Battery DC converter

[mchambin]

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

Not a chance it would significantly lower the voltage drop.
Firstly, they will not share current equally.
Secondly, assuming equal share, the drop will be very little because of the V versus I of diodes.

 

[miro1360]

Not a chance it would significantly lower the voltage drop.
Firstly, they will not share current equally.
Secondly, assuming equal share, the drop will be very little because of the V versus I of diodes.

I am also not sure, in simulation diode which I suggested have this behavior:

https://ctrlv.cz/shots/2017/11/28/suw8.png (load 430mA)

as you can see, more parallel theoreticaly leads to decreasing current through one diode and voltage drop is less in result, but yes, reality can be different ... still not 0.2V but is closer

 

[mchambin]

Of course it theoretically decreases the voltage drop.
The point is: You can parall tons of diodes the decrease will not be significant.
See it this way: Ten diodes in // is the same as a single diode that has a junction 10 times larger.

 

[miro1360]

or even better this one:
VS-STPS20L15D-N3 Vishay
https://ctrlv.cz/shots/2017/11/28/tFqx.png
or this
yes, try some for higher current, more parallel decrease also temperature and voltage should be better ...

 

[Fob69]

This one : VS-10BQ015HM3-5BT was given to be -0,21V at 1A and i have -0,3V at 450 ma ... I will try tomorrow with 3 or 4 in parrallel

B.

 

[mchambin]

Ok, now I see.
From the datasheet:
At 1A 125°C ....Vf is 0.21V
At 1À 25°C....Vf is 0.33V

So this 0.2V is misleading.
You have 0.33V, if this is true, it is a good performance for a Shotsky diode.

Look at power Germanium diodes. You should find true below 0.3V.

 

[Fob69]

Yes i have.
Gonna buy a used grill on ebay

 

[mchambin]

For some odd raison I missed why you need diodes.
There might be a solution using ultra caps.
They are capacitors with so huge capacities, they can be used as batteries.
They have less capacity than batteries, but can be quick charged much faster.

 

[Fob69]

For some odd raison I missed why you need diodes.
There might be a solution using ultra caps.
They are capacitors with so huge capacities, they can be used as batteries.
They have less capacity than batteries, but can be quick charged much faster.

I need diods to adjut lifepo4 output batteries voltage without to loose the vey low impedance.
I use batteries because i want ultra low noise supply and AC isolation for devices upstream my DAC (downsream Delock MFC and Olimex lime player). Lifepo4 batteries is IME from far the best result in SQ.

 

[mchambin]

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.

 

[Fob69]

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.

 

[Fob69]

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.

...

 

[gentlevoice]

Hi ... maybe you already found out yourself but

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

 

[Fob69]

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.

 

[JPS64]

How is deep discharge managed?
Are the LiFePO4 protected?
Don't forget, they go low to 2V!

JP

 

[Fob69]

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.

 

[Fob69]

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.

 

[Fob69]

 

[Fob69]

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.

 

[gentlevoice]

Hi again,

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. 2½ 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