017, 06:05 PM   #39
Fob69 is offline Fob69  France
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Quote:
Originally Posted by mchambin View Post
You can use LM337 for a ultra low noise supply.
There is no need for huge caps or sophisticated add ons.
Cascading two LM337 will give zero ripple.
You were rigth. i just test the LM337 instead of the TPS7A and the result is very good with float charge with two lifepo4 as a buffer. Even better than the TPS7A4700. I suspect that the TPS7A is too short in curent for my delock MFC and that it increases the noise.

I have a lot of heat with the LM337. I have to check how long i takes now to flat my 6,4V battery.

Last edited by Fob69; 6th December 2017 at 06:24 PM.
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Old 7th December 2017, 06:19 PM   #40
gentlevoice is offline gentlevoice  Denmark
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Battery DC converter
Hi again,

Quote:
Is there a way to manage the risk of full discharge of my lifepo4 3,3v buffer in case i forget to switch off ?

B.
.. a suggestion could be to build an LM555 based timing circuitry that switches on the charger after e.g. 2 hours of listening time - that is the charger is off as long as the LM555 is "set". It could be done e.g. with a relay which is controlled by the LM555. If your charging circuitry is connected to the AC mains in isolation an on/off clock in the AC mains could do the same ...

Cheers,

Jesper
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